NMR AND MOLECULAR MODELING - APPLICATION TO WINE AGING

Red wine contains polyphenols called tannins which are very important for its taste and longevity. These polymers consist in repeating units of catechin and its epimer epicatechin. During ageing, slow condensat ion reactions take place which lead to new chemical structures. Among the possible reactions, we have focused our attention on acetaldehyde cross-linking, Catechin was used as a model for the production of poly mers with acetaldehyde, Two reaction product fractions have been isola ted by liquid chromatography. Mass measurement indicated that these fr actions contain dimers. NMR (1D and 2D) and molecular modelling were t hen used to study the structure and conformations of these products. T he first product consist in a pure dimer with the two catechin moietie s connected with an ethyl bridge on the carbon 6 and 8. The second fra ction was a mixture of two dimers (50/50). NMR measurements showed tha t it could be two symmetrical dimers involving the same carbon for eac h catechin moiety (6 or 8).