Cold vapour atomic fluorescence studies on the behaviour of mercury(II) and mercury(II)-thiol complexes. An alternative route for characterization of –SH binding groups

Abstract

The behaviour of HgII and HgII-thiol complexes (RSH=-cysteine, -penicillamine, propane-2-thiol, glutathione, thiosalicylic acid ) following their reduction with alkaline sodium tetrahydroborate to give Hg0 has been studied by using a continuous flow reaction system coupled with atomic fluorescence spectrometric (AFS ) detection. The quantitative reduction of HgII to Hg0 takes place with a specific amount of sodium tetrahydroborate according to the stoichiometric reaction of mercury with alkaline NaBH 4. The complete reduction of HgII-thiol complexes to Hg0 requires a molar excess of NaBH 4 of up to six orders of magnitude, depending on the type of complex. Under an appropriate excess of reductant, HgII and its thiol complexes are not distinguishable giving the same AF molar response. The method allows the discrimination of HgII from HgII-thiol complexes without any preliminary separation. Applications to the indirect titration of thiols and to the determination of the number of accessible KSH groups in pure ovalbumin samples are reported. stoichiometry, KSKHgKR, and have been preferred to HgII,

Mechanisms of chemical generation of volatile hydrides for trace element determination (IUPAC Technical Report)

“…it has been verified that a chemical amount ratio for THB/Hg is 0.25 ± 0.02 for Hg in the concentration range (10 -10 -10 -6 ) mol L -1 Hg II [130]. The experimental results confirmed the stoichiometry of reaction 43.…”

“…One more example is given by Hg, which can be determined by reduction of Hg II by NaBH 4 in alkaline media (pH = 13) [130]. For this reaction…”

Application of Mercury Cold Vapor Atomic Fluorescence Spectrometry to the Characterization of Mercury-Accessible −SH Groups in Native Proteins

“…The behavior of Hg II and Hg II -thiol complexes, at nanomolar level (0.01 mol dm Ϫ3 phosphate buffer, pH 7.2, 0.05 mol dm Ϫ3 NaCl), following their reduction with alkaline sodium tetrahydroborate to give Hg 0 , was previously investigated by using a continuous flow reaction system coupled with AFS detection (10). The aim of this section is to give a concise description of the working principles of the method.…”

“…In a previous paper the potentialities of alkaline NaBH 4 in performing the selective reduction of inorganic Hg II and its thiolic complexes have been investigated (10). By choosing the degree of selectivity as a function of the reductant concentration and detecting the evolved Hg 0 by AFS, a sensitive analytical tool has been obtained for the investigation and characterization of Hg II -thiol complexes present in solution at nanomolar level.…”

“…In the present work we applied the CVAFS method previously proposed (10) to the study of several native thiolic proteins and enzymes (ovalbumin, hemoglobin, glyceraldehyde-3-phosphate dehydrogenase, aldolase, pyruvate kinase, hexokinase, lactate dehydrogenase, alcohol dehydrogenase, creatine phosphokinase, lysozyme, and cytochrome c). The results obtained in the estimation of the average number of ϪSH groups in native proteins with the proposed method are reported and compared with those reported in the literature using different methods.…”