Heterogenous fluorescence decay of (4→6)-and (4→8)-linked dimers of (+)-catechin and (-) epicatechin as a result of rotational isomerism.

Abstract

The time-resolved fluorescence of (+)-catechin and ( -)-epicatechin decays as a single exponential. In contrast dimers formed from (+)-catechin and (-)-epicatechin have more complex decays unless rotation about the interflavan bond is constrained by the introduction of a new ring. The fluorescence decay in unconstrained dimers is adequately described by the sum of two exponentials. In a peracetylated dimer, the relative preexponential factors are in excellent agreement with the relative populations of two rotational isomers deduced from high-resolution NMR spectra. Removal of the acetyl group does not significantly change the ratio of the preexponential factors, but it yields a first-order NMR spectrum. The reduction in the energy barrier between the rotational isomers upon removal of the acetyls groups causes interconversion of the isomers to become fast on the NMR time scale. However, resolution of the two populations is maintained on the fluorescence time scale

Citation

Bergmann, Wolfgang R.; Barkley, Mary D.; Hemingway, Richard W.; Mattice, Wayne. 1987. Heterogenous fluorescence decay of (4→6)-and (4→8)-linked dimers of (+)-catechin and (-) epicatechin as a result of rotational isomerism. Journal of the American Chemical Society 109(22):6614-6619