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  • kinetics
  • Springer  (176)
  • Public Library of Science (PLoS)
  • 1990-1994  (176)
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  • 1
    Electronic Resource
    Electronic Resource
    The kinetics of the solvolysis of chloropentacyanocobaltate(III) ions in water containing 2-methoxyethanol or diethylene glycol: A contrast with the effect of more hydrophobic cosolvents (1994)
    Springer
    Journal of solution chemistry 23 (1994), S. 1089-1100 
    Details
    ISSN: 1572-8927
    Keywords: Solvolysis ; kinetics ; aqueous solvent mixtures ; Co(III) complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of the solvolysis of [Co(CN)5Cl]3− have been investigated in water +2-methoxyethanol and water + diethylene glycol mixtures. Although the addition of these linear hydrophilic cosolvent molecules to water produces curvature in the variation of log(rate constant) with the reciprocal of the dielectric constant, their effect on the enthalpy and entropy of activation is minimal, unlike the effect of hydrophobic cosolvents. The application of a Gibbs energy cycle to the solvolysis in water and in the mixtures using either solvent-sorting or TATB values for the Gibbs energy of transfer of the chloride ion between water and the mixture shows that the relative stability of the emergent solvated Co(III) ion in the transition state compared to that of Co(CN)5Cl3− in the initial state increases with increasing content of cosolvent in the mixture. By comparing the effects of other cosolvents on the solvolysis, this differential increase in the relative stabilities of the two species increases with the degree of hydrophobicity of the cosolvent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00976258
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  • 2
    Electronic Resource
    Electronic Resource
    Kinetics of the solvolysis oftrans-dichlorotetra-(4-t-butylpyridine)-cobalt(III) ions in water +t-butyl alcohol mixtures (1990)
    Springer
    Journal of solution chemistry 19 (1990), S. 1073-1084 
    Details
    ISSN: 1572-8927
    Keywords: Solvolysis ; kinetics ; mixtures of water+cosolvent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Rates of solvolysis of the complex cation [Co(4tBupy)4Cl2]+ have been determined in mixtures of water with the hydrophobic solvent, t-butyl alcohol. The solvent composition at which the extremum is found in the variation of the enthalpy ΔH* and the entropy ΔS* of activation correlates well with the extremum in the variation of the relative partial molar volume of t-butyl alcohol in the mixture and the straight line found for the variation of ΔH* with ΔS* is coincident with the same plot for water + 2-propanol mixtures. A free energy cycle is applied to the process initial state (C n+) going to the transition state [M(n+1)+...Cl−] in water and in the mixture using free energies of transfer of the individual ionic species, ΔG t o (i), from water into the mixture. Values for ΔG t o (i) are derived from the solvent sorting method and from the TATB/TPTB method: using data from either method, changes in solvent structure on going from water into the mixture are found to stabilize the cation in the transition state, M(n+1)+, more than in the initial state, C n+. This is compared with the application of the free energy cycle to the solvolysis of complexes [Co(Rpy)4Cl2]+ and [Coen2LCl]+ in mixtures of water with methanol, 2-propanol or t-butyl alcohol: the above conclusion regarding the relative stabilization of the cations holds for all these complexes in their solvolyses in water+alcohol mixtures using values of ΔG t o (Cl−) from either source.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00649452
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of ionic interactions on the rates of reduction of Cu(II) with H2O2 in aqueous solutions (1992)
    Springer
    Journal of solution chemistry 21 (1992), S. 1271-1287 
    Details
    ISSN: 1572-8927
    Keywords: Cu(II) ; kinetics ; reduction ; temperature dependence ; H2O2, NaCl, NaBr, NaClO4
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The rates of reduction of Cu(II) with H2O2 have been measured in NaCl and NaBr solutions and mixtures with NaClO4 as a function of pH (6 to 9), temperature (5 to 45°C) and ionic composition (0.1 to 6M). The effect of pH on the rates was found to be independent of temperature and ionic composition. The rates increased as a function of [H+] raised to the power of 1.3 to 1.6. Speciation calculations indicate that this pH dependence can be attributed to Cu(OH)2 being the reactive species. The rate constants in NaCl and NaBr and mixtures with NaClO4 were independent of ionic strength, but proportional to the halide concentration raised to the power of 2.0 (0.2 to 2.6M). These results can be attributed to Cu(OH)2Cl 2 2− being the reactive species to reduction with H2O2. The Cu(I) halide complexes formed from the reduction are not easily oxidized with O2 or H2O2. The faster rates in Br− solutions, which form stronger complexes with Cu+, support this contention. Measurements made in NaCl with added NaHCO3, NaB(OH)4 EDTA, NTA and glycine were also made. These measurements indicate that the CuL complexes (L=B(OH) 4 − , CO 3 2− , EDTA, NTA, and glycine) are not very reactive to reduction with H2O2. The addition of Mg2+ or Ca2+ caused the rates to increase due to the formation of MgL or CaL complexes and the resultant release of reactive Cu2+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00667222
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  • 4
    Electronic Resource
    Electronic Resource
    Thermodynamics of coupled reactions by the method of dynamic titration: the Nickel(II)-salicylate ion system (1994)
    Springer
    Journal of solution chemistry 23 (1994), S. 483-500 
    Details
    ISSN: 1572-8927
    Keywords: Thermodynamics ; kinetics ; chemical relaxation ; temperature-jump ; amplitudes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Amplitudes of chemical relaxation signals can provide useful information as to the thermodynamics of coupled chemical reactions. The temperature-jump technique has been used to investigate the thermodynamic behavior of the Nickel(II)-3,5-dinitrosalicylate system in buffer solution, where complex formation steps are coupled to proton transfer steps. The analysis of the relaxation curves is based on the transformation of a set of coupled elementary reactions into a set of uncoupled ‘normal reactions.’ By analogy with classical titrations, the experiments have been performed by changing the metal ion concentration at constant ligand concentration and pH. Each measured amplitude is associated in this way to a point of a ‘dynamic titration’ and a procedure is formulated by which the values of the equilibrium constants and enthalpies of the normal reactions are simultaneously obtained by simple linear plots. From the dependence of these parameters on suitable functions of the concentrations of the reactants the values of ΔG° and ΔH° of the individual steps are derived. It is shown that the addition of a buffer (instead of an indicator) influences the stoichiometric coefficients of the normal reaction in such a way that measurable amplitudes are produced in systems that, as the presently investigated, in unbuffered solution would remain insensitive to the external perturbation. The circumstances under which the dynamic method offers advantages over the classical techniques are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00972614
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  • 5
    Electronic Resource
    Electronic Resource
    A method to determine the relative value of the barriers of carbon chain growth and termination in Fischer-Tropsch synthesis: elementary reaction kinetics for chain growth (1993)
    Springer
    Catalysis letters 19 (1993), S. 93-97 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00765205
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  • 6
    Electronic Resource
    Electronic Resource
    Kinetics and mechanisms of the low-temperature degradation of cellulose (1994)
    Springer
    Cellulose 1 (1994), S. 26-56 
    Details
    ISSN: 1572-882X
    Keywords: low-temperature degradation ; kinetics ; mechanisms ; electrical insulation ; transformers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A critical review is given of the degradation of cellulose in the low-temperature region (below about 300°C) of power transformer operation. The large number of kinetic studies, under a variety of environmental conditions from Kraft paper in insulating oil, to cotton and paper in oxygen, are considered in terms of a first-order polymer chain scission model. In many cases, the data are replotted to suit the model. A common activation energy of 111±6 kjmol−1 is calculated and it is shown that the pre-exponential factor, rather than the activation energy, is sensitive to the oxidizing nature of the environment and the susceptibility to degradation of the material. The chemical mechanisms of degradation are reviewed, and conclusions and recommendations are made regarding chemical condition monitoring and life prediction of electrical insulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00818797
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  • 7
    Electronic Resource
    Electronic Resource
    Oxidation of carbidic carbon on a rhodium surface (1994)
    Springer
    Catalysis letters 27 (1994), S. 79-90 
    Details
    ISSN: 1572-879X
    Keywords: kinetics ; carbon ; oxygen ; recombination ; rhodium ; surface characterisation ; XPS ; AES
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Different mechanisms of atomic carbon and oxygen recombination on a rhodium surface are studied with Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The kinetics of adsorbed carbidic carbon oxidation (carbon coverageθ c ≈ 0.1–0.3 ML) by gas-phase oxygen that proceeds by a Langmuir-Hinshelwood reaction mechanism, provides the value of the activation energy for recombination (E rec ⇂t ≈ 170±20 kJ/mol).E rec ⇂t depends slightly on the carbon coverage. An Eley-Rideal type of reaction was observed for adsorbed oxygen and atomic gas-phase carbon recombination which occurs in a dynamic regime. The low value found for the activation energy (near zero) is consistent with the mechanism that this exothermic reaction is too fast for energy dissipation into the substrate; the energy is mainly transferred into translational, vibrational and rotational energy of CO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806980
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  • 8
    Electronic Resource
    Electronic Resource
    Dynamics and self-organization of catalytic systems (1994)
    Springer
    Topics in catalysis 1 (1994), S. 305-314 
    Details
    ISSN: 1572-9028
    Keywords: non-Langmuir ; kinetics ; non-linear dynamics ; oscillations ; chaos ; self-organization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of a catalytic reaction is frequently formulated in terms of simple concepts of the Langmuir type. Apart from limitations arising from the non-uniformity of the catalyst's surface and from the coverage dependence of the rate “constants”, several other complications may come into play. These may arise on the “quantum level” where energy flow between the various degrees of freedom may cause failure of simple transition state theory, as well as on the “continuum level” where formulation of rate equations in terms of coupled non-linear differential equations may give rise to a rich scenario of spatio-temporal self-organization, including kinetic oscillations, chaos, and formation of concentration patterns. Several of these phenomena are illustrated by selected examples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01492284
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  • 9
    Electronic Resource
    Electronic Resource
    The polymerization of sickle hemoglobin in solutions and cells (1993)
    Springer
    Cellular and molecular life sciences 49 (1993), S. 110-117 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01989414
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  • 10
    Electronic Resource
    Electronic Resource
    The influence of sulfur dioxide on propane oxidation activity over supported platinum and palladium (1994)
    Springer
    Catalysis letters 30 (1994), S. 41-51 
    Details
    ISSN: 1572-879X
    Keywords: propane ; oxidation ; platinum ; palladium ; sulfur dioxide ; alumina ; zirconia ; activity ; acidity ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Earlier studies have shown that sulfur dioxide and metal-support interaction can strongly influence propane oxidation over platinum. In particular, oxidation activity is enhanced when platinum is supported on sulfated γ-alumina or zirconia compared to γ-alumina. Therefore, it is of interest to compare the performance of palladium under the same experimental conditions. Four model catalysts were examined: Pt/γ-alumina, Pt/zirconia, Pd/γ-alumina and Pd/zirconia. The metal loading was kept at or below 0.05 wt% to emphasize changes in activity attributable to metal-support interaction. Reaction rates were measured with and without sulfur dioxide. Surface sulfation was analyzed by measuring acid strength and evaluating spectra obtained by Fourier-transform infrared spectroscopy. In contrast to platinum, sulfation does not promote propane oxidation on Pd/γ-alumina, and Pd/zirconia is less active than Pd/γ-alumina.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00813671
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  • 11
    Electronic Resource
    Electronic Resource
    Kinetics of the gas-solid heterogeneous photocatalytic oxidation of trichloroethylene by near UV illuminated titanium dioxide (1990)
    Springer
    Catalysis letters 4 (1990), S. 345-354 
    Details
    ISSN: 1572-879X
    Keywords: Ultraviolet heterogeneous photocatalysis ; oxidation ; trichloroethylene ; titania ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Kinetics of the gas/solid heterogeneous photocatalytic oxidation of dilute trichloroethylene (TCE) vapors by ultraviolet-illuminated titanium dioxide have been determined using a fixed-bed dynamic photoreactor. Reaction rate dependences on inlet TCE, oxygen and water vapor concentrations were found to consist of both reactant sensitive and insensitive regions. In the reactant sensitive regions, measured limiting apparent reaction rate orders for TCE, oxygen and water vapor are 0.8, 1.7 and — 3, respectively. Water vapor in the reactant stream lowersinitial reaction rates relative to corresponding water free conditions, but is required to sustain photocatalytic activity for extended periods of time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00765320
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  • 12
    Electronic Resource
    Electronic Resource
    Spectrophotometric determination of mercury with 5,10,15,20-tetrakis(3-chloro-4-sulfophenyl)porphine by flow injection analysis (1994)
    Springer
    Microchimica acta 113 (1994), S. 81-89 
    Details
    ISSN: 1436-5073
    Keywords: flow injection analysis (FIA) ; mercury ; porphyrin ; kinetics ; spectro-photometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 5,10,15,20-tetrakis(3-chloro-4-sulfophenyl)porphine (m-Cl-TPPS4) was synthesized and used for the Spectrophotometric determination of mercury by flow injection analysis. A pseudo-first-order reaction kinetic mechanism was proposed with a rate constant of 0.8 min−1 for Hg(II) withm-Cl-TPPS4 in the presence of 8-hydroxyquinoline in a medium of 1.0M acetic acid and sodium acetate buffer solution (pH 6.22). In the optimum conditions of reaction temperature (85 ° C), stopped-flow time (60 s) and sampling volume (100 μl), the method's relative standard deviation was 0.82% (n = 12) at 5.0 μg ml−1 mercury, with a linear range of 0–12.0 μg ml−1 and an analytical frequency of 60h−1. The detection limit (3σ) was 0.025 μg ml−1. Interference studies showed that most metal ions co-existing with Hg2+ could be tolerated at 100-fold excess levels, but Zn2+, Cu2+ and Mn2+ needed to be masked. The method has been applied to the analysis of water samples with satisfactory results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01243140
