4-mercaptoimidazoles derived from the naturally occurring antioxidant ovothiols 2. Computational and experimental approach of the radical scavenging mechanism

The radical-scavenging mechanism of fourteen 4-mercaptoimidazoles, derived from the natural family of ovothiols, was studied via a QSAR approach, cyclic voltammetry, ESR and NMR spectroscopy. A significant correlation was found between the DPPH scavenging abilities of test compounds and thermodynamic parameters like overall ease of disulphide formation. The production of a disulphide compound via thiyl radical formation is proposed. Upon DPPH scavenging, hydrogen abstraction from thiols yields transient short-lived thiyl radicals, which were characterised by ESR and rapidly dimerise to form a disulphide compound. Cyclic voltammetry showed that the best DPPH scavengers exhibit low oxidation potentials for their oxidation to disulphides.