Intramolecular copigmentation in malvidin-3-O-(6-O-p-coumaryl)-glucoside: Insights from experimental and theoretical study.

Intramolecular copigmentation, a natural phenomenon occurring widely in acylated anthocyanins, can stabilize anthocyanins to a great extent and produce color changes. In this study, the mechanism underlying the intramolecular copigmentation of malvidin-3-O-(6-O-p-coumaryl)-glucoside (MvCG) was systematically elucidated using experimental and theoretical approaches. Color analysis by UV-vis spectroscopy revealed an obvious bathochromic shift for MvCG compared to its non-acylated form, as well as higher thermostability of the former. Two dimensional NOESY spectra indicated close proximity between the coumaryl group and anthocyanin B ring in space. Deeper insights into the relationship between the conformational features and optical properties were acquired through TDDFT calculations. Based on the results, the most reasonable conformation of MvCG was proposed: the coumaryl group folded over the anthocyanin B ring in an aslant-parallel arrangement, generating intramolecular copigmentation interactions.