Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China.
Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352.
Proc Natl Acad Sci U S A. 2020 Feb 18;117(7):3397-3404. doi: 10.1073/pnas.1914813117. Epub 2020 Feb 3.
Organisms use inorganic ions and macromolecules to regulate crystallization from amorphous precursors, endowing natural biominerals with complex morphologies and enhanced properties. The mechanisms by which modifiers enable these shape-preserving transformations are poorly understood. We used in situ liquid-phase transmission electron microscopy to follow the evolution from amorphous calcium carbonate to calcite in the presence of additives. A combination of contrast analysis and infrared spectroscopy shows that Mg ions, which are widely present in seawater and biological fluids, alter the transformation pathway in a concentration-dependent manner. The ions bring excess (structural) water into the amorphous bulk so that a direct transformation is triggered by dehydration in the absence of morphological changes. Molecular dynamics simulations suggest Mg-incorporated water induces structural fluctuations, allowing transformation without the need to nucleate a separate crystal. Thus, the obtained calcite retains the original morphology of the amorphous state, biomimetically achieving the morphological control of crystals seen in biominerals.
生物体会利用无机离子和生物大分子来调控从无定形前体中的结晶过程，从而赋予天然生物矿物复杂的形貌和增强的性能。然而，对于调节剂如何实现这些保持形状的转化机制，我们还知之甚少。我们使用原位液相透射电子显微镜，在添加剂存在的情况下，跟踪从无定形碳酸钙到方解石的演变过程。对比分析和红外光谱的结合表明，广泛存在于海水和生物体液中的镁离子以浓度依赖的方式改变了转化途径。这些离子将多余的（结构）水带入无定形基质中，因此在没有形貌变化的情况下，脱水会引发直接转化。分子动力学模拟表明，镁结合的水会引起结构波动，从而无需成核就能进行转化。因此，所得到的方解石保留了无定形状态的原始形貌，仿生地实现了生物矿物中所见晶体的形态控制。
