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

Salla Koskela,Shennan Wang,Peter Matthew Paul Fowler,Qi Zhou,Fangchang Tan

doi:10.1021/acssuschemeng.1c02407

Abstract

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.

Highlights

To overcome the environmental problems caused by excessive use of petroleum-based plastics,[1,2] development of highperforming biodegradable materials from renewable feedstocks such as plant biomass is becoming increasingly important.[3]Plant cell wall-derived cellulose nanomaterials, including cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs), have obtained a key position in this regard due to their attractive properties including lightweight, high mechanical performance, biocompatibility, and biodegradability, making them ideal building blocks for new, advanced materials.[4−6] CNCs are crystalline cellulose with a stiff, rodlike morphology, which can be prepared, e.g., from natural wood cellulose fibers.[4]
We have shown that the recombinant enzymes NcLPMO9E and NcLPMO9F produced in P. pastoris (Figure S1, Supporting Information) are active on synthetic substrates 2,6-dimethoxyphenol and Amplex Red (Figure S2, Supporting Information) and contain the catalytic copper on their active site.[33]
The results indicate that the Lytic polysaccharide monooxygenases (LPMOs)-oxidized CNC suspensions could form a pseudo-chiral nematic liquid crystalline phase mediated by the long-range repulsions originating from the weak C1 carboxylic acid groups

Summary

Introduction

To overcome the environmental problems caused by excessive use of petroleum-based plastics,[1,2] development of highperforming biodegradable materials from renewable feedstocks such as plant biomass is becoming increasingly important.[3]Plant cell wall-derived cellulose nanomaterials, including cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs), have obtained a key position in this regard due to their attractive properties including lightweight, high mechanical performance, biocompatibility, and biodegradability, making them ideal building blocks for new, advanced materials.[4−6] CNCs are crystalline cellulose with a stiff, rodlike morphology, which can be prepared, e.g., from natural wood cellulose fibers.[4]. A typical method of producing CNCs is acid hydrolysis employing concentrated sulfuric acid to hydrolyze the more accessible, less-ordered cellulose.[7]

Methods

Results

Conclusion