INTERACTIONS BETWEEN VANADATE AND 1,2-AROMATIC DIOLS. COMPLEX FORMATION AND OXIDATION-REDUCTION
The kinetics of the interaction between vanadate oxoanion and 1,2-aromatic diols in basic media (pH 8-9, ionic strength 0.5 M (NH4C1), 25 OC) have been studied by stopped-flow spectroscopy. Three distinct transients are observed after mixing. In order of increasing reaction lifetime the transients are assigned to complex formation, reduction of V(V) to V(IV), and further reactions of the intermediate oxidation product. The rate of complex formation increases with increasing pH; a similar effect has been found for the formation of a bis(l,2-aromatic diol) complex of molybdate. The rate of the oxidation-reduction reaction increases with decreasing pH. This effect has been interpreted as the proton-transfer-assisted formation of monooxovanadium(1V) from the parent cis-dioxovanadium(V) complex. Qualitatively, these results model the reversal of the specific vanadate inhibition of mammalian [Na,K]-ATPase by catecholamines.