Electrochemical and antioxidant properties of rutin

Monitoring Oxidative Status in Winemaking by Untargeted Linear Sweep Voltammetry

An electrochemical portable device based on linear sweep voltammetry was evaluated for studying the redox behavior of polyphenolic compounds in industrial scale winemaking to infer the effects of selected early processing steps on the vinification trials of Pinot gris, Chardonnay, Vermentino and Sangiovese grapes. For each sample, the redox behavior showed a distinctive voltammetric signal pattern related to the processing step during winemaking, therefore being useful as a potential fingerprint for wine identification and to provide insights about the phenolic content. For instance, there was a high correlation (R² = 0.72) between the total phenolic compounds (PhenOx) and the easily oxidizable compounds (EasyOx), the latter representing approx. 30% on average of the total phenolics. Furthermore, the maceration of red grapes was concluded after 29 days based on information driven by the phenolics pattern. As expected, during alcoholic fermentation, white wines showed a lower content of phenolic compounds than those found in red wines, with an average ratio PhenOx/EasyOx of about 4.7, 5.0 and 3.6 for Chardonnay, Pinot gris and Vermentino, respectively. The portable tool with miniaturized disposable electrodes showed interesting analytical features that can be exploited for on-site and real-time quality control for monitoring change in phenolic composition during wine processing and storage, and for tailoring winemaking practices to enhance the color stability of products.

Spectro-electrochemical characterization and quantification of Rutin in aqueous media

From UV-Vis spectrophotometric measurements the acidity constants of Rutin in aqueous media, at 25 °C and 0.1 M ionic strength, were determined as: pK₁ = 4.392 ± 0.167, pK₂ = 7.130 ± 0.050, pK₃ = 8.661 ± 0.042 and pK₄ = 12.354 ± 0.020 and the molar absorptivity coefficients of all the Rutin pH-dependent species were reported as a function of wavelength. Furthermore, the electrochemical behavior of Rutin at neutral pH was investigated using a bare carbon paste electrode, CPE. It was found that both: Rutin electrochemical oxidation and reduction are reversible, adsorption-controlled processes, involving 2 electron transfers. Moreover, the bare CPE was used for the electrochemical quantification of Rutin in neutral aqueous media, displaying the following features: (1.078 ± 0.440) μM, (3.594 ± 0.400) μM and (0.308 ± 0.014) μA μM^-1 for the detection and quantification limits and sensitivity, respectively, within the 1-11 μM linear range. Meanwhile the spectrophotometric method displayed the following analytical features: (3.385 ± 1.318) μM, (11.283 ± 3.114) μM and (0.0120 ± 0.0001) AU μM^-1 for the detection and quantification limits and sensitivity, respectively within the 11-110 μM linear range. In like manner, the bare CPE is also shown as a robust electrochemical sensor that allows Rutin quantification even in the presence of ascorbic acid, commonly found in Rutin samples.

Cyclic voltammetry of natural flavonoids on MWNT-modified electrode and their determination in pharmaceuticals

The determination of rutin, quercetin and taxifolin in pharmaceutical dosage forms using cyclic voltammetry on multi-walled carbon nanotube modified glassy carbon electrode (MWNT-GCE) has been developed. The surface of the electrode created has been characterized by atomic force microscopy. Electrode modification with MWNT increases the surface average roughness (190-fold) and structures it. There are two oxidation steps at 0.22 and 0.80, 0.23 and 0.80, 0.26 and 0.86 V on cyclic voltammograms of taxifolin, quercetin and rutin, respectively, in phosphate buffer solution of pH 7.4. The linear dynamic range is 1.4–28 and 28–210, 2.0–220 and 0.52–210 μM with detection limits of 0.71, 1.0 and 0.26 μM for rutin, quercetin and taxifolin, respectively. The relative standard deviation of flavonoids determination in pharmaceuticals does not exceed of 7%. The data obtained are in good agreement with coulometric determination.

Electrochemical investigation of flavonolignans and study of their interactions with DNA in the presence of Cu(II)

Flavonolignans, silybin and its derivatives (2,3-dehydrosilybin, 7-O-methylsilybin, 20-O-methylsilybin) and isosilybin were studied using ex situ (adsorptive transfer, AdT) cyclic and square wave voltammetry (SWV). The two oxidation steps were described for flavonolignans at potentials E(p1) +0.5 V and E(p2) +0.85 V depending on experimental conditions. An additional oxidation peak at E(p3) +0.35 V was observed only for 2,3-dehydrosilybin. The anodic currents of flavonolignans are related to their electron transfer processes (oxidation of hydroxyl groups), which was supported by density functional theory (DFT) and B3P86 theory level. Our electrochemical results confirmed that 2,3-dehydrosilybin is a relatively strong antioxidant, which is strictly associated with oxidation at E(p3). The oxidation processes and antioxidant parameters of flavonolignans can be affected by transition metal complexation via hydroxyl groups. We found that silybin and 2,3-dehydrosilybin are able to chelate transition metals, especially Cu(2+). The formation of silybin/Cu complexes was studied by AdT SWV and the observation was also confirmed using fluorescence spectroscopy. The electrochemical investigation of DNA interactions and damage caused in the presence of silybin/Cu complex and hydrogen peroxide is described. We present evidence that flavonolignans are involved not only in antioxidant abilities but also in the prooxidation effects under in vitro conditions.