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  • kinetics  (61)
  • Springer  (61)
  • Springer-Verlag
  • 1990-1994  (61)
  • 1985-1989
  • 1970-1974
  • 1992  (61)
Collection
Publisher
Years
  • 1990-1994  (61)
  • 1985-1989
  • 1970-1974
Year
  • 1
    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.
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  • 2
    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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  • 3
    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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  • 4
    ISSN: 1432-0428
    Keywords: Atherosclerosis ; diabetes mellitus ; glycation ; LDL metabolism ; kinetics ; experimental
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Hyperglycaemia in diabetes mellitus is responsible for the process of non-enzymatic glycosylation of different proteins. Since we did not find elevated glycated apolipoprotein B levels in diabetic patients, an altered glycated apolipoprotein B metabolism was suspected in diabetic patients. Experiments in normal rabbits showed that non-reductive (in vitro) glycated low density lipoprotein (gly-LDL) was cleared at a slower rate than control LDL and thus stayed longer in the circulation (vascular mean residence time: 10 vs 8 h, p〈0.001). The body mean residence time for gly-LDL was 22 h vs 17 h for control LDL. In diabetic animals the catabolic parameters of both LDL preparations changed towards a faster clearance, the effect being greatest for gly-LDL (total mean residence times of gly-LDL pre-diabetic: 19 h, diabetic: 16 h; control LDL pre-diabetic and diabetic: 14 h). The difference in clearance between glycated and control LDL was thus strongly reduced. Virtually no antibody complexed to gly-LDL could be measured. The results suggest an increased activity of the non-receptor mediated pathway in diabetes mellitus, possibly co-responsible for an increased atherosclerotic risk.
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  • 5
    ISSN: 1573-904X
    Keywords: lipoxygenase ; 5-lipoxygenase inhibitor ; kinetics ; borate catalysis ; N-hydroxyurea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Zileuton (N-(1-benzo[b]thien-2-ylethyl)N-hydroxyurea) is a powerful 5-lipoxygenase inhibitor. The chemical degradation of Zileuton and related hydroxyurea derivatives was studied in aqueous solutions as a function of pH and temperature. The pH profile for the degradation of Zileuton shows an acid-catalyzed region at pH values below 2, water hydrolysis of the protonated form at pH values from 3 to 8, and water hydrolysis of the unprotonated form at pH values greater than 9. Hydrolysis of the hydroxyurea moiety to give the hydroxylamine derivative represents the main degradation pathway for Zileuton. This product, however, is not stable and is present at low concentrations at pH values below 6 and not observed at pH values greater than 7. Further decomposition of the hydroxylamine derivative leads to the observed degradation products. Air oxidation to the isomeric oximes accounts for the observed products at pH values greater than 7. Hydrolysis of the oximes to the ketone derivative accounts for the observed products at pH values 2 to 6. Parallel decomposition pathways to the alcohol derivative were noted under strongly acidic conditions, pH 0 to 2.
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  • 6
    ISSN: 1573-904X
    Keywords: cyclic hexapeptide ; degradation ; aqueous solution ; kinetics ; mechanism ; pH-rate profile ; energetics ; somatostatin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A highly active cyclic hexapeptide analogue of somatostatin, Cyclo(N-Me-L-Ala-L-Tyr-D-Trp-L-Lys-L-Val-L-Phe), L-363,586, was found to improve the control of postprandial hyperglycemia in diabetic animals when given in combination with insulin. The compound is reported to be relatively stable in blood, nasal cavity, and intestinal lumen but undergoes rapid degradation in aqueous solution. The objective of this study was to elucidate the degradation mechanisms based on the kinetic data and the structure of the degradation products. Both pH and temperature had a profound influence on the instability of the peptide in aqueous solution. The data indicated that the peptide was most stable at a pH of about 4.7. The pH-rate profile exhibited specific acid catalysis at a pH less than 3.0 and base catalysis above pH 10.5. The kinetic pK a was determined to be 9.7. This pK a could be attributed to the tyrosine residue. The mechanisms of degradation under acidic and alkaline conditions appear to be different. Identification of the fragments obtained using mass spectrometry and amino acid sequencing suggest that the cyclic compound was cleaved to yield a linear fragment, which underwent further cleavage at both peptide linkages alpha to the trypto-phanyl residue. The indole group of that residue is probably the potential nucleophile attacking the adjacent carbonyls. A rate equation for the degradation of the hexapeptide has been proposed.
