Speciation 98: Abstracts

The complex formation between oxovanadium(IV) and phosphate bioligands is of relevance for the activity of the metal ion in cellular systems. For instance, it has been reported that the trapping of VO²⁺ by ATP slows the rate of oxidation of the vanadyl(IV) ion to vanadate(V) which, on the other hand, can catalyze the non-enzymatic hydrolysis of the nucleotide.

The complexation of oxovanadium(IV) by nucleotides was the object of extensive spectroscopic and potentiometric investigation. Several schemes were proposed, but none of them was able to provide a comprehensive description of the complex systems. We have investigated the interaction of VO(IV) with a number of nucleotide biomolecules, like AMP, ADP, ATP and GMP. The results were checked by comparison with model systems involving phosphates, nucleic bases and sugars.

The general reaction scheme implies that, in acidic media, nucleotides chelate the metal ion through unshared oxygen atoms belonging to the polyphosphate chain, whereas vicinal cis oriented hydroxyls of the ribose moiety are the binding set in alkaline solution. Species with mixed phosphate-ribose coordination as well as dihydroxo-bridged dimers formed by molecules coordinating through either the phosphate or the ribose residues were also detected. Due to the poor affinity of VO²⁺ towards N-donors, the adenine moiety is not able to bind VO²⁺. In adenosine, the ribose unit provides the ligand with couples of vicinal cis oriented hydroxyls, the right arrangement to form stable five-membered chelated rings. Lacking of C(2') OH group bereaves 2'-deoxy-ADP of the couple of cis hydroxyls and only diphosphate chelation is observed with this ligand.

In the VO(IV)-guanosine-5'-monophosphate system, a monomer dimer equilibrium, arising from the intermolecular binding of phosphate groups to the metal ion, has been substantiated.

Back to the list of abstracts