The Aqueous Vanadium III, IV and V Systems

Acidification of vanadate(V) solutions yields yellow solutions of decavanadate n = 0-3, depending on the pH) or, for pH values 2, the colourless hydrated dioxovanadium monocation, [V02(H20)4]+. If these V -containing solutions are reduced, gradual formation of vanadyl (blue), V + (green) and V + (violet) 

The one-electron redox reactions for the three oxidation states of relevance are represented by Equations (2.1a)-(2.1c). Table 2.1 contains the standard potentials ( °) for the three redox pairs together with the respective potentials at pH 7, assuming equal 

The more positive the potential is, the stronger is the electron affinity of the oxidised form. Inspection of Table 2.1 thus reveals that, under aerobic conditions, is stable whereas, in anoxic environments, which normally prevail in the cytoplasm, reducing agents such as ascorbate, glutathione and NADH readily reduce to V 0 +, 

Bioinorganic Vanadium Chemistry Dieter Rehder 2008 John Wiley Sons, Ltd 

Baes-Messmer diagram for the aqueous vanadium system. Standard redox potentials (in V) vs the normal hydrogen electrode (NHE) are given. The two parallel dashed lines running from the upper left to the lower right indicate the range of stability of water. Reproduced from C. F. Baes and R. E. Messmer, The Hydrolysis of Cations, pp. 197-210. Copyright (1976), with permission from John Wiley Sons, Ltd. 

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