Conformations and time‐resolved fluorescence of oligomers of (−)‐epicatechin with 4β → 8 interflavan bonds

Abstract

AbstractOligomers of (−)‐epicatechin with 4β → 8 interflavan bonds, and as many as five monomer units, have been studied by conformational analysis and time‐resolved fluorescence. The conformational analysis yields 2x−1 conformations for each oligomer with x monomer units. There are two conformations accessible at each interflavan bond. These conformations are denoted by + and −. The dominant conformations for the trimer and higher oligomers have an interaction between the phenolic hydroxyl groups on monomers i and i+2. This interaction involves the hydroxyl group at C(5) on monomer i, and either C(13) or C(8) of monomer i+2, depending on whether the conformation of the two intervening interflavan bonds is + + or + −, respectively. Minor contributions to the ensemble for the tetramer and pentamer are made by conformations that contain the sequence of successive interflavan bonds denoted by −+ or −−. In −+ the interaction between monomer units i and i + 2 involves an aliphatic hydroxyl with a phenolic hydroxyl, and there are no hydroxyl‐hydroxyl interactions between units iand i + 2 in −−. The onset of a different decay law for the fluorescence when x increases from 3 to 4 may be associated with the appearance of the −+ and −− conformations as minor constituents in the ensemble.