Theoretical study of the structure and acidity of condensed tannin monomers
Low level of polyphenols absorption is due among other things to the formation of irreversible complexes between non-heminic iron (Fe2+, Fe3+) and these polyphenols through their hydroxyl groups. Understanding of these complexes formation mechanisms led us to explore hydroxyl groups acidity of these polyphenols monomers (catechin, epicatechin, gallocatechin and epigallocatechin) mainly found in food. Quantum chemistry modelling, more precisely the functional density theory (DFT) method, associated to 6-311G (d, p) base was used in gas phase. Spectroscopic, thermodynamic descriptors and geometric parameters resulting from calculations showed a slight stability of catechin compared to epicatechin and gallocatechin compared to epigallocatechin. As for the acidity of these monomers hydroxyl groups, the results show that it decreases similarly as follows: O4’ > O5> O7 > O5’> O3 for Catechin and epicatechin; O3’ > O5> O4’ > O7 > O5’ > O3 and O3’ > O4’ > O5 > O7 > O5’> O3 respectively for gallocatechin and epigallocatechin.
Keywords: Catechin, Epicatechin, Gallocatechin, Epigallocatechin, Acidity, DFT.