Shiga Tânia M, Xiao Weihua, Yang Haibing, Zhang Ximing, Olek Anna T, Donohoe Bryon S, Liu Jiliang, Makowski Lee, Hou Tao, McCann Maureen C, Carpita Nicholas C, Mosier Nathan S
Department of Botany & Plant Pathology, Purdue University, West Lafayette, IN 47907 USA.
Present Address: Department of Food Science and Experimental Nutrition, University of São Paulo, Av. Prof. Lineu Prestes, 580, Bloco 14, São Paul, SP 05508-000 Brazil.
Biotechnol Biofuels. 2017 Dec 27;10:310. doi: 10.1186/s13068-017-0999-2. eCollection 2017.
The crystallinity of cellulose is a principal factor limiting the efficient hydrolysis of biomass to fermentable sugars or direct catalytic conversion to biofuel components. We evaluated the impact of TFA-induced gelatinization of crystalline cellulose on enhancement of enzymatic digestion and catalytic conversion to biofuel substrates.
Low-temperature swelling of cotton linter cellulose in TFA at subzero temperatures followed by gentle heating to 55 °C dissolves the microfibril structure and forms composites of crystalline and amorphous gels upon addition of ethanol. The extent of gelatinization of crystalline cellulose was determined by reduction of birefringence in darkfield microscopy, loss of X-ray diffractability, and loss of resistance to acid hydrolysis. Upon freeze-drying, an additional degree of crystallinity returned as mostly cellulose II. Both enzymatic digestion with a commercial cellulase cocktail and maleic acid/AlCl-catalyzed conversion to 5-hydroxymethylfurfural and levulinic acid were markedly enhanced with the low-temperature swollen cellulose. Only small improvements in rates and extent of hydrolysis and catalytic conversion were achieved upon heating to fully dissolve cellulose.
Low-temperature swelling of cellulose in TFA substantially reduces recalcitrance of crystalline cellulose to both enzymatic digestion and catalytic conversion. In a closed system to prevent loss of fluorohydrocarbons, the relative ease of recovery and regeneration of TFA by distillation makes it a potentially useful agent in large-scale deconstruction of biomass, not only for enzymatic depolymerization but also for enhancing rates of catalytic conversion to biofuel components and useful bio-products.
纤维素的结晶度是限制生物质有效水解为可发酵糖或直接催化转化为生物燃料成分的主要因素。我们评估了三氟乙酸（TFA）诱导的结晶纤维素凝胶化对增强酶解和催化转化为生物燃料底物的影响。
棉短绒纤维素在零下温度的TFA中低温溶胀，随后缓慢加热至55°C，可溶解微纤丝结构，并在加入乙醇后形成结晶和无定形凝胶的复合物。通过暗视野显微镜下双折射的降低、X射线衍射能力的丧失以及对酸水解抗性的丧失来确定结晶纤维素的凝胶化程度。冻干后，会恢复额外程度的结晶度，主要为纤维素II。低温溶胀的纤维素显著增强了用商用纤维素酶混合物进行的酶解以及马来酸/氯化铝催化转化为5-羟甲基糠醛和乙酰丙酸的过程。加热使纤维素完全溶解时，水解和催化转化的速率及程度仅略有提高。
纤维素在TFA中的低温溶胀显著降低了结晶纤维素对酶解和催化转化的抗性。在防止氟代烃损失的封闭系统中，通过蒸馏相对容易回收和再生TFA，这使其成为大规模解构生物质的潜在有用试剂，不仅用于酶促解聚，还可提高催化转化为生物燃料成分和有用生物产品的速率。
