EPR CHARACTERIZATION OF THE CR-V INTERMEDIATES IN THE CR-VI/V OXIDATIONS OF ORGANIC SUBSTRATES AND OF RELEVANCE TO CR-INDUCED CANCERS

An empirical method has been developed for determining the coordination number of Cr-V complexes (five- or six-coordinate) and the donor groups bound to Cr-V from the measured g(iso) and A(iso) values. The g(iso) values depend only on the nature of the donor groups and the number of each group, which is very useful in the characterisation of the coordination number and donors. By contrast, the A(iso) values appear to be sensitive to the nature of the equatorial donor atoms and the coordination geometry. Strong correlations have been found between the g(iso) values of isoelectronic Cr-V and V-IV complexes and between the A(iso) values of analogous complexes of these two metal ions. These, combined, have been used to understand the solution chemistry of Cr-V using EPR spectroscopy. Such studies have also been invaluable in unravelling the biochemistry that occurs in cell media and cells exposed to carcinogenic Cr-VI and, hence, possible mechanisms of Cr-induced cancers.