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 β-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 lengthλ D ${\left({\lambda }_{D}\right)}$ 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 for the oligosaccharide on the IL-coated clay.