13-03: Improved pretreatment with Cu(bpy)-catalyzed oxidation

Cu-containing enzymes such as laccases and the recently recognized family of carbohydrate monooxygenases (GH61) play a critical role in the oxidative degradation of plant cell walls in nature and offer the potential to inform and direct effective oxidative pretreatment strategies. Cu-diimine complexes as homogeneous catalysts are capable of diffusing into plant cell walls during pretreatment and we have identified that alkaline hydrogen peroxide pretreatment catalyzed by Cu(bpy) complex increases the enzymatic digestibility of plant cell walls for many types of biomass including significant improvements for hybrid poplar.  Modifications to cell wall polymers after catalyzed pretreatment were characterized and NMR studies on the lignin solubilized from hybrid poplar suggest oxidative modification on the Cα carbon, which potentially facilitates Dakin oxidation and subsequent lignin depolymerization. Catalyzed pretreatment was also shown to introduce carboxyl groups onto cellulose and decrease its degree of polymerization. Microscopic characterization of hybrid poplar after catalytic pretreatment using Transmission Electron Microscopy (TEM) revealed disrupted regions of the cell wall where copper-containing nanoparticles are identified.  We were able to demonstrate that with 10 minutes of catalytic pretreatment under ambient condition, the 24 hour enzymatic glucan digestibility of hybrid poplar can be improved from 18% to 63%. Furthermore, reaction conditions are identified that result in improvement in lignocellulose digestibility with moderate input of chemicals and minimum impact on downstream processing including ethanol fermentation.