Theoretical studies on the noncovalent interaction of fructose and functionalized ionic liquids

As a new kind of solvent and catalyst, the functionalized ionic liquids (ILs) had been successfully used in the conversion of fructose to high value-added biofuels. In this work, a detailed density functional theory (DFT) calculation had been carried out to investigate the interactions of fructose-ILs system. To study the effect of different anions and cations on the interaction with fructose, 25 different kinds of functionalized imidazolium-based ILs were calculated by using M06-2X-D3/6-311 + G** level. It was found that the interaction energies of fructose-anions were higher than those of the fructose-cations. The interaction will become stronger for the fructose and ILs when the alkyl chain of imidazolium-based cations was replaced with a functional group (COOH, OH or HSO₃). However, when the length of the alkyl chain increased, it will result in a decrease in interaction energy due to the steric effect. In the anions (Y-SO₃), the greater electronegativity of SO₃ will lead to strong interaction with fructose. Also, this work simulates the interaction of fructose and ion pairs, with the results showing that hydrogen bonds (H-bonds) and π-stacking play an important role in the system. The present study provided basic aids to understand the structures and noncovalent interaction of fructose and functionalized ILs as well as the microscopic mechanism of fructose dissolution in the ILs.