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Effect of Fenton Pretreatment on C1 and C6 Oxidation of Cellulose and its Enzymatic Hydrolyzability
- Yang, Jing, Tu, Maobing, Xia, Changlei, Keller, Bryan, Huang, Yang, Sun, Fubao Fuelbio
- ACS sustainable chemistry & engineering 2019 v.7 no.7 pp. 7071-7079
- adsorption, cellulases, cellulose, electrostatic interactions, enzymatic hydrolysis, glycosidic linkages, hydrolysis, nuclear magnetic resonance spectroscopy, oxidation, sodium hydroxide, sorption isotherms
- Cellulose oxidation plays an important role in improving enzymatic hydrolysis by making cellulose more accessible. To determine whether C1 or C6 oxidation in Fenton pretreatment can boost hydrolysis rate of cellulose, we examined the structural changes of cellulose by ¹³C NMR and correlated the C1 oxidation with the hydrolysis yield of Fenton pretreated Avicel. The sequential alkaline (NaOH) and Fenton pretreatments (AFP) significantly increased the 72 h hydrolysis yield of Avicel by 35% as compared to the control group. Langmuir adsorption isotherms showed that Fenton pretreatment increased the adsorption capacities (Γₘ) but decreased the affinity between cellulase enzymes and cellulose, which resulted in a higher 72 h hydrolysis yield but a lower initial hydrolysis rate. Spectra from ¹³C NMR showed that C1 and C6 oxidations of AFP-Avicel were 19.6% and 3.5%, respectively. A good correlation was observed between the 72 h hydrolysis yield and C1 oxidation. The results indicated that the C1 oxidation generated more accessible sites for cellulase enzyme hydrolysis which led to a higher 72 h hydrolysis yield. However, observations of C6 oxidization were consistent with the reduction of enzyme binding by electrostatic repulsion and a lower initial hydrolysis rate. Cleavage of glycosidic bonds and oxidation of C1 by Fenton reaction is similar to lytic polysaccharide monooxygenases (LPMOs).