Thermodynamic studies on the complexation of cobalt(II) with dopamine in a cosolvent system

Equilibrium constants for formation of a cobalt(II) complex with the bidentate ligand dopamine have been studied with spectrophotometric methods in water + ethanol cosolvent systems at 15, 25, and 35 ( +/- 0.1. 1) degrees C and an ionic strength of 0.2 mol center dot dm(-3). The ionic strength was maintained using sodium chloride and a phosphate buffer. The stability constants of the complex and the resulting Gibbs energy changes are obtained. The results are discussed in terms of the effect of solvent on protonation and complexation.