Thermodynamics of the interaction of ruthenium(III) polyaminecarboxylate complexes with bio-relevant ligands. Deactivation of the complexes as NO scavengers by thiol ligands.

The acid-base and complex-formation equilibria of [Ru(H(2)dtpa)(H(2)O)], where dtpa = diethylenetriaminepentaacetate, with a series of bio-relevant ligands having various functional groups, viz. thiol, amine, imidazole and carboxylate, were investigated using potentiometric and spectrophotometric techniques. The pK(a) values for [Ru(H(2)dtpa)(H(2)O)] were found to be 2.28 and 3.48 for the uncoordinated carboxylic acid groups and 8.83 for the coordinated water molecule. The complexes formed are of 1:1 stoichiometry and their formation-constants were determined. The effect of dioxane on the acid-base and complex-formation equilibria of the Ru(III) complex was studied. The displacement reaction of coordinated NO by the investigated ligands showed that thiols can compete with NO in their reaction with [Ru(III)(dtpa)(H(2)O)](2-). The results reveal that the Ru(III) complex is deactivated as a NO scavenger by thiolate ligands.