Beijing Engineering Research Centre of Cellulose and Its Derivatives, School of Materials Science and Engineering, Beijing Institute of Technology, 100081 Beijing, P.R. China.
J Phys Chem Lett. 2022 Jun 23;13(24):5424-5430. doi: 10.1021/acs.jpclett.2c00781. Epub 2022 Jun 9.
While strong water association with cellulose in plant cell walls and man-made materials is well-established, its molecular scale aspects are not fully understood. The thermodynamic consequences of having water molecules located at the microfibril-microfibril interfaces in cellulose fibril aggregates are therefore analyzed by molecular dynamics simulations. We find that a thin layer of water molecules at those interfaces can be in a state of thermal equilibrium with water surrounding the fibril aggregates because such an arrangement lowers the free energy of the total system. The main reason is enthalpic: water at the microfibril-microfibril interfaces enables the cellulose surface hydroxyls to experience a more favorable electrostatic environment. This enthalpic gain overcomes the entropic penalty from strong immobilization of water molecules. Hence, those particular water molecules stabilize the cellulose fibril aggregates, akin to the role of water in some proteins. Structural and functional hypotheses related to this finding are presented.
尽管水与植物细胞壁和人造材料中的纤维素强烈结合的现象已得到充分证实，但人们对其分子尺度方面仍不完全了解。因此，通过分子动力学模拟分析了水分子位于纤维素纤维聚集物的微纤维-微纤维界面处的热力学后果。我们发现，由于这种排列方式降低了整个系统的自由能，因此在这些界面处的薄水层可以与纤维聚集物周围的水处于热平衡状态。主要原因是焓：位于微纤维-微纤维界面处的水使纤维素表面的羟基经历更有利的静电环境。这种焓的增加克服了水分子强固定化带来的熵罚。因此，这些特殊的水分子稳定了纤维素纤维聚集物，类似于水在某些蛋白质中的作用。本文提出了与这一发现相关的结构和功能假设。
