Harada Yosuke, Suzuki Tadashi, Ichimura Teijiro, Xu Yao-Zhong
Department of Chemistry and Materials Science, Tokyo Institute of Technology, 2-12-1 Ohokayama, Meguro-ku, Tokyo 152-8551, Japan.
J Phys Chem B. 2007 May 17;111(19):5518-24. doi: 10.1021/jp0678094. Epub 2007 Apr 18.
Excited-state dynamics of 4-thiothymidine (S4-TdR) and its photosensitization to molecular oxygen in solution with UVA irradiation were investigated. Absorption and emission spectra measurements revealed that UVA photolysis of S4-TdR gives rise to a population of T1(pipi*), following S2(pipi*) --> S1(npi*) internal conversion. In transient absorption measurement, the 355 nm laser photolysis gave broad absorption (380-600 nm) bands of triplet S4-TdR. The time-resolved thermal lensing (TRTL) signal of S4-TdR containing the thermal component due to decay of triplet S4-TdR was clearly observed by the 355 nm laser excitation. The quantum yield for S1 --> T1 intersystem crossing was estimated to be unity by a triplet quenching experiment with potassium iodide. In the presence of molecular oxygen, the photosensitization from triplet S4-TdR gave rise to singlet oxygen O2 (1Deltag) with a quantum yield of 0.50. Therapeutic implications of such singlet oxygen formation are discussed.
研究了4-硫代胸腺嘧啶核苷（S4-TdR）的激发态动力学及其在UVA照射下在溶液中对分子氧的光敏化作用。吸收光谱和发射光谱测量表明，S4-TdR的UVA光解在S2（ππ*）→S1（nπ*）内转换后产生了T1（ππ*）粒子群。在瞬态吸收测量中，355nm激光光解产生了三线态S4-TdR的宽吸收带（380 - 600nm）。通过355nm激光激发，清晰地观察到了包含由于三线态S4-TdR衰变导致的热成分的S4-TdR的时间分辨热透镜（TRTL）信号。通过用碘化钾进行的三线态猝灭实验，估计S1→T1系间窜越的量子产率为1。在分子氧存在的情况下，三线态S4-TdR的光敏化产生了单线态氧O2（1Δg），量子产率为0.50。讨论了这种单线态氧形成的治疗意义。
