286
tion potential of the studied compound in certain media, which are
usually chosen to fit with physiological conditions (i.e., buffer at
pH 7.4) [1, 4].
Polyphenolic compounds act as good antioxidants and radical
scavengers [5] and their antioxidant activity can be estimated by
electrochemical measurement. In particular, the cleavage of one
electron from a polyphenol (a radical cation is formed) can be followed by a proton cleavage from phenolic group, yielding a radical
[6] which can be highly reactive toward environment and can
quench potentially harmful free radicals. Intermolecular hydrogen
bonds are of significant importance for the stability of the radical
and anionic species [7].
Electrochemical properties are generally measured using one
pair of electrodes or three-electrode setup, where the redox processes take place at the electrode–solution interface. The obtained
electroanalytical signal is related to the concentration of electroactive species at the electrode surface. The electrochemical voltammetric signal and its detailed examination can be used to determine
the mechanism of formation of the first reduction or oxidation
intermediates and to help solve the complicated redox mechanisms
of the studied compounds. Cyclic voltammograms are usually
recorded at different scan rates to obtain information about the
process at the electrode. The analysis of peak currents in dependence on the rate of polarization is important to assess whether the
redox process is controlled by diffusion or by adsorption. A significant increase in the scan rate can result in the appearance of new
redox peaks in the forward or backward scans, due to a product
formed at the electrode [8, 9]. When diffusion-controlled conditions for Nernstian behavior are fulfilled, the electrochemical signals recorded at different scan rates and concentrations yield data
on the influence of coupled chemical reaction (C) on the measured
currents. Since chemical reactions directly affect the concentration
of the electroactive species available at the electrode surface, the
interpretation of the cyclic voltammograms recorded in different
conditions (e.g., at different pH values) gives unique information
about the reaction scheme. In particular, the analysis of oxidation
waves allows us to distinguish between reaction schemes entailing
EC (electron transfer followed by chemical reaction), CE (the
chemical reaction precedes the electron transfer), ECE, EE, ECEC,
etc., as well as disclose oxidation or reduction coupling with catalytic processes [10, 11]. For instance, the shift of peak potential in
solutions at different pH values means that protons participate in
redox process [12, 13].
It was shown that metabolic oxidation of some drugs may be
successfully simulated by electrochemical methods because the
main biotransformation of drugs is based on reduction and oxidation processes [14–16]. For instance, Guaiquil et al. found the
same oxidation products of vitamin C found by previous electroRomana Sokolová and Ilaria Degano
tion potential of the studied compound in certain media, which are
usually chosen to fit with physiological conditions (i.e., buffer at
pH 7.4) [1, 4].
Polyphenolic compounds act as good antioxidants and radical
scavengers [5] and their antioxidant activity can be estimated by
electrochemical measurement. In particular, the cleavage of one
electron from a polyphenol (a radical cation is formed) can be followed by a proton cleavage from phenolic group, yielding a radical
[6] which can be highly reactive toward environment and can
quench potentially harmful free radicals. Intermolecular hydrogen
bonds are of significant importance for the stability of the radical
and anionic species [7].
Electrochemical properties are generally measured using one
pair of electrodes or three-electrode setup, where the redox processes take place at the electrode–solution interface. The obtained
electroanalytical signal is related to the concentration of electroactive species at the electrode surface. The electrochemical voltammetric signal and its detailed examination can be used to determine
the mechanism of formation of the first reduction or oxidation
intermediates and to help solve the complicated redox mechanisms
of the studied compounds. Cyclic voltammograms are usually
recorded at different scan rates to obtain information about the
process at the electrode. The analysis of peak currents in dependence on the rate of polarization is important to assess whether the
redox process is controlled by diffusion or by adsorption. A significant increase in the scan rate can result in the appearance of new
redox peaks in the forward or backward scans, due to a product
formed at the electrode [8, 9]. When diffusion-controlled conditions for Nernstian behavior are fulfilled, the electrochemical signals recorded at different scan rates and concentrations yield data
on the influence of coupled chemical reaction (C) on the measured
currents. Since chemical reactions directly affect the concentration
of the electroactive species available at the electrode surface, the
interpretation of the cyclic voltammograms recorded in different
conditions (e.g., at different pH values) gives unique information
about the reaction scheme. In particular, the analysis of oxidation
waves allows us to distinguish between reaction schemes entailing
EC (electron transfer followed by chemical reaction), CE (the
chemical reaction precedes the electron transfer), ECE, EE, ECEC,
etc., as well as disclose oxidation or reduction coupling with catalytic processes [10, 11]. For instance, the shift of peak potential in
solutions at different pH values means that protons participate in
redox process [12, 13].
It was shown that metabolic oxidation of some drugs may be
successfully simulated by electrochemical methods because the
main biotransformation of drugs is based on reduction and oxidation processes [14–16]. For instance, Guaiquil et al. found the
same oxidation products of vitamin C found by previous electroRomana Sokolová and Ilaria Degano