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  • 13
    Electronic Resource
    Electronic Resource
    Increased sensitivity of an enzyme immunoassay (ELISA) for the determination of triazine herbicides by variation of tracer incubation time (1992)
    Springer
    Microchimica acta 108 (1992), S. 29-40 
    Details
    ISSN: 1436-5073
    Keywords: atrazine ; terbuthylazine ; sequential binding ; kinetics ; cross-reactivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Immunoassays for triazine herbicides were tested for their reaction to the variation of the tracer incubation time. By application of a sequential technique the measuring range of atrazine could be expanded to five decades and the total duration of the test could be reduced to about 30 min. In an optimized version a lower detection limit of 9 pmol/l (2 ng/l) was achieved. The detection limit of a sensitive immunoassay for terbuthylazine is also below the concentration limit demanded of the German drinking water regulation (100 ng/l) and reaches 130 pmol/l (30 ng/l). Short tracer incubation times did not lead to increased cross-reactivities in contrast to theoretical models [1, 2]. Different mechanisms, which could cause a shift of the center point of the calibration curve, are discussed, including kinetic considerations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01240369
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  • 14
    Electronic Resource
    Electronic Resource
    Effect of mineral nutrients on the kinetics of methane utilization by methanotrophs (1993)
    Springer
    Biodegradation 4 (1993), S. 163-170 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00695118
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  • 15
    Electronic Resource
    Electronic Resource
    Slow release rate: Individual granules and population behaviour (1994)
    Springer
    Nutrient cycling in agroecosystems 39 (1994), S. 39-42 
    Details
    ISSN: 1573-0867
    Keywords: Controlled release fertilizers ; kinetics ; mechanism ; nutrient supply ; rate of release ; slow release fertilizers (SRF)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Individual granules within a given granule population of a slow-release fertilizer (SRF) have a different release pattern. The populations studied differed both in relation to the time delay before the start of the release process and to the duration of the release. An association between a short delay period and a rapid release was found. The random reease distribution can be approximated using first-order rate equations. In cases, a term describing a “lag” period should be added. The distribution of release timing among the fertilizer granules may allow a long-lasting nutrient supply to the plant, as long as there are enough granules within the root zone to allow a uniform supply pattern.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00750155
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  • 16
    Electronic Resource
    Electronic Resource
    Quantitative aspects of cellular turnover (1991)
    Springer
    Antonie van Leeuwenhoek 60 (1991), S. 175-191 
    Details
    ISSN: 1572-9699
    Keywords: growing systems ; kinetics ; murein wall ; nucleic acid ; protein ; turnover
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Living organisms do not just grow by synthesizing cellular components. As part of the necessary steps for existence, some components are degraded after synthesis. Even for bacteria in balanced, exponential growth some substances, under some conditions, are turned over. In other phases of growth turnover can be much more extensive, but it is still selective. This review covers studies with animals as a way to put the studies on microorganisms in perspective. The history, the mathematics, and experimental design of turnover experiments are reviewed. The important conclusion is that most of the proteins during balanced growth are very stable in bacteria, although ribosomal proteins are degraded under starvation conditions. Another generalization is that the process of wall enlargement in general is associated with obligatory turnover of the peptidoglycan.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00430364
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  • 17
    Electronic Resource
    Electronic Resource
    A comparison of pyridoxal 5′-phosphate dependent decarboxylase and transaminase enzymes at a molecular level (1991)
    Springer
    Cellular and molecular life sciences 47 (1991), S. 1104-1118 
    Details
    ISSN: 1420-9071
    Keywords: Transaminase ; decarboxylase ; serine hydroxymethyltransferase ; pyridoxal 5′-phosphate ; enzyme mechanism ; stereochemistry ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Pyridoxal 5′-phosphate is a coenzyme for a number of enzymes which catalyse reactions at Cα of amino acid substrates including transaminases, decarboxylases and serine hydroxymethyltransferase. Using the X-ray coordinates for a transaminase, aspartate aminotransferase, and the results of stereochemical and mechanistic studies for decarboxylases and serine hydroxymethyltransferase, an active-site structure for the decarboxylase group is constructed. The structure of the active-site is further refined through active-site pyridoxyllysine peptide sequence comparison and a 3-D catalytic mechanism for the L-α-amino acid decarboxylases is proposed. The chemistry of serine hydroxymethyltransferase is re-examined in the light of the proposed decarboxylase mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01918374
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  • 18
    Electronic Resource
    Electronic Resource
    Kinetics of redox cycling of iron coupled with fulvic acid (1993)
    Springer
    Aquatic sciences 55 (1993), S. 103-111 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00877439
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  • 19
    Electronic Resource
    Electronic Resource
    Absorption of intramuscular phenobarbitone in children with severe falciparum malaria (1992)
    Springer
    European journal of clinical pharmacology 42 (1992), S. 107-110 
    Details
    ISSN: 1432-1041
    Keywords: Phenobarbitone ; Cerebral malaria ; P.falciparum ; kinetics ; drug absorption ; children
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The absorption of intramuscular phenobarbitone 7 mg·kg−1 was studied in 11 Karen children aged between 1.7 and 11 y with severe falciparum malaria. Eight of the children were comatose. Clinical findings were compared with those in 9 further children with severe malaria of similar age range (four of whom were unconscious), who received an identical placebo. One child, who had received placebo, had repeated convulsions and died 1 h after admission to hospital. The remainder made an uncomplicated recovery. There were no convulsions subsequent to treatment, although the study was too small to assess anticonvulsant efficacy. There was no observable toxicity, but phenobarbitone recipients had a significant tendency to deepen in their level of coma or to become sleepy within the 4 h after drug administration. Phenobarbitone was rapidly absorbed, reaching a mean (range) peak concentration of 34.2 [29.3–42.6] μmol·l−1 in a median (range) of 4 (2.5–12) h. These values are comparable to those previously reported in healthy children and in children with febrile convulsions. Intramuscular phenobarbitone is well absorbed in children with severe malaria; the optimum prophylactic anticonvulsant dose remains to be determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00314929
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  • 20
    Electronic Resource
    Electronic Resource
    Kinetics of atrial natriuretic peptide in young and elderly subjects (1992)
    Springer
    European journal of clinical pharmacology 42 (1992), S. 449-452 
    Details
    ISSN: 1432-1041
    Keywords: Atrial natriuretic peptide ; kinetics ; ageing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary To study the influence of age on the kinetics of atrial natriuretic peptide (ANP) in man, human (99–126) ANP 2.0 μg·min−1 was infused IV for 60 min in 8 healthy young (18 to 25 y) and 9 healthy elderly (71 to 84 y) subjects. Both baseline ANP values and the levels at the end of infusion were higher in the elderly subjects. The mean residence time of ANP in the two age groups was not significantly different, whereas total body clearance (CL) was markedly diminished in the elderly as compared to the young subjects (mean±SD 3.1±1.0 l·min−1 and 6.2±4.1 l·min−1, respectively). The apparent volume of distribution at steady state was lower in the elderly than in the young, but the difference was not significant (mean±SD 44±19 and 103±111, respectively. The decrease in CL largely explained the higher ANP levels found in the elderly subjects. The MRT and the plasma half-life of the terminal phase did not differ between the two groups. In the elderly but not in the young subjects the calculated endogenous creatinine clearance was closely correlated with the CL (r=0.90, P〈0.001), thereby emphasizing the importance of the kidney in the metabolic clearance of ANP in the elderly.
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    Interaction of talinolol and sulfasalazine in the human gastrointestinal tract (1992)
    Springer
    European journal of clinical pharmacology 42 (1992), S. 461-462 
    Details
    ISSN: 1432-1041
    Keywords: Talinolol ; Sulfasalazine ; β-adrenoceptor-blocking drugs ; absorption ; drug interaction ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The absorption of talinolol (TA) 50 mg was investigated without and together with the co-administration of sulfasalazine (SASP) 4 g in 11 healthy young volunteers, in order to clarify gastrointestinal transit of TA. Without SASP, the tmax of TA was 2.8 h, Cmax was 112 ng·ml−1 and the half life was 12 h; the AUCo-t was 958 ng·ml−1·h. In the case of concomitant administration of SASP, TA was found only in serum from 3 individuals, with a Cmax of 23 ng·ml−1 and a mean AUCo-t of 84 ng·ml−1·h. TA was not detectable in 5 subjects and it was at the limit of detection (2 ng·ml−1) in 3 subjects. Pharmacokinetic analysis was not possible in any of those individuals. The reason for the interaction appears to be the adsorption of TA by SASP. An interval of 2–3 h should elapse between giving SASP and other drugs.
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    Bioavailability of controlled release carbamazepine estimated by mixed effect modelling (1993)
    Springer
    European journal of clinical pharmacology 44 (1993), S. 231-235 
    Details
    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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    Comparison of non-kinetic and kinetic approaches to individualization of gentamicin dosage (1990)
    Springer
    European journal of clinical pharmacology 39 (1990), S. 155-159 
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    ISSN: 1432-1041
    Keywords: Gentamicin ; Dosage ; kinetics ; dose individualization ; dose prediction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary A prospective study was carried out in 40 acutely ill patients to compare the non-kinetic and kinetic approaches to individualization of the dosage regimen of gentamicin. The patients were divided into two equal groups. For the non-kinetic group, the doses were derived from the physician's personal experience, on a mg/kg basis, and by use of nomograms. The total daily dose ranged from 1.43 to 4.5 mg/kg. Based on serum concentration measurements, the dosage regimen for individual patient was calculated by Sawchuk-Zaske's method. The calculated doses were compared to the prescribed doses in each patient. Of the patients on empirically prescribed doses 65% received 36% more drug than the calculated dose and 20% received 36% less than the calculated dose. The calculated dosing intervals were greater than the recommended intervals in 60% of the patients. The gentamicin trough concentration was 〉 2 μg/ml in 70% of the patients. There was a significant tendency to overdosage of the patients. For the kinetic group, following administration of the calculated dose, the steady-state peak and trough concentrations in each patient were measured. The correlation of measured to predicted steady-state serum concentrations was excellent (r=0.9968, p〈0.05). About 85% of the served trough concentrations and 90% of the peak values fell within the therapeutic range. The mean of the prediction error (ME), mean absolute error (MAE), mean squared error (MSE), and root mean squared error (RMSE) of the trough and peak concentrations were calculated. The 95% confidence interval of the ME for the trough and peak concentrations included zero, which shows that the prediction was not significantly biased. A significant relationship between gentamicin clearance and the ratio of the peak and trough concentrations achieved to the administered dose (r=0.873, 0.916 for trough and peak, respectively) was found. The findings suggest that the individualized approach to dosage determination using pharmacokinetic principles, in conjunction with daily monitoring of serum gentamicin concentrations, may provide safe and effective therapy.
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    Single and multiple dose pharmacokinetics of etizolam in healthy subjects (1991)
    Springer
    European journal of clinical pharmacology 40 (1991), S. 181-185 
    Details
    ISSN: 1432-1041
    Keywords: Etizolam ; α-hydroxyetizolam ; healthy subjects ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The pharmacokinetics of etizolam, a new thienodiazepine derivative, has been examined after single and multiple (0.5 mg tablet) (0.5 mg b.d for 1 week) oral therapeutic doses in healthy volunteers. The single-dose kinetic profile of etizolam suggested that absorption after oral dosage was reasonably rapid, the maximum plasma concentration (Cmax) being attained within 0.5–2 h in all subjects. The mean elimination half-life (t1/2) averaged 3.4 h. Consistent with this, steady-state concentration were rapidly achieved and accumulation was extremely limited. Predicted average plasma concentrations (Cp) did not differ significantly from those actually measured at steady-state, suggesting that the kinetics of etizolam was linear, at least at therapeutic doses. The mean wash-out t1/2 was comparable to the elimination t1/2 of the single dose, which means that the drug probably has no effect on hepatic microsomal enzymes and other kinetic variables after repeated dosing. At steady state plasma concentrations of the main metabolite, α-hydroxyetizolam, were higher and disappeared more slowly (mean t1/2 8.2 h) than those of the parent compound. Taken with the fact that in animals the metabolite shows almost the same potency of pharmacological action as etizolam, this suggests that it may contribute significantly to the clinical effects of the parent compound. Based on the kinetic characteristics of the parent drug and its metabolite, etizolam can be regarded as a short-acting benzodiazepine, with elimination kinetics between those of short-intermediate derivatives and ultra-rapidly eliminated benzodiazepines.
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    Somewhere between fiction and reality (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 51-70 
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    ISSN: 1572-8943
    Keywords: kinetics ; solid-state reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wurde der Einflu\ verschiedener experimenteller Bedingungen (z.B. Probenmasse, Atmosphäre, Aufheizgeschwindigkeit) auf die Zersetzung von NH4VO3, CaCO3 und V2O5 untersucht. Die Ergebnisse zeigen eindeutig, da\ Reaktionsweg und kinetische Parameter in Wirklichkeit nicht die einzelne Verbindung charakterisieren, sondern eher die Kombination von experimentellen Bedingungen und untersuchter Verbindung. Hierdurch ist es meistens unmöglich, “Standardbedingungen≓ zur Berechnung kinetischer Parameter zu wählen, da unter verschiedenen Umständen ganz andere Reaktionswege beschritten werden können.
