氨基酸修饰的手性多酸的电子结构和光学活性的理论研究

Theoretical Study on Electronic Structure and Optical Activity of Chiral Polyoxometalates Modified by Amino Acids

采用密度泛函理论(DFT)方法研究了L-O2CCHCH3NH3(L-Alanine)修饰的手性多酸[SeⅣMo6O21(L-alanine)3]2-,[SbⅢMo6O21(L-alanine)3]3-及[BiⅢMo6O21(L-alanine)3]3-的几何结构、电子结构以及紫外-可见(UV-Vis)谱和电子圆二色(ECD)谱.通过对电荷转移跃迁性质的分析,探讨了多酸中杂原子对手性光学性质的影响.结果表明,杂原子(Se,Sb,Bi)对多酸的几何结构影响较大,且对该类体系的UV-Vis谱的吸收峰的强度和峰形都有显著的影响.其ECD谱的转动吸收方向和强度以及吸收峰位和峰形也因杂原子的不同而发生明显变化.低能区UV-Vis谱和ECD谱的产生主要源自多酸中氧原子的p轨道到Mo原子d轨道的电荷转移跃迁,而对于高能区的UV-Vis谱和ECD谱的产生,则主要为多酸中杂原子以及与杂原子直接相连的氧原子p轨道到Mo原子d轨道的电荷转移跃迁.

The geometrical strucutres, electronic structures, UV-visible （UV-Vis） absorption and electronic circular dichroism（ECD） spectra of chiral polyoxometalates（POMs） [ Sen M06021 （ L-alanine ）3 ]2-, [ Sb m Mo6 021 （L-alanine） 3 ] 3- and [ Bi m Mo6 O21 （ L-alanine ） 3 ] 3- modified by L-O2 CCHCH3 NH3 （ L-alanine ） have been explored via the density functional theory （DFF） method. The effect of heteroatoms on optical activities of studied compounds has been determined. The result indicates that the geometrical structures, UV- Vis spectra absorption intensity and peak shape are affected by heteroatoms. The rotational absorption direction and strength of the ECD spectra significantly change from Sen, Sb to Bi. The UV-Vis and ECD spectra in the low-energy range are mainly ascribed to the charge-transfer（CT） transitions from the p orbitals of O atoms to the d orbitals of Mo atoms in the POMs, and the both spectra in the high-energy range are mainly from the heteroatoms in the POMs and the p orbitals of the O atoms connecting with heteroatoms to the d orbitals of Mo atoms. These conclusions are significant for understanding the electronic structures and chiral spectroscopy properties of this kind of amino acids modifying POMs.