Understanding the interacting mechanism between ionic liquids (ILs) and solute molecules is important for the application of ILs in separation processes. The interactions between a series of solutes (water, ethanol, propylene, propyne, heptane, and toluene) and the anion/cation/ion pair of 1,3-dimethylimidazolium methylsulfate ([DMIM][MS]) were studied using one-to-one complex by quantum chemical calculations. The calculated results show that the H-bond between the anion and solutes is the dominant factor in determining the interaction between the IL and solutes. Furthermore, the relationship between the calculated electronic characteristics and experimentally observed behavior is also discussed. (C) 2014 Elsevier B.V. All rights reserved.