NANOSCALE INVESTIGATIONS OF THE EFFECTS OF CELLULOSIC AND NONCELLULOSIC COMPONENTS ON CELLULASE-LIGNOCELLULOSIC BIOMASS INTERACTIONS

Baran Arslan Arslan

This thesis provides a detailed investigation of the effects of specific biomass components on the overall nanoscale interaction forces present between cellulose degrading enzymes and lignocellulosic biomass using atomic force microscopy (AFM). To do that, a set of reference lignocellulosic biomass substrates with controlled physiochemical properties and chemical composition of xylan, acetone extractives, lignin and cellulose were used. AFM cantilevers were decorated with controlled chemical functionalities to model cellulases. Nanoscale interaction forces were then probed between the model reference substrates and the model cellulase surfaces in a liquid environment. Finally, theoretical and statistical models were combined with our experimental data to decouple the forces into specific and nonspecific components. Our results indicated that permanent dipole−dipole interactions dominated the adhesion of hydrophilic model cellulases to lignosulfonates, whereas hydrophobic interactions facilitated the adhesion of hydrophobic model cellulases to Kraft lignin. In addition, we showed that the hydrophobic domains and chemical moieties involved in hydrogen bonding and polar interactions were homogeneously distributed on all substrates investigated but with distribution densities that depended on the pretreatment method used to prepare the substrates. In addition, the types of forces governing carbohydrate-binding module (CBM)-lignocellulosic biomass interactions were identified and quantified. Our results indicated that the overall adhesion forces of biomass to CBM increased linearly with surface lignin coverage with kraft lignin showing the highest forces among lignin types investigated. Xylan and acetone extractives’ contents increased the attractive forces between CBM and lignin-free substrates, most likely through hydrogen bonding forces. Finally, the effects of the conformational properties of biomass biopolymers on the nanoscale interaction forces present between a model hydrophobic cellulase and lignocellulosic biomass reference substrates were explored. Our results revealed that xylan collapses cellulose microfibrils and facilities attractive forces to the hydrophobic model surface, whereas acetone extractives cause steric repulsion to the hydrophobic model surface and reduces the adhesion strength. In summary, the results obtained here improved our fundamental understanding of nanoscale cellulase-lignocellulosic biomass interactions. With such improved understanding, developing better biomass treatments to avoid nonproductive binding of cellulase enzymes to biomass surfaces and increase the efficacy of enzymatic hydrolysis of cellulose can be achieved.

NANOSCALE INVESTIGATIONS OF THE EFFECTS OF CELLULOSIC AND NONCELLULOSIC COMPONENTS ON CELLULASE-LIGNOCELLULOSIC BIOMASS INTERACTIONS

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