| Research Abstract |
It has been found that the enzymes in the pentose phosphate pathway, which produces a biological reducing agent, NADPH, are localized in the cytoplasm of vanadocytes of certain ascidians. We have reported that vanadium (V) can be reduced by NADPH in the presence of edta. In this project, we tried to find out that which type of coexisting ligand is effective in reducing vanadium (V) by NADPH.
We used aminopolycarboxylates and their derivatives, and amino acids as a coexisting ligand. The ligands can be classified into three groups according to their ability to promote the reduction of vanadium (V) on the basis of the visible absorption and ESR spectral measurements. Group 1 : ida, pda, nta, hedtra, heida, eddp, his ; Group 2 : asp, asn, glu, gln, thr, trp ; Group 3 : gly, ser, met
The reduction of vanadium (V) to vanadium (IV) has been observed definitely using a ligand in Group 1. On the other hand, a reduction of vanadium (V) was scarcely observed when a compound in Group 3 was used as a coexisting ligand. Group 2 ligands are situated in the intermediate.
Tetra-, quinque-, and hexa-dentate ligands that have a large chelate effect are belonging to Group 1. Bidentate ligands or tridentate ligands in which the coordinating ability of the third functionality is very weak are belonging to Group 3. It should be important to study further the ability of coexisting ligands in the reduction of vanadium (V) from the viewpoint of the complex formation constants of the coexisting ligand and the electrochemical properties of the vanadium (V) complex.
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