Equilibrium Studies of the Dimethyltin(IV) Complexes with Tyrosine, Tryptophan, and Phenylalanine

Abstract

The formation constants of the species formed in the systems H þ þ dimethyltin(IV) þ tyrosine, tryptophan, and phenylalanine as well as H þ þ tyrosine, tryptophan, and phenylalanine have been determined in aqueous solution in the pH range (1.5 to 9.5) at a constant temperature (25 °C) and constant ionic strength (0.1 mol 3 dm À3 NaClO 4 ), using a combination of spectrophotometric and potentiometric techniques. The composition of the formed complexes were determined, and it was shown that dimethyltin(IV) forms three mononuclear 1:1 species with all the ligands, of the type MHL, ML, and MH À1 L, where M and L represent metal ion and each amino acid, respectively. A complex distribution curve depending on the pH and metalÀligand ratio is given, and influences of the ligands side chains on the stability constants of the formed species are discussed. 1 H NMR investigations in aqueous solution confirmed the species formation and led us to propose their probable structures.