Structure, stability, and ligand exchange of copper(II) complexes with oxidized glutathione

Formation constants and structures of copper(II) complexes with oxidized glutathione (L) have been determined by computer modelling of spectrophotometric and NMR relaxation measurements data over a wide range of pH (1-13) and metal and ligand concentrations in aqueous KNO3 (1 M) at 298 K. Among 11 found complexes, four forms were characterized for the first time. Based on a comparison of thermodynamic, relaxation, and optical and EPR spectroscopy parameters the structural conclusions were made. In particular, the CuLH2 and CuLH− complexes both contain two isomers which are similar to mono- and bis-aminoacid copper(II) complexes. In the Cu2L and Cu3L22- species one of the copper atoms is bound only with the carboxylate or carbonyl groups and the others are coordinated similarly to aminoacid chelates. Along with the last, in Cu2LH-22- two bridging OH− groups in one isomer or two chelate rings including deprotonated peptide nitrogen and glycinyl carboxylate oxygen in another are also present. In Cu3L2H-46- the mixed variant of coordination between CuL2− (CuN2O2) and Cu2LH-44-(CuN3O) is realized. The structures of polynuclear complexes have been optimized in density functional theory computations. Rate constants of ligand exchange reactions of Cu(LH)24- and CuL26- with participation of the LH3− and L4− forms were determined for the first time. Factors determining rates of these processes have been revealed and their proceeding by associative substitution mechanism shown.