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  • evolution  (111)
  • kinetics  (94)
  • Springer  (205)
  • Institute of Physics
  • 1995-1999  (118)
  • 1990-1994  (87)
  • 1940-1944
  • 1997  (118)
  • 1993  (87)
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  • 1995-1999  (118)
  • 1990-1994  (87)
  • 1940-1944
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  • 1
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    Springer
    Entomologia experimentalis et applicata 82 (1997), S. 37-44 
    ISSN: 1570-7458
    Keywords: Barbarea vulgaris ; Cruciferae ; Phyllotreta nemorum ; Chrysomelidae ; Alticinae ; flea beetle ; plant defence ; genetics ; sex-linkage ; X- and Y-chromosome ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A polymorphism in host plant exploitation has been discovered in the flea beetle, Phyllotreta nemorum L. (Coleoptera: Chrysomelidae: Alticinae) where one resistant population is able to use Barbarea vulgaris R.Br. ssp. arcuata (Opiz.) Simkovics (Brassicaceae) as a host plant while a susceptible population is not. Crosses (F1, F2, and backcrosses) between the two flea beetle populations were made, and survival of the progeny on B. v. ssp. arcuata was measured. The ability of P. nemorum larvae to survive in this plant species depended on the presence of major, dominant genes (R-genes). The two most abundant R-genes in the resistant flea beetle population were X- and Y-linked, respectively. The use of B. v. ssp. arcuata as a natural host plant by the resistant population of P. nemorum seems to be an extension of the host plant range of the species. The role of sex-linked genes in the evolution of host range is discussed.
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  • 2
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    Entomologia experimentalis et applicata 82 (1997), S. 25-35 
    ISSN: 1570-7458
    Keywords: Barbarea vulgaris ; Cruciferae ; Phyllotreta nemorum ; Chrysomelidae ; Alticinae ; flea beetle ; plant defence ; resistance ; host plant ; variation ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Several sorts of variation in the interaction between the insect, Phyllotreta nemorum L. (Coleoptera:Chrysomelidae:Alticinae), and the plant, Barbarea vulgaris R.Br. (Brassicaceae), have been discovered: 1) genetic differences in the levels of defences in the plant, 2) genetic differences in the ability of insects to cope with the plant defences, 3) seasonal variation in levels of defences in the plant, and 4) differences between leaf types in levels of defences. Two plant accessions were suitable for larval development throughout the season while the remaining nine accessions were more or less unsuitable for larvae from the ‘susceptible’ T-population at least at certain times of the year. All accessions were suitable for the ‘resistant’ E-population throughout the year. There was a seasonal variation in levels of defences in some accessions which were unsuitable for the T-population during the summer period when beetles were present, but not during autumn and spring when the beetle were hibernating. Upper (younger) cauline leaves of these accessions had higher levels of defences than lower (older) cauline leaves. The resistant E-population used B. vulgaris as a natural host plant while the susceptible T-population did not. The use of B. vulgaris as a natural host plant by the E-population of P. nemorum seems to be an extension of the host plant range of the species. Variation in plant defences may have facilitated the switch in host plant use by the resistant flea beetle population.
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  • 3
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    Journal of insect behavior 6 (1993), S. 715-735 
    ISSN: 1572-8889
    Keywords: Aphrodisiac ; cockroach ; evolution ; mating behavior ; sex pheromone ; sternal glands ; tergal glands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two chemical signals are essential in all cockroach sexual behavioral sequences: the sex pheromone released by one partner, generally the female (for long distance attraction), and an aphrodisiac sex pheromone produced exclusively by male tergal glands (for female mounting and tergal contact or “feeding” behavior). Unlike the other cockroach groups, the males of the Oxyhaloinae species produce both chemical signals: the pheromone and the aphrodisiac. The occurrence of three patterns of mating behavior (A, B, and C), the production of male sex pheromones, and the existence in the male of developed sternal and tergal glands in seven related Oxyhaloinae species, make these cockroaches a useful model for studying the evolution of mating behavior patterns. The various types of mating behavior were not classified in the previous studies by Roth and Barth. In this report, they have been named type A (female in upper position), B (male in upper position), and C (male and female end to end). In type A mating, the male tergal glands, which are licked by the females, are well developed, whereas in types B and C, there is no licking of the male's tergal secretion by the females and the tergal glands are much less developed; the aphrodisiacs secreted by the tergal glands may no longer act in this case through contact chemoreception, but through an olfactory process involving volatile components. One common sex pheromone component seems to be acetoin. I suggest that the mating behavior tends from A toward B and C during the evolutionary process with a concomitant regression of the tergal glands and changes in the aphrodisiac emission levels. The mating behavioral sequences of cockroaches (Dictyoptera) and crickets (Orthoptera) show a striking degree of similarity and are probably examples of convergent evolution.
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  • 4
    ISSN: 1572-8889
    Keywords: Belostomatidae ; giant water bugs ; paternal care ; eggs ; reproduction ; behavior ; brooding ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Males of the giant water bug Lethocerus medius(Guerin) typify their monobasic subfamily, the Lethocerinae, in that they do not brood eggs attached to their backs as do males of all members of the subfamily Belostomatinae. Exclusive male parental investment as expressed in the Belostomatinae is extremely rare behavior among animals, and evolution of the trait is obscure. Lethocerus mediusmales apparently remain with their mates through oviposition and are consistently found in attendance of eggs after the female has departed. This behavior may enhance paternity assurance at no cost in opportunity for polygyny. Two double clutches of eggs were found, from which we infer the potential for polygynous matings and shared parental investment. Male L. mediusbrood attended egg clutches above the surface of the water, where they may moisten them, shade them, and defend them against predation. Egg attendance/brooding by L. mediusand other Lethocerusspecies may represent a plesiomorphic state from which paternal back- brooding evolved in the Belostomatinae.
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  • 5
    ISSN: 1572-8757
    Keywords: characterisation ; equilibria ; kinetics ; micropore size distribution ; n-butane ; nutshell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Adsorption equilibria and dynamics ofn-butane on two activated carbon samples prepared from the physical activation of nutshell are studied in this paper. The micropore size distribution (MPSD) is considered as the main source of solid heterogeneity. Lennard-Jones' potential theory and Dubinin's theory (TVFM) are used in the equilibria data to derive the MPSD, which is well fitted by a Gamma distribution function. The adsorption energy distribution derived from the MPSD is very asymmetric for both the samples studied, and this energy distribution used in the HMSD/HMSMD kinetics models for the study of adsorption dynamics ofn-butane.
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  • 6
    ISSN: 1572-879X
    Keywords: Fischer-Tropsch synthesis ; reaction activation barrier ; carbon chain growth and termination ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A method is established, by which the difference of the reaction activation barriers of carbon chain growth and termination in Fischer-Tropsch (FT) synthesis can be determined from experiments. A FT synthesis is carried out on Fe/Zn catalyst. We apply the method to analyze the experimental result and obtain the difference of reaction activation barriers of carbon chain growth and termination of α-olefins on the catalyst.
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  • 7
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    Cellulose 4 (1997), S. 1-5 
    ISSN: 1572-882X
    Keywords: paper ; degradation ; ageing ; kinetics ; modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
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  • 8
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    Cellular and molecular life sciences 49 (1993), S. 1027-1036 
    ISSN: 1420-9071
    Keywords: Archaea (archaebacteria) ; extreme halophiles ; archaeol phospholipids ; archaeol glycolipids ; membrane function ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Archaebacteria (archaea) are comprised of three groups of prokaryotes: extreme halophiles, methanogens and thermoacidophiles (extreme thermophiles). Their membrane phospholipids and glycolipids are derived entirely from a saturated, isopranoid glycerol diether,sn-2,3-diphytanylglycerol (‘archaeol’) and/or its dimer, dibiphytanyldiglyceroltetraether (‘caldarchaeol’). In extreme halophiles, the major phospholipid is the archaeol analogue of phosphatidylglycerolmethylphosphate (PGP-Me); the glycolipids are sulfated and/or unsulfated glycosyl archaeols with diverse carbohydrate structure characteristic of taxons on the generic level. Biosynthesis of these archaeol-derived polar lipids occurs in a multienzyme, membrane-bound system that is absolutely dependent on high salt concentration (4 M). The highly complex biosynthetic pathways involve intermediates containing glycerol ether-linked C20-isoprenyl groups which are reduced to phytanyl groups to give the final saturated polar lipids. In methanogens, polar lipids are derived both from archaeol and caldarchaeol, and thermoacidophiles contain essentially only caldarchaeol-derived polar lipids. The function of these membrane polar lipids in maintaining the stability, fluidity and ionic properties of the cell membrane of extreme halophiles, as well as the evolutionary implications of the archaeol and caldarchaeol-derived structures will be discussed.
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  • 9
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    Cellular and molecular life sciences 49 (1993), S. 110-117 
    ISSN: 1420-9071
    Keywords: Polymerization ; sickle hemoglobin ; sickle cell disease ; kinetics ; thermodynamics ; polymer domains ; nucleation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The polymerization of sickle hemoglobin occurs by the same mechanisms in solutions and in cells, and involves the formation of 14 stranded fibers from hemoglobin molecules which have assumed a deoxy quaternary structure. The fibers form via two types of highly concentration-dependent nucleation processes: homogeneous nucleation in solutions with hemoglobin activity above a critical activity, and heterogeneous nucleation in similarly supersaturated solutions which also contain hemoglobin polymers. The latter pathway is dominant, and creates polymer arrays called domains. The individual polymers bend, but also cross-link, and the resulting mass behaves as a solid. The concentration of polymerized hemoglobin increases exponentially unless clamped by rate limiting effects such as oxygen delivery.
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  • 10
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    Cellular and molecular life sciences 49 (1993), S. 317-319 
    ISSN: 1420-9071
    Keywords: Chitin ; cuticle ; evolution ; vertebrates ; bony fish ; Blenniidae ; Paralipophrys trigoides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Lectin binding, endo-chitinase binding and enzymatic degradation studies show that the epidermal cuticle of the bony fishParalipophrys trigloides (Blenniidae) is chitinous. This is the first evidence that a vertebrate species possesses a chitinous tissue. Recently aXenopus gene has been identified which has significant sequence similarity to the catalytic domain of yeast chitin synthase III, a chitin producing enzyme1,2. Taken together these two findings imply that chitin synthesis capability may be a basic vertebrate feature.
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  • 11
    ISSN: 1572-8773
    Keywords: aromatic donor molecules ; horseradish peroxidase ; kinetics ; lactoperoxidase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Based on kinetic evidence, it has been shown for the first time that the mode of binding of aromatic donor molecules is similar in horseradish peroxidase and lactoperoxidase; also that the nature of the heme plays an important role in the reaction with hydrogen peroxide, and has no effect on the reaction of the intermediate compound II with aromatic substrates.
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  • 12
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    Entomologia experimentalis et applicata 66 (1993), S. 3-12 
    ISSN: 1570-7458
    Keywords: evolution ; coevolution ; selection ; insect attack ; plant defense ; competition ; enemy free space ; chemoreception ; specialization ; plant recognition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Most hypotheses concerning the evolution of insect-plant relationships are based on the assumptions that, (1) phytophagous insects reduce plant fitness, and that (2) insect-plant relationships are the result of unconstrained selection. It can be shown, however, that there is little evidence to support these assumptions. As an alternative, it is proposed that the evolution of insect-plant relationships results primarily from autonomous evolutionary events; namely from heritable functional changes within the insects' nervous system that determine plant recognition and ultimately host plant specificity. These changes cannot be evoked by selective ecological agents. They originate from intrinsic changes (mutationssensu lato) within the insect genome. Ecological factors play a secondary role: by either supporting or preventing the establishment of the new genotype with the novel food preference.
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  • 13
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    Biodegradation 4 (1993), S. 163-170 
    ISSN: 1572-9729
    Keywords: factorial analysis ; kinetics ; methane ; methanotrophs ; nutrients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of different mineral nutrients on the kinetics of methane biodegradation by a mixed culture of methanotrophic bacteria was studied. The substrate factors examined were ammonia, iron, copper, manganese, phosphate, and sulphide. The presence of iron in the growth medium had a strong effect on the yield coefficient. Yield coefficients up to 0.49 mg protein per mg methane were observed when iron was added at concentrations of 0.10–5.0 mg/l. Iron addition also increased the maximum methane utilization rate. The same effect was observed after addition of ammonium to a medium where nitrate was the only nitrogen source. The observed Monod constant for methane utilization increased with increasing concentration of ammonia. This shows that ammonia is a weak competitive inhibitor as observed by other researchers. Relatively high levels of both ammonia (70 mg/l) and copper (300 µg/l) inhibited the methane degradation, probably due to the toxic effect of copper-amine complexes.
