Correlations of computational ionization energy with experimental oxidation potential and with antioxidant efficiencies in catechins

• Published in: Chemical physics Vol. 522; pp. 77 - 83
• Main Authors: Nagaoka, Shin-ichi, Nakayama, Naofumi, Teramae, Hiroyuki, Nagashima, Umpei
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.2019
• Subjects: Antioxidant efficiency; ARAC and ATREC values; Catechins; Ionization energy; Oxidation potential; SOAC value; Ionization energy; ARAC and ATREC values; Catechins; SOAC value; Oxidation potential; Antioxidant efficiency
• ISSN: 0301-0104
• DOI: 10.1016/j.chemphys.2019.02.002

[Display omitted] •Catechins function as antioxidants in biological systems being prone to oxidation.•Ionization energy is closely related to antioxidant activity in catechins.•Previous ionization-energy calculations did not reproduce experimental results.•We have clarified computational conditions for reproducing them.•We have shown correlation between the ionization energy and antioxidant activity. Ionization energies of catechins were calculated by using B3LYP density functional method with 6-31G** basis set. Then, conformations of catechins were extensively explored. Geometry optimizations starting from the explored conformers were made not only for the neutral species but also for the radical cation. The ionization energy of each catechin was estimated as the energy difference between the most stable geometries obtained for the neutral species and radical cation. Tendency of experimental oxidation potential in catechins is well reproduced by this calculation, and the ionization energy correlates well with the singlet-oxygen quenching efficiency in case that stereochemistry of attachment at the 3-position is common. Electron transfer from catechins plays an important role in the singlet-oxygen quenching, free-radical scavenging and recycling from vitamin E radical to vitamin E. The reason for discrepancy among antioxidant efficiencies with regard to the ionization energy dependence is explained.