Solvation of Carbohydrates in N,N' -Dialkylimidazolium Ionic Liquids : A Multinuclear NMR Spectroscopy Study

The solvation of carbohydrates in N,N′-dialkylimidazolium ionic liquids (ILs) was investigated by means of 13C and 35/37Cl NMR relaxation and 1H pulsed field gradient stimulated echo (PFG-STE) diffusion measurements. Solutions of model sugars in 1-n-butyl-3-methylimidazolium chloride ([C4mim]Cl), 1-allyl-3-methylimidazolium chloride ([C═C2mim]Cl), and 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) were studied to evaluate the effects of cation and anion structure on the solvation mechanism. In all cases, the changes in the relaxation times of carbon nuclei of the IL cations as a function of carbohydrate concentration are small and consistent with the variation in solution viscosities. Conversely, the 35/37Cl and 13C relaxation rates of chloride ions and acetate ion carbons, respectively, have a strong dependency on sugar content. For [C2mim][OAc], the correlation times estimated from 13C relaxation data for both ions reveal that, as the carbohydrate concentration increases, the reorientation rate of t...