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  • Chemistry  (77,998)
  • Inorganic Chemistry  (7,478)
  • Magnetism
  • photosynthesis
  • Wiley-Blackwell  (77,979)
  • Springer  (227)
  • Nature Publishing Group (NPG)  (3)
  • Paris, France  (1)
  • Station Océanographique de Salammbô  (1)
  • 2015-2019  (4)
  • 1990-1994  (51,041)
  • 1970-1974  (27,165)
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  • 1
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    Sur l'eau normale méditerraneenne: 1ère partie: Historique, discussion des méthodes, propositions (2016)
    Station Océanographique de Salammbô | Paris, France
    Details
    Publication Date: 2021-05-19
    Description: La détermination de la chloruration des eaux de mer est effectuée depuis de nombreuses années par la méthode volémetrisque de Moher.
    Description: Published
    Keywords: Volumetric analysis ; Sea water ; Chemistry ; Density ; Water density ; Chlorination ; Methodology ; Marine
    Repository Name: AquaDocs
    Type: Book/Monograph/Conference Proceedings , Refereed
    Format: 28pp.
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  • 2
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    Misplaced faith (2015)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2015-06-05
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉England -- Nature. 2015 Jun 4;522(7554):6. doi: 10.1038/522006a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26040858" target="_blank"〉PubMed〈/a〉
    Keywords: Chemistry ; *Public Opinion ; Research Personnel/*ethics/standards ; Retraction of Publication as Topic ; Science/ethics/*standards ; Scientific Misconduct/*statistics & numerical data ; *Trust
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    The rapid rise of a research nation (2015)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2015-12-18
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zhou, Yingying -- England -- Nature. 2015 Dec 17;528(7582):S170-3. doi: 10.1038/528S170a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26673023" target="_blank"〉PubMed〈/a〉
    Keywords: Biological Science Disciplines ; Chemistry ; China ; Diffusion of Innovation ; Ecology ; Economic Recession ; Humans ; International Cooperation ; Nobel Prize ; Physics ; Research/economics/manpower/standards/*statistics & numerical data ; Research Personnel/education/standards/supply & distribution ; Time Factors
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 4
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    At the very heart of progress (2015)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2015-12-18
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉O'Meara, Sarah -- England -- Nature. 2015 Dec 17;528(7582):S179-81. doi: 10.1038/528S179a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26673025" target="_blank"〉PubMed〈/a〉
    Keywords: Bibliometrics ; Chemistry ; China ; Cities/*statistics & numerical data ; Personnel Selection ; Research/manpower/organization & administration/*statistics & numerical data
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of nickel on certain physiological and biochemical behaviors of an acid tolerantChlorella vulgaris (1994)
    Springer
    BioMetals 7 (1994), S. 193-200 
    Details
    ISSN: 1572-8773
    Keywords: Chorella vulgaris ; acid tolerance ; ATPase ; nickel toxicity ; nutrient uptake ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract This study concerns the inhibitory effects of acid pH and nickel on growth, nutrient (NO3 - and NH4 +) uptake, carbon fixation, O2 evolution, electron transport chain and enzyme (nitrate reductase and ATPase) activities of acid tolerant and wild-type strains of Chlorella vulgaris. Though a general reduction in all these variables was noticed with decreasing pH, the tolerant strain was found to be metabolically more active than the wild-type. A reduced cation (NH4 +, Na+, K+ and Ca2+) uptake, coupled with a facilitated influx of anions (NH4 +, PO4 3- and HCO3 -), suggested the development of a positive membrane potential in acid tolerant Chlorella. Nevertheless, a tremendous increase in ATPase activity at decreasing pH revealed the involvement of superactive ATPase in exporting H+ ions and keeping the internal pH neutral. A difference in Na+ and K+ efflux of the two strains at decreasing pH suggests there is a difference in membrane permeability. The low toxicity of Ni in the acid tolerant strain may be due to the low Ni uptake brought about by a change in membrane potential as well as in permeability. Hence, the development of superactive ATPase and a change in both membrane potential and permeability not only offers protection against acidity, but also co-tolerance to metals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00140491
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  • 6
    Electronic Resource
    Electronic Resource
    Modelling the constancy of X (1994)
    Springer
    Astrophysics and space science 216 (1994), S. 153-154 
    Details
    ISSN: 1572-946X
    Keywords: Chemistry ; Molecular Hydrogen ; Cloud Models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Observations of the CO J=1-0 line are commonly used as a tracer for molecular material in clouds. The ratio of the H2 column density to the integrated intensity of this line,X, is often taken to be constant, despite theoretical and observational uncertainty. We have tried to identify how this ratio depends on cloud parameters, testing a simple theoretical argument suggesting its invariance with respect to density. The apparent constancy can be understood if clouds are clumpy on scales of Av ≈ 1-2 mag.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00982486
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  • 7
    Electronic Resource
    Electronic Resource
    Modification of carbonic anhydrase activity by antisense and over-expression constructs in transgenic tobacco (1994)
    Springer
    Plant molecular biology 25 (1994), S. 377-385 
    Details
    ISSN: 1573-5028
    Keywords: carbonic anhydrase ; antisense ; over-expression ; tobacco ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The activity and location of carbonic anhydrase has been modified by transformation of tobacco with antisense and over-expression constructs. Antisense expression resulted in the inhibition of up to 99% of carbonic anhydrase activity but had no significant impact on net CO2 assimilation. Stomatal conductance and susceptibility to water stress appeared to increase in response to the decline in carbonic anhydrase activity. An over-expression construct designed to increase cytosolic carbonic anhydrase abundance resulted in a significant increase in net activity, a small increase in stomatal conductance but little impact on CO2 assimilation. Chloroplastic carbonic anhydrase activity was enhanced by the expression of an additional construct which targeted the polypeptide to the organelle. The increase in chloroplastic carbonic anhydrase appeared to be accompanied by a concomitant increase in Rubisco activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00043867
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  • 8
    Electronic Resource
    Electronic Resource
    Over-production of the D1 protein of photosystem II reaction centre in the cyanobacterium Synechococcus sp. PCC 7942 (1994)
    Springer
    Plant molecular biology 26 (1994), S. 709-721 
    Details
    ISSN: 1573-5028
    Keywords: gene expression ; photosynthesis ; protein turnover ; psbA ; tac promoter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The unicellular cyanobacterium Synechococcus sp. PCC 7942 has three psbA genes encoding two different forms of the photosystem II reaction centre protein D1 (D1:1 and D1:2). The level of expression of these psbA genes and the synthesis of D1:1 and D1:2 are strongly regulated under varying light conditions. In order to better understand the regulatory mechanisms underlying these processes, we have constructed a strain of Synechococcus sp. PCC 7942 capable of over-producing psbA mRNA and D1 protein. In this study, we describe the over-expression of D1:1 using a tac-hybrid promoter in front of the psbAI gene in combination with lacI Q repressor system. Over-production of D1:1 was induced by growing cells for 12 h at 50 μmol photons m-2 s-1 in the presence of 40 or 80 μg/ml IPTG. The amount of psbAI mRNA and that of D1:1 protein in cells grown with IPTG was three times and two times higher, respectively. A higher concentration of IPTG (i.e., 150 μg/ml) did not further increase the production of the psbAI message or D1:1. The over-production of D1:1 caused a decrease in the level of D1:2 synthesised, resulting in most PSII reaction centres containing D1:1. However, the over-production of D1:1 had no effect on the pigment composition (chlorophyll a or phycocyanin/number of cells) or the light-saturated rate of photosynthesis. This and the fact that the total amounts of D1 and D2 proteins were not affected by IPTG suggest that the number of PSII centres within the membranes remained unchanged. From these results, we conclude that expression of psbAI can be regulated by using the tac promoter and lacI Q system. However, the accumulation of D1:1 protein into the membrane is regulated by the number of PSII centres.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00013756
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  • 9
    Electronic Resource
    Electronic Resource
    Iron deprivation in cyanobacteria (1994)
    Springer
    Journal of applied phycology 6 (1994), S. 199-210 
    Details
    ISSN: 1573-5176
    Keywords: cyanobacteria ; iron deficiency ; photosynthesis ; siderophores ; flavodoxin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Iron is an essential component of electron transport in almost all living organisms. It is particularly important to phototrophs like cyanobacteria because 22–23 irons are required for a complete functional photosynthetic apparatus. Since the low solubility of Fe+++ above neutral pH in oxic ecosystems severely limits the biological availability of iron to aquatic microorganisms, cyanobacteria and other microbes have developed a number of responses to cope with iron deficiency. Cyanobacterial responses to iron stress include the synthesis of an efficient, siderophore-based system to scavenge iron and the substitution of ferredoxin with flavodoxin. An additional response in cyanobacteria involves the alteration of the light-harvesting apparatus that includes the appearance of a new, iron-stress-induced, photosystem II, chlorophyll-binding protein. Although cytochromec-553 has a potential non-iron-containing replacement in plastocyanin, a copper-containing protein, iron stress appears to favor the utilization of cytochromec-553 because siderophores also bind copper and form a complex that is excluded from the cell. This paper is intended primarily as a review of molecular and physiological responses of actively growing cyanobacterial cultures to conditions of iron stress, where iron is present but essentially insoluble, and to differentiate these responses from iron starvation, where the amount of iron in the system is not sufficient for cell growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02186073
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  • 10
    Electronic Resource
    Electronic Resource
    Use of chlorophyll fluorescence to estimate the effect of photoinhibition in outdoor cultures ofSpirulina platensis (1994)
    Springer
    Journal of applied phycology 6 (1994), S. 31-34 
    Details
    ISSN: 1573-5176
    Keywords: fluorescence ; photoinhibition ; photosynthesis ; Spirulina ; temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Chlorophyll fluorescence measurements were used to evaluate the effect of temperature on photoinhibition inSpirulina platensis cultures grown in tubular reactors outdoors. Cultures grown at 35 °C during the day time showed a lower reduction in the Fv/Fm ratio as compared to cultures grown at 25 °C. It is demonstrated that the lower temperature photoinhibited cells can undergo a complete recovery once transferred to low light and higher temperature. This recovery does not take place when 100 µg ml-1 chloramphenicol is added to cells. The recovery is light dependent and cells incubated in the dark at low temperature do not show a recovery in the Fv/Fm ratio. The data presented strongly support the hypothesis that photoinhibition takes place in outdoorSpirulina cultures. At the same time it is demonstrated that fluorescence measurements can be used as a fast reliable indication for photoinhibition in outdoor algal cultures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02185901
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  • 11
    Electronic Resource
    Electronic Resource
    Use of macroalgae for marine biomass production and CO2 remediation: a review (1994)
    Springer
    Journal of applied phycology 6 (1994), S. 45-60 
    Details
    ISSN: 1573-5176
    Keywords: biofilter ; biofuels ; CO2 ; macroalgae ; marine biomass ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Biomass production from macroalgae has been viewed as important mainly because of the need for pollution abatement. Environmental considerations will increasingly determine product and process acceptability and drive the next generation of economic opportunity. Some countries, including Japan, are actively promoting "green" technologies that will be in demand worldwide in the coming decades. Should an international agreement on CO2-reduction be ratified, its effective use for energy production would be of high priority. This report shows that macroalgae have great potential for biomass production and CO2 bioremediation. Macroalgae have high productivity, as great or greater than the most productive land plants, and do not compete with terrestrial crops for farm land. The review focuses on recent data on productivity, photosynthesis, nutrient dynamics, optimization and economics. Biomass from macroalgae promises to provide environmentally and economically feasible alternatives to fossil fuels. Nevertheless, the techniques and technologies for growing macroalgae on a large-scale and for converting feedstocks to energy carriers must be more fully developed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02185904
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  • 12
    Electronic Resource
    Electronic Resource
    What kind of lamp for the cultivation of algae? (1994)
    Springer
    Journal of applied phycology 6 (1994), S. 309-313 
    Details
    ISSN: 1573-5176
    Keywords: light source ; emission spectrum ; photosynthesis ; algae ; absorption ; efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A method for quantitative evaluation of light sources from the point of their suitability for algal cultivation is described. Two parameters are used for the evaluation: (1) amount of photons emitted in the spectral region absorbed by algae per consumed unit of electrical energy; (2) fraction of photons intercept by the algae that got effectively transformed into chemical energy. The value of parameter (2) depends on the emission spectrum of the light source, the absorption spectrum of the algae, quantum capacity of the algae and on conditions of cultivation. The method permits the assessment of the differences in algal productivity under light of various light sources with respect to other recent methods for comparison.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02181944
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  • 13
    Electronic Resource
    Electronic Resource
    Turbulence in mass algal cultures and the role of light/dark fluctuations (1994)
    Springer
    Journal of applied phycology 6 (1994), S. 331-335 
    Details
    ISSN: 1573-5176
    Keywords: turbulence ; photosynthesis ; Chlorella ; light/dark cycles ; mass transfer rates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In mass algal cultures, some form of agitation is usually provided; among other effects, this moves the organisms though an optically dense profile and provides mixing. During this transport, medium frequency fluctuations in the light energy supply are perceived by the algae, which are of the order of 1 Hz and less. It has been suggested that turbulence with the resultant light/dark cycles of medium frequency enhances productivity. However, turbulence has two major influences in a well mixed system: it facilitates fluctuating light regimes and increases the transfer rates between the growth medium and the cultured organism. An estimation of productivity as oxygen liberation was measured under laminar and turbulent flow rates, and varying light/dark ratios. Increased turbulence, which increased exchange rates of nutrients and metabolites between the cells and their growth medium, together with increased light/dark frequencies, increased productivity and photosynthetic efficiency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02181947
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  • 14
    Electronic Resource
    Electronic Resource
    Progress in the research of artemisinin-related antimalarials: An update (1994)
    Springer
    Pharmacy world & science 16 (1994), S. 169-180 
    Details
    ISSN: 1573-739X
    Keywords: Antimalarials ; Artemisia annua L ; Artemisinin ; Biosynthesis ; Chemistry ; Clinical trials ; Pharmacology ; Phytochemistry ; Sesquiterpenes ; Toxicology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Artemisinin, a sesquiterpene lactone endoperoxide isolated fromArtemisia annua L., and a number of its semisynthetic derivatives have shown to possess antimalarial properties. They are all eflective againstPlasmodium parasites that are resistant to the newest and commonly used antimalarial drugs. This article gives a survey of the literature dealing with artemisinin-relaled antimalarial issues that have appeared from the end of 1989 up to the beginning of 1994. A broad range of medical and pharmaceutical disciplines is covered, including phytochemical aspects like the selection of high-producing plants, analytical procedures, and plant biotechnology. Furthermore, the organic synthesis of artemisinin derivatives is discussed, as well as their mechanism of action and antimalarial activity, metabolism and pharmacokinetics, clinical studies, sideeffects and toxicology, and biological activities other than antimalarial activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01872865
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  • 15
    Electronic Resource
    Electronic Resource
    Genetic variation in pigeon pea (Cajanus cajan (L.) Mill sp.) in response to successive cycles of water stress (1994)
    Springer
    Plant and soil 158 (1994), S. 193-201 
    Details
    ISSN: 1573-5036
    Keywords: photosynthesis ; osmotic adjustment ; stomatal conductance ; relative water content ; water potential ; water relations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Four pigeon pea [Cajanus cajan (L.) Mill sp.] cultivars were studied during two cycles of development of water stress and recovery. During these two cycles the genetic variation in vegetative development, leaf water potential, relative water content, photosynthesis, and stomatal conductance was followed. Plants were grown in a greenhouse and irrigated every seventh day. On two occasions (30 days and 80 days from sowing) water was withheld for 13 days in one group of plants and 16 days in another. Control plants were irrigated as usual. The four cultivars differed in their response to drought, with ICPL 215 being the most tolerant cultivar. In the plants exposed to the 13-day water stress, the first stress cycle resulted in preconditioning of plants such that higher values for carbon dioxide exchange rate and relative water content were observed in the second stress cycle. The longer stress period (16 days) resulted in some damage to the photosynthetic capacity and in a slow recovery rate in both cycles. During the second drought cycle the plants retained a water content above the critical value, possibly due to osmotic adjustment. It seems that water status parameters, especially relative water content, may serve as indicators of drought tolerance in pigeon pea varieties and may be useful in breeding programs for cultivation of pigeon pea under semiarid conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00009494
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  • 16
    Electronic Resource
    Electronic Resource
    Model studies of chlorophyll fluorescence reabsorption at chloroplast level under different exciting conditions (1994)
    Springer
    Photosynthesis research 40 (1994), S. 67-74 
    Details
    ISSN: 1573-5079
    Keywords: light conditions ; theoretical model ; barley leaf ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A theoretical model is presented describing the distortion of chlorophyll fluorescence spectra of a chloroplast or a group of chloroplasts by the effect of fluorescence reabsorption. Model calculations using the experimental data show that the primary reabsorption effect occurs already within one chloroplast and the spectral distortion depends significantly on the excitation regime of the chloroplast. A theoretical dependence of the distortion function, defined as a change in the F(685)/F(735) fluorescence band ratio, on the mean chlorophyll concentration in a chloroplast is predicted for different light excitation regimes. The distortion of measured chlorophyll fluorescence spectra at 77 K of chloroplast suspension adsorbed on filter papers of two strongly different diffusive reflectivities and at different mean chlorophyll concentrations are discussed with the help of the presented theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00019046
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  • 17
    Electronic Resource
    Electronic Resource
    UV-B damage and protection at the molecular level in plants (1994)
    Springer
    Photosynthesis research 39 (1994), S. 475-489 
    Details
    ISSN: 1573-5079
    Keywords: DNA repair ; flavonoids ; gene expression ; oxidative stress ; photosynthesis ; promoter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Influx of solar UV-B radiation (280–320 nm) will probably increase in the future due to depletion of stratospheric ozone. In plants, there are several targets for the deleterious UV-B radiation, especially the chloroplast. This review summarizes the early effects and responses of low doses of UV-B at the molecular level. The DNA molecules of the plant cells are damaged by UV due to the formation of different photoproducts, such as pyrimidine dimers, which in turn can be combatted by specialized photoreactivating enzyme systems. In the chloroplast, the integrity of the thylakoid membrane seems to be much more sensitive than the activities of the photosynthetic components bound within. However, the decrease of mRNA transcripts for the photosynthetic complexes and other chloroplast proteins are among very early events of UV-B damage, as well as protein synthesis. Other genes, encoding defence-related enzymes, e.g., of the flavonoid biosynthetic pathway, are rapidly up-regulated after commencement of UV-B exposure. Some of the cis-acting nucleotide elements and trans-acting protein factors needed to regulate the UV-induced expression of the parsley chalcone synthase gene are known.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00014600
