Elektrochemische Oxydation von Flavonoiden an einer glasartigen Kohlenstoffelektrode

Abstract

Mitoxantrone is an anthracycline used as an antitumour antibiotic for leukaemia and breast cancer treatment, due to its interaction with DNA. However, the molecular mechanism of the antitumour action is not completely understood. Using a glassy carbon electrode the electrochemical oxidation of mitoxantrone was shown to be a complex, pH-dependent, irreversible electrode process involving several metabolites. Comparison of the electrochemical oxidation behaviour of mitoxantrone, ametantrone and aminantrone enabled a deeper understanding of the mechanism and showed the relevance of electrochemical data for the understanding of the cytotoxicity of mitoxantrone. Since mitoxantrone and its oxidation products adsorb strongly on the electrode surface, causing severe problems of electrode fouling, reproducible electroanalytical determinations could only be done at very low concentrations and in an aqueous buffer supporting electrolyte containing 30% ethanol. The detection limit obtained was 10 À7 M.

Rapid Voltammetric Screening Method for the Assessment of Bioflavonoid Content Using the Disposable Bare Pencil Graphite Electrode

“…The slope values of the Epa = f(pH) dependencies (where Epa represents the anodic peak potential, with Epa2 and Epa3 the peak potentials of peak a2 and a3, respectively) (Figure 4b) were close to the theoretical one of 0.059 V/pH from the Nernst equation, indicating that in the HESP oxidation reactions, an equal number of protons and electrons were transferred. According to Figure 4a, the highest anodic signal was recorded in BRB solution pH 1.81, these findings being in accordance to the data previously reported in the literature for HESP oxidation at carbon-based [16,23] and boron-doped diamond electrodes [5]. This is supported by the general behavior of flavonoids at extremely low pH values deter-…”

“…This is supported by the general behavior of flavonoids at extremely low pH values determined by the resonance effect on active OH groups, which are preserving the antioxidant effect of flavonoids due to stabilization of flavylium cation. Therefore, the influence of the According to Figure 4a, the highest anodic signal was recorded in BRB solution pH 1.81, these findings being in accordance to the data previously reported in the literature for HESP oxidation at carbon-based [16,23] and boron-doped diamond electrodes [5]. This is supported by the general behavior of flavonoids at extremely low pH values determined by the resonance effect on active OH groups, which are preserving the antioxidant effect of flavonoids due to stabilization of flavylium cation.…”

“…The first electrochemical investigations of flavonoids were based on their reduction at mercury electrodes, but the presence of the hydroxyl groups in their structure enables also their electrooxidation. This was investigated since the 1980s, starting with the glassy carbon electrode (GCE) [16] and employing many other electrodes either bare [5,[17][18][19], electroactivated [20,21] or modified with different carbon based materials like carbon nanotubes [22][23][24] or graphene derivatives [25][26][27][28], nanomaterials [26,[28][29][30], polymeric films [27,28,31], etc. Unfortunately, most of the electrodes encounter problems due to the electroactive surface fouling during the electrochemical investigations, especially when these are based on the oxidation of phenolic compounds, which can generate phenoxy radicals able to polymerize and produce a film covering the electrode surface.…”

Automated Voltammetric Determination of Reducing Compounds in Beer

“…This is due to the depletion of electrochemically active compounds from beer at the electrode interface, associated with an initial expansion of the diffusion layer and hence a decreasing concentration gradient. These substances should be especially o-dihydroxylated aromatic compounds (e.g., many flavonoid polyphenols) which can be oxidized forming o-quinones at potentials between 0.4 and 0.8 V [33][34][35]. p-Quinoid structures (e.g., from ellagic acid, ellagotannins) can be formed at even lower potentials [35].…”

“…These substances should be especially o-dihydroxylated aromatic compounds (e.g., many flavonoid polyphenols) which can be oxidized forming o-quinones at potentials between 0.4 and 0.8 V [33][34][35]. p-Quinoid structures (e.g., from ellagic acid, ellagotannins) can be formed at even lower potentials [35]. However, the diffusion layer was kept constant from a certain width by intensive stirring, and a rather high working potential was chosen.…”