Establishment of the Chemical Equilibria of Different Types of Pyranoanthocyanins in Aqueous Solutions: Evidence for the Formation of Aggregation in Pyranomalvidin-3-O-coumaroylglucoside-(+)-catechin
Establishment of the Chemical Equilibria of Different Types of Pyranoanthocyanins in Aqueous Solutions: Evidence for the Formation of Aggregation in Pyranomalvidin-3-O-coumaroylglucoside-(+)-catechin
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DOI：
10.1021/jp1045673
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发表时间：
2010-10-21
影响因子：
3.3
通讯作者：
de Freitas, Victor
中科院分区：
文献类型：
--
作者：
Cruz, Luis;Petrov, Vesselin;de Freitas, Victor
通过紫外-可见光谱法确定了与(+)-儿茶素、(-)-表儿茶素和儿茶酚基团（以及相应的香豆素基葡萄糖苷化合物）连接的pyranomalvidin-3-葡糖苷的化学平衡。吡喃环C和D之间的共轭双键提供了更高的电子离域，阻止了2位水的亲核攻击。因此，除了黄离子（AH(+)）外，还通过增加pH值确定了碱A、碱A（-）和碱A(2-)，并用分光光度法测定了它们的酸度常数。pyranomalvidin-3-O-coumaroylglucoside-(+)-儿茶素在较高浓度下形成了二聚体，通过激子模型处理的数据表明，单体形成了j型聚集体，偶极矩方向相反，在距中心5.2埃的距离上旋转了174度。
The chemical equilibria of the pyranomalvidin-3-glucosides linked to (+)-catechin, (-)-epicatechin, and catechol moieties (and the respective coumaroylglucoside Compounds) were established by means of UV-vis spectroscopy. The conjugated double bonds among pyranic rings C and D provide a higher electronic delocalization that prevents the nucleophilic attack of water at position 2. Consequently, besides flavylium cation (AH(+)), the bases A, A(-), and A(2-) have been identified by increasing pH, and the respective acidity constants were determined by spectrophotometry. The formation of dimers at higher concentration was observed for pyranomalvidin-3-O-coumaroylglucoside-(+)-catechin, and the respective data treated by the exciton model suggests the for-nation of a chiller where the monomers form J-type aggregates with the dipolar moments in opposite directions and rotated by 174 degrees at a distance of 5.2 angstrom (from the center).