title: Lipoic acid and dihydrolipoic acid. A comprehensive theoretical study of their antioxidant activity supported by available experimental kinetic data.
abstract: The free radical scavenging activity of lipoic acid (LA) and dihydrolipoic acid (DHLA) has been studied in nonpolar and aqueous solutions, using the density functional theory and several oxygen centered radicals. It was found that lipoic acid is capable of scavenging only very reactive radicals, while the dehydrogenated form is an excellent scavenger via a hydrogen transfer mechanism. The environment plays an important role in the free radical scavenging activity of DHLA because in water it is deprotonated, and this enhances its activity. In particular, the reaction rate constant of DHLA in water with an HOO(•) radical is close to the diffusion limit. This has been explained on the basis of the strong H-bonding interactions found in the transition state, which involve the carboxylate moiety, and it might have implications for other biological systems in which this group is present.
authors.affiliation: Departamento de Física y Química Teórica, Facultad de Química, Universidad Nacional Autonoma de Mexico , Av Universidad 3000, Copilco Universidad, Coyoacán, Ciudad de Mexico DF 04510, Mexico.
authors.forename: Romina
authors.initials: R
authors.lastname: Castañeda-Arriaga
authors.forename: J Raul
authors.initials: JR
authors.lastname: Alvarez-Idaboy
mesh_terms: D016166:Free Radical Scavengers / Q000737:chemistry / Q000494:pharmacology*; D005609:Free Radicals / Q000737:chemistry; D006860:Hydrogen Bonding; D007700:Kinetics; D008958:Models, Molecular; D011522:Protons; D008063:Thioctic Acid / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D014867:Water / Q000737:chemistry
chemical_list: D016166:Free Radical Scavengers; D005609:Free Radicals; D011522:Protons; D014867:Water; D008063:Thioctic Acid; C015144:dihydrolipoic acid