Department of Bioproducts and Biosystems, Aalto University, P.O. Box 16300, FI-00076 Aalto, Finland.
Bioproducts Institute, Departments of Chemical & Biological Engineering, Chemistry, and Wood Science, The University of British Columbia, 2360 East Mall, Vancouver, BC V6T 1Z3, Canada.
ACS Nano. 2020 Jun 23;14(6):6921-6930. doi: 10.1021/acsnano.0c01327. Epub 2020 May 27.
The complex nature of typical colloids and corresponding interparticle interactions pose a challenge in understanding their self-assembly. This specifically applies to biological nanoparticles, such as those obtained from chitin, which typically are hierarchical and multidimensional. In this study, we obtain chitin nanocrystals by one-step heterogeneous acid hydrolysis of never-dried crab residues. Partial deacetylation facilitates control over the balance of electrostatic charges (ζ-potential in the range between +58 and +75 mV) and therefore affords chitin nanocrystals (DE-ChNC) with axial aspect (170-350 nm in length), as determined by cryogenic transmission electron microscopy and atomic force microscopy. We find that the surface amines generated by deacetylation, prior to hydrolysis, play a critical role in the formation of individual chitin nanocrystals by the action of a dual mechanism. We directly access the twisting feature of chitin nanocrystals using electron tomography (ET) and uncover the distinctive morphological differences between chitin nanocrystals extracted from nondeacetylated chitin, ChNC, which are bundled and irregular, and DE-ChNC (single, straight nanocrystals). Whereas chitin nanocrystals obtained from dried chitin precursors are known to be twisted and form chiral nematic liquid crystals, our ET measurements indicate no dominant twisting or handedness for the nanocrystals obtained from the never-dried source. Moreover, no separation into typical isotropic and anisotropic phases occurs after 2 months at rest. Altogether, we highlight the critical role of drying the precursors or the nanopolysaccharides to develop chirality.
典型胶体的复杂性质及其相应的粒子间相互作用给理解其自组装带来了挑战。这特别适用于生物纳米粒子，如从甲壳素中获得的那些，它们通常是分层和多维的。在这项研究中，我们通过一步异质酸水解从未干燥的蟹壳残渣中获得壳聚糖纳米晶体。部分脱乙酰化有助于控制静电电荷的平衡（ζ-电位在+58 到+75 mV 之间），从而提供具有轴向（长度为 170-350nm）的壳聚糖纳米晶体（DE-ChNC），如低温透射电子显微镜和原子力显微镜所确定的。我们发现，在水解之前通过脱乙酰化产生的表面胺在单个壳聚糖纳米晶体的形成中通过双重机制发挥关键作用。我们使用电子断层扫描（ET）直接访问壳聚糖纳米晶体的扭曲特征，并揭示了从未脱乙酰化壳聚糖中提取的壳聚糖纳米晶体之间的独特形态差异，ChNC 是捆绑和不规则的，而 DE-ChNC（单个，直的纳米晶体）。虽然已知来自干燥壳聚糖前体的壳聚糖纳米晶体是扭曲的并形成手性向列液晶，但我们的 ET 测量表明，从未干燥来源获得的纳米晶体没有明显的扭曲或手性。此外，在静置 2 个月后，没有分离成典型的各向同性和各向异性相。总之，我们强调了将前体或纳米多糖干燥以开发手性的关键作用。
