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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Methods were developed for quantitating epimerization to epihetacillin and hydrolysis to ampicillin in the alkaline degradation of hetacillin, and both rates in deuterium oxide at 35 degrees and in water at various temperatures were determined. In each case, plots of log k for the epimerization against pH or pD yielded straight lines with a positive slope, which verified the first-order dependence on the hydroxide ion or deuteroxide ion. The activation energy of the epimerization process was 21.2 kcal/mole. In aqueous solution at high pH, epimerization rather than conversion to ampicillin represents a major pathway of hetacillin degradation, although the beta-lactam ring of the hetacillin molecule is highly resistant to attack by the hydroxide ion.
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PMID:Hydrolysis and epimerization kinetics of hetacillin in aqueous solution. 1 91

The stability of prostaglandin E1 and dinoprostone was investigated at the extremes of the pH range (less than or equal to 3 and greater than or equal to 10) in the sequence prostaglandin E leads to prostaglandin A leads to prostaglandin B. The degradation rate is first order with hydrogen-ion and hydroxide-ion concentrations. Separation and analysis of the E prostaglandins were accomplished by TLC and UV spectrophotometry. At the lowest pH values and at elevated or low temperatures, significant amounts of 15-epiprostaglandin E were present. Apparent activation energies for the total dinoprostone loss, calculated from elevated temperature data, were 21 kcal/mole in the strongly acidic region and about 18 kcal/mole at pH 3. Corresponding studies in the alkaline region led to a derived arrhenius activation energy of 15 kcal/mole with the appearance of significant amounts of 8-isoprostaglandin E. This difference in activation energies may reflect the different mechanisms operant at high and low pH values.
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PMID:Stability of prostaglandin E1 and dinoprostone (prostaglandin E2) under strongly acidic and basic conditions. 2 Dec 82

The formation rate of aspirin from the prodrug was determined as a function of the pH, temperature, and dielectric constant of the solvent spectrophotometrically and was confirmed by high-pressure liquid chromatography. Aspirin formation was first order with respect to the prodrug and zero order with respect to the hydroxide-ion concentrations. The hydrolysis rate was independent of buffer concentration but very sensitive to the dielectric constant of the solvents. The half-life for the formation of aspirin at 37 degrees was 7 min. The activation energy for the hydrolysis was 23.7 kcal/mole. The results suggest that the hydrolysis of the prodrug to aspirin proceeds by an SN1-type mechanism.
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PMID:Kinetics and mechanism of hydrolysis of 1-(2'-acetoxybenzoyl)-2-deoxy-alpha-D-glucopyranose, a novel aspirin prodrug. 3 21

The kinetics of degradation of cefazolin and cephalexin in aqueous solution were investigated at 60 degrees C and constant ionic strength over the entire pH range. The observed degradation rates were obtained by measuring the residual cephalosporin and were shown to follow pseudo-first-order-kinetics. They were influenced significantly by solvolytic and hydroxide ion catalysis. No primary salt effect was observed in the acid or basic pH region. Of the buffer systems employed in the kinetics studies only the phosphate buffer system showed a catalytic effect. The pH-rate profile for cefazolin showed a degradation minimum between pH 5.5 and 6.5. Cephalexin did not show a pH minimum in that region. The apparent energies of activation were determined for cefazolin and cephalexin at pH 5.5 and were calculated to be 24.3 Kcal/mole and 26.2 Kcal/mole, respectively. The agreement between the calculated theoretical pH-rate profiles and the experimental points for both compounds support the hypothesis presented concerning the reactions involved in their respective degradation pathways.
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PMID:Kinetics of degradation of cefazolin and cephalexin in aqueous solution. 3 81

Samples of lobster hemocyanin (Homarus americanus) under conditions of reversible reaction between whole (25 S) and half (17 S) molecules have been subjected to accurately known nitrogen pressures in analytical ultracentrifuge cells. A modified pressurization chamber of the type developed by Schumaker and colleagues has been constructed for this purpose. The molecular weight was then determined at the top (liquid-gas) meniscus, by means of the Archibald method. The logarithmic dependence upon pressure of the derived equilibrium constant then gave directly the volume of reaction. Experiments were performed in veronal-citrate buffers at pH 8, where the molar volume of formation of whole (dodecameric) molecules from half molecules appears to be negative, and at pH 8.46 in veronal-citrate buffer in the presence of 0.003 molar free calcium ion, where the molar volume of formation was estimated to be + 390 cm3/mole. In glycine-sodium hydroxide buffer at pH 9.6 containing 0.0047 molar free calcium, the molar volume of formation of whole molecules was estimated to be +120 +/- 70 cm3, corresponding to an estimated difference in partial specific volume between whole molecules and half molecules of only 1.3 (10)-4cm3/gram. The correctness of the sign of this value in glycine buffer has been verified by pressure-jump light-scattering experiments.
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PMID:Volume of reaction by the Archibald ultracentrifuge method (lobster hemocyanin). 96 12

The most common disorders of hypopigmentation in children are pityriasis alba, vitiligo, nevus depigmentosus, and tinea versicolor. Pityriasis alba usually presents as ill defined, scaly patches of hypomelanosis on the cheeks of children with an atopic diathesis. The face is also a favored site for vitiligo, but the distribution is periorificial, and the pigment loss is complete because of a destruction of melanocytes. Vitiligo is an acquired, progressive disorder in contrast to nevus depigmentosus, which is a stable, congenital leukoderma. The localized form of nevus depigmentosus must be distinguished from an ash leaf spot, the earliest cutaneous manifestation of tuberous sclerosis, whereas the systematized form may be confused with hypomelanosis of Ito, another neurocutaneous disorder. The lesions of tinea versicolor favor the upper trunk of adolescents, and potassium hydroxide examination of the associated scale reveals hyphal and yeast forms of P. orbiculare. Any inflammatory process in the skin such as dermatitis or psoriasis can resolve with areas of hypopigmentation.
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PMID:Disorders of hypopigmentation in children. 187 Sep 14

