Structural and antioxidative features of chlorogenic acid

Abstract

This work contributes to the structure clarification of chlorogenic acid (5-O-caffeoylquinic acid, 5CQA) by comparing the experimental and simulated IR, Raman, 1H-NMR, 13C-NMR, and UV-vis spectra. The lowest-energy conformers in the gas-phase and solution were used for all calculations. Very good agreement between all experimental and simulated spectra indicates correct arrangement of the atoms in the 5CQA molecule. In addition, the bond dissociation enthalpies, proton affinities, electron transfer enthalpies, ionization potentials, and proton dissociation enthalpies for 5CQA were used for thermodynamic consideration of the major antioxidative mechanisms: HAT (Hydrogen Atom Transfer), SPLET (Sequential Proton-Loss Electron-Transfer), and SET-PT (Single Electron Transfer - Proton Transfer). It was found that HAT may be the predominant mechanism in nonpolar solvents, while HAT and SPLET are competitive pathways in polar media. All quantum-chemical calculations were carried out by means of the MN12-SX method. Its performance is similar to those of the B3LYPD2, B3LYP-D3, and M06-2X functionals.