科研之友
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摘要
Global energy issue raised the necessity to develop second-generation biofuels, and biorefinery of cellulosic biomass becomes a promising solution. Various pretreatments were used to overcome the cellulose nature of recalcitrance and improve the enzymatic digestibility, but the lack of mechanism understanding hindered the development of effi-cient and cost-effective technologies of cellulose utilization. Using structure-based analysis, we demonstrate that the improved hydrolysis efficiency caused by ultrasonication was ascribed to the changed cellulose properties rather than the increased dissolubility. Further, isothermal titration calorimetry (ITC) analysis suggested that enzymatic di-gestion of cellulose is an entropically favored reaction driven by hydrophobic forces other than an enthalpically fa-vored reaction. The changes in cellulose properties and thermodynamic paramenters due to ultrasonication accounted for the improved accessibility. Ultrasonication-treated cellulose showed porous, rough and disordered mor-phology, accompanying with the loss of crystalline structure. Despite the unaffected unit cell structure, ultrasonication expanded the crystalline lattice by increasing grain sizes and average cross-sectional area, resulting in the transforma-tion from cellulose I to cellulose II, with the decreased crystallinity, better hydrophilicity and increased enzymatic bio-accessibility. Furthermore, FTIR combined with two-dimensional correlation spectroscopy (2D-CoS) verified that the sequential shift of hydroxyl group and intramolecular/intermolecular hydrogen bonds, the functional groups governing cellulose crystal structure and stability, accounted for the ultrasonication-induced transition of cellulose crystalline structure. This study provides a comprehensive picture of cellulose structure and property response caused by mechanistic treatments and will open up avenues to develop novel pretreatments for efficient utilization.
