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Title

Theoretical parameters to characterize antioxidants - Part 2 - The cases of melatonin and carvedilol

Authors
Migliavacca, E.
Ancerewicz, J.
Testa, Bernard
Published in Helvetica Chimica Acta. 1998, vol. 81, no. 7, p. 1337-1348
Abstract This theoretical study focuses on two indole derivatives, melatonin (1) and carvedilol (8), with the objective of improving our understanding of the molecular mechanisms underlying their radical-scavenging activity. Quantum-mechanical calculations were carried out using the AMI semi-empirical method, some results being confirmed by nb initio (3-21G) calculations. The quantum-chemical descriptor Delta H-ox (relative adiabatic oxidation potential) and the shape of the SOMO (singly occupied molecular orbital) indicate that the stabilization of its radical cation can partially explain the well-documented antioxidant efficacy of melatonin. This stabilization may result from electrostatic interactions and from a hyperconjugative effect existing in a Family of conformers of the melatonin radical cation having the side chain almost perpendicular to the plane of the aromatic rings. Furthermore, 6-hydroxymelatonin (7) appears to be a better free-radical scavenger than melatonin (1) in agreement with experimental results. According to the theoretical parameters Delta H-ox and Delta H-abs (relative bond dissociation enthalpy), carvedilol (8) is not a good antioxidant, in contrast to its ring-hydroxylated metabolites whose powerful antioxidant effects are explained by the formation of an oxyl radical stabilized by delocalization over the carbazole nucleus
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MIGLIAVACCA, E. et al. Theoretical parameters to characterize antioxidants - Part 2 - The cases of melatonin and carvedilol. In: Helvetica Chimica Acta, 1998, vol. 81, n° 7, p. 1337-1348. https://archive-ouverte.unige.ch/unige:9950

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