CHEMICAL STUDY FOR REDUCTION AND ACCUMULATION MECHANISM OF VANADIUM BY ASCIDIANS

已发现磷酸戊糖途径中的酶定位于某些海鞘细胞的胞质中，该途径产生生物还原剂NADPH。我们曾报道在EDTA存在下，钒(V)可以被NADPH还原。在本项目中，我们试图找出哪种共存配体对NADPH还原钒(V)是有效的。我们使用氨基多羧酸盐及其衍生物，氨基酸作为共存配体。根据可见光吸收光谱和电子自旋共振光谱的测量，这些配体可以根据它们促进钒(V)还原的能力而分为三类。第一组：IDA、PDA、NTA、Hedtra、Heida、EDDP、His；第二组：Asp、Asn、Glu、Gln、Thr、Trp；第三组：Gly、Ser、Meta。在第一组中的一个配体的作用下，钒(V)被还原成(IV)。另一方面，当第三组中的一个化合物作为共存配体时，几乎没有观察到钒(V)的还原。第二族配体属于中间体，四齿、五齿和六齿配体具有较强的螯合作用，属于第一族配体，第三官能团配位能力很弱的二齿配体或三齿配体属于第三族配体。从共存配体的络合形成常数和钒(V)络合物的电化学性质的角度进一步研究共存配体还原钒(V)的能力是非常重要的。

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, metThe 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.