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  • 18
    Electronic Resource
    Electronic Resource
    Photosynthetic electrogenic events in native membranes ofChloroflexus aurantiacus. Flash-induced charge displacements within the reaction center-cytochromec 554 complex (1994)
    Springer
    Photosynthesis research 41 (1994), S. 135-143 
    Details
    ISSN: 1573-5079
    Keywords: photosynthesis ; electrometry ; membrane potential ; electron transfer ; charge displacement ; electrostatic ; Chloroflexus aurantiacus ; Rhodopseudomonas viridis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The thermophilic phototrophChloroflexus aurantiacus possesses a photosynthetic reaction center (RC) containing a pair of menaquinones as primary (QA) and secondary (QB) electron acceptors and a bacteriochlorophyll dimer (P) as a primary donor. A tetraheme cytochromec 554 with two high(H)- and two low(L)-potential hemes operates as an immediate electron donor for P. The following equilibrium Em,7 values were determined by ESR for the hemes in whole membrane preparations: 280 mV (H1), 150 mV (H2), 95 mV (L1) and 0 mV (L2) (Van Vliet et al. (1991) Eur. J. Biochem. 199: 317–323). Partial electrogenic reactions induced by a laser flash inChl. aurantiacus chromatophores adsorbed to a phospholipid-impregnated collodion film were studied electrometrically at pH 8.3. The photoelectric response included a fast phase of ΔΨ generation (τ 〈 10 ns, phase A). It was ascribed to the charge separation between P+ and QA − as its amplitude decreased both at high and low Eh values (Em,high=360±10 mV, estimated Em,low∼\s-160 mV) in good agreement with Em values for P/P+ and QA/QA − redox couples. A slower kinetic component appeared upon reduction of the cytochromec 554 hemes (phase C). With H1 reduced before the flash the amplitude of phase C was equal to 15–20% of that of phase A and its rise time was 1.2–1.3 μs: we attribute this phase to the electrogenic electron transfer from H1 to P+. Pre-reduction of H2 decreased the τ value to about 700–800 ns and increased the amplitude of phase C to 30–35% of that of phase A. Pre-reduction of L1 further accelerated phase C (up to τ of 500 ns) and induced a reverse electrogenic phase with τ of 12 μs and amplitude equal to 10% of phase A. Upon pre-reduction of L2 the rise time of phase C was decreased to about 300 ns and its amplitude decreased by 30%. The acceleration in the onset of phase C is explained by the acceleration of the rate-limiting H1 ⇒ P electrogenic reaction after reduction of the other hemes due to their electrostatic influence; a P-H1-(L1-L2)-H2 alignment of redox centers with an approximately rhombic arrangement of the cytochromec 554 hemes is proposed. The observed reverse phase is ascribed to the post-flash charge redistribution between the hemes. Redox titration of the amplitude of phase C yielded the Em,8.3 values of H1, H2 and L2 hemes: 340±10 mV for H1, 160±20 mV for H2 and −40±40 mV for L2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02184153
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  • 19
    Electronic Resource
    Electronic Resource
    Pigment interactions in chlorosomes of various green bacteria (1994)
    Springer
    Photosynthesis research 41 (1994), S. 175-180 
    Details
    ISSN: 1573-5079
    Keywords: Chlorobium ; Chloroflexus ; chlorophyll ; light-harvesting ; photosynthesis ; resonance Raman
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Resonance Raman experiments were performed on different green bacteria. With blue excitation, i.e. under Soret resonance or preresonance conditions, resonance Raman contributions were essentially arising from the chlorosome pigments. By comparing these spectra and those of isolated chlorosomes, it is possible to evaluate how the latter retain their native structure during the isolation procedures. The structure of bacteriochlorophyll oligomers in chlorosomes was interspecifically compared, in bacteriochlorophyllc- and bacteriochlorophylle- synthesising bacteria. It appears that interactions assumed by the 9-keto carbonyl group are identical inChlorobium limicola, Chlorobium tepidum, andChlorobium phaeobacteroides. In the latter strain, the 3-formyl carbonyl group of bacteriochlorophylle is kept free from intermolecular interactions. By contrast, resonance Raman spectra unambiguously indicate that the structure of bacteriochlorophyll oligomers is slightly different in chlorosomes fromChloroflexus auranticus, either isolated or in the whole bacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02184158
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  • 20
    Electronic Resource
    Electronic Resource
    The formation and characterization of the in vitro polymeric aggregates of bacteriochlorophyllc homologs fromChlorobium limicola in aqueous suspension in the presence of monogalactosyl diglyceride (1994)
    Springer
    Photosynthesis research 41 (1994), S. 235-243 
    Details
    ISSN: 1573-5079
    Keywords: bacteriochlorophyll ; chlorosomeChlorobium limicola ; green bacteria ; photosynthesis ; monogalactosyl diglyceride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Artificial aggregates of bacteriochlorophyllc (BChlc) were formed in an aqueous medium in the presence of a lipid, monogalactosyl diglyceride (MGDG), and the optical properties of those aggregates were studied by absorption and circular dichroism (CD) mainly. Four BChlc homologs, ([E,E]BChlc F, [P,E]BChlc F, [E,M]BChlc F and [I,E]BChlc F), were isolated from the green photosynthetic bacteriumChlorobium limicola strain 6230. Above 0.0004%, MGDG induced a red-shift of the absorption maxima of BChlc aggregates. At 0.003% MGDG BChlc aggregates showed absorption maxima in the range of 724 to 745 (±3) nm with a shift of 12 to 24 (±3) nm depending on the homolog species. Four kinds of BChlc-MGDG aggregates showed characteristic CD spectra. [E,M]BChlc F gave rise to a CD spectrum similar to that of chlorosomes, while the other three gave spectra of opposite sign. These aggregates are sensitive to 1-hexanol treatment; in a saturating amount (0.85%) of 1-hexanol, all the homologs gave a monomer-like absorption spectrum peaking at 670nm. At an intermediate concentration (0.5%), [E,M]BChlc F showed an enhanced CD intensity, as observed in native chlorosomes. Resonance Raman spectra of the monomer-like BChlc samples indicated that the keto vibrational band at ca. 1640 cm−1 was considerably weakened by the 0.85% 1-hexanol treatment, however the 1680 cm−1 band characteristic of a free keto group did not appear. These results indicate that the artificial aggregates formed by purified BChlc homologs and MGDG are good models for studying chlorosomes structure.
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    URL: http://dx.doi.org/10.1007/BF02184164
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    Sensitivity of the relative Fpl level of chlorophyll fluorescence induction in leaves to the heat stress (1994)
    Springer
    Photosynthesis research 39 (1994), S. 201-204 
    Details
    ISSN: 1573-5079
    Keywords: automatic determination ; fluorescence parameters ; fluorometer ; induction curve ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The (Fpl-Fo)/Fv value of the fluorescence induction curve is shown to be a more suitable parameter to detect a wider range of heat stress damage to thylakoid membranes as compared to quantities t 1/2 (time of fluorescence rise from Fo to (Fo+Fm)/2 level) and % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaa0aaaeaacq% aHepaDaaaaaa!39D5!\[\overline \tau \] (the fluorescence induction time defined as the area above the induction curve normalized to Fv=1). A method for exact and automatic Fpl determination is presented. A break point in the quality and behaviour of the fluorescence induction curve of barley leaves incubated at 49°C was reached at the moment (about 240 s) when the transformation of PS II active (QB-reducing) to PS II inactive (QB-non-reducing) centres was completed. The meaning of the standard Fv and Fv/Fm parameter was then changed. The method of Fpl determination described here may help to increase the analytical value of the standard chlorophyll fluorometers.
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    URL: http://dx.doi.org/10.1007/BF00029387
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    The role of iron in phytoplankton photosynthesis, and the potential for iron-limitation of primary productivity in the sea (1994)
    Springer
    Photosynthesis research 39 (1994), S. 275-301 
    Details
    ISSN: 1573-5079
    Keywords: chlorosis ; diagnostic ; flavodoxin ; iron-limitation ; photosynthesis ; phytoplankton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Iron supply has been suggested to influence phytoplankton biomass, growth rate and species composition, as well as primary productivity in both high and low NO3 − surface waters. Recent investigations in the equatorial Pacific suggest that no single factor regulates primary productivity. Rather, an interplay of bottom-up (i.e., ecophysiological) and top-down (i.e., ecological) factors appear to control species composition and growth rates. One goal of biological oceanography is to isolate the effects of single factors from this multiplicity of interactions, and to identify the factors with a disproportionate impact. Unfortunately, our tools, with several notable exceptions, have been largely inadequate to the task. In particular, the standard technique of nutrient addition bioassays cannot be undertaken without introducing artifacts. These so-called ‘bottle effects’ include reducing turbulence, isolating the enclosed sample from nutrient resupply and grazing, trapping the isolated sample at a fixed position within the water column and thus removing it from vertical movement through a light gradient, and exposing the sample to potentially stimulatory or inhibitory substances on the enclosure walls. The problem faced by all users of enrichment experiments is to separate the effects of controlled nutrient additions from uncontrolled changes in other environmental and ecological factors. To overcome these limitations, oceanographers have sought physiological or molecular indices to diagnose nutrient limitation in natural samples. These indices are often based on reductions in the abundance of photosynthetic and other catalysts, or on changes in the efficiency of these catalysts. Reductions in photosynthetic efficiency often accompany nutrient limitation either because of accumulation of damage, or impairment of the ability to synthesize fully functional macromolecular assemblages. Many catalysts involved in electron transfer and reductive biosyntheses contain iron, and the abundances of most of these catalysts decline under iron-limited conditions. Reductions of ferredoxin or cytochrome f content, nitrate assimilation rates, and dinitrogen fixation rates are amongst the diagnostics that have been used to infer iron limitation in some marine systems. An alternative approach to diagnosing iron-limitation uses molecules whose abundance increases in response to iron-limitation. These include cell surface iron-transport proteins, and the electron transfer protein flavodoxin which replaces the Fe-S protein ferredoxin in many Fe-deficient algae and cyanobacteria.
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    URL: http://dx.doi.org/10.1007/BF00014588
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    Molecular topology of the Photosystem II chlorophyll a binding protein, CP 43: Topology of a thylakoid membrane protein (1994)
    Springer
    Photosynthesis research 40 (1994), S. 11-19 
    Details
    ISSN: 1573-5079
    Keywords: photosynthesis ; membrane protein ; protein structure ; light harvesting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have used antibodies generated against synthetic peptides to determine the topology of the 43 kD chlorophyll a binding protein (CP 43) of Photosystem II. Based on the pattern of proteolytic fragments detected (on western blots) by peptide specific antibodies, a six transmembrane span topological model, with the amino and carboxyl termini located on the stromal membrane surface, is predicted. This structure is similar to that predicted for CP 47, a PS II chlorophyll a binding protein (Bricker T (1990) Photosynth Res 24: 1–13). The model is discussed in reference to the possible location of chlorophyll binding sites.
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    URL: http://dx.doi.org/10.1007/BF00019041
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  • 24
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    The Wageningen Rhizolab — a facility to study soil-root-shoot-atmosphere interactions in crops (1994)
    Springer
    Plant and soil 161 (1994), S. 275-287 
    Details
    ISSN: 1573-5036
    Keywords: crop growth ; gas exchange ; minirhizotrons ; nutrients ; photosynthesis ; respiration ; rhizotron ; root observation ; root growth ; water balance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A research facility is described for the integrated study of soil-root-shoot-atmosphere relationships in crops. The Wageningen Rhizolab has been in use since 1990, and consists of two rows, each with eight below-ground compartments aligned along a corridor. A rain shelter automatically covers the experimental area at the start of rainfall. Compartments are 125 cm × 125 cm and 200 cm deep. Each compartment has a separate drip irrigation system. Crop canopy photosynthesis, respiration, and transpiration can be measured simultaneously and continuously on four out of eight compartments at a time. Each compartment can be filled with a selected soil material (repacked soil) and is accessible from the corridor over its full depth. Multiple sensors for measuring soil moisture status, electrical conductivity, temperature, soil respiration, trace gases and oxygen are installed in spatial patterns in accordance with the requirements of the experiments. Sensors are connected to control and data-acquisition devices. Likewise, provisions have been made to sample manually the soil solution and soil atmosphere. Root observation tubes (minirhizotrons) are installed horizontally at depth intervals ranging from 5 cm (upper soil layers) to 25 cm (below 1 m). The facility is at present in use to study growth and development of vegetation (crops) in relation to drought, nutrient status, soil-borne diseases, and underground root competition. One important application is the study of elevated CO2 concentration and climate change and the way they affect crops and their carbon economy. Growth and development of field grown vegetables and winter cover crops are also evaluated. The common aspect of those studies is to gain a better understanding of crop growth under varying environmental conditions, and to collect datasets that may help to improve mechanistic crop growth simulation models that can address suboptimal growth conditions.
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    URL: http://dx.doi.org/10.1007/BF00046399
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    Effects of nitrogen supply on the acclimation of photosynthesis to elevated CO2 (1994)
    Springer
    Photosynthesis research 39 (1994), S. 389-400 
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    ISSN: 1573-5079
    Keywords: elevated CO2 ; nitrogen supply ; photosynthesis ; acclimation ; growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A common observation in plants grown in elevated CO2 concentration is that the rate of photosynthesis is lower than expected from the dependence of photosynthesis upon CO2 concentration in single leaves of plants grown at present CO2 concentration. Furthermore, it has been suggested that this apparent down regulation of photosynthesis may be larger in leaves of plants at low nitrogen supply than at higher nitrogen supply. However, the available data are rather limited and contradictory. In this paper, particular attention is drawn to the way in which whole plant growth response to N supply constitutes a variable sink strength for carbohydrate usage and how this may affect photosynthesis. The need for further studies of the acclimation of photosynthesis at elevated CO2 in leaves of plants whose N supply has resulted in well-defined growth rate and sink activity is emphasised, and brief consideration is made of how this might be achieved.
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    URL: http://dx.doi.org/10.1007/BF00014593
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    The influence of ammonia on the growth and photosynthesis of Ruppia drepanensis Tineo from Doñana National Park (SW Spain) (1994)
    Springer
    Hydrobiologia 275-276 (1994), S. 219-231 
    Details
    ISSN: 1573-5117
    Keywords: Ruppia drepanensis ; ammonia toxicity ; temperature effects ; photosynthesis ; growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In a laboratory experiment, Ruppia drepanensis Tineo seedlings from a brackish marsh in Southern Spain were grown at 20 and 30 °C, at three different nitrogen levels. These levels were obtained by the addition of a slow release fertilizer (23% NH4NO3 by weight) to a sediment mixture of sand and clay (3:1). Several morphometric parameters were recorded during the first five weeks of the experiment, and photosynthesis and respiration were measured after 7 weeks of growth. Results showed a significant reduction of growth and development with increasing nitrogen and temperature levels. Dark respiration increased strongly at high nitrogen levels. At the same time, net photosynthesis at 250 and 500 µE m-2 s-1, Pm, Km and LCP were not affected by either factor. We attribute these phenomena to ammonia toxicity, since relatively high total ammonia (NH3 + NHf4 p+) levels were found in the interstitial water.
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    URL: http://dx.doi.org/10.1007/BF00026713
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    Environmental control of phytoplankton productivity in turbulent turbid systems (1994)
    Springer
    Hydrobiologia 289 (1994), S. 65-72 
    Details
    ISSN: 1573-5117
    Keywords: photosynthesis ; selective environments ; resuspension ; disturbance ; rivers ; shallow lakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Factors affecting phytoplankton productivity are analysed in turbid systems, such as shallow lakes and rivers. When resuspension from the sediment or loading from the catchment significantly increases inorganic (non-algal) turbidity and hence light attenuation potentials for high production are not realised. Energy available for phytoplankton growth is strongly regulated by underwater light availability which depends on the critical mixing depth, fluctuating light intensities and algal circulation patterns. Higher production rates in shallow waters are often compensated by greater algal respiration due to higher water temperatures when compared to deeper lakes. Total daily integral production of turbulent, turbid environments can be predicted from a combination of easily measured variables such as maximum photosynthetic rates, algal biomass, surface irradiance and some measure of underwater light attenuation.
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    URL: http://dx.doi.org/10.1007/BF00007409
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    Effects of homobrassinolide application on plant metabolism and grain yield under irrigated and moisture-stress conditions of two wheat varieties (1994)
    Springer
    Plant growth regulation 14 (1994), S. 173-181 
    Details
    ISSN: 1573-5087
    Keywords: homobrassinolide ; irrigated ; membrane stability ; moisture-stress ; nitrate reductase activity ; photosynthesis ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Homobrassinolide (BR) was applied either as a seed treatment or foliar spray to two contrasting wheat varieties, viz. C306 (drought tolerant) and HD2329 (drought susceptible), to examine its effects on plant metabolism and grain yield under irrigated and moisture-stress/rainfed conditions. BR application resulted in increased relative water content, nitrate reductase activity, chlorophyll content and photosynthesis under both conditions. BR application also improved membrane stability (lower injury). These beneficial effects resulted in higher leaf area, biomass production, grain yield and yield related parameters in the treated plants. All the treatments were significantly better than the untreated control. Generally, 0.05 ppm either as a seed treatment or foliar spray was more effective than the 0.01 ppm treatment. The drought-tolerant genotype C306 showed more response to BR application under moisture-stress/rainfed condition than HD 2329. Increased water uptake, membrane stability and higher carbon dioxide and nitrogen assimilation rates under stress seemed to be related to homobrassinolide-induced drought tolerance.
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    URL: http://dx.doi.org/10.1007/BF00025220
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    Development and ecological importance of phytoplankton in a large lowland river (River Meuse, Belgium) (1994)
    Springer
    Hydrobiologia 289 (1994), S. 139-155 
    Details
    ISSN: 1573-5117
    Keywords: potamoplankton ; regulated river ; transport of carbon and nutrients ; photosynthesis ; respiration ; dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The ecological importance of the River Meuse phytoplankton with regard to carbon and nutrient transport has been examined in two reaches of the Belgian course of the river. Field measurements of total particulate organic carbon (POC), particulate organic nitrogen (PON) and particulate phosphorus (PP) show that the large autochtonous production of organic matter strongly affects the carbon and nutrient budget of the aquatic system. During the growing season, phytoplankton accounts for nearly 60% of the POC and dominates the PON. Calculations of the carbon and oxygen budget in the upper reach of the Belgian Meuse demonstrates that the ecosystem is autotrophic, i.e. that autochtonous FPOM (fine particulate organic matter) production is the major carbon input. This suggests that in large lowland rivers, primary production (P) may exceed community respiration (R), i.e. P:R〉1, whereas they are assumed to be heterotrophic (P:R〈1) in the River Continuum concept. The question of maintenance of phytoplankton in turbid mixed water columns is also addressed, and the case of the River Meuse is treated on the basis of studies of photosynthesis and respiration (ETS measurements). The results suggest that the potamoplankton may show some low-light acclimation, through an increase of chlorophyll a relative to biomass, when it comes to deep downstream reaches, and that algal respiration rate may be reduced. A simulation of the longitudinal development of the algal biomass shows the different phases of algal growth and decline along the river and brings support to the ‘importation hypothesis’ for explaining maintenance of potamoplankton in the downstream reaches.
