COMPARATIVE-STUDY OF RU(BPZ)(3)(2-2 AS PHOTOSENSITIZERS OF DNA CLEAVAGE AND ADDUCT FORMATION() RU(BIPY)(3)(2+) AND RU(BPZ)(2)CL)

The efficiency of ruthenium complexes for photosensitizing DNA damage depends on the oxidizing character of their ligands, Here we report on the difference in behavior of tris(2.2'-bipyrazyl)ruthenium(II) (Ru[b pz](3)(2+)), tris(2,2'-bipyridyl)ruthenium(II) (Ru[bipy](3)(2+)) and c is-dichlorobis(2,2'-bipyrazyl)ruthenium(II) (Ru[bpz](2)Cl-2), Upon irr adiation at 436 nm, Ru(bpz)(3)(2+) was far less stable than Ru(bipy)(3 )(2+). Ru(bpz)(3)(2+) in phosphate buffer containing NaCl undergoes a photoanation reaction leading to the formation of Ru(bpz)(2)Cl-2, as p reviously reported also in organic media, In the presence of phage phi X174 DNA, Ru(bpz)(3)(2+) photosensitized the formation of single stra nd breaks with an efficiency that was, at the beginning of irradiation , similar to that of Ru(bipy)(3)(2+). After 8 min of irradiation, the cleavage efficiency of Ru(bpz)(3)(2+) reached a plateau that may corre spond to its photodecomposition, For the same conditions, Ru(bpz)(2)Cl -2 did not induce DNA breakage, Scavenging experiments showed that, in the presence of oxygen, DNA cleavage induced by Ru(bpz)(3)(2+) partly resulted from the formation of singlet oxygen and hydroxyl radical wh ile in the absence of oxygen an additionnal mechanism involving electr on transfer between the excited state of the ruthenium complex and DNA is proposed, The ICP measurement showed that Ru(bpz)(3)(2+) and Ru(bp z)(2)Cl-2 gave rise to covalent binding onto DNA in contrast with Ru(b ipy)(3)(2+), which did not bind to DNA under the experimental conditio ns, The results are discussed with regard to the potential use of thes e photosensitizers in phototherapy.