On Polymeric Gold(I) Complexes with Glutathione in Aqueous Solutions

Abstract

The study addresses reactions involving gold(I) glutathione complexes in aqueous solutions at T = 25°C and I = 0.2 M (NaCl) in the pH range of 7.20–6.06 (C_Au = (5–10) × 10^–4 M). Using mass spectrometry, it was shown that at C_GS > C_Au, polymeric species \({\text{A}}{{{\text{u}}}_{{\text{4}}}}({\text{GS}})_{4}^{*}\) and \({\text{A}}{{{\text{u}}}_{n}}({\text{GS}})_{{n + 1}}^{*}\), where n ≤ 4, can exist, together with monomeric \({\text{Au}}({\text{GS}})_{2}^{*}\) (the symbol * means the sum of species with different degrees of protonation). According to UV spectroscopy data, in the range of 0.5 < C_GS/C_Au < 3, all spectra can be described, within the experimental error, as linear combinations of the spectra of four species, including \({\text{Au}}({\text{GS}})_{2}^{*}\). The proportion of \({\text{Au}}({\text{GS}})_{2}^{*}\) decreases with decreasing pH. The equilibrium constant for 0.25 \({\text{A}}{{{\text{u}}}_{{\text{4}}}}({\text{GSH}})_{4}^{{4 - }}\) + \({\text{GSH}}_{2}^{ - }\) = \({\text{Au}}({\text{GSH}})_{2}^{{3 - }}\) + H⁺ amounts to log K = –4.4 ± 0.1 (I = 0.2 M, NaCl).