利用差分光谱和TD-DFT计算揭示山奈酚的解离及金属络合机理

为了揭示山奈酚的解离及金属络合过程机理, 测定山奈酚在解离(pH=2.01~13.00)和与铜离子络合(0.1~2710.9 μmol/L)过程的紫外–可见光光谱, 经过差分处理得到各反应阶段的特征光谱。结合量子化学理论计算方法, 基于密度泛函理论以及含时密度泛函理论, 计算可能的各种去质子化、络合结构及对应的电子吸收光谱。通过对比实验值与计算值发现: 解离过程按7, 4′, 3, 5号酚基的顺序依次去质子化; 在低浓度Cu²⁺(<67.9 μmol/L)时, 4号和5号酚基与Cu²⁺络合; 在高浓度Cu²⁺(67.9~2710.9 μmol/L)时, 3号和4号酚基与Cu²⁺络合。在山奈酚的解离、与Cu²⁺络合过程中, 计算光谱与差分光谱能够很好地吻合, 特征峰的出现是由于解离、络合前后活性基团电子分布的变化、光子照射时最高占据分子轨道到最低未占据分子轨道能量吸收的变化导致, 揭示了山奈酚解离及金属络合过程的机理。

Revealing the Mechanism of Hydrolysis and Metal Complexation ofKaempferol by Differential Absorbance Spectra and TD-DFT Calculations

In order to reveal the mechanism of hydrolysis and metal complexation of kaempferol, the UV-vis spectra of kaempferol in hydrolysis process (pH from 2.01 to 13.00) and in Cu(II) complexation process (from 0.1 to 2710.9 μmol/L) was obtained, and the characteristic spectra at various reaction stages was obtained by differential treatment. Combined with quantum chemical theoretical computation, a variety of possible deprotonation structures, complexation structures and corresponding electron absorption spectra were calculated based on DFT (Density Functional Theory) and TD-DFT (Time-Dependent Density Functional Theory). The experimental results are compared with the calculated values and it indicates that the hydrolysis process is in the deprotonation order of 7, 4′, 3, 5 phenolic group; at low concentrations of Cu(II) (<67.9 μmol/L), Cu(II) chelated with 4,5 phenolic group simultaneously; at high concentration of Cu(II) (67.9–2710.9 μmol/L), Cu(II) chelated with 3,4 phenolic group simultaneously. The calculated spectra is consistent with experimental spectra in hydrolysis and Cu(II) complexation process of kaempferol. The appearance of characteristic peaks is due to the change of the electron distribution of the active groups before and after hydrolysis and Cu(II) complexation, resulting in the changes of energy gap from HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital) during photon irradiation. The mechanism of hydrolysis and metal complexation process of kaempferol was revealed.