Enzyme mimetics for cellulose hydrolysis

The approach to developing a cellulolytic enzyme mimetic is to determine the important physical and chemical parameters affecting the two primary functional domains: the catalytic domain and the cellulose binding domain. This dissertation shows that (1) carboxylic acids have superior selectivity for the hydrolysis of polymers of β(1 → 4) glucose when compared to mineral acids due to decreased ability to catalyze the degradation of glucose, and (2) that certain aromatic, planar compounds through enthalpically driven adsorption can be used to selectively concentrate these compounds to the surface of cellulose. Through focus on the dicarboxylic acid, maleic acid, and the mineral acids, sulfuric and nitric acid, a new understanding has been achieved of the role of acid pKa in glucose degradation. The measured difference in glucose degradation between maleic acid and mineral acids give maleic acid greater selectivity in hydrolysis of cellulose to glucose, as opposed to glucose degradation products. This difference in selectivity results in better glucose yields from maleic acid hydrolysis of cellulose. While the total extent of cellulose solubilization was equivalent for microcrystalline cellulose (Avicel ®) treated with 50mM solutions of either maleic or sulfuric acids, substantially higher yields of glucose were achieved using maleic acid. This is a most significant result because of its fundamental and practical impact on hydrolysis of cellulose in lignocellulosic biomass. The second required functionality of the enzyme mimetic is the ability to adsorb to cellulose from aqueous solution at hydrolysis conditions. Numerous compounds were screened for adsorption to cellulose using a rolled cotton stationary phase chromatographic system below hydrolysis conditions. Aromatic, planar chemical structures appear to be key indicators of cellulose adsorption. The preliminary results were also confirmed for a form of microcrystalline cellulose, Avicel®, at temperatures and pressures approaching hydrolysis conditions. Indole, the side-chain of the amino acid tryptophan, has been shown to reversibly adsorb to cellulose at temperatures between 30 and 120°C. Trypan blue was shown to be irreversibly adsorbed to cotton cellulose at temperatures below 55°C. This confirms the hypothesis presented in the work on the role of hydrophobic, enthalpically driven interaction between cellulose and the cellulose-binding component of cellulolytic enzymes