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  • 14
    ISSN: 1573-0417
    Keywords: colonization ; evolution ; lakes ; Norway ; deglaciation ; land uplift ; invertebrates ; Chironomidae ; Porifera ; Bryozoa ; diatoms ; Charophyta ; tsunami
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Invertebrate colonization of lakes following the uplift of land from the sea was studied in four lakes, currently situated between 39 and 24 m a.s.l., on the central Norwegian coast. The lakes were isolated from the sea between 9500 and 7700 years B.P. Animal and algal remains picked from core samples showed that the first colonizers preserved as fossils were usually members of the Chironomidae, Daphnidae/Chydoridae, Acarina, Porifera (Ephydatia mülleri and Spongilla lacustris), Bryozoa (Cristatella mucedo and Plumatella spp.) and Charophyta (Chara sp.). Of the chironomids, the genus Chironomus was present in the oldest lacustrine layers of all four lakes, but other genera recorded at the marine/lacustrine boundary were Dicrotendipes, Procladius (?), Einfeldia, Microtendipes, and Glyptotendipes. Remains of the caddis fly family Limnephilidae were also present in the earliest lacustrine sediments in Kvennavatnet and Kvernavatnet. The oldest invertebrate fauna is typical for mesotrophic lakes. However, chironomids and mites have been present in this area from at least about 10 500 years B.P. A diverse chironomid community was established between 300 and 800 years after isolation from the sea at Kvernavatnet on the island of Hitra, while only between 80 and 120 years passed before a comparably diverse community developed at Kvennavatnet on the mainland coast. A similar development of the invertebrate fauna occurred in Kvennavatnet, Kvernavatnet and Storkuvatnet. However, Litjvatnet deviates greatly from the ‘normal’ pattern because a tsunami disturbed the bottom sediments and fauna. The tsunami, a gigantic sea wave, was caused by a submarine slide from the Norwegian continental slope. It reached Litjvatnet, today located 24 m a.s.l., but was not traced in Storkuvatnet at 30 m a.s.l. This event happened about 7200 years B.P.
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  • 15
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    Antonie van Leeuwenhoek 71 (1997), S. 159-178 
    ISSN: 1572-9699
    Keywords: aromatic pathways ; chlorobenzenes ; evolution ; genes ; plasmids ; pseudomonas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Chlorobenzenes are substrates not easily metabolized by existing bacteria in the environment. Specific strains, however, have been isolated from polluted environments or in laboratory selection procedures that use chlorobenzenes as their sole carbon and energy source. Genetic analysis indicated that these bacteria have acquired a novel combination of previously existing genes. One of these gene clusters contains the genes for an aromatic ring dioxy-genase and a dihydrodiol dehydrogenase. The other contains the genes for a chlorocatechol oxidative pathway. Comparison of such gene clusters with those from other aromatics degrading bacteria reveals that this process of recombining or assembly of existing genetic material must have occurred in many of them. Similarities of gene functions between pathways suggest that incorporation of existing genetic material has been the most important mechanism of expanding a metabolic pathway. Only in a few cases a horizontal expansion, that is acqui sition of gene functions to accomodate a wider range of substrates which are then all transformed in one central pathway, is observed on the genetic level. Evidence is presented indicating that the assembly process may trigger a faster divergence of nearby gene sequences. Further ‘fine-tuning’, for example by developing a proper regulation, is then the next step in the adaptation.
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  • 16
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    Antonie van Leeuwenhoek 71 (1997), S. 265-270 
    ISSN: 1572-9699
    Keywords: bacteria ; DNA ; evolution ; genome ; RNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This review examines evolution of bacterial genomes with an emphasis on RNA based life, the transition to functional DNA and small evolving genomes (possibly plasmids) that led to larger, functional bacterial genomes.
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  • 17
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    Antonie van Leeuwenhoek 71 (1997), S. 257-263 
    ISSN: 1572-9699
    Keywords: bacteria ; energy ; evolution ; genome ; metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This article examines the relationship between (or dependence of) bacterial evolution in prokaryotes and metabolism, and the changing physical-chemical conditions present during early evolution.
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  • 18
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    Antonie van Leeuwenhoek 71 (1997), S. 363-368 
    ISSN: 1572-9699
    Keywords: assembly ; anode ; bacteria ; cathode ; DNA ; evolution ; genetics ; molecular ; surfaces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Molecular evolution is examined in bacteria with an emphasis on mineral surfaces, membranes, cathodes and anodes. In early molecular evolution, cathode-anode system may have been naturally occurring on a nm to µm scale. Secondly, the cathode-anode system could have been separated by a primitive, permeable lipid or microsphere on a mineral surface, that was a precursor of a more advanced membrane with a charge differential on either side of the membrane. These aspects will be considered from a theoretical evolutionary perspective.
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  • 19
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    Antonie van Leeuwenhoek 72 (1997), S. 251-259 
    ISSN: 1572-9699
    Keywords: bacteria ; catalysis ; DNA ; enzyme ; evolution ; microorganisms ; optimization ; RNA ; time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Microbial populations (and life) not only evolve, they optimize. The transition from a random, unorganized, lifeless Earth to the present situation, where the Earth is virtually covered with nucleic acids and diverse and complex species, required numerous molecular changes and the integration of metabolic pathways over billions of years. Primitive prokaryotic life was dependent on and constrained by the physical-chemical conditions on the Earth, while slowly reshaping conditions present. In this review, molecular evolution and molecular optimization are examined with an emphasis on the order in which evolutionary events occurred.
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  • 20
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    Insectes sociaux 40 (1993), S. 325-335 
    ISSN: 1420-9098
    Keywords: Formicidae ; social parasitism ; PCR ; 18 S ribosomal RNA ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The evolutionary relationship between socially parasitic ants and their hosts is still an unsolved problem. We have compared a 1.2 kb sequence of the 18 S ribosomal RNA genes of the parasitic antsDoronomyrmex kutteri, Harpagoxenus sublaevis andChalepoxenus muellerianus to the sequence of the host speciesLeptothorax acervorum andL. recedens (all subfamily Myrmicinae, tribe Leptothoracini) and to an out-group antCamponotus ligniperda (Formicinae). We found that parasitic species and the host species and alsoCamponotus ligniperda differ at less than 1% of the base positions of the 1.2 kb segment of the 18S rRNA gene. The sequences showed 80.3% identity to the 18 S ribosomal RNA genes of the beetleTenebrio molitor and only 66.5% to that of the dipteranDrosophila melanogaster.
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  • 21
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    Aquatic sciences 55 (1993), S. 103-111 
    ISSN: 1420-9055
    Keywords: iron(III) (hydr)oxide ; fulvic acid ; iron redox cycling ; dissolution ; surface reactivity ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The kinetics of conversion of iron(III) (hydr)oxides to ferrous iron mediated by fulvic acid have been investigated in order to improve the understanding of the redox cycling of iron at the oxic-anoxic boundary in natural waters. Under the conditions similar to natural waters, fulvic acid is able to reduce the iron(III) (hydr)oxide. The kinetics of the reaction depend on the reactivity of iron(III) (hydr)oxides and the reducing power of the fulvic acid. The rate of reaction is 60 nm/h obtained under following conditions: total concentration of Fe(III) 1.0 × 10−4 M, pH 7.5, fulvic acid 5 mg/L. The rate is considered as a net result of reduction and oxidation in the 〉 FeIII-OH/Fe(II) “wheel” coupled with fulvic acid. In a real natural water system, reductants other than fulvic acid may be of importance. The results obtained in the laboratory, however, provide evidence that the Fe(OH)3(s)/Fe(II) redox couple is able to act as an electron-transfer mediator for the oxidation of natural organic substances, such as fulvic acid by molecular oxygen either in the absence of microorganisms or as a supplement to microbial activity.
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  • 22
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    European journal of clinical pharmacology 52 (1997), S. 505-506 
    ISSN: 1432-1041
    Keywords: Key words Ibuprofen; effervescent tablets ; kinetics ; bioavailability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
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    European journal of clinical pharmacology 44 (1993), S. 231-235 
    ISSN: 1432-1041
    Keywords: Carbamazepine ; kinetics ; population pharmacokinetics ; bioavailability ; controlled release ; non-linear model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The absorption properties of a conventional tablet of carbamazepine (T) and a controlled release form of carbamazepine (TCR) have been compared using a nonlinear mixed effect model (NONMEM). Plasma carbamazepine concentration data were obtained from an open, steady-state, crossover bioavailability study in which 494 measurements were obtained from 13 patients, with an equal number of samples per patient for each dosage form. The pharmacokinetic model used was a one-compartment open model with first-order absorption and elimination. The objective function was used as a measure of the goodness of fit of the model to the data. Body weight was an important determinant of carbamazepine clearance (CL) but not volume of distribution (V). Accounting for the interindividual variability in volume of distribution did not significantly influence the objective function. Including different rates of absorption (ka) for the two dosage forms resulted in a significant improvement in the objective function, as well as reducing the interindividual variability in the rate of absorption. Adding a parameter for relative bioavailability (f) of TCR improved the objective function statistically, but an unrealistic value for V was obtained, and the absorption and elimination rates appeared to be transposed in the classical “flip-flop” manner. Fixing V to the value obtained before introducing f did not change the objective function and permitted estimation of f without the confounding influence of excessive parameters. The final population parameter estimates (standard error of estimate) were: CL, 0.0522 (0.0019) l·h−1·kg−1; V, 63.7 (FIXED)l; kaT, 0.312 (0.064) h−1; kaTCR, 0.149 (0.016) h−1; f, 1.01 (0.0326); variance (additive) in CL, 0.291 (0.083) (l·h−1·kg−1)2; residual intrasubject error variance (additive), 0.572 (0.082) (mg·l−1)2. The 95% confidence interval of the extent of absorption (f) of 93.6%–107.4% was well within the generally accepted range of ±20%, while the rate of absorption of Tegretol CR was significantly slower than that of Tegretol, as expected for a controlled release product.
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    Journal of thermal analysis and calorimetry 39 (1993), S. 15-20 
    ISSN: 1572-8943
    Keywords: alloys ; high-temperature sulphidation ; kinetics ; new thermobalane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wird ein neue Apparat zur Untersuchung der Hochtemperatur-Sulfidierung von Metallen in H2/H2S Atmosphare beschrieben. Der Unterschied zwischen diesem Apparat und dem fruher benutzten, besteht im Gasdosierungsystem. Wasserstoff reagiert teilweise mit Schwefel, was eine stabile Zusammensetzung des Gasgemisches beim niedrigen Schwefeldampfdruck sichert. Gewichtsmessungen von Metallen und Legierungen konnen in diesem System bei Temperaturen von 1073 bis 1473 K mit einer Genauigkeit von 10−6 g ausgefuhrt werden.
    Notes: Abstract A new thermogravimetric apparatus for studying the kinetics of metal sulphidation in a H2/H2S gas mixture is described. The main difference between this device and other equipment is the application of hydrogen to obtain a H2/H2S mixture at suitable sulphur partial pressures at a total mixture pressure of 1 atm. The use of the carrier gas allows the measurement of sulphidation kinetics under dynamic conditions and consequently over a much wider pressure range of sulphur vapour, down to 10−12 atm.
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    Journal of thermal analysis and calorimetry 39 (1993), S. 65-74 
    ISSN: 1572-8943
    Keywords: electrical conductivity ; hydrazone complexes ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Bei zwei verschiedenenpH-Werten wurden die Zn-, Cd- und Hg-Komplexe von Isatinisonicotinoylhydrazon hergestellt. Diese wurden thermisch untersucht (TG, DTG, DTA) und die Gleichstromleitfähigkeit von gepreßten Pulverproben als eine Funktion der Temperatur untersucht. Sowohl für die Liganden als auch für die Komplexe wurden die Aktivierungsenergien (ΔE) berechnet, wobei sich für die Liganden niedrigere Werte ergaben. Man fand, daß die Größe von ΔE durch die Art des Metalles und denpH-Wert bei der Herstellung beeinflußt wird.
    Notes: Abstract The complexes of Zn, Cd and Hg of isatin isonicotinoyl hydrazone were prepared at two differentpHs. Their thermal studies (TG, DTG and DTA) have been made and the DC electrical conductivity of compressed powder samples as a function of temperature was investigated. The activation energies (ΔE) were calculated for the ligand and the complexes which showed that the ligand has a lower value of ΔE than the complexes. The magnitude of ΔE was found to be affected by the nature of the metal and thepH of preparation.
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    Journal of thermal analysis and calorimetry 39 (1993), S. 75-86 
    ISSN: 1572-8943
    Keywords: chlorination ; kinetics ; WO3+CCl4 reaction
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    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels Thermogravimetrie wurde die Chlorierungskinetik von alkaliversetztem (K und Li) Wolframtrioxid untersucht, wobei CCl4 als Chlorierungsreagens fungierte. Die Reaktivität der modifizierten Proben wurden mit der von reinem WO3 verglichen. Für die reinen und für die alkaliversetzten Proben wurden ähnliche scheinbare Aktivierungsenergien gefunden. Der Zusatz von Kalium verursacht jedoch eine starke Abnahme der ursprünglichen Reaktionsgeschwindigkeit, während oberflächiges Lithium keinen Effekt zeigt. Während der Chlorierung wurde eine ständige Senkung der linearen Reaktionsgeschwindigkeit für beide Proben festgestellt, was mit Rückhalteeffekten von oberflächigen Nebenprodukten und Alkalizusätzen erklärt wird. Zur Beschreibung der isothermen TG-Kurven wurde ein entsprechendes kinetisches Modell angenommen, welches auf einer monoton steigenden Inhibition dieser Proben basiert. Die auf der Grundlage dieses Modelles berechnete Kurve stimmt recht gut mit den experimentellen Ergebnissen überein.
