Structure and Self-Assembly of Lytic Polysaccharide Monooxygenase-Oxidized Cellulose Nanocrystals

Cellulose-derived nanomaterial building blocks, including cellulose nanocrystals (CNCs), have become increasingly important in sustainable materials development. However, the preparation of CNCs requires hazardous chemicals to introduce surface charges that enable liquid crystalline phase behavior, a key parameter for obtaining self-organized, nanostructured materials from CNCs. Lytic polysaccharide monooxygenases (LPMOs), oxidative enzymes that introduce charged carboxyl groups on their cleavage sites in aqueous reaction conditions, offer an environmentally friendly alternative. In this work, two C1-oxidizing LPMOs from fungus Neurospora crassa, one of which contained a carbohydrate-binding module (CBM), were investigated for CNC preparation. The LPMO-oxidized CNCs shared similar features with chemical-derived CNCs, including colloidal stability and a needle-like morphology with typical dimensions of 7 ± 3 nm in width and 142 ± 57 nm in length for CBM-lacking LPMO-oxidized CNCs. The self-organization of the LPMO-oxidized CNCs was characterized in suspensions and solution cast films. Both LPMO-oxidized CNCs showed electrostatically driven self-organization in aqueous colloidal suspension and pseudo-chiral nematic ordering in solid films. The CBM-lacking LPMO generated a higher carboxyl content (0.70 mmol g–1), leading to a more uniform CNC self-organization, favoring LPMOs without CBMs for CNC production. The obtained results demonstrate production of stable colloidal CNCs with self-assembly by C1-oxidizing LPMOs toward a completely green production of advanced, nanostructured cellulose materials.