    Notes: Abstract The influence of various experimental conditions such as sample weight, atmosphere and heating rate on the decomposition of NH4VO3, CaCO3 and V2O5 has been investigated. Results obtained clearly indicate that the course of the reactions and — in turn — the kinetic parameters, are not intrinsic to the particular compound and that they characterize rather the combination of experimental conditions and investigated compound. Such a situation makes it almost impossible to choose ‘standard conditions’ for the calculation of kinetic parameters, because under different circumstances quite different reaction-pathways can occur.
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    URL: http://dx.doi.org/10.1007/BF02109108
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    Possibilities of two non-isothermal procedures (temperature- or rate-controlled) for kinetical studies (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 71-87 
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    ISSN: 1572-8943
    Keywords: CRTA ; kinetics ; TA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wird die Anwendbarkeit von herkömmlicher Thermoanalyse (TA) und geschwindigkeitsgesteuerter Thermoanalyse (CRTA) bei kinetischen Untersuchungen diskutiert. Die TA Technik kann eine zuverlässige kinetische Information und sinnvolle kinetische Parameter besonders bei Feststoffumsetzungen liefern. Die CRTA Technik ist andererseits mehr für Zersetzungsprozesse geeignet, bei denen ein oder mehrere Gase freigesetzt werden. Für beide Techniken wird eine einheitliche und geeignete Methode zu kinetischen Analyse vorgeschlagen. Als Beispiel wird diese Methode zur Analyse des Kristallisationsprozesses von Chalkogenidgläsern sowie der Zersetzung von Dolomit angewendet.
    Notes: Abstract The applicability of both conventional Thermal Analysis (TA) and Controlled Rate Thermal Analysis (CRTA) for kinetic analysis is discussed. It is shown that TA method can give a reliable kinetic information and meaningful kinetic parameters especially for solid state transformation. On the other hand the CRTA method is more suitable for decomposition process where one or more gasses are evolved. A consistent and reliable method of kinetic analysis is proposed for both techniques. This method is illustrated to analyze the crystallization process of chalcogenide glass and the decomposition of dolomite.
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    Thermodynamic and kinetic properties of hydrogen adsorption on thin iron layers (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 1999-2003 
    Details
    ISSN: 1572-8943
    Keywords: calorimetry ; hydrogen adsorption ; kinetics ; thermodynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels kalorimetrischer und volumetrischer Messungen im Temperaturbereich von 298 bis 363 K wurden die thermodynamischen Eigenschaften der Wasserstoffadsorption an Eisenschichten untersucht. Die kinetischen Eigenschaften wurden mit Hilfe der Dekonvulotion kalorimetrischer Thermogramme ermittelt und mit Literaturangaben zum Haftkoeffizienten verglichen.
    Notes: Abstract Thermodynamic properties of hydrogen adsorption on iron layers evaporated under UHV conditions have been determined from calorimetric and volumetric measurements over the temperature range from 298 K to 363 K. Kinetic properties have been determined with the help of deconvolution of calorimetric curves and compared with the literature data on the sticking coefficient.
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    Thermogravimetric analysis of ZnCl2 catalyzed degradation of PVC (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 2349-2357 
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    ISSN: 1572-8943
    Keywords: dehydrochlorination process ; kinetics ; PVC ; ZnCh catalyzed degradation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels TG wurden die kinetischen Parameter des Dehydrochlorierungsprozesses (DHCL) von PVC und von mit verschiedenen Mengen von ZnCl2 versetztem PVC bestimmt. Diese Werte wurden mit denjenigen verglichen, die man bei der spektroskopischen Analyse der Zersetzung von ZnCl2-haltigen PVC-Filmen bei verschiedenen Temperaturen im sichtbaren UV-Bereich erhalten hatte. Die Werte der scheinbaren Aktivierungsenergie (E a) sinken mit zunehmendem ZnCl2-Gehalt und die hier erhaltenen Werte sind vergleichbar gut mit denen der vorangehenden Arbeit. Der katalytische Effekt von ZnCl2 auf PVC DHCL-Vorgänge wurde erklärt.
    Notes: Abstract The kinetic parameters of dehydrochlorination (DHCL) process of PVC and PVC mixed with different amount of ZnCl2 have been determined by using thermogravimetric analysis. These values have been compared with those obtained by using UV-visible spectroscopic analysis of PVC film containing ZnCh degraded at different temperatures. The values of apparent activation energy (E a) decreases with the increase of the amount of ZnCl2 and the values obtained in the present work are in reasonable comparison with previous works. The catalytic effect of ZnCl2 on PVC DHCL process is explained here.
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    A new thermobalance for studies of the high-temperature sulphidation of metals and alloys (1993)
    Springer
    Journal of thermal analysis and calorimetry 39 (1993), S. 15-20 
    Details
    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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    Thermal and temperature dependence of electrical conductivity studies on Zn, Cd and Hg hydrazone complexes (1993)
    Springer
    Journal of thermal analysis and calorimetry 39 (1993), S. 65-74 
    Details
    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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    Effect of alkali additives on the kinetics of WO3+CCl4 reaction (1993)
    Springer
    Journal of thermal analysis and calorimetry 39 (1993), S. 75-86 
    Details
    ISSN: 1572-8943
    Keywords: chlorination ; kinetics ; WO3+CCl4 reaction
    Source: Springer Online Journal Archives 1860-2000
    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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    Comparative studies on the curing kinetics and thermal stability of tetrafunctional epoxy resins using various amines as curing agents (1993)
    Springer
    Journal of thermal analysis and calorimetry 39 (1993), S. 229-238 
    Details
    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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    Isothermal bulk polymerization ofp-alkylaryl methacrylates by DSC (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 709-713 
    Details
    ISSN: 1572-8943
    Keywords: enthalpy of polymerization ; free radical polymerization ; kinetics ; p-alkylphenyl methacrylates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels DSC wurden im Temperaturbereich 348–373 K Reaktionsweg und Kinetik der radikalischen Raumpolymerisation vonp-Alkylphenylmethacrylaten mit AIBN Initiator untersucht. Dabei wurden die Polymerisationsenthalpie, der Monomerrest-gehalt als auch die Geschwindigkeitskonstanten und die Aktivierungsenergien der Gesamt-reaktion bestimmt. Ähnliche Werte für die Gesamtgeschwindigkeitskonstanten weisen darauf hin, daß die relativ kleinen Alkylsubstituenten inp-Stellung des Phenylringes die Polymerisationsgeschwindigkeit nur in sehr kleinem Maße — wenn überhaupt — beeinflussen.
    Notes: Abstract The course and kinetics of free radical polymerization in bulk ofp-alkylphenyl methacrylates with AIBN initiator were studied by DSC, in the temperature range 348–373 K. The enthalpy of polymerization, the residual monomer content, as well as the overall reaction rate constants and the activation energies were determined. The similar values of the overall rate constants indicate that the relatively small alkyl substituents inp-position of the phenyl ring affect the polymerization rate to a very small, if any, extent.
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    The determination of a complex kinetic expression of oil shale pyrolysis using combined non-isothermal and isothermal TG (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 729-738 
    Details
    ISSN: 1572-8943
    Keywords: kinetics ; oil shale pyrolysis ; TG
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die im allgemeinen benutzte Kinetikgleichung in der Thermoanalyse von Ölschieferpyrolyse wurde auf der Grundlage einer einfachen kinetischen Gleichung erster Ordnung der Kerogenzersetzung erhalten. Mittels nichtisothermer (NI) oder isothermer (I) TG kann sowohl die Aktivierungsenergie als auch die Reaktionsgeschwindigkeitskonstante der Ölschieferpyrolyse bestimmt werden. Die unter Anwendung von NI oder I ermittelten kinetischen Parameter ermöglichen jedoch keine gute Voraussage des Kerogenumsatzes bei anderen Bedingungen. Es werden hier die Vergleichsergebnisse aus NI- bzw. I-TG von verschiedenen Ölschiefern als auch die Auswirkungen auf die sogenannte kombinierte nichtisotherme und isotherme TG (NI/I) besprochen. Die erhaltenen Ergebnisse zeigen, daß ein Mechanismus angenommen werden muß, der auf einem komplexen Reaktionsschema aus mehr als aus einer einfachen Reaktion basiert.
    Notes: Abstract The kinetic expression commonly used in the thermal analysis of oil shale pyrolysis was derived on the basis of a simple first order kinetic equation of kerogen decomposition. The activation energy, as well as the reaction rate constant of oil shale pyrolysis could be determined by using non-isothermal (NI) or isothermal (I) TG. However, the kinetic parameters determined by using either NI or I did not enable the good prediction of the kerogen conversion at other conditions. The comparative results of the NI and I-TG of different oil shales are discussed in the study, as well as the effects of the so-called combined non-isothermal and isothermal TG (NI/I). The obtained results indicate that a mechanism must be postulated based on a complex reaction scheme which involves more than one simple reaction.
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    On the maximum reaction rate and inflexion points on the DTG curve (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 721-728 
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    ISSN: 1572-8943
    Keywords: kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es werden einige theoretische Überlegungen bezüglich des Einflusses der Form der Konversionsfunktionf(α) auf die Werte der Konversionsrate bei maximalen Reaktionsgeschwindigkeiten (αmax) sowie auf Inflexionspunkte (α∞) der DTG-Kurve angestellt. Die erhaltenen Gleichungen sind unabhängig von der Form vonf(α) durch eine all-gemeine Gültigkeit charakterisiert.
    Notes: Abstract The authors present some theoretical considerations concerning the influence of the form of the conversion functionf(α) on the values of the degree of conversion corresponding to the maximum value of the reaction rate (αmax) as well as on the inflexion points (αinf) of the DTG curve. The obtained equations are characterized by a general validity no matter the form off(α).
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    The effect of water vapour pressure on the thermal dehydration of yttrium formate dihydrate (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 1793-1799 
    Details
    ISSN: 1572-8943
    Keywords: hydrated salts ; kinetics ; thermal dehydration ; yttrium formate dihydrate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels isothermer Gravimetrie und bei verschiedenen Wasserdampfdrücken zwischen 5×10−4 und 8 Torr wurde die Kinetik der thermischen Dehydratation von Yttriumformiat-Dihydrat untersucht. Die Dehydratation wird als dreidimensionale Phasengrenzreaktion R3 beschrieben. Dabei wurde ein ungewöhnlicher Einfluß des athmosphärischen Wasserdampfdruckes auf die Dehydratationsgesch windigkeit beobachtet: mit steigendem Wasserdampfdruck wächst die Geschwindigkeit zunächst ebenfalls an, durchquert ein Maximum und sinkt dann nach und nach auf einen konstanten Wert ab. Diese Erscheinung ähnelt dem Smith-Topley-Effekt. Der Mechanismus dieser Erscheinung kann auf der Grundlage der Kristallinität der dehydratierten Produktephase diskutiert werden.
    Notes: Abstract The kinetics of the thermal dehydration of yttrium formate dihydrate was studied by means of isothermal gravimetry under various water vapour pressures from 5×10−4 to 8 torr. On the whole, the dehydration was described as the three dimensional phase boundary reaction, R3. An unusual dependence of the rate of dehydration on the atmospheric water vapour pressure was observed: with increasing water vapour pressure, the rate increased at first, passed through a maximum, and then decreased gradually to a constant value. These phenomena were similar to the Smith-Topley effect. The mechanism of the phenomena can be described on the basis of the crystallinity of the dehydrated product phase.
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    Flash calcination of kaolinite studied by DSC, TG and MAS NMR (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 2053-2065 
    Details
    ISSN: 1572-8943
    Keywords: calcination ; high temperature reactions ; kaolinite ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Strukturelle Veränderungen bei der Dehydroxylierung von Kaolinit wurden durch die Anwendung einer Blitz-Kalzination untersucht, um kinetisch eingefrorene Kalzinationsprodukte zu erhalten. Der Prozentsatz der Dehydroxylierung wurde durch Veränderung der Verweilzeit im Ofen, durch Ofentemperatur und/oder Heizgeschwindigkeit modifiziert. Diese Kalzinationsbedingungen beeinflußten zwar die Reaktionskinetik, aber die Produkte hingen nur vom Ausmaß der Dehydroxylierung ab. Abweichungen bei Lage und Enthalpie der endothermen Umwandlung zu Metakaolinit und die exotherme Hochtemperaturreaktion von Metakaolinit wurden mittels DSC der Blitz-Kalzinationsprodukte verfolgt und in Beziehung zur Thermogravimetrie gebracht. 27Al Magic-Angle-Spinning NMR Spektren bei hohen magnetischen Feldstärken und Drehgeschwindigkeiten erlauben es, die Reaktion von Kaolinit zu verfolgen und liefern neue Informationen über die Natur der bei der Dehydroxylierung gebildeten Substanzen.
    Notes: Abstract The structural changes occurring during the dehydroxylation of kaolinite have been followed using flash calcination to produce kinetically frozen calcines. The percentage of dehydroxylation was varied by changing the furnace residence time or temperature and/or heating speed. These calcination conditions affected the reaction kinetics, but the products depended only on the extent of dehydroxylation. Changes in the position and enthalpy of the endothermic transformation to metakaolinite and the high temperature exothermic reaction of metakaolinite have been followed using Differential Scanning Calorimetry of the flash calcines and related to Thermogravimetry. 27Al magic-angle-spinning NMR spectra, at high magnetic fields and spin rates, enabled the reaction of kaolinite to be monitored and provides new information on the nature of the species formed in the course of dehydration.