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  • 7
    ISSN: 1573-904X
    Keywords: salmon calcitonin ; stability ; kinetics ; peptide ; degradation ; pH–rate profile ; HPLC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
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  • 8
    ISSN: 1573-8744
    Keywords: salbutamol ; kinetics ; dynamics ; first-pass effect ; route of administration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This study assessed the influence of dose and route of administration on salbutamol kinetics and hypokaliemic effect. Salbutamol plasma kinetics were studied in a first group of 6 rabbits who received 60, 800, and 60 μg/kg by the intravenous (iv), oral (po), and intratracheal (it) routes, respectively, at 1-week intervals. A second group of 6 rabbits received 120, 2400, and 120 μg/kg of salbutamol by the same three routes. Multiple blood samples were withdrawn to assay salbutamol and potassium. Following iv salbutamol (60 μg/kg), total plasma clearance was 82±5 ml/min per kg, apparent volume of distribution was 5.0±0.5 l/kg, and terminal half- life was 41±2 min. Similar values were estimated when 120 μg/kg of salbutamol was administered iv or was given po or it. The bioavailability of po and it salbutamol was approximately 1 and 20%, respectively. For the first group, the maximal decrease in plasma potassium elicited by salbutamol was 0.80±0.19, 0.48±0.22, and 0.78±0.46 mmol/l, and for the second group, maximal decrement was 1.31±0.37, 0.70±0.24, and 0.84±0.17 mmol/l for the iv, po, and it routes, respectively. Compared to salbutamol peak plasma concentrations, maximal decrease in plasma potassium appeared between 60 and 108 min later for the iv route, 90 and 25 min later for po and it routes, and for this reason, the hypokaliemic effect was not associated to salbutamol plasma concentrations. The hypokaliemic effect was dependent upon the route, e.g., po〉it〉iv. It is concluded that (i) salbutamol plasma kinetics are first-order independently of the route of administration, and (ii) salbutamol hypokaliemic effect is modulated by the dose and the route of administration.
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  • 9
    ISSN: 1573-9171
    Keywords: radiolysis ; clusters ; kinetics ; mercury ; aqueous solution ; optical spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Pulsed radiolysis, EPR, and optical spectroscopy were used to investigate the radiation-induced reduction of Hg 2 2+ ions in aqueous solutions. It was shown that the Hg 2 + ions that form as a result of the reduction reaction react rapidly with Hg 2 2+ with formation of Hg 4 3+ . Constants of formation and disappearance of these ions were determined. The process of disappearance of this species results in the formation of more complex clusters containing six or more mercury atoms. Further complication of the clusters affords colloidal metal particles.
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  • 10
    ISSN: 1573-9171
    Keywords: radicals ; addition ; dioxolane ; telomers ; telomerization ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The telomerization of 3,3,3-trifluoropropene with 2-methyl-1,3-dioxolane gives predominantly cyclic telomers as shown by13C NMR and gas chromatography-mass spectrometry. This reaction is accompanied by the rearrangement of transient free radical intermediates via 1,5-H-migration.
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  • 11
    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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  • 12
    ISSN: 1573-9171
    Keywords: kinetics ; decomposition ; ozonide ; triphenylphosphite ; ozonation ; voltammetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The electrochemical characteristics of reduction of triphenylphosphite ozonide at a stationary platinum electrode were determined in acetonitrile at between −30 and −11°C. The feasibility of employing voltammetric methods to investigate the reactions of phosphite ozonides was demonstrated in a model study of the kinetics of the thermal decomposition of (C6H5O)3PO3 and its reaction with triphenylphosphite.
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  • 13
    ISSN: 1573-9171
    Keywords: dimerization ; kinetics ; ethylene ; organomagnesium compound ; 1-butene ; selectivity ; catalytic activity ; polarography ; reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of an organomagnesium compound on the dimerization of ethylene to 1-butene was studied. The organomagnesium compound increases the catalytic activity of the Ti(OC4H9)4-Al(C2H5)3 system by 5–10 times. A high degree of selectivity (up to 99%) with respect to 1-butene was obtained. This makes it possible to eliminate a series of technological difficulties involved in the industrial production of 1-butene. The kinetics of the reduction of Ti(OC4H9)4 by butylmagnesium chloride were studied by ESR and polarography.
