Natural phenolic compounds are abundant in the vegetable kingdom, occurring mainly as secondary metabolites in a wide variety of chemical structures. Around 10,000 different plant phenolic ...derivatives have been isolated and identified. This review provides an exhaustive overview concerning the electron transfer reactions in natural polyphenols, from the point of view of their in vitro antioxidant and/or pro‐oxidant mode of action, as well as their identification in highly complex matrixes, for example, fruits, vegetables, wine, food supplements, relevant for food quality control, nutrition, and health research. The accurate assessment of polyphenols’ redox behavior is essential, and the application of the electrochemical methods in routine quality control of natural products and foods, where the polyphenols antioxidant activity needs to be quantified in vitro, is of the utmost importance. The phenol moiety oxidation pathways and the effect of substituents and experimental conditions on their electrochemical behavior will be reviewed. The fundamental principles concerning the redox behavior of natural polyphenols, specifically flavonoids and other benzopyran derivatives, phenolic acids and ester derivatives, quinones, lignins, tannins, lignans, essential oils, stilbenes, curcuminoids, and chalcones, will be described. The final sections will focus on the electroanalysis of phenolic antioxidants in natural products and the electroanalytical evaluation of in vitro total antioxidant capacity.
The mechanism of electrochemical oxidation of morin has been studied using cyclic, differential pulse and square‐wave voltammetry techniques in aqueous electrolyte with solid, insoluble morin hydrate ...mechanically transferred to a glassy carbon electrode surface, over a wide pH range. The oxidation mechanism proceeds in sequential steps, related with the hydroxyl groups in the three aromatic rings and the oxidation is pH dependent over part of the pH range the oxidation potentials are shifted to lower values with increasing pH. Oxidation of the 2′,4′dihydroxy moiety at the B ring of morin occurs first, at very low positive potentials, and is a one electron one proton reversible reaction. The hydroxyl groups oxidized at more positive potentials were shown to undergo an irreversible oxidation reaction.
Glassy carbon electrodes (GCE) were modified with poly(glutamic acid) acid films prepared using three different procedures: glutamic acid monomer electropolymerization (MONO), evaporation of ...poly(glutamic acid) (PAG) and evaporation of a mixture of poly(glutamic acid)/glutaraldehyde (PAG/GLU). All three films showed good adherence to the electrode surface. The performance of the modified GCE was investigated by cyclic voltammetry and differential pulse voltammetry, and the films were characterized by atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). The three poly(glutamic acid) modified GCEs were tested using the electrochemical oxidation of ascorbic acid and a decrease of the overpotential and the improvement of the oxidation peak current was observed. The PAG modified electrode surfaces gave the best results. AFM morphological images showed a polymeric network film formed by well-defined nanofibres that may undergo extensive swelling in solution, allowing an easier electron transfer and higher oxidation peaks.
The electrochemical behaviour of indole and a group of indole‐containing compounds with a substituent at the C3 position, indol‐3‐acetamide (IAM), tryptamine, gramine, indole acetic acid (IAA), ...indole propionic acid (IPA), indole butyric acid (IBA) and tryptophan, was investigated at a glassy carbon electrode, in order to determine their oxidation pathways. Indole undergoes one irreversible pH dependent oxidation, whereas the oxidation process of indole derivatives was more complex, a two step, the oxidation at C2 position on the pyrrole ring followed by the hydroxylation at the C7 position of the benzene moiety of indoles, irreversible pH dependent oxidation.
An electrochemical nucleic acid (NA)-based biosensor is a biosensor that integrates a nucleic acid as the biological recognition element and an electrode as the electrochemical signal transducer. The ...present report provides concepts, terms, and methodology related to biorecognition elements, detection principles, type of interactions to be addressed, and construction and performance of electrochemical NA biosensors, including their critical evaluation, which should be valuable for a wide audience, from academic, biomedical, environmental, and food-testing, drug-developing, etc. laboratories to sensor producers.
Electrochemical Oxidation of Quercetin Brett, Ana Maria Oliveira; Ghica, Mariana-Emilia
Electroanalysis (New York, N.Y.),
November 2003, Letnik:
15, Številka:
22
Journal Article
Recenzirano
Odprti dostop
The mechanism of electrochemical oxidation of quercetin on a glassy carbon electrode has been studied using cyclic, differential pulse and square‐wave voltammetry at different pH. It proceeds in a ...cascade mechanism, related with the two catechol hydroxyl groups and the other three hydroxyl groups which all present electroactivity, and the oxidation is pH dependent. Quercetin also adsorbs strongly on the electrode surface; and the final oxidation product is not electroactive and blocks the electrode surface. The oxidation of the catechol 3′,4′‐dihydroxyl electron‐donating groups, occurs first, at very low positive potentials, and is a two electron two proton reversible reaction. The hydroxyl group oxidized next was shown to undergo an irreversible oxidation reaction, and this hydroxyl group can form a intermolecular hydrogen bond with the neighboring oxygen. The other two hydroxyl groups also have an electron donating effect and their oxidation is reversible.
