| Photodynamic Therapy (PDT) is a method to selectively kill cancer cells through the absorption of visible light by a photosensitizer. Currently used PDT agents are oxygen-dependent, however, there is a need to develop new drugs that are oxygen-independent. Metal complexes represent a new promising class of PDT agents that can work well in the presence and absence of oxygen.; The complex Pt(dppz)Cl2 (dppz = dipyrido[3,2-a:2' ,3'-c]phenazine) was synthesized and characterized, and its DNA binding and photocleavage properties are reported and compared to those of ciplatin, Pt(NH3)2Cl2, and the related complex Pt(bpy)Cl2 (bpy = 2,2'-bipyridine). It was shown that Pt(dppz)Cl2 intercalates between the DNA bases, while Pt(NH3)Cl2 and Pt(bpy)Cl2 bind covalently to the duplex. Upon irradiation (lambdairr > 395 nm, 20 min) Pt(dppz)Cl2 is able to photocleave plasmid DNA both in air and in the absence of oxygen, resulting in the nicked form.{09}In contrast, cisplatin and Pt(bpy)Cl2 are photochemically inactive towards DNA under these irradiation conditions.; [Rh2(mu-O2CCH3)2(R 1,R2-dppz)2]2+ (R1 = R2 = NO2, Cl, H, CH3, OCH3, 15-crown-5, 18-crown-6 or R1 = H, R2 = Cl, CH3, OCH 3) complexes were also investigated for their photoreactivity toward DNA. The complexes do not intercalate into the DNA duplex, but they cleave DNA upon irradiation with lambda > 500 nm. The percent photocleavage decreases with the increase in the reduction potential of the R1,R2 -dppz ligand (as the ligand easier to reduce). A linear relationship between 1/[DNA]nicked and the free energy |DeltaG°| for charge recombination was established. It was also shown that free axial positions are required for dirhodium complexes to be photoactive.; Many ruthenium complexes exhibit DNA light switch behavior, where they are non-emissive in water and become luminescent upon intercalation into the DNA duplex. These complexes may act as probes of DNA structures or sensors. The emission intensity of [Ru(bpy)2(tpphz)]2+ (tpphz = tetrapyrido[3,2-a:2',3'-c:3 ″, 2″-h:2″, 3″-j] phenazine) and [Ru(bpy)2(taptp)] 2+ (taptp = 4,5,9,18-tetraazaphenanthreno[9,10-b] triphenylene) increases by factors 50- and 4-fold upon the addition of DNA, respectively. The emission from intercalated [Ru(bpy)2(tpphz)]2+ is quenched statically in the presence of Co2+ and Zn2+ ions, and the emission can be fully restored by the addition of EDTA. The emission of [Ru(bpy)2(tpphz)]2+ can be reversibly turned "on" and "off" over the several cycles. Owing to the absence of additional coordination sites, the emission of DNA-intercalated [Ru(bpy)2(taptp)]2+ is not quenched by transition metal ions in solution. |
