DNA NICKING BY A TRINUCLEAR CHROMIUM COMPLEX

In an attempt to prepare a site-selective DNA cleavage reagent, a trin uclear Cr(III) complex, [Cr3O(O2CCH3)(6)(H,O)(3)](+), was tested for D NA cleavage ability. The complex was shown to nick double-stranded, su percoiled DNA in a concentration- and time-dependent fashion in the pr esence of H2O2. This nicking was inhibited by inclusion of glycerol in the reaction mixture, suggesting a radical-based mechanism for the DN A nicking. The nicking of the DNA by the complex could not be repaired intracellularly by repair enzymes in E. coli, resulting in E. coli ce lls that could not grow in the presence of ampicillin. Significantly, H-2 NMR studies demonstrate that the complex is stable in the reaction mixture over a 2h period and further suggest that the nicking can be attributed to [Cr3O(O2CCH3)(6)(H2O)(3)](+). The trinuclear complex can also hydrolyze phosphate mono-and diester compounds in the presence o f H2O2; however, the mechanism to hydrolyze these compounds appears to differ from the mechanism used to nick DNA. Studies to determine the mechanism used by the complex to perform its activities reveal that no Cr(V)=O species is produced in the mixtures and that hydroxyI radical s are formed. These results suggest a homolytic cleavage of H2O2 by co mplex, where the hydroxyl radicals are responsible for the DNA nicking and a Cr(IV)-OH species might be responsible for the phosphate ester hydrolyses. (C) 1998 Elsevier Science S.A.