Vinylcatechin Dimers Are Much Better Copigments for Anthocyanins than Catechin Dimer Procyanidin B3

The binding constants (K) for the interaction of three copigments (CP), two epimeric vinylcatechin dimers (CP1 and CP2), and catechin dimer B3 (CP3) with two pigments, malvidin-3-glucoside (oenin) and malvidin-3,5-diglucoside (malvin), were determined. The K values clearly show that both vinylcatechin dimers have much higher affinity for oenin and malvin than dimer B3: K(CP2) > K(CP1) >> K(CP3). Quantum mechanics and molecular dynamics calculations were also performed to interpret the binding data and specify the relative arrangement of the pigment and copigment molecules within the complexes.