    Notes: Abstract The chlorination kinetics of alkali-added (K and Li) tungsten trioxide were studied by thermogravimetry, using gaseous CCl4 as chlorinating agent. The reactivity of the modified samples was compared to the results on the chlorination of pure WO3. Similar apparent activation energies were found for the pure and alkali-added samples. However, potassium additive resulted in a strong decrease of the initial reaction rate, while surface lithium has no influence on it. During the chlorination a continuous decrease of the linear reaction rate was observed for both samples, which was explained by retarding effects of surface by-products and alkali additives. For describing the isothermal TG curves an appropriate kinetic model, based on the monotonously increasing inhibition of these species was assumed. The curve calculated with this model fits well to the experimental results.
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    Journal of thermal analysis and calorimetry 39 (1993), S. 229-238 
    ISSN: 1572-8943
    Keywords: epoxy resins ; kinetics ; thermal stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Vernetzungsreaktionen der Epoxidharze Tetraglycidyl-diamino-diphenyl-methan (TGDDM) und Tetraglycidyl-methylen-bis(o-toluidin) (TGMBT) unter Verwendung von Diaminodiphenylsulfon (DDS), Diaminodiphenylmethan (DDM) und Diethylentriamin (DETA) als Vernetzungsmittel wurden kinetisch mittels DSC untersucht. Die dynamischen Scans im Temperaturbereich 20°–300°C wurden analysiert, um unter Anwendung einiger empirischer Gleichungen die Aktivierungsenergie und die Reaktionsordnung des Vernetzungsprozesses zu ermitteln. Die Aktivierungsenergie der einzelnen Epoxy-Systeme liegt im Bereich 71.9–110.2 kJ·mol−1. An der ausgehärteten Harze wurde mittels TG in einer statischen Luftatmosphäre un deiner Aufheizgeschwindigkeit von 10 Grad/min die Kinetik des termischen Abbaues untersucht. Man fand, daß die thermiscehn Abbaureaktionen in einem Schritt ablaufen und ihre Aktivierungsenergie im Intervall 27.6–51.4 kJ·mol−1 liegt.
    Notes: Abstract The curing reactions of the epoxy resins tetraglycidyl diaminodiphenyl methane (TGDDM) and tetraglycidyl methylenebis (o-toluidine) (TGMBT) using diaminodiphenyl sulfone (DDS), diaminodiphenyl methane (DDM) and diethylenetriamine (DETA) as curing agents were studied kinetically by differential scanning calorimetry. The dynamic scans in the temperature range 20°–300°C were analyzed to estimate the activation energy and the order of reaction for the curing process using some empirical relations. The activation energy for the various epoxy systems is observed in the range 71.9–110.2 kJ·mol−1. The cured epoxy resins were studied for kinetics of thermal degradation by thermogravimetry in a static air atmosphere at a heating rate of 10 deg·min−1. The thermal degradation reactions were found to proceed in a single step having an activation energy in the range 27.6–51.4 kJ·mol−1.
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  • 28
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    Journal of thermal analysis and calorimetry 48 (1997), S. 917-923 
    ISSN: 1572-8943
    Keywords: copper compound ; coupled technique ; kinetics ; macrocyclic complex ; non-isothermal
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The thermal decomposition process of the complex [Cu(NBOCTB)][Cu(NO3)4] H2O has been studied by TG and DTG technique, and possible intermediates of the thermal decomposition have also been conjectured from the TG and DTG curves. The results suggest that the decomposition of the complex involves five steps: The non-isothermal kinetics of steps 1, 2 and 3 have been studied by means of the Achar and Coats-Redfern method based on TG and DTG curves. Step 1 is a ‘Coring and Growth’ mechanism (n= 1), its kinetic equation may be expressed as: dα/dt=Ae−E/RT(1−α). Steps 2 and 3 are both ‘two order chemical reaction’ mechanisms, their kinetic equations can be expressed as: dα/dt=Ae−E/RT(1−α)2.
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  • 29
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    Journal of thermal analysis and calorimetry 49 (1997), S. 87-94 
    ISSN: 1572-8943
    Keywords: kinetics ; poly(di-propyl itaconates) ; polymer structure ; thermal degradation
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Non-isothermal thermogravimetry was performed in a dynamic nitrogen atmosphere, on a series of poly(di-n-propyl itaconates) (PDnPI) and poly(di-iso-propyl itaconates) (PDiPI) which had been prepared in the presence of various amounts of the chain transfer agentn-dodecyl mercaptan (DDM). Differential thermogravimetry (DTG) showed that both polymers degraded in two stages. The DTG curve of PDnPI had a large first peak followed by a smaller shoulder, whereas the DTG curve of PDiPI was composed of two peaks of almost equal heights. The addition of DDM during the polymerisations in both cases resulted in a similar decrease in the relative area of the first peak.
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  • 30
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    Journal of thermal analysis and calorimetry 49 (1997), S. 183-191 
    ISSN: 1572-8943
    Keywords: kinetics ; thermooxidative degradation
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The results of non-isothermal kinetic analysis of the thermooxidative degradation in air and oxygen of an unsaturated polyester resin are presented. It has been shown that the thermooxidative degradation in oxygen occurs at lower temperatures than the thermooxidative degradation in air. The kinetic parameters of the thermooxidative degradation depend on the heating rate and the oxygen pressure. Two straight lines of InAvs. E (A is the preexponential factor andE is the activation energy), characteristic for the compensation effect, have been obtained for the thermooxidative degradation in air and in oxygen respectively. The difference between the intercepts of these straight lines can be explained by dependence of the pre-exponential factor on the oxygen pressure.
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    Journal of thermal analysis and calorimetry 49 (1997), S. 857-862 
    ISSN: 1572-8943
    Keywords: analytical methods ; kinetics ; powder milk ; temperature
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    Topics: Chemistry and Pharmacology
    Notes: Abstract This work present comparative results on powder milk storage quality, obtained from analytical methods. Protein content was determined conventional (Kjeldahl) and colorimetric with biuret reagent at 540 nm and integral quality by thermogravimetric and biological methods. A method was developed for the protein separation of powder milk. Powder milk was submitted to degradation processes at 45, 60 and 80°C for 20 days. The results indicated that protein content values were inconsistent if determinations by Kjeldahl and colorimetric methods and biological tests were compared. There is evidence of thermal decomposition of powder milk as detected by biological and thermogravimetric methods.
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    Journal of thermal analysis and calorimetry 49 (1997), S. 937-941 
    ISSN: 1572-8943
    Keywords: kinetics ; mebendazole ; quality control ; technology
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A study was made of the thermal behavior of the starting materials, their mixtures and the resulting mebendazole tablets. The thermal curves were obtained with a Shimadzu thermobalance, model TGA-50, using an air flow of 50 mL min−1 and a heating rate of 10°C min−1 in the temperature interval 30–900°C. The reaction constant velocities for the mebendazole salt and tablets were determined isothermally, using the Arrhenius expression. The thermal stability of mebendazole tablets is lower than that of the mebendazole salt, due to the presence of starch and lactose in the composition. Analysis of the data reveals that thermogravimetry is a powerful tool in pharmaceutical technology and quality control.
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  • 33
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    Journal of thermal analysis and calorimetry 48 (1997), S. 343-348 
    ISSN: 1572-8943
    Keywords: activation energy ; combustion ; crude oil ; differential scanning calorimetry ; kinetics ; thermogravimetric analysis
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A weighted mean activation energy method was applied to describe the reactivity and combustibility of crude oils via simultaneous TG/DTG. Thermal experiments were conducted with a non-isothermal method at a heating rate of 10
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    Journal of thermal analysis and calorimetry 48 (1997), S. 385-401 
    ISSN: 1572-8943
    Keywords: dehydration and decomposition ; kinetics ; Fe(III) chloride
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Fe(III) chloride hydrate (FeCl3·xH2O) undergoes simultaneous dehydration and dehydrochlorination from its molten phase in the temperature range 100–200
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    Journal of thermal analysis and calorimetry 48 (1997), S. 413-425 
    ISSN: 1572-8943
    Keywords: alcoholic fermentation ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The control of alcoholic fermentation is necessary to obtain a quality wine. The overall dynamic and phenomenological modelling already applied to the simulation of this type of reaction enables us to suggest, in this study, a simple model (of which two variants), are relatively satisfactory. The first variant does not take into account the variation of the ambient temperature; the model translates exactly the first phase of the experimental curve or the moment when highest temperatures are measured. The relaxation phase is less well described because of influence of variation of the ambient temperature is relatively important. The second one considers the system depending on the ambient temperature, the model is correct for the relaxation phase too (the reaction temperature decreases, it nears the ambient temperature). The advantage of this model: It permits one to determine the reaction enthalpy and the kinetic parameters.
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  • 36
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    Journal of thermal analysis and calorimetry 48 (1997), S. 623-634 
    ISSN: 1572-8943
    Keywords: bismalleimide/carbon fiber composite ; DMA ; kinetics ; TSC
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The correlation between structure/microstructure and thermomechanical properties has been investigated by the Thermally Stimulated Creep (TSC) technique in a high performance thermostable thermoset matrix composite. The high resolving power of this technique allows us to analyse the α retardation mode. The kinetics of molecular movements liberated at the glass transition has been investigated by the technique of fractional loading: the analysis of each elementary process gives the real compliance and the retardation time as a function of temperature. The values of the activation parameters show the existence of a compensation phenomenon which characterizes the microstructure. It also gives access to the loss compliance of the composite material as a function of temperature and frequency. The predictive calculation of loss compliance has been validated by the results obtained by dynamic mechanical analysis (DMA).
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    Journal of thermal analysis and calorimetry 48 (1997), S. 769-782 
    ISSN: 1572-8943
    Keywords: kinetics ; non-linear optimization ; reactor time constants ; software ; time constants of sensors
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    Topics: Chemistry and Pharmacology
    Notes: Abstract All temperature sensors have a finitely time constant. The influence of the sensor time constant gts on the results of kinetic evaluation is demonstrated at four reaction types. The ignorance of the sensor indolence gives incorrect activation parameters. Therefore the determination of Τs is necessary. For the estimation of parameters the nonlinear evaluation program TA-kin was used. With its help it is possible to find the real parameters, also when Τs=32 s, if the real Τs-value was entered.
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    Journal of thermal analysis and calorimetry 49 (1997), S. 1517-1525 
    ISSN: 1572-8943
    Keywords: β-cyclodextrin ; cinnamyl alcohol ; kinetics ; thermal analysis
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The stability of β-cyclodextrin-cinnamyl alcohol inclusion complex (β-CD·C9H10·8H2O) was investigated using TG and DSC. The mass loss took place in three stages: the dehydration occurred between 50–120°C; the dissociation of β-CD·C9H10O occurred in the range of 210–260°C; and the decomposition of β-CD began at 280°C. The dissociation of β-CD·C9H10O was studied by means of thermogravimetry, and the results showed: the dissociation of β-CD·C9H10O was dominated by a two-dimensional diffusion process (D2). The activation energyE was 161.2 kJ mol−1, the pre-exponential factorA was 4.5×1013 min−1. Cyclodextrin is able to form inclusion complexes with a great variety of guest molecules, and the interesting of studies focussed on the energy binding cyclodextrin and the guest molecule. In this paper, β-cyclodextrin-cinnamyl alcohol inclusion complex was studied by fluorescence spectrophotometry and infrared absorption spectroscopy, and the results show: the stable energy of inclusion complexes of β-CD with weakly polar guest molecules consists mainly of Van der Waals interaction.
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  • 39
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    Journal of thermal analysis and calorimetry 49 (1997), S. 1553-1564 
    ISSN: 1572-8943
    Keywords: deconvolution ; differential scanning calorimetry ; feedforward neural networks ; kinetics ; signal filtering ; simulations ; thermal analysis
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Feedforward neural networks have been used for kinetic parameters determination and signal filtering in differential scanning calorimetry. The proper learning function was chosen and the network topology was optimized, using an empiric procedure. The learning process was achieved using simulated thermoanalytical curves. The resilient-propagation algorithm have led to the best minimization of the error computed over all the patterns. Relative errors on the thermodynamic and kinetic parameters were evaluated and compared to those obtained with the usual thermal analysis methods (single scan methods). The errors are much lower, especially in presence of noisy signals. Then, our program was adapted to simulate thermal effects with known thermodynamic and kinetic parameters, generated electrically, using a PC computer and an electronic interface on the serial port. These thermal effects have been generated by using an inconel thread.
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    Journal of thermal analysis and calorimetry 49 (1997), S. 1467-1475 
    ISSN: 1572-8943
    Keywords: CRTA ; DSC ; kinetics ; synthetic brochantite ; TG-DTA ; thermal decomposition
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The reaction pathway of the thermal decomposition of synthetic brochantite, Cu4(OH)6SO4, to copper(II) oxide was investigated through the detailed kinetic characterization of the thermal dehydration and desulferation processes. The dehydration process was characterized by dividing into two overlapped kinetic processes with a possible formation of an intermediate compound, Cu4O(OH)4SO4. The dehydrated sample, Cu4O3SO4, was found first to be amorphous by means of XRD, followed by the crystallization to a mixture of CuO and CuO-CuSO4 at around 776 K. The specific surface area and the crystallization behaviour of the amorphous dehydrated compound depend largely on the dehydration conditions. The thermal desulferation process is influenced by the gross diffusion of the gaseous product SO3, which is governed by the advancement of the overall reaction interface from the top surface of the sample particle assemblage to the bottom.
