Bottom-Up Approach to Understand Chirality Transfer across Scales in Cellulose Assemblies

Abstract

Cellulose is a polysaccharide that displays chirality across different scales, from the molecular to the supramolecular level. This feature has been exploited to generate chiral materials. To date, the mechanism of chirality transfer from the molecular level to higher-order assemblies has remained elusive, partially due to the heterogeneity of cellulose samples obtained via top-down approaches. Here, we present a bottom-up approach that uses well-defined cellulose oligomers as tools to understand the transfer of chirality from the single oligomer to supramolecular assemblies beyond the single cellulose crystal. Synthetic cellulose oligomers with defined sequences self-assembled into thin micrometer-sized platelets with controllable thicknesses. These platelets further assembled into bundles displaying intrinsic chiral features, directly correlated to the monosaccharide chirality. Altering the stereochemistry of the oligomer termini impacted the chirality of the self-assembled bundles and thus allowed for the manipulation of the cellulose assemblies at the molecular level. The molecular description of cellulose assemblies and their chirality will improve our ability to control and tune cellulose materials. The bottom-up approach could be expanded to other polysaccharides whose supramolecular chirality is less understood.

Recent Developments in Solid-Phase Glycan Synthesis

“…cellulose 54,21 , chitin 54,21,47 , starch 45 , and glycogen 45 ) were prepared with full control over their length and sequence. Site specific modifications 21 were systematically introduced to establish structure-properties correlations and shine light on fundamental aspect of polysaccharide conformation and aggregation 108,109,110,111 . In this regard, the insertion of 13 C-or 19 Flabeled units permitted solution-phase NMR conformational studies, otherwise hampered by the severe chemical shift degeneracy of glycans.…”

“…Site-specific modifications 21 were systematically introduced to establish structure-property correlations and to shine light on fundamental aspects of polysaccharide conformations and aggregation. [107][108][109][110] In this regard, the insertion of 13 C-or 19 F-labeled units permitted solution-phase NMR conformational studies, which are otherwise hampered by the severe chemical shift degeneracy of glycans. 52,53 Even so, many more glycosylation methodologies should be explored to expand the scope of glycan synthesis on solid-phase even further.…”

Advanced applications of cellulose nanocrystals: a mini review

“…Due in part to the variability of the cellulose samples obtained via top-down methods, the process of chirality transfer from the molecular level to higher-order assemblies has remained mysterious to this point. To shed light on origin of chirality in CNCs, authors in ref 205 , suggested the use of well-defined cellulose oligomers as tools to explain how chirality is transferred from a single oligomer to supramolecular assemblies outside of a single cellulose crystal. This signifies that authors try to make CNC particles from their glucose precursors.…”

Deoxyfluorination tunes the aggregation of cellulose and chitin oligosaccharides and highlights the role of specific hydroxyl groups in the crystallization process

“…19,20 In contrast, bottom-up approaches guarantee precise saccharide sequences and patterns of modification, important determinants of the materials and biological properties. [21][22][23][24][25] Perturbing the primary sequence of an oligosaccharide with non-natural residues offers a strategy to systematically tune the macroscopic properties of a material. In addition, this approach provides indirect information on the role of the replaced unit (or functional group).…”

“…19,20 In contrast, bottom-up approaches guarantee precise saccharide sequences and patterns of modification, important determinants of the materials and biological properties. 21–25…”