Qin Hong, Ma Changli, Gärtner Sabrina, Headen Thomas F, Zuo Taisen, Jiao Guisheng, Han Zehua, Imberti Silvia, Han Charles C, Cheng He
STFC ISIS Facility, Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom.
Institute for Advanced Study, Shenzhen University, Shenzhen 508060, China.
Struct Dyn. 2021 Feb 10;8(1):014901. doi: 10.1063/4.0000065. eCollection 2021 Jan.
Trehalose is chosen as a model molecule to investigate the dissolution mechanism of cellulose in NaOH/urea aqueous solution. The combination of neutron total scattering and empirical potential structure refinement yields the most probable all-atom positions in the complex fluid and reveals the cooperative dynamic effects of NaOH, urea, and water molecules in the dissolution process. NaOH directly interacts with glucose rings by breaking the inter- and intra-molecular hydrogen bonding. Na, thus, accumulates around electronegative oxygen atoms in the hydration shell of trehalose. Its local concentration is thereby 2-9 times higher than that in the bulk fluid. Urea molecules are too large to interpenetrate into trehalose and too complex to form hydrogen bonds with trehalose. They can only participate in the formation of the hydration shell around trehalose via Na bridging. As the main component in the complex fluid, water molecules have a disturbed tetrahedral structure in the presence of NaOH and urea. The structure of the mixed solvent does not change when it is cooled to -12 °C. This indicates that the dissolution may be a dynamic process, i.e., a competition between hydration shell formation and inter-molecule hydrogen bonding determines its dissolution. We, therefore, predict that alkali with smaller ions, such as LiOH, has better solubility for cellulose.
选择海藻糖作为模型分子来研究纤维素在氢氧化钠/尿素水溶液中的溶解机理。中子全散射与经验势结构精修相结合，得出了复合流体中最可能的全原子位置，并揭示了氢氧化钠、尿素和水分子在溶解过程中的协同动力学效应。氢氧化钠通过破坏分子间和分子内的氢键直接与葡萄糖环相互作用。因此，钠离子在海藻糖水合壳层中带负电的氧原子周围聚集。其局部浓度因此比本体流体中的浓度高2至9倍。尿素分子太大，无法渗透到海藻糖中，且过于复杂，无法与海藻糖形成氢键。它们只能通过钠桥参与海藻糖周围水合壳层的形成。作为复合流体中的主要成分，水分子在氢氧化钠和尿素存在下具有紊乱的四面体结构。当混合溶剂冷却至-12°C时，其结构不变。这表明溶解可能是一个动态过程，即水合壳层形成与分子间氢键之间的竞争决定了其溶解。因此，我们预测，离子较小的碱，如氢氧化锂，对纤维素具有更好的溶解性。
