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Digitale Medien

Aqueous uranyl complexes. 3. Potentiometric measurements of the hydrolysis of uranyl(VI) ion at 25°C (1995)

Palmer, Donald A. ; Nguyen-Trung, C.

Springer

Journal of solution chemistry 24 (1995), S. 1281-1291

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ISSN: 1572-8927

Schlagwort(e): Hydrolysis ; uranyl ; potentiometric ; thermodynamics ; aqueous

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie

Notizen: Abstract Potentiometric titrations of uranyl(VI) solutions were conducted using a standard glasslcalomel electrode combination over the pH range 3 to 12 at 0.1 molkg−1 ionic strength with tetramethylammonium trifluoromethanesulfonate as the supporting electrolyte. The electrodes were calibrated directly on the hydrogen ion concentration scale during the initial stage of each titration. The species, UO 2 2+ , (UO2)2(OH) 2 2+ , (UO2)3(OH) 5 + , (UO2)3(OH) 7 − , (UO2)3(OH) 8 2− , and (UO2)3(OH) 10 4− identified in an earlier Raman study were compatible with the analysis of the titration data. Based on this analysis and application of the extended Debye-Hückel treatment, the polynuclear species indicated above were assigned overall formation constants at 25°C and at infinite dilution of −5.51±0.04, −15.3±0.1, −27.77±0.09, −37.65±0.14, and −62.4±0.3, respectively. The results are discussed in reference to hydrolysis quotients reported in the literature for the first three species. Formation quotients for the last two species have not been reported previously.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00972833

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Digitale Medien

Test chamber exposure of humans to 1,6-hexamethylene diisocyanate and isophorone diisocyanate (1995)

Tinnerberg, H. ; Skarping, G. ; Dalene, M. ; [weitere]

Springer

International archives of occupational and environmental health 67 (1995), S. 367-374

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ISSN: 1432-1246

Schlagwort(e): 1,6-Hexamethylene diisocyanate ; Isophorone diisocyanate ; Human exposure ; Hydrolysis ; Biological monitoring

Quelle: Springer Online Journal Archives 1860-2000

Thema: Medizin

Notizen: Abstract An isocyanate generation apparatus was developed and stable isocyanate atmospheres were obtained. At a concentration of 5 μg 1,6-hexamethylene diisocyanate (HDI) per m3 the precision was found to be 7% (n = 5). Three volunteers were each exposed to three different concentrations of HDI (11.9, 20.5, and 22.1 μg/m3) and three concentrations of isophorone diisocyanate (IPDI) (12.1, 17.7, and 50.7 μg/m3), in an exposure chamber. The duration of the exposure was 2 h. Urine and blood samples were collected, and hydrolysed under alkaline conditions to the HDI and IPDI corresponding amines, 1,6-hexamethylene diamine (HDA) and isophorone diamine (IPDA), determined as their pentafluoropropionic anhydride amides (HDA-PFPA and IPDA-PFPA). The HDA-and IPDA-PFPA derivatives were analysed using liquid chromatography mass spectrometry with thermospray monitoring negative ions. When working up samples from the exposed persons without hydrolysis, no HDA or IPDA was seen. The average urinary excretion of the corresponding amine was 39% for HDI and 27% for IPDI. An association between the estimated inhaled dose and the total excreted amount was seen. The average urinary elimination half-time for HDA was 2.5 h and for IPDA, 2.8 h. The hydrolysis condition giving the highest yield of HDA and IPDA in urine was found to be hydrolysis with 3 M sodium hydroxide during 4 h. No HDA or IPDA could be found in hydrolysed plasma (〈 ca 0.1 μg/l).