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    URL: http://dx.doi.org/10.1007/BF00007415
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    An active Mehler-peroxidase reaction sequence can prevent cyclic PS I electron transport in the presence of dioxygen in intact spinach chloroplasts (1994)
    Springer
    Photosynthesis research 41 (1994), S. 429-437 
    Details
    ISSN: 1573-5079
    Keywords: photosynthesis ; ascorbate peroxidase ; Mehler reaction ; cyclic PS I ; chlorophyll fluorescence ; 9-aminoacridine fluorescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Simultaneous measurements of 9-aminoacridine (9-AA) fluorescence quenching, O2-uptake and chlorophyll fluorescence of intact spinach chloroplasts were carried out to assess the relationship between the transthylakoidal ΔpH and linear electron flux passing through Photosystem II. Three different types of O2-dependent electron flow were investigated: (1) Catalysed by methyl viologen; (2) in the absence of a catalyst and presence of an active ascorbate peroxidase (Mehler-peroxidase reaction); (3) in the absence of a catalyst and with the ascorbate peroxidase being inhibited by KCN (Mehler reaction). The aim of this study was to assess the relative contribution of ΔpH-formation which is not associated with electron flow through Photosystem II and, which should reflect Photosystem I cyclic flow under the different conditions. The relationship between the extent of 9-AA fluorescence quenching and O2-uptake rate was found to be almost linear when methyl viologen was present. In the absence of methyl viologen (Mehler reaction) an increase of 9-AA fluorescence quenching to a value of 20% at low light intensities was associated with considerably less O2-uptake than in the presence of methyl viologen, indicating the involvement of cyclic flow. These findings are in agreement with a preceding study of Kobayashi and Heber (1994). However, when no KCN was added, such that the complete Mehler-peroxidase reaction sequence was operative, the relationship between 9-AA fluorescence quenching and the flux through PS II, as measured via the chlorophyll fluorescence parameter ΔF/Fm′ × PAR, was identical to that observed in the presence of methyl viologen. Under the assumption that methyl viologen prevents cyclic flow, it is concluded that there is no significant contribution of cyclic electron flow to ΔpH-generation in intact spinach chloroplasts.
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    Effects of two sesquiterpene lactones isolated fromArtemisia annua on physiology ofLemna minor (1994)
    Springer
    Journal of chemical ecology 20 (1994), S. 969-978 
    Details
    ISSN: 1573-1561
    Keywords: Artemisinin ; arteannuic acid ; photosynthesis ; respiration ; chlorophyll ; Lemna minor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The effects of artemisinin and arteannuic acid extracted fromArtemisia annua on the physiology ofLemna minor were evaluated. Changes in frond production, growth, dry weight, and chlorophyll content ofL. minor were determined. Photosynthesis and respiration were evaluated with a differential respirometer. Artemisinin (5 µM) inhibitedL. minor frond production and dry weight 82 and 83%, relative to methanol controls. Chlorophyll content was reduced 44% by artemisinin (2.5 µM). Arteannuic acid (10 µM) was less active, inhibiting frond production 61% and reducing chlorophyll content 66% at 5 µM. Artemisinin (1 µM) reducedL. minor photosynthesis 30% and 2.5 µM reduced respiration 39%. Arteannuic acid had no significant effect on photosynthesis or respiration at the levels tested.
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    Photosynthetic electron transport and anaerobic metabolism in purple non-sulfur phototrophic bacteria (1994)
    Springer
    Antonie van Leeuwenhoek 66 (1994), S. 151-164 
    Details
    ISSN: 1572-9699
    Keywords: purple non-sulfur bacteria ; Rhodobacter ; photosynthesis ; CO2 fixation ; anaerobic respiration ; gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Purple non-sulfur phototrophic bacteria, exemplifed byRhodobacter capsulatus andRhodobacter sphaeroides, exhibit a remarkable versatility in their anaerobic metabolism. In these bacteria the photosynthetic apparatus, enzymes involved in CO2 fixation and pathways of anaerobic respiration are all induced upon a reduction in oxygen tension. Recently, there have been significant advances in the understanding of molecular properties of the photosynthetic apparatus and the control of the expression of genes involved in photosynthesis and CO2 fixation. In addition, anaerobic respiratory pathways have been characterised and their interaction with photosynthetic electron transport has been described. This review will survey these advances and will discuss the ways in which photosynthetic electron transport and oxidation-reduction processes are integrated during photoautotrophic and photoheterotrophic growth.
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    Protein structure, electron transfer and evolution of prokaryotic photosynthetic reaction centers (1994)
    Springer
    Antonie van Leeuwenhoek 65 (1994), S. 311-329 
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    ISSN: 1572-9699
    Keywords: photosynthesis ; chlorophyll ; bacteriochlorophyll ; reaction center ; electron transfer ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosynthetic reaction centers from a variety of organisms have been isolated and characterized. The groups of prokaryotic photosynthetic organisms include the purple bacteria, the filamentous green bacteria, the green sulfur bacteria and the heliobacteria as anoxygenic representatives as well as the cyanobacteria and prochlorophytes as oxygenic representatives. This review focuses on structural and functional comparisons of the various groups of photosynthetic reaction centers and considers possible evolutionary scenarios to explain the diversity of existing photosynthetic organisms.
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    Genetic variation for resistance to low-temperature photoinhibition of photosynthesis in maize (Zea mays L.) (1994)
    Springer
    Euphytica 80 (1994), S. 85-93 
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    ISSN: 1573-5060
    Keywords: maize ; Zea mays ; photoinhibition ; photosynthesis ; low-temperature adaptation ; breeding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Sixty-seven inbred lines of maize were evaluated for resistance to low-temperature photoinhibition of photosynthesis, using a pulse-modulated chlorophyll fluorescence technique. The evaluation procedure was based on leaf discs, which were exposed to a high irradiance (1000 µmol/m2/s) at 7°C. The efficiency of open PSII reaction centres as a reflection of overall photosynthesis was measured before and after a photoinhibition-inducing treatment. Exposure of leaf discs to photoinhibitory condition for 2, 4, and 8 hours resulted in an efficiency reduction of 30, 53 and 83%, respectively. Testing of inbred lines showed large differences for photoinhibition susceptibility. The difference in photosynthetic efficiency between the most extreme lines after a treatment of eight hours was 39%. Resistance to photoinhibition was shown to be relevant under cool field conditions. It proved to be a trait strongly amenable to selection.
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    Optimal acclimation of the C3 photosynthetic system under enhanced CO2 (1994)
    Springer
    Photosynthesis research 39 (1994), S. 401-412 
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    ISSN: 1573-5079
    Keywords: photosynthesis ; elevated CO2 ; source-sink interactions ; Rubisco
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A range of studies of C3 plants have shown that there is a change in both the carbon flux and the pattern of nitrogen allocation when plants are grown under enhanced CO2. This paper examines evidence that allocation of nitrogen both to and within the photosynthetic system is optimised with respect to the carbon flux. A model is developed which predicts the optimal relative allocation of nitrogen to key enzymes of the photosynthetic system as a function of CO2 concentration. It is shown that evidence from flux control analysis is broadly consistent with this model, although at high nitrogen and under certain conditions at low nitrogen experimental data are not consistent with the model. Acclimation to enhanced CO2 is also assessed in terms of resource allocation between photosynthate sources and sinks. A means of assessing the optimisation of this source-sink allocation is proposed, and several studies are examined within this framework. It is concluded that C3 plants probably possess the genetic feedback mechanisms required to efficiently ‘smooth out” any imbalance within the photosynthetic system caused by a rise in atmospheric CO2.
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    URL: http://dx.doi.org/10.1007/BF00014594
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    Biochemical and molecular basis for impairment of photosynthetic potential (1994)
    Springer
    Photosynthesis research 39 (1994), S. 453-462 
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    ISSN: 1573-5079
    Keywords: photosynthesis ; Rubisco ; ozone ; oxidative stress ; rbcS mRNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ozone induces reductions in net photosynthesis in a large number of plant species. A primary mechanism by which photosynthesis is reduced is through impact on carbon dioxide fixation. Ozone induces loss in Rubisco activity associated with loss in concentration of the protein. Evidence is presented that ozone may induce oxidative modification of Rubisco leading to subsequent proteolysis. In addition, plants exposed to ozone sustain reduction in rbcS, the mRNA for the small subunit of Rubisco. This loss in rbcS mRNA may lead to a reduced potential for synthesis of the protein. The regulation of O3-induced loss of Rubisco, and implications of the decline in this protein in relation to accelerated senescence are discussed.
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    URL: http://dx.doi.org/10.1007/BF00014598
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    Reminiscence about‘Chloropseudomonas ethylicum’ and the FMO-protein (1994)
    Springer
    Photosynthesis research 41 (1994), S. 3-5 
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    ISSN: 1573-5079
    Keywords: bacteriochlorophylla-protein ; green sulfur bacteria ; Prosthecochloris aestuarii ; Chlorobium limicola ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In 1961 the green sulfur bacterium-containing mixed culture known as‘Chloropseudomonas ethylicum’ was brought to Brookhaven National Laboratory (USA) from Moscow State University (USSR). The water-soluble bacteriochlorophylla-protein (FMO-protein) was extracted, purified and characterized by absorption and circular dichroism spectroscopy, by X-ray crystallography and by primary structure determination.
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    URL: http://dx.doi.org/10.1007/BF02184138
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    Rates of vectorial proton transport supported by cyclic electron flow during oxygen reduction by illuminated intact chloroplasts (1994)
    Springer
    Photosynthesis research 41 (1994), S. 419-428 
    Details
    ISSN: 1573-5079
    Keywords: 9-aminoacridine fluorescence ; cyclic electron transport ; Mehler reaction ; photosynthesis ; photosystems ; transthylakoid proton gradient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The light-dependent quenching of 9-aminoacridine fluorescence was used to monitor the state of the transthylakoid proton gradient in illuminated intact chloroplasts in the presence or absence of external electron acceptors. The absence of appreciable light-dependent fluorescence quenching under anaerobic conditions indicated inhibition of coupled electron transport in the absence of external electron acceptors. Oxygen relieved this inhibition. However, when DCMU inhibited excessive reduction of the plastoquinone pool in the absence of oxygen, coupled cyclic electron transport supported the formation of a transthylakoid proton gradient even under anaerobiosis. This proton gradient collapsed in the presence of oxygen. Under aerobic conditions, and when KCN inhibited ribulose bisphosphate carboxylase and ascorbate peroxidase, fluorescence quenching indicated the formation of a transthylakoid proton gradient which was larger with oxygen in the Mehler reaction as electron acceptor than with methylviologen at similar rates of linear electron transport. Apparently, cyclic electron transport occured simultaneously with linear electron transport, when oxygen was available as electron acceptor, but not when methylviologen accepted electrons from Photosystem I. The ratio of cyclic to linear electron transport could be increased by low concentrations of DCMU. This shows that even under aerobic conditions cyclic electron transport is limited in isolated intact chloroplasts by excessive reduction of electron carriers. In fact, P700 in the reaction center of Photosystem I remained reduced in illuminated isolated chloroplasts under conditions which resulted in extensive oxidation of P700 in leaves. This shows that regulation of Photosystem II activity is less effective in isolated chloroplasts than in leaves. Assuming that a Q-cycle supports a H+/e ratio of 3 during slow linear electron transport, vectorial proton transport coupled to Photosystem I-dependent cyclic electron flow could be calculated. The highest calculated rate of Photosystem I-dependent proton transport, which was not yet light-saturated, was 330 μmol protons (mg chlorophyll h)−1 in intact chloroplasts. If H+/e is not three but two proton transfer is not 330 but 220 μmol (mg Chl H)−1. Differences in the regulation of cyclic electron transport in isolated chloroplasts and in leaves are discussed.
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    Pigment orientation changes accompanying the light state transition in Synechococcus sp. PCC 6301 (1994)
    Springer
    Photosynthesis research 40 (1994), S. 35-44 
    Details
    ISSN: 1573-5079
    Keywords: allophycocyanin ; chlorophyll a ; linear dichroism ; phycobilisome ; photosynthesis ; state transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Low temperature (77 K) linear dichroism spectroscopy was used to characterize pigment orientation changes accompanying the light state transition in the cyanobacterium, Synechococcus sp. PCC 6301 and those accompanying chromatic acclimation in Porphyridium cruentum in samples stabilized by glutaraldehyde fixation. In light state 2 compared to light state 1 intact cells of Synechococcus showed an increased alignment of allophycocyanin parallel to the cells' long axis whereas the phycobilisomethylakoid membrane fragments exhibited an increased allophycocyanin alignment parallel to the membrane plane. The phycobilisome-thylakoid membrane fragments showed less alignment of a short wave-length chlorophyll a (Chl a) Qy transition dipole parallel to the membrane plane in state 2 relative to state 1. To aid identification of the observed Chl a orientation changes in Synechococcus, linear dichroism spectra were obtained from phycobilisome-thylakoid membrane fragments isolated from red light-grown (increased number of PS II centres) and green light-grown (increased number of PS I centres) cells of the red alga Porphyridium cruentum. An increased contribution of short wavelength Chl a Qy transition dipoles parallel to the long axis of the membrane plane was directly correlated with increased levels of PS II centres in red light-grown P. cruentum. Our results indicate that the transition to state 2 in cyanobacteria is accompanied by an increase in the orientation of allophycocyanin and a decrease in the orientation of Chl a associated with PS II with respect to the thylakoid membrane plane.
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    Photoinhibition of photosynthesis in chilled potato leaves is not correlated with a loss of Photosystem-II activity (1994)
    Springer
    Photosynthesis research 40 (1994), S. 75-92 
    Details
    ISSN: 1573-5079
    Keywords: chilling temperature ; oxygen toxicity ; photoinhibition ; photosynthesis ; photosystems ; superoxide dismutase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When 23 °C-grown potato leaves (Solanum tuberosum L.) were irradiated at 23 °C with a strong white light, photosynthetic electron transport and Photosystem-II (PS II) activity were inhibited in parallel. When the light treatment was given at a low temperature of 3 °C, the photoinhibition of photosynthesis was considerably enhanced, as expected. Surprisingly, no such stimulation of photoinhibition was observed with respect to the PS II function. A detailed functional analysis of the photosynthetic apparatus, using in-vivo fluorescence, absorbance, oxygen and photoacoustic measurements, and artificial electron donors/acceptors, showed a pronounced alteration of PS I activity during light stress at low temperature. More precisely, it was observed that both the pool of photooxidizeable reaction center pigment (P700) of PS I and the efficiency of PS I to oxidize P700 were dramatically reduced. Loss of P700 activity was shown to be essentially dependent on atmospheric O2 and to require a continued flow of electrons from PS II, suggesting the involvement of the superoxide anion radical which is produced by the interaction of O2 and the photosynthetic electron-transfer chain through the Mehler reaction. Mass spectrometric measurements of O2 exchange by potato leaves under strong illumination did not reveal, however, any stimulation of the Mehler reaction at low temperature, thus leading to the conclusion that O2 toxicity mainly resulted from a chilling-induced inhibition of the scavenging system for O2-radicals. Support for this interpretation was provided by the light response of potato leaves infiltrated with an inhibitor (diethyldithiocarbamate) of the chloroplastic Cu-Zn superoxide dismutase. It was indeed possible to simulate the differential inhibition of the PS II photochemical activity and the linear electron transport observed during light stress at low temperature by illuminating at 23 °C diethyldithiocarbamate-poisoned leaves. The experimental data presented here suggests that (i) the previously reported resistance of PS I to photoinhibition damage in-vivo is not an intrinsic property of PS I but results from efficient protective systems against O2 toxicity, (ii) PS I is photoinhibited in chilled potato leaf due to the inactivation of this PS I defence system and (iii) PS I is more sensitive to superoxide anion radicals than PS II.
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    Sixty years in algal physiology and photosynthesis (1994)
    Springer
    Photosynthesis research 40 (1994), S. 207-221 
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    ISSN: 1573-5079
    Keywords: photosynthesis ; unicellular algae ; ion effects ; manganese ; blue light ; synchronized growth ; algal mass cultures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This personal perspective records research experiences in chemistry and biology at four German universities, two before and two after World War II. The research themes came from cytophysiology of green unicellular algae, in particular their photosynthesis. The function of inorganic ions in photosynthesis and dark respiration was investigated at different degrees of specific mineral stress (deficiencies), and the kinetics of recovery followed after the addition of the missing element. Two types of recovery of photosynthesis were observed: indirect restitution via growth processes and immediate normalisation. From the latter case (K+, phosphate, Mn++) the effect of manganese was emphasized as its role in photosynthetic O2 evolution became established during our research. Other themes of our group, with some bearing on photosynthesis were: synchronization of cell growth by light-dark change and effects of blue (vs. red) light on the composition of green cells. Some experiences in connection with algal mass cultures are included. Discussion of several editorial projects shows how photosynthesis, as an orginally separated field of plant biochemistry and biophysics, became included into general cell physiology and even ecophysiology of green plants. The paper contains an appreciation of the authors' main mentor Kurt Noack (1888–1963) and of Ernst Georg Pringsheim (1881–1970), founder of experimental phycology.
