Monday, April 30, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Confocal Raman microscopy and confocal fluorescence microscopy were employed side by side to understand ionic liquid pretreatment of corn stover stem at the cell level using 1-ethyl-3-methylimidazolium acetate. Tissue specific features related to deconstruction efficiency were revealed by comparing three different cell types including tracheids, sclerenchyma cells and parenchyma cells. Confocal fluorescence microscopy was used to visualize the morphology changes of the three cell types during ionic liquid pretreatment. Raman imaging was used to monitor the corresponding compositional changes. Temporal lignin and cellulose maps were produced, and cellulose and lignin dissolution at different layers of cell walls was elucidated. Quantitative temporal dissolution profiles of lignin were generated based on the Raman maps of lignin and temporal cell wall swelling profiles were generated based on the confocal images to compare the effect of ionic liquid pretreatment on different cell types. Our results suggest a synergistic mechanism of lignocellulose dissolution regarding cellulose and lignin dissolution and cell wall swelling. Surprisingly, with a much thicker cell wall and a much higher original lignin content than parenchyma cells, tracheids show much faster lignin and cellulose dissolution and cell wall swelling. Sclerenchyma cells show intermediate level of lignin dissolution rate, while the cellulose dissolution rate and degree of cell wall swelling is close to tracheids. Our results provide valuable new insights towards the mechanism of ionic liquid pretreatment and can guide the efforts on cell wall engineering for efficient cell wall deconstruction. Methods established in our work can be easily extended to other systems.