关键词: 植物多酚; 钒(Ⅴ); 密度泛函理论; 吸收光谱

Abstract:

EGCG was used as the model molecule to study the coordination mechanism and the spectra of plant polyphenol to vanadium(Ⅴ). Based on the analysis of UV-Vis spectrum, it was identified that the doubly-coordinated complex between the center metal V(Ⅴ) and the ligand EGCG is dominant. Two absorption peaks were measured at 588 and 710 nm for the solution containing EGCG and V(Ⅴ). The absorption spectrum calcualtion using TDDFT predicts that the maximium absorption value is very close to the experimentally observation. The molecular orbital analysis attributes the peaks at 588 and 710 nm to the electron transitions from one-side and two-side ligands respectively to the d orbital of the center metal V(Ⅴ). DFT-B3LYP method was employed to optimize the geometries of reactants, intermediates, transition states and coordination products along the reaction pathway. The energy barriers for the elemetary steps were calcualted. A four-member transition state was checked in the formation of the doubly-coordinated complex. Both experiment and theoretical calcualtion confirm that the doubly-coordinated product is prior to the singly-coordinated one.

Key words: Plant polyphenol; Vanadium; Density functional theory; Absorption spectrum