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    Gene nomenclature recommendations for green photosynthetic bacteria and heliobacteria (1994)
    Springer
    Photosynthesis research 41 (1994), S. 27-28 
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    ISSN: 1573-5079
    Keywords: photosynthesis ; reaction center ; green bacteria ; heliobacteria ; gene ; chlorosome ; cytochrome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Recommendations are given for naming of genes coding for reaction center, antenna and electron transport proteins in green photosynthetic bacteria and heliobacteria
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    URL: http://dx.doi.org/10.1007/BF02184142
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    Redox effects on the bacteriochlorophyll α-containing Fenna-Matthews-Olson protein fromChlorobium tepidum (1994)
    Springer
    Photosynthesis research 41 (1994), S. 89-96 
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    ISSN: 1573-5079
    Keywords: photosynthesis ; Chlorobium tepidum ; antenna ; bacteriochlorophylla protein ; energy transfer ; chlorosome ; green bacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The BChla-containing Fenna-Matthews-Olson (FMO) protein from the green sulfur bacteriumChlorobium tepidum was purified and characterized. Fluorescence spectra indicate that efficient excited state quenching occurs at neutral or oxidizing redox potentials. The major fluorescence lifetime at room temperature is approximately 60 ps in samples that are in neutral or oxidizing conditions, and approximately 2 ns in samples where the strong reductant sodium dithionite has been added. A similar change is observed in pump-probe picosecond absorbance difference experiments, where the long life time component increases after dithionite addition. A 16 Gauss wide EPR signal with g factor =2.005 is observed in samples without dithionite. This signal largely disappears upon addition of dithionite. Dithionite induces large reversibile changes in the 77 K absorbance spectra of the purified FMO protein and in whole cells. These results indicate that the FMO protein contains redox active groups, which may be involved in the regulation of energy transfer. Room temperature circular dichroism and low temperature absorption spectra show that dithionite also induces conformational or structural changes of the FMO protein complex.
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    URL: http://dx.doi.org/10.1007/BF02184148
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    Responses to drought and flooding in tropical forage grasses (1994)
    Springer
    Plant and soil 164 (1994), S. 97-105 
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    ISSN: 1573-5036
    Keywords: alcohol dehydrogenase ; drought ; flooding ; photosynthesis ; tropical grasses ; water potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Long dry seasons or permanent flooding, typical of tropical savannas, severely limit the growth of pasture plants. This study compares the responses of water relations, carbon assimilation and alcohol dehydrogenase (ADH) activity to drought and flooding in four perennial C4 grasses: the tufted or caespitose Hyparrhenia rufa and Andropogon gayanus (CIAT 621) and the stoloniferous Brachiaria mutica and Echinochloa polystachya. Plants of the four species were subjected to medium term flooding (20–25 days) and moderate drought in a greenhouse. Leaf water potential (Ψ), stomatal conductance (Gs) and photosynthesis rate (Pn) were measured throughout the experiment and ADH activity was measured in flooded and control plants. Moderate drought produced similar effects in all grasses reducing Gs which caused reduced Pn. Net photosynthesis compensation point was reached at the lowest Ψ in A. gayanus which was considered as the most drought tolerant. The responses to flooding varied across species. Andropogon gayanus and H. rufa showed early stomatal closure without concurrent decrease in Ψ and leaf turgor. This low Gs was responsible of reduced Pn and growth rate. There was a slight increase of Gs in the middle of the flooding period and both grasses recovered pre-stress Gs and Pn after drainage. ADH activity increased markedly only in A. gayanus under flooding suggesting that this grass was the most flood-sensitive. Stomatal aperture, Pn and ADH activity in B. mutica and E. polystachya were not affected by flooding. The higher flood-tolerance in these grasses might be attributed to enhanced oxygen diffusion to the roots through the hollow stolons, development of advantitious rootlets and large aerenchyma in the roots which compensate for the reduction of soil oxygen and permit the maintenance of root activity.
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    Gene action and heritability for photosynthetic activity in two wheat crosses (1994)
    Springer
    Euphytica 76 (1994), S. 235-238 
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    ISSN: 1573-5060
    Keywords: Triticum aestivum ; wheat ; photosynthesis ; gene action ; heritability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Gene action and heritability for photosynthetic activity were estimated from generation means in two wheat crosses during two stages (5 th leaf and flag leaf between 2 and 5 days after anthesis). Six generations were available for each cross: parents (P1 and P2), F1, F2 and backcrosses (BC1 and BC2). Correlations between some morphophysiological characters and photosynthetic activity of the flag leaf was also determined. The joint scaling test described by Mather & Jinks was used to determine the gene action. It showed that them; [d]; [h]; [i], [l] (mean, additivity, dominance, additive x additive interallelic interaction effects, dominance x dominance interallelic interaction effects) model fits the two crosses at both measurement times. All the model genetic components were significant for the flag leaf, however for the 5 th leaf only [h]; [i] and [l] were significant. The presence of additive and additive x additive effects suggested the possibility of selecting for this character using the flag leaf so as to obtain pure inbred lines. Dominance effects [h] were negative and dominance x dominance effects [l] were positive. Broad sense heritability values were medium to low. There were no correlations between the studied morphophysiological characters and the photosynthetic activity.
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    URL: http://dx.doi.org/10.1007/BF00022168
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    Singlet oxygen production in thylakoid membranes during photoinhibition as detected by EPR spectroscopy (1994)
    Springer
    Photosynthesis research 39 (1994), S. 191-199 
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    ISSN: 1573-5079
    Keywords: photoinhibition ; photosynthesis ; protein degradation ; singlet oxygen ; TEMP (2,2,6,6-tetramethylpiperidine) ; thylakoid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Exposure of isolated spinach thylakoids to high intensity illumination (photoinhibition) results in the well-characterized impairment of Photosystem II electron transport, followed by degradation of the D1 reaction centre protein. In the present study we demonstrate that this process is accompanied by singlet oxygen production. Singlet oxygen was detected by EPR spectroscopy, following the formation of stable nitroxide radicals from the trapping of singlet oxygen with a sterically hindered amine TEMP (2,2,6,6-tetramethylpiperidine). There was no detectable singlet oxygen production during anaerob photoinhibition or in the presence of sodium-azide. Comparing the kinetics of the loss of PS II function and D1 protein with that of singlet oxygen trapping suggests that singlet oxygen itself or its radical product initiates the degradation of D1.
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    URL: http://dx.doi.org/10.1007/BF00029386
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    Changes in the antenna size of Photosystem I and Photosystem II in Synechococcus sp. strain PCC 7942 grown in the presence of SANDOZ 9785 — a Photosystem II inhibitor (1994)
    Springer
    Photosynthesis research 41 (1994), S. 303-313 
    Details
    ISSN: 1573-5079
    Keywords: cyanobacteria ; excitation energy ; herbicide ; photochemical apparatus ; photosynthesis ; pyridazinone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract SANDOZ 9785, also known as BASF 13.338, is a pyridazinone derivative that inhibits Photosystem II (PS II) activity leading to an imbalance in the rate of electron transport through the photosystems. Synechococcus sp. strain PCC 7942 cells grown in the presence of sublethal concentration of SANDOZ 9785 (SAN 9785) for 48 hours exhibited a 20% decrease in Chl a per cell. However, no changes were observed in the content of phycocyanin per cell, the size of the phycobilisomes or in the PS II:PS I ratio. From an estimate of PS II electron transport rate under varying light intensities and spectral qualities and analysis of room temperature Chl a fluorescence induction, it was deduced that growth of Synechococcus PCC 7942 in the presence of SAN 9785 leads to a redistribution of excitation energy in favour of PS II. Though the redistribution appears to be primarily caused by changes affecting the Chl a antenna of PS II, the extent of energetic coupling between phycobilisomes and PS II is also enhanced in SAN 9785 grown Synechococcus PCC 7942 cells. There was a reduction in the effective size of PS I antenna based on measurement of P700 photooxidation kinetics. These results indicate that when PS II is partially inhibited, the structure of photosynthetic apparatus alters to redistribute the excitation energy in favour of PS II so that the efficiency of utilization of light energy by the two photosystems is optimized. Our results suggest that under the conditions used, drastic structural changes are not essential for redistribution of excitation energy between the photosystems.
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    Acclimation of photosynthesis to increasing atmospheric CO2: The gas exchange perspective (1994)
    Springer
    Photosynthesis research 39 (1994), S. 351-368 
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    ISSN: 1573-5079
    Keywords: CO2 enrichment ; gas exchange ; greenhouse effect ; photosynthesis ; responses to CO2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The nature of photosynthetic acclimation to elevated CO2 is evaluated from the results of over 40 studies focusing on the effect of long-term CO2 enrichment on the short-term response of photosynthesis to intercellular CO2 (the A/Ci response). The effect of CO2 enrichment on the A/Ci response was dependent on growth conditions, with plants grown in small pots (〈 5 L) or low nutrients usually exhibiting a reduction of A at a given Ci, while plants grown without nutrient deficiency in large pots or in the field tended to exhibit either little reduction or an enhancement of A at a given Ci following a doubling or tripling of atmospheric CO2 during growth. Using theoretical interpretations of A/Ci curves to assess acclimation, it was found that when pot size or nutrient deficiency was not a factor, changes in the shape of A/Ci curves which are indicative of a reallocation of resources within the photosynthetic apparatus typically were not observed. Long-term CO2 enrichment usually had little effect or increased the value of A at all Ci. However, a minority of species grown at elevated CO2 exhibited gas exchange responses indicative of a reduced amount of Rubisco and an enhanced capacity to metabolize photosynthetic products. This type of response was considered beneficial because it enhanced both photosynthetic capacity at high CO2 and reduced resource investment in excessive Rubisco capacity. The ratio of intercellular to ambient CO2 (the Ci/Ca ratio) was used to evaluate stomatal acclimation. Except under water and humidity stress, Ci/Ca exhibited no consistent change in a variety of C3 species, indicating no stomatal acclimation. Under drought or humidity stress, Ci/Ca declined in high-CO2 grown plants, indicating stomata will become more conservative during stress episodes in future high CO2 environments.
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    Effects of UV-B radiation on photosynthesis and growth of terrestrial plants (1994)
    Springer
    Photosynthesis research 39 (1994), S. 463-473 
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    ISSN: 1573-5079
    Keywords: global climate change ; ozone depletion ; photosynthesis ; Photosystem II ; productivity ; UV-B radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The photosynthetic apparatus of some plant species appears to be well-protected from direct damage from UV-B radiation. Leaf optical properties of these species apparently minimizes exposure of sensitive targets to UV-B radiation. However, damage by UV-B radiation to Photosystem II and Rubisco has also been reported. Secondary effects of this damage may include reductions in photosynthetic capacity, RuBP regeneration and quantum yield. Furthermore, UV-B radiation may decrease the penetration of PAR, reduce photosynthetic and accessory pigments, impair stomatal function and alter canopy morphology, and thus indirectly retard photosynthetic carbon assimilation. Subsequently, UV-B radiation may limit productivity in many plant species. In addition to variability in sensitivity to UV-B radiation, the effects of UV-B radiation are further confounded by other environmental factors such as CO2, temperature, light and water or nutrient availability. Therefore, we need a better understanding of the mechanisms of tolerance to UV-B radiation and of the interaction between UV-B and other environmental factors in order to adequately assess the probable consequences of a change in solar radiation.
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    State adaptations in the cyanobacterium Synechcoccus 6301 (PCC): Dependence on light intensity or spectral composition? (1994)
    Springer
    Photosynthesis research 40 (1994), S. 107-117 
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    ISSN: 1573-5079
    Keywords: photosynthesis ; state adaptations ; shade adaptation ; cyanobacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A profile of high light to intense self-shading conditions was constructed using a white light source and cultures of the cyanobacterium Synechococcus 6301; this profile approximates to a natural self-shading gradient of decreasing light intensity and PS II/PS I excitation ratio. Samples of S.6301 were placed along this profile and allowed to state adapt. To separate the effects of light intensity and wavelength on state adaptation, samples were also placed in a shade profile produced by a white light source and neutral density filters. After adaptation, samples were fixed in their resulting state by the addition of glutaraldehyde, and fluorescence measurements were made at 35° C or –160 °C. It is concluded: 1. Under conditions of deep shade (〈5 μmol m−2s−1 PAR) and weak shade (〉200 μmol m−2s−1 PAR), cells adapt to a low PS II fluorescence state (state 2); in moderate shade (20–60 μmol m−2s−1PAR) cells adapt to a high PS II fluorescence state (state 1). We suggest these findings provide evidence for the operation of different factors on the control of state adaptations in cyanobacteria; one set operates at low light and another at high light intensities. 2. Under conditions of self-shading, there is little evidence to support the contention that state adaptations in cyanobacteria are produced by wavelength-dependent changes in the PS II/PS I excitation ratio, instead, it appaers they are produced by changes in the intensity of incident irradiation. 3. The observed fluorescence changes do not appear to involve major changes in the phycobilisome sensitisation of PS II and PS I. Instead, it appears that these changes are effected by alterations in ΦF of PS II (i.e. changes in PS II excitation density caused by alterations in the rate constants controlling spillover to PS I, photochemistry, fluorescence emission or thermal deactivation.
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    An enzyme and13C-NMR study of carbon metabolism in heliobacteria (1994)
    Springer
    Photosynthesis research 41 (1994), S. 75-88 
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    ISSN: 1573-5079
    Keywords: photosynthesis ; carbon assimilation ; photosynthetic bacteria ; citric-acid cycle ; pyruvate synthase ; fermentation ; heliobacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Heliobacteria are a group of anoxygenic phototrophs that can grow photoheterotrophically in defined minimal media on only a limited range of organic substrates as carbon sources. In this study the mechanisms which operate to assimilate carbon and the routes employed for the biosynthesis of cellular intermediates were investigated in a newHeliobacterium strain, HY-3. This was achieved using two approaches (1) by measuring the activities of key enzymes in cell-free extracts and (2) by the use of13C nuclear magnetic resonance (NMR) spectroscopy to analyze in detail the labelling pattern of amino-acids of cells grown on [13C] pyruvate and [13C] acetate.Heliobacterium strain HY-3 was unable to grow autotrophically on CO2/H2 and neither (ATP)-citrate lyase nor ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBPcase) were detectable in cell-free extracts. The enzyme profile of pyruvate grown cells indicated the presence of a pyruvate:acceptor oxidoreductase at high specific activity which could convert pyruvate to acetyl-Coenzyme A. No pyridine nucleotide dependent pyruvate dehydrogenase complex activity was detected. Of the citric-acid cycle enzymes, malate dehydrogenase, fumarase, fumarate reductase and an NADP-specific isocitrate dehydrogenase were readily detectable but no aconitase or citrate synthase activity was found. However, the labelling pattern of glutamate in long-term 2-[13C] acetate incorporation experiments indicated that a mechanism exists for the conversion of carbon from acetyl-CoA into 2-oxoglutarate. A 2-oxoglutarate:acceptor oxidoreductase activity was present which was also assayable by isotope exchange, but no 2-oxoglutarate dehydrogenase complex activity could be detected. Heliobacteria appear to use a type of incomplete reductive carboxylic acid pathway for the conversion of pyruvate to 2-oxoglutarate but are unable to grow autotrophically using this metabolic route due to the absence of ATP-citrate lyase.
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    Spectroscopic evidence for the presence of an iron-sulfur center similar to Fx of Photosystem I inHeliobacillus mobilis (1994)
    Springer
    Photosynthesis research 41 (1994), S. 115-123 
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    ISSN: 1573-5079
    Keywords: photosynthesis ; bacteriochlorophyll ; electron acceptor ; iron-sulfur center ; Photosystem I ; heliobacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Treatment of membranes ofHeliobacillus mobilis with high concentrations of the chaotropic agent urea resulted in the removal of the iron-sulfur centers FA and FB from the reaction center, as indicated by EPR spectra under strongly reducing conditions. In urea-treated membranes, transient absorption measurements upon a laser flash indicated a recombination between the photo-oxidized primary donor P798+ and a reduced acceptor with a time constant of 20 ms at room temperature. Benzylviologen, vitamin K-3 and methylene blue were found to accept electrons from the reduced acceptor efficiently. A differential extinction coefficient of 225–240 mM−1 cm−1 at 798 nm was determined from experiments in the presence of methylene blue. Transient absorption difference spectra between 400 and 500 nm in the presence and absence of artificial acceptors indicated that the electron acceptor involved in the 20 ms recombination has an absorption spectrum similar to that of an iron-sulfur center. This iron-sulfur center was assigned to be analogous to FX of Photosystem I. Our results provide evidence in support of the presence of FX in heliobacteria, which was proposed on the basis of the reaction center polypeptide sequence (Liebl et al. (1993) Proc. Natl. Acad. Sci. USA 90: 7124–7128). Implications for the electron transfer pathway in the reaction center of heliobacteria are discussed.
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    Molecular organization of bacteriochlorophyll in chlorosomes of the green photosynthetic bacteriumChloroflexus aurantiacus: Studies of fluorescence depolarization accompanied by energy transfer processes (1994)
    Springer
    Photosynthesis research 41 (1994), S. 181-191 
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    ISSN: 1573-5079
    Keywords: energy transfer ; green bacteria ; photosynthesis ; picosecond spectroscopy ; pigment system ; (Chloroflexus aurantiacus)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Examination was made of changes in fluorescence polarization plane by energy transfer in the chlorosomes of the green photosynthetic bacterium,Chloroflexus aurantiacus. Fluorescence anisotropy in the picosecond (ps) time region was analyzed using chlorosomes suspended in solution as well as those oriented in a polyacrylamide gel. When the main component of BChlc was preferentially excited, the decay of fluorescence anisotropy was found to depend on wavelength. In the chlorosome suspension, the anisotropy ratio of BChlc changed from 0.31 to 0.24 within 100 ps following excitation. In the baseplate BChla region, this ratio decreased to a negative value (−0.09) from the initial 0.14. In oriented samples, the degree of polarization remained at 0.68 for BChlc, and changed from 0.25 to −0.40 for the baseplate BChla by excitation light whose electric vector was parallel to the longest axis of chlorosomes. In the latter case, there was a shift from 0.30 to −0.55 by excitation perpendicular to the longest axis. Time-resolved fluorescence polarization spectra clearly indicated extensive changes in polarization plane accompanied by energy transfer. The directions of polarization plane of emission from oriented samples were mostly dependent on chlorosome orientation in the gel but not on that of the polarization plane of excitation light. Orientations of the dipole moment of fluorescence components was consistent with that of absorption components as determined by the linear dichroism (Matsuura et al. (1993) Photochem. Photobiol. 57: 92–97). A model for molecular organization of BChlc anda in chlorosomes is proposed based on anisotropic optical properties.
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    Evolution of heliobacteria: Implications for photosynthetic reaction center complexes (1994)
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    Photosynthesis research 41 (1994), S. 285-294 
    Details
    ISSN: 1573-5079
    Keywords: heliobacteria ; reaction center ; photosynthesis ; 16S rRNA sequence ; cyanobacteria ; Gram-positive bacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The evolutionary position of the heliobacteria, a group of green photosynthetic bacteria with a photosynthetic apparatus functionally resembling Photosystem I of plants and cyanobacteria, has been investigated with respect to the evolutionary relationship to Gram-positive bacteria and cyanobacteria. On the basis of 16S rRNA sequence analysis, the heliobacteria appear to be most closely related to Gram-positive bacteria, but also an evolutionary link to cyanobacteria is evident. Interestingly, a 46-residue domain including the putative sixth membrane-spanning region of the heliobacterial reaction center protein shows rather strong similarity (33% identity and 72% similarity) to a region including the sixth membrane-spanning region of the CP47 protein, a chlorophyll-binding core antenna polypeptide of Photosystem II. The N-terminal half of the heliobacterial reaction center polypeptide shows a moderate sequence similarity (22% identity over 232 residues) with the CP47 protein, which is significantly more than the similarity with the Photosystem I core polypeptides in this region. An evolutionary model for photosynthetic reaction center complexes is discussed, in which an ancestral homodimeric reaction center protein (possibly resembling the heliobacterial reaction center protein) with 11 membrane-spanning regions per polypeptide has diverged to give rise to core of Photosystem I, Photosystem II, and of the photosynthetic apparatus in green, purple, and heliobacteria.