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    Journal of thermal analysis and calorimetry 50 (1997), S. 455-462 
    ISSN: 1572-8943
    Keywords: kinetics ; statistical analysis
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A statistical technique based on the Wilcockson criterion is suggested for estimation of the reproducibility of thermoanalytical experiments. Reduction of the whole physicochemical process to a quasi-one-stage process is described.
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  • 42
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    Journal of thermal analysis and calorimetry 50 (1997), S. 425-430 
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    Keywords: decomposition ; kinetics ; non-isothermal
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The authors present the results concerning the thermal behaviour of three polynuclear coordination compounds of Nd(III) and Co(II) or Fe(III) with triptophan. For the dehydration steps the values of the non-isothermal kinetic parameters have been determined.
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    Journal of thermal analysis and calorimetry 49 (1997), S. 1227-1241 
    ISSN: 1572-8943
    Keywords: inorganic sulphates ; kinetics ; mechanism ; thermodynamics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Thermal decomposition of different inorganic sulphates are presented. A number of techniques, but mainly TG and DTA, are used to prove the mechanism and kinetics of CaSO4, BaSO4, FeSO4·xH2O, Al2(SO4)3·xH2O under various gas atmospheres. It is shown how the partial pressure of gas components and heating rate may effect the mechanism and kinetic parameters. There are also examples on the effects of some additives and initial treatment on the thermal processes. On the base of the results obtained some recommendations are given concerning the precautions to be taken into account in the thermal decomposition studies and the sulphur recovering.
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    Journal of thermal analysis and calorimetry 49 (1997), S. 1477-1484 
    ISSN: 1572-8943
    Keywords: CRTA ; kinetics ; particle size distribution ; rate jump method
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetic curves at infinite temperature for the solid-state reactions of the interface shrinkage type were drawn theoretically by taking account the particle size distribution in the sample mixture. The CRTA curves for the reactions with the particle size distribution can be drawn by utilizing the universal kinetic curves at infinite temperature. The proper kinetic treatment for the CRTA curves with the particle size distribution is discussed in connection with the property of the kinetic equation with respect to the particle size distribution. The present kinetic consideration is taken as a simulation for the reactions with a certain distribution in α among the reactant particles, produced preferably by the mass and heat transfer phenomena during the thermoanalytical measurements. The merit of the rate jump method by a single cyclic CRTA curve is also discussed on the basis of the present results.
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    Journal of thermal analysis and calorimetry 49 (1997), S. 1161-1170 
    ISSN: 1572-8943
    Keywords: basicity ; dinitramides ; kinetics ; oxidation ; tanδ ; transition temperatures
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The dinitramide salts of ammonia (ADN), hexamethylenetetramine (HDN), potassium (KDN), and sodium (NaDN) showed a linear relationship between the DSC rate of decomposition at the peak maximum and the DEA tanδ value at the low temperature transition peak. As the cation basicity increased in the series ADN〈HDN〈KDN〈NaDN, there was an increase in the low temperature transition peak, the energy barrier for relaxation, and the decomposition peak temperature, and a decrease in the tanδ value at the low temperature transition peak, specific heat capacity, and the rate and enthalpy of decomposition. The more basic salts were more thermally stable (i.e., higher decomposition temperature) and less energetic (i.e., lower enthalpy of decomposition). The more internal free volume (disorder) present in these salts, the higher the rates of relaxation and decomposition. Five aluminum powders of different surface areas were analyzed by DSC in platinum sample pans, and it was found that the enthalpy and rate of oxidation increased as the particle size of Al decreased while the enthalpy of the Al melt decreased. TG showed a two-step weight gain in the oxidation of Al with plateaus in the 650 and 1130°C regions and the percent weight gain increased as the particle size of Al decreased. Variable DSC and TG heating rate studies showed that the activation energies for the first step in the oxidation process increased as the particle size of Al increased.
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  • 46
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    Journal of thermal analysis and calorimetry 50 (1997), S. 33-50 
    ISSN: 1572-8943
    Keywords: Ba[Cu(C2O4)2(H2O)]·5H2O ; decomposition ; dehydration ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The thermal behaviour of Ba[Cu(C2O4)2(H2O)]·5H2O in N2 and in O2 has been examined using thermogravimetry (TG) and differential scanning calorimetry (DSC). The dehydration starts at relatively low temperatures (about 80°C), but continues until the onset of the decomposition (about 280°C). The decomposition takes place in two major stages (onsets 280 and 390°C). The mass of the intermediate after the first stage corresponded to the formation of barium oxalate and copper metal and, after the second stage, to the formation of barium carbonate and copper metal. The enthalpy for the dehydration was found to be 311±30 kJ mol−1 (or 52±5 kJ (mol of H2O)−1). The overall enthalpy change for the decomposition of Ba[Cu(C2O4)2] in N2 was estimated from the combined area of the peaks of the DSC curve as −347 kJ mol−1. The kinetics of the thermal dehydration and decomposition were studied using isothermal TG. The dehydration was strongly deceleratory and the α-time curves could be described by the three dimensional diffusion (D3) model. The values of the activation energy and the pre-exponential factor for the dehydration were 125±4 kJ mol−1 and (1.38±0.08)×1015 min−1, respectively. The decomposition was complex, consisting of at least two concurrent processes. The decomposition was analysed in terms of two overlapping deceleratory processes. One process was fast and could be described by the contracting-geometry model withn=5. The other process was slow and could also be described by the contracting-geometry model, but withn=2. The values ofE a andA were 206±23 kJ mol−1 and (2.2±0.5)×1019 min−1, respectively, for the fast process, and 259±37 kJ mol−1 and (6.3±1.8)×1023 min−1, respectively, for the slow process.
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    Journal of thermal analysis and calorimetry 48 (1997), S. 359-366 
    ISSN: 1572-8943
    Keywords: decomposition ; kinetics ; non-isothermal
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Results are presented on the thermal behaviour of two derivatives of malic acid. The decomposition intermediates obtained at about 400
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    Journal of thermal analysis and calorimetry 39 (1993), S. 87-95 
    ISSN: 1572-8943
    Keywords: gamma radiation effects ; graphite-hematite system ; kinetics
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    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels isothermer und dynamischer TG wurde im Graphit-Eisen(III)oxidsystem in Luft der Einfluß von60Co-Gammastrahlung und von verschiedenen Probenzusammensetzungen auf die Reduktion von Hämatit zu Eisen untersucht. Entsprechend verschiedener theoretischer Modelle heterogener Reaktionen wurde eine kinetische Analyse der isothermen Daten durchgeführt und die Ergebnisse zeigten, daß das dreidimensionale Phasengrenzenmodell die beste Übereinstimmung liefert. Die Analyse der dynamischen TG-Daten wurde mittels der Integralmethode von Ozawa, der Coats-Redfem-Methode und einer zusammengesetzten Methode auf der Grundlage der modifizierten Coats und Redfern Gleichung durchgeführt. Die Aktivierungsparameter wurden berechnet und die Ergebnisse der verschiedenen Methoden miteinander verglichen und diskutiert. Strahlung scheint keine Änderung des Reaktionsmodelles oder des Mechanismus hervorzurufen. Durch Bestrahlung gibt es aber ein Absinken der Aktivierungsenergie und des Frequenzfaktors sowie ein Absinken der Halbwertszeit der Reaktion, was bei höheren Temperaturen und höherer Dosis bemerkenswert groß ist.
    Notes: Abstract The effects of60Co-gamma radiation and of various sample composition on the reduction of hematite to iron in the graphite-iron(III) oxide system in air were studied using isothermal and dynamic TG techniques. Kinetic analysis of isothermal data were performed according to various theoretical models of heterogeneous reactions and the results showed that the three-dimensional phase boundary model gives the best fit of data. Analysis of dynamic TG data were made using Ozawa integral method, Coats-Redfern method and a composite method based on the modified Coats and redfern equation. The activation parameters were calculated and the results of the different methods were compared and discussed. Radiation apparently did not introduce a change in the reaction model or mechanism. However, there is a decrease in activation energy and frequency factor upon irradiation and a decrease in the half-life time of the reaction which is remarkable at the higher temperatures and higher doses.
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  • 49
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    Journal of thermal analysis and calorimetry 39 (1993), S. 217-220 
    ISSN: 1572-8943
    Keywords: DSC ; edible oils ; isothermal method ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Unter Einsatz der isothermen Methode wurden kinetische Untersuchungen der thermooxidativen Zersetzung einiger Speiseöle durchgeführt. Zur Bestimmung des Umwandlungsgrades wurde ein DS-Kalorimeter von DuPont eingesetzt. Grundlage der Untersuchung bildeten Leinöl, Rizinusöl und Olivenöl.
    Notes: Abstract The thermooxidative decompositions of some edible oils were investigated. Isothermal measurements of convention were made with a Du Pont differential scanning calorimeter. Linseed oil, castor oil, olive oil and cod-liver oil were investigated.
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  • 50
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    Journal of thermal analysis and calorimetry 39 (1993), S. 351-358 
    ISSN: 1572-8943
    Keywords: epoxy resin ; kinetics ; polyamide hardener
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels DSC wurde die Optimierung des Einsatzverhältnisses von Epoxidnovolackharz Dobeckot E4 und Polyamidhärtungsmittel EH411 durchgeführt. Die Daten ergaben, daß ein Harz-Polyamid-Verhältnis von 100∶40 bzw. 100∶50 das Optimum zu sein scheint, bei dem die Aushärtung am größten ist. Mittels isothermer und dynamischer DSC-Methoden wurden die kinetischen Parameter für diese Ansätze ermittelt. Unter Anwendung der isothermen DSC-Methode im Temperaturbereich 70°–90°C wurde die Geschwindigkeitskonstante für den Aushärtungsprozeß dieser Ansätze ermittelt. Diese wurden mittels Extrapolation der erhaltenen Angaben für höhere Temperaturen auch für die Temperatur 201°C (Raumtemperatur) vorhergesagt. Vorhergesagte und experimentell ermittelte Werte stehen in guter Übereinstimmung zueinander.
    Notes: Abstract The optimization of proportions of novolac epoxy resin, Dobeckot E4 and polyamide hardener, EH411 has been established by DSC and the data indicates that resin-polyamide, 100∶40 and 100∶50, appear to be optimum where ‘extent of cure’ is maximum. The kinetic parameters for these formulations have been evaluated using isothermal and dynamic modes by employing DSC. The rate constants have been evaluated for curing process of these formulations using isothermal DSC mode in the temperature range of 70°–90°C. These have also been predicted at 20°±1°C (room temperature) by extrapolating the data obtained at elevated temperatures. A comparison of the predicted values with the experimental values shows that there is a good agreement between them.
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    Journal of thermal analysis and calorimetry 49 (1997), S. 45-56 
    ISSN: 1572-8943
    Keywords: accommodation function ; fractional reaction ; kinetics ; solid-state reaction ; thermal analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The physico-geometric kinetics for the solid-state reactions by thermoanalytical (TA) measurements were reexamined by focusing some fundamental aspects: (1) the fundamental kinetic equation, (2) the kinetic model function, (3) the fractional reaction α, and (4) the apparent kinetic parameters. It was pointed out that some pitfalls in the practical kinetic study are originated by the disagreement between the kinetic information from the TA measurements and the theory of the physico-geometric kinetics. In order to increase the degree of coordination between the theory and practice, several attempts were made from both the theoretical and experimental points of views. The significance of the apparent kinetic parameters was discussed with a possible orientation for obtaining the reliable kinetic parameters.
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  • 52
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    Journal of thermal analysis and calorimetry 49 (1997), S. 255-260 
    ISSN: 1572-8943
    Keywords: catalytic degradation ; kinetics ; polyethylene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract HZSM-5 zeolite was screened as catalyst for high density polyethylene degradation at 450
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  • 53
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    Journal of thermal analysis and calorimetry 49 (1997), S. 261-268 
    ISSN: 1572-8943
    Keywords: kinetics ; phenol-formaldehyde resins ; pyrolysis-GC ; thermal degradation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Phenol-formaldehyde resins (I andII), synthesised at a monomer feed ratio of F/P = 1.0 and 1.5, were cured at 130
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  • 54
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    Journal of thermal analysis and calorimetry 49 (1997), S. 17-32 
    ISSN: 1572-8943
    Keywords: Arrhenius equation ; compensation ; distinguishability ; kinetics ; mechanisms ; nonisothermal
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    Topics: Chemistry and Pharmacology
    Notes: Abstract This paper is a review of some of the controversial kinetic aspects of thermal analysis, starting from the ‘šesták questions’ posed in 1979 and looking at developments in some areas since that time. Aspects considered include: temperature programmes and variations, models and mechanisms, kinetic parameters, distinguishability and extent of fit of kinetic models, complementary evidence for kinetic models, the Arrhenius equation and the compensation effect. The value of the ideas of non-isothermal kinetics in chemical education is emphasized.
