(755c) The Cellulose Hydrogen Bonds Network Changed By Pretreatments and Enzymatic Digestibility

The bioconversion of cellulose into simple sugars or chemicals has attracted extensive attentions for the sustainable development in recent decades.  However, the recalcitrant nature of crystalline cellulose, which is in essence due to the presence of strong crystalline hydrogen-bonding, contributes to the low cellulose saccharification efficiency. In this research, we try to identify the hydrogen bonds network of crystalline cellulose changed by different pretreatments and investigate the interaction between the hydrogen bonds type and the enzyme hydrolysis. The methods of FTIR (fourier transform Infrared spectroscopy) and H/D (hydrogen/deuterium) exchange were employed to study the hydrogen bond network of crystalline cellulose. The results showed that the interchain O(6)H-O(3) HBs became the major hydrogen bond component after pretreatments. However, the proportion of intrachain HBs, including O(3)H-O(5) and O(2)H-O(6), slightly decreased. It was also found that the intrachain/interchain HBs ratio of crystalline cellulose was strongly correlated with cellulose allomorph changed by different pretreatments. As the results of FTIR showed, the transformation of crystalline allomorph from native cellulose I to cellulose II, III would lead to an increase in the number of interchain hydrogen bonds and a decrease in the number of cellulose intrachain hydrogen bonds. The order of crystalline cellulose interchain/intrachain HBs ratio was as follows: cellulose II > cellulose III > cellulose I. Compared to cellulose interchain HBs, the intrachain HBs of crystalline cellulose seemed to be more difficult for cellulase to access and break. Cellulose enzymatic hydrolysis rate had strongly positive correlation with cellulose interchain/intrachain HBs ratio. In addition, the results of H/D exchange experiments indicated that the number of the active HBs in crystalline cellulose had no significant impact on cellulose digestibility.