Coordination properties of l-cysteine and its derivatives towards dietethyltin(IV) in aqueous solution

Abstract

Complex formation equilibria of L-cysteine (LH3), S-methyl-L-cysteine (LH2) and N-acetyl-L-cysteine (LH2) with diethyltin(IV) were studied in aqueous solution (I = 0.1 M NaClO4). The formation constants of the complexes were determined by potentiometric equilibrium measurements. Besides the carboxil-oxygen, thiol-sulphur of L-cysteine and of its N-acetyl derivative were shown to be deprotonated and coordinated to the metal in the acidic region. Due to the stabilizing effect of additional thioether coordination in case of S-methyl-L-cysteine the formation of an MLH complex was detected. In case of L-cysteine and its S-methyl derivative, amino nitrogen served as third donor atom at higher pH. N-acetyl-L-cysteine participated in the complex formation only by two donor atoms in the whole pH range studied (2–11). For the system containing L-cysteine as ligand, Mössbauer investigations in quick-frozen solutions based on the partial quadrupole splitting concept reflected the geometry of the species formed. © 1995, Walter de Gruyter. All rights reserved.