Speciation 98: Abstracts
T. Kiss,1 K. Petrohán, P. Buglyó,2 D. Sanna, G. Micera,3 J. Costa Pessoa and C. Madeira4
1 Department of Inorganic and Analytical Chemistry,
Jozsef Attila University, P.O.Box 440, H-6701 Szeged, Hungary;
2 Department of Inorganic and Analytical Chemistry,
Kossuth University, P.O.Box 21, H-4010 Debrecen, Hungary;
3 Dipartimento di Chimica, Universita di Sassari, Via Vienna 2,
I-00710 Sassari, Italy;
4 Centro Quimica Estrutural,
Instituto Superior Tecnico, Av. Rovisco Pais, 1096 Lisboa, Portugal
Vanadium can act as an enzyme regulator in various phosphate-metabolizing reactions, suggesting binding between vanadium and the protein side-chains.1 Its interactions with oligopeptides in the physiological pH range, via coordination of the deprotonated peptide-N- group have been proved to involve vanadium in oxidation state V.3-5
In the oxidation state of (IV) amide coordination of a few synthetic ligands to VO(IV) has been observed in the solid state. In aqueous solution, however, no unambiguous proof has been obtained for VO(IV)-promoted amide deprotonation and coordination, although this was strongly suggested in some glycine/alanine dipeptide complexes by CD and EPR measurements.9 In order to make the donor group environment more favorable for VO(IV) binding, the terminal -NH2 group was replaced by a hard phenolate as anchoring donor group: the solution speciation and structural characterization of the VO(IV) complexes of the dipeptide analogue 2-OH-hippuric acid (HOC6H4C(O)NHCH2COOH, salicylglycine, SalGly) are reported here.
Complexes of various stoichiometries were detected, characterised by spectroscopic (electronic absorption and EPR) techniques and partly isolated from aqueous solution. The results unambiguously prove that the metal ion induced deprotonation and coordination of the peptide-amide occurs in the weakly acidic pH range (pKVOA=4.76). To date this is the only aqueous system in which a VO(IV) complex involving metal-peptide bond is the predominant species at physiological pH.
