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采用密度泛函理论方法在B3LYP和混合基组(C、H原子采用6-31G(d);Mg、N、O采用6-311++G(2d,p))水平对含L-苏氨酸侧链的四苯基卟啉镁衍生物L-Thr-TPPMg的基态几何构型进行了优化,获得了稳定的分子构型。以获得的稳定构型为基础,在相同基组水平进行了红外吸收光谱研究;采用含时密度泛函理论方法,在相同基组水平进行了紫外吸收光谱和电子圆二色谱研究。理论研究发现:(1)L-苏氨酸的羧基氧原子与镁原子之间存在配位作用。(2)氮镁配位键、氧镁配位键的伸缩振动在IR谱中的1022 cm~(-1)、278 cm~(1)处呈现特征吸收峰。(3)理论UV谱存在Soret带和Q带吸收。Q带吸收峰主要由HOMO→LUMO的荷移跃迁贡献;Sorer带的吸收峰主要由HOMO-1→LUMO的荷移跃迁贡献。(4)Sorct区表现出分裂的ECD谱。第1 Cotton效应主要来源于分子由HOMO-1→LUMO的荷移跃迁;第2 Cotton效应主要由HOMO-1→LUMO+1的荷移跃迁贡献。上述跃迁均为π→π~*的荷移跃迁。
Density functional theory (DFT) was used to investigate the effect of L-threonine on L-threonine in B3LYP and mixed base groups (6-31G (d) for C and H atoms and 6-311 ++ G (2d, p) The ground-state geometry of L-Thr-TPPMg, an acidic side chain tetraphenylporphyrin derivative, was optimized and a stable molecular configuration was obtained. Based on the obtained stable configuration, infrared absorption spectroscopy was carried out at the same basic group level. The time-dependent density functional theory method was used to study the UV absorption spectra and electron circular dichroism spectra at the same basic group level. Theoretical studies found that: (1) L-threonine carboxyl oxygen atoms and magnesium atoms exist between the coordination role. (2) The stretching vibration of magnesium-magnesium coordination bond and oxygen-magnesium coordination bond showed characteristic absorption peaks at 1022 cm -1 and 278 cm -1 in IR spectrum. (3) The theoretical UV spectrum has Soret band and Q band absorption. The absorption band of Q band mainly contributes to the charge transfer transition from HOMO → LUMO; the absorption band of Sorer band mainly contributes to the charge transfer transition from HOMO-1 → LUMO. (4) Sorct region showed a split ECD spectrum. The first Cotton effect is mainly derived from the charge-transfer transition of HOMO-1 → LUMO. The second Cotton effect is mainly contributed by the charge-transfer transition of HOMO-1 → LUMO + 1. The above transitions are all π → π ~ * transitions of charge.