Speciation 98: Abstracts

An increasing interest has recently been payed to the role of vanadium in biological systems. The reasons for this are that as vanadate(V) vanadium behaves as phosphate antagonist, and as oxovanadium(IV)²⁺-ion it has a very flexible coordination sphere allowing to substitute for divalent metal ions in the enzyme active centers. A series of vanadium complexes have also been investigated as insulin-mimetic agents, and some of them have been found to be effetcive in lowering the plasma glucose level. The mechanism of the action is still unknown.

In spite of these facts the solution coordination chemistry of vanadium ions is fairly unexplored. Oxovanadium(IV)²⁺-ions readily undergo hydrolysis and as a competitive process may deprotonate alcoholic hydroxy groups in the presence of an anchoring donor group. Our investigations on the bahaviour of series of N-D-gluconylamino acid ligands (glycine, b-alanine and serine as amino acids) towards oxovanadium(IV)²⁺-ions were intended to monitor whether they are able to prevent the hydrolysis of the metal ions acting as effective complex forming agents. In order to determine the composition of the complexes formed we utilized potentiometric and spectrophotometric titrations, since CD and EPR spectroscopies gave information about their solution structure. The results show that the ligands coordinates the metal ion in the pH range 2-10. N-D-gluconylamino acids form complexes with only 1:1 ligand to metal ratio, not like the previously investigated carbohydrates. Two equivalents of hydroxyde per metal ions were consumpted up to pH 4.5. According to the spectroscopic measurements these deprotonation processes presumably belong to the loss of protons from an alcoholic hydroxyl and the amide groups. With the increasing pH dinuclear species are also formed in the solutions.

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