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    Simultaneous thermal analyses for thermal dissociation studies on ZrO2 (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 2129-2135 
    Details
    ISSN: 1572-8943
    Keywords: kinetics ; thermal dissociation ; ZrO2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Im Temperaturintervall von 300 K bis 2670 K wurde im Hochvakuum und bei verschiedenen Aufheizgeschwindigkeiten das thermische Verhalten von Zirkoniumoxid ZrO2 untersucht. Die Experimente wurden mit Hilfe eines schweizer Universal Mettler Thermoanalysators, ausgerüstet mit einem SHT Super-Hochtemperatur-Ofen, ausgeführt. Flüchtige Produkte wurden simultan dazu mit einem Massenspektrometer QMG-101 der Balzers-Company analysiert. Die Auswertung der durch aufgezeichneten TG-, DTG-, DTA- und EGA-Kurven zeigt den komplexen Charakter des untersuchten Prozesses. Die Elementarschritte der Gesamtreaktion wurden definiert und berücksichtigt. Weiterhin wurde der Mechanismus der Thermodissoziation von ZrO2 auch in Abhängigkeit von der Aufheizgeschwindigkeit diskutiert.
    Notes: Abstract The behaviour of zirconium oxide ZrO2 during its heating in the temperature range 300–2670 K under high-vacuum conditions and at different heating rates has been studied. The experiments were performed with a Swiss made Universal Mettler thermoanalyser equipped with a super-high-temperature furnace SHT. Volatile products were analyzed simultaneously by means of a Balzers QMG-101 mass spectrometer. An analysis of the TG, DTG, DTA and EGA curves recorded simultaneously has shown the complex character of the studied process. The elementary steps of the overall process were defined and taken into consideration. The mechanism of the thermal dissociation reaction of ZrO2 as function of the hearing rate was discussed too.
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    Lattice energy of organic ionic crystals and its importance in analysis of features, behaviour and reactivity of solid-state systems (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 2195-2210 
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    ISSN: 1572-8943
    Keywords: kinetics ; lattice energy ; solid-state systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wird eine allgemeine Methode zur theoretischen Ableitung der Kristallgitterenergie von ionischen Verbindungen, insbesondere von Verbindungen mit einatomigen Ionen beschrieben. Anschließend werden die Möglichkeiten einer theoretischen Voraussage der Gitterenergie komplexer organischer und anorganischer Ionenverbindungen diskutiert. Zuletzt wird die Bedeutung der Gitterenergie bei der Untersuchung der Eigenschaften und des Verhaltens von Feststoffsystemen im Zusammenhang mit der Aussicht auf die Entwicklung eines Modelles zur Beschreibung der Kinetik von Feststoffprozessen gezeigt.
    Notes: Abstract A general approach to the theoretical evaluation of the crystal lattice energy of ionic substances, particularly those composed of monoatomic ions, is outlined in detail. Subsequently, the possibilities of theoretical prediction of the lattice energy of complex organic and inorganic ionic substances are discussed. Lastly, the importance of the lattice energy in examinations of the properties and behaviour of solid-state systems, is treated, together with the prospects of developing a model describing the kinetics of solid-state processes.
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    Zersetzung von Phosphor-Rohrstoffen durch Säuren (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 1683-1690 
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    ISSN: 1572-8943
    Keywords: kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Auf Grund der bestimmten thermokinetischen Kurven der Zersetzung von Phosphor-Rohstoffen mit Säuren wurde die Abhängigkeit des Umwandlunsgrades der einzelnen Reagenten von solchen Faktoren wie Zeit, Enthalpie u. konstante Zerlegungeschwindigkeit bestimmt.
    Notes: Abstract On the basis of the thermokinetic curves of the phosphor deposits with acids the dependence of the conversion degree upon the time, the enthalpy and the reaction rate constant were determined.
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    Role of heat and gas transport processes in thermal analysis (1992)
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    Journal of thermal analysis and calorimetry 38 (1992), S. 197-211 
    Details
    ISSN: 1572-8943
    Keywords: gas/heat transport ; kinetics ; quasi static-methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Beim Verlauf von Feststoffreaktionen spielen Wärme- und Gastransport eine wesentliche Rolle. Eine Standardisierung der experimentellen Bedingungen wäre deshalb erforderlich, was jedoch bisher nur bezüglich der Erarbeitung von Simultantechniken gelang. Au\erdem sind diese beiden Transportprozesse dafür verantwortlich, da\ man ausgehend von nichtisothermen Kurven keine kinetischen Parameter berechnen kenn. Quasistatische Methoden scheinen geeignet zu sein, um den störenden Einflu\ dieser Transportprozesse zu eliminieren.
    Notes: Abstract In the course of solid phase reactions heat and gas transport processes play a dominant role. Therefore, it would be necessary to standardize the experimental conditions which succeeded only in part with the elaboration of the simultaneous techniques. Likewise the two transport processes are responsible for the fact that on the basis of non-isothermal curves one cannot calculate kinetic parameters of the reactions. The quasi static-methods seem to be suitable for the elimination of the pernicious effect of these transport processes.
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    Derivatographic investigations of polycarbonates (1992)
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    Journal of thermal analysis and calorimetry 38 (1992), S. 2211-2219 
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    ISSN: 1572-8943
    Keywords: kinetics ; polycarbonates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Derivatographische, nichtisotherme Untersuchungen der Zersetzung von Polycarbonaten in Luft liefern nutzbringende Informationen über die charakteristischen Zersetzungstemperaturen und die scheinbaren Aktivierungsenergien der untersuchten Zersetzungsschritte. Dabei wurde folgende Reihenfolge der scheinbaren Aktivierungsenergie der Pyrolyseschritte beobachtet: PC-M PC-C PC-A. Wegen der Abschirmung der Esterketten durch ortho-Methylsubstituenten sind die Werte E für PC-M am höchsten.
    Notes: Abstract Derivatographic non-isothermal investigations of the decomposition of PC in air provide useful information on the characteristic decomposition temperatures and the apparent activation energies of the observed steps of decomposition. The following sequence of apparent activation energies of the pyrolysis step was obtained: PC-M〉PC-C〉PC-A. The values ofE for PC-M are the highest, due to shielding of the ester linkages by the ortho-methyl substituents.
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    Kinetics of isothermal decomposition of γ-irradiated and unirradiated Co(II) succinato complex (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 2377-2383 
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    ISSN: 1572-8943
    Keywords: Co(II) succinate complex ; isothermal decomposition ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Unter Anwendung von isothermen und dynamischen thermogravimetrischen Methoden wurde eine kinetische Untersuchung der Dehydratation und der Zersetzung von γ-bestrahltem und unbestrahltem Na2[Co(C4H4O4)2]·7H2O durchgeführt. Die thermische Dehydratation erfolgt in einem Schritt, bestimmt durch ein Random-Keimbildungsmodell (A3), während die Zersetzung der wasserfreien Salze durch ein phasengrenzenkontrolliertes Modell bestimmt wird (R3). Die bei drei Aufheizgeschwindigkeiten erhaltenen kinetischen Parameter stehen in guter Übereinstimmung; jedoch weichen die isotherm geschätzten kinetischen Parameter etwas von den dynamisch ermittelten ab. Bestrahlung mehrt sowohl die Dehydratations- als auch die Zersetzungsreaktionen, beläßt deren Mechanismus jedoch unverändert. Die Aktivierungsenergie sinkt mit zunehmender Strahlungsdosis.
    Notes: Abstract A kinetic study of the dehydration and decomposition of γ-irradiated and unirradiated Na2[Co(C4H4O4)2]·7H2O has been studied using isothermal and dynamic thermogravimetric methods. The thermal dehydration occurs in one step regulated by a random nucleation model (A3), while the decomposition of anhydrous salt is controlled by a phase boundary controlled model (R3). The kinetic parameters obtained at three heating rates are in good agreement; however, the values of the kinetic parameters estimated isothermally are slightly different from those estimated dynamically. Irradiation enhanced both the dehydration and the decomposition reactions but did not modify their mechanisms. The activation energy decreases as the irradiation dose increases.
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    On the fractional conversion α in the kinetic description of solid-state reactions (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 2553-2557 
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    ISSN: 1572-8943
    Keywords: kinetics ; solid-state reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract For the kinetic description of the solid-state reactions, the dependence of the apparent kinetic parameters on the sample mass and/or particle size is discussed mathematically in relation to some problems on the fractional conversion a. As for the reaction proceeding according to the contracting geometry model, the use of the specific rate constant, independent of the sample mass and particle size, is recommended to obtain the sample mass-independent Arrhenius parameters. It is also pointed out that the distribution of α within the assembly of sample particles disturbs the successful use of α in the kinetic description of the solid-state reactions.
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    Kinetic study of surface nucleated MgO-CaO-Al2O3-SiO2 glasses (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 2639-2647 
    Details
    ISSN: 1572-8943
    Keywords: kinetics ; MgO-CaO-Al2O3-SiO2 glasses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Vorliegende Arbeit untersucht mittels thermoanalytischen Untersuchungen die Berechtigung von drei verschiedenen Methoden zur Ermittlung der Aktivierungsenergie der Kristallisation bei Gläsern mit Oberflächen-Kristallisationskeimen im System MgO-CaO-Al2O3-SiO2, wobei Anorthit- und Diopsidkristalle ausgeschieden werden. Die anhand der Kissinger-Gleichung erhaltenen Werte für die Aktivierungsenergie der Kristallisation sind vergleichbar mit denen, die von anderen Autoren für ähnliche Glassysteme erhalten wurden: 90–150 kcal/mol. Die Ergebnisse der kinetischen Analyse mittels der Einfach-Kristallisationspeak Methode sollten korrigiert werden, indem man die Dimensionalität des Kristallwachstums berücksichtigt.
    Notes: Abstract The paper investigated, by means of thermal analysis measurements, the validity of three different methods for the evaluation of the activation energy of crystallization for surface nucleated glasses belonging to the MgO-CaO-Al2O3-SiO2 system, separating anorthite and diopside crystals. The values obtained from Kissinger equation of the activation energy for crystallization are comparable with those obtained by other authors for similar glassy systems, 90 to 150 kcal/mol. The results of the kinetic analysis using single-crystallization-peak method should be corrected taking into account the dimensionality of crystal growth.
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    Thermal analysis and kinetic study of decomposition processes of some pesticides (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 2669-2682 
    Details
    ISSN: 1572-8943
    Keywords: kinetics ; pesticides ; thermodynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels simultanen TG-DSC-Messungen und kinetischen Berechnungen bei der DTG-Technik wurde eine thermische Analyse einiger Pestizide durchgeführt. Mit dieser Methode wurde versucht, Verbindungen mit ähnlichen Strukturen anhand der Form und Anzahl von Peaks ihrer thermoanalytischen Kurven zu gruppieren und ihre Eigenschaften mittels thermodynamischen und kinetischen Mengen zu charakterisieren. Geringe Änderungen in der Struktur der Komponenten einer Klasse verursachen größere Veränderungen der thermodynamischen und kinetischen Größen, was in enger Übereinstimmung mit den beobachteten Unterschieden ihrer biologischen Aktivität steht.
    Notes: Abstract The thermal analysis of some pesticides using simultaneous TG-DSC measurements and kinetic calculations by the dynamic TG technique have been carried out. With this technique it was attempted to group compounds with similar structures according to the shape and number of peaks of their thermoanalytical curves and to characterize their features by means of thermodynamic and kinetic quantities. Small variations in the structure of the components of a class make larger variations in the thermodynamic and kinetic values being in close agreement with the observed differences in their biological behaviour.
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    The thermal degradation kinetics of poly(chlorethylmethacrylates) (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 267-275 
    Details
    ISSN: 1572-8943
    Keywords: kinetics ; poly(chlorethyl methacrylates)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels TG wurde in Gegenwart und in Abwesenheit von Sauerstoff die Kinetik des thermischen Abbaues von Poly(2-mono, 2,2-di- und 2,2,2-trichlorethylmethacrylat) und des nichtchlorierten Poly(ethylmethacrylat) untersucht. Die mit der Flynn-Wall Methode bestimmte Gesamtenergie des thermischen Abbaues steigt mit wachsendem Chlorgehalt des Polymers, wenn der Abbau ohne Sauerstoff erfolgt. In Gegenwart von Sauerstoff wird dieser Trend genau umgekehrt. Mittels DTG konnten die zwei wichtigsten nichtoxidativen Thermolysereaktionen, Depolymerisierung und Vernetzung, als kompetitive Reaktionen nachgewiesen werden. Ganz allgemein wird die thermische Stabilität der untersuchten Polymere durch Sauerstoff herabgesetzt.
    Notes: Abstract The thermal degradation kinetics of poly(2-mono-, 2,2-di- and 2,2,2-trichlorethyl methacrylate) and of the non-chlorinated poly(ethyl methacrylate) were studied by TG in the absence and presence of oxygen. The overall thermal degradation energy, determined by the Flynn-Wall method, increases with increasing chlorine content of the polymer when the degradation is performed in the absence of oxygen, while the trend is reversed in the presence of oxygen. Competition between the two major non-oxidative thermolysis reactions, depolymerization and crosslinking, could be monitored by DTG. Generally, the thermal stability of the investigated polymers is reduced by oxygen.
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    High-speed versatile device for investigating thermal decomposition processes (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 391-396 
    Details
    ISSN: 1572-8943
    Keywords: intensive heating and cooling method and technique ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wird eine neue Methode und ein neues Verfahren von thermoanalytischen Versuchen zur Untersuchung thermischer Zersetzungsprozesse sowie auch zur Bestimmung kinetischer und thermophysikalischer Eigenschaften von Feststoffen und Flüssigkeiten bei intensivem Erhitzen oder Abkühlen beschrieben.
    Notes: Abstract A new method and technique of TA-experiment are suggested for investigating thermal decomposition processes, as well as for determining kinetic and thermophysical characteristics of solid and liquid substances under conditions of intensive heating or cooling.