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  • 14
    ISSN: 1573-9171
    Keywords: azalactones ; hydrolysis ; kinetics ; mechanism ; catalysis ; metal complexes ; enantioselectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The hydrolysis of 2-methyl-4-benzyl-5(4H)oxazolone (MBA) in a mixture of water and MeCN has been studied — both the spontaneous reaction and that catalyzed by a complex of Cu(II) with (S)-2-[(N-benzylpropyl)amino]benzaldoxime (1). It has been shown that the complex 1 is an effective catalyst for the hydrolysis of MBA (chymotrypsin does not catalyze MBA hydrolysis). The mechanism of MBA hydrolysis catalyzed by this complex includes the formation of a mixed catalyst—substrate complex in which the MBA is coordinated with the metal ion through the N 3 atom. It is suggested that the oxygen atom of the ionized oxime group in such a complex attacks the imine C 2 atom of the MBA intramolecularly; this is the rate-determining stage. The change in the order of hydrolysis with respect to the catalyst from 1 to 1/2 when the concentration of 1 is increased indicates that the complex catalyst exists in aqueous solution in two forms, dimeric and monomeric, which are in equilibrium, and only the monomeric form of the complex is responsible for the catalysis. With an excess of the substrate we observe inhibition of the MBA hydrolysis — possibly an indirect indication of participation in the transition state by a water molecule coordinated in an apical position of the complex, which is displaced by excess substrate.
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Russian chemical bulletin 41 (1992), S. 822-828 
    ISSN: 1573-9171
    Keywords: catalysis ; kinetics ; protonation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetic characteristics of the model reaction of electron transfer and the reaction of acylation of aromatic amines by aromatic acid anhydrides were investigated as a function of the concentration of acid catalyst and a correlation was established between the type of this function and the characteristics of protonation of the amines. The rate constants of the catalytic and noncatalytic flows of the forward and reverse reactions in the phthalic anhydride—p-toluidine system were determined as a function of the molarity and proton-acceptor properties of the solvent. The mechanism of acid-base catalysis was examined as a sequence of proton and electron transfer processes.
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  • 16
    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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  • 17
    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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  • 18
    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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  • 19
    ISSN: 1573-0778
    Keywords: batch culture ; continuous culture ; hybridoma ; kinetics ; specific rates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract For the mouse hybridoma cell line VO 208, kinetics of growth, consumption of glucose and glutamine, and production of lactate, ammonia and antibodies were compared in batch and continuous cultures. At a given specific growth rate, different metabolic activities were observed: a 40% lower glucose and glutamine consumption rate, but a 70% higher antibody production rate in continuous than in batch culture. Much higher metabolic rates were also measured during the initial lag phase of the batch culture. When representing the variation of the specific antibody production rate as a function of the specific growth rate, there was a positive association between growth and antibody production in the batch culture, but a negative association during the transient phase of the continuous culture. The kinetic differences between cellular metabolism in batch and continuous cultures may be result of modifications in the physiology and metabolism of cells which, in continuous cultures, were extensively exposed to glucose limitations.
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  • 20
    ISSN: 1573-9171
    Keywords: vinyl monomers ; radical oxidation ; inhibitors ; phenols ; reactivity ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Rate constants were measured for the addition of the 2,4,6-tri(tert-butyl)phenoxyl radical (logk 10, [liter/(mole · sec)]) to the double bond of styrene (9.73 − 4621/T), methyl methacrylate (10.1 − 4972.7/T) and butylacrylate (7.68 − 4313.9/T); and for addition of the 2,4,6-tribromophenoxyl radical to styrene (k 10=0.5;T=323 K). A simulation based on these constants for the inhibited oxidation of styrene under conditions similar to those of monomer storage demonstrated the need to take account of this reaction when analyzing kinetic schemes describing the inhibited oxidation process.
