DFT study of radical scavenging activity of sesame oil lignans and selected in vivo metabolites of sesamin

Abstract DFT calculation of various molecular descriptors was carried out in order to examine the radical scavenging properties of sesame oil lignans and some selected metabolites of sesamin formed in vivo . The major sesame oil lignans, namely sesamin and sesamolin may present antioxidant activity through hydrogen atom transfer, though lacking a phenolic group. This can be achieved via the contribution of allylic hydrogen atoms according to C–H bond dissociation enthalpy (BDE) values. Even so, the predicted activity is not higher than that of some phenolic derivatives (e.g. pinoresinol) or metabolites bearing catechol moieties. The contribution of non-phenolic hydrogen atoms may result in the formation of planar or semi-planar conjugated compounds. Some of the tested lignans (e.g. sesaminol, sesamolinol) may be efficient electron donors comparable to active flavonoids according to ionization potential (IP) values. Neutral sesamol can be an efficient electron donor rather than hydrogen atom donor according to IP and net electrophilicity values. Only computation in water could partially justify literature experimental findings on the higher reactivity of sesamol over that of sesamin. The metabolites of sesamin, bearing one or two catechol groups were found as the most efficient hydrogen atom donors and most prone to ionization. Therefore, they could be capable to act efficiently via hydrogen atom transfer (HAT) or sequential proton loss electron transfer (SPLET) in real systems as shown by gas-phase and calculations in solvents (benzene, water). Thus, these metabolites may account for the high in vivo antioxidant activity of sesamin. Examination of the succeeding products of metabolism indicated the progressive loss of radical scavenging efficiency which was predicted to be negligible in the compounds excreted from the body of mammals.