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    URL: http://dx.doi.org/10.1007/BF02184169
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    The photoproduction of superoxide radicals and the superoxide dismutase activity of Photosystem II. The possible involvement of cytochrome b559 (1994)
    Springer
    Photosynthesis research 41 (1994), S. 327-338 
    Details
    ISSN: 1573-5079
    Keywords: photosynthesis ; Photosystem II ; superoxide radical ; superoxide dismutase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the present study the light induced formation of superoxide and intrinsic superoxide dismutase (SOD) activity in PS II membrane fragments and D1/D2/Cytb559-complexes from spinach have been analyzed by the use of ferricytochrome c (cyt c(III)) reduction and xanthine/xanthine oxidase as assay systems. The following results were obtained: 1.) Photoreduction of Cyt c (III) by PS II membrane fragments is induced by addition of sodium azide, tetracyane ethylene (TCNE) or carbonylcyanide-p-trifluoromethoxy-phenylhydrazone (FCCP) and after removal of the extrinsic polypeptides by a 1M CaCl2-treatment. This activity which is absent in control samples becomes completely inhibited by the addition of exogenous SOD. 2.) The TCNE induced cyt c(III) photoreduction by PS II membrane fragments was found to be characterized by a half maximal concentration of c1/2=10 μM TCNE. Simultaneously, TCNE inhibits the oxygen evolution rate of PS II membrane fragments with c1/2≈ 3 μM. 3.) The photoproduction of O2 − is coupled with H+-uptake. This effect is diminished by the addition of the O2 −-trap cyt c(III). 4.) D1/D2/Cytb559-complexes and PS II membrane fragments deprived of the extrinsic proteins and manganese exhibit no SOD-activity but are capable of producing O2 − in the light if a PS II electron donor is added. Based on these results the site(s) of light induced superoxide formation in PS II is (are) inferred to be located at the acceptor side. A part of the PS II donor side and Cyt b559 in its HP-form are proposed to provide an intrinsic superoxide dismutase (SOD) activity.
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    URL: http://dx.doi.org/10.1007/BF00019410
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    Thermoluminescence as a probe of Photosystem II in intact leaves: Non-photochemical fluorescence quenching in peas grown in an intermittent light regime (1994)
    Springer
    Photosynthesis research 41 (1994), S. 371-379 
    Details
    ISSN: 1573-5079
    Keywords: photosynthesis ; chlorophyll fluorescence ; high energy-state quenching ; calcium release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have measured thermoluminescence (TL) and chlorophyll fluorescence from leaves of peas grown under an intermittent light regime (IML) and followed changes in those leaves during greening. IML peas show low variable fluorescence and a certain capacity for reversible non-photochemical quenching. It has been suggested that reversible quenching may be caused by pH-dependent release of Ca2+ from Photosystem II (PS II) (Krieger and Weis (1992) Photosynthetica 27: 89–98). Under conditions in which reversible non-photochemical quenching occurs, a TL band at around 50 °C is observed, in the presence of DCMU, in IML leaves. A band in this temperature range has previously been observed in PS II depleted of Ca2+ (Ono and Inoue (1989) Biochimica et Biophysica Acta 973: 443–449). The 50 °C band disappears upon dark adaptation. In mature leaves, no significant band is seen at 50 °C. It is concluded that, in IML leaves, reversible quenching may be related to the release of Ca2+ from Photosystem II. However, it seems that in the mature system, under most conditions, such release does not contribute significantly to quenching
    Type of Medium: Electronic Resource
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    Measurements of mesophyll conductance, photosynthetic electron transport and alternative electron sinks of field grown wheat leaves (1994)
    Springer
    Photosynthesis research 41 (1994), S. 397-403 
    Details
    ISSN: 1573-5079
    Keywords: electron transport rate ; mesophyll conductance to CO2 diffusion ; photosynthesis ; photorespiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosynthetic electron transport drives the carbon reduction cycle, the carbon oxidation cycle, and any alternative electron sinks such as nitrogen reduction. A chlorophyll fluorescence— based method allows estimation of the total electron transport rate while a gas-exchange-based method can provide estimates of the electron transport needed for the carbon reduction cycle and, if the CO2 partial pressure inside the chloroplast is accurately known, for the carbon oxidation cycle. The gas-exchange method cannot provide estimates of alternative electron sinks. Photosynthetic electron transport in flag leaves of wheat was estimated by the fluorescence method and gasexchange method to determine the possible magnitude of alternative electron sinks. Under non-photorespiratory conditions the two measures of electron transport were the same, ruling out substantial alternative electron sinks. Under photorespiratory conditions the fluorescence-based electron transport rate could be accounted for by the carbon reduction and carbon oxidation cycle only if we assumed the CO2 partial pressure inside the chloroplasts to be lower than that in the intercellular spaces of the leaves. To further test for the presence of alternative electron sinks, carbon metabolism was inhibited by feeding glyceraldehyde. As carbon metabolism was inhibited, the electron transport was inhibited to the same degree. A small residual rate of electron transport was measured when carbon metabolism was completely inhibited which we take to be the maximum capacity of alternative electron sinks. Since the alternative sinks were small enough to ignore, the comparison of fluorescence and gas-exchange based methods for measuring the rate of electron transport could be used to estimate the mesophyll conductance to CO2 diffusion. The mesophyll conductance estimated this way fell as wheat flag leaves senesced. The age-related decline in photosynthesis may be attributed in part to the reduction of mesophyll conductance to CO2 diffusion and in part to the estimated decline of ribulose 1,5-bisphosphate carboxylase amount.
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    Changes in the photosynthetic light response curve during leaf development of field grown maize with implications for modelling canopy photosynthesis (1994)
    Springer
    Photosynthesis research 42 (1994), S. 217-225 
    Details
    ISSN: 1573-5079
    Keywords: photosynthesis ; leaf age ; maize
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Changes in the photosynthetic light-response curve during leaf development were determined for the fourth leaf of maize crops sown on 23 April and 10 June. Temperatures were unusually mild during late spring/early summer and neither crop experienced chilling damage. The concept of thermal time was used to take into account the effects of different temperature regimes on developmental stage, thereby enabling photosynthetic light-response data to be combined for both crops to describe the general response. Large variations in the upper asymptote (Asat) and convexity (Θ) of the light-response curve occurred during leaf development, but the maximum quantum yield of CO2 assimilation remained relatively constant throughout. Dark respiration rates showed a small but significant decrease with leaf age and generally ranged between 5 and 10% of Asat. A simple mathematical model was developed to assess the sensitivity of daily leaf photosynthesis (AL) to reductions in the Asat, Θ and the initial slope (Φ) of the light-response curve at different stages of leaf development. On bright sunny days, and at all developmental stages, AL was ca. twice as sensitive to reductions in Asat than to reductions in Φ and Θ. In overcast conditions, however, all three parameters contributed significantly to reductions in leaf photosynthesis, although the contribution of Φ was greatest during early leaf growth, while older leaves were most sensitive to depressions in Asat. The implications of these results for modelling the sensitivity of canopy photosynthesis to chill-induced photoinhibition of the light-response curve are discussed.
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    Image formation of alkyl-pendent aromatic polyimide by photocoupling with aromatic ketones (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 214 (1994), S. 57-65 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Positive und negative Photostrukturen wurden in einem Polyimid (PI) aus 4,4′-Biphthalsäureanhydrid (BPA) und 4,4′-Diamino-3,3′-dimethyldiphenylmethan (DADMDPM), PI(BPA/DADMDPM) erzeugt, nachdem dieses mit Michlers Keton (MK) bzw. Benzophenon (BP) dotiert und einer ultravioletten Strahlung von 400 ± 50 nm ausgesetzt und naß entwickelt wurde. Das Prinzip der positiven Abbildung basiert auf dem Photokupplungseffekt von MK mit PI, der die Löslichkeit des Polyimids erhöht und so die Entwicklung eines Positivmusters ermöglicht. Die Erzeugung negativer Muster wird durch intermakromolekulare Wasserstoffbrücken zwischen der Carbonylgruppe des Imid-Rings und der Hydroxygruppe, die bei der photoinduzierten Kupplung von Benzophenon mit dem Polyimid gebildet wird, bewirkt. Die lithographische Auswertung zeigt, daß der mit MK dotierte, positive Polyimidfilm nicht in der Lage ist, brauchbare Muster zu erzeugen, da die UV-Wellenlängen von MK absorbiert werden, wodurch die Photokupplung in den tieferen Schichten des Films verhindert wird. Andererseits können in dem 0,6 μm dicken, mit Benzophenon dotierten Polyimidfilm sogar 2 μm schmale Linien aufgelöst werden.
    Notes: Positive and negative photostructures are formed after the polyimide (PI) of 4,4′-biphthalic anhydride (BPA) and 4,4′-diamino-3,3′-dimethyldiphenylmethane (DADMDPM), PI(BPA/DADMDPM) is doped with Michler′s ketone (MK) and benzophenone (BP), respectively, and is subjected to UV light (400 ± 50 nm) irradiation and solvent development. The principle of positive feature formation is based on the photocoupling of MK with PI, which increases PI solubility and thus enables a positive pattern to be developed. The phenomenon of negative photopatterning results from intermacromolecular H-bonding between the carbonyl group of the imide ring and the hydroxy group which is formed in the photoinduced coupling reaction between BP and PI. Lithographic evaluation shows that the MK-doped positive-acting PI film cannot form useful patterns because UV wavelengths are strongly absorbed by MK, which limits the depth of photocoupling in the film. On the other hand, 2-μm-wide lines can be resolved in the BP-doped negative-acting 0.6-μm-thick PI film.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052140106
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    Blends of polyamide 6 and poly(etheraroylhydrazide)s prepared concurrently with polyhydrazide polymerization (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 214 (1994), S. 101-113 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Polyhydrazid/Polyamid-Blends (PEHZ12/PA6) wurden durch Niedrigtemperatur-Polykondensation von 4,4′-Dichlorformyl-α,ω-diphenoxydodecan und Terephthaloyldihydrazid (TDH) zu Poly(etheraroylhydrazid) in Gegenwart von Polyamid 6 synthetisiert. Die DSC-Analysen lassen vermuten, daß die zwei Polymerkomponenten nicht wechselwirken. Bei der Extraktion des PA6-Anteils der Blends mit Ameisensäure zeigt die Charakterisierung des PEHZ12-Extraktionsrückstands aber, daß zumindest bei bestimmten Zusammensetzungen Wechselwirkungen zwischen den Komponenten auftreten. Modellreaktionen erlauben die Annahme, daß die PEHZ12-Polymerisation zwischen den Amino-Endgruppen des PA6 und den wachsenden PEHZ12-Polymerketten abläuft.
    Notes: Poly(etheraroylhydrazide) is synthesized in the presence of PA6 by means of low-temperature condensation polymerization of 4,4′-dichloroformyl-α,ω-diphenoxydodecane with terephthaloyl dihydrazide (TDH) in order to prepare polyhydrazide/poly-amide 6 (PEHZ12/PA6) blends. The thermal analysis of the blends by DSC seems to indicate that the two polymers are not interacting. Nevertheless, when the blends are subjected to an extraction process with formic acid in order to remove the PA6, the characterization of the residual PEHZ12 reveales that some interactions do occur between the constituent polymers, at least for selected compositions. Model experiments permit to hypothesize that the polymerization of PEHZ12 proceeds with a chemical interaction between amino end groups of PA6 and growing PEHZ12 chains.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052140110
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    Die kristallisation von polybutylenterephthalat (PBT) und polycarbonat (PC) im polymerblend PBT/PC (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 214 (1994), S. 179-196 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The crystallization behavior of PBT as well as PC is changed in the controlled-processed blend due to intermolecular interactions between the different macromolecules in molten state.If the kinetics of the crystallization process prevents a crystallization-induced separation, the partial miscibility of the amorphous phases, measured by the glass transition temperatures, will lead to a decrease of the crystallinity of PBT. The crystallinity, normalized to the concentration of PBT in the blend, is independent from the concentration of PC at low coolling rates.At high cooling rates, PBT is crystallizing stepwise in the blend PBT/PC 40/60 wt.-%. The crystallization temperature in the anisothermic crystallization process is increased at low contents of PC due to a changed nucleation mechanism. The half-time of crystallization is increasing in blends with an increasing PC-content in isothermic crystallization experiments.The normally amorphous PC crystallizes considerably fast in presence of PBT in PC-rich blends. The crystallization or change in the state of order of PC was measured in situ by X-ray diffraction. Calorimetric experiments confirm this result and allow a quantitative estimation of the PC-crystallinity, which amounts to some 20% in the blend PBT/PC 5/95 wt.-%.
    Notes: Das Kristallisationsverhalten sowohl von PBT als auch von PC ist im definiert verarbeiteten Blend infolge intermolekularer Wechselwirkungen zwischen den unterschiedlichen Molekülen in der Schmelze verändert.Die über die Glasübergangstemperaturen gemessene teilweise Mischbarkeit der amorphen Phasen führt bei PBT zu einer Erniedrigung des Kristallinitätsgrades, wenn die kinetischen Bedingungen des Kristallisationsprozesses keine kristallisationsbedingte Entmischung zulassen. Der auf den PBT-Anteil normierte Kristallinitätsgrad ist bei kleinen Abkühlgeschwindigkeiten vom PC-Anteil unabhängüg.In der Mischung PBT/PC 40/60 Gew.-% kommt es bei hohen Kühlraten zu einer fraktionierten Kristallisation. Die Kristallisationstemperatur bei anisothermer Kristallisation ist bei geringen PC-Gehalten durch Änderung des Keimbildungsmechanismus erhöht. Bei isothermer Kristallisation steigt mit zunehmendem PC-Anteil die Kristallisationshalbwertszeit des PBT an.Das normalerweise amorphe PC kann in Gegenwart von PBT in den PC-reichen Mischungen besonders schnell kristallisieren, wobei der Kristallisations- bzw. Ordnungsprozeß des PC in situ mittels der Röntgenbeugung gemessen wurde. Kalorimetrische Untersuchungen bestätigen dieses Ergebnis und erlauben eine quantitative Abschätzung des PC-Kristallinitätsgrades zu ca. 20% im Blend PBT/PC 5/95 Gew.-%.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052140116
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    Photoreactions in halogen-containing negative-tone novolac resists (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 214 (1994), S. 197-210 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Elementaranalytische sowie NMR-, IR- und UV-spektroskopische Untersuchungen zeigen, daß die Photolyse von Halogenphenolnovolaken zur Substitution der Halogenatome durch Wasserstoff, der Bildung chinoider Gruppen und intermolekularen Vernetzung führt. Die Geschwindigkeit der Halogeneliminierung hängt von der Art des Halogens ab. Sie steigt in der Reihenfolge F 〈 Cl 〈 Br 〈 I. Die Chloreliminierung aus der 4-Position ist gegenüber der aus der 2- und 3-Position begünstigt. Außerdem verläuft die Abspaltung para-ständiger Chloratome aus Dimeren schneller als aus Trioder Tetrameren. ESR-Messungen bei 77 K sowie die Laserblitzphotolyse bei 296 K deuten auf die intermediäre Bildung von Phenoxyl- und Arylradikalen. Lithographische Tests belegen die hohe UV-Empfindlichkeit von Resisten auf der Basis von Halogenphenolnovolaken. Im Vergleich zu nichthalogenhaltigen Novolakresisten wird eine 6 - 10fache (System: 4-Chlorphenolnovolak/4,4′-Bisazidobiphenyl (5%)) bzw. eine ca. 25fache (System: 4-Chlorphenol-/m-Cresolnovolak/Hexamethoxymethylmelamin (5%)) Steigerung der Empfindlichkeit erreicht. Zur Interpretation wird ein Mechanismus postuliert, demzufolge die durch Halogenabspaltung hervorgerufene Sekundärradikalbildung zu einer zusätzlichen Vernetzung beiträgt. In den melaminhaltigen Resisten katalysiert der gebildete Halogenwasserstoff (Hal· + RH → H-Hal + R·) außerdem die Reaktion der Melaminverbindung mit der Novolakmatrix.
    Notes: The photolysis of halogenophenol novolacs is determined by the substitution of halogens by hydrogen and the formation of quinoid groups and intermolecular crosslinks. This is concluded from elemental analysis, NMR, IR and optical absorption measurements. The rate of halogen release depends on the chemical nature of the halogen. It increases in the order F 〈 Cl 〈 Br 〈 I. Chlorine elimination from 4-position is favored over that from 2- and 3-position. Moreover, dimers release chlorine from 4-position much more readily than trimers and tetramers. ESR measurements at 77 K and flash photolysis studies at 296 K yielded evidence for the intermediate existence of phenoxyl and aryl radicals. Lithographic tests demonstrated the high UV-sensitivity of resist formulations based on halogen-containing novolacs. The increase in sensitivity relative to that of formulations based on nonhalogenated novolacs is 6 to 10fold system: 4-chlorophenol novolac/4,4′-bisazidobiphenyl (5%) and ca. 25fold system: 4-chlorophenol/m-cresol novolac/hexamethoxymethylmelamine (5%). A postulated reactions mechanism concerning the sensitivity increase takes into account that halogen elimination results in the formation of additional radicals that accelerate the rate of crosslinking. Moreover, hydrogen halide generated by hydrogen abstraction of halogen radicals (Hal· + RH → H-Hal + R·) provides for the acid required to catalyze the reaction of the melamine compound with the novolac matrix.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052140117
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    Crystallization behavior of polypropylene filled with calcium carbonate of various shape (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 215 (1994), S. 11-24 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Calciumcarbonate unterschiedlicher Teilchenform (sphäarisch, kubisch und nadelfäormig) wurden mit Polypropylen (PP) in einer Zwei-Walzen-Mäuhle gemischt und anschließend zu Platten gepreßt. Der Einflußder Teilchenform auf das Kristallisationsverhalten der PP/CaCO3-Composite, d.h. Kristallisationspeaktemperatur (Tmax), Kristallisationsverlauf usw., wurde mittels Differentialkalorimetrie untersucht. Der Wert von Tmax häangt von der Größe der Gesamtoberfläache der CaCO3-Teilchen ab; Tmax ist bei nadelfäormigen Teilchen gräoßer als bei kubischen oder sphäarischen und hauangt in allen Fäallen der nicht-isothermen Kristallisation von der Abkäuhlgeschwindigkeit und der vorher erreichten maximalen Temperatur ab.
