The mechanism of DNA damage induced by Cr(III) complexes is currently unknown even though it is considered to be the ultimate biologically active oxidation state of chromium. In this study, we have employed the Salmonella reversion assay to identify mutagenic Cr(III) complexes. Cyclic voltammetry was used to differentiate the redox kinetics between mutagenic and selected nonmutagenic Cr(III) species. Plasmid relaxation of supercoiled DNA was employed to show in vitro interactions with plasmid DNA and correlate the interactions with the electrochemical behavior and biological activity. The results of this study demonstrate that the mutagenic Cr(III) complexes identified in the Salmonella reversion assay display characteristics of reversibility and positive shifts of the Cr(III)/Cr(II) redox couple consistent with the ability of these Cr(III) complexes to serve as cyclical electron donors in a Fenton-like reaction. These same mutagenic complexes display an ability to relax supercoiled DNA in vitro, presumably by the induction of single-strand breaks. Nonmutagenic complexes were selected to test different ligands to determine how the ligand directs the activity of Cr(III) complexes. All nonmutagenic complexes tested thus far have shown classical irreversibility, more negative reduction potentials, and an inability to relax supercoiled plasmid DNA. These results suggest that the mechanism by which chromium complexes potentiate mutagenesis involves an oxygen radical as an active intermediate. These data also demonstrate the effect of associated ligands with regard to the ability of a metal to generate an active redox center.

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Ennobled open-circuit potential (E corr ) for type 316L stainless steel (SS [UNS S31603]) exposed to fresh river water was investigated using microelectrodes to measure dissolved oxygen (DO), hydrogen peroxide (H 2 O 2 ), and local E corr within biofouling deposits. Galvanostatic techniques were used to measure capacitance (C) and to titrate reducible surface material. Results indicated deposits were uniformly aerobic and did not contain elevated levels of cathodic depolarizers. Development of ennobled potential was related to E corr near the beginning of exposure and occurred on surfaces with as little as 3% to 5% biofouling coverage. Galvanostatic measurements revealed a strong correlation between C and E corr as E corr increased during biofouling. Galvanostatic reduction measurements indicated increased abundance of reducible surface-bound material during the same period. Results suggested an ennoblement mechanism involving modifications of the metal oxide surface.