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). The results reveal that the Ru(III) complex is deactivated as a NO scavenger by thiolate ligands.