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  • 55
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    Journal of thermal analysis and calorimetry 49 (1997), S. 1025-1037 
    ISSN: 1572-8943
    Keywords: crystallographic evaluation ; evaluation with difference procedure ; kinetics ; Rietveld refinement ; X-ray diffraction ; temperature resolved
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Time and temperature resolved X-ray diffraction was used for thermal analysis. Series of diffraction patterns were measured, while the samples are heated/cooled stepwise or isothermally with freely selectable temperature programs. The method was applied for the investigation of the phase transitions of ammonium nitrate and HMX (1,3,5,7-tetranitro-1,3,5,7-tetraaza-cyclooctane), when the identification of phases was required. Its capability in the field of kinetics is demonstrated with the isothermal investigation of the solid state reaction of ammonium nitrate with copper oxide and the non-isothermal investigation of the high temperature corrosion of nickel, which was performed by means of a difference procedure. For obtaining structural details peak fitting and Rietveld refinement were applied for the investigation of ammonium nitrate and HMX.
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  • 56
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    Journal of thermal analysis and calorimetry 49 (1997), S. 617-625 
    ISSN: 1572-8943
    Keywords: combustion ; kinetics ; lignite ; thermal analysis
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Beypazari lignite was investigated by differential scanning calorimetry (DSC), thermogravimetry (TG), high pressure thermogravimetry (HPTG) and combustion cell experiments. All the experiments were conducted at non-isothermal heating conditions with a heating rate of 10°C min−1, in the temperature range of 20–700°C. DSC-TG data were analysed using an Arrhenius-type reaction model assuming a first-order reaction. For the HPTG data the Coats and Redfern equation was used for kinetic analysis. In the combustion cell experiments the Fassihi and Brigham approach was used in order to calculate kinetic data. Finally a comparison is made between the kinetic results.
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  • 57
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    Journal of thermal analysis and calorimetry 49 (1997), S. 609-615 
    ISSN: 1572-8943
    Keywords: combustion ; crude oil ; kinetics ; thermogravimetric analysis
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    Topics: Chemistry and Pharmacology
    Notes: Abstract High pressure thermogravimetric analysis (HPTG) was used in order to study the oxidation of crude oil in a porous medium under pressurised conditions for simulation of in-situ combustion during oil recovery. Three distinct reaction regions were observed from the HPTG curves in an oxidising environment subjected to a constant heating rate. These were low temperature oxidation, fuel deposition and high temperature oxidation. The method of Coats and Redfern was used to obtain kinetic parameters and the results are discussed.
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  • 58
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    Journal of thermal analysis and calorimetry 49 (1997), S. 1527-1533 
    ISSN: 1572-8943
    Keywords: β-cyclodextrin ; cinnamic aldehyde ; kinetics ; thermal analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The stability of the inclusion complex of β-CD with cinnamic aldehyde was investigated by means of TG and DSC. The mass loss takes place in three stages: dehydration occurs at 50–120°C; dissociation of β-CD·C9H8O proceeds in the range 200–260°C; and decomposition of β-CD begins at 280°C. The kinetics of the dissociation of β-CD·C9H8O was studied by means of thermogravimetry both at constant temperature and with linearly increasing temperature. The results demonstrate that the dissociation of β-CD·C9H8O is dominated by a one-dimensional diffusion process. The activation energyE is 160 kJ mol−1, and the pre-exponential factorA is 5.8×1014 min−1. Scanning electron microscope observations and the results of crystal structure analysis are in good agreement with those of thermogravimetry.
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  • 59
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    Journal of thermal analysis and calorimetry 49 (1997), S. 1485-1492 
    ISSN: 1572-8943
    Keywords: bias ; constant temperature stability ; isothermal crystallization ; kinetics ; oxidative induction time
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Oxidative induction time (OIT), constant temperature stability (CTS) and isothermal crystallization are examples of isothermal time-to-event (TTE) measurements obtained using differential scanning calorimetry. In TTE experiments, a test specimen is heated/cooled at a constant rate from the setup temperature to an isothermal test temperature. Once the test temperature is achieved, a clock is started and the time to the thermal event (e.g., onset to oxidation, thermal decomposition or crystallization exotherm peak) is measured. Such TTE values may be used to rank stability of the material at the test temperature. Some portion of the reaction of interest, however, takes place during the pre-isothermal period as the test specimen approaches the test temperature. This amount of reaction is unmeasured and represents a bias in the resultant TTE value. An equation has been derived and numerically integrated to estimate this bias. This approach shows that the bias is dependent upon the activation energy of the test reaction, the heating/cooling rate used and the temperature range between the melting temperature and the test temperature. For commonly used heating rates, the bias for OIT and CTS tests is small. Further, the myth that isothermal crystallization kinetics determinations required high cooling rates is dispelled with the bias of less than 0.9 min resulting from heating rates as low as 10°C min−1. Knowledge of magnitude of this bias permits the selection of experimental conditions without the expense of high heating/cooling rate apparatus or extra cost cooling accessories.
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  • 60
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    Journal of thermal analysis and calorimetry 50 (1997), S. 533-545 
    ISSN: 1572-8943
    Keywords: Cu-19 at% Al ; dislocations ; kinetics ; segregation
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A model is proposed to describe the kinetics of solute segregation to partial dislocations in solid solutions of cold-rolled alloys. The case when half edge and half screw dislocations are present is considered. The model gives account of the kinetic behaviour observed in a deformed Cu-19 at% Al alloy where two unknown processes could be assessed during calorimetric isothermal experiments. The faster process corresponds to segregation to screw dissociated dislocations while the slower one corresponds to segregation to edge dissociated dislocations. Experimental activation energies, larger for edge dislocations, are close to that for pipe diffusion along the partials corrected by pinner binding energy terms. It is also predicted that segregation occurs faster as the dislocation density is increased. A quantitative comparison of experimental results with model predictions is given.
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  • 61
    ISSN: 1573-4889
    Keywords: oxidation ; Incoloy 909 ; superalloy ; scale ; high temperature ; kinetics
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of an Fe-38Ni-13Co-4.7Nb-1.5Ti-0.4Si superalloy (Incoloy 909 type alloy), was investigated at temperatures between 1000 K and 1400 K in Ar-(1, 10%)H20 atmosphere using metallographic, electron probe microanalysis, and X-ray diffraction techniques. The oxide scales consist of an external scale and an internal scale which has an intergranular scale (above 1200 K) and an intergranular scale. The oxide phases in each scale are identified asα-Fe2,O3 (below 1200 K) or FeO (above 1300 K) and CoO · Fe2O3 and FeO · Nb2O5, respectively. The morphologies, the oxide phases and the oxidation rates do not depend on the partial pressure of H2O in the range between one and ten percent in Ar gas. The rate constants for the intergranular-scale formation in this alloy are about one-tenth as large as those in Fe-36%Ni alloy reported previously. At all the temperatures the scales grow according to a parabolic rate law and the apparent activation energies for the processes are estimated.
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  • 62
    ISSN: 1573-4889
    Keywords: oxidation ; kinetics ; iron ; iron-nitride
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of α-Fe and ɛ-Fe2N1−z at 573 K and 673 K in O2 at 1 atm was investigated by thermogravimetrical analysis, X-ray diffraction, light-optical microscopy, scanning electron microscopy and electron probe X-ray microanalysis. Upon oxidation at 573 K and 673 K, on α-Fe initially α-Fe2O3 develops, whereas on ɛ-Fe2N1−z initially Fe3O4 develops. In an early stage of oxidation the oxidation rate of ɛ-Fe2N1−z appears to be much larger than of α-Fe. This can be attributed largely to an effective surface area available for oxygen uptake, which is much larger for ɛ-Fe2N1−z than for α-Fe due to the porous structure of ɛ-Fe2N1−z as prepared by gaseous nitriding of iron. The development of a magnetite layer in-between the hematite layer and the α-Fe substrate, at a later stage of oxidation, enhances layer-growth kinetics. After 100 min oxidation at 673 K the (parabolic) oxidation rates for α-Fe and ɛ-Fe2N1−z become about equal, indicating that on both substrates the oxide growth is controlled by the same rate limiting step which is attributed to short-circuit diffusion of iron cations. Oxidizing ɛ-Fe2N1−z increases the nitrogen concentration in the remaining ɛ-iron nitride, because the outward flux of iron cations, necessary for oxide growth, leads to an accumulation of nitrogen atoms left behind.
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  • 63
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    Oxidation of metals 48 (1997), S. 171-184 
    ISSN: 1573-4889
    Keywords: TiAl, corrosion ; high-temperature ; kinetics ; nitrogen dependence
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxide scale formation on γ-TiAl at 800 and 900°C was studied using high temperature X-ray diffraction as anin situ-method. The experiments were performed in air and in He with 20 vol.% O2. The formation of alumina in the form of α-Al2O3 and of TiO2 in the form of rutile was observed in both atmospheres and the formation of TiN was detected in air. Depending on the atmosphere the diffraction peaks of two different additional phases were detected, which do not exist in any data base nor in the Ti-Al-O phase diagram. One of them, the Z-phase, appears in He with 20 vol.% O2 and the other, the X-phase, in air. The Zphase was also found at room temperature after oxidation at 900°C in air. The growth of both phases, X and Z, starts immediately with the oxidation process and follows the parabolic rate law.
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  • 64
    ISSN: 1573-4889
    Keywords: oxidation ; titanium ; rutile ; scale ; high temperature ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation behavior of pure titanium has been investigated in the temperature range of 1000 K to 1300 K in CO2 or Ar-10%CO2. Optical microscopy, electron probe microanalyses, and X-ray measurements on the oxide scales formed during oxidation indicate that their structures are nearly independent of temperature and the corrosion atmosphere. The scales consisted of two layers, an external one and an internal one, having a rutile (TiO2) structure. The parabolic rate law was confirmed for growth of the external scale and the permeation depth of oxygen in titanium with apparent activation energies of 266 and 226 kJ/mol, respectively. The rate-determining diffusion species in the oxidation processes are discussed.
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  • 65
    ISSN: 1573-4927
    Keywords: glycophorins ; gorilla ; evolution ; gene family ; gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Homologues of MN blood group antigens, encoded by members of the glycophorin A (GPA) gene family, are expressed in man, anthropoid apes, and some species of Old World monkeys. Previous studies had shown that a three-gene framework, most closely related to that in man, is present in the chimpanzee. Here we report the genomic structure, transcript map, and protein expression of the GYPA locus in gorillas. Compared to the corresponding human and chimpanzee homologues, gorilla GPA, GPB, and GPB/E genes each showed a high degree of sequence identity, with the same exon-intron organization. However, the expression of exons III, IV, or V encoding the extracellular or membrane domains of homologous glycophorins varied among the three species. Gorilla GPA and GPB/E genes were unique in that the former occurred in two allelic forms with or without the expression of exon III, whereas the latter contained one (ψ exon III) instead of two silenced exons (ψ exons III and IV). Differences from human but not chimpanzee GPA also included the presence of a hybrid M/N epitope and the absence of the sequon for N-glycosylation. Owing to the retention of a functional exon III, gorilla GPB was more similar to chimpanzee GPB than human GPB. A transspecies allele was identified in the gorilla that gave rise to the Henshaw (He)-like antigen similar to that found in man. These results provide further insight into the model for evolution of the GPA gene family, indicating that the mechanisms underlying inter- and intraspecific polymorphism of glycophorins could predate the divergence of gorillas as the consequence of gene duplication and diversification.
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  • 66
    ISSN: 1573-4846
    Keywords: zirconium butoxide ; titanium butoxide ; kinetics ; hydrolysis ; condensation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A continuous flowing-rapid mixing technique was combined with FTIR, SAXS and electrical conductivity to study the early stages of polymer formation and growth during the acid-catalyzed hydrolysis and condensation of titanium and zirconium alkoxides. Reaction times as short as 80 milliseconds were investigated. FTIR spectroscopy was used to monitor the water and M–OR concentrations during the reaction. Hydrolysis of ∼25–50% of the alkoxy groups was facile. The FTIR and SAXS data showed that condensation was also very rapid. The activity and mobility of the ions in the solution were monitored by electrical conductivity measurements. The decrease in the normalized solution conductivity during the reaction correlated with the loss of [M–OR]. Furthermore, the radius of gyration of the growing polymers increased rapidly in regimes where the conductivity and [M–OR] decreased fastest. This finding suggests that the mobility of some of the charge carrying species decreases because of the growth in size of the polymers.
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  • 67
    ISSN: 1573-4889
    Keywords: binary alloys ; oxidation ; transient state ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The initial transient stage in the oxidation of binary alloys forming scales exclusively composed of the most stable oxide is examined by means of a simplified approach which avoids the numerical integration of the diffusion equation for the transport of the metal components in the alloy. At variance with previous solutions to this problem obtained by means of numerical methods, this treatment takes into account also the effect of the gas-scale reaction at the outer surface of the oxide. The concentration of the most-reactive component at the alloy surface changes gradually with time from the initial bulk value towards the corresponding steady-state value without involving any minimum, while the overall rate of the reaction presents a gradual transition from an initial nearly linear towards final parabolic behavior.
