Caffeine hetero-association with 3,5-di-O-caffeoylquinic acid, 3,4-di-O-caffeoylquinic acid and 4,5-di-O-caffeoylquinic acid in aqueous solution has been investigated by one-dimensional (1D) and two-dimensional (2D) high resolution ¹H and ¹³C NMR spectroscopy. Self-association of the di-O-caffeoylquinic acid isomers has been studied as well. Caffeine-di-O-caffeoylquinic acid isomers association constants were measured. The value of the association constant of the caffeine-di-O-caffeoylquinic acid complexes is compatible with previous studies and within the typical range of reported association constants for other caffeine-polyphenols complexes. Structural features of the three different complexes have also been investigated by NMR spectroscopy combined with quantum chemical calculations, and the complex conformation is discussed. Our results show that stacking interactions drive the formation of the complexes and that multiple equilibria are present in the interaction of caffeine with 3,4-di-O-caffeoylquinic acid and 4,5-di-O-caffeoylquinic acid while the complex with 3,5-di-O-caffeoylquinic acid seems to be better defined.

中文翻译：

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水溶液中咖啡因与二-O-咖啡酰奎宁酸异构体的异构缔合的NMR研究。

通过一维（1D）研究了咖啡因与3,5-二-O-咖啡酰奎尼酸，3,4-二-O-咖啡酰奎尼酸和4,5-二-O-咖啡酰奎尼酸的水溶液缔合和二维（2D）高分辨率¹ H和¹³13 C NMR光谱。还已经研究了二-O-咖啡酰奎宁酸异构体的自缔合。测量咖啡因-二-O-咖啡酰奎尼酸异构体的缔合常数。咖啡因-二-O-咖啡酰奎尼酸配合物的缔合常数的值与先前的研究是相容的，并且在其他咖啡因-多酚配合物的报道的缔合常数的典型范围内。还通过NMR光谱结合量子化学计算研究了三种不同配合物的结构特征，并讨论了配合物的构象。我们的结果表明，堆积相互作用驱动复合物的形成，并且咖啡因与3,4-二-O-咖啡酰奎尼酸和4,5-二-O-咖啡酰奎尼酸的相互作用中存在多重平衡，而复合物与3 ，