    Notes: Calcium carbonate of various particle shape (spheric, cubic, needle-shaped type) and polypropylene (PP) were mixed on a two roll mill and the mixture was pressed into plates. The effect of particle shape on the crystallization behavior of PP/CaCO3 composites, such as crystallization peak temperature (TMAX), crystallized pattern, etc., was investigated with differential scanning calorimetry measurements. The value of TMAX is explained by the total surface area of added CaCO3 particles; TMAX of needle-shaped series is larger than that of cubic or spheric ones. TMAX of various shaped CaCO3-filled PP totally depends on the cooling rate and maximum temperature in the non-isothermal crystallization, respectively.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052150102
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    Cationic polyelectrolytes, XIIPart. XI cf.8.. PEG-precursor for water-soluble cationic polymers with tertiary n-atoms in the main chain (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 215 (1994), S. 107-119 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Durch Polyaddition von Polyethylenglykol (PEG) Oligoglycidylethern (Mn (PEG): 396,587, 1437 und 3554) mit asymmetrischen Diaminen, wie N,N-Dimethylund N,N-Diethyl-1,3-diaminopropan, wurden wasserläosliche kationische Polymere erhalten. Die Eigenschaften der kationischen Polymeren sind vom urspräunglichen PEG-Molekulargewicht und der Diaminreaktivitäat abhäangig. PEG mit Mn = 396 zeigt das beste Verhalten. In verdäunnten wäassrigen Läosungen und in wäassrigen 2M NaCl-Läosungen der Polymeren wurde das Polyelektrolytverhalten veranschaulicht. Die Gegenwart der PEG Kette bestimmt das Polyelektrolytverhalten in den 2M NaCl Läosungen.
    Notes: Water-soluble cationic polymers were obtained by polyaddition of poly(ethylene glycol) (PEG) diglycidylethers (M̄n of PEG were 396, 587, 1437 and 3554, resp.) with asymmetrical diamines such as N,N-dimethyl-1,3-diaminopropane and N,N-diethyl-1,3-diaminopropane. The cationic polymer properties depend on the PEG initial molecular weight and on the diamine reactivity too. PEG with M̄n = 396 had the best behaviour in these reactions. The polyelectrolyte feature of cationic polymers was emphasized both in dilute aqueous solutions and in 2M aqueous NaCl solutions. The polyelectrolyte behaviour in 2M aqueous NaCl solution is determined by the PEG chain presence.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052150109
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    Untersuchungen zur reaktion von o-kresol mit formaldehyd unter verwendung tertiärer amine (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 215 (1994), S. 139-145 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Reaktion von o-Kresol mit Formaldehyd wurde unter Verwendung verschiedener tertiäarer Amine als Katalysatoren untersucht. Der Einfluß der Reaktionsparameter Basizitäat, Temperatur, Reaktionszeit und Formaldehydkonzentration wird diskutiert. Für die bevorzugte Bildung von 2,4-Bis(hydroxymethyl)-6-methylphenol wurden optimierte Synthesebedingungen erarbeitet. Die Bildung von Zwei-bzw. Mehrkernprodukten konnte nicht ausgeschlossen werden.
    Notes: The reaction between o-cresol and formaldehyde was investigated using various tertiary amines as catalysts. The influence of the reaction parameters basicity, temperature, reaction time and concentration of formaldehyde was discussed. To yield preferentially 2,4-bis(hydroxymethyl)-6-methylphenol the conditions of synthesis were optimized. The formation of bi- and polynuclear products cannot be avoided.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052150112
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    Effect of addition of cellulose powder on the viscometric behavior of liquid crystalline solutions of ethyl cellulose in m-cresol (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 215 (1994), S. 189-200 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Scherviskositäat fläussigkristalliner Ethylcellulose, die mit Cellulosepulver unterschiedlicher Partikelgräoße gefäullt war, wurde bei konstantem Schergefäalle mit einem Kegel-Platte-Viskosimeter bestimmt. Der Einfluß des Cellulosepulvergehalts, des Läange/Breite-Verhäaltnisses der Pulverteilchen und der Temperatur auf das viskose Verhalten und die Phasenäubergäange wird diskutiert. Der Zusatz von Cellulosepulver erhäoht die Viskositäat und verringert die Aktivierungsenergie des Fließens(Ea), ohne jedoch die Phasenäubergäange zu beeinflussen. Die Viskositäat und die Aktivierungsenergie sind abhäangig vom Läange/Breite-Verhäaltnis der Pulverteilchen; mit zunehmender Gräoße dieses Verhäaltnisses wird die Viskositäatszunahme beschleunigt und die Aktivierungsenergie des Fließens erhäoht, wäahrend die Aktivierungsenergie mit steigendem Pulvergehalt abnimmt. Die Phasenumwandlungen sind unabhäangig von der Partikelform. Der Einfluß des Pulvergehalts auf Viskositäat und Aktivierungsenergie ist abhäangig von der Art der fläussigen Phase; in der anisotropen Phase ist der Einfluß geringer als in der isotropen Phase. Dies scheint von der Ausrichtung der Pulverteilchen und der stäabchenfäormigen Molekäule herzuräuhren.
    Notes: Steady-state shear viscosity for the liquid crystalline ethyl cellulose solution filled with cellulose powders was determined using a cone-plate-type viscometer and the effects of cellulose powder content, powder aspect ratio and temperature on the viscometric behavior and phase transformation were discussed. The addition of powder increased the viscosity and decreased the activation energy (Ea) for flow, but did not affect the phase transformation. The viscosity and Ea depended on the aspect ratio; with greater aspect ratio, the viscosity enhancement was accelerated and Ea as well as the decrease in Ea with powder content increased. The phase transformation did not depend on the aspect ratio, the dependences of viscosity and of Ea on powder content depended on the solution phase; the dependences for the anisotropic phase were smaller than those for the isotropic one. The findings appeared to originate from the alignments of powders and rod-like molecules.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052150116
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    Oxygen uptake methods as a tool to determine the mechanism of action of hindered amine light stabilizers1Paper presented at the “15th Annual International Conference on Advances in the Stabilization and Degradation of Polymers” in Luzern (Switzerland), June 2-4, 1993. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 216 (1994), S. 37-44 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The UV-degradation of an unstabilized and two HALS stabilized polyethylene (PE) films is described. The degradations are characterized by measuring the oxygen uptake, the formation of CO and CO2, the FT-IR spectra, the mechanical properties, the stabilizer concentration and the oxygen content of the film.The oxygen uptake of the unstabilized PE film led to the expected changes in the IR spectra and embrittlement of the film, while the oxygen uptake by the HALS stabilized films caused only minor changes. The differences between the results for the unstabilized and the HALS stabilized polymers are explained assuming that the initiation of the photodegradation of PE is due to charge transfer complexes.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052160103
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    Current of status of exploitation of radical scavenging stabilizers in advanced polymer stabilizationPaper presented at the “15th Annual International Conference on Advances in the Stabilization and Degradation of Polymers” in Luzern (Switzerland), June 2-4, 1993. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 216 (1994), S. 135-146 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Principal chemical pathways characteristic of active participation of radical scavenging polymer stabilizers (phenols, aromatic, hydroaromatic and hindered aliphatic amines) are outlined. Pathways resulting in a partial depletion or distortion of activity of stabilizers, in formation of polymer discolouring products, or in interactions in bifunctional stabilizers are involved.
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    Poly(butyleneterephtalate) photolysis and photooxidation : Identification of the ir-absorbing productsPaper presented at the “15th Annual International Conference on Advances in the Stabilization and Degradation of Polymers” in Luzern (Switzerland), June 2-4, 1993. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 216 (1994), S. 155-167 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Irradiations (λ≥300 nm) of poly(butyleneterphtalate) films were carried out in both vacum and air. Photoproducts were investigated by FTIR spectroscopy, chemical derivatization reactions and physical treatments. The repartition of photoproducts in the polymer was shown to be heterogeneous. A scheme accounting for the main routes of PBT photolysis was found on the basis of photoproducts identification. Most of oxidation products were analogous to vacum photolysis species; the mechanism of photooxidation proposed implied both pure photolytical processes and a photo-induced oxidation route.
    Additional Material: 8 Ill.
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    Photo- and radiation-induced degradation of synthetic polymers: Polymer structure and stabilityPaper presented at the “15th Annual International Conference on Advances in the Stabilization and Degradation of Polymers” in Luzern (Switzerland), June 2-4, 1993. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 216 (1994), S. 225-241 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of polymer density, processing conditions (quenching of annealing), degree of crystallinity, size of crystallite and mobility of polymer chains on the photo-and radiation-induced degradation and the polymer stability have been studied by UV, FTIR spectroscopic, viscosity and mechanical property measurements. Four kinds of annealed or quenched polyethylene (PE) films varying densities were used to the studies. Polystyrene (PSt) films were used to investigate the effect of chain mobility on polymer degradation. The following results were obtained. 1.In linear low density (LLD) PE, greater amounts of crosslinking (irradiated in vacuum) and chain scission (irradiated in air) were noticed than in mediun density (MD) PE and high density (HD) PE samples.2.Polyene formation is favored in the case of the irradiation in vacuum for LLDPE.3.Polymer stability evaluated by mechanical property such as elongation at break (%) is superior in LLDPE to MDPE and HDPE for annealed and quenched samples.4.Segmental motion of polymer chain also affects the polymer stability
    Additional Material: 19 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052160115
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    Eigenschaften von binären mischungen aus polyethylenen hoher dichte mit ultrahoher und normaler molmasse (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 217 (1994), S. 43-49 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The study is on two component blends of high density polyethylenes, having normal and ultra-high molecular weight. The polyethylenes were homogenized by two routes: in powder state or by rolling in melt, then pressed at temperatures in the range from 140°C to 220°C. Comparative studies showed that the way of homogenizing of the components does practically not affect the main mechanical properties of the blends when pressed at temperatures ≥ 160°C. Of special interest are the characteristics of those systems where ultra-high molecular weight polyethylene is the matrix component.
    Notes: Untersucht wurden binäre Mischungen von Polyethylenen hoher Dichte rnit normaler und ultrahochmolekularer Molmasse, die auf zweierlei Weise - in Pulverform oder durch Walzen im Schmelzezustand - homogenisiert und bei Temperaturen zwischen 140 und 220°C gepreßt waren.Es wurde festgestellt, daß die Art der Homogenisierung der Komponenten praktisch keinen Einfluß auf die Eigenschaften bei Preßtemperaturen ≥ 160°C hat. Von besonderem Interesse sind die Eigenschaften der Systeme, in welchen das ultrahochmolekulare Polyethylen die Rolle der Matrixkomponente spielt.
    Additional Material: 4 Ill.
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    Rôle des pigments dans une réaction de polymérisation sous lumière UV-visible (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 218 (1994), S. 81-109 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Das Verhalten eines neuartigen photoinitiierenden Systems, das die Polymerisation von pigmenthaltigen Schichten großer Dicke in einem Reaktionsschritt gestattet, wird dargestellt. Die verschiedenen Wechselwirkungen, die in einem pigmenthaltigen System auftreten, werden qualitativ beschrieben, und der Anteil der von einem Photoinitiator absorbierten Lichtintensität wird berechnet. Neben dem Absorptions- und Reflexionsverhalten von verschiedenen Pigmentklassen werden die optischen Eigenschaften verschiedener Strahlungsquellen untersucht, um die Strahlungsbereiche zu finden, die am besten mit den optischen Parametern der Pigmente korrespondieren. Weiterhin wird die Beschleunigung von Polymerisationen durch die photokatalytische Wirkung einiger Pigmente behandelt.
    Notes: Ce travail sur le rôe des pigments définit le comportement d'un nouveau systeme photosensible qui permet de polymériser des milieux épais et pigmentés selon un procédé en une seule étape. Les différentes interactions présentes en milieu pigmenté sont décrites de façon qualitative, et la part de l'intensité lumineuse absorbée par un photo-amorceur dans un systéme pigmenté est evaluée. Les propriétés optiques telles que l'absorption et la réflectance des différentes familles chimiques de pigments sont déterminées, et, en paralléle, les propriétés optiques des différentes sources d'irradiation sont étudiées de manière à répondre au mieux aux fenêtres de transmission des pigments. L'effet photocatalytique de certains pigments est mentionné, ceci afin d'amkliorer la réaction de polymérisation.
    Additional Material: 18 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052180107
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    Molar mass distribution of polybutadiene synthesized with nickel-based Ziegler-Natta catalysts, I (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 218 (1994), S. 153-162 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Herstellung von cis-1,4-Polybutadien erfolgte mittels Polymerisation von 1,3-Butadien mit einem Katalysatorsystem, das in einer zweistufigen Reaktion gebildet wird: (1) BF3 · O(C2H5)2 und Al(C2H5)3, (2) Ni(OOC8H15)2 und Al(C2H5)3, genannt in-situ-Katalysatorsystem.Die Molmassenverteilungen (MMD) der erhaltenen Polymeren sind mit der Größenausschlußchromatographie (SEC) untersucht worden. Sie lassen sich mit Summen aus Schulz-Flory-Funktionen (SFF) beschreiben. Veränderte Katalysatorformierungs- und Polymerisationsbedingungen beeinflussen die Parameter der SFF. Veränderte Peakflächen und Molmassenmittelwerte der Einzelpeaks zeigen, daß die Polymerisation über mehrere Arten aktiver Zentren verläuft.
    Notes: Cis-1,4-polybutadiene was produced by polymerization of 1,3-butadiene using a catalyst system formed by a two-step formation, Namely (1) BF3 . O(C2H5)2 and Al(C2H5)3, (2) Ni(OOC8H15)2 and Al(C2H5)3 named in-situ-catalyst.The molar mass distributions (MMD) of the polybutadienes are investigated by means of size exclusion chromatography (SEC). The MMD's were fitted by a sum of Schulz-Flory-Functions (SFF). Changed catalyst formation and polymerization conditions influenced the parameters of the SFF. Changed areas and changed molar mass averages indicate a polymerization with more than one peak maximum and kind of active species and lead to a better understanding of the polymerization.
    Additional Material: 9 Ill.
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    Synthesis and characterization of epoxy resins containing chromium acrylate (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 219 (1994), S. 1-10 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Durch Umsetzung von Chromacrylat mit Bisphenol A und einem Überschuß Epichlorhydrin wurden neuartige Epoxid-Harze hergestellt. Epoxy-Äquivalentgewicht, Gehalt an Hydroxygruppen und hydrolysierbarem Chlor sowie die Viskosität wurden bestimmt, und die Harze wurden mittels IR- und 1H-NMR-Spektroskopie charakterisiert. Die thermischen Eigenschaften der bei 30°C für 24 h mit Ciba Geigy HY 850 (aliphatisches Amin) gehärteten Harze wurden gemessen. Die Harze besitzen eine gute thermische und chemische Stabilität und eine gute elektrische Leitfähigkeit. Die Reaktion verläuft nach erster Ordnung; die Aktivierungsenergie beträgt 47 kJ mol-1 bzw. 34 kJ mol-1 mit bzw. ohne Chromacrylat. Aus spektroskopischen Untersuchungen wird geschlossen, daß das Chrom mit Bisphenol A einen Komplex bildet, der die Epoxidierung beschleunigt.
    Notes: Novel epoxy resins containing chromium acrylate have been synthesized by reacting chromium acrylate with bisphenol-A and excess epichlorohydrin. The quantities such as epoxy equivalent weight, hydroxy content, hydrolyzable chlorine content and viscosity have been determined. The resins have been characterized by IR and 1H NMR spectroscopy. The cured resins were evaluated for thermal properties. The curing of resins was carried out with Ciba Geigy HY 850 (aliphatic amine adduct) at 30°C for 24 h. The cured resins have excellent thermal and chemical resistance, in addition to an excellent electrical conductivity. The reaction follows first order kinetics with an activation energy of 47 kJ mol-1 and 34 kJ mol-1 in the presence and absence of chromium acrylate, respectively. The chromium forms a complex with bisphenol-A, as indicated by spectroscopic studies, which increases epoxidation.
    Additional Material: 6 Ill.
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    Interpenetrating polymer networks based on liquid natural rubber. 1. Synthesis and effect of nco/oh ratio on physical and mechanical properties (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 219 (1994), S. 67-76 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Interpenetrierende Polymernetzwerke (IPNs) aus Polystyrol und Polyurethan auf der Basis von hydroxyterminiertem Naturkautschuk mit unterschiedlichen NCO/OH-Verhältnissen wurden unter verschiedenen Reaktionsbedingungen hergestellt und zu widerstandsfähigen Filmen verarbeitet. Die IPNs wurden durch ihre physikalischen, mechanischen und morphologischen Eigenschaften wie Dichte, Shore-A-Härte, Vernetzungsdichte, Zugfestigkeit und Reißdehnung charakterisiert. Mit steigendem Polystyrolgehalt erhöhen sich auch Dichte, Shore-A-Härte und Zugfestigkeit, während die Reißdehnung abnimmt. Die Untersuchungen der Vernetzungsdichte lassen eine Phasenumkehr vermuten.
    Notes: Interpenetrating polymer networks (IPNs) of polyurethane based on hydroxyterminated natural rubber with varying NCO/OH ratios and polystyrene were synthesized under different experimental conditions. These IPNs were found to make tough films. The IPNs were characterized by their physical, mechanical and morphological properties like density, Shore-A hardness, crosslink density, tensile strength and elongation at break. The IPNs exhibited an increasing trend in density, Shore-A hardness and tensile strength with increasing polystyrene content, while elongation at break decreased with similar variation in polystyrene content. The crosslink density measurements indicated a possible phase inversion process.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052190106
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    Plasma treatment of polyethylene ultrafiltration membranes (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 219 (1994), S. 117-124 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der Einfluß einer Plasmabehandlung von Ultrafiltrationsmembranen aus Polyethylen auf die Fouling- und Reinigungseigenschaften bei der Filtration von Rinderserumalbumin werden diskutiert. Bei 2,45 GHz erzeugtes Luft-Plasma steigert die Hydrophilie der Membranoberfläche von 0 auf 60%. Der Durchfluß bleibt bei 90 bis 99%. Mit Plasma behandelte Membranen sind leichter zu reinigen als unbehandelte; dennoch sind sie anfälliger für die Ablagerung von Rinderserumalbumin.
