Modeling the mechanism of action of lycopene as a hydroxyl radical scavenger.

The anti-oxidant action of lycopene as a hydroxyl radical scavenger through hydrogen abstraction and addition reaction mechanisms has been investigated. Geometries of seven different conformations of lycopene were optimized employing density functional theory in gas phase which was followed by treatment of their solvation in aqueous media. Thus the all-trans conformation of lycopene was found to be most stable in both gas phase and aqueous media. Four overlapping fragments of all-trans lycopene were considered for calculations of Gibbs barrier energies and rate constants. It is found that several hydrogen atoms can be abstracted from lycopene by a hydroxyl radical barrierlessly. Further, it is shown that addition of an OH radical can also take place to each of the various carbon atoms of lycopene with fairly low barrier energies. Thus lycopene is shown to be an effective anti-oxidant.