Mechanistic studies of relevance to the biological activities of chromium

Cellular uptake of Cr(VI), followed by its reduction to Cr(III) with the formation of reactive Cr(V/IV) intermediates, is a generally accepted cause of Cr(VI)-induced genotoxicity and carcinogenicity. Recently, Cr(III) oxidation to Cr(V) and/or Cr(VI) in biological systems came into consideration as a possible reason of anti-diabetic activities of some Cr(III) complexes, as well as of long-term toxicities of such complexes. The current review (with 142 references) summarizes the existing knowledge on the mechanisms of biologically relevant redox reactions of Cr(VI/V/IV/III) complexes. Applications of global kinetic analysis techniques, in conjunction with the methods for characterization of reactive intermediates (such as X-ray absorption spectroscopy, electrospray mass spectrometry, and EPR spectroscopy), for understanding the chemical basis of Cr biological activities, are illustrated with the examples from the authors' research.