Energetics of Oligosaccharide Adsorption on Ionic Liquid-Clay Composites.

Well-Tempered Metadynamics (WT-MetaD) simulations indicate that composite materials made up of Na-Montmorillonite (Na-MMT) coated with ionic liquids (ILs) having hydrophilic cations serve as good adsorbents for a hexameric (1,4) linked b-D-glucopyranoside (BGLC). Hydrophilic IL cations are effectively coated on the negative charges lining the Na-MMT surface while attracting simultaneously the polar oligosaccharides. In this work we have used two less conventional polyethylene glycol (PEG) based IL cations, [mim2 peg1]2+ and [mim2 peg2]2+, paired with [tf2N]- and Cl- anions. Another strongly hydrophilic ion combination, [C2OHmim][Cl], also showed great promise in effective oligosaccharide adsorption on the Na-MMT surface. The study reveals that the topological polar surface area (TPSA), the octanol-water partition coefficient (log PO/W), the length of the cationic side chain and the Debye screening length  of the IL are some of the most important factors affecting the adsorption of hydrophilic oligosaccharides on the clay-IL composites. Among all the systems studied, [mim2 peg2][tf2N]2 having the highest TPSA and a long screening length emerged as the best adsorbent of the oligosaccharide on the IL-coated clay.