(111a) Unveiling the Ionic Liquid Deconstruction of Lignocellulosic Biomass Using Glycome Profiling
Certain ionic liquids (ILs) are capable of effectively overcoming plant cell wall recalcitrance; however, the underlying mechanisms are not fully understood. To better understand how certain ionic liquids deconstruct biomass, we applied an immunological approach (“glycome profiling”) that employs a comprehensive suite of plant glycan-directed monoclonal antibodies to monitor cell wall structural/compositional/extractability changes in switchgrass biomass. A range of ILs with very diverse chemical and solvent properties was tested under typical pretreatment conditions, with 1-butyl-3-methylimidazolium chloride ([C4mim][Cl]) solubilizing and regenerating cellulose, N-ethyl-N-(furanyl-2-methyl) ethanamine dihydrogen phosphate ([FurEt2NH][H2PO4]), N-ethyl-N-(4-methoxybenzyl) ethanamine dihydrogen phosphate ([p-AnisEt2NH][H2PO4]) and cholinium lysinate ([Ch][Lys]) extracting large fraction of lignin, and 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) solubilizing both lignin and cellulose. Glycome profiling studies on pretreated biomass residues, in combination with wet chemistry quantification and 13C CP/MAS NMR and 2D HSQC NMR analysis, revealed distinct changes in the composition and extractability of non-cellulosic cell wall glycans, suggesting different deconstruction mechanisms caused by different ILs. Interestingly, all ILs induced the disruption of lignin-polysaccharide interactions as reflected by a loss of pectins and arabinogalactan epitopes in less harsh extracts (oxalate and carbonate) and significantly increased extractability of hemicellulosic glycans in oxalate, carbonate, 1M KOH and 4M KOH extracts. This study establishes a deeper scientific understanding of IL pretreatment and provides insights on the rational design of task-specific ILs for biomass deconstruction.