Guanine-rich DNA sequences are able to form G-quadruplexes, being involved in important biological processes and representing smart self-assembling nanomaterials that are increasingly used in DNA ...nanotechnology and biosensor technology. G-quadruplex electrochemical biosensors have received particular attention, since the electrochemical response is particularly sensitive to the DNA structural changes from single-stranded, double-stranded, or hairpin into a G-quadruplex configuration. Furthermore, the development of an increased number of G-quadruplex aptamers that combine the G-quadruplex stiffness and self-assembling versatility with the aptamer high specificity of binding to a variety of molecular targets allowed the construction of biosensors with increased selectivity and sensitivity. This review discusses the recent advances on the electrochemical characterization, design, and applications of G-quadruplex electrochemical biosensors in the evaluation of metal ions, G-quadruplex ligands, and other small organic molecules, proteins, and cells. The electrochemical and atomic force microscopy characterization of G-quadruplexes is presented. The incubation time and cations concentration dependence in controlling the G-quadruplex folding, stability, and nanostructures formation at carbon electrodes are discussed. Different G-quadruplex electrochemical biosensors design strategies, based on the DNA folding into a G-quadruplex, the use of G-quadruplex aptamers, or the use of hemin/G-quadruplex DNAzymes, are revisited.
The cancer treatment based on monoclonal antibodies has become one of the most successful therapeutic strategies. Among the monoclonal antibodies, nivolumab (NIVO) stands out as being a relatively ...new anticancer drug. The NIVO‐dsDNA interaction was evaluated, in incubated solutions, by differential pulse voltammetry, UV‐Visible spectrophotometry and gel electrophoresis, and in situ with dsDNA‐, polyG‐ or polyA‐electrochemical biosensors, by differential pulse voltammetry, electrochemical impedance spectroscopy, and quartz crystal microbalance. The interfacial behaviour of the dsDNA‐electrochemical biosensor was also investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The NIVO‐dsDNA interaction mechanism caused, for shorter times, the binding of the NIVO to DNA, resulting in a NIVO‐dsDNA complex, and for longer times, the relaxation/unwinding of this complex structure. The monoclonal antibody NIVO did not promote oxidative damage to DNA.
Binding interactions: The interaction mechanism between the anticancer monoclonal antibody nivolumab and DNA was investigated. The NIVO‐dsDNA molecular mechanism interaction caused, for shorter times, the binding of the NIVO to DNA, resulting in a NIVO‐dsDNA complex, and for longer times, the relaxation/unwinding of the dsDNA. The monoclonal antibody NIVO did not promote oxidative damage to dsDNA.
Keratin is the main protein in hair strands. The process of dyeing hair with permanent dyes is quite complex and involves oxidative reactions between precursors, such as p‐toluenediamine (PTD) and ...p‐aminophenol (PAP), and coupler agents, in alkaline and oxidative medium, inside the hair. The electrochemical behaviour of native and denatured human hair keratin, assessed by using a keratin multilayer film adsorbed on glassy carbon electrode, and its interaction with hair dye precursors, PTD and PAP, by using electrochemical techniques, was investigated. Native and denatured keratin electrochemical oxidation showed two oxidation peaks; the first was first attributed to the cysteine amino acid residues, and the second to the cysteine and methionine amino acids residues. The PTD‐ and PAP‐keratin‐hair dye interactions induced damage, causing the unfolding of the keratin morphological structure, and new additional peaks of the cysteine and tyrosine amino acid residues were revealed.
Dyeing to unfold: The electrochemical behaviour of human hair keratin and its interaction with hair dye precursors, p‐toluenediamine and p‐aminophenol, is investigated by using electrochemical techniques. The electrochemical oxidation of keratin occurs through the oxidation of the cysteine and methionine amino acid residues. The interaction between keratin and hair dye precursors induces damage, which causes the morphological structure of keratin to unfold.
Electrochemical Oxidation of Rutin Ghica, Mariana-Emilia; Brett, Ana Maria Oliveira
Electroanalysis (New York, N.Y.),
March 2005, Letnik:
17, Številka:
4
Journal Article
Recenzirano
Odprti dostop
An electrochemical investigation of rutin oxidation on a glassy carbon electrode was carried out using cyclic voltammetry, differential pulse voltammetry and square‐wave voltammetry over a wide pH ...interval. The electrochemical oxidation is a complex process, which proceeds in a cascade mechanism, related with the 4‐hydroxyl groups of the rutin molecule. The catechol 3′,4′‐dihydroxyl group is the first to be oxidized by a two‐electron – two‐proton reversible oxidation reaction, followed by an irreversible oxidation reaction due to the 5,7‐dihydroxyl group. Both mechanisms are pH dependent. An adsorption process is also observed and the oxidation products block the electrode surface.
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