Thiols, determination

Fenton SS, Fahey RC (1986) Analysis of biological thiols determination of thiol components of disulfides and thioesters. Anal Biochem 154 34-42... 

Radical reactions have some stereochemical features that can be compared directly with their ionic counterparts, especially when the radical centre is adjacent to an existing stereogenic centre. The tris(trimethylsilyl)silyl radical adds to chiral ketones like 3-phenyl-2-butanone 7.59 to give a radical 7.60 flanked by a stereogenic centre. The hydrogen atom abstraction from a thiol, determines the relative stereochemistry, and the products 7.61 and 7.62 are analogous to those from the hydride reduction of the ketone. They are formed in the same sense, and the stereochemistry is explained by the Felkin-Anh picture 7.60. 

Andersson A, Isaksson A, Brattstrom L, et al. Homocysteine and other thiols determined in plasma by HPLC and thio-specific postcolumn derivatization. Clin Chem 1993 39 1590-7. 

In ion and ion-pair chromatography, pH of the postcol-umn reaction solution is adjusted by the acetic acid solution in the postcolumn reaction module because the separation pH is different from the pH of the iodine-azide reaction course (for details see Table 3). In reversed-phase chromatography, sodium azide solution plays two roles as a constituent of the mobile phase and as the reaction medium for the iodine-azide reaction. Therefore, pH adjustment for thiol determination is performed only once in the mobile phase without any additional pH correction of the postcolumn reaction solutions. Consequently, the procedure is simplified and no extra operations concerning the introduction of other solutions are required. 

The reactivity of 63 towards BSA was compared with that of compoimd 62 under different reactional conditions. It appeared that, except when the reaction was performed at room temperature and neutral pH, the number of metallo-carbonyl units bound per protein always exceeded the initial number of thiols determined by the EUman s method. In certain conditions, alkylation of histidines and lysines was also proved to occur [91],... 

Thiols are shipped ia every conceivable container size. Dmms and cans can be of carbon steel for most thiols, provided color is not a determining factor. Tmck, rail, and isocontainer shipments should be set up to utilize a vapor return line from the tank to the shipping container. This substantially minimizes the amount of odor that escapes. Phillips Petroleum Company and Atochem North America can supply further information regarding the handling and properties of many thiols. 

The yellow form (11) on acidification is converted to the more stable thiol form (12). On oxidation, typically with alkaline ferhcyanide, yellow form (11) is irreversibly converted to thiochrome [299-35-4] (14), a yellow crystalline compound found naturally in yeast but with no thiamine activity. In solution, thiochrome exhibits an intense blue fluorescence, a property used for the quantitative determination of thiamine. 

The product is a hemithioacetal. In the rate-determining step, the general acid HA donates a proton to the carbonyl oxygen, thus assisting the nucleophilic attack of the thiol on the carbonyl carbon. 

MO studies (AMI and AMI-SMI) on the tautomerism and protonation of 2-thiopurine have been reported [95THE(334)223]. Heats of formation and relative energies have been calculated for the nine tautomeric forms in the gas phase. Tire proton affinities were determined for the most stable tautomers 8a-8d. Tire pyrimidine ring in the thiones 8a and 8b has shown a greater proton affinity in comparison with the imidazole ring, or with the other tautomers. In solution, the thione tautomers are claimed to be more stabilized by solvent effects than the thiol forms, and the 3H,1H tautomer 8b is the most stable. So far, no additional experimental data or ab initio calculations have been reported to confirm these conclusions. 

The thiol shows a preference to react w ith propagating radicals with a tenninal S unit (Scheme 7.21). This selectivity is due both to chemospecificity in the reaction with thiol and to the relative concentrations of the various propagating species (determined by the reactivity ratios). 

The various oxidation states of sulfur have been determined by polarography. The electrochemical oxidation of sulfide ions in aqueous solution may lead to the production of elementary sulfur, polysulfides, sulfate, dithionate, and thiosulfate, depending on the experimental conditions. Disulfides, sulfoxides, and sulfones are typical polarographically active organic compounds. It is also found that thiols (mer-captans), thioureas, and thiobarbiturates facilitate oxidation of Hg resulting thus in anodic waves. 

Under physiological conditions, transfer of Et3PAufrom hemoglobin to albumin has been observed. The transfer is direct and does not require a low-molecular weight thiol such as GSH as an intermediary and indicates that inter-protein transfer of gold can occur spontaneously. The rapid and efficient manner of establishing this equilibrium (for transauration ) could determine many ofthe effects of intracellular and extracellular chemistry of gold. 

Lewis, S.D., Misra, D.C. and Shafer, J.A. (1980) Determination of interactive thiol ionizations in bovine serum albumin, glutathione, and other thiols by potentiometric difference titration. Biochemistry, 19, 6129-6180. 

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