Vanadium(III) binding strengths of small biomolecules

The hydrolysis of vanadium(III) and the complex formation reactions between V(111) and weakly coordinating [glycine (GLY), DL-aspartic acid (ASP), D-penicillamine (PEN), DL-histidine (HIS)] or strongly coordinating [N,O] donor [picolinic (PIC) or 6-methylpicolinic acid (MePIC)] and [O,O] donor [maltol (MALT), 1,2-dimethyl-3-hydroxy4-(1H)-pyridinone (DHP), tiron (TIR)] ligands were studied at 25.0 degrees C and an ionic strength of 0.20 M (KCl) in aqueous solution using combined pH-potentiometric and UV-vis spectroscopic techniques. Although some interaction between the amino acids and V(III) was found, we could not obtain reliable models for these systems owing to the intensive hydrolysis of the metal ion and the formation of polynuclear hydroxo complexes. With pyridine carboxylates or [O,O] donor ligands 1:1, 1:2 (in the latter case, also 1:3 species) were found to be present as major complexes in solution. The similarities and differences in binding V(III) by these ligands are discussed.