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    A kinetic study of water evolution from a molten hydrated salt (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 421-428 
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    ISSN: 1572-8943
    Keywords: kinetics ; meso lithium potassium tartrate dihydrate ; molten hydrated salt
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Meso-Lithiumkaliumtartrat-Dihydrat schmilzt noch vor der Dehydratation, eine kinetische Untersuchung dieser Reaktion wurde vollzogen. Dieses System ist interessant für die Abschätzung kinetischer Parameter von Prozessen mit gleichbleibender Geschwindigkeit ohne Gegenwart zugesetzter Lösungsmittel. Die Ergebnisse sind von Interesse bei überlegungen zu Mechanismen von Feststoffreaktionen oder Reaktionen im kondensierten Zustand, bei denen Schmelzen als Möglichkeit auftritt. Die Freisetzung der ersten 1.2 H2O aus den Einkristall-Dihydratreaktanden ist eine Reaktion nullter Ordnung, anschlie\end wird die Geschwindigkeit verlangsamt und unterliegt bis 1.6 H2O einem Ausdruck erster Ordnung. Der Vorgang weist eine hohe Aktivierungsenergie auf: 23010 kJ/mol (bei 350–380 K). Die Freisetzung des restlichen Wassers erfolgt in einer langsameren Reaktion erster Ordnung, man erhält das wasserfreie Salz. Die Dehydratation von zerkleinerten pulverisierten Reaktanden verlief anfangs relativ schneller, verlangsamt dann jedoch ganz und gar und unterliegt einer ersten Reaktionsordnung. Es wird geschlu\folgert, da\ die Dehydratation des Salzes durch die Freisetzungsgeschwindigkeit des Wassers an der Oberfläche kontrolliert wird, wobei das Wasser innerhalb der Reaktionsschmelze relativ beweglich ist.
    Notes: Abstract Meso lithium potassium tartrate dihydrate melted before dehydration and a kinetic study of this reaction has been completed. This system is of interest in establishing the kinetic characteristics of a homogeneous rate process in the absence of added solvent. Results are of interest in considering the mechanisms of solid or condensed state reactions where melting is a possibility. The evolution of the initial 1.2H2O from the single crystal dihydrate reactants was zero order, the rate then became deceleratory and the first order expression was obeyed to 1.6H2O. The activation energy of the process was high, 230±10 kJ mol−1 (350–380 K). Evolution of the remaining water occurred by a slower first-order process to give the anhydrous salt. The dehydration of crushed powder reactant was initially relatively more rapid but was deceleratory throughout, obeying the first order equation. It is concluded that salt dehydration is controlled by the rate of surface release of water that is comparatively mobile within the reactant melt.
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    Significance of the kinetics of thermal decomposition of NaHCO3 evaluated by thermal analysis (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 429-435 
    Details
    ISSN: 1572-8943
    Keywords: compensation effect ; experimental conditions ; kinetics ; NaHCO3 ; thermal decomposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels TG wurden sowohl bei konstanter als auch bei linear ansteigender Temperatur die Arrheniusschen Konstanten und das Kinetikgesetz der thermischen Zersetzung von Natriumhydrogencarbonat bestimmt. Dabei wurde der Einflu\ der Probengrö\e (0.5–10mg) und der Partikelgrö\e auf das Geschwindigkeitsverhalten untersucht. Mit Proben kleiner als etwa 5 mg ist der Einflu\ der Aufheizgeschwindigkeit nicht so gro\, wie bei grö\eren Proben. Die ermittelten Arrheniusschen Parameter und das ermittelte Kinetikgesetz, bestimmt mittels der Methode von Ozawa, stehen in ausgezeichneter übereinstimmung mit den isotherm ermittelten Resultaten. Die Aktivierungsenergie E bei einer Probe mit einer Masse von etwa 1 mg war nahezu konstant, unabhängig vom Reaktionsgrad. Jede änderung des Arrheniusschen Parameters infolge von veränderten Versuchsbedingungen wurde in Verbindung mit dem kinetischen Kompensationseffekt diskutiert.
    Notes: Abstract The Arrhenius parameters and kinetic obedience were determined by TG at constant temperatures as well as at linearly increasing temperatures for the thermal decomposition of sodium hydrogencarbonate. Effects of the sample size (0.5–10 mg) and the particle size on the rate behavior were examined. With such a sample size smaller than ca. 5 mg, an effect of the heating rate was not so critical as is the case with the larger sample size. The Arrhenius parameters and kinetic obedience determined by use of the Ozawa method were in excellent agreement with those determined isothermally. The activation energyE determined with ca. 1 mg of sample was nearly constant independently of the fractional reactiona. Any change in the Arrhenius parameters with different experimental conditions was dicussed in connection with the kinetic compensation effect.
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    Factors affecting the experimentally resolved shapes of TG curves (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 575-582 
    Details
    ISSN: 1572-8943
    Keywords: kinetics ; shapes of TG curves
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Unter theoretischen Aspekten bezüglich derjenigen Faktoren, die die experimentelle Auflösung thermogravimetrischer Kurven beeinflussen, wird ein möglicher Weg zur Steigerung der Genauigkeit thermogravimetrischer Untersuchungen diskutiert.
    Notes: Abstract From a theoretical consideration concerning the factors affecting the experimentally resolved shapes of thermogravimetric curves, the possible way to increase the accuracy of the thermogravimetric measurements were discussed.
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    Modelling of diffusion-controlled solid-solid reactions (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 935-941 
    Details
    ISSN: 1572-8943
    Keywords: kinetics ; solid-solid reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wird ein Modell zur Beschreibung des einleitenden Schrittes von diffusionskontrollierten Feststoffreaktionen beschrieben. Die erhaltene kinetische Gleichung wurde zur Bestimmung der Aktivierungsenergie der Reaktion LiCl(s) + NaF(s)=LiF(s) + NaCl(s) aus DTA-Daten angewendet.
    Notes: Abstract A model describing the initial step of diffusion-controlled solid-solid reactions is presented. The kinetic equation obtained was used to evaluate the activation energy of the reaction LiCl(s)+NaF(s)=LiF(s)+NaCl(s) from DTA data.
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    URL: http://dx.doi.org/10.1007/BF01979426
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    A comparison of some integral methods (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 929-933 
    Details
    ISSN: 1572-8943
    Keywords: integral methods ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Integrationsmethoden zur Berechnung kinetischer Parameter von heterogenen Reaktionen unter nicht isothermen Bedingungen werden im allgemeinen nach der Methode der kleinsten Quadrate erarbeitet und der ermittelte Korrelationskoeffizient dient als ein Kriterium für die Auswahl der besten Integrationsmethode. Mittels drei verschiedenen Integrationsmethoden wurde eine Analyse verschiedener experimenteller Daten durchgeführt. Die Ergebnisse zeigen, daß dieses Kriterium allein nicht ausreicht, um ausreichende Informationen über die kinetischen Parameter zu liefern. Es scheint deshalb, daß die Verwendung der einen oder anderen Integrationsmethode einfach eine Wahl des Anwenders darstellt.
    Notes: Abstract The integral methods proposed to compute the kinetic parameters of heterogeneous reactions under non-isothermal conditions are usually worked by the help of the least squares method and the obtained correlation coefficient is taken as a criterion to choose the best integral method. An analysis of several experimental data by mean of three different integral methods was performed by us and the results pointed out that this criterion, by itself, is not enough to provide reliable information on the kinetic parameters. It appears, thus, that the use of an integral method or another is a simple matter of researcher's choice.
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    URL: http://dx.doi.org/10.1007/BF01979425
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    The thermal degradation kinetics of poly(di-n-alkylitaconates) (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 953-959 
    Details
    ISSN: 1572-8943
    Keywords: kinetics ; poly(di-n-alkyl itaconates) ; thermal stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels nichtisothermer und auch isothermer TG wurde die nichtoxidative thermische Zersetzungskinetik von Poly(di-n-alkylitakonaten) untersucht, dabei bewegt sich die Länge der Alkylkette von Methyl bisn-Oktyl. Die Aktivierungsenergie der thermischen Zersetzung und die charakteristischen Masseverlusttemperaturen nehmen mit steigender Substituentlänge ab. Aussehen der DTG-Kurven hängt von der Größe der Alkylkette ab. Die verschiedenen DTG-Maxima wurden verschiedenen Initiierungs schritten der Depolymerisierung zugeschrieben. Man fand, daß im Intervall Mw zwischen 104 und 107 g·mol die thermische Stabilität der Poly(di-n-hexylitakonate) unabhängig von der anfänglichen molaren Masse der Probe ist.
    Notes: Abstract The non-oxidative thermal degradation kinetics of poly(di-n-alkyl itaconates), ranging from the methyl to then-octyl derivatives, were studied by non-isothermal and isothermal TG. The thermal degradation activation energy and characteristic mass loss temperatures were found to decrease with increasing substituent size. The shapes of the DTG curves were dependent on the size of the alkyl substituent. The different DTG maxima were ascribed to various modes of initiation of depolymerisation. The thermal stability of poly(di-n-hexyl itaconate) was found to be independent of the initial molar mass of the sample in the range ofM w from 104 to 107 g/mol.
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    Rapid thermal analysis of processes of thermal decomposition of mineral salts (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 981-988 
    Details
    ISSN: 1572-8943
    Keywords: kinetics ; mineral salts ; rapid TA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Für thermische Zersetzung und Synthese von Mineralsalzen wurden die kinetischen Kurven unter den Bedingungen schnellen Aufheizens in Annäherung der Aufheizbedingungen in einem Niedertemperatur-Plasmastrom ermittelt. Die kinetischen Eigenschaften wurden zur Berechnung der Umwandlungen bei einem chemischen Plasmareaktor verwendet.
    Notes: Abstract Kinetic curves of thermal decomposition and synthesis of mineral salts are obtained in the conditions of rapid heating approaching the heating conditions in a low-temperature plasma flow. The kinetic characteristics are used in calculations of transformations in the path of a chemical plasma reactor.
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    Different kinetic equations analysis (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 1509-1524 
    Details
    ISSN: 1572-8943
    Keywords: kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Cu(II)-komplexe von Acenaphthoquinonmono-(4-methyl-quinolinyl)-hydrazon (AMH) der allgemeinen Zusammensetzung [CuLX2] (mitL=AMH;X=Cl, Br, I, OAc oder NO3) -ausgenommen die Sulfato-komplexe, die über die allgemeine Zusammensetzung [CuLSO4]2 verfügen — wurden hergestellt und mittels Elementaranalyse, Messungen des magnetischen Momentes, Leitfähigkeitsmessungen, IR, elektronen- und EPR-spektroskopischen Techniken und durch Thermoanalyse untersucht. Für alle Komplexe wurde eine planare Geometrie gefunden. Die TG-Kurven zeigen, daß die Komplexe in einem Schritt zersetzt werden, wobei am Ende dieses Schrittes CU2O gebildet wird.
    Notes: Abstract A software is described enabling kinetic analysis under non-isothermal or isothermal conditions from DSC, or from TG data. The program offers thirteen methods of kinetic analysis for DSC, three for isothermal analysis and two for TG, with eight different functions for the choice of the proper mechanism for each of them.
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    Computer simulation of thermal analysis in heat-flux DSC applied to metal solidification (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 1949-1957 
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    ISSN: 1572-8943
    Keywords: alloys ; heat-flux differential scanning calorimetry ; kinetics ; metals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wird ein allgemeine mathematische Behandlung von Wärmefluß-DSC gegeben. Es verbindet Gleichungen für den Wärmetransport in der Kalorimeterzelle mit einer Annäherung der Verfestigung von Metall oder Legierung, die in diesem Gerätetyp durchgeführt werden. Es werden die Unterschiede zwischen: Temperaturevolution, Kinetik latenter Wärme und Unterkühlungsevolution innerhalb der Probe und zwischen: Temperaturevolution, aufgezeichnetes Signal und gemessene Unterkühlung an der Monitorstation diskutiert.
    Notes: Abstract A general mathematical treatment for heat-flux differential scanning calorimetry is given. It combines equations derived for heat transfer in the calorimeter cell with an approach to the solidification of metal or alloy carried out in this type of instrument. The differences are discussed between temperature evolution, kinetics of latent heat and undercooling evolution within the sample, and temperature evolution, recorded signal and measured undercooling at the monitoring station.
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    URL: http://dx.doi.org/10.1007/BF01979604
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    Flow-microcalorimetric determination of enzymatic activities of the Trichoderma viridae-cellulase complex (1992)
    Springer
    Journal of thermal analysis and calorimetry 38 (1992), S. 1979-1988 
    Details
    ISSN: 1572-8943
    Keywords: cellulase complex ; enzymatic activities ; flow-microcalorimetryl ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wird eine Methode zur Bestimmung der enzymatischen Aktivität des Trichoderma viridae Zellulase Komplexes beschrieben. Dazu wurde ein LKB 2277 Thermoaktivitätsmonitor und ein kontinuierlicher Flüsigkeitsmischer verwendet. Bei der Bestimmung der enzymatischen Aktivität von Proben des rohen Zellulasekomplexes wurden drei Substanzen verwendet: Zellobiose, Karboxymethylzellulose (CMC) und Hemizellulose. Anhand der Ergebnisse wurden einige kinetische Parameter für die Zellobiaseaktivität ermittelt. Außerdem wurde eine Endprodukt-Inhibition von Zellobiase sowie Karboxymethylzellulaseaktivität durch Glukose beobachtet. Das beschriebene Verfahren erlaubt eine direkte Bestimmung der verschiedenen Enzymaktivitäten des Zellulasekomplexes. Wegen ihrer hohen Empfindlichkeit und Einfachheit handelt es sich hier um ein sehr nützliches Werkzeug zur Untersuchung des Zellulasekomplexes, indem die optimalen Bedingungen für die enzymatische Spaltung zelluloser Substanzen bestimmt und verschiedene Mechanismen von Feedback-Kontrolle durch die Produkte der Enzymtätigkeit beobachtet werden. Das Verfahren trägt vollkommen allgemeinen Charakter und kann auch bei anderen Ezymsystemen Anwendung finden.
