Chromium toxicity: spectral and electrochemical studies of Cr(VI) reduction by biomimicking molecules

Abstract

The reductive abilities of a variety of biomimicking molecules, including OH-containing ones such as, saccharides and their derivatives, nucleotides and their components and mixed group ligands have been determined in vitro using absorption spectra and electrochemical characterisations and were explained based on the nature of the reductants. While the reductive coefficients of these molecules showed a linear correlation with respect to oxidation potential of the ligand (E^a_P) and/or reduction potential (E^c_p) of the final Cr(III)-products, in any given set, such as hexoses, pentoses, polyols, glycols, saccharide derivatives, nucleotides and their components and mixed group ligands, the plot of all the reductants reported in this paper exhibited interesting correlations with respect to these electrochemical parameters. These correlations are expected to be important in the identification of species in routine analysis carried out with pollutants. As reduction of Cr(VI) to Cr(III) by saccharides and their derivatives progresses via soluble and reactive intermediates of Cr(V) having long t_½ periods, this may be implicated in the transport of toxic chromium salts from soil to plants and their ultimate entry into the biosphere causing ecological hazards. Based on the results obtained on chromate reduction studies, a working model has been proposed for the toxicity of Cr(VI).