Why are some cyano-based ionic liquids better glucose solvents than water?

Among different classes of ionic liquids (ILs), those with cyano-based anions have been of special interest due to their low viscosity and enhanced solvation ability for a large variety of compounds. Experimental results from this work reveal that the solubility of glucose in some of these ionic liquids may be higher than in water – a well-known solvent with enhanced capacity to dissolve mono- and disaccharides. This raises questions on the ability of cyano groups to establish strong hydrogen bonds with carbohydrates and on the optimal number of cyano groups at the IL anion that maximizes the solubility of glucose. In addition to experimental solubility data, these questions are addressed in this study using a combination of density functional theory (DFT) and molecular dynamics (MD) simulations. Through the calculation of the number of hydrogen bonds, coordination numbers, energies of interaction and radial and spatial distribution functions, it was possible to explain the experimental results and to show that the ability to favorably interact with glucose is driven by the polarity of each IL anion, with the optimal anion being dicyanamide.

This work was developed within the scope of the projects POCI- 01-0145-FEDER-007679|UID/CTM/50011/2013 (CICECO) and POCI-01-0145-FEDER-006984|UID/EQU/50020/2013 (LSRE-LCM), financed by national funds through the FCT/MEC and co-financed by FEDER under the PT2020 Partnership Agreement. The authors thank the Fundaça˜o para a Cieˆncia e Tecnologia (FCT) for Programa Investigador FCT and for the exploratory project grant (EXPL/ QEQ-PRS/0224/2013). M. L. S. B. and H. P. also acknowledge FCT for the PhD grants SFRH/BD/74551/2010 and SFRH/BD/ 85248/2012, respectively. E. J. M. acknowledges support from the US Air Force Office of Scientific Research, grant number AFOSR-FA9550-14-1-0306. Thanks are due as well to the Center for Research Computing at the University of Notre Dame for providing access to computational resources.