Excited State Dynamics of Physiologically Active Molecules : Picosecond and Nanosecond Time Resolved Vibrational Spectroscopy

主要研究结果如下：(1)8-甲氧基补骨脂素（8-MOP）是一种光活化的皮肤病药物，在光化学反应中表现出与补骨脂素（Ps）和5-甲氧基补骨脂素（5-MOP）完全不同的行为。皮秒时间分辨吸收光谱显示，8-MOP的最低激发单重态S和最低激发三重态T_1的波长和寿命与Ps和5-MOP有很大不同。从头算DFT计算表明，只有8-MOP在T_1状态下呈开环结构。这就是为什么8-MOP的T_1寿命比其他补脂素短得多的原因。与其他补骨脂素相比，8-MOP的副作用要小得多，这一事实可能是由于补骨脂素环的断裂抑制了8-MOP与DNA嘧啶碱基的相互作用。(2) pyridoxal -5-磷酸（PLP） Shiff碱是氨基酸中与甲基转化有关的重要辅酶。为了了解该反应的机理，我们测量了PLP模型化合物吡哆醛5-磷酸甲胺Shiff碱的皮秒时间分辨拉曼光谱和吸收光谱。对该化合物进行从头算DFT计算，得到最可能的结构和正常频率。(3)烟酰胺腺嘌呤二核苷酸的还原形式（NADH）是一种在体内氧化还原反应中起重要作用的辅酶。时间分辨拉曼光谱和紫外可见吸收光谱显示NADH的光氧化反应涉及三个瞬态和溶剂化电子。在370nm和560nm处表现出吸收谱带，在1627cm^<-1>处表现出拉曼谱带的瞬态物质可以归属于阳离子自由基NADH^<+*>，并随着时间的推移转化为中性自由基NAD^*，说明NADH氧化还原反应是三步反应。

The main results of this research are as follows :(1) 8-Methoxypsoralen (8-MOP), a photo-activated medicine for skin diseases, exhibited completely different behavior in the photochemical reaction compared to psoralen (Ps) and 5-methoxypsoralen (5-MOP). Picosecond time-resolved absorption spectra revealed that the wavelengths and lifetimes of the lowest excited singlet state S, and lowest excited triplet state T_1 of 8-MOP were quite different from those of Ps and 5-MOP. Ab initio DFT calculations showed that only 8-MOP took an open-ring structure in the T_1 state. This is the reason why the lifetime of T_1 of 8-MOP is extremely short compared to other psoralens. The fact that the adverse side effect of 8-MOP is much less compared to other psoralens may be understood if the cleavage of the psoralen-ring inhibits the interaction of 8-MOP with pyrimidine bases of DNA.(2) Pyridoxal-5-phosphoric acid (PLP) Shiff base is an important coenzyme related to the transformation of methyl groups in amino acids. In order to understand the mechanism of this reaction, picoseconds time-resolved Raman and absorption spectra of pyridoxal 5-phosphoric acid methylamine Shiff base, a model compound of PLP, were measured. Ab initio DFT calculations were carried out for this compound to obtain the most probable structure and normal frequencies.(3) Nicotinamide adenine dimucleotide in the reduced form (NADH) is a coenzyme which plays important roles in the oxidation-reduction reaction in vivo. Time-resolved Raman and UV-visible absorption spectra reveal that three transients and solvated electrons were involved in the photo-oxidation reaction of NADH. The transient species exhibiting the absorption bands at 370nm and 560nm and the Raman band at 1627cm^<-1> can be assigned to the cation radical NADH^<+*> which is converted into the neutral radical NAD^* with time This suggests that three-step process is operative in the oxidation -reduction reaction of NADH.