OXOVANADIUM(IV) COMPLEXATION BY ADENOSINE 5'-DI-PHOSPHATE AND 5'-TRI-PHOSPHATE AND NUCLEOTIDE BUILDING-BLOCKS

Complex formation between oxovanadium(IV) and the bioligands adenosine 5'-diphosphate (ADP), adenosine 5'-triphosphate (ATP), adenine, adeno sine and 2'-deoxyadenosine 5'-diphosphate (dADP) was investigated in a queous solution by EPR, electronic absorption spectroscopy, and pH-pot entiometry. The reaction scheme implies that, in acidic media, nucleot ides chelate the metal ion through unshared oxygen atoms of the polyph osphate chain, whereas vicinal cis-oriented hydroxyls of the ribose mo iety are the binding set in alkaline solution. Species with mixed co-o rdination were also detected. Dihydroxo-bridged dimers can be formed b y ATP and ADP molecules co-ordinating through both the phosphate and r ibose residues; however, formation of dihydroxo-bridged dimers with mi xed chelation is the most favoured. Owing to the poor affinity of VO2 towards N-donors, adenine is not able to bind VO2+ within the whole m easurable Ph range. In adenosine the ribose unit provides the ligand w ith pairs of vicinal cis-oriented hydroxyls, the right arrangement to form stable five-membered chelated rings. Lack of a C(2)OH group means that dADP does not possess a pair of cis hydroxyls and only diphospha te chelation is observed with this ligand.