Abstract
Understanding the fine details of the self‐assembly of building blocks into complex hierarchical structures represents a major challenge en route to the design and preparation of soft‐matter materials with specific properties. Enzymatically synthesised cellodextrins are known to have limited water solubility beyond DP9, a point at which they self‐assemble into particles resembling the antiparallel cellulose II crystalline packing. We have prepared and characterised a series of site‐selectively fluorinated cellodextrins with different degrees of fluorination and substitution patterns by chemoenzymatic synthesis. Bearing in mind the potential disruption of the hydrogen‐bond network of cellulose II, we have prepared and characterised a multiply 6‐fluorinated cellodextrin. In addition, a series of single site‐selectively fluorinated cellodextrins was synthesised to assess the structural impact upon the addition of one fluorine atom per chain. The structural characterisation of these materials at different length scales, combining advanced NMR spectroscopy and microscopy methods, showed that a 6‐fluorinated donor substrate yielded multiply 6‐fluorinated cellodextrin chains that assembled into particles presenting morphological and crystallinity features, and intermolecular interactions, that are unprecedented for cellulose‐like materials.
Highlights
We demonstrate that the presence of a single fluorine atom per cellodextrin chain did not exert a substantial impact on the morphology and crystalline structure of the material, while the presence of multiple 6deoxy-6-fluoroglucose units yielded an unprecedented crystalline allomorph for a cellulose-like material
cellobiose phosphorylase (CBP) was removed from the reaction mixture by affinity chromatography (His6 tag nickel column purification) and the desired products were purified by gel filtration chromatography
We have demonstrated the enzymatic incorporation of singly and multiply fluorinated glucose residues into cellodextrin chains
Summary
Cellulose is an abundant natural biopolymer used extensively in industry as a raw material for the production of paper, textile, food thickeners, dietary fibre, etc.[1,2] The current use of cellulose increasingly involves nanosized cellulose particles (nanocellulose), which is a promising class of renewable material due to its intrinsic characteristics and potential for a broad range of industrial applications.[3,4,5] The development of nanocellulose-based materials relies on assembly-driven processes, the manipulation of which can have an impact on mechanical properties or bring additional functionality to the material.[6,7,8,9,10]. Chemistry - A European Journal published by WileyVCH GmbH The ability to systematically modify the structure of oligoand polysaccharides presents new opportunities to gain insight into the hierarchical self-assembly of carbohydrate-based materials.[29] In connection with this study, we had a need for the site-specific introduction of probes into cellulose to report on local structure and solvation, and potentially to modulate material properties. We demonstrate that the presence of a single fluorine atom per cellodextrin chain did not exert a substantial impact on the morphology and crystalline structure of the material, while the presence of multiple 6deoxy-6-fluoroglucose units yielded an unprecedented crystalline allomorph for a cellulose-like material
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