title: Direct observation and quantitative characterization of singlet oxygen in aqueous solution upon UVA excitation of 6-thioguanines.
abstract: The incorporation of 6-thioguanine (6-TG) into DNA increases the risk of (1)O(2)-initiated skin cancer. We herein provide the first report on quantitative characterization of the photoactivity of 6-thioguanines including 6-TG and 6-thioguanosine. Time-resolved singlet oxygen luminescence was observed directly for the first time after UVA irradiation of 6-thioguanines in both CHCN(3) and aqueous solutions. Their photosensitization was characterized by the quantum yield of singlet oxygen production, showing a dramatic decrease over time from the initial 0.49-0.58 to zero. Experiments performed on both 6-TG and 6-thioguanosine did not show any significant difference in the quantum yield of singlet oxygen production, indicating that there was no potential participation of 7H- and 9H-tautomers. Our findings provide a primary basis for a better understanding of molecular events of thiopurine drugs in biological systems.
authors.affiliation: Department of Chemistry and Biochemistry, Jackson State University, Jackson, Mississippi 39217, USA.
authors.forename: Yazhou
authors.initials: Y
authors.lastname: Zhang
authors.forename: Xianchun
authors.initials: X
authors.lastname: Zhu
authors.forename: Joshua
authors.initials: J
authors.lastname: Smith
authors.forename: Makeisha T
authors.initials: MT
authors.lastname: Haygood
authors.forename: Ruomei
authors.initials: R
authors.lastname: Gao
mesh_terms: D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011789:Quantum Theory; D026082:Singlet Oxygen / Q000032:analysis*; D012996:Solutions / Q000737:chemistry; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013866:Thioguanine / Q000737:chemistry*; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry
chemical_list: D012996:Solutions; D014867:Water; D026082:Singlet Oxygen; D013866:Thioguanine