Department of Bioproducts and Biosystems, Aalto University, Espoo, Finland.
VTT Technical Research Centre of Finland, Espoo, Finland.
Biomacromolecules. 2021 Feb 8;22(2):898-906. doi: 10.1021/acs.biomac.0c01600. Epub 2021 Jan 7.
A new type of polysaccharide (hemicellulose) nanocrystal, bearing the shape of an anisotropic nanoflake, emerged from a dimethyl sulfoxide (DMSO) dispersion of wood-based xylan through heat-induced crystallization. The dimensions of these xylan nanocrystals were controlled by the crystallization conditions. 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. This corroborates with the identical H NMR relaxation time between DMSO and xylan, indicative of intimate mixing of the two at the tens of nanometer length scale. X-ray and electron diffraction indicated a 2-fold helical helix along the chain in a monoclinic unit cell with an antiparallel arrangement, with chains placed on the 2-fold helix axes: at the corner and at the center. The 2-fold helical structure is unique for xylan for which only a 3-fold helical form has been reported. The DMSO molecules participated in the crystallization, and they were shown to be vital in stabilizing the crystalline structure. The manipulation of temperature, concentration, and incubation time of the xylan/DMSO dispersion provided pathways for the crystallization to form size-adjustable nanocrystals. As 20-30% of biomass consists of hemicelluloses, this work will serve as a starting point to understand the controlled assembly of hemicelluloses to discover their full application potential.
一种新型多糖（半纤维素）纳米晶体，具有各向异性纳米薄片的形状，通过热诱导结晶从基于木材的木聚糖的二甲基亚砜（DMSO）分散体中出现。这些木聚糖纳米晶体的尺寸由结晶条件控制。固态 NMR 中的尖锐信号表明具有有序的晶体结构。晶胞由两个不对称的木糖残基组成，DMSO 分子以主客体型排列存在于多个局部环境中。这与 DMSO 和木聚糖之间相同的 H NMR 弛豫时间相吻合，表明两者在数十纳米的长度尺度上紧密混合。X 射线和电子衍射表明，在单斜晶胞中，沿链存在 2 倍螺旋螺旋，排列为反平行，链位于 2 倍螺旋轴上：在角和中心。2 倍螺旋结构是木聚糖所特有的，因为仅报道了 3 倍螺旋形式。DMSO 分子参与了结晶，它们对于稳定晶体结构至关重要。木聚糖/DMSO 分散体的温度、浓度和孵育时间的控制为形成可调节尺寸的纳米晶体提供了途径。由于 20-30%的生物质由半纤维素组成，这项工作将作为理解半纤维素的受控组装以发现其全部应用潜力的起点。
