ISSN:
1432-1327
Keywords:
Key words Vanadate
;
Peroxovanadate
;
Dithiothreitol
;
Redox buffer
;
Equilibria
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract Dithiothreitol (CH2SHCHOHCHOHCH2SH), under neutral conditions in aqueous medium, reacts readily and reversibly with vanadate to form longlived complexes. The ligand, vanadium and proton stoichiometries were established from concentration and pH studies. The two predominant products each contained two vanadium(V) nuclei and one dithiothreitol and carried an overall doubly negative charge. The equilibrium shifted toward a triply negative charge with increase in pH through the pK a range of the products. The 51V 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 coordination 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 source of a strong stabilizing interaction leading to the very favourable formation constants (overall about 107 at pH 7). The coordination shell about the individual vanadiums each contained one sulfur in the one product and one sulfur about one vanadium and only oxygen about the other vanadium in the second product. Under neutral 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 are observed. Addition of excess dithiothreitol regenerates the dithiothreitol/vanadate complexes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s007750050179
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