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  • 21
    ISSN: 1573-9171
    Keywords: enol acetate ; rearrangement ; kinetics ; 2,4-dichlorophenyl(1H-1,2,4-triazol-1-ylmethyl)ketone ; 2,4-dichlorophenyl(5-acetyl-1H-1,2,4-triazol-1-ylmethyl)ketone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of rearrangement of 2,4-dichlorophenyl(1H-1,2,4-triazol-1-ylmethyl)ketone enol acetate into 2,4-dichlorophenyl(5-acetyl-1H-1,2,4-triazol-l-ylmethyl)ketone were investigated by1H NMR spectroscopy. It was shown that this rearrangement is a first-order reaction. The rate constant was measured in the 129–156°C range and the activation parameters of the reaction were determined. A hypothesis concerning the intramolecular character of the observed rearrangement was drawn based on the kinetic data.
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  • 22
    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+.
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  • 23
    Electronic Resource
    Electronic Resource
    Springer
    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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  • 24
    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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  • 25
    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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  • 26
    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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  • 27
    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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  • 28
    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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  • 29
    Electronic Resource
    Electronic Resource
    Springer
    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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  • 30
    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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  • 31
    ISSN: 1573-5117
    Keywords: trace metals ; uptake ; kinetics ; development ; growth ; adsorption ; Chironomus riparius
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cadmium, Zn, Pb and Cu uptake and effects in larvae ofChironomus riparius (Meigen) were studied in an integrated laboratory investigation, in which metal analyses in different instar stages, uptake kinetics and effects on development and growth were considered in three separate experiments. In short-term experiments with fourth instar larvae, it was demonstrated that only a minor portion of metals was adsorbed on the larval exoskeletons. No conclusive evidence on the uptake mechanism was found, but active uptake of trace metals seemed highly unlikely. In partial life cycle experiments, all four metals studied were readily accumulated in chironomid larvae. Uptake could be described satisfactorily utilizing a first-order one-compartment uptake model which incorporated growth. In all cases steady state conditions were approached and high uptake and elimination rate constants were estimated. Distinct differences between essential (Zn and Cu) and non-essential (Cd and Pb) metals were noted. Larval growth was significantly impaired upon exposure. Finally, long-term exposure experiments with low Cd concentrations (0.010 and 0.025 mg 1−1) resulted initially in growth impairment and high mortality in first instar stages, but surviving larvae restored growth and adults emerged even before control adults. In similar experiments with Zn (0.1 and 1.0 mg 1−1), development of larvae was significantly retarded. High Zn concentrations in larvae were noted and almost no adult midges emerged.
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  • 32
    ISSN: 1573-2592
    Keywords: Intravenous immunoglobulin ; kinetics ; secondary hypogammaglobulinemia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Fifteen patients with low-grade B-cell tumours were given 3-weekly infusions for 1 year of intravenous immunoglobulin (IVIg) at a dose of 0.4 g/kg. Serial measurements of serum IgG levels were made; analysis of eight samples taken at intervals after the end of the last (17th) infusion showed that the half-life of IgG in such patients was no shorter than in normal individuals. To look at the average rates of catabolism of IgG during the year serum IgG was measured at four time points (pre, post, day 7, and day 21) after the 5th, 8th, 13th, and 17th infusions; these data showed that there were no changes in catabolism. Finally, there was a significant correlation (P〈0.005) between the pretreatment serum IgG level and the increase to the mean trough level achieved after the fifth and subsequent infusions (in each individual). These data suggest that the catabolic rate of IgG is normal in patients with low-grade B-cell tumours and that it is not altered by regular IVIg infusions once a steady state is reached. Significant correlation of the increment of serum IgG with the endogenous synthesis level supports the theory that the IgG half-life is proportional to the IgG level at any given time.
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  • 33
    ISSN: 1573-9171
    Keywords: kinetics ; transesterification ; acid esters ; sodium phenolate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The rate constants for the substitution of the para-nitrophenoxide ion by the phenoxide and hydroxide ions in phosphates and phosphonates are enhanced upon the addition of hexamethylphosphorotriamide (HMPTA) to water. The lack of alkaline hydrolysis of the esters in 90% aqueous HMPTA containing PhONa is a consequence of the formation of the PhOH... OH complex, which is nonreactive.
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  • 34
    ISSN: 1573-9171
    Keywords: lyotropic liquid crystals ; mixed micelles ; SF ; decylamine ; decylammonium chloride ; p-nitrophenyldimethyl thiophosphate ; dealkylation ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of decomposition of p-nitrophenyldimethyl thiophosphate (1) were investigated spectrophotometrically in the n-decylammonium chloride-n-decylamine-water system (DAC-DA-H2O), in which micellar or lamellar liquid-crystalline phases are formed as a function of the concentration of components. It was shown that1 is dealkylated in both phases. An increase in the surface charge density of associates decreases the rate of dealkylation. The activation energy in the lamellar phase is significantly higher than in the micellar phase.