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  • 68
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    Journal of chemical ecology 23 (1997), S. 1527-1547 
    ISSN: 1573-1561
    Keywords: Secondary metabolites ; chemical defense ; evolution ; ascidians ; sponges
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract We used three chemical fractions (spanning a wide range of polarities) from the extracts of four marine invertebrates, the spongesCrambe crambe andHemimycale columella and the ascidiansCystodytes dellechiajei andPolysyncraton lacazei, to test inhibition of cell division, photosynthesis, and settlement. We used assay organisms from the same habitat, seeking to determine whether a species may display diverse, ecologically relevant bioac-tivities and, if so, whether the same types of compound may be responsible for such activities. Cell division was strongly inhibited by the spongeC. crambe. A dichloromethane fraction fromC. crambe prevented development of sea urchinParacentrotus lividus eggs at a concentration of 10 μg/ml, as did the butanolic fraction, but at higher concentrations (50 and 100 μg/ml). At 50 μg/ml, the aqueous fraction ofC. crambe allowed cell division but prevented eggs from developing beyond the gastrula stage. Similar results were recorded with the dichloromethane fraction ofP. lacazei and from the aqueous fraction ofH. columella. Photosynthesis was unaffected by any of the species at 50 μg/ml. Larval settlement was inhibited by one or another fraction from the four species surveyed at a concentration of 50 μg/ml, althoughC. crambe exhibited the greatest amount of activity. We therefore found that various fractions displayed the same type of bioactivity, while compounds from the same fraction were responsible for multiple activities, suggesting that secondary metabolites are multiple-purpose tools in nature, which is relevant to our understanding of species ecology and evolution. Moreover, results showed that the assessment of the role of chemical compounds is significantly influenced by the assay organism, fractionation procedure, concentration, and duration of experiments. All these factors should be carefully considered when testing ecological hypotheses of the roles of chemically-mediated bioactivities.
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  • 69
    ISSN: 1573-2932
    Keywords: fractionation ; redistribution ; saturation ; kinetics ; heavy metals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Solid-phase transformations of Cd, Cu, Cr, Ni and Zn, added as soluble salts at several levels to two arid-zone soils, were studied over a period of one year. The soils were maintained under a saturated-paste regime and sampled periodically. A selective sequential dissolution procedure was employed to determine the changes in metal distribution among six operationally defined solid-phase fractions. A function, Uts was introduced to measure the fractional attainment of equilibrium of the soils following a perturbation. The direction and rate of redistribution of the added metals in the soils were affected by the nature of the metal, the soil properties and the metal loading level. Cd added to the soils was transferred from the exchangeable (EXC) into the carbonate (CARB) fraction. When soluble Cu, Cr, Ni and Zn were added at low loading levels, metals were transferred from the reducible oxides(RO) bound and easily reducible oxides (ERO) bound fractions and the EXC fraction, into the CARB fraction. However, at the higher loading level, metals were transferred from the EXC and CARB fractions into the organic matter bound (OM), ERO and RO fractions. The Uts function approached lower values as incubation continued but remained removed from 1. The overall flux of metals among fractions was the combined result of the readjustment of the metals in the native soil to changing conditions due to saturation, and the transfer of added soluble metals to the less labile fractions.
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  • 70
    ISSN: 1573-4846
    Keywords: zirconium butoxide ; titanium butoxide ; kinetics ; hydrolysis ; condensation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A continuous flowing-rapid mixing technique was combined with FTIR, SAXS and electrical conductivity to study the early stages of polymer formation and growth during the acid-catalyzed hydrolysis and condensation of titanium and zirconium alkoxides. Reaction times as short as 80 milliseconds were investigated. FTIR spectroscopy was used to monitor the water and M−OR concentrations during the reaction. Hydrolysis of ∼25–50% of the alkoxy groups was facile. The FTIR and SAXS data showed that condensation was also very rapid. The activity and mobility of the ions in the solution were monitored by electrical conductivity measurements. The decrease in the normalized solution conductivity during the reaction correlated with the loss of [M−OR]. Furthermore, the radius of gyration of the growing polymers increased rapidly in regimes where the conductivity and [M−OR] decreased fastest. This finding suggests that the mobility of some of the charge carrying species decreases because of the growth in size of the polymers.
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  • 71
    ISSN: 1573-4943
    Keywords: Sulphydryl groups ; multiple ; hemoglobin ; kinetics ; ionizable groups
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Pigeon hemoglobin has eight reactive sulphydryl groups per (tetramer) molecule, as determined by Boyer titration with p-chloromercuribenzoate. However, only four of these are titra-table with 5,5′-dithiobis(2-nitrobenzoate) under the same experimental conditions. The time course of the reaction of pigeon hemoglobin with 5,5′-dithiobis(2-nitrobenzoate) is biphasic. In thepH range 6–9, the fast phase is between one and two orders of magnitude faster than the slow phase. For the fast phase,k app, the apparent second-order rate constant, increases monotonously withpH. Quantitative analysis reveals that the reactionof the sulphydryl group responsible for this phase is coupled to the ionization of two groups with pK a values of 6.15±0.1 and 8.5±0.1. These pK a values are assigned to HisHC3(146)β and to the CysF9(93)β sulphydryl group, respectively. For the slow phase thek app vs.pH profiles are bowl-shaped. Analysis reveals that the reaction of the sulphydryl group to which this phase may be attributed is coupled to the ionization of two groups with mean pK a values of 6.53±0.1 and 8.25±0.1. Examination of the structure of hemoglobin allows us to assign these values to HisG19(117)β and CysB5(23)β, respectively. The CysB5(23)β sulphydryl is in the region of the molecule where amino acid substitutions have been found to give rise to significant changes in the oxygen affinity of hemoglobin [Huanget al. (1990),Biochemistry 29, 7020–7023.
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    Plant molecular biology 23 (1993), S. 409-413 
    ISSN: 1573-5028
    Keywords: cDNA ; cloning ; rice ; L5 ; ribosomal 5 S RNA-binding protein ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A rice (Oryza sativa L.) cDNA clone coding for the cytoplasmic ribosomal protein L5, which associates with 5 S rRNA for ribosome assembly, was cloned and its nucleotide sequence was determined. The primary structure of rice L5, deduced from the nucleotide sequence, contains 294 amino acids and has intriguing features some of which are also conserved in other eucaryotic homologues. These include: four clusters of basic amino acids, one of which may serve as a nucleolar localization signal; three repeated amino acid sequences; the conservation of glycine residues. This protein was identified as the nuclear-encoded cytoplasmic ribosomal protein L5 of rice by sequence similarity to other eucaryotic ribosomal 5 S RNA-binding proteins of rat, chicken, Xenopus laevis, and Saccharomyces cerevisiae. Rice L5 shares 51 to 62% amino acid sequence identity with the homologues. A group of ribosomal proteins from archaebacteria including Methanococcus vanniellii L18 and Halobacterium cutirubrum L13, which are known to be associated with 5 S rRNA, also related to rice L5 and the other eucaryotic counterparts, suggesting an evolutionary relationship in these ribosomal 5 S RNA-binding proteins.
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  • 73
    ISSN: 1573-5028
    Keywords: cDNA sequences ; evolution ; fructose-1,6-bisphosphate aldolase ; Spinacia oleracea ; transit peptide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We report the sequences of full-length cDNAs for the nuclear genes encoding the chloroplastic and cytosolic fructose-1,6-bisphosphate aldolase (EC 4.1.2.13) from spinach. A comparison of the deduced amino-acid sequences with one another and with published cytosolic aldolase sequences of other plants revealed that the two enzymes from spinach share only 54% homology on their amino acid level whereas the homology of the cytosolic enzyme of spinach with the known sequences of cytosolic aldolases of maize, rice and Arabidopsis range from 67 to 92%. The sequence of the chloroplastic enzyme includes a stroma-targeting N-terminal transit peptide of 46 amino acid residues for import into the chloroplast. The transit peptide exhibits essential features similar to other chloroplast transit peptides. Southern blot analysis implies that both spinach enzymes are encoded by single genes.
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  • 74
    ISSN: 1573-5028
    Keywords: C4 metabolism ; evolution ; GC content ; gene family ; PEPC ; Sorghum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Although housekeeping functions have been shown for the phosphoenolpyruvate carboxylase (EC 4.1.1.31, PEPC) in plants and in prokaryotes, PEPC is mainly known for its specific role in the primary photosynthetic CO2 fixation in C4 and CAM plants. We have shown that in Sorghum, a monocotyledonous C4 plant, the enzyme is encoded in the nucleus by a small multigene family. Here we report the entire nucleotide sequence (7.5 kb) of the third member (CP21) that completes the structure of the Sorghum PEPC gene family. Nucleotide composition, CpG islands and GC content of the three Sorghum PEPC genes are analysed with respect to their possible implications in the regulation of expression. A study of structure/function and phylogenetic relationships based on the compilation of all PEPC sequences known so far is presented. Data demonstrate that (1) the different forms of plant PEPC have very similar primary structures, functional and regulatory properties, (2) neither apparent amino acid sequences nor phylogenetic relationships are specific for the C4 and CAM PEPCs and (3) expression of the different genes coding for the Sorghum PEPC isoenzymes is differently regulated (i.e. by light, nitrogen source) in a spatial and temporal manner. These results suggest that the main distinguishing feature between plant PEPCs is to be found at the level of genes expression rather than in their primary structure.
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  • 75
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    Biochemical genetics 31 (1993), S. 473-484 
    ISSN: 1573-4927
    Keywords: hydroxyacyl glutathione hydrolase (glyoxalase II) ; chromosome mapping ; evolution ; Mus musculus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract In man, the gene for hydroxyacyl glutathione hydrolase (HAGH; glyoxalase II) is closely linked to the α-globin locus (HBα) on Chromosome 16. HAGH polymorphism in the mouse has now enabled the mapping of the murine homologue. Deletion mapping, congenic strain studies, and characterization of 41 recombinant inbred strains establish that the mouseHagh locus lies very close to the α-globin pseudogene (Hba-ps4) in the vicinity of the major histocompatibility locus (H-2) on chromosome 17. Several other loci have been identified previously that are also closely linked to the human α-globin locus but near the α-globin pseudogeneHba-ps4 in the mouse. These linkage relationships suggest that during the evolution of mice a translocation occurred that subdivided the α-globin locus, leaving one inactive α-globin gene still associated with theHagh locus and linked sequences, while moving and inserting the active α-globin locus and all distal sequences into an internal location on another autosome, the predecessor to mouse chromosome 11.
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  • 76
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    Biochemical genetics 31 (1993), S. 329-341 
    ISSN: 1573-4927
    Keywords: actin superfamily ; Drosophila genetics ; ATPase domain ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Diverse proteins that are 35% to 55% identical to actins have been discovered recently in yeasts, nematodes, and vertebrates. In order to study these proteins systematically and relate their functions to those of conventional actins, we are isolating the corresponding genes from the genetically tractable eukaryote,Drosophila melanogaster. Here we report the isolation and partial characterization of aDrosophila homologue of theSchizosaccharomyces pombe act2 gene. Degenerate oligonucleotide primers specifying peptides that are highly conserved within the actin protein superfamily were used in conjunction with polymerase chain reaction (PCR) to amplify a portion of theDrosophila gene that we have namedactr66B. The corresponding full-length cDNA sequence encodes a protein of 418 residues that is 65% identical to the product of theS. pombe act2 gene, 80% identical to the bovineact2 homologue, but only 48% identical to the principalDrosophila cytoplasmic actin encoded by theAct5C actin gene. Alignment of the yeast, bovine, andDrosophila actin-related proteins shows that they have four peptide insertions, relative to conventional actins, three of which are well placed to modify actin polymerization and one that is likely to perturb the binding of myosin. Locations of two of the fiveactr66B introns are conserved betweenDrosophila and yeast genes, further attesting that they evolved from a common ancestor and are likely to encode proteins having similar functions. We demonstrate that theDrosophila gene is located on the left arm of chromosome 3, within subdivision 66B. Finally, we show by RNA blot-hybridization that the gene is expressed at low levels, relative to conventional nonmuscle actin, in all developmental stages. From these and other observations we infer that the actr66B protein is a minor component of all cells, perhaps serving to modify the polymerization, structure, and dynamic behavior of actin filaments.
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  • 77
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    Biochemical genetics 31 (1993), S. 473-484 
    ISSN: 1573-4927
    Keywords: hydroxyacyl glutathione hydrolase (glyoxalase II) ; chromosome mapping ; evolution ; Mus musculus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract In man, the gene for hydroxyacyl glutathione hydrolase (HAGH; glyoxalase II) is closely linked to the α-globin locus (HBα) on Chromosome 16. HAGH polymorphism in the mouse has now enabled the mapping of the murine homologue. Deletion mapping, congenic strain studies, and characterization of 41 recombinant inbred strains establish that the mouseHagh locus lies very close to the α-globin pseudogene (Hba-ps4) in the vicinity of the major histocompatibility locus (H-2) on chromosome 17. Several other loci have been identified previously that are also closely linked to the human α-globin locus but near the α-globin pseudogeneHba-ps4 in the mouse. These linkage relationships suggest that during the evolution of mice a translocation occurred that subdivided the α-globin locus, leaving one inactive α-globin gene still associated with theHagh locus and linked sequences, while moving and inserting the active α-globin locus and all distal sequences into an internal location on another autosome, the predecessor to mouse chromosome 11.
