Reversible covalent chemistry of carbon dioxide unlocks the recalcitrance of cellulose for its enzymatic saccharification

Abstract

To overcoming the natural recalcitrance of cellulose for glucose production via enzymatic hydrolysis, a new strategy of destroying hydrogen bond donor to reconstruct cellulose's hydrogen bonding network was developed via a mild reversible reaction of cellulose with CO₂ catalyzed by organic bases. The reaction dynamics of cellulose with CO₂ in the presence of organic bases was studied by using in situ IR. Investigation also included how the organic bases in pretreatment media and pretreatment parameters including CO₂ pressure, pretreatment temperature and time affected the physical-chemical structure of cellulose by Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Atomic force microscopy (AFM) and subsequent enzymatic scarification of cellulose. The findings showed that dissolution activation efficiency significantly correlated to various parameters, that can be optimized to be the tetramethyl guanidine (TMG)/CO₂/DMSO solvent system at 50 °C, 2 MPa of CO₂ for 2 h, by which a complete transformation the cellulose crystalline structure from I to II, and 100% glucose yield were achieved. The recyclability and usability are also investigated.

Keywords: Cellulose; Enzymatic hydrolysis; Glucose; Organocatalysis; Reversible covalent chemistry of CO(2).