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00381050

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Digitale Medien

Scavenging of reactive oxygen species by letosteine, a molecule with two blocked -SH groups (1995)

Gressier, B. ; Lebegue, N. ; Brunet, C. ; [weitere]

Springer

Pharmacy world & science 17 (1995), S. 76-80

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ISSN: 1573-739X

Schlagwort(e): Acetylcysteine ; Antioxidants ; Free radicals ; Hydrolysis ; Letosteine ; Mercaptoethanesulfonate ; Peroxides ; Sulfhydryl compounds ; Superoxide

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie

Notizen: Abstract Acute production of reactive oxygen species by polymorphonuclear neutrophils during the respiratory burst may induce tissue injuries. In thisin vitro study, it was demonstrated that letosteine, a mucolytic agent containing two blocked thiol groups, had antioxidant activity, but only when it was first submitted to alkaline hydrolysis. In a cell-free system, hydrogen peroxide, hypochlorous acid and hydroxyl radical concentrations were reduced by half by letosteine concentrations of 200, 15 and 350 μol/l, respectively. The mechanism of letosteine action may be related to the -SH group liberatedin vitro by hydrolysis, which seemed to react by scavenging the reactive oxygen species in the same way as acetylcysteine and MESNA, freethiol drugs known for their antioxidant properties. So, letosteine, a compound with blocked -SH groups whichin vivo can metabolically become free, may have a therapeutic application in preventing oxidative tissue injury damage induced by the respiratory burst.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF01875435

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Digitale Medien

Hydrolysis of phosphate esters with polymer-supported catalysts containing cyclodextrin pendant group (1995)

Hu, Cho-Chun ; Chen, Wei-Hsi ; Liu, Chuen-Ying ; [weitere]

Springer

Journal of inclusion phenomena and macrocyclic chemistry 23 (1995), S. 289-303

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ISSN: 1573-1111

Schlagwort(e): Hydrolysis ; phosphate esters ; polymer supported catalyst ; cyclodextrin pendant group

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie

Notizen: Abstract Polymer-supported catalysts of several kinds, includingβ-cyclodextrin (P-CD),β-cyclodextrin-diethylenetriamine (P-CD-DETA), andβ-cyclodextrin-N-methylhydroxamate (P-CD-NMHA)-containing polymers, as well as their corresponding metal complexes, were synthesized and examined as catalysts for the hydrolysis of phosphate esters. The kinetic measurements were performed in a phosphate buffer (0.05 M, pH 8.2) at a temperature of 25.0±0.1 °C. Each kinetic run was initiated on introducing ester stock solution (0.13 ml) containing diphenylp-nitrophenyl phosphate (DPPNPP) in dioxane (0.010 M). The rate of hydrolysis of DPPNPP was evaluated by measuring the absorbance of liberatedp-nitrophenol at 402 nm. The dissociation constants between DPPNPP and the polymers P-CD, P-CD-DETA and P-CD-NMHA obtained from Eadie-type plots were 16.8, 16.4 and 8.0 (×10−3 M) and the acceleration factors were 1.5, 2.8 and 8.6 respectively. Hence P-CD-NMHA is the most promising catalyst. The activation parameters, preexponential factor (A) and activation energy using P-CD-NMHA as catalyst, areA=1.2×109 min−1 andE a=43 kJ/mol respectively; the latter was about 12 kJ/mol lower than the activation energy of spontaneous hydrolysis. The results indicate that the catalytic power of P-CD-NMHA may reflect the combined behavior of molecular recognition and nucleophilicity.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00707933

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Digitale Medien

The biological significance of storage granules in rat parathyroid cells (1995)

Setoguti, T. ; Inoue, Y. ; Wild, P.