    Notes: Abstract A method for measuring enzymatic activities of the Trichoderma viridae cellulase complex is described. The LKB 2277 Thermal activity monitor and a flow-mix mode were used. Enzymatic activities of samples of a crude cellulose complex have been determined using three substrates: cellobiose, carboxymethyl cellulose (CMC) and xylan. Some kinetic constants for cellobiase activity have been evaluated from the obtained results. A process of the end-product inhibition of cellobiase resp. carboxymethyl cellulase activity by glucose has been observed too. The described method allows a direct determination of various enzymatic activities of the cellulase complex. Because of the high sensitivity and the simplicity, the method is a very suitable tool for studying the cellulase complex, determining the optimal conditions of enzymatic break-down of the cellulosic materials and observing various mechanisms of the feed-back control by products of enzymatic action. The procedure is completely general in nature and is applicable to other enzymatic systems.
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    URL: http://dx.doi.org/10.1007/BF01979607
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    Gamma-radiation effects on the reduction of hematite to iron in the graphite-iron(III) oxide system (1993)
    Springer
    Journal of thermal analysis and calorimetry 39 (1993), S. 87-95 
    Details
    ISSN: 1572-8943
    Keywords: gamma radiation effects ; graphite-hematite system ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    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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    Isothermal DSC investigation of the kinetics of thermooxidative decomposition of some edible oils (1993)
    Springer
    Journal of thermal analysis and calorimetry 39 (1993), S. 217-220 
    Details
    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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    URL: http://dx.doi.org/10.1007/BF01981734
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    Study on curing of novolac epoxy resin (1993)
    Springer
    Journal of thermal analysis and calorimetry 39 (1993), S. 351-358 
    Details
    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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    Comparative studies on species-specific reactivity between renin and angiotensinogen (1994)
    Springer
    Molecular and cellular biochemistry 131 (1994), S. 43-47 
    Details
    ISSN: 1573-4919
    Keywords: angiotensinogen ; kinetics ; recombinant protein ; renin ; species specificity ; transgenic mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The renin-angiotensin system (RAS) is the most important regulator of electrolyte homeostasis and blood pressure. Our recently generated transgenic mice carrying either the human renin (hREN) or human angiotensinogen (hANG) genes did not develop hypertension but dual gene strains obtained by cross-mating separate lines of mice exhibited a chronically sustained increase in blood pressure, suggesting the presence of species-specific reactivity between renin and angiotensinogen. In order to examine this specificity, the present study was designed to perform a strictly comparative study on hydrolysis of hANG by hREN and mouse submandibular renin (mREN)in vitro by using pure proteins. The recombinant hANG (rhANG) and the synthetic human-type tridecapeptide (hTDP), Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Val-Ile-His, corresponding to the N-terminal sequences of hANG, were used to determine the species specificity of recombinant hREN (rhREN) and mREN. While hTDP was cleaved by both rhREN with similar Km and with the same order of kcat, rhANG was cleaved by mREN with 16.7-fold higher Km and with 28.2-fold lower kcat than by rhREN. These results showed that kcat/Km value of mREN for rhANG was 468-fold lower than that for rhREN acting on rhANG.
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    Oxide particles in Ag-Mg alloys formed by internal oxidation (1992)
    Springer
    Oxidation of metals 37 (1992), S. 65-80 
    Details
    ISSN: 1573-4889
    Keywords: internal oxidation ; kinetics ; alloys ; silver ; oxide particles ; coalescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Gravimetric measurements at low temperatures (〈600°C) and for dilute Ag-Mg alloys have given further information about the mechanism of oxide formation. This investigation shows that the fixation rate of oxygen is very high, which assumes the existence of species in an oxidized form, including one or two magnesium atoms called “elementary species” and denoted as MgO* and Mg2O*. When there are no free magnesium atoms, there is a coalescence process with the fixation of oxygen atoms or MgO* and Mg2O*: this process leads to the formation of the first “clusters” including an oxygen excess. At low temperatures, the thermal fluctuations do not permit significant changes. There is no significant increase in cluster size, but a rearrangement of these clusters toward a compact structure with the release of excess oxygen. Their size is less than 1 nm.
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    High-temperature oxidation of zirconium-hydride powders (1992)
    Springer
    Oxidation of metals 38 (1992), S. 89-98 
    Details
    ISSN: 1573-4889
    Keywords: kinetics ; oxidation ; zirconium hydride
    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 kinetics of zirconium-hydride powders were studied in the temperature range of 298–1378 in air at atmospheric pressure. TG, DTA, DSC, x-ray analysis, and scanning electron microscopy were used. The results obtained are in accordance with the proposed pseudo-parabolic model of zirconium-hydride oxidation. This model includes the initial linear mode of oxide growth with oxygen diffusion through a non-solid film of ZrO2 of variable depth and a stationary diffusion process followed by oxide sintering. It has been established that the activation energy of the limiting stage of oxidation (238.3 kJ/mol) coincides with the activation energy of oxygen self-diffusion in monocline ZrO2.
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    Variations in the kinetic response of several different phosphate-dependent glutaminase isozymes during acute metabolic acidosis (1991)
    Springer
    Molecular and cellular biochemistry 108 (1991), S. 113-123 
    Details
    ISSN: 1573-4919
    Keywords: phosphate-dependent glutaminase ; acute metabolic acidosis ; kinetics ; kidney tubules ; enterocytes ; hepatocytes ; brain tissue
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary We describe the kinetic modifications to mitochondrial-membrane-bound phosphate-dependent glutaminase in various types of rat tissue brought about by acute metabolic acidosis. The activity response of phosphate-dependent glutaminase to glutamine was sigmoidal, showing positive co-operativity, the Hill coefficients always being higher than 2. The enzyme from acidotic rats showed increased activity at subsaturating concentrations of glutamine in kidney tubules, as might be expected, but not in brain, intestine or liver tissues. Nevertheless, when brain and intestine from control rats were incubated in plasma from acutely acidotic rats enzyme activity increased at 1 mM glutamine in the same way as in kidney cortex. The enzyme from liver tissue remained unaltered. S0.5 and nH values decreased significantly in kidney tubules, enterocytes and brain slices preincubated in plasma from acidotic rats. The sigmoidal curves of phosphate-dependent glutaminase shifted to the left without any significant changes in Vmax. The similar response of phosphate-dependent glutaminase to acute acidosis in the kidney, brain and intestine confirms the fact that enzymes from these tissues are kinetically identical and reaffirms the presence of an ammoniagenic factor in plasma, either produced or concentrated in the kidneys of rats with acute acidosis.
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    Corrosion in SO2 of chromium and manganese at high temperature (1990)
    Springer
    Oxidation of metals 33 (1990), S. 279-299 
    Details
    ISSN: 1573-4889
    Keywords: corrosion SO2 ; chromium ; manganese ; kinetics ; scale analysis ; phase diagram stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The corrosion of chromium and manganese by pure SO2 has been investigated in the temperature range 890–1350 K at SO2 pressure from 0.01–0.5 atm. Both metals oxidize according to a parabolic rate law, and the scales consist of an inner region containing a mixture of oxide and sulfide (Cr2O3+ CrS or MnO and MnS) and an outer region of oxide (Cr2O3 or MnO). These two metals have similar thermodynamic behavior, and the main mechanism of reaction is considered to be the direct reaction of the metal with SO2. The results also indicate that in the absence of trace amounts of oxygen, and at sufficiently low temperature (〈950 K), the formation of Mn3O4 does not occur only if a complete description of the atmosphere generated by a SO2-O2-S2 mixture was considered.
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    Improvement of nonisothermal oxidation behavior of fe and fe-cr alloys by superficially applied reactive oxide coatings (1990)
    Springer
    Oxidation of metals 34 (1990), S. 101-121 
    Details
    ISSN: 1573-4889
    Keywords: nonisothermal oxidation ; kinetics ; iron ; iron-chromium alloys ; reactive-oxide coating
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The nonisothermal oxidation behavior of pure iron and a few iron-chromium alloys in dry air has been studied. The effects of a superficial coating of a reactive oxide, CeO2, on the oxidation behavior were studied. Linear heating rates of 3 K/min and 6 K/min were maintained up to a final temperature ranging from 1273–1473 K. Coatings were applied either from a slurry or an aqueous bath. The CeO2 coating has been found to be effective not only in decreasing the nonisothermal oxidation rate but also in improving the scale adherence. Moreover, the coated samples withstood a number of heating cycles without scale rupture. The mass gain of the samples as a function of temperature was recorded by means of a sensitive balance, and the scales have been characterized by SEM, EPMA, and x-ray diffraction analysis.
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    The internal-nitriding behavior of 310 stainless steel with and without Al and Ti additions (1990)
    Springer
    Oxidation of metals 34 (1990), S. 473-496 
    Details
    ISSN: 1573-4889
    Keywords: Internal nitriding ; 310 stainless steel ; austenitic ; kinetics ; microhardness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The internal-nitriding behavior in ammonia-hydrogen atmospheres of type-310 stainless steel and 310 to which either 2 wt.% Ti or 3 wt.% Al were added was studied over the range of 550–950°C. An Fe-24Cr binary alloy was included to assess the role of a BCC crystal structure vs the FCC crystal structure of 310 stainless steel. The BCC alloy exhibited the most rapid kinetics as expected. X-ray diffraction showed only the presence of CrN in all the alloys up to 735°C. At 850°C and above, both CrN and Cr2N were detected. The nonformation of TiN and AlN at lower temperatures is attributed to nucleation problems. Precipitates were extremely fine (unresolvable even at 20,000×) at 563°C and became much coarser with increasing temperature. The precipitate density, size, and shape varied across the internal-nitriding zone at the higher temperatures. External scaling was noted at 850°C and above, however, it was not a continuous film. The activation energy of internal nitriding from 563–735°C ranged from 3.8 kcal/mol for 310+2Ti to 18.2 kcal/mol for 310+3Al; from 850–950°C, the activation energy ranged from 44 (310+2Ti) to 56.6 kcal/mol (310+3Al). Microhardness profiles show that an intermediate zone exists between the nitride case and the base metal. The origin of this zone is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00664427
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    The high-temperature oxidation behavior of vanadium-aluminum alloys (1991)
    Springer
    Oxidation of metals 36 (1991), S. 439-464 
    Details
    ISSN: 1573-4889
    Keywords: V-A1 alloy ; Cr and Ti additions ; oxidation ; kinetics ; V2O5 ; Al2O3
    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 in air of pure vanadium, V-30Al, V-30Al-10Cr, and V-30Al-10Ti (weight percent) was investigated over the temperature range of 700–1000° C. The oxidation of pure vanadium was characterized by linear kinetics due to the formation of liquid V2O5 which dripped from the sample. The oxidation behavior of the alloys was characterized by linear and parabolic kinetics which combined to give an overall time dependence of 0.6–0.8. An empirical relationship of the form: ΔW/A=Bt + Ct1/2 + D was found to fit the data well, with the linear contribution suspected to be from V2O5 formation for V-30Al and V-30Al-10Cr, and a semi-liquid mixture of V2O5 and Al2O3 for V-30Al-10Ti. The parabolic term is presumed related to the formation of a solid mixture of V2O5 and Al2O3 for V-30Al and V-30Al-10Cr, and TiO2 for V-30Al-10Ti The addition of aluminum was found to reduce the oxidation rate of vanadium, but not to the extent predicted by the theory of competing oxide phases proposed by Wang, Gleeson, and Douglass. This was attributed to the formation of a liquid-oxide phase in the initial stages of exposure from which the alloys could not recover. Ternary additions of chromium and titanium were found to decrease the oxidation rate further, with chromium being the most effective. The oxide scales of the alloys were found to be highly porous at 900° C and 1000° C, due to the high vapor pressure of V2O5 above 800° C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01151591
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    Plasma nitriding of Fe-18Cr-9Ni in the range of 723–823 K (1991)
    Springer
    Oxidation of metals 36 (1991), S. 143-156 
    Details
    ISSN: 1573-4889
    Keywords: plasma nitriding ; Fe-18Cr-9Ni ; CrN precipitates ; nitrogen diffusion ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract To clarify the mechanism of plasma nitriding, we examined the optical microstructure, the hardness, the precipitation, and the concentration of dissolved nitrogen in Fe-18Cr-9Ni nitrided using plasma in the range of 723–823 K. Compared with ammonia-gas nitriding, the features of plasma nitriding are the formation of small chromium-nitride precipitates (CrN), the absence of an externally nitrided layer, the high concentration of dissolved nitrogen, and the high hardness (HV=1200). The diffusion coefficient of nitrogen in the present alloy was determined using the growth rate of the internally nitrided layer, based on calculations used in internal oxidation. Plasma- and gas-nitriding were also compared with respect to the growth rate of the nitrided layer.
