核苷酸和芳香酮的电子转移和质子转移反应研究

利用时间分辨的激光闪光光解方法在1∶1乙腈/水溶液中得到了4种核苷酸和芳香酮的瞬态吸收光谱,通过瞬态吸收光谱的变化研究了鸟苷酸、腺苷酸、胞苷酸、胸腺苷酸猝灭二苯甲酮、呫吨酮激发三重态的反应。由于实验中生成了抽氢自由基和负离子自由基,以及核苷酸正离子在水中的快速抽氢反应,推断出芳香酮和鸟苷酸、腺苷酸的反应机理是先发生电子转移后发生质子转移。而在芳香酮和胞苷酸、胸腺苷酸的反应中没有观察到相应的抽氢自由基和负离子自由基的瞬态吸收峰,由此推断出它们和胞苷酸、胸腺苷酸没有发生电子转移和质子转移反应。对瞬态吸收峰处的时间衰减曲线进行拟合得到了核苷酸猝灭芳香酮的速率常数,可以看到随着反应自由能变ΔG的增大,反应速率常数逐渐减小。

Studies on Photoinduced Electron and Proton Transfer Reactions of Nucleic Acid and Aromatic Ketone

The transient absorption spectra of two aromatic ketones (benzophenone (BP), xanthone (XT)) and four nucleic acids (guanosine 5'-monophosphate (GMP), adenosine 5 '-monophosphate (AMP), cytidine 5 '-monophosphate (CMP), thymidine 5'-monophosphate (TMP)) were obtained in 1:1 CH_3CN/H_2O solution by using time-resolved laser flash photolysis at 355 nm. From the changes of the transient absorption spectra the authors can conclude that photoinduced proton transfer following electron transfer from GMP and AMP to excited BP and XT occurs, which is in accordance with free energy change of the reac-tions. For CMP and TMP, electron transfer and proton transfer do not appear because no ketyl and anion radical are generated.In addition, the rate constants for electron transfer from GMP, AMP, CMP, and TMP m the excited BP and XT were deter-mined. As can be seen, there is a good correlation between k_q and the free energy changes (△G) of the electron transfer reaction.