Institute for Catalysis, Hokkaido University, Kita 21 Nishi 10, Kita-ku, Sapporo, Hokkaido 001-0021, Japan.
Phys Chem Chem Phys. 2021 Aug 4;23(30):15908-15916. doi: 10.1039/d1cp01650d.
Mechanochemistry enables unique reaction pathways in comparison to conventional thermal reactions. Notably, it can achieve selective hydrolysis of cellulose and chitin, a set of abundant and recalcitrant biomass, by solvent-free ball-milling in the presence of acid catalysts. Although the merits of mechanochemistry for this reaction are known, the reaction mechanism is still unclear. Here, we show how the mechanical forces produced by ball-milling activate the glycosidic bonds of carbohydrate molecules towards hydrolysis. This work uses experimental and theoretical evaluations to clarify the mechanism. The experimental results reveal that the ball-mill accelerates the hydrolysis by mechanical forces rather than local heat. Meanwhile, the classical and quantum mechanics calculations indicate the subnano to nano Newton order of tensile and compressive forces that activate polysaccharide molecules in the ball-milling process. Although previous studies have taken into account only the stretching of the molecules, our results show that compressive forces are stronger and effective for the activation of glycosidic bonds. Accordingly, in addition to stretching, compression is crucial for the mechanocatalytic reaction. Our work connects the classical physics of ball-milling on a macro scale with molecular activation at a quantum level, which would help to understand and control mechanochemical reactions.
机械化学能够实现与传统热反应相比独特的反应途径。值得注意的是，它可以通过无溶剂球磨在酸催化剂存在下实现纤维素和壳聚糖的选择性水解，这是一组丰富而顽固的生物质。尽管机械化学在这种反应中的优点是众所周知的，但反应机制仍不清楚。在这里，我们展示了球磨产生的机械力如何激活碳水化合物分子的糖苷键以促进水解。这项工作使用实验和理论评估来阐明机制。实验结果表明，球磨通过机械力而非局部热量加速水解。同时，经典和量子力学计算表明，在球磨过程中，拉伸和压缩力的亚纳米到纳米牛顿量级可以激活多糖分子。尽管以前的研究只考虑了分子的拉伸，但我们的结果表明，压缩力更强且对糖苷键的激活更有效。因此，除了拉伸，压缩对于机械催化反应也是至关重要的。我们的工作将宏观尺度上的球磨经典物理学与量子水平上的分子激活联系起来，这有助于理解和控制机械化学反应。