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    URL: http://dx.doi.org/10.1007/BF00938459
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    Morphological characteristics of the oxidation of niobium II: The role of stresses on high-temperature morphologies (1994)
    Springer
    Oxidation of metals 41 (1994), S. 235-250 
    Details
    ISSN: 1573-4889
    Keywords: niobium ; oxidation ; morphology ; kinetics ; stresses
    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 of niobium at high temperature (900°C) leads to reaction products with “exotic” morphologies. Morphological and kinetics analysis have been undertaken with Nb platelets. A growth mechanism of the oxide at the edges of the platelet is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01080782
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    The effect of purity on high-temperature oxidation of zirconium (1994)
    Springer
    Oxidation of metals 42 (1994), S. 223-237 
    Details
    ISSN: 1573-4889
    Keywords: kinetics ; scale ; oxidation ; zirconium ; purity
    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 kinetics of zirconium of different purities were studied over the temperature range of 600–1300°C (α- and β-phases). The structure of the oxidized specimens was examined. TGA, XRD, EPMA, SEM, metallographic analysis, and microhardness measurements were carried out. Impurity elements were found to increase the oxidation rate of technical zirconium. The mechanism of the effect of impurity elements on zirconium oxidation was shown to differ for the α- and β-phases. Activation energies were calculated for the parabolic and linear stages of oxidation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01052024
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    The effect of purity on the high-temperature oxidation of hafnium (1994)
    Springer
    Oxidation of metals 42 (1994), S. 249-263 
    Details
    ISSN: 1573-4889
    Keywords: kinetics ; scale ; oxidation ; hafnium ; purity
    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 kinetics of hafnium of different purities were studied in the temperature range of 800–1200°C. This paper concerns the structure studies of the oxidized samples. TGA, XRD, SEM methods, and microhardness measurements were used. Hafnium oxidation follows the parabolic rate law, changing with time to the linear one. Oxidation-reaction products are HfO2(moncl) and α-solid solution of oxygen in hafnium. Anomalous oxidation behavior of hafnium having a high impurity content was found in the range 800–950°C. Activation energies for the parabolic and linear oxidation stages were calculated.
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    URL: http://dx.doi.org/10.1007/BF01052026
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    Enzymology of ADP-ribose polymer synthesis (1994)
    Springer
    Molecular and cellular biochemistry 138 (1994), S. 33-37 
    Details
    ISSN: 1573-4919
    Keywords: poly(ADP-ribose) polymerase ; structure ; chemistry ; kinetics ; automodification ; mechanism(s)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract In this minireview, we summarize recent advances on the enzymology of ADP-ribose polymer synthesis. First, a short discussion of the primary structure and cloning of poly(ADP-ribose) polymerase (PARP) [EC 2.4.2.30], the enzyme that catalyzes, the synthesis of poly(ADP-ribose), is presented. A catalytic distinction between the multiple enzymatic activities of PARP is established. The direction of ADP-ribose chain growth as well as the molecular mechanism of the automodification reaction catalyzed by PARP are described. Current approaches to dissect ADP-ribose polymer synthesis into individual reactions of initiation, elongation and branching, as well as a partial mechanistic characterization of the ADP-ribose elongation reaction at he chemical level are also presented. Finally, recent developments in the catalytic characterization of PARP by site-directed mutagensis are also briefly summarized.
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    URL: http://dx.doi.org/10.1007/BF00928440
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    On the oxidation of iron in CO2+CO mixtures: II. Reaction mechanisms during initial oxidation (1991)
    Springer
    Oxidation of metals 35 (1991), S. 107-137 
    Details
    ISSN: 1573-4889
    Keywords: iron ; oxidation in CO2+CO mixtures ; kinetics ; reaction mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Oxidation of high purity iron in CO 2 and CO2 + COmixtures at different total pressures (0.1–1 atm.) has been studied at 1000–1200°C. While paper I of this study emphasized studies of the relation between scale morphology and reaction kinetics, this paper focuses on the reaction mechanism during the initial oxidation involving growth of wüstite films and scales. The reaction behavior is analyzed in terms of coupled kinetics comprising a surface reaction and diffusional transport through the scale. A classical model derived by C. Wagner, based on the assumption that the properties and defect concentrations in the scale surface are exactly the same as in bulk wüstite equilibrated in CO 2 +CO mixtures, does not provide a satisfactory description of the reaction kinetics and the gas-pressure dependence of the surface reaction. As an alternative model, it is suggested that the gasous molecules/species interacts with the surface to form surface complexes, and that surface complexes withCO2 serve as preferred reaction sites for the surface reaction.
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    URL: http://dx.doi.org/10.1007/BF00666503
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    High-temperature oxidation of titanium-hydride powders (1990)
    Springer
    Oxidation of metals 33 (1990), S. 177-189 
    Details
    ISSN: 1573-4889
    Keywords: kinetics ; oxidation ; titanium hydride ; rutile
    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 kinetics of titanium-hydride powders were studied in the temperature range of 298–1378 K in air at atmospheric pressure. DTA, DSC, X-ray analysis, and scanning electron microscopy were used. Oxidation was found to take place by TiHxOy oxyhydride phases formation. The oxidation reaction rate at temperatures above 870 K was limited by diffusion of oxygen atoms through a rutile scale formed on the surface. The activation energy and preexponential values of the Arrhenius equation for different interaction stages as well as transformation enthalpies were calculated.
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    URL: http://dx.doi.org/10.1007/BF00665675
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    Interaction of Mn-Cu solid solutions with nitrogen in the range of 780–860° C (1991)
    Springer
    Oxidation of metals 35 (1991), S. 397-404 
    Details
    ISSN: 1573-4889
    Keywords: copper alloys ; nitridation ; kinetics ; scale structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract One of the characteristic features of Mn-Cu binary alloys nitrided by gaseous nitrogen is that one of the two constitutive elements (Mn) can form nitrides, while the other one (Cu) does not give any stable compound with nitrogen. The only mixed manganese-copper nitride is the CuMn 3 N compound. The reaction kinetics with nitrogen are very slow and there is no internal nitriding. For alloys containing less than 20 at.% Mn, nitrogen reacts very little. The nitride scale formed on the alloys of greater Mn concentrations is a mixed nitride whose formula is Cu 1−x Mn 3+x N. The techniques of examination used are SEM, EMA, and GDS analysis.
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    URL: http://dx.doi.org/10.1007/BF00664710
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    Kinetics and mechanism of high-temperature sulfidation of an Fe-23.4Cr-18.6Al Alloy in H2S-H2 atmospheres (1992)
    Springer
    Oxidation of metals 38 (1992), S. 1-32 
    Details
    ISSN: 1573-4889
    Keywords: sulfidation ; Fe-Cr-Al alloys ; kinetics ; structures ; sulfide compositions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Sulfidation of an Fe-23.4Cr-18.6Al (at.%) alloy was investigated in H2S-H2 atmospheres, $$10^{ - 6} \leqslant {\text{P}}_{{\text{S}}_{\text{2}} } \leqslant 10^2 $$ Pa, at 973 K. It was found over this pressure range that sulfidation after an early transient period followed the parabolic rate law, being diffusion controlled. An investigation was carried out of the scales formed during early transient sulfidation over the sulfur pressure range $${\text{p}}_{{\text{S}}_{\text{2}} } = 10^{ - 6} - 10^{ - 2} $$ Pa. Fully developed scales were multilayered consisting of an inner compact layer of equiaxed grains, an intermediate layer of equiaxed and columnar grains exhibiting a small degree of porosity, and an outer porous layer of distinct plates and needles. The grains of the inner and intermediate layers contained quarternary sulfide phases. The following phases were identified: spinels (CrFe)Al2S4 and (FeAl)Cr2S4, hexagonal (FeCr)Al2S4, (CrAlFe)2S3, and (CrAlFe)5S6. The plates and needles were composed of hexagonal (FeCr)Al2S4 and (CrAlFe)2S3 at $${\text{p}}_{{\text{S}}_{\text{2}} } \geqslant 10^{ - 6} $$ and 10−5 Pa from which pyrrhotite, FeS, grew at $${\text{p}}_{{\text{S}}_{\text{2}} } \geqslant 10^{ - 4} $$ .
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    URL: http://dx.doi.org/10.1007/BF00665042
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    Dependence of reaction rate of 5,5′-dithiobis-(2-nitrobenzoic acid) to free sulfhydryl groups of bovine serum albumin and ovalbumin on the protein conformations (1992)
    Springer
    The protein journal 11 (1992), S. 187-192 
    Details
    ISSN: 1573-4943
    Keywords: 5,5′-Dithiobis(2-nitrobenzoic acid) ; bovine serum albumin ; ovalbumin ; kinetics ; protein conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of protein conformations on the reaction rate of Ellman's reagent, 5,5′-dithiobis (2-nitrobenzoic acid) (DTNB) with sulfhydryl (SH) groups of proteins was examined. The stopped-flow method was applied to follow the reaction of DTNB with SH group of two proteins, bovine serum albumin (BSA) and ovalbumin (OVA), at various concentrations of guanidine hydrochloride and urea. The rates for both the proteins were faster in guanidine than in urea. The rate sharply depended on the protein conformations, which were monitored by changes of helix contents on the basis of the circular dichroism measurements. The reaction rate of DTNB with SH groups of BSA was maximal around 2 M guanidine and 5 M urea. On the other hand, the reaction rate of DTNB with OVA was maximal at 3.5 M guanidine, while it gradually increased with an increase in the urea concentration. The amount of reactive SH group participating in the reaction with DTNB was also estimated by the absorbance change at 412 nm. The magnitudes of absorbance change for the reaction with free SH groups of OVA at low concentrations of the denaturants were appreciably smaller than those for BSA with one free SH group. Most of the four SH groups of OVA might react with DTNB above 5 M guanidine, although only a part of them did even at 9 M urea.
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    URL: http://dx.doi.org/10.1007/BF01025224
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    Hemoglobins with multiple reactive sulphydryl groups: The reaction of pigeon hemoglobin with 5,5′-dithiobis (2-nitrobenzoic acid) (1993)
    Springer
    The protein journal 12 (1993), S. 639-646 
    Details
    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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    Purification and characterization of diaphorases from someDrosophila species (1992)
    Springer
    Biochemical genetics 30 (1992), S. 305-315 
    Details
    ISSN: 1573-4927
    Keywords: Drosophila ; diaphorase ; purification ; kinetics ; immunochemical characteristics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Diaphorase-1 and diaphorase-2 were isolated from twoDrosophila species,D. virilis andD. melanogaster, and purified by gel filtration, affinity chromatography, immunoaffinity chromatography, and ion-exchange chromatography. The molecular weights of both enzymes were the same in each species. The molecular weight of diaphorase-1 was the same under both denaturating and nondenaturating conditions, close to 60,000, indicating a monomeric structure. Sodium dodecyl sulfate (SDS) electrophoresis of the purified diaphorase-2 revealed the presence of a single protein band of 55,000 Da, while the molecular weight of the native enzyme was found to be 67,000. The two diaphorases were further characterized by their pH optima, isoelectric points, and kinetic parameters, and antibodies were raised in rabbits against the purified enzymes fromD. virilis. The antibodies showed no cross-reactions but recognized the corresponding diaphorases inD. melanogaster andD. novamexicana as well asD. virilis. The data obtained confirmed the hypothesis of an independent genetic control of diaphorase-1 and diaphorase-2 inDrosophila.
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    Purification and characterization of diaphorases from someDrosophila species (1992)
    Springer
    Biochemical genetics 30 (1992), S. 305-315 
    Details
    ISSN: 1573-4927
    Keywords: Drosophila ; diaphorase ; purification ; kinetics ; immunochemical characteristics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Diaphorase-1 and diaphorase-2 were isolated from twoDrosophila species,D. virilis andD. melanogaster, and purified by gel filtration, affinity chromatography, immunoaffinity chromatography, and ion-exchange chromatography. The molecular weights of both enzymes were the same in each species. The molecular weight of diaphorase-1 was the same under both denaturating and nondenaturating conditions, close to 60,000, indicating a monomeric structure. Sodium dodecyl sulfate (SDS) electrophoresis of the purified diaphorase-2 revealed the presence of a single protein band of 55,000 Da, while the molecular weight of the native enzyme was found to be 67,000. The two diaphorases were further characterized by their pH optima, isoelectric points, and kinetic parameters, and antibodies were raised in rabbits against the purified enzymes fromD. virilis. The antibodies showed no cross-reactions but recognized the corresponding diaphorases inD. melanogaster andD. novamexicana as well asD. virilis. The data obtained confirmed the hypothesis of an independent genetic control of diaphorase-1 and diaphorase-2 inDrosophila.
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    Structural stability of lipase from wheat germ in alkalinepH1 (1991)
    Springer
    The protein journal 10 (1991), S. 291-299 
    Details
    ISSN: 1573-4943
    Keywords: Lipase ; wheat germ ; inactivation ; structure-function ; kinetics ; conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The present investigation shows the effect of alkalinepH on the structure-function relationship of lipase from wheat germ. There is a 70% decrease in lipase activity atpH 10.0, which decreases to 93% atpH 12.0 as compared to neutralpH activity (Rajendranet al. 1990). This change is shown to be as a result of loss ofa-helical structure with a concomitant increase in aperiodic structure. The results with fluorescence spectra and tyrosyl ionization indicate gradual exposure of aromatic side chains of tyrosine and tryptophan to the bulk solvent along with the structural changes. The enzyme is in an extended form at alkalinepH with a volume change of -1300 ml/mol as also indicated by increase in reduced viscosity to 12.5 ml/g and significant decrease in sedimentation coefficient. The kinetics of the reaction points to a cooperative pseudo first-order reaction as determined by stopped-flow kinetic analysis in the ultraviolet region. The inactivation mechanism appears to follow a two-step mechanism of a fast and a slow reaction.
