title: Designing molecules for PDT: red light-induced DNA cleavage on disulfide bond activation in a dicopper(II) complex.
abstract: The binuclear copper(II) complex [Cu)(RSSR)2](1), where RSSR is a dianionic Schiff base derived from 2-(thioethyl)salicylaldimine having a disulfide bond is prepared, structurally characterized by X-ray crystallography and its photo-induced DNA cleavage activity studied. The Schiff base ligand H2RSSR is also structurally characterized. The crystal structure of shows the discrete dimeric nature of the complex with each metal showing square-planar geometry with a CuN2O2 coordination (Cu...Cu, 5.011(1)A). The tetradentate Schiff base RSSR acts as a linker of two copper centers. The sulfur atoms in the disulfide unit do not show any apparent interaction with the metal ion. Complex 1, which is cleavage inactive in the dark in the presence of reducing agents, shows significant cleavage of supercoiled pUC19 DNA on exposure to UV light of 312 nm or visible light of different wavelengths under aerobic conditions, in the absence of any additives. DNA cleavage data from control experiments reveal involvement of the disulfide unit as a photosensitizer undergoing photo-induced S-S bond cleavage on exposure to UV light and the resulting species activates molecular oxygen to form singlet oxygen (1O2) that causes DNA cleavage following a type-II process. Photo-induced DNA cleavage by 1 on red-light exposure using a CW laser of 632.8 nm or a pulsed ruby laser of 694 nm is proposed to involve sulfide radicals in a type-I process and hydroxyl radicals as the reactive species.
authors.affiliation: Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, 560012, India.
authors.forename: Shanta
authors.initials: S
authors.lastname: Dhar
authors.forename: Munirathinam
authors.initials: M
authors.lastname: Nethaji
authors.forename: Akhil R
authors.initials: AR
authors.lastname: Chakravarty
mesh_terms: D003300:Copper / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004247:DNA / Q000528:radiation effects*; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism*; D015195:Drug Design; D008024:Ligands; D008958:Models, Molecular; D010100:Oxygen / Q000378:metabolism; D010777:Photochemistry; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000138:chemical synthesis / Q000737:chemistry; D012545:Schiff Bases; D026082:Singlet Oxygen / Q000494:pharmacology; D014466:Ultraviolet Rays
chemical_list: D004220:Disulfides; D008024:Ligands; D017319:Photosensitizing Agents; D012545:Schiff Bases; D026082:Singlet Oxygen; D003300:Copper; D004247:DNA; D010100:Oxygen