On the redox interaction of HAuCl4 with thiomalate, as well as with cysteine and glutathione in aqueous solutions

Abstract

The process of AuCl4− reduction by thiomalate (mercaptosuccinate, TM*,–OOCCH2CH(SH)COO−) at CAu = (2–10) × 10−4 M and CTM/CAu < 2 in aqueous solution was studied. Most of the experiments were performed at I = 0.2 M (NaCl), pH 2.00, t = 25 °C, and τ < 20 min. At CTM < CAu, a fast process (τ < 3 s) occurs at the initial stage, AuCl4− + 2TM* = AuTM* + TMox, where AuTM* is a polymer complex of gold(I) (AumTMm*), TMox is a partially oxidized thiomalate. Further slower reduction of AuCl4− proceeds both due to TM from AuTM* and further oxidation of TMox. The change in the concentration of some forms during the process is calculated. In addition to AuCl4−, AuTM* and TMox, the solution contains other gold(I) complexes. A common feature of the process is a much slower change in the concentration of AuTM* compared to the concentrations of other forms. The ratio between products depends on CTM/CAu, with an increase in CTM, the fraction of AuTM* increases. The rate of the process is strongly influenced by the concentration of chloride; with increasing CCl, the rate increases. With increasing pH, the process slows down greatly. An increase in temperature leads to an acceleration of the process, but the ratio of products changes little. To further clarify the features of the process, the reduction of AuCl4− using AuTM* was also studied. The use of cysteine and glutathione instead of TM* did not show significant differences in the nature of the process and the resulting products.