Reactivity of Tunichromes: Reduction of Vanadium (V) and Vanadium (IV) toVanadium (III) at Neutral pH. (Reannouncement with New Availability Information)

摘要

It is well known that some species of ascidians concentrate vanadium from seawater 10(exp 3)-10(exp 7) fold. However, despite the effort of many groups, the mechanism for this concentration and the biological role of vanadium has remained elusive. It has been suspected that tunichromes (a family of ascidian blood pigments) are involved in this, extraordinary accumulation by complexation and/or reduction, but any relationship between tunichromes and vanadium in vivo has not been revealed. We now have obtained the first evidence showing the ability of tunichrome to generate V(III) in vitro. Reactions-between synthetic tunichrome (Mm-1) and V(V) or V(IV) were carried out in pH 7 buffer. In order to determine the oxidation state(S) of the product vanadium, product mixtures were adjusted to pH 2 and the V(IV) EPR signal of each mixture was measured. Subsequent treatment with 02 converted V(III) to V(IV) at pH 2, and any increase in the EPR signal was measured. Mm-1 was found to completely reduce V(V) (I mol-equiv) to V(III). Furthermore, Mm-1 reduces V(IV) to v(III), apparently after complexation of Mm-1 is complete.... Ascidians, Vanadium, Tunichromes, Electron paramagnetic spectroscopy.