The Interactions of Chromium(III) Compounds with Biological Substrates

Jennifer Fox
Furman University

Transition metal complexes of Cr(III) with three aromatic diimine ligands have several attractive features. These chiral octahedral compounds are capable of binding to DNA with a binding constant on the order of ≥ M-1 when one diimine ligand intercalates between the base pairs of DNA. The 2Eg excited state of these complexes is thermodynamically capable of oxidizing the guanine base of DNA. The compounds are also strongly phosphorescent in aqueous solution at room temperature, and the intensity of this emission is quenched in the presence of guanine-containing nucleotides, consistent with an electron transfer deactivation pathway involving guanine oxidation and Cr(III) reduction. In addition to DNA and mononucleotides, amino acids such as tryptophan and tyrosine quench the emission of chromium tris(diimine) compounds, presumably also via a redox pathway. Varying the identity of the intercalating ligand and the two non-intercalating ancillary ligands around the Cr(III) center affects the compound's excited state oxidizing power, binding constant to DNA, and the stereoselectivity of the binding preference. The ability to oxidize DNA upon irradiation at wavelengths in the 350 - 440 nm region is interesting because it initiates DNA strand cleavage and may prove to be a useful and selective way to destroy tumor DNA.