Speciation 98: Abstracts

Complexation by several -amino acids and simple peptides have recently received much attention. The preparation of complexes with GlyGly, GlyAla, GlyPhe and GlyTyr has been reported, the latter characterized by X-ray diffraction.¹ Solution studies based on spectroscopic measurements have been published for several simple dipeptides and glutathione.

In this presentation several difficulties found in speciation of V^IVO-peptide solutions are discussed. These studies should involve potentiometric and spectroscopic methods. With optically active peptides circular dichroism can be used and is extremely informative about the formation of complexes with VO²⁺. ESR may help in identification of equatorial ligands, particularly if N^-_amide is involved or not. ESEEM may also help particularly in distinction of equatorial vs. axial coordination by nitrogen.

For each stoichiometry in solution several isomers may be envisaged. As vanadium in V^IVO may become an optically active centre, most complexes therefore contain at least two dissymmetric centres, the structures considered normally corresponding to one of the two possible diasteriomers.

For aqueous solutions containing relatively high dipeptide-to-vanadium ratios (e.g. L:M > 10) the equatorial coordination geometry for one of the important stoichiometries normally found at pH 7-9 may be described as represented in I. General characteristics of the ESR and circular dichroism of I will be discussed. Preliminary results of potentiometric and spectroscopic studies of the V^IVO-glutathione systems will also be presented.

I

References

1. (a) A.J. Tasiopoulos, Y.G. Deligiannakis, J.D. Woolins, A.M.Z. Slawin and T.A. Kabanos, J. Chem. Soc. Chem. Commun., in press;
   (b) A.J. Tasiopoulos, A.T. Vlahos, A.D. Keramidas, T.A. Kabanos, Y.G. Deligiannakis, C.P. Raptopoulou and A. Terzis, Angew. Chem. Int. Ed. Engl., 1996, 35, 2531.
   

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