6-02: Investigations on the Biophysical Nature of Biomass Recalcitrance

Emphasis on the concept of “biomass recalcitrance”, a description for the resistance of lignocellulosics to enzymatic degradation, has been prevalent during the recent biomass conversions research boom. A majority of efforts in this regard have strategized to overcome the “close physical association” between plant cell wall polymers thought as the primary contributor to recalcitrance. To a lesser extent, studies have sought to understand the biophysical factors responsible for resistance. We seek to expand this knowledge by investigating the inhibitory potential different lignocellulosic polymers impart on the lignocellulose matrix. Utilizing bench-scale saccharification studies with isolated celluloses, xylans, pectins, xyloglucan, beta-glucan, mannan, and lignins we determine comparative inhibitory potentials and then relate this to low-field nuclear magnetic resonance (LF-NMR) data in an effort to discern whether the distribution and constraint of water associated with the polymers is related to their inhibitory contributions. Data indicate that simple carbohydrate chains have the greatest inhibitory potential towards cellulose hydrolysis and allow speculation that the potential for these polymers to constrain water may be loosely correlated. This work is then followed by quartz crystal microbalance (QCM; with dissipation, D) experimentations to investigate the degree and strength with which selected polymers freely associate with cellulose surfaces and degrading enzymes. Data acquired from these studies may help us elucidate whether the inhibitory nature of cell wall polymers is more strongly associated with steric hindrances tied to tight associations with cell wall components or more with the potential for these polymers to divert enzymatic systems through non-productive binding interactions.