AQUEOUS INTERACTIONS OF VANADATE AND PEROXOVANADATE WITH DITHIOTHREITOL - IMPLICATIONS FOR THE USE OF THIS REDOX BUFFER IN BIOCHEMICAL INVESTIGATIONS

Dithiothreitol (CH2SHCHOHCHOHCH2SH), under neutral conditions in aqueo us medium. reacts readily and reversibly with vanadate to form long-li ved complexes. The ligand, vanadium and proton stoichiometries were es tablished from concentration and pH studies. The two predominant produ cts each contained two vanadium(V) nuclei and one dithiothreitol and c arried an overall doubly negative charge. The equilibrium shifted towa rd a triply negative charge with increase in pH through the pK(a) rang e of the products. The V-51 NMR spectra clearly showed two resonances for each product (-352 and -362 ppm for one and -399 and -526 ppm for the other), thus establishing there are chemical differences in the co ordination about each vanadium, A coordination scheme was proposed for each product. The common motif proposed was the presence of a cyclic [VO](2) core as the sourer of a strong stabilizing interaction leading to the very favourable formation constants (overall about 10(7) at pH 7). The coordination shell about the individual vanadiums each contai ned one sulfur in the one product and one sulfur about one vanadium an d only oxygen about the other vanadium in the second product. Under ne utral conditions the reduction of V(V) to V(IV) requires in the order of 90 min. However. if hydrogen peroxide, in greater than a 2:1 molar ratio over dithiothreitol, is included in the reaction medium, all the dithiothreitol is rapidly oxidized, and peroxovanadium(V) complexes a re observed. Addition of excess dithiothreitol regenerates the dithiot hreitol/vanadate complexes.