Voltammetric Study of the Interaction of Pentoxifylline (PTX) With Zn(II) in the Presence and Absence of Cysteine

Abstract

The interaction of pentoxifylline (PTX) with Zn(II) in the presence and absence of cysteine at physiological pH (7.40) was investigated for the first time by square-wave and cyclic voltammetry techniques. The Zn(II)-PTX complex was found to be an electroinactive inert complex, the composition of the formed complex is 1 : 1 (metal : ligand), and the logarithm of its stability constant (log β<inf>1:1</inf>) was determined as 3.46 by direct monitoring of the current of free zinc(II). The logarithm of the stability constant (log β<inf>1:2</inf>) and stoichiometry of the complexation of Zn(II) with cysteine were determined to be 9.94 and 1:2, respectively. The stability constants were in agreement with those calculated from electronic spectral data. In the presence of cysteine, Zn(II)-PTX dissociated and an irreversible peak for Zn(II)-cysteine appeared at -1.342V. Cysteine prevents complex formation of Zn(II) with PTX. © 2005 Taylor & Francis Group Ltd.