Physical Chemistry, University of Konstanz, Universitätsstrasse 10, 78457, Konstanz, Germany.
School of Chemical Engineering, State Key Laboratory of Chemical Engineering, Shanghai Key Laboratory of Multiphase Materials Chemical Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, P.R. China.
Angew Chem Int Ed Engl. 2016 Sep 26;55(40):12206-9. doi: 10.1002/anie.201604179. Epub 2016 Sep 9.
Amorphous intermediate phases are vital precursors in the crystallization of many biogenic minerals. While inherent short-range orders have been found in amorphous calcium carbonates (ACCs) relating to different crystalline forms, it has never been clarified experimentally whether such orders already exist in very small clusters less than 2 nm in size. Here, we studied the stability and structure of 10,12-pentacosadiynoic acid (PCDA) protected ACC clusters with a core size of ca. 1.4 nm consisting of only seven CaCO3 units. Ligand concentration and structure are shown to be key factors in stabilizing the ACC clusters. More importantly, even in such small CaCO3 entities, a proto-calcite short-range order can be identified but with a relatively high degree of disorder that arises from the very small size of the CaCO3 core. Our findings support the notion of a structural link between prenucleation clusters, amorphous intermediates, and final crystalline polymorphs, which appears central to the understanding of polymorph selection.
无定形中间相是许多生物矿化晶体形成的重要前体。虽然已经发现与不同晶体形式相关的无定形碳酸钙 (ACC) 中存在固有短程有序，但尚未通过实验澄清在小于 2nm 的非常小的簇中是否已经存在这种有序。在这里，我们研究了由大约 1.4nm 大小的仅包含七个 CaCO3 单元的核心组成的 10,12-二十五碳二炔酸 (PCDA) 保护的 ACC 簇的稳定性和结构。配体浓度和结构是稳定 ACC 簇的关键因素。更重要的是，即使在如此小的 CaCO3 实体中，也可以识别出原方解石短程有序，但由于 CaCO3 核的非常小尺寸，会出现相对较高的无序度。我们的发现支持了成核前簇、无定形中间相和最终结晶多晶型之间存在结构联系的观点，这对于理解多晶型选择至关重要。