New York, NY [u.a.] : Wiley-Blackwell

Microscopy Research and Technique 32 (1995), S. 148-163

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ISSN: 1059-910X

Schlagwort(e): Secretory granules ; Calcium ; Parathyroid hormone storage and release ; Hydrolysis ; Trans Golgi network ; Vacuolar bodies ; Life and Medical Sciences ; Cell & Developmental Biology

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Allgemeine Naturwissenschaft

Notizen: Both prosecretory and storage granules are concomitantly formed at the trans Golgi network including the innermost Golgi cisterna. Prosecretory granules develop into small secretory granules that release their contents by exocytosis finely regulated by a complex mechanism for maintaining calcium homeostasis. In the rat parathyroid cells, storage granules are large secretory granules storing parathyroid hormone for an emergency supply. The hormone is rapidly discharged by exocytosis when serum calcium concentration is decreased. The granules are constantly produced even under conditions of low serum calcium concentration in the regions of 8 mg/dl. The granule content is constantly hydrolyzed when not discharged, leading to a decreased core and finally to the formation of vacuolar bodies. The fate of the vacuolar bodies is unknown. Hypercalcemic conditions accelerate hydrolysis. The threshold value of calcium concentration required for the release of storage granule contents is between 8.0 and 7.5 mg/dl and that of calcium concentration for accelerating degradation of storage granules is about 11.5 mg/dl. Sympathetic stimulation causes storage granules to be discharged regardless of hypercalcemia or hypocalcemia. Parasympathetic stimulation accelerates hydrolysis. The degradation of storage granules seems to be closely associated with an intracellular regulatory mechanism for parathyroid hormone secretion. © 1995 Wiley-Liss, Inc.

Zusätzliches Material: 18 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/jemt.1070320209

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Digitale Medien

The Reaction of Oxides with Water at High Pressures and TemperaturesDedicated to Prof. Dr. H. Brockmann on the occasion of his 60th birthday (1964)

Wendlandt, H. G. ; Glemser, O.

Weinheim : Wiley-Blackwell

Angewandte Chemie International Edition in English 3 (1964), S. 47-54

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ISSN: 0570-0833

Schlagwort(e): Oxides ; Water ; High-pressure chemistry ; Hydrolysis ; Chemistry ; General Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: The reactions of the oxides SiO2, MoO3, and WO3 with steam at temperatures between 400 and 700 °C and pressures of 5 to 500 atm were studied by means of the transfer method. The results were evaluated by a new method. In the system Sio2/H2O the formation of gaseous Si(OH)4, Si2O(OH)6, and [SiO2(OH)2]x was found to occur in three different water-density ranges. In the systems MoO3/H2O and WO3/H2O the gaseous compounds MoO2(OH)2 and WO2(OH)2, which were already known, exist up to densities of approximately 0.05g/cm3. At higher densities, at which the supercritical phase begins to show the properties of a liquid to an ever increasing extent, isopolymolybdic or isopolytungstic acids appear.

Zusätzliches Material: 7 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/anie.196400471

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Digitale Medien

Proton Transfer, Acid-Base Catalysis, and Enzymatic Hydrolysis. Part I: ELEMENTARY PROCESSESPart II (Catalytic Mechanisms) will appear shortly in this journal.Dedicated to Dr. W. Foerst on the occasion of his 65th birthday (1964)

Eigen, M.

Weinheim : Wiley-Blackwell

Angewandte Chemie International Edition in English 3 (1964), S. 1-19

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ISSN: 0570-0833

Schlagwort(e): Proton transfer ; Catalysis ; Enzyme catalysis ; Hydrolysis ; Chemistry ; General Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: The proton occupies a special position as a promoter and mediator in chemical reactions occurring in solution. Many reactions in organic chemistry are catalysed by acids or bases; likewise, most enzymes contain active groups which promote acid-base catalysis. To understand the reaction mechanisms involved, it is necessary to identify the elementary steps as well as their course in time. Systematic investigation of these elementary steps as well as their course in time. Systematic investigation of these elementary steps has become possible only with the development of new methods for studying very fast reactions. The present paper reviews the information obtained in this type of investigation. The result is a relatively complete picture of the elementary proton transfer mechanisms and a comprehensive description of the modes and laws of acid-base and enzymatic catalysis.

Zusätzliches Material: 12 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/anie.196400011

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