Speciation 98: Abstracts

A variety of biological systems involving vanadium have emerged in the past years pointing out that metal ion's significance in nature.¹ Prominent among those stand metalloproteins and metalloenzymes, in the biological active centers of which vanadium evolves as the metal catalyst bound to amino acid residues and organic cofactors. Alternative vanadium nitrogenases² and haloperoxidases³ are representative examples of enzymes encompassing vanadium in their active sites and performing different yet crucial catalytic processes (nitrogen reduction and organic substrate halogenation, respectively). Vanadium, however, emerges equally active outside of protein systems, either stimulating or inhibiting their biological function.⁴ Carboxylic acids are components of biological fluids capable of interacting with metal ions essential to biological processes. Citric acid is prominent among the natural metal ion binders in a biological milieu⁵ and stands to potentiate vanadium's involvement in those processes.

Driven by the largely unknown mechanistic details of vanadium interactions with biomolecules, we have focused on the chemistry⁶ of that metal with citric as well as other tricarboxylic and dicarboxylic acids. Our approach targeted primarily the aqueous chemistry of citric acid with vanadium(III) under varying pH conditions. As a result of the synthetic biomimetic chemistry developed, novel dimeric vanadium-citrate complexes were isolated from aqueous solutions. The dimeric species were characterized spectroscopically (FTIR, UV/Visible, etc.). Their three dimensional X-ray crystal structure determination confirmed the spectroscopically found vanadyl moiety as the central feature in the complexes containing the citrate ligand bound to it in different modes as a function of the pH. Further exploration of the reactivity of those complexes toward hydrogen peroxide yielded new species, which were isolated. The spectroscopic and structural features of the new complexes will be discussed⁷ and their potential role in biological fluids will be dwelled on.

Rerefences

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   b) Gresser, M. J.; Tracey, A. S. in "Vanadium in Biological Systems", Chasteen, N. D. (ed.). Dordrecht: Kluwer; 1990, 63-79.
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6. a) Djordjevic, C.; Vuletic, N.; Renslo, M. L.; Puryear, B. C.; Alimard, R. Molec. Cellul. Biochem., 1995, 153, 25-29.
   b) Djordjevic, C.; Renslo, M. L.; Sinn, E. Inorg. Chim. Acta, 1995, 233, 97-102.
7. Tsaramyrsi, M; Salifoglou, A. to be submitted for publication.

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