Conclusion of the work: A new type hemicellulose nanocrystal was obtained in the shape of an anisotropic flake composed of xylan, forming crystallosolvates with DMSO. The dimensions of these nanocrystals can be controlled by the crystallization conditions (xylan concentration, incubation time and temperature). Sharp signals in solid state NMR indicated a well-ordered crystal structure. The unit cell is constituted of two asymmetric xylose residues and DMSO molecules resided in a host-guest type of arrangement with more than one local environment. The crystal growth direction was in the direction perpendicular to the pyranose plane, which is similar to the crystallization behavior of cellulose oligomers or chitin oligomers in aqueous system. The molecular weight of xylan measured by dissolving the nanocrystals were much higher than the thickness of the crystals, implying chain folding in the crystals. X-ray and electron diffraction indicated a 2-fold helical helix along the chain in a monoclinic unit cell with an antiparallel arrangement. The 2-fold helical structure is unique for xylan for which only 3-fold helical form has been reported. Xylan/DMSO dispersions provided pathways for the crystallization to form size-adjustable xylan nanocrystals. These are new insights into the structure of hemicellulose, leading to a new platform for hemicellulose-based materials, such as biomimetic toughening, drug delivery, biosensors and bioactive systems. It also serves as an indicator to point out that the full potential of biomass components is far from being fulfilled at present.
Reprinted with permission from Biomacromolecules2021 22 (2), 898–906
DOI: 10.1021/acs.biomac.0c01600. Copyright 2021 American Chemical Society.