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  • 78
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    Biochemical genetics 31 (1993), S. 329-341 
    ISSN: 1573-4927
    Keywords: actin superfamily ; Drosophila genetics ; ATPase domain ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Diverse proteins that are 35% to 55% identical to actins have been discovered recently in yeasts, nematodes, and vertebrates. In order to study these proteins systematically and relate their functions to those of conventional actins, we are isolating the corresponding genes from the genetically tractable eukaryote,Drosophila melanogaster. Here we report the isolation and partial characterization of aDrosophila homologue of theSchizosaccharomyces pombe act2 gene. Degenerate oligonucleotide primers specifying peptides that are highly conserved within the actin protein superfamily were used in conjunction with polymerase chain reaction (PCR) to amplify a portion of theDrosophila gene that we have namedactr66B. The corresponding full-length cDNA sequence encodes a protein of 418 residues that is 65% identical to the product of theS. pombe act2 gene, 80% identical to the bovineact2 homologue, but only 48% identical to the principalDrosophila cytoplasmic actin encoded by theAct5C actin gene. Alignment of the yeast, bovine, andDrosophila actin-related proteins shows that they have four peptide insertions, relative to conventional actins, three of which are well placed to modify actin polymerization and one that is likely to perturb the binding of myosin. Locations of two of the fiveactr66B introns are conserved betweenDrosophila and yeast genes, further attesting that they evolved from a common ancestor and are likely to encode proteins having similar functions. We demonstrate that theDrosophila gene is located on the left arm of chromosome 3, within subdivision 66B. Finally, we show by RNA blot-hybridization that the gene is expressed at low levels, relative to conventional nonmuscle actin, in all developmental stages. From these and other observations we infer that the actr66B protein is a minor component of all cells, perhaps serving to modify the polymerization, structure, and dynamic behavior of actin filaments.
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  • 79
    ISSN: 1573-5028
    Keywords: calcium-binding protein ; centrin ; EF hand ; evolution ; green algae
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    Topics: Biology
    Notes: Abstract Centrin (= caltractin) is a ubiquitous, cytoskeletal protein which is a member of the EF-hand superfamily of calcium-binding proteins. A centrin-coding cDNA was isolated and characterized from the prasinophyte green alga Scherffelia dubia. Centrin PCR amplification primers were used to isolate partial, homologous cDNA sequences from the green algae Tetraselmis striata and Spermatozopsis similis. Annealing analyses suggested that centrin is a single-copy-coding region in T. striata and S. similis and other green algae studied. Centrin-coding regions from S. dubia, S. similis and T. striata encode four colinear EF-hand domains which putatively bind calcium. Phylogenetic analyses, including homologous sequences from Chlamydomonas reinhardtii and the land plant Atriplex nummularia, demonstrate that the domains of centrins are congruent and arose from the two-fold duplication of an ancestral EF hand with Domains 1+3 and Domains 2+4 clustering. The domains of centrins are also congruent with those of calmodulins demonstrating that, like calmodulin, centrin is an ancient protein which arose within the ancestor of all eukaryotes via gene duplication. Phylogenetic relationships inferred from centrin-coding region comparisons mirror results of small subunit ribosomal RNA sequence analyses suggesting that centrin-coding regions are useful evolutionary markers within the green algae.
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  • 80
    ISSN: 1573-4943
    Keywords: Hemoglobin ; sulphydryl group ; ionizable groups ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Dog hemoglobin has four sulphydryl groups per (tetramer) molecule located at the G18(111)a and F9(93)β positions. The two sulphydryls at the G18(111)a positions are unreactive toward nonmercurial sulphydryl reagents, but those at the F9(93)β positions are reactive toward these reagents. We have studied the kinetics of the reaction of dog hemoglobin with 5,5′-dithiobis (2-nitrobenzoic acid) as a function ofpH. At allpH values studied, the reaction is kinetically monophasic. Quantitative analysis of thepH dependence of the apparent second-order rate constant shows that two ionizable groups are linked to the reaction of the sulphydryl group. TheirpK a values are 5.57 and 9.0. These values are assigned to HisHC3(146)β and to the CysF9(93)β sulphydryl. We find that dog carbonmonoxyhemoglobin is significantly—almost an order of magnitude—less reactive than the aquomet, azidomet, and oxy derivatives. This result may be due to a greater tendency (at acidpH) for the salt bridge between HisHC3(146)β and AspFG1(94)β to form in the carbonmonoxy than in the other derivatives. Formation of this salt bridge is known to hinder access to the CysF9(93)β sulphydryl [Perutz, M. F. (1970),Nature 228, 734–739].
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  • 81
    ISSN: 1573-5028
    Keywords: Rubisco activase ; rca ; rbcLrbcS ; cyanobacteria ; expression ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A gene encoding ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase (rca) was found downstream from the rbcLrbcS operon in the heterocystous cyanobacterium Anabaena sp. strain CA. Two unknown open reading frames were shown to be located between rbcS and rca in strain CA and all the genes, rbcLrbcS, ORF1, ORF2, and rca were in the same transcriptional orientation. The deduced amino acid sequence of the Anabaena Rubisco activase showed both similarities and differences to the plant enzyme with considerable differences at the carboxy and amino termini. Proposed ATP-binding sites were conserved in the cyanobacterial protein. Recombinant cyanobacterial Rubisco activase, however, reacted with antisera to spinach Rubisco activase. Hybridization studies, using the Anabaena sp. strain CA rca gene as a heterologous probe, detected homologous sequences in heterocystous Anabaena/Nostoc strains but not in unicellular or nonheterocystous filamentous cyanobacteria, suggestive of a close evolutionary relationship of chloroplasts and heterocystous cyanobacteria.
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  • 82
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    The journal of membrane biology 132 (1993), S. 167-178 
    ISSN: 1432-1424
    Keywords: red cell ; glucose transport protein ; GLUT1 ; kinetics ; rapid reactions ; tryptophan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The kinetics of the initial phases of d-glucose binding to the glucose transport protein (GLUT1) of the human red cell can be followed by stopped-flow measurements of the time course of tryptophan (trp) fluorescence enhancement. A number of control experiments have shown that the trp fluorescence kinetics are the result of conformational changes in GLUT1. One shows that nontransportable l-glucose has no kinetic response, in contrast to d-glucose kinetics. Other controls show that d-glucose binding is inhibited by cytochalasin B and by extracellular d-maltose. A typical time course for a transportable sugar, such as d-glucose, consists of a zero-time displacement, too fast for us to measure, followed by three rapid reactions whose exponential time courses have rate constants of0.5–100 sec+−1 at 20°C. It is suggested that the zero-time displacement represents the initial bimolecular ligand/GLUT1 association. Exponential 1 appears to be located at, or near, the external membrane face where it is involved in discriminating among the sugars. Exponential 3 is apparently controlled by events at the cytosolic face. Trp kinetics distinguish the K d of the epimer, d-galactose, from the K dfor d-glucose, with results in agreement with determinations by other methods. Trp kinetics distinguish between the binding of the α- and β-d-glucose anomers. The exponential 1 activation energy of the β-anomer, 13.6 ± 1.4 kcal mol+−1, is less than that of α-d-glucose, 18.4 ± 0.8 kcal mol+−1, and the two Arrhenius lines cross at ≈23.5°C. The temperature dependence of the kinetic response following α-d-glucose binding illustrates the interplay among the exponentials and the increasing dominance of exponential 2 as the temperature increases from 22.3 to 36.6°C. The existence of these interrelations means that previously acceptable approximations in simplified reaction schemes for sugar transport will now have to be justified on a point-to-point basis.
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  • 83
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    The journal of membrane biology 133 (1993), S. 145-160 
    ISSN: 1432-1424
    Keywords: Acetabularia ; K+ channels ; kinetics ; planar lipid bilayers ; voltage dependence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Plasma membrane from Acetabularia acetabulum was prepared by aqueous-polymer two-phase partitioning and incorporated into planar 1-palmitoyl-2-oleoyl phosphatidylethanolamine bilayers by stirring in the presence of a (cis∶trans) 325∶100 mm KCl gradient. Under these conditions five distinct K+-selective channels were observed which had unitary chord-conductances (determined between 30 mV either side of the reversal potential) and frequencies of incorporation (in parentheses) of 1,600 pS (26%), 485 pS (21%), 259 pS (53%), 140 pS (37%) and 27 pS (37%). Two Cl−-selective channels were also observed, which had unitary chord-conductances of 8 and 48 pS and were present in 21 and 16% of bilayers, respectively. The voltage dependencies of channel open probability (P o ), open-state time constant (τ o) and closed-state time constant (τ c) were determined for the 259, 140 and 27 pS K+ channels. The P o of all three channels increased with increasingly positive membrane potentials. Thus, since these channels were oriented with their extracellular face adjacent to the cis chamber, which was grounded, all would exhibit outward rectification in vivo. Changes in P o were effected by modulation of τ c in all channels, which shortened as membrane potentials became more positive, and also of τ o in the 140 and 27pS channels, which increased as membrane potentials became more positive. Extracellular (cis) KCl concentration (and/or the KCl gradient across the bilayer) affected the P o of all three K+ channels, shifting the P o /membrane potential relationship in the direction of the change in the potassium reversal potential. In all channels this was achieved largely by changes in τ c .
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  • 84
    ISSN: 1573-9171
    Keywords: benzyl bromide, trimethylvinylsilane, addition ; radicals ; metal-complex initiation ; kinetics ; mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The general kinetics of the addition of benzyl bromide to trimethylvinylsilane in the presence of the Fe(CO)5—DMF system has been studied. The reaction orders with respect to each reagent found in the study correspond to a radical chain mechanism of the process. The metal-complex system takes part only in the initiation stage and only at a strictly defined ratio of the components.
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  • 85
    ISSN: 1573-9171
    Keywords: kinetics ; organomercury nitroxyls ; organothallium nitroxyls ; coordination bond ; hydrazobenzene ; reduction ; rate constant
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    Topics: Chemistry and Pharmacology
    Notes: Abstract An increase is found in the reactivity of organomercury and organothallium nitroxyl mono- and biradicals of the imidazoline type in comparison with the analogous compounds without organometallic fragments. This is explained by the formation of coordination bonds N→Hg, N→Tl, and N→O→Hg.
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  • 86
    ISSN: 1573-9171
    Keywords: cationic polymerization ; polyisobutylene ; Lewis acids ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Polymerization of isobutylene in hexane at −78 °C under the action of the complex AcBr · 2AlBr3 (Ac-2) affords polyisobutylene having C=O groups at the head and C-Br or C=C groups at the tail of all the molecules. The presence of the latter indicates that there occurs proton elimination from the growing carbocation with the formation of a superacid HBr · 2AlBr3 which is unable to initiate the polymerization repeatedly under given contitions. This makes it possible to consider proton elimination as the reaction of the decay of active centers with the rate constantk d. This value has been calculated from the rate of accumulation of the polymeric molecules having terminal C=C bonds:k d=3.5 · 10−4 s−1. The rate constant of chain growthk g has been determined from polymerization kinetics and from the content of active centers:k g=6.2 L mol−1 s−1.
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  • 87
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    Russian chemical bulletin 42 (1993), S. 1027-1031 
    ISSN: 1573-9171
    Keywords: nitroxyls ; hydrazobenzene ; reduction ; tetranitromethane ; oxidation ; kinetics ; constants ; mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The values of isotropic HFS constantsa N were obtained for nitroxyl radicals (NR) of the piperidine series in hexane and water. The interrelation between rate constants for NR reduction and oxidation reactions, isotropic HFS constantsa N, inductive constants σ″ of the piperidine substituents, and electrochemical characteristics of NR were found. The dependence of the rate constants for the reduction of NR by hydrazobenzene (HB) and its oxidation by tetranitromethane (TNM) upon the Hammett type inductive constantsσ EPR, obtained using HFS constantsa N as the basis, was analyzed. The solvent effect on the reduction and oxidation reaction rate constants, the kinetic isotopic effect of the reduction reaction for a number of NR-HB systems, and alternative reaction mechanisms are considered.
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  • 88
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    Russian chemical bulletin 42 (1993), S. 1811-1815 
    ISSN: 1573-9171
    Keywords: hydroxylammonium nitrate ; preparation ; thermal decomposition ; kinetics ; mechanism
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of thermal decomposition of melted hydroxylammonium nitrate have been investigated by the rate of heat production in the temperature range 84.8–120.9°C. The decomposition proceeds with autocatalysis and up to 60 % of conversion the rate of the process increases proportionally to the square of the degree of decomposition. The initial rate is proportional to the square of the concentration of HNO3 formed due to dissociation of the salt. The activation energy of this process is 15.3±1.8 kcal/mol. It is suggested that the initial stage the process proceeds via interaction between N2O3 and NH3OH+, whereas the subsequent acceleration is due to oxidation of NH3OH+ by nitrogen oxides formed as well as by nitrous acid.