    Notes: The effect of plasma treatment of polyethylene ultrafiltration membranes on fouling and cleaning phenomena during filtration of bovine serum albumin solutions is discussed. Air-plasma of 2.45 GHz raises the membrane surface hydrophilicity from 0 up to 60%. The flux is maintained at 90-99%. Plasma-treated membranes are easier to clean than untreated polyethylene membranes. Despite that, the plasma-modified membranes are susceptible to more intensive deposition of albumin.
    Additional Material: 4 Tab.
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    Preparation and characteristics of immobilized glucose oxidase on membranes of photosensitive polymers (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 219 (1994), S. 101-115 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Immobilisierung von Glucose-Oxidase in einer Poly(vinylalkohol) (PVAL)-Membran in Gegenwart von UV-Photoinitiatoren wurde untersucht. Enzym-Membranen wurden aus PVAL-Diazoharz- und PVAL-Photoinitiator-Systemen durch Vernetzung mit UV-Licht hergestellt. Mit diesen immobilisierten Glucose-Oxidase-Membranen wurde eine wirkungsvolle Enzymelektrode entwickelt, deren Eigenschaften untersucht wurden. Der Einfluß der Photoinitiatorkonzentration in Poly(vinylalkohol) und der UV-Bestrahlungsdauer auf den Grad der Unlöslichkeit sowie die Aktivitätsausbeute der Membran wurden mit Glucose als Substrat untersucht. Temperatur- und pH-Abhängigkeit der relativen Aktivität, Stabilität bei mehrmaligem Gebrauch, Lagerstabilität und Kalibrierungsdiagramme der Enzym-Membranen wurden ermittelt. Eine beim Erstgebrauch auftretende Instabilitätserscheinung der Membranen wurde ebenfalls untersucht.
    Notes: A study of the immobilization of glucose oxidase on a poly(vinyl alcohol) (PVAL) membrane in the presence of UV sensitizers was carried out. Enzyme membranes were prepared from PVAL-diazoresin and PVAL-sensitizer systems, crosslinked by means of UV irradiation. An effective enzyme electrode was developed by using the immobilized glucose oxidase membrane, and its characteristics were investigated. The effects of the concentration of sensitizers in poly(vinyl alcohol) and UV irradiation time on the degree of insolubility as well as the activity yield of the membrane were examined for the immobilized glucose oxidase using glucose as a substrate. Temperature and pH dependences of the relative activity, stability in repeated use, storage stability and calibration plots of the enzyme membranes were evaluated. The unstability phenomenon, found in the initial use of the immobilized glucose oxidase membrane, which was prepared from PVAL-sensitizer system, was also investigated.
    Additional Material: 11 Ill.
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    Auswirkungen von Sterilisationsverfahren auf biologisch abbaubare Kunststoffe (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 219 (1994), S. 11-26 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Biopol, Biocellat and Mater-Bi, three biologically decomposable plastics have been tested for their use in medical industries. Biopol did not loose its stress and stiffness under sterilisation, and was also resistant against temperature and alcohol. Mater-Bi and Biocellat, the two other materials, did not satisfy the test applications. Water vapor sterilisation, temperature up to 60°C, at higher temperatures this material will embrittle.
    Notes: Für den Einsatz biologisch abbaubarer Kunststoffe in der pharmazeutischen Industrie und Medizintechnik wurden Produkte verschiedener Hersteller, wie Biopol, Biocellat und Mater-Bi untersucht. Dabei zeigte vor allem Biopol das notwendige Anforderungsprofil, d.h. die Anwendbarkeit aller Sterilisationsverfahren ohne Festigkeitsbzw. Steifigkeitsverluste sowie Temperatur- und Alkoholbeständigkeit. Dagegen wiesen die Werkstoffe Mater-Bi und Biocellat einige Schwachstellen auf. Bei Mater-Bi lagen diese bei der Wasserdampfsterilisation sowie bei der geringen thermischen und Medienbeständigkeit. Biocellat versprödet dagegen durch die erhöhte Temperatur bei der Dampfsterilisation, d.h. daß ein Einsatz über 60°C nicht möglich wäre.
    Additional Material: 5 Ill.
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    Polymers and copolymers based on vinyl tetrazoles, 2Part 1 cf.10.. Alkylation of poly(5-vinyl tetrazole) (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 219 (1994), S. 89-99 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Alkylierung von Poly(5-vinyltetrazol) mit Dimethylsulfat und tert-Butylalkohol sowie Alkylhalogeniden RHal (R=CH3, C2H5, CH2—CH=CH2, n-C4H9 und t-C4H9) und die Kinetik dieser Reaktion wurden untersucht, um eine neue Herstellungsmethode für tetrazolhaltige Polymere mit wertvollen Eigenschaften zu entwickeln. Die vergleichenden Untersuchungen über die isomere Zusammensetzung und die spektroskopischen Daten von Poly(N-alkyl-5-vinyltetrazol)en, die durch die Alkylierung von Poly(5-vinyltetrazol) sowie durch die Copolymerisation der entsprechenden Monomeren hergestellt wurden, wurden mit IR-, 1H-NMR- und 13C-NMR-Spektroskopie durchgeführt. Der Alkylierungsumsatz beträgt bis zu 99,8%; dadurch können polymere Produkte erhalten werden, deren Zusammensetzung, Struktur und Eigenschaften denen der Homo- und Copolymeren sehr ähnlich sind.
    Notes: Alkylation of poly(5-vinyl tetrazole) with dimethyl sulfate and tert-butyl alcohol as well as with alkyl halides RHal (R=CH3, C2H5, CH2—CH=CH2, n-C4H9, t-C4H9) has been studied under various conditions in order to develop a new method of synthesis of tetrazole-containing polymers having a complex of valuable properties. The kinetic study of the process and comparison of isomeric compositions and spectroscopic characteristics (IR, 1H NMR and 13C NMR) of poly(N-alkyl-5-vinyl tetrazole)s synthesized by alkylation of poly(5-vinyl tetrazole) and of those prepared by (co)polymerization of the corresponding vinyl tetrazoles have been carried out. The alkylation is found to proceed to high conversion extents (up to 99.8%) and enables to obtain a wide variety of polymeric products having the composition, structure and properties very similar to those of homo- and copolymers.
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    Dyes for nonlinear optics prepared from 2-hydroxyethyl methacrylate. Nonlinear properties of the resulting copolymers (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 220 (1994), S. 75-87 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Farbstoffe mit nichtlinearen optischen Eigenschaften wurden in einer zweistufigen Synthese aus 2-Hydroxyethylmethacrylat (HEMA), 4-Carboxybenzaldehyd und verschiedenen Anilinderivaten hergestellt. Die Farbstoffe (aromatische Iminester von HEMA) wurden mit Styrol copolymerisiert, die erhaltenen Copolymere wurden mit DSC sowie IR-, 1H NMR- und UV-VIS-Spektroskopie charakterisiert, und ihre nichtlinearen Eigenschaften wurden untersucht. Es zeigte sich, daß die nichtlinearen Koeffizienten d31 und d33 vom Farbstoffgehalt der Copolymeren und der Art der elektronenspendenden Gruppen abhängig sind.
    Notes: Dyes for nonlinear optics have been synthesized in two steps from 2-hydroxyethyl methacrylate (HEMA), 4-carboxybenzaldehyde and various substituted anilines. The obtained dyes (aromatic imine esters of HEMA) have been copolymerized with styrene, the copolymers characterized by DSC as well as IR, 1H NMR and UV-VIS spectroscopy, and studied for their nonlinear properties. The d31 and d33 nonlinear coefficients proved to be dependent on the dye content of the copolymers and on the nature of electrondonating groups.
    Additional Material: 4 Ill.
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    Viscosity behaviour of multivalent metal ion-containing carboxymethyl cellulose solutions (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 220 (1994), S. 123-132 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der Einfluß von Ca2+-bzw. Al3+-Ionen auf das Viskositätsverhalten (Salzverträglichkeit) wäßriger Lösungen von Natriumcarboxymethylcellulose (CMC) sowohl mit unterschiedlichem Polymerisationsgrad (DP) als auch mit unterschiedlichem Substitutionsgrad (DS) und verschiedenartiger Substitutentenverteilung wurde untersucht. Aus Viskositätsmessungen mit einem Rotationsviskosimeter bei einer Scherrate von 500 s-1 geht hervor, daß die relative Abnahme der Viskosität im Ergebnis des Zusatzes der mehrwertigen Metallkationen unabhängig vom DP (im Bereich von 160 bis 900) der CMC ist. Homogen hergestellte CMC-Proben 2 mit einem größeren Gehalt an 2,3,6-Tri-O-carboxymethylglucose-Einheiten in der Polymerkette weisen im Vergleich zu heterogen hergestellten CMCs 1 bei gleichem Gesamt-DS eine höhere Salzverträglichkeit auf.
    Notes: The influence of Ca2+-and Al3+-ions, respectively, upon the viscosity behaviour (so-called salt tolerance) of aqueous solutions of sodium carboxymethyl cellulose (CMC) with different degree of polymerization (DP) and, on the other hand, with both different degree of substitution (DS) and distribution of substituents, was investigated. Viscosimetry by means of a rotational rheometer at a shear rate of 500 s-1 shows that the relative drop in viscosity as a result of addition of the multivalent metal cations is independent of DP (ranging from 160 to 900) of the CMC samples. Homogeneously synthesized CMCs (2) with a higher content of 2,3,6-tri-O-carboxymethyl glucose units in the polymer chain possess a significantly higher salt tolerance than those (1) prepared under heterogeneous reaction conditions at comparable total DS values.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052200111
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    Modification of melamine-formaldehyde moulding compounds with ethylene/vinyl acetate copolymers (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 222 (1994), S. 61-87 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Melamin-Formaldehyd-Harz-Formmassen (MF) wurden durch mechanisches Mischen mit Ethylen-Vinylacetat-Copolymeren (EVA) und teilverseiftem EVA modifiziert, wobei Etherbindungen zwischen dem hydrolysierten EVA und dem MF-Harz nachgewiesen werden konnten, die die mechanischen Eigenschaften von spritzgepreßten Formteilen im Vergleich zur Modifizierung mit EVA verbessern. Der Zusatz solcher Modifikatoren erhöht die Duktilität und verringert im Falle von EVA die Nachschwindung der überaus steifen MF-Matrix, solange der Modifikatoranteil gering bleibt. Dagegen werden die Steifigkeit und die Wärmeformbeständigkeit verschlechtert. Die durch solche unvernetzten Polymeren erreichbare Steigerung der Schlagzähigkeit bleibt allerdings unzureichend.
    Notes: Melamine-formaldehyde moulding compounds (MF) were modified by mechanical mixing with ethylene/vinyl acetate copolymers (EVA) and with partially hydrolysed EVA. Ether linkages between the hydrolysed material and the MF resin improve the mechanical properties of the transfer moulded parts containing the hydrolysed material compared to those made with EVA. The use of both modifying polymers improves the ductility and, in case of the partially hydrolysed material, the postshrinkage of the extremely rigid MF matrix, as long as the modification polymer content is kept low. On the contrary, Young's modulus and the heat deflection temperature are deteriorated. The improvement in impact strength by use of those uncrosslinked polymers is still insufficient.
    Additional Material: 17 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052220106
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    Synthesis and properties of biodegradable copolyesteramides: Nylon 6,6/∊-caprolactone copolymers, 1 (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 222 (1994), S. 111-123 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Eine Reihe von Copolyesteramiden mit Molekulargewichten zwischen 1000 und 7000 (GPC, NMR) wurden aus Adipinsäure/1,6-Hexandiamin/∊-Caprolacton bzw. Nylon 6,6-Salz/∊-Caprolacton hergestellt. Die thermischen Eigenschaften der synthetisierten Polymeren (Glasübergangs-, Schmelz-, und Zersetzungstemperaturen, Schmelzenthalpien) wurden durch DSC- und TGA-Messungen bestimmt und in Bezug auf das Comonomerverhältnis in der Ausgangsmischung diskutiert. Die Übereinstimmung der Copolymerzusammensetzung mit dem Ausgangscomonomerverhältnis wurde mit FT-IR- und NMR-Spektroskopie untersucht. Die Bioabbaubarkeit der Copolyesteramide wurde durch enzymatische Hydrolyse geprüft.
    Notes: A series of copolyesteramides based on adipic acid/1,6-hexane diamine/∊-caprolactone and Nylon 6,6 salt/∊-caprolactone were synthesized. Their molecular weights, determined by gel permeation chromatography and NMR spectroscopy, were found to lie within the range from 1000 up to 7000. Their thermal properties (glass transitions, melting points and heats of melting, and decomposition temperatures) were recorded with diferential scanning calorimetry and thermogravimetry, respectively, and correlated to the comonomer feed composition. The FT-IR and NMR spectra were also recorded in order to confirm the composition of the copolyesteramides and to compare them with that of the comonomer feed. The biodegradability of the synthesized copolymers was tested by enzymatic hydrolysis.
    Additional Material: 4 Ill.
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    Study of the condensation products of abietic acid with formaldehyde at high temperatures (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 222 (1994), S. 165-174 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Durch sulfonsäurekatalysierte Umsetzung von Abietinsäure und Paraformaldehyd bei hohen Temperaturen wurden neuartige Kondensationsprodukte erhalten. Als Nebenprodukte der Polykondensation werden eine Ketoverbindung sowie Wasser und Kohlendioxid gebildet. Die Carboxygruppen der Abietinsäure sind an der Kondensationsreaktion beteiligt. In Abwesenheit von Paraformaldehyd wurde das Abietinsäure/Sulfonsäurekatalysator-System untersucht, um zusätzliche Informationen über die Reaktion zu erhalten. Der Reaktionsverlauf hängt von der Temperatur und der chemischen Struktur des Katalysators ab. Ein möglicher Reaktionsmechanismus der Kondensation wird diskutiert.
    Notes: New condensation products have been synthesized by heating abietic acid and formaldehyde at high temperatures in the presence of sulfonic-type acid catalysts. The main polycondensation reaction is associated with a secondary one which leads to a ketonic compound, carbon dioxide and water. The carboxylic groups of abietic acid participate in this condensation reaction. The behaviour of the abietic acid-sulfonic acid catalyst system was studied in absence of formaldehyde to acquire additional information about the reaction. The process is defined by the reaction temperature and chemical nature of the catalyst. A possible mechanism of the condensation reaction is discussed on the basis of the obtained results.
    Additional Material: 2 Ill.
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    Tailored polymers by cationic ring-opening polymerization (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 223 (1994), S. 1-11 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: After a general classification of the cationic ring-opening polymerizations (CROP's) according to their polymerization mechanism, a number of examples of tailored polymers based on CROP are presented. The monomers used for the synthesis of these tailored structures are tetrahydrofuran (THF), N-tert-butyl aziridine (TBA), 2-methyl-1,3-oxazoline (MeOX) and 1,3-dioxolane (DXL).The polymer structures include different block and graft copolymers, macromonomers, star-shaped polymers, polymer networks and interpenetrating polymer networks (IPNs).
    Additional Material: 1 Tab.
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    Massgeschneiderte PolymereVortrag anläßlich der Tagung der Fachgruppe “Makromolekulare Chemie” der Gesellschaft Deutscher Chemiker über “Fortschritte in der Polymersynthese” in Bad Nauheim, 21.-22. März 1994. Synthesestrategien für Telechele, Makromonomere, Block- und Pfropfcopolymere (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 223 (1994), S. 29-46 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: In diesem Beitrag wird ein überblick über neuere Entwicklungen auf dem Gebiet der Synthese von Telechelen, Makromonomeren, Block- und Pfropfcopolymeren gegeben. Synthesestrategien aus den Bereichen der Polykondensation, der radikalischen, anionischen und kationischen Polymerisation, der Kettenspaltung sowie der Criss-Cross-Cycloaddition werden diskutiert.
    Notes: New developments in the synthesis of telechelics, macromonomers, block- and graftcopolymers are presented. Synthetic strategies for them are demonstrated with examples from different fields such as polycondensation, radical, anionic, and cationic polymerization, chain cleavage and criss-cross-cycloaddition.
    Additional Material: 1 Tab.
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    Alkane als initiatoren zur radikalischen polymerizationHerrn Professor Dr. rer. nat. Dr.-Ing. E.h. Hansjörg Sinn mit den besten Wünschen zum 65. Geburtstag gewidmet (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 223 (1994), S. 69-79 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Alkanes with highly substituted carbon-carbon bonds can be cleaved in free radicals by homolytic dissociation under the influence of thermal energy. The energy of dissociation is mainly determined by the type and size of the respective substituents. For tetraarylbutane dinitriles the temperatures of decomposition are in the range of other technically used initiators. But nevertheless, these compounds are up to now rather seldom used to initiate free radical polymerizations. This is connected with the special mechanism of initiation: the formed highly substituted alkyl radicals are relatively stable and show only a rather low reactivity against the usually used monomers. Therefore, in the beginning of the polymerization the radical concentration is rather high which leads not only to addition to monomers but also to a pronounced primary radical termination. In some cases this termination process is reversible which results in an unusual polymerization kinetics. Depending on the type of monomer and the degree of reversibility of the primary radical termination, either a period of “dead-end” polymerization follows or the cleavage of the oligomers at the chain end results in a re-initiation process with a “normal” polymerization with increased rate. The reaction mechanism, kinetics and some possible applications of such initiating alkanes are reported.
    Additional Material: 3 Ill.
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    Cycloolefin-copolymere: Eine neue klasse transparenter thermoplasteHerrn Prof. Dr. H. Sinn zum 65. Geburtstag gewidmet. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 223 (1994), S. 121-133 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Untersuchungen wesentlicher Aspekte der Polymerisation und der Eigenschaftsmodifikation auf Metallocen-Katalyse basierender Cycloolefin-Copolymere (COC) zeigen, daß mit dieser Monomer-Katalysator-Kombination eine neue Klasse transparenter Thermoplasten zugänglich gemacht wird. COC können mit Metallocenen in beliebiger zusammensetzung und mit kontrollierter Mikrostruktur hergestellt werden. Die somit erreichte und durch zusätzliche Modifikationen noch erweiterbare Breite des Eigenschaftsspektrums ermöglicht vielfältige Anwendungen dieser neuen Polymerklasse. Die wichtigsten Schlüsselfaktoren im rohstofflich-technologischen Bereich, die diese Struktur- und Eigenschaftsvielfalt ergeben, werden beispielhaft beschrieben.