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    A two-component, non-aqueous route to silica gel (1994)
    Springer
    Journal of sol gel science and technology 2 (1994), S. 35-41 
    Details
    ISSN: 1573-4846
    Keywords: carboxylic acids ; mechanism ; kinetics ; ultrafine porosity ; CO2 adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new means for generating silica gel has been developed. Simple two component systems comprising tetraalkoxysilanes and strong carboxylic acids such as formic acid can react rapidly to give transparent monolithic gels. The acid serves as solvent, water source, and catalyst for both hydrolysis and condensation. Water need not be present as an initial reactant; it is generated in situ during the reaction. The gelation reaction is at least two orders of magnitude faster than those conducted in conventional acid-catalyzed aqueous systems at comparable pH*. Kinetic evidence indicates a lowering of the activation energy of condensation reactions, believed to be associated with reaction of silyl carboxylates and silanol groups. Physical properties of the dry gels such as bulk density more closely resemble conventional acid-catalyzed gels than those associated with other rapidly gelling systems. Dry gels often exhibit porosity so fine that nitrogen (at 77°K) is not absorbed at significant rates. Independent evidence of porosity arises from comparison of skeletal and bulk densities, sample immersion in water and adsorption isotherms of CO2.
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    Substitution of the amino acid at position 102 with polar and aromatic residues influences substrate specificity of lactate dehydrogenase (1994)
    Springer
    The protein journal 13 (1994), S. 129-133 
    Details
    ISSN: 1573-4943
    Keywords: Lactate dehydrogenase ; kinetics ; mutagenesis ; specificity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The Gin residue at amino acid position 102 ofBacillus stearothermophilus lactate dehydrogenase was replaced with Ser, Thr, Tyr, or Phe to investigate the effect on substrate recognition. The Q102S and Q102T mutant enzymes were found to have a broader range of substrate specificity (measured byk cat/K m) than the wild-type enzyme. However, it is evident that either Ser or Thr at position 102 are of a size able to accommodate a wide variety of substrates in the active site and substrate specificity appears to rely largely on size discrimination in these mutants. The Q102F and Q102Y mutant enzymes have low catalytic efficiency and do not show this relaxed substrate specificity. However, their activities are restored by the presence of an aromatic substrate. All of the enzymes have a very low catalytic efficiency with branched chain aliphatic substrates.
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    Determination of the rate of rapid lipid transfer induced by poly(ethylene glycol) using the SLM Fourier transform phase and modulation spectrofluorometer (1991)
    Springer
    Journal of fluorescence 1 (1991), S. 105-112 
    Details
    ISSN: 1573-4994
    Keywords: Phase fluorometry ; lipid exchange ; membrane fusion ; kinetics ; poly(ethylene glycol) ; diphenyl hexatrient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Rate constants were determined for the transfer of the fluorescent lipid probe 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5-hexatrienyl)phenyl]ethyl] oxy]carbonyl]-3-sn-phosphatidylcholine (DPHpPC) between large, unilamellar extrusion vesicles composed either of dipalmitoyl phosphatidylcholine (DPPC) or of DPPC mixed with a small amount (0.5 mol%) of lyso phosphatidylcholine (Lyso PC). Transfer of the lipid probe in the presence of varying concentrations of poly(ethylene glycol) (PEG) was monitored using the SLM 48000-MHF Multi-Harmonic Fourier Transform phase and modulation spectrofluorometer to collect multifrequency phase and modulation fluorescence data sets on a subsecond time scale. The unique ability of this instrument to yield accurate fluorescence lifetime data on this time scale allowed transfer to be detected in terms of a time-dependent change in the fluorescent lifetime distribution associated with the lipid-like DPHpPC probe. This probe demonstrates two short fluoresence decay times (ca. 1.1–1.4 and 4.3–4.8 ns) in a probe-rich environment but a single long lifetime (ca. 7 ns) in a probe-poor environment. A simple two-state model for initial lipid transfer was used to analyze the multifrequency data sets collected over a 4-s time frame to obtain the time rate of change of the concentrations of donor and acceptor probe populations following rapid mixing of vesicles with PEG. The ability to measure fluorescence lifetimes on this time scale has allowed us to show that the of rate of lipid transfer increased dramatically at 35% PEG in both fusing and nonfusing vesicle systems. These results are interpreted in terms of a distinct interbilayer structure associated with intimate bilayer contact induced by high and potentially fusogenic concentrations of PEG.
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    Hemoglobins with multiple reactive sulphydryl groups: The reaction of dog hemoglobin with 5,5′-dithiobis (2-nitrobenzoate) (1993)
    Springer
    The protein journal 12 (1993), S. 33-37 
    Details
    ISSN: 1573-4943
    Keywords: Hemoglobin ; sulphydryl group ; ionizable groups ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    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].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01024911
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    DEDO: A specific, fluorescent inhibitor for spectroscopic investigations of Na,K-ATPase (1994)
    Springer
    Journal of fluorescence 4 (1994), S. 287-290 
    Details
    ISSN: 1573-4994
    Keywords: Na,K-ATPase ; fluorescent inhibitor ; kinetics ; energy transfer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The interaction between the fluorescent ouabain derivative DEDO and purified renal Na,K-ATPase (isolated from different animal species) is investigated. Equilibrium binding studies provide a pK value of about 7.5 and a stoichoimetric coefficient of 1. Nonmodified ouabain exhibits the same affinity to the rabbit enzyme; the enzyme originating from the other sources binds DEDO 10 times less strongly than ouabain. Kinetic studies indicate that this is the consequence of a 10 times higher dissociation rate constant of the complexes formed with DEDO. The fluorescence emission intensity of DEDO is enhanced, being dependent on the enzyme source. The single decay time of DEDO is 3 ns in the absence and 21 ns in the presence of the rabbit enzyme and 14 ns in the presence of the pig renal enzyme. This result suggests that the fluorophore of DEDO is bound to a very hydrophobic environment of the enzyme. Further characterization of the static fluorescence spectra provides evidence for energy transfer between Trp residues of the enzyme and DEDO. Distance estimations suggest that one or two Trp residues are likely to be located in the proximity of the fluorophore.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01881441
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    Stopped-flow fluorescence studies of the interaction of a mutant form of cytochrome b5 with lipid vesicles (1994)
    Springer
    Journal of fluorescence 4 (1994), S. 227-233 
    Details
    ISSN: 1573-4994
    Keywords: Cytochrome b5 ; site-directed mutagenesis ; kinetics ; fluorescence ; membrane-binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Cytochrome b5 binds spontaneously to lipid vescles and also self-associates in aqueous solution. Two mutant proteins have been generated, one has a self-association constant which is less than that of the native protein, while the other has a larger self-association constant. All three proteins have Trp in the membrane-binding domain but as aqueous solutions of these proteins contain differing amounts of monomeric protein, the kinetics of fluorescence enhancement, when the proteins are mixed with lipid vesicles, are complex. Similar complex kinetics are seen when the Trp are quenched by the addition of bromolipid vesicles. The mutant which has Trp 108 and 112 both replaced by Leu does not self-associate and shows monoexponential stopped-flow fluorescence kinetics. Identical rate constants are seen with this mutant for fluorescence enhancement by POPC and fluorescence quenching by three bromolipids with bromines at the 6,7-, 9,10-, and 11,12-positions of thesn-2 acyl chain. This rate constant is only 1% of the calculated collisional rate constant and it is suggested that the reduced rate is caused by a reduction in the number of productive collisions rather than by a slow rate of penetration of the membrane-binding domain into the bilayer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01878455
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    Na activation delays and their relation to inactivation in frog skeletal muscle (1990)
    Springer
    The journal of membrane biology 118 (1990), S. 233-242 
    Details
    ISSN: 1432-1424
    Keywords: Na channels ; skeletal muscle ; kinetics ; chloramine-T ; electrophysiology ; current inactivation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Delays in the development of activation of Na currents were studied using voltage-clamped frog skeletal muscle fibers. Na currents elicited by a depolarizing voltage step from a hyperpolarized membrane potential were delayed in their activation when compared to Na currents elicited from the resting potential. The magnitude of the delay increased with larger hyperpolarizing potentials and decreased with larger depolarizing test potentials. Delays in activation observed following chloramine-T treatment that partially removes inactivation did not differ from delays observed before treatment. Longer exposures of the muscle fiber to chloramine-T led to a complete loss of inactivation, coincident with an elimination of the hyperpolarization-induced delays in activation. Steady-state slow inactivation was virtually unaffected by prolonged exposures of the fibers to chloramine-T that eliminated fast inactivation. The results show that chloramine-T acts at a number of sites to alter both activation and inactivation. Markov model simulations of the results show that chloramine-T alters fundamental time constants of the system by altering both activation and inactivation rate constants.
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    URL: http://dx.doi.org/10.1007/BF01868607
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    Inhibition of inward rectifying tonoplast channels by a vacuolar factor: Physiological and kinetic implications (1991)
    Springer
    The journal of membrane biology 122 (1991), S. 251-258 
    Details
    ISSN: 1432-1424
    Keywords: patch-clamp ; plant vacuole ; single-channel inhibition ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Regulation of ion-channel activity must take place in order to regulate ion transport. In case of tonoplast ion channels, this is possible on both the cytoplasmic and the vacuolar side. Isolated vacuoles of youngVigna unguiculata seedlings show no or hardly any channel activity at tonoplast potentials 〉80 mV, in the vacuole-attached configuration. When the configuration is changed to an excised patch or whole vacuole, a fast (excised patch) or slow (whole vacuole) increase of inward rectifying channel activity is seen. This increase is accompanied by a shift in the voltage-dependent gating to less hyperpolarized potentials. In the whole vacuole configuration the level of inward current increases and also the activation kinetics changes. Induction of channel activity takes up to 20 min depending on the age of the plants used and the diameter of the vacuole. On the basis of the estimated diffusion velocities, it is hypothesized that a compound with a mol wt of 20,000 to 200,000 is present in vacuoles of young seedlings, which shifts the population of channels to a less voltage-sensitive state.
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    URL: http://dx.doi.org/10.1007/BF01871425
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    Initial steps of αand β-d-glucose binding to intact red cell membrane (1993)
    Springer
    The journal of membrane biology 132 (1993), S. 167-178 
    Details
    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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    URL: http://dx.doi.org/10.1007/BF00239006
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    Characterization of ion channels from Acetabularia plasma membrane in planar lipid bilayers (1993)
    Springer
    The journal of membrane biology 133 (1993), S. 145-160 
    Details
    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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    URL: http://dx.doi.org/10.1007/BF00233795
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    Study of the mechanism of the addition of benzyl bromide to trimethylvinylsilane in the presence of the Fe(CO)5—DMF system (1993)
    Springer
    Russian chemical bulletin 42 (1993), S. 1352-1356 
    Details
    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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    URL: http://dx.doi.org/10.1007/BF00699930
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    Relative kinetics of the homolytic addition of 2-phenyl-1,3-dioxolane to unsaturated compounds (1992)
    Springer
    Russian chemical bulletin 41 (1992), S. 1289-1292 
    Details
    ISSN: 1573-9171
    Keywords: radicals ; addition ; dioxolane ; polar effect ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The CH2 = CHX olefins form a series relative to their reactivity in reactions with 2-phenyl-1,3-dioxolan-2-yl radicals, which qualitatively correlates with the electron-withdrawing capacity of substituent X: CN ≈ CO2Me 〉〉 SiMe3 ≈ C4H9. This behavior indicates that the dioxolanyl radical is nucleophilic.
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    URL: http://dx.doi.org/10.1007/BF00864202
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    The influence of the mercury and thallium atoms in organomercury and organothallium nitroxyl radicals on their reactivity (1993)
    Springer
    Russian chemical bulletin 42 (1993), S. 205-207 
    Details
    ISSN: 1573-9171
    Keywords: kinetics ; organomercury nitroxyls ; organothallium nitroxyls ; coordination bond ; hydrazobenzene ; reduction ; rate constant
    Source: Springer Online Journal Archives 1860-2000
    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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    URL: http://dx.doi.org/10.1007/BF00700013
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    Cationic polymerization of hydrocarbon monomers under the action of acyl halide complexes with Lewis acids (1993)
    Springer
    Russian chemical bulletin 42 (1993), S. 837-840 
    Details
    ISSN: 1573-9171
    Keywords: cationic polymerization ; polyisobutylene ; Lewis acids ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    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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    URL: http://dx.doi.org/10.1007/BF00698941
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    Reactions of hydrazobenzene and tetranitromethane with nitroxyl radicals (1993)
    Springer
    Russian chemical bulletin 42 (1993), S. 1027-1031 
    Details
    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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    URL: http://dx.doi.org/10.1007/BF00704192
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    Kinetics and mechanism of thermal decomposition of hydroxylammonium nitrate (1993)
    Springer
    Russian chemical bulletin 42 (1993), S. 1811-1815 
    Details
    ISSN: 1573-9171
    Keywords: hydroxylammonium nitrate ; preparation ; thermal decomposition ; kinetics ; mechanism
    Source: Springer Online Journal Archives 1860-2000
    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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    URL: http://dx.doi.org/10.1007/BF00698993
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    Some laws governing the alkylation of 6-tert-butyl-2-methylphenol with methyl acrylate in the presence of a phenoxide (1993)
    Springer
    Russian chemical bulletin 42 (1993), S. 457-460 
    Details
    ISSN: 1573-9171
    Keywords: kinetics ; mechanism ; 6-tert-butyl-2-methylphenol ; alkylation with methyl acrylate
    Source: Springer Online Journal Archives 1860-2000
    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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    URL: http://dx.doi.org/10.1007/BF00698430
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