Nucleobase oxidation of DNA by (terpyridyl)chromium(III) derivatives

The chromium(III) complexes [Cr(ttPY)(2)](ClO4)(3) (1) and [Cr(Brphtpy)(2)](ClO4)(3) (2), containing the terpyridyl derivatives ttpy and Brphtpy [ttpy = p-tolylterpyridine; Brphtpy = (p-bromophenyl)terpyridine] have been synthesized and characterized by ESI-MS, electronic spectroscopy, and cyclic voltammetry. Absorption titration and thermal denaturation studies reveal that both complexes are moderate binders of calf thymus DNA (CT DNA), while viscosity measurements show that they bind with partial intercalation. Binding of the two chromium complexes to DNA and mononucleotides dGMP, dAMP, dCMP, and dTMP decreases the emission intensity of complex 2. However, the emission intensity of complex 1 is quenched only by DNA and the nucleotides dGMP and dATAP. Excited state potentials of both 1 and 2 have been estimated to be 1.65 and 1.85 V vs. NHE. These results demonstrate that 2 is a stronger photooxidant than 1, and other (diimine) chromium complexes, and that it can oxidize nucleobases. The photonuclease activity of 1 and 2 has been confirmed by gel electrophoresis. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)