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

Autori
Martinez, Sanja ; Valek, Lidija ; Petrović, Željka ; Metikoš-Huković, Mirjana ; Piljac, Jasenka

Izvornik
Journal of electroanalytical chemistry (1992) (1572-6657) 584 (2005), 2; 92-99

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
catechin ; oxidation ; cyclic voltammetry ; molecular modeling

Sažetak
The mechanism of catechin electro-oxidation at various pH was studied using cyclic voltammetry (C. V.) on the glassy carbon (G. C.) electrode and PM3 semi empirical calculations. The influence of activation of the surface of the G.C. electrode on C.V. results has been discussed. Mixed adsorption- diffusion control has been observed by applying mechanistic criteria of C. V. to the results obtained at the activated electrode. The calculated catechin diffusion coefficient D = 2.78 x 10-6 cm2 s-1. A linear increase of the current peak has been observed with the increase of substrate concentration up to 40 mikromol dm^-3 (surface coverage 10-11 mol cm^-2). In the whole investigated pH range, the dE/dpH value is very close to the anticipated Nernstian dependence of - 59 mV per 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 deltaHoF (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. Upon the increase in pH the mechanistic pathway of catechin oxidation changes from phenol/cation radical/phenoxyl radical to phenol/phenolate monoanion/phenoxyl radical. In the reaction with a free radical this is equivalent to the change from hydrogen to electron donation.

Izvorni jezik
Engleski

Znanstvena područja
Kemija, Kemijsko inženjerstvo

POVEZANOST RADA