A Theoretical and Experimental Study of a Two-step Quasireversible Surface Redox Reaction by Square-wave Voltammetry

An extended theoretical treatment of a two-step surface redox reaction under the conditions of square-wave voltammetry (SWV) is presented. The theoretical model is applicable to any reversibility of both redox steps of the EE reaction. The integral equations representing this theoretical model were solved numerically. The apparent reversibility of the redox steps depends on two dimensionless kinetic parameters, κ1 and κ2, defined as κ1 = ks,1/f and κ2 = ks,2/f, where ks,1 and ks,2 are the standard rate constants of the first and second redox steps, respectively, and f is the excitation signal frequency. The response consists of either a single or two separate SW peaks, depending mainly on the difference between the formal potentials of the first and second redox steps as well as on the ratio of the kinetic parameters κ1/κ2. The effect of the electron transfer coefficients of both redox steps is also discussed. A part of the theoretical results are qualitatively illustrated by SW voltamograms of the azo-dye Sudan-III

Square-Wave Voltammetry of 1-Benzyl-tetrazole-5-thiol

Basic electrochemical characteristics of 1-benzyl-tetrazole-5-thiol in acid medium were investigated applying classical (DC) polarography, cyclic (CV) and square-wave voltammetry (SWV). During the HMDE life-time, a compound was spontaneously formed between the mercury and thiol and deposited on the HMDE surface. The surface precipitation process results in formation of a multilayer film on the electrode surface. The SW response of the investigated component mainly depends on the structure of the film

Adsorption Effects in Square-Wave Voltammetry of an EC Mechanism

The influence of adsorption of the electroactive species on the square-wave voltammetric responses of two different EC mechanisms is theoretically studied. Theoretical models for the EC electrode mechanism, coupled with adsorption of the reactant but not of the product of the redox reaction and for the surface EC mechanism in which both the reactant and the product are strongly adsorbed, are developed. The reversible and the quasireversible redox reactions of both electrode mechanisms are considered. Relationships between the properties of the SW response and the parameters of both redox reactions and SW excitation signal are analyzed. The theory is compared qualitatively with the SW voltammograms of azobenzene recorded in an acidic medium

Non–enzymatic Amperometric Sensor for H2O2 Based on MnCO3 Thin Film Electrodes

The present study describes development of a non–enzymatic amperometric sensor for detection of H2O2 based on MnCO3 thin film electrodes. The film was deposited on electroconductive FTO coated glass substrates using simple chemical bath deposition method. The phase composition of the thin film was confirmed by X-ray diffraction analysis. The electrochemical properties and the sensor sensitivity towards H2O2 were examined using cyclic voltammetry and chronoamperometry in 0.1 M phosphate buffer solution with pH = 7.5. It was revealed that the sensing mechanism is based on electrocatalytic oxidation of H2O2, involving Mn species as redox mediators. According to the results, the best sensor response towards H2O2 was found at E = +0.25 V, with detection limit and sensor sensitivity of 10.0 µM and 2.64 µA cm–2 mM–1 (for the range of 0.09–1.8 mM), respectively, associated with R2 = 0.999. This work is licensed under a Creative Commons Attribution 4.0 International License

Bioactive Phenolic Compounds from Lingonberry (Vaccinium vitis-idaea L.): Extraction, Chemical Characterization, Fractionation and Cellular Antioxidant Activity

Lingonberries contain high contents of bioactive compounds such as chlorogenic acids and anthocyanins. In addition to radical scavenging and antioxidant activities, these compounds can protect cells from DNA damage. For this reason, lingonberries might be well suited for nutraceuticals or natural biomedicines. To assess these applications, the present study characterized and identified the most effective extract, only consisting of anthocyanins, copigments or a mixture of both, obtained from a lingonberry juice concentrate. An extract was generated by using a XAD-7 column followed by fractionation into anthocyanins and copigments using adsorptive membrane chromatography. After identification of main polyphenols by HPLC–photodiode array–electrospray ionization–tandem mass spectrometry, free radical scavenging activity was analyzed by electron spin resonance spectroscopy using 2,2-diphenyl-1-picrylhydrazyl and galvinoxyl radicals. Furthermore, cyclic voltammetry analyses and the Trolox equivalent antioxidant capacity (TEAC) assay were applied. Finally, the reactive oxygen species (ROS) reducing effects of the lingonberry extract and its fractions were evaluated in HepG2 cells. While the combination of anthocyanins and copigments possessed the highest antioxidant activities, all samples (XAD-7 extract, anthocyanin and copigment fraction) protected cells from oxidative stress. Thus, synergistic effects between phenolic compounds may be responsible for the high antioxidant potential of lingonberries, enabling their use as nutraceuticals