Theoretical and experimental investigations on the structure related biological activity of (+) catechin and (-) epicatechin

Abstract

The monomeric flavan-3-ols, namely (+) catechin (CT) and (-) epicatechin (ECT) are two important antioxidants available in nature. These are the important constituents of grapes, green tea, blueberries and cocoa. The structural related properties such as preferential site and favored mechanism for antioxidant activity have been identified. Biological activities of CT/ECT and biomolecules extracted from the grape seed (GSE) have been performed and comparative analysis was carried out. In addition, bioconjugates have been obtained and their biological activity is also been explored. Fresh grapes (Vitis vinifera) were collected from the Madhampatti at Coimbatore, Tamil Nadu, India. The density functional theory (DFT) method has been used to identify the preferential radical scavenging mechanism of CT and ECT out of H-atom transfer (HAT), single-electron transfer-proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) at B3LYP/6-311G (2d,2p) level of theory. Parameters related to the above mechanisms, such as bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA) and electron transfer enthalpy (ETE) in gas and solvent different mediums were investigated. 4 -OH site from the catechol ring is identified as the scavenging site for both the compounds. The scavenging ability of CT and ECT was investigated experimentally using a 2, 2-diphenyl-1-picrylhydrazyl (DPPH ) assay. Even though the thermodynamical parameters for the CT/ECT- DPPH interaction concludes that these two antioxidants can interact spontaneously in an exothermic process, the relatively high antioxidant potential of ECT has been identified with the half-maximal inhibitory concentration. newlineThe antioxidant and antibacterial activity of pure CT /ECT/GSE and its bioconjugates have been evaluated using assay namely DPPH and ABTS.+ assay, and against S. aureus and E. coli bacteria respectively.