Fig. 5

Structures representing solvation by Cl⁻ of transition states in 90% GVL/10% H₂O (w/w). a The protonation of the C2 hydroxyl and the elimination of water to form the oxocarbenium ion and (b) the deprotonation of the oxocarbenium ion to form the enol. The Cl⁻ (green sphere) in both transition state structures directly interacts with the active protons (yellow sphere) and resides in the hydrophilic shell that surrounds fructose. The active hydrophilic cavity which is shown via the ball-and-stick structures is encapsulated by the hydrophobic shell comprising GVL. The structures on the left-hand side show the hydrophobic outer shell via simple stick figures, whereas those on the right-hand side depict the atoms in the hydrophobic shell as CPK structures to better highlight the inner hydrophilic cavity and the outer hydrophobic shell. The high concentration of GVL localizes the H⁺ and Cl⁻ ions at the active site, enabling Cl⁻ to promote the reaction. The structures of transition states for fructose dehydration carried out in 90% GVL/10% H₂O (w/w)