Mechanistic Insights into the Crystallization of Amorphous Calcium Carbonate (ACC)
Mechanistic Insights into the Crystallization of Amorphous Calcium Carbonate (ACC)
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DOI：
10.1021/cg300676b
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发表时间：
2012-07-01
影响因子：
3.8
通讯作者：
Shaw, Samuel
中科院分区：
文献类型：
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作者：
Bots, Pieter;Benning, Liane G.;Shaw, Samuel
许多生物在结晶碳酸钙生物矿化过程中使用无定形碳酸钙(ACC)作为控制颗粒形状/大小和相稳定性的手段。在这里，我们提出了一个原位小角和广角X射线散射(SAXS/WAXS)研究的机理和动力学的ACC结晶在快速时间尺度(秒)。结合离线固相和溶液的表征，我们发现ACC通过三个阶段的过程结晶成球状球石。首先，水合无序的ACC形成，然后迅速转变为更有序和脱水的ACC；与此相结合，球状陨石通过球晶生长机制形成。其次，当溶液相对于球泡石的过饱和度充分降低时，机理转变为ACC的溶解和球泡石晶体的生长。第三阶段由球石颗粒的Ostwald熟化控制。将这些信息与以前的研究相结合，使我们能够从机理上理解从ACC到球状陨石再到方解石的非生物结晶过程。我们认为这是ACC碳酸钙生物矿化的潜在非生物机制。然后，有机体(例如，使用有机化合物)增强或改变这一过程，以形成复杂的生物矿物。本研究还强调了原位时间分辨SAXS/WAXS在快速结晶反应研究中的适用性。
Many organisms use amorphous calcium carbonate (ACC) during crystalline calcium carbonate biomineralization, as a means to control particle shape/size and phase stability. Here, we present an in situ small- and wide-angle X-ray scattering (SAXS/WAXS) study of the mechanisms and kinetics of ACC crystallization at rapid time scales (seconds). Combined with offline solid and solution characterization, we show that ACC crystallizes to vaterite via a three-stage process. First, hydrated and disordered ACC forms, then rapidly transforms to more ordered and dehydrated ACC; in conjunction with this, vaterite forms via a spherulitic growth mechanism. Second, when the supersaturation of the solution with respect to vaterite decreases sufficiently, the mechanism changes to ACC dissolution and vaterite crystal growth. The third stage is controlled by Ostwald ripening of the vaterite particles. Combining this information with previous studies, allowed us to develop a mechanistic understanding of the abiotic crystallization process from ACC to vaterite and all the way to calcite. We propose this is the underlying abiotic mechanism for calcium carbonate biomineralization from ACC. This process is then augmented or altered by organisms (e.g., using organic compounds) to form intricate biominerals. This study also highlights the applicability of in situ time-resolved SAXS/WAXS to study rapid crystallization reactions.