Catechin antioxidant action at various pH studied by cyclic voltammetry and PM3 semi-empirical calculations

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 2005-10, Vol.584 (2), p.92-99
• Main Authors: Martinez, S., Valek, L., Petrović, Ž., Metikoš-Huković, M., Piljac, J.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Catechin; Cyclic voltammetry; Electrochemistry; Food industries; Fundamental and applied biological sciences. Psychology; General aspects; Miscellaneous; Molecular biophysics; Molecular modeling; Oxidation; Physical chemistry in biology
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/j.jelechem.2005.07.015

The mechanism of catechin electro-oxidation at various pH was studied using cyclic voltammetry (CV) on the glassy carbon (GC) electrode and PM3 semi-empirical calculations. The influence of activation of the surface of the GC electrode on CV results has been discussed. Mixed adsorption–diffusion control has been observed by applying mechanistic criteria of CV to the results obtained at the activated electrode. The calculated catechin diffusion coefficient D = 2.78 × 10 −6 cm 2 s −1. A linear increase of the current peak has been observed with the increase of substrate concentration up to 40 μmol dm −3 (surface coverage Γ ∼ 10 −11 mol cm −2). In the whole investigated pH range, the d E/dpH value is very close to the anticipated Nernstian dependence of −59 mV/pH indicating that the slope is not affected by the different sequences of e − and H + transfer. Molecular modeling results show a decrease of ≈5 kcal mol −1 in ΔHoF (between radical and parent molecule) and a decrease of ≈6 eV in IP (of the parent molecule) when the parent molecule is changed from neutral to monoanionic form of catechin showing that both processes – hydrogen and electron abstraction are facilitated by deprotonation. Electrochemical oxidation of catechin is known to proceed as a two step one-electron oxidation of the B-ring of o-phenolic groups. Upon an increase in the pH, the mechanistic pathway of catechin electro-oxidation in both oxidation steps changes from an eH to the He process. In the reaction with a free radical, this may induce the change from hydrogen to electron donation.