Tarascou Isabelle, Barathieu Karine, Simon Cécile, Ducasse Marie-Agnès, André Yann, Fouquet Eric, Dufourc Erick J, de Freitas Victor, Laguerre Michel, Pianet Isabelle
Laboratoire de Chimie Organique et Organométallique, UMR 5802-CESAMO, Université Bordeaux 1, 351 cours de la Libération, 33405 Talence, France.
Magn Reson Chem. 2006 Sep;44(9):868-80. doi: 10.1002/mrc.1867.
The three-dimensional structures of 5 procyanidin dimers have been determined in a hydro-alcoholic medium and in water using 2D NMR and molecular mechanics. They are made from monomers of catechin (CAT) and epicatechin (EPI)-B1: EPI-CAT, B2: EPI-EPI, B3: CAT-CAT, B4: CAT-EPI and B2g: EPI-EPI-3-O-gallate. These tannins exist in two conformations that are in slow exchange in the NMR timescale (s), one is compact and the other extended. The compact form is found to dominate (76-98%) when the dimer is made of at least one CAT monomer (B1, B3, B4). Both forms are found in even proportions only in the case of procyanidin B2. The latter tannin can be converted into a dominant compact form when the lower EPI unit is galloylated. The finding of a predominant compact form for procyanidin dimers is discussed in relation with tannin-saliva protein interactions that are of importance for the wine-tasting/making processes.
利用二维核磁共振和分子力学方法，已在水醇介质和水中测定了5种原花青素二聚体的三维结构。它们由儿茶素（CAT）和表儿茶素（EPI）单体组成：B1：EPI-CAT、B2：EPI-EPI、B3：CAT-CAT、B4：CAT-EPI和B2g：EPI-EPI-3-O-没食子酸酯。这些单宁以两种构象存在，在核磁共振时间尺度（秒）上缓慢交换，一种是紧凑的，另一种是伸展的。当二聚体由至少一个CAT单体（B1、B3、B4）组成时，发现紧凑形式占主导（76-98%）。仅在原花青素B2的情况下，两种形式以相等比例存在。当下游EPI单元被没食子酰化时，后一种单宁可转化为占主导的紧凑形式。结合单宁与唾液蛋白的相互作用讨论了原花青素二聚体主要为紧凑形式这一发现，这种相互作用对品酒/酿酒过程很重要。
