Phenolic Stilbenes Research Articles

Antioxidative and prooxidative action of stilbene derivatives.

The effects of stilbene derivatives, including resveratrol, diethylstilboestrol and stilbene, as antioxidants or prooxidants were examined. Resveratrol and diethylstilboestrol, but not stilbene, strongly inhibited NADPH- and adenosine 5'-diphosphate (ADP)-Fe3+-dependent lipid peroxidation at the initial and propagation stages. In addition, phenolic stilbenes also inhibited ultraviolet light-induced lipid peroxidation. Resveratrol and diethylstilboestrol efficiently scavenged 2,2'-azobis-(2-amidinopropane)-dihydrochloride peroxyl radicals. However, 2,2'-diphenyl-p-picrylhydrazyl radicals were trapped only by resveratrol, but not by diethylstilboestrol. These results suggest that the inhibitory effect of phenolic stilbenes on lipid peroxidation was due to their scavenging ability of lipid peroxyl and/or carbon-cantered radicals. Resveratrol efficiently reduced ADP-Fe3+, but not EDTA-Fe3+. Stilbenes and diethylstilboestrol did not reduce either ADP-Fe3+ or EDTA-Fe3+. The strand breaks of DNA were stimulated during the interaction of resveratrol with ADP-Fe3+ in the presence of H2O2. These results suggest that phenolic stilbenes act as antioxidants of membrane lipids and that resveratrol has a prooxidative effect DNA damage during interaction with ADP-Fe3+ in the presence of H2O2.

Antioxidative and Prooxidative Action of Stilbene Derivatives

Abstract:The effects of stilbene derivatives, including resveratrol, diethylstilboestrol and stilbene, as antioxidants or prooxidants were examined. Resveratrol and diethylstilboestrol, but not stilbene, strongly inhibited NADPH‐ and adenosine 5′‐diphosphate (ADP)‐Fe3+‐dependent lipid peroxidation at the initial and propagation stages. In addition, phenolic stilbenes also inhibited ultraviolet light‐induced lipid peroxidation. Resveratrol and diethylstilboestrol efficiently scavenged 2,2′‐azobis‐(2‐amidinopropane)‐dihydrochloride peroxyl radicals. However, 2,2′‐diphenyl‐p‐picrylhydrazyl radicals were trapped only by resveratrol, but not by diethylstilboestrol. These results suggest that the inhibitory effect of phenolic stilbenes on lipid peroxidation was due to their scavenging ability of lipid peroxyl and/or carbon‐cantered radicals. Resveratrol efficiently reduced ADP‐Fe3+, but not EDTA‐Fe3+. Stilbenes and diethylstilboestrol did not reduce either ADP‐Fe3+ or EDTA‐Fe3+. The strand breaks of DNA were stimulated during the interaction of resveratrol with ADP‐Fe3+ in the presence of H2O2. These results suggest that phenolic stilbenes act as antioxidants of membrane lipids and that resveratrol has a prooxidative effect DNA damage during interaction with ADP‐Fe3+ in the presence of H2O2.

The early oxidative biodegradation steps of residual kraft lignin models with laccase

A number of model compounds resembling the fundamental bonding patterns of residual kraft lignin, including a series of stilbenes, were incubated with laccase from Trametes versicolor in the presence and absence of delignification ‘mediators’ ABTS and HBT. The condensed kraft lignin model compounds seem to undergo initial degradation by laccase mainly via benzylic oxidation, demethylation and hydroxylation reactions. Phenolic 5-5′, diphenylmethane and α-5 lignin models were found to be degraded mainly via side-chain oxidation reactions. Among the models studied, a phenolic stilbene was found to be the most reactive, yielding several products showing side-chain oxidation/transposition, demethoxylation and hydroxylation reactions. Non-phenolic 5-5′, diphenylmethane and stilbene model compounds were found unreactive even in the presence of the laccase-mediator system.

Discoloration of α-Carbonyl-Free Lignin Model Compounds Under UV Light Exposure

Abstract A series of α-carbonyl-free lignin model compounds was prepared and adsorbed onto bleached chemical pulp. The rates of discoloration of these materials, under simulated solar light exposure, were established and compared to that of peroxide bleached methylated (alkali and dimethyl sulfate) and nonmethylated chemithermomechanical pulps. Phenolic phenylcoumarone and phenolic stilbenes were found to be the most sensitive chromophores under UV irradiation, both inducing a strong yellowing. Also, monophenolic biphenyl and biphenylmethane entities were shown to be prone to discolouration in contrast to the biphenolic and dimethylated ones. Moreover, the catechol structures which are known to be easily oxidizable into ortho quinones, display significant yellowing only when their absorption spectra are shifted above 300 nm where the light source emits. The behaviour of the phenolic stilbenes and the biphenyl catechol is reminiscent of the behaviour of CTMP. This indicates the possible involvement of such structures as being mainly responsible for the discoloration of lignocellulosic materials under UV irradiation. A mechanism is proposed to account for the photoyellowing of the models involving a cyclohexadienone hydroperoxide as intermediate, which is formed by UV irradiation from a complex between the phenol and ground state oxygen.