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  • 35
    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.
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  • 36
    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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  • 37
    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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  • 38
    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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  • 39
    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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  • 40
    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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  • 41
    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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  • 42
    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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  • 43
    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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  • 44
    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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  • 45
    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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  • 46
    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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  • 47
    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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  • 48
    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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  • 49
    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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  • 50
    Electronic Resource
    Electronic Resource
    Springer
    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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  • 51
    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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  • 52
    Electronic Resource
    Electronic Resource
    Springer
    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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  • 53
    Electronic Resource
    Electronic Resource
    Springer
    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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  • 54
    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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  • 55
    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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  • 56
    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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  • 57
    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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  • 58
    ISSN: 1572-9729
    Keywords: anaerobic fermentation ; olive mill waste ; kinetics ; support
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Two materials of different structure, sepiolite and bentonite, evaluated as supports for the microorganisms effecting anaerobic fermentation, behaved differently towards condensation water from thermally concentrated olive mill wastewater from a kinetic point of view. Assuming the overall anaerobic digestion process to conform to first-order kinetics, the apparent kinetic constant for the digester including sepiolite as support was 1.12 day-1, while that of the digester using the bentonite support was 0.73 day-1. Thus, the apparent kinetic constant of the process was increased by 35% with the use of sepiolite. The yield coefficient, Yp/s, was 0.344 and 0.318 litres CH4 STP/g COD for the sepiolite and bentonite supports respectively.
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  • 59
    ISSN: 1435-1536
    Keywords: Adsorption-desorptionkinetics ; kinetics ; ionexchange ; lysozyme ; Sephadex C-25
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The ion-exchange reaction of lysozyme with carboxymethyl Sephadex C-25 was followed by conductivity change as a function of time just after the rapid mixing of the protein solution with the Sephadex suspension. A single relaxation process was observed; the conductivity increased exponentially with time in the 100 s scale. In this process, protons were released from the Sephadex C-25 in the same time scale. The relaxation process slowed down with an increase in the lysozyme concentration, but it quickened upon the addition of HCl. On the other hand, the ζ potential on the Sephadex C-25 surface changed from a negative value to a positive one with an increase in the amount of lysozyme adsorbed on the surface. On the basis of these data, the relaxation process was attributed to the ion-exchange reaction of lysozyme with several protons of carboxymethyl groups of the Sephadex.
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  • 60
    ISSN: 1435-1528
    Keywords: Bose-Einstein statistics ; relaxation ; aging ; kinetics ; relaxation time ; spectrum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract This paper explores the properties of a relaxation function derived from a differential equation mimicking the distribution mechanism of Bose-Einstein statistics in the time domain. Within a significant portion of the process, the relaxation quantity n decreases linearly with log time. The relation between dn/dt and n is an exponential one. In this respect, the present approach produces results largely equivalent to those obtained using the hypothesis of stress-dependent thermal activation or a box-like spectrum of relaxation times, τ. The τ spectrum of the model proposed here is discrete, with integer valued fractions of a characteristic -centering the equations.
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  • 61
    ISSN: 1435-1536
    Keywords: Ultrasonic relaxation ; kinetics ; hydrogen bonds ; counterion interactions ; polyelectrolytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The ultrasonic absorption coefficient has been measured as a function of frequency between 5 MHz and 3.1 GHz for aqueous solutions of polyacrylic acid and of its sodium, potassium, and tetraethylammonium salts. Unlike an aqueous solution of propionic acid, all polymer solutions clearly exhibit excess absorption. Within the frequency range under consideration the excess absorption spectra can be analytically represented by two Debye-type relaxation terms. At 25°C the corresponding relaxation times adopt values between 3 and 12.4 ns, and between 0.12 and 0.22ns, respectively. The former process is discussed in accordance with previous models. The relaxation of the polyacrylic acid solutions is assumed to be related to the formation of hydrogen bonds of the polymeric molecules and that of the polyacrylate solutions may be due to interactions of counterions with chain segments. The latter process, the existence of which has been first proven in this study, is likely to reflect rotational motions of carboxyl groups.
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