Novel DNA photocleavage properties of [Cr(NN)3]3+ complexes

The aim of this study was to investigate the ability of chromium(III) tris-diimine complexes, [Cr(NN)3]3+, to induce DNA photodamage and to examine its capability to impair the survival of irradiated bacteria with the purpose of using these compounds as photocleavage reagents. [Cr(NN)3]3+ complexes, where NN stands for the ligands: phen (1,10-phenanthroline), 5-Mephen, 4,7-diMephen, 3,4,7,8-tetraMephen, 5-Phphen and 5-Clphen were used for this purpose. Their properties of DNA photocleavage were investigated by electrophoretic studies and assays of the photosensitization of transformed bacteria. The results clearly indicate that [Cr(NN)3]3+ complexes promote the photocleavage of plasmid DNA with varied degrees of efficiency after 12 h of irradiation. The combination of DNA, [Cr(NN)3]3+ and light proved to be required to induce the breakdown of DNA. Irradiated plasmid DNA-[Cr(NN)3]3+ association is also capable of impairing the transforming capacity of bacteria. These results provide evidence which confirms the responsibility and essential role of the excited state of [Cr(NN)3]3+ for inducing damage. Moreover, assays of the photosensitization of transformed bacterial suspensions suggest that Escherichia coli may be photoinactivated by irradiation in the presence of [Cr(NN)3]3+ complexes.