    Notes: Investigation of the polymerization process and property modification of metallocene-based cycloolefin copolymers (COC) shows that this monomer-catalyst combination enables synthesis of a new class of transparent thermoplastic polymers. Metallocene catalysis offers much opportunity to vary the composition and microstructure of the copolymers. The breadth of the polymer spectrum which can be further widened by polymer modification enables many applications for this new class of thermoplastics. The key parameters that control structure and properties in the COC family are discussed in this paper.
    Additional Material: 6 Ill.
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    Funktionalisierte Kammpolymere: Synthesen, modifizierung und anwendungen (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 223 (1994), S. 165-175 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The present paper deals with the synthesis and modification of functionalized polymers characterized by a special molecular architecture. The reactivity of a functionalized polymer with comb-like structure can be controlled in a significant manner by the crystalline order of the side chains. In contrast, photocrosslinking of comblike polymers containing cinnamic components in the side chains influences the crystallization process. The air drying process of a modified polybutadiene system with comb-like structure was shown to depend sensitively on the side chain order. Enzymatic synthesis of new monomers and polymers is briefly reviewed. The complexing capability of cyclodextrines were used to synthesize polyrotaxanes. Finally, the synthesis of a chiral polymerizable dendrimer containing eight estergroups in the monomer unit is presented.
    Additional Material: 8 Ill.
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    Intramolekular vernetzte poly(organosiloxan)partikel (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 223 (1994), S. 203-216 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Intramolecularly crosslinked poly(organosiloxane) particles are prepared by means of emulsion polycondensation or emulsion polymerization of alkoxysilanes or cyclic organic siloxanes. Starting from these intramolecularly crosslinked poly(organosiloxane) particles, graft copolymers are obtained by free-radical emulsion polymerization of unsaturated olefinic monomers (e.g. acrylates, styrene) in the presence of (functionalized) organosiloxanes. Intramolecularly crosslinked poly(siloxane) particles and their graft copolymers are characterized by means of light scattering (in dispersion), electron microscopy and thermal analyses (DSC, DMTA).
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052230115
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    Study on poly(2,6-dimethyl-1,4-phenylene oxide)/SBS triblock copolymer blends (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 214 (1994), S. 153-167 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der Zusammenhang zwischen der Mischbarkeit und den physikalischen Eigenschaften von Polymerblends aus Poly(2,6-dimethyl-1,4-phenylenoxid) (PPO), die in unterschiedlichen Zusammensetzungen in einem Doppelschneckenextruder mit Polystyrol, schlagzähem Polystyrol oder Styrol-Butadien-Copolymeren hergestellt wurden, wird diskutiert. Die Verträglichkeit der Komponenten wurde mittels DSC und DMA, die Morphologie der Blends mittels SEM untersucht. Mit abnehmendem Polystyrolanteil wurde eine schlechtere Mischbarkeit bei den Blends beobachtet, deren Kerbschlagempfindlichkeit sich erhöhte. Die Untersuchungsergebnisse werden mit dem Micellmodell interpretiert.
    Notes: The relationship between the miscibility and the physical properties of polymer blends of poly(2,6-dimethyl-1,4-phenylene oxide) and polystyrene (PS), high-impact polystyrene (IPS) and poly(styrene-block-butadiene-block-styrene) (SBS), which are blended in different compositions by a twin-screw extruder is discussed. The three types of SBS that were used are SBS1, SBS2 and SBS3 having different styrene/butadiene ratios. Dynamic mechanical analysis and differential scanning calorimetry were used to study the miscibility. The morphology was examined by SEM. The miscibility of the blends decreases with decreasing PS content. The notch sensitivity is improved by blending. Finally, the micelle model was used to explain the testing phenomena.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052140114
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    Water-soluble polyamides as potential drug carriers, VIIPresented in part at the Symposium on Water-soluble Polymers, 198th National Meeting Am. Chem. Soc., Miami Beach, Florida, 10-16 September 1989. For Part VI, cf1.. Synthesis of polymers containing intrachain- or extrachain-type amine ligands by interfacial polymerization (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 214 (1994), S. 137-152 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Aliphatische Polyamide mit Poly(ethylenoxid)-Kettensegmenten unterschiedlicher Länge wurden durch Grenzflächenpolymerisation aus Succinylchlorid und Jeffamine ED-900 (O,O'-Bis(2-aminopropyl)poly(ethylenglykol) 800) bzw. Jeffamine ED-2001 (O,O'-Bis(2-aminopropyl)poly(ethylenglykol) 1900) zur Verwendung als Trägersubstanzen für Medikamente synthetisiert. Copolyamide mit kurzkettigen Diamin- und Jeffamine-Segmenten sowie Polyamide aus Cystin und Diamineinheiten wurden auf die gleiche Weise hergestellt. Die Polymerisationen wurden im zweiphasigen System Dichlormethan/Wasser bei Temperaturen um 0°C durchgeführt. Die Polymerprodukte wurden durch stufenweise Dialyse in wäßriger Phase bis zu einem Molekulargewicht von 25000 fraktioniert, nach Gefriertrocknung als wasserlösliche Harze oder Feststoffe erhalten und durch Mikroanalyse sowie 1H NMR-Spektroskopie charakterisiert. Die inhärenten Viskositäten liegen im Bereich von 10-20 ml/g. Die Eignung eines repräsentativen Zielmoleküls zur Bindung von Medikamenten wurde durch eine kovalente Verankerung einer als Medikamentmodell fungierenden Ferrocen-Verbindung untersucht. Dabei wurde ein wasserlösliches Polymer-Ferrocen-Konjugat erhalten.
    Notes: Aliphatic polyamides comprising poly(ethylene oxide) chain segments of various lengths, designed for use as drug carriers, are synthesized by interfacial polymerization of succinyl chloride with the two Jeffamine types ED-900 and ED-2001, formally described by the supplier as O,O'-bis(2-aminopropyl)poly(ethylene glycol) 800 and O,O'-bis(2-aminopropyl)poly(ethylene glycol) 1900. Copolyamides comprising both short-chain diamine and Jeffamine segments are similarly prepared, as are polyamides made up of cystine and diamine segments. The polymerizations are performed in a two-phase methylene chloride-water system at temperatures near or below 0°C. The product polymers, crudely fractionated by staged aqueous-phase dialysis at an ultimate molecular-mass cut-off of 25000, are collected after freeze-drying as water-soluble resins or solids and are characterized microanalytically and by 1H NMR spectroscopy. Inherent viscosities are in the range of 10-20 ml g-1. The drug-binding potential of a representative target polymer is probed by the covalent anchoring of a ferrocene compound used as a drug model, giving a water-soluble polymer-ferrocene conjugate.
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    Studies on vinyl ester resin and its urethane derivative as coating materials (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 214 (1994), S. 211-216 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Über die Anwendung von Vinylesterharzen aus dem Diglycidylether von Bisphenol A sowie dessen Urethanderivat als Beschichtungsmaterial wird berichtet. Die mit den Harzen beschichteten Flußstahlplatten wurden auf Oberflächenglanz, Kratzfestigkeit und Chemikalienbeständigkeit untersucht. Harze mit Styrolanteil zeigen deutlich verbesserte Beschichtungseigenschaften.
    Notes: The present paper is concerned with the coating applications of a vinyl ester resin derived from diglycidyl ether of bisphenol-A and its urethane derivative. The mild steel panels coated with the synthesized resins were evaluated for their gloss on the surface, scratch hardness and chemical resistance. The incorporation of styrene in the resin systems improves the properties of coatings remarkably.
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    Silica gel supported zirconocene dichloride/methylalumoxane catalysts for ethylene polymerization: Effects of heterogenation on activity, polymer microstructure and product morphology (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 215 (1994), S. 47-57 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Das Katalysatorsystem Zirkonocendichlorid/Methylalumoxan wurde auf Siliciumdioxid aufgebracht, um Katalysatoren fur die Suspensions- order Gasphasenpolymerisation von Ethylen herzustellen. Die häochste Aktivitäat wurde für eine sandwichartige, dreilagige Verankerung von Zirkonzentren auf der Träageroberfläache gefunden. Dieneuen Katalysatorsysteme besitzen eine im Vergleich zu den entsprechenden homogenen Katalysatoren geringere Aktivitäat. Die Immobilisierung der aktiven Katalysatorzentren führt zu einer deutlichen Erhäohung der Polymermolmassen. Dabei bleibt die enge Molekulargewichtsverteilung der Polymerprodukte nahezu erhalten. Solche auf Träager aufgebrachte Metallocen-Katalysatoren käonnten für die Herstellung von Polyethylenen mit kontrollierter Rheologie Anwendung finden.
    Notes: The system zirconocene dichloride/methylalumoxane was supported on silica in order to provide ethylene polymerization catalysts for suspension or gas phase processes. Highest activity was found for a sandwich-like, three layer anchoring of the zirconium centers on the support surface. The new catalyst systems show a decrease of activity compared to polymerization experiments in homogeneous phase. However, the molecular weights are increased and the weight distributions remain narrow by immobilization of the active catalyst sites. Those supported metallocene catalysts could find application for the synthesis of polyethylene materials with controlled rheology.
    Additional Material: 3 Ill.
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    Evaluation of poly(butyl acrylate-co-ethylene glycol dimethacrylate) sorbents for chromatographic separation of biomolecules (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 215 (1994), S. 129-138 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Vernetzte Copolmere aus Butylacrylat (BA) und Ethylenglycol-dimethacrylat (EGDMA) wurden auf ihre Eignung als stationäare Phase für die Chromatographie untersucht. Es wurde festgestellt, daß gering vernetzte Copolymere (〈 30 Gew.-% EGDMA) nicht poräos sind, wäahrend Matrices mit mehr als 40 Gew.-% EGDMA eine konstante Porositäat aufweisen. Eine Erhäohung des Vernetzergehaltes beeinflußt hauptsäachlich die Hydrophobie der Oberfläache. Zwei Meßmethoden für diese Eigenschaft werden diskutiert: Die Absorption von Alkylalkoholen und von Aminosäauren. Für letztere wurde aus der Steigung der Beziehung zwischen der Sälenkapazitäat und dem Hydrophobie-Parameter der Aminosäauren ein Matrix-Hydrophobie-Index berechnet und dieser mit den bekannten Energien der Wechselwirkung von Alkylalkohol—CH2 Gruppen mit der Polymermatrix verglichen. Die Vorteile der Verwendung des Hydrophobie-Indexes bei der Bewertung von polymeren Sorbentien werden aufgezeigt.
    Notes: Copolymers of butyl acrylate (BA) crosslinked with ethylene glycol dimethacrylate (EGDMA) were evaluated as potential chromatographic packings. It was found that slightly crosslinked copolymers (up to 30 wt.-% EGDMA) did not provide porous material, while for matrices which exceeded 40 wt.-% of EGDMA the porous structure remained unchangeable. The increase of crosslinker content mostly affected the surface hydrophobicity. Two methods of measurement of this property were discussed: Sorption of alkyl alcohols and amino acids. Taking the latter for testing, a polymer matrix hydrophobicity index was calculated as the slope of dependence of column capacity vs. amino acid hydrophobicity parameter. The indices were verified against well-established interaction energies of —CH2— groups of alkyl alcohols and polymer surfaces. Some benefits of the use of the hydrophobicity index in evaluation of polymer sorbents were demonstrated.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052150111
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  • 96
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    Epoxysiloxane resins by the condensation of 3-glycidyloxypropyltrimethoxysilane with diphenylsilanediolDedicvated to Prof. Dr. Dr.-Ing. E. h. Hansjörg Sinn on the occasion of his 65th birthday (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 218 (1994), S. 111-126 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Kondensation von 3-Glycidyloxypropyltrimethoxysilan I mit Diphenylsilandiol II wurde untersucht. Abhängig von Lösungsmittel, Temperatur und Katalysator werden unterschiedliche Primärprodukte erhalten. Die Reaktion in Masse bei 120°C mit Titan(IV)-isopropylat als Katalysator liefert ein transparentes Harz A. Das eduktfreie Produkt wurde IR-, 1H- und 13C-NMR-spektroskopisch charakterisiert und chromatographisch mit GPC und HPLC untersucht. Die trimeren und tetrameren Siloxane bestehen aus Diphenylsilan- und 3-Glycidyloxypropylmethoxysilaneinheiten. Das Verhältnis von cyclischen zu linearen Molekülen beträgt 2:1. Höhermolekulare Verbindungen entstehen nur in geringen Mengen. Das Epoxysiloxangemisch löst sich in unterschiedlichen organischen Lösungsmitteln und ist mit kommerziell verfügbaren Epoxiden mischbar. Die Zeitabhs̈ngigkeit von Viskosität und Epoxidwert bei der Lagerung unter Normalbedingungen wurden gemessen und mit HPLC verfolgt . Die Lagerstabilität wurde durch eine zusätzliche thermische Behandlung verbessert.
    Notes: Condensation of 3-glycidyloxypropyltrimethoxysilane I with diphenylsilanediol II was investigated. Depending on solvent, temperature and catalyst, different products were obtained. Bulk reaction at 120°C using titanium(IV)-isopropylate as a catalyst provided the transparent resin A. A was characterised by IR, 1H- and 13C-NMR spectroscopy and contained no reactants. GPC and HPLC studies revealed that A consists of trimer and tetramer siloxanes of pertinent diphenylsilane and 3-glycidyloxypropylmethoxysilane moieties. The proportion of cyclic to linear molecules was evaluated 2:1. Only small amounts of high-molecular-weight compounds were observed. The epoxysiloxane product proved to be miscible with various organic solvents and with commercial epoxy resins. Time dependence of viscosity and epoxy content were recorded during ambient storage and monitored by HPLC. Pot-life was improved by a subsequent thermal procedure.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052180108
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  • 97
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    Molar mass distribution of polybutadiene synthesized with nickel-based Ziegler-Natta catalysts, IIPart I cf.14. (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 218 (1994), S. 163-170 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Cis-1,4-Polybutadien wurde durch Polymerisation von 1,3-Butadien mit Katalysatorsystemen hergestellt, die Ni(OOC8H15)2 und Al(C2H5)3 sowie die Lewissäuren BF3 · O(C2H5)2 oder TiCl4 enthalten. Die Molmassenverteilungen (MMD) der erhaltenen Polybutadiene wurden mit der Größenausschlußchromatographie (SEC) untersucht. Sie lassen sich mit Summen aus Schulz-Flory-Funktionen (SFF) beschreiben. Da eine Art aktiver Zentren eine SFF ergibt, die durch Molmassenmittelwerte definiert ist, lassen sich verschiedene Molmassenverteilungen nach Bandentrennung auf gleiche und verschiedene Arten aktiver Zentren untersuchen. In den untersuchten Systemen lassen sich zwei vergleichbare und eine unterscheidbare Art aktiver Zentren zuordnen. Auf diese Weise wurde das Kettenwachstum in Abhängigkeit von den Komponenten und Katalysatorformierungsbedingungen untersucht.
    Notes: Cis-1,4-polybutadiene was produced by polymerization of 1,3-butadiene using a catalyst system containing Ni(OOC8H15)2 and Al(C2H5)3 and the Lewis acids BF3 · O(C2H5)2 or TiCl4. The molar mass distributions (MMD) of the polybutadienes are investigated by means of size exclusion chromatography (SEC). The MMD's were fitted by a sum of Schulz-Flory-Functions (SFF). Taking into account that one kind of active species gives one SFF defined by molar mass averages, one comparable active species in both systems and one different were found. This way it was tried to find a relationship between the grown up of the active species depending on components and reactions conditions.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1994.052180112
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  • 98
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation of oligosaccharides containing N-acetyl neuraminic acid (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 11-20 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: αD-N-acetyl neuraminic acid (Neu5Ac, sialic acid) is a commonly occurring carbohydrate residue in various cell surface glycolipids and glycoproteins. This residue is linked terminally or internally to Gal residues via an α(2 → 3) or α(2 → 6) linkage. In the cell surface receptor, sialyl-LewisX, a terminal α(2 → 3) linkage is present. Previous studies from our laboratory have shown that in solution LewisX adopts a relatively rigid structure. In order to model the Neu5Ac residue, vacuum molecular dynamics of this monosaccharide were compared with simulations that explicitly include solvent water. The dynamical average of the monosaccharide conformation obtained from the two simulations was similar. Vacuum calculations for the disaccharide Neu5Ac α(2 → 3) Gal β-O-methyl show that a number of low energy minima are accessible to this disaccharide. Molecular dynamics simulations starting from the low energy minima show conformational transitions with a time scale of 10-50 ps among several of the minima while large barriers between other minima prevent transitions on the time scale studied. Simulations of this disaccharide in the presence of solvent show fewer conformational transitions, illustrating a dampening effect of the solvent that has been observed in some other studies. Our results are most consistent with an equilibrium among multiple conformations for the Neu5Ac α(2 → 3) Gal β linkage. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360340103
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  • 99
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    The effect of the L-azetidine-2-carboxylic acid residue on protein conformation. IV. Local substitutions in the collagen triple helix (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 51-60 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The properties of collagen are affected by the replacement of Pro by imino acid analogues. The structural effect of the low-level local substitution of L-azetidine-2-carboxylic acid (Aze) has been analyzed by computing the energy of CH3CO-(Gly-Pro-Pro)4-NHCH3 triple helices in which a single residue of one strand has been replaced by Aze. When Aze is in position Y of a (Gly-X-Y) unit, low-energy local deformations are introduced in the triple helix, i.e., it becomes more flexible. On the other hand, the flexibility of the triple helix is not increased with Aze in position X. The energy of the triple helix to coil transition is not changed significantly by this amount of substitution. In an earlier study, we have demonstrated that the regular substitution of Aze in every tripeptide distorts or destabilizes the triple helix to a large extent [A. Zagari, G. Némethy, & H. A. Scheraga (1990) Biopolymers, Vol. 30, pp. 967-974 ]. Thus, it appears that a high level of substitution is required to cause the observed chemical and biological effects of Aze on collagen. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Tab.
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    URL: http://dx.doi.org/10.1002/bip.360340107
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  • 100
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    Microwave dielectric study on bound water of globule proteins in aqueous solution (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 357-364 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A dielectric relaxation peak due to bound water of globule proteins in aqueous solution was observed at first by the use of a time domain reflectometry. This peak locates around 100 MHz as well as that of the aqueous DNA solution and the moist collagen, and has a relaxation strength in proportion to surface of the globule protein except for trypsin and pepsin of hydrolase. It is suggested that this peak is caused by orientation of bound water molecules on the protein surface. The number of bound water molecules estimated is in good agreement with that obtained by other method such as x-ray analysis. The solution exhibits another peak below 100 MHz, which is caused by the rotation of globule protein supplemented by migration of the counterion. Its relaxation time is completely proportional to the molecular weight of the protein. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340307
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