Kinetic and redox characteristics of phenoxyl radicals of eugenol and isoeugenol: A pulse radiolysis study

Abstract

The phenoxyl radicals of eugenol (EgOH) and isoeugenol (iEgOH) were generated by the specific one-electron oxidant N 3 и using pulse radiolysis technique, and were characterized by their absorption spectra, decay and formation kinetics, and one-electron reduction potential (E 7 1 ) values. Reactivities of eugenol phenoxyl radical with the biologically important molecule, trolox C (analogue of vitamin E, ␣-tocopheral), were determined. Reactions of OH with these phenols were studied at different pHs and suitable mechanisms for these reactions were suggested. Scavenging abilities of the phenols toward highly damaging Brи, NO 2 и, and CCl 3 O 2 и radicals were evaluated.

Methoxyphenols—antioxidant principles in food plants and spices: Pulse radiolysis, EPR spectroscopy, and density functional theory calculations*

“…This is clearly reflected in the consistently high rate constants for the scavenging of •N 3 radicals (Table I). In those experiments, where comparison with literature data was possible 11–15, the higher pH or the higher concentration of acetonitrile slowed down both the scavenging and the decay rate constants for eugenol and iso‐eugenol whereas no such effect seems to influence the kinetics of formation of the curcumin radical. Both previous studies 12, 13 are in agreement that the radical formed from curcumin is the phenoxyl radical.…”

“…Pulse radiolysis experiments provided rate constants for the reaction with azide radicals (•N 3 ), decay rates of the respective phenoxyl radicals—depicted in Table I together with literature values for eugenol, iso‐eugenol 11, 15, curcumin 12, 13, and ferulic and sinapic acid 16. All substances scavenge the electrophilic •N 3 radical with near to diffusion‐controlled rates, and enhanced solubilization of eugenol and iso‐eugenol with acetonitrile 12 shows only a marginal effect on the kinetic parameters.…”

A computational methodology for accurate predictions of rate constants in solution: Application to the assessment of primary antioxidant activity

“…It should also be noted that discrepancies of such a magnitude, and also larger, can be found among experimental values for a specific reaction. For example, for the glutathione + • OH reaction (A) the reported experimental values range from 3.48 × 10 9 to 4.4 × 10 10 M −1 s −1 , which means that one experimental value is 12.6 times larger than the other. Other example is reaction F (melatonin + • OH), with experimental values ranging from 1.2 × 10 10 to 6.0 × 10 10 M −1 s −1 , that is, five times apart.…”

Intracellular antioxidant effect of vanillin, 4-methylguaiacol and 4-ethylguaiacol: three components in Chinese Baijiu

“…Different radical sources, substrates, reaction conditions, and mechanisms seemed to be responsible for the different results of in vitro chemical assays. Regarding the antioxidant activity of guaiacol and vanillin, three reaction mechanisms have been proposed: the hydrogen transfer (HT) from the phenolic OH, [36][37][38] the single electron transfer (SET) from the guaiacol and vanillin to the radical, 8,39,40 and sequential proton electron transfer (SPET) mechanism. 3 Moreover, it was found that the environment plays an important role in the peroxyl scavenging activity of guaiacol and vanillin.…”