Complex-formation reactions and stability constants for mixed-ligand complexes of diaqua(2-picolylamine)palladium(ii) with some bio-relevant ligands

Abstract

The complex-formation reactions of [Pd(Pic)(H₂O)₂]²⁺ (pic = 2-Picolylamine) with selected bio-relevant ligands, containing different functional groups, were investigated. Stoichiometry and stability constants for the complexes formed are reported. The results show the formation of 1 : 1 complexes with amino acids and dicarboxylic acids. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was examined. Peptides form both 1 : 1 complexes and the corresponding deprotonated amide species. Structural effects of the peptide on the amide deprotonation were investigated. DNA pyrimidinic constituents, such as uracil, uridine, thymidine and thymine, form 1 : 1 and 1 : 2 complexes, whereas purinic constituents, such as inosine 5′-monophosphate (5′-IMP) and guanosine 5′-monophosphate (5′-GMP), form only 1 : 1 complexes. Both DNA constituents and cyclobutane dicarboxylate (CBDCA) react with [Pd(Pic)(H₂O)₂]²⁺ forming [Pd(Pic)(CBDCA-O)DNA], where (CBDCA-O) represents cyclobutane dicarboxylate coordinated by one carboxylate oxygen atom. The concentration distribution of the complexes in solution was evaluated. The effect of dioxane on the acid dissociation constants of CBDCA and the formation constant of its complex with Pd(Pic)²⁺ is reported. The effect of increasing chloride concentration on the formation of the CBDCA complex was investigated.