Specific ion effects influence a variety of aqueous processes such as micelle formation, polymer aggregation, and protein solubility and follow the Hofmeister series. We studied the effects of eleven anions on the thermodynamics of caffeine partitioning between aqueous and cyclohexane phases. Well-hydrated anions such as CO32- and SO42- decrease the standard Gibbs free energy for caffeine transfer from the aqueous to cyclohexane phase and promote the transfer process. On the other hand, weakly hydrated anions such as ClO4- and SCN- salt caffeine into the aqueous phase and hinder the caffeine transfer. Moreover, the enthalpy and entropy of caffeine transfer in the presence of salts were obtained. Caffeine transfer from the aqueous to cyclohexane phase is an endothermic process driven by the entropy change for caffeine transfer. The anion-caffeine interactions are further investigated by using 13C and 1H NMR and ATR-FTIR spectroscopy. The mechanisms for how anions interact with caffeine and affect its partitioning will be discussed.

Specific anion effects on caffeine partitioning between aqueous and cyclohexane phases

253rd National Meeting (2017)

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