Interactions of caffeine and 1-butyl-3-methylimidazolium salicylate ionic liquid in water – Solubility, volumetric, acoustic, viscometric and refractometric studies supported by MD simulation

Abstract

In this study, a detailed physicochemical characterization of caffeine in 0.1 mol∙kg−1 of 1-butyl-3-methylimidazolium salicylate (abbreviation [Bmim][Sal]) aqueous solutions is performed based on density, speed of sound, refractive index and viscosity measurements in the temperature range from T = (293.15–313.15) K. [Bmim][Sal] slightly increases the solubility of caffeine in water. Data obtained from the volumetric and viscosimetric measurements indicate that [Bmim][Sal] promotes the self-aggregation of caffeine in water. Molecular dynamic simulations provided insight into how [Bmim][Sal] increases caffeine solubility in water. At higher temperatures, the salicylate anion has stronger interactions with caffeine through π–π interactions than at lower temperatures.