title: Effects of light energy and reducing agents on C60-mediated photosensitizing reactions.
abstract: Many biomolecules contain photoactive reducing agents, such as reduced nicotinamide adenine dinucleotide (NADH) and 6-thioguanine (6-TG) incorporated into DNA through drug metabolism. These reducing agents may produce reactive oxygen species under UVA irradiation or act as electron donors in various media. The interactions of C60 fullerenes with biological reductants and light energy, especially via the Type-I electron-transfer mechanism, are not fully understood although these factors are often involved in toxicity assessments. The two reductants employed in this work were NADH for aqueous solutions and 6-TG for organic solvents. Using steady-state photolysis and electrochemical techniques, we showed that under visible light irradiation, the presence of reducing agents enhanced C60 -mediated Type-I reactions that generate superoxide anion (O2(.-)) at the expense of singlet oxygen ((1)O2) production. The quantum yield of O2(.-) production upon visible light irradiation of C60 is estimated below 0.2 in dipolar aprotic media, indicating that the majority of triplet C60 deactivate via Type-II pathway. Upon UVA irradiation, however, both C60 and NADH undergo photochemical reactions to produce O2(.-), which could lead to a possible synergistic toxicity effects. C60 photosensitization via Type-I pathway is not observed in the absence of reducing agents.
authors.affiliation: Chemistry and Physics Department, SUNY College at Old Westbury, Old Westbury, NY.
authors.forename: Michael
authors.initials: M
authors.lastname: Quinones
authors.forename: Yazhou
authors.initials: Y
authors.lastname: Zhang
authors.forename: Penelope
authors.initials: P
authors.lastname: Riascos
authors.forename: Huey-Min
authors.initials: HM
authors.lastname: Hwang
authors.forename: Winfred G
authors.initials: WG
authors.lastname: Aker
authors.forename: Xiaojia
authors.initials: X
authors.lastname: He
authors.forename: Ruomei
authors.initials: R
authors.lastname: Gao
mesh_terms: D004247:DNA / Q000737:chemistry*; D037741:Fullerenes / Q000737:chemistry*; D009243:NAD / Q000737:chemistry; D017319:Photosensitizing Agents / Q000737:chemistry*; D066244:Proton Magnetic Resonance Spectroscopy; D019163:Reducing Agents / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D037741:Fullerenes; D017319:Photosensitizing Agents; D019163:Reducing Agents; D009243:NAD; D004247:DNA; C069837:fullerene C60