Liquid nanostructure of choline lysinate with water and a model lignin residue

Abstract

The structure of the ionic liquid choline lysinate ([Ch][Lys]) and its water mixtures, including a dissolved model lignin residue, guaiacol, is revealed at atomic and nanoscale resolution using neutron diffraction. The performance of [Ch][Lys] for biomass pretreatment depends on both its detailed H-bonding capacity and bicontinuous polar/apolar nanostructure, which is stabilised by lysinate adopting an H-bonded cyclic conformer that enhances its amphiphilicity. These features are heightened by the addition of water, which forms nanoscale pockets but also extends the H-bonding network within the IL polar domains while largely preserving its bicontinuous nanostructure, rendering the ionic liquid–water mixture an effective solvent for organic molecules bearing various functional groups. A model representative lignin compound, guaiacol, is found to H-bond through its phenol group to both the anion and water, destabilising the lysinate cyclic conformer and altering the liquid nanostructure.