Vanadium II , III , and IV

Unlike V(II), both the V(III) and V(IV) oxidation states are stable in water. However, neither the V(III) nor the V(IV) oxidation states are easily maintained in the presence of oxygen if the pH is neutral or above, although, under acidic conditions, both these states are rather easily maintained. Somewhat surprisingly, the V(IV) species is more readily oxidized by 02 than is the V(III) species. In aqueous acidic solution, the vanadium(III) ion exists as a hexaqua octahedral complex that can deprotonate to form the 2+ and 1+ species, dependent on pH. Additionally, di, tri and tetra polymeric forms are known. Structures have been proposed and their formation constants determined [10], The occurrence of the various polymeric forms in the presence of sulfate has also been described and is particularly relevant to concentration of vanadium by bioaccumulators [10], 

Complexes of vanadium(III) typically have octahedral coordination, though other coordinations are certainly not unusual, particularly with bulky ligands where trigonal bipyramidal coordination is adopted. Nitrogen- and oxygen-containing mul- 

Yamaguchi, and H. Michibata. 2003. Chloride channel in vanadocytes of a vanadium-rich ascidian Ascidia sydneiensis samea. Comp. Biochem. Physiol. B Biochem. Mol. Biolog. 136 91-98. 

Michibata, H., T. Uyama, and K. Kanamori. 1998. The accumulation mechanism of vanadium by ascidians. In Vanadium compounds. Chemistry, biochemistry and therapeutic applications, A.S. Tracey and D.C. Crans (Eds.), American Chemical Society, Washington, D.C., pp. 248-258. 

Nakanishi, P. Frank, and K.O. Hodgson. 1995. Vanadium in ascidians and the chemistry of tunichromes. In Vanadium and its role in life. H. Sigel and A. Sigel (Eds.), Marcel Dekker, Inc., New York, pp. 423 190. 

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It is possible to measure the formation of various radicals such as reactive oxygen species in cells. Reactive oxygen species (ROS) activate the nuclear factor of activated T cell transcription factor (NFAT), which is associated with its dephosphorylation, nuclear translocation, and increased affinity for DNA binding. Vanadium activation of nuclear factor of activated T cells (NFAT) was found to correlate with formation of the ROS H202 and was dependent upon the activity of calcium channels [39], In activated human neutrophiles, vanadium(II), (III), and (IV) increased hydroxyl radical formation and attenuation of myeloperoxidase activity, whereas V(V) did not show these effects. Similar results were seen in a cell-free system [40], Increased lipid peroxidation in liver but not in kidneys was found in normal rats treated with vanadate [41]. 

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