Insight into the structure-function relationships of deep eutectic solvents during rice straw pretreatment

Rice straw pretreatment mediated by choline chloride (ChCl) or lactic acid (Lac) sequences deep eutectic solvents (DESs) was investigated in this work. Hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) proved to be both important for DESs pretreatment efficiency. DESs containing lots of hydroxyl or amino groups with a high intermolecular hydrogen-bond (H-bond) strength exhibited weak biomass deconstruction abilities. The presence of strong electron-withdrawing groups in DESs was benefit for xylan removal, thus furnishing higher cellulose digestibility. The relationships between the properties of DESs, xylan removal and cellulose digestibility of pretreated biomass were established. It was found that xylan removal was negatively correlated with the pKa values of HBDs, and the enzymatic cellulose digestibility of the residues was linearly and positively related to xylan removal instead of delignification. These results provide a preliminary reference for rational design of novel DESs for biomass pretreatment.