Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, D-24098 Kiel, Germany.
J Phys Chem B. 2009 Dec 24;113(51):16365-76. doi: 10.1021/jp904883n.
The optically excited electronic states of hydrogen-bonded homo- and heterodimers of guanosine (G) and deoxycytidine (C) were investigated by femtosecond fluorescence up-conversion spectroscopy. The base pairs were prepared in CHCl(3) solution by employing tert-butyldimethylsilyl (TBDMS) groups at the OH positions of the ribose (G) or deoxyribose (C) moieties to enhance the solubilities of the nucleosides in organic solvents. The H-bonded complexes that were obtained were characterized by FTIR spectroscopy. Fluorescence lifetime measurements were performed following electronic excitation at a series of UV wavelengths from lambda(pump) = 294 nm, close to the electronic origins of the bases, to lambda(pump) = 262 nm, where significant excess vibronic energy is deposited in the molecules, at nucleoside concentrations of c(0) = 0.1 and 1.0 mM. The experimental results revealed the existence of an ultrafast deactivation pathway for the optically prepared electronically excited state(s) of the G.C Watson-Crick base pair, which was found to have a lifetime of tau(GC) = 0.30(3) ps (with 2sigma error limits) irrespective of the pump wavelength. A similar short decay time, tau(GG) = 0.32(2) ps, was observed for the respective excited G.G homodimer. In contrast, the excited G monomer displayed a significantly longer-lived and wavelength-dependent deactivation, requiring three time constants, between 0.43(6) ps < or = tau(G,1) < or = 1.2(1) ps, 4.2(8) ps < or = tau(G,2) < or = 8(1) ps, and tau(G,3) = 195(32) ps. Self-complexation of C, on the other hand, led to a longer-lived excited state with a lifetime estimated between 1 ps < or = tau(CC) < or = 10 ps, compared to the dominant initial subpicosecond decay time of the C monomer of tau(C,1) = 0.80(4) ps.
通过飞秒荧光上转换光谱法研究了氢键同型和异型二聚体鸟嘌呤（G）和脱氧胞苷（C）的光激发电子态。通过在核糖（G）或脱氧核糖（C）部分的 OH 位置使用叔丁基二甲基甲硅烷基（TBDMS）基团，将碱基对制备在 CHCl 3 溶液中，以提高核苷在有机溶剂中的溶解度。通过傅里叶变换红外光谱对获得的氢键复合物进行了表征。在核苷浓度为 c(0) = 0.1 和 1.0 mM 时，在一系列从 lambda(pump) = 294 nm（接近碱基的电子起源）到 lambda(pump) = 262 nm（其中显著的过剩振动能量沉积在分子中）的 UV 波长下进行电子激发，进行了荧光寿命测量。实验结果表明，对于 G.C Watson-Crick 碱基对的光制备电子激发态，存在超快失活途径，其寿命为 tau(GC) = 0.30(3) ps（2sigma 误差极限），与泵浦波长无关。对于各自的激发 G.G 同型二聚体，观察到相似的短衰减时间 tau(GG) = 0.32(2) ps。相比之下，激发的 G 单体表现出明显更长寿命和波长依赖性的失活，需要三个时间常数，0.43(6) ps < or = tau(G,1) < or = 1.2(1) ps，4.2(8) ps < or = tau(G,2) < or = 8(1) ps 和 tau(G,3) = 195(32) ps。另一方面，C 的自络合导致激发态的寿命更长，估计在 1 ps < or = tau(CC) < or = 10 ps 之间，而 C 单体的主要初始亚皮秒衰减时间为 tau(C,1) = 0.80(4) ps。
