FORMATION OF AN ALUMINUM COMPLEX OF 5-O-CAFFEOYLQUINIC ACID WITH CHIRAL MOLECULAR STACKING UNDER VACUOLAR CONDITION

摘要

5-O-Caffeoylquinic acid (neochlorogenic acid, 5CQ) is an essential co-pigment for blue coloration of hydrangea. 5CQ solubilizes a water insoluble aluminum complex of 3-O-glucosyldelphinidin (Dp3G) to give a water-soluble blue complex, in which both Dp3G and 5CQ chelate a single Al~(3+) ion. However, its isomer, 3-O-caffeoylquinic acid (chlorogenic acid, 3CQ), has no such effect and does not give blue complex. It was clarified that 5CQ was complexed with Al~(3+) with a chiral molecular stacking under physiological vacuolar condition as aq. solution at pH 4.0. However, 3CQ did not give such complex with Al~(3+). The difference in aluminum complexation between the isomers may result from the difference configuration of 5-OH and 3-OH group in quinic acid.