Phenolic antioxidants: electrochemical behavior and the mechanistic elements underlying their anodic oxidation reaction

Abstract

Electrochemical analysis has been widely used to assess activities of reductant antioxidants, but the mechanistic factors that determine reducing ability and their corresponding correlations remain to be explored further. In the present paper, the reactivity of a selection of phenolic compounds in anodic oxidation was investigated by cyclic voltammetry (CV). The effects of electron-donation ability, deprotonation equilibrium, stability of radicals and chemical hardness on reducing capacity were studied by computational chemistry methods and multiple linear regression analysis. The results suggested that all these factors made significant contributions to reducing potency although electron-donation ability of the parent molecule plays the most important role in the electrode reaction. With the majority of the compounds examined, the occurrence of multiple electrochemical reactions leading to irreversible anodic oxidation was implied by: (i) the characteristics of the radical cation intermediate; (ii) the propensity of the deprotonation reaction; and (iii) the reactivity of the parent molecule. Upon correlation analysis of oxidation potential and computed physicochemical descriptors, some new light was shed on the mechanism by which phenolic compounds act as antioxidant reductants in free radical reactions. A satisfactory multi-descriptor theoretical QSAR model was derived, which might be of predictive significance in the screening or design of new antioxidants.

Quantitative determination of the phenolic antioxidants using voltammetric techniques

“…The system studied here is characterized by the exchange of only one electron (Cheng et al, 2002). Although it is well known that in voltammetric techniques, differential pulse is more sensitive than classic voltammetry, in this work the antioxidant determination was performed using different voltammetric techniques, as presented in Fig.…”

“…Studies of electrochemical behaviour of these antioxidants using amperometric techniques have been reviewed and tested at bare electrode and modified electrode (Chevion, Roberts, & Chevion, 2000;Fuente, Batanero, Tasco´n, Va´squez, & Acuna˜, 1999;Gonza´lez, Ruiz, Ya´n˜ez-Seden˜o, & Pingarro´n,1994;Ni, Wang, & Kokot, 2000;Riber, Fuente, Vazquez, Tasco´n, & Sa´nchez Batanero, 2000;Surareungchai & Kasiwat, 2000); besides the agreed methods, chromatography with electrochemical detectors is also used (King, Joseph & Kissinger, 1980;Baldwin & Thomsen, 1991;Bianchi et al, 1997). In the case of the electrochemical methods, when the mixture has more than two antioxidant components present, the voltammetric waves of these antioxidants are closely overlapped and it is difficult to analyse them individually (Cheng et al, 2002;Ni et al, 2000). Recently some chemometric approaches, such as principal component regression (PCR) and partial least square regression (PLSR), have been introduced for the determination of mixtures of synthetic antioxidants with three or more components (Galeano Diaz, Guiberteau Cabanillas, Alexandre Franco, Salinas, & Vire (1998) ;Richards, Bessant, & Saini, 2002).…”

“…Electrochemical methods or techniques, for example, polarographic and voltammetric techniques (differential pulse polarography, absorptive voltammetry and linear sweep voltammetry, etc. ), generally possess high sensitivity and are extensively used in analytical chemistry (Campanella, Bonanni, Bellantoni, Favero, & Tomassetti, 2004;Cheng, Ren, Li, Chang, & Chen, 2002;Korotkova, Korbainov, & Shevchuk, 2002;Pournaghi-Azar, Hydarpour, & Dastangoo, 2003;Yang & Huang, 2002). Studies of electrochemical behaviour of these antioxidants using amperometric techniques have been reviewed and tested at bare electrode and modified electrode (Chevion, Roberts, & Chevion, 2000;Fuente, Batanero, Tasco´n, Va´squez, & Acuna˜, 1999;Gonza´lez, Ruiz, Ya´n˜ez-Seden˜o, & Pingarro´n,1994;Ni, Wang, & Kokot, 2000;Riber, Fuente, Vazquez, Tasco´n, & Sa´nchez Batanero, 2000;Surareungchai & Kasiwat, 2000); besides the agreed methods, chromatography with electrochemical detectors is also used (King, Joseph & Kissinger, 1980;Baldwin & Thomsen, 1991;Bianchi et al, 1997).…”

Electrochemistry of vitamin E hydro-alcoholic solutions

“…These peaks (II and III) were not reported before in these conditions, and they may certainly have implications for the antioxidant activity of vitamin E in biological conditions, provided that the fate of electrogenerated species is an important question in the biological system. 28 Zhu and Zhang, 19 who studied the electrochemistry of vitamin E in methanol/acetate buffer solution 4:1 (v/v), did not report the occurrence of peaks II and III probably because an anodic switching potential (E λ,a ) of +0.80 V / Ag/AgCl was applied, as did Jaiswal et al 21 in surfactant/ethanol/water solutions. In addition, vitamin E has been found to present just a single oxidation process in other solvent systems or working electrodes.…”

Differentiation between phenol- and amino-substances in voltammetry determination of synthetic antioxidants in oils

“…Moreover, antioxidants are substances that can be oxidised electrochemically very easily [34,35]. The analysis is to be always performed in an acidic medium, using e.g.…”