L-缬氨酸旋光异构的两种光反应可能途径

利用密度泛函理论(DFT)和从头算分子轨道理论对L-缬氨酸的旋光异构光反应机理进行了研究. 分别用B3LYP和MP2方法在6-311++G(d, p)基组级别上全优化得到了S₀和T₁态反应路径上的反应物、产物、中间体以及过渡态结构的几何构型, 给出了反应能垒, 利用含时密度泛函理论(TD-DFT)中的B3LYP/6-311++G(d, p)方法优化得到了S₁态反应路径上的平衡态几何构型. 通过分析反应途径上各个驻点的几何构型特征, 确定了L-缬氨酸在激发态可能通过手性碳上的氢原子以羰基氧或氨基氮为中转媒介发生质子迁移来完成旋光异构反应. 进一步用自洽反应场理论中的极化连续模型(PCM)方法探讨了溶剂化效应对旋光异构反应机理的影响.

Two Possible Photoreaction Pathways of L-Valine Optical Isomerization

The photoreaction mechanism of L-valine optical isomerization was studied by the density functional theory (DFT) and ab initio molecular orbital theory. The geometric parameters of reactant, product, intermediates, and transition states on the reaction paths in S₀ and T₁ states were optimized at the level of B3LYP and MP2 methods and 6-311++G(d, p) basis sets and the reaction energy barriers were obtained by the same methods. The equilibrium geometries on the S₁ state of valine were also optimized by the method of time dependent density functional theory (TD-DFT) with B3LYP/6-311++G(d, p) level. Through the analysis of each stationary point geometric feature on the reaction path, the photoreaction mechanisms of L-valine optical isomerization were proposed in which the whole reaction was accomplished through hydrogen transfer with the help of carbonyl O or amino N atom in excited state. Furthermore the effect of solvent on the reaction mechanism of isomers was discussed by the method of polarizable continuum model (PCM) of self consistent reaction field theory.