The membrane-bound succinate dehydrogenase (SDH; EC 1.3.99.1) of Bacillus pumilus strain 5 was investigated as succinate:ferricyanide oxidoreductase activity at 27 degrees C. A Km of 8.3 x 10(-3) M was obtained, and the Vmax was 1.8 x 10(-6) mole succinate dehydrogenated min-1 mg-1 membrane protein, at a substrate (succinate) concentration below 40 x 10(-3) M. Above this succinate concentration the Km was 102 x 10(-3) M and the Vmax was 3.7 x 10(-6) mole succinate min-1 mg-1 membrane protein. Para-benzoquinone or 2,4-dinitrophenylhydrazine, in micromolar amounts inhibited the enzyme by serving as an electron sink. Hydroxyl radical (OH.) scavengers, mannitol and benzoate, activated the enzyme, while superoxide dismutase (SOD) had no effect on the enzyme. Thus, the mechanism of electron transfer from succinate to Fe(CN)3-(6) through SDH does not involve superoxide (O2-) as a rate-limiting intermediate.
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PMID:Membrane-bound succinate dehydrogenase of Bacillus pumilus strain 5: effects of modulators of monoelectron transfer. 251 38

We examined the stability of uric acid in dilute aqueous ammonium hydroxide solution by mass spectrometry. Uric acid decomposes in ammonium hydroxide even as dilute as 15 mmol/L when the mole ratio of ammonium hydroxide to uric acid is 50:1. There are at least four products of the decomposition, two of which have been identified as allantoin and urea. The slope of the decomposition curve indicates that uric acid is destroyed at an initial rate of 2-3% per hour. In ammonium hydroxide at a concentration of 1 mmol/L and a mole ratio of ammonium hydroxide to uric acid of less than or equal to 3.4, uric acid is not detectably decomposed. Evidently, any method for determination of uric acid that involves treating the analyte with ammonium hydroxide before analysis may destroy it. Therefore, a published method described as being "definitive" for uric acid (J Clin Chem Clin Biochem 1985; 23:129-35) could produce incorrect results because it involves storing the uric acid in 15 mmol/L ammonium hydroxide at a mole ratio of ammonium hydroxide to uric acid of greater than 120:1.
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PMID:The stability of uric acid in ammonium hydroxide. 318 Apr 23

A method is presented for analysis of gamma-carboxyglutamic acid based on its derivatization with phenylisothiocyanate and reverse phase HPLC analysis of the resulting phenylthiocarbamyl derivative. Proteins were hydrolyzed with sodium hydroxide and the hydrolysates were desalted on Dowex 50 eluted with ammonium hydroxide. The resulting amino acid mixtures were derivatized with phenylisothiocyanate and the phenylthiocarbamyl derivatives were separated under isocratic conditions on either C18 or C8 reverse phase columns using 0.14 M Tris, 0.05% triethylamine, titrated to pH 7.5 with glacial acetic acid, plus 2% acetonitrile, and detected by absorbance at 254 nm. The method is linear over the range from 10 to 1000 pmol of gamma-carboxyglutamic acid and the limit of detection is near 2 pmol. The utility of the method was verified for analysis of purified prothrombin yielding a value of 10.3 mol of gamma-carboxyglutamic acid per mole in agreement with sequence data. No gamma-carboxyglutamate was detectable for acid-hydrolyzed samples of prothrombin, nor in acid- or base-hydrolyzed samples of bovine serum albumin. Application of this method failed to corroborate the reported presence of gamma-carboxyglutamate in a putative mitochondrial gamma-carboxyglutamate-containing calcium-binding protein. The method was also tested for determination of beta-carboxyaspartate, beta-hydroxyaspartate, phosphoserine, phosphothreonine, and phosphotyrosine in an attempt to identify an unknown material which appeared in preparations of the mitochondrial protein.
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PMID:Analysis of gamma-carboxyglutamic acid by reverse phase HPLC of its phenylthiocarbamyl derivative. 326 14

The rate of production of thiol groups by alkaline cleavage of disulfide bonds in the black-eyed pea (Vigna unguiculata) trypsin and chymotrypsin inhibitor (BTCI) was determined from thiol quantitation with 5, 5'-dithiobis-(2-nitrobenzoic acid), and increase in absorption at 240 nm. Rate constants were estimated at pH's 12.8, 13.0, 13.5, and 25 degrees C. At pH 13.0, the second-order rate constant was obtained as a function of temperature. The energy of activation was Ea = 10.7 kcal/mole, while the change in activation free energy was delta G not equal to = 21.6 kcal/mole. The results obtained fit the hydrolysis mechanism, in which S-S split occurs through a nucleophilic attack of a hydroxide ion on the disulfide bond. Urea (8M), unexpectedly, showed an effect of attenuation on the hydrolysis rate of disulfide bonds in BTCI.
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PMID:Alkaline cleavage of disulfide bonds in the black-eyed pea trypsin and chymotrypsin inhibitor. 406 66


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