Department of Chemistry and Biochemistry, James Madison University , Harrisonburg, Virginia 22807, United States.
J Phys Chem B. 2017 Feb 23;121(7):1649-1659. doi: 10.1021/acs.jpcb.6b12150. Epub 2017 Feb 8.
This work investigates the interactions of a series of 11 anions with caffeine by utilizing C and H NMR and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The aim of this study is to elucidate the molecular mechanisms of ion interactions with caffeine and to study how these interactions affect caffeine aggregation in aqueous solution. The chemical shift changes of caffeine C and H in the presence of salts provide a measure for anions' salting-out/salting-in abilities on individual carbon and hydrogen atoms in caffeine. The relative influences of anions on the chemical shift of individual atoms in the caffeine molecule are quantified. It is observed that strongly hydrated anions are excluded from the carbons on the six-member ring in caffeine and promote caffeine aggregation. On the other hand, weakly hydrated anions decrease caffeine aggregation by accumulating around the periphery of the caffeine molecule and binding to the ring structure. The ATR-FTIR results demonstrate that strongly hydrated anions desolvate the caffeine molecule and increase aggregation, while weakly hydrated anions have the opposite effects and salt caffeine into solution.
本工作利用 C 和 H NMR 以及衰减全反射傅里叶变换红外（ATR-FTIR）光谱研究了一系列 11 种阴离子与咖啡因的相互作用。本研究的目的是阐明离子与咖啡因相互作用的分子机制，并研究这些相互作用如何影响咖啡因在水溶液中的聚集。盐存在时咖啡因 C 和 H 的化学位移变化为阴离子对咖啡因中单个碳原子和氢原子的盐析/盐溶能力提供了一种衡量标准。定量研究了阴离子对咖啡因分子中各个原子化学位移的相对影响。结果表明，强水合阴离子被排除在咖啡因的六元环上的碳原子之外，并促进咖啡因聚集。另一方面，弱水合阴离子通过在咖啡因分子的外围聚集并与环结构结合来减少咖啡因的聚集。ATR-FTIR 结果表明，强水合阴离子使咖啡因分子去溶剂化并增加聚集，而弱水合阴离子则产生相反的效果，并将咖啡因盐溶解在溶液中。
