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

（1）8-甲氧基补骨脂素（8-MOP）是一种治疗皮肤病的光活化药物，其光化学反应行为与补骨脂素（Ps）和5-甲氧基补骨脂素（5-MOP）完全不同。皮秒时间分辨吸收光谱表明，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有很大的不同。从头算密度泛函计算表明，8-MOP在T_1态为开环结构。这就是为什么8-MOP的T_1寿命比其它杀虫剂短的原因。与其他紫杉醇相比，8-MOP的不良副作用小得多的事实可以理解，如果紫杉醇环的切割抑制8-MOP与DNA的嘧啶碱基的相互作用。(2)吡哆醛-5-磷酸（PLP）希夫碱是一种重要的辅酶，与氨基酸中甲基的转化有关。为了了解该反应的机理，测量了PLP模型化合物吡哆醛5-磷酸甲胺希夫碱的皮秒时间分辨拉曼光谱和吸收光谱。对该化合物进行了从头算DFT计算，得到了最可能的结构和正常频率。(3)还原型烟酰胺腺嘌呤二核苷酸（Nicotinamide adenine diminucleotide in reduced form，NADH）是一种辅酶，在体内氧化还原反应中起重要作用。时间分辨拉曼光谱和紫外-可见吸收光谱表明，NADH光氧化反应中存在三个瞬态过程和溶剂化电子。在370 nm和560 nm处的吸收带以及1627 cm-2处的拉曼谱带的瞬态产物<-1>可以归属于阳离子自由基NADH^+*&gt;，其随时间转变为中性自由基NAD^*。这表明在NADH的氧化还原反应中存在三步过程。

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.