Monday, April 30, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Mass transport limitations within the porous matrix of cellulosic materials restrict the ability of cell wall degrading enzymes to hydrolyze cellulose into fermentable sugars. The study of the diffusion of probe molecules into and out of cellulosic substrates can help us elucidate the pore size distribution and the underlying mass transport limitations within these materials. In this study, fluorescently-labeled dextrans with molecular weights ranging from 20kDa to 500kDa were used as probes to assess diffusion and entrapment in the porous structure of filter paper and pretreated biomass. These probes have hydrodynamic radii that are comparable to the size of cellulases and can give insights into the diffusion hindrance and entrapment encountered as these enzymes hydrolyze cellulosic particles. Experiments show that it takes more time for dextrans with larger size to diffuse out of the filter paper particles over time. These results imply the correlation of characteristic fluorescence decay constants with dextran size, meaning that entrapment and diffusion in the porous structure was dependent on probe size. The results also underscore the necessity of pretreatment, which can disrupt the crystal structure of cellulose, increase the pore size within biomass, and reduce the loss of enzymatic activity caused by entrapment.