Electrochemical characterization of bioactive hydroxyxanthones by cyclic voltammetry

Abstract

a b s t r a c tThe present study reports the electrochemical behavior of several phenolic and catecholic-substituted 2,3-diarylxanthones on a glassy carbon electrode, challenged by cyclic voltammetry at different pH values (4.0, 7.4, and 11.0). Higher pH values required lower anodic and cathodic peak voltages. The oxidation of catecholic groups occurred at lower peak potentials in a reversible and pH dependent manner. Anodic peak potentials appeared at higher pH values and were attributed to the electrochemically irreversible oxidation of the phenolic groups. The number and position of hydroxyl substituents were the determinants for the electrochemical behavior and found to correlate with the scavenging activity for reactive oxygen (ROS) and nitrogen species (RNS). A xanthone with two catechol units presented the lowest anodic potential voltage (E pa = 0.15 V) and proved to be the most effective ROS and RNS scavenger.

Electroanalytical Study of Macluraxanthone: A Natural Product with a Strong Antioxidant and Antimalarial Activity

“…Figure shows the CVs of 10 μ mol L −1 macluraxanthone (McX) and osajaxanthone (OjX), in pH 7.69 supporting electrolyte solution at ν = 25 mV s −1 . As can be observed, the overall CV profile of McX within the investigated potential range is very similar to the CVs reported for polyphenols with a catechol moiety, namely some natural xanthones ,, synthetic hydroxyxanthones , and important flavonoids, such as rutin and quercetin , among other compounds . As in these cases, the CV of McX shows a couple of anodic and cathodic peaks at lower positive potentials (E pa1 =201 mV and E pc1 =140 mV, respectively) and an anodic peak at higher potentials (E pa2 =745 mV), with no cathodic counterpart.…”

“…Figure a shows the effect of pH solution on the voltammetric peaks P a1 and P c1 (ascribed to catechol/o‐quinone redox couple). It can be clearly seen that, as the pH varies both peaks are displaced along the potential′s axis, following a similar trend to that found for other polyphenol molecules with a catechol group . Increasing the pH solution, shifts the McX anodic and cathodic peak potentials (E pa1 and E pc1 , respectively) towards less positive values.…”

“…The i pa1 is greater at pH<7, and the i pc1 reaches its maximum at pH around 7. The decrease in the anodic peak current (i pa1 ) with the increasing of pH is a voltammetric characteristic very common to almost all polyphenolic compounds in aqueous solutions −. Virtually independent on the nature of the working electrode and its surface condition, or even of the normal deaeration of the solutions, the decrease of i pa1 is most probably due to the rapid chemical oxidation (including auto‐oxidation) of these polyphenolic compounds and concurrent side reactions of their derivatives in alkaline solutions (e. g., hydroxylation and polymerization of o‐quinonoic products) .…”

“…Meanwhile, the voltammetric behaviour of both xanthones at more positive potentials is probably related with the irreversible electrooxidation of the phenol moieties existing in each one of them (namely, the 1‐hydroxyl group of A‐ring, common to both molecules, and the 7‐hydroxyl group on the B‐ring, exclusive of osajaxanthone (see Fig 1). Comparing the positions and widths of peak P a,o of OjX and P a2 of McX, it can be observed that the osajaxanthone's peak starts to develop at less positive potentials than the macluraxanthone's peak.…”

Characterization of 2,3-diarylxanthones by electrospray mass spectrometry: gas-phase chemistry versus known antioxidant activity properties

“…Oxidation mechanisms were proposed and the electrochemical profiles of these xanthones corroborated their biological properties. Xanthone XH9, the most effective ROS and RNS scavenger, presented the lowest anodic potential voltage ( E pa = 0.15 V at pH 7.4 vs Ag/AgCl) …”