Electrochemical reactivity of biologically active quinone/hydroquinone sesquiterpenoids on glassy carbon electrodes

Abstract

The redox reactivity of avarone and avarol, a quinone/hydroquinone couple isolated from the marine sponge Dysidea avara, was investigated by cyclic voltammetry, using a glassy carbon electrode. Both oxidation of avarol and reduction of avarone in aqueous ethanol (1: 1 V/V) take place by a 2 em process at a wide range of pH values; in acetonitrile, however, the reduction of avarone occurs as a stepwise electron transfer process. The mechanisms, as well as the scope and limitations of the method are discussed with reference to the biological activity of the two sesquiterpenoids.

Phase Behavior of a New Class of Anthraquinone-Based Discotic Liquid Crystals

“…On the other hand, peak 4 is scarce because it is so anodically shifted, but its presence was seen in all of the compounds. Peak 4 is ascribed to a stabilized AQ radical anion, which might be because of the consequence of either an ion-pairing interaction or a protonated AQ radical anion, as reported earlier. − …”

“…In the anodic scan, an additional broad peak (just after peak 3) is observed for all of the compounds. The reoxidation of radical anion (nonstabilized) to the neutral AQ (backward path of eq ) is probably the reason for this unusual phenomena, as reported earlier. − In this case, one can consider another equilibrium because the integration of peak 2 is unequal to the charge consumed in peak 3, which indicates that there might be formation of different chemical species between the reactions of two AQ dianions. Literature survey reveals disproportionation (forward path of eq ) and comproportionation (backward path of eq ) redox reactions for quinone derivatives. , It is observed that, upon formation of the AQ dianion (at a scan rate of 0.05 V s –1 ), a portion of the dianionic species might undergo a comproportionation reaction to form AQ radical anions.…”

Reactivity and Biological Activity of the Marine Sesquiterpene Hydroquinone Avarol and Related Compounds from Sponges of the Order Dictyoceratida

“…The formation of avarol semiquinone anion radicals was confirmed by electrochemical methods [75,76] and by EPR spectroscopy of products of air-oxidation of avarol and methanol reduction of avarone [77]. Still, we believed that evidence of semiquinone radical formation in biochemical reactions was insufficient.…”

Anthraquinone-Based Discotic Liquid Crystals

“…The first oxidation peak is attributed to the reverse reaction of eqs and . The second oxidation wave, which is only observed at scan rates >500 mV·s −1 , is attributed to either an ion-pair between the electrolyte cation and the radical anion or to a protonated radical anion, which could arise from adventitious water. − For AQ series 3 , two reduction peaks, which are typically well separated in underivatized AQ, are labeled as shoulder 1 and peak 2 in Figure . The first reduction shoulder 1 (forward direction of eq ) to the radical anion requires reductive potentials around −1.0 V. Peak 2 is attributed to the further one-electron reduction of the radical anion to the dianionic species (forward direction of eq ).…”

“…Peak 4 is unusual because it is so anodically shifted, but its appearance was found in each AQ derivative synthesized. Peak 4 is attributed to a stabilized AQ radical anion, which could result from either an ion-pairing interaction or a protonated AQ radical anion. − Reversal of the scanning direction after shoulder 1 results in the growth of peak 4 at a sweep rate of 50 mV·s −1 . An expansion of the slow scan rate in Figure is included in the Supporting Information to highlight different redox behavior at scan rates <50 mV·s −1 .…”