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    Russian chemical bulletin 42 (1993), S. 457-460 
    ISSN: 1573-9171
    Keywords: kinetics ; mechanism ; 6-tert-butyl-2-methylphenol ; alkylation with methyl acrylate
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A kinetic scheme of the reaction between 6-tert-butyl-2-methylphenol and methyl acrylate in the presence of an alkali metal phenoxide has been proposed. The rate constants of the elementary steps describing the catalytic mechanism have been calculated. The reaction gives methyl 3-(5-tert-butyl-4-hydroxy-3-methylphenyl)propionate as the only product (Calkylation). The nature of the metal cation does not affect the reaction mechanism.
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  • 90
    ISSN: 1573-9171
    Keywords: H-complexes ; polyimide ; 3,3′,4,4′-benzophenonetetracarboxylic acid, diethyl ester ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of thermal imidization of the H-complexes derived from the diethyl ester of 3,3′,4,4′-benzophenonetetracarboxylic acid (EBZP) and various diamines have been studied. A comparison of kinetic parameters obtained for the imidization of H-complexes based on ethyl or methyl esters of this acid has disclosed the differences in the behavior of each of the two H-bonds and the contribution of each bond to the mechanism of polyimide formation from the respective H-complexes.
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  • 91
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    Plant systematics and evolution 184 (1993), S. 89-100 
    ISSN: 1615-6110
    Keywords: Primulaceae ; Coris ; Palynology ; pollen morphology ; pollen ultrastructure ; pollenkitt ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Pollen grain morphology, sculpturing, and wall ultrastructure are investigated in two species ofCoris (Primulaceae),C. monspeliensis L. andC. hispanica Lange. The study includes both acetolysed and unacetolysed pollen. No evidence of any major palynological difference is recorded between these two species, apart from a somewhat larger pollen inC. monspeliensis. However,Coris can be distinguished from the remaining members of thePrimulaceae by the conjunction of relatively large pollen grains, prominent margo, and particular tectal pattern causing a reticulate surface with minute luminal perforations decreasing towards the colpi. From both these distinctive features, and others typically primulaceous, some evolutionary considerations are inferred. Finally, the higher proportion of irregular grains inC. hispanica is interpreted in light of environmental stress.
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  • 92
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    Plant systematics and evolution 184 (1993), S. 195-206 
    ISSN: 1615-6110
    Keywords: Crassulaceae ; Sedum rupestre ; Chromosome numbers ; hybridization ; allopolyploidy ; chloroplast DNA RFLP ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract InSedum rupestre L. a polyploid series (x = 16) occurs in which aneuploid chromosome numbers and odd levels of ploidy prevail. The most common and widely distributed cytotype,S. rupestre subsp.rupestre, is 2n = 112. Plants resemblingS. rupestre subsp.rupestre can be obtained by hybridizing the tetraploid cytotypes ofS. forsterianum Sm. (2n = 48) andS. rupestre subsp.erectum 't Hart (2n = 64). Comparison of these artificial hybrids with their parents and a large number of plants ofS. rupestre subsp.rupestre (2n = 112) from nature showed thatS. rupestre subsp.rupestre and the artificial hybrids are morphologically indistinguishable, and intermediate betweenS. forsterianum andS. rupestre subsp.erectum. MorphologicallyS. rupestre subsp.rupestre is closer to subsp.erectum than toS. forsterianum. Chloroplast DNA restriction patterns ofS. rupestre subsp.rupestre, however, resembleS. forsterianum more closely. The combined results of the hybridization experiments, the analysis of the cpDNA restriction patterns, and the morphological variation indicate the allopolyploid origin ofS. rupestre subsp.rupestre.
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    Plant systematics and evolution 184 (1993), S. 241-257 
    ISSN: 1615-6110
    Keywords: Romulea ; Iridaceae ; Herkogamy ; gynodioecy ; reproductive systems ; biogeography ; evolution ; phenetics ; Flora of the Mediterranean ; Morocco
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Herkogamy and gynodioecy were studied in the Moroccan species ofRomulea. Several types of herkogamy are shown to occur in the different species, with each type corresponding to a characteristic perianth size. The degree of differentiation between female and hermaphrodite morphs varies among the different gynodioecious species. Herkogamy is considered to have evolved prior to the development of the gynodioecious condition. An evolutionary interpretation is proposed based on the degree of herkogamy and of gynodioecy in the different species.
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    Plant systematics and evolution 184 (1993), S. 259-283 
    ISSN: 1615-6110
    Keywords: Angiosperms ; Asteraceae ; Astereae ; Cladistics ; evolution ; phylogeny ; classification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract TheAstereae were surveyed and the genera arranged in 23 informal groups. The generic groups were used to sample representative genera for a cladistic analysis based on morphological characters. The resulting cladogram was used for discussion of evolution and subtribal classification within the tribe. The lower basic chromosome numbers x = 4, 5, 6, and 8 are interpreted as reductions from a primitive x = 9. The subtribeGrangeinae occupies a phylogenetically basal position as sister group to the rest of the tribe. This may be divided into two large groups, largely corresponding to the homochromousSolidagininae and to the heterochromousAsterinae sensu lato, i.e. including theBellidinae, Hinterhuberinae, Conyzinae, andBaccharidinae. The latter four subtribes are derived within theAsterinae, and hence reduced to synonymy. Several intercontinental relationships indicate that a geographical subdivision of the tribe should be avoided, although in our analysis most of the groups proved to be restricted to one of five major regions.
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    Plant systematics and evolution 185 (1993), S. 207-217 
    ISSN: 1615-6110
    Keywords: Crassulaceae ; Sedum acre ; S. samium ; S. litoreum ; S. ser.Alpestria ; Chemotaxonomy ; pyrrolidine alkaloids ; piperidine alkaloids ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The 16 species of theSedum acre-group were investigated for the presence of alkaloids. They areS. acre ofS. ser.Acria, S. alpestre, S. annuum, S. apoleipon, S. borissovae, S. euxinum, S. grisebachii, S. laconicum, S. multiceps, S. sexangulare, S. tuberiferum, S. tuberosum, S. ursi, andS. urvillei ofS. ser.Alpestria, S. samium ofS. ser.Samia, andS. litoreum ofS. ser.Litorea. S. acre differs significantly from the other species. It contains sedamine, “hydroxy” sedamine, and a number of 2,6-disubstituted piperidine alkaloids. The leafy parts of the species ofS. ser.Alpestria, S. ser.Samia, andS. ser.Litorea contain 4 piperidine alkaloids which also occur inS. acre, and in addition 4 pyrrolidine alkaloids not present inS. acre. The composition of the alkaloid fraction agrees with the infrageneric classification (series) based on the hybridization patterns of the species (comparia).
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    Plant systematics and evolution 187 (1993), S. 127-134 
    ISSN: 1615-6110
    Keywords: Poaceae ; Triticum ; Aegilops ; Hybrids ; amphidiploids ; meiotic non-reduction ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Meiosis was studied in aT. turgidum ×Ae. longissima hybrid (ABS1, 2n = 21) and in backcrosses of its amphidiploid toT. turgidum. Analysis of PMCs of the hybrid showed that non-reductional meiosis led to the production of a large number of non-reduced male gametes. The hybrid showed high seed set. All progeny had 2n = 42. The BC1 plants (2n = 35, AABBS1) showed the expected meiotic pairing of 14II + 7I. At anaphase I, univalents behaved in a non-reductional way. The possible role of meiotic non-reduction is discussed in terms of the evolution of theTriticum-Aegilops complex.
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  • 97
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    Plant systematics and evolution 187 (1993), S. 213-241 
    ISSN: 1615-6110
    Keywords: Ascomycetes ; Bunodophoron ; Caliciales ; Calycidium ; Leifidium ; Sphaerophoraceae ; Sphaerophorus ; Cladistics ; classification ; evolution ; systematics ; phylogeny
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A phylogenetic analysis of the familySphaerophoraceae (Caliciales, lichenized ascomycetes) has resulted in a new generic classification. Notes on character evolution are given. The generaSphaerophorus s. str.,Bunodophoron andLeifidium, gen. nov., are accepted.Pleurocybe andPseudosphaerophorus are considered synonyms ofBunodophoron andThysanophoron is considered synonym toSphaerophorus. The following new combinations are proposed:Bunodophoron coomerense (Ohlsson)Wedin,B. diplotypum (Vain.)Wedin,B. dodgei (Ohlsson)Wedin,B. flaccidum (Kantvilas & Wedin)Wedin,B. formosanum (Zahlbr.)Wedin,B. imshaugii (Ohlsson)Wedin,B. insigne (Laurer)Wedin,B. kinabaluense (M. Satô)Wedin,B. macrocarpum (Ohlsson)Wedin,B. madagascareum (Nyl.)Wedin,B. microsporum (Ohlsson)Wedin,B. murrayi (Ohlsson)Wedin,B. notatum (Tibell)Wedin,B. ohlssonii (Wedin)Wedin,B. patagonicum (C. W. Dodge)Wedin,B. ramuliferum (I. M. Lamb)Wedin,B. scrobiculatum (C. Bab.)Wedin,B. tibellii (Wedin)Wedin,B. whakapapaense (Wedin)Wedin, andLeifidium tenerum (Laurer)Wedin.
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  • 98
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    Plant systematics and evolution 188 (1993), S. 197-211 
    ISSN: 1615-6110
    Keywords: Gymnosperms ; Pinaceae ; Pinus ; cpDNA variation ; molecular systematics ; evolution ; Flora of Eurasia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The genusPinus includes over 90 species with approximately 24 species native to Asia. We have analyzed the chloroplast (cp) DNA variation of 18Pinus species, including 15 Asian, two Eurasian, and one European species using seven restriction enzymes and ten non-overlapping probes and inferred their phylogenetic relationships. Results of phenetic and cladistic approaches to phylogeny reconstruction were largely in agreement, suggesting two major lineages within the genus and confirmed the ancient character of haploxylon and diploxylon subgenera. Species from sectionParrya appear to have diverged earliest from the hypothesized phylogenetic centre for the haploxylon pines, withP. bungeana andP. gerardiana forming two basal, monotypic lineages. The range of estimated pairwise nucleotide substitutions per site ( $$\mathop d\limits^ \sim $$ ) was higher among haploxylon pines than among diploxylon species. CpDNA divergence was found to be low within the sectionSylvestres, relative to the divergence among haploxylon species, suggesting that the radiation of this group of taxa from its common ancestor occurred after the diversification of other groups. The low cpDNA divergence in this subsection corroborated earlier evidence for its phylogenetic cohesiveness and existence as a monophyletic group.
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  • 99
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    Plant systematics and evolution 206 (1997), S. 33-45 
    ISSN: 1615-6110
    Keywords: Compositae ; Barnadesioideae ; Doniophyton ; Chuquiraga ; Argentina ; Chile ; evolution ; systematics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This revision describes, illustrates and documents morphological variation inDoniophyton (Compositae, Barnadesioideae), restricted to Argentina and Chile. Two species are recognized,D. anomalum andD. weddellii (sp. nova), possessing distinct morphological and chromosomal features, elevational tolerances, and nearly allopatric distributions.Doniophyton weddellii occurs primarily in central to northern Andean Chile and Argentina from 1900–4000 m a. s. l.;D. anomalum is found principally in centralwestern Argentina and south into Patagonia at 0–1800 m a. s. l. Close relationship exists withChuquiraga of subfam.Barnadesioideae. It is hypothesized thatDoniophyton evolved out ofChuquiraga in the high central Andes between Chile and Argentina. It is suggested thatD. weddellii differentiated first, correlating with an aneuploid chromosomal decrease from n = 27 (inChuquiraga) to n = 25. Further evolution and chromosomal decrease to n = 24 resulted inD. anomalum, with accompanying migration into southern Andes and Patagonia. Nomenclatural changes result from examination of protologues and type specimens:Doniophyton anomalum replaces the commonly used nameD. patagonicum, and a new species,D. weddellii, is described for the taxon masquerading under the routinely used superfluous nameD. andicola.
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  • 100
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    International journal of anthropology 8 (1993), S. 53-60 
    ISSN: 1824-3096
    Keywords: mandible ; evolution ; function ; morphometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This study was carried out on 56 mandibles belonging to skeletal remains recovered from archaeological excavations in Israel dated to 6.000 BP. or less, 2 Neandertal mandibles dating between 50.000–60.000 BP. and 2 early H. sapiens sapiens mandibles both dating to circa 92.000 yr BP. Mandibular body length, the distance from the anterior border of the symphysis to a line bisecting the first molar (distance 1), and the distance from the line bisecting the first molar to the mandibular angle (distance 2) were measured. Distance 1, showed little variation between specimens. However, distance 2 showed a significant difference between sexes and between early and late specimens. For all specimens examined there was a low nonsignificant correlation, between the length of the mandible and distance 1, while there was a high correlation between the length of the mandibular body and distance 2. There was little or no correlation between distance 1 and 2. We propose that the human mandible, as a lever arm, can be divided into two functional parts; an anterior part which shows little change over the last 90000 years, and a posterior part which differs in accordance with the length of the mandibular corpus. These changes in distance 2 appear to correlate to changes in body size and diet, suggesting that as proposed by Hylander (1988) chewing rather than incision has played the main role in evolutionary trends of the hominid mandible. This is also in accordance with mandibular growth during development where the lengthening of the jaw takes place mostly in the posterior part by remodeling in the ramus area (Enlow, 1990) both during individual development (ontogenesis) and through evolutionary changes (phylogenesis).
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