Amorphous Calcium Carbonate is Stabilized in Confinement
Amorphous Calcium Carbonate is Stabilized in Confinement
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DOI：
10.1002/adfm.201000248
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发表时间：
2010-07-09
影响因子：
19
通讯作者：
Christenson, Hugo K.
中科院分区：
文献类型：
--
作者：
Stephens, Christopher J.;Ladden, Sophie F.;Christenson, Hugo K.
生物矿物质通常在局部体积内形成，使生物体能够很好地控制成矿过程。本文通过在两个相交的半圆柱体接触点周围形成的环形楔形体的边界内析出CaCO3来研究这种限制对结晶的影响。圆柱体被功能化，在金表面自组装了硫代十六烷酸单分子膜。这种结构使得能够系统地研究限制的影响，因为表面间隔从接触点处的零持续增加到宏观(Mm)间隔。当取向的方解石晶体在较大的(-gt；10微米)分离时形成，当表面分离接近无限制晶体的尺寸(5-10微米)时，观察到具有不规则形态和部分结晶性的颗粒。进一步增加约束对晶化过程有显著影响，在微米级分离时形成扁平的无定形CaCO3(ACC)颗粒。这些ACC颗粒在保持在楔形体内时表现出显着的稳定性，但在分离钢瓶时迅速结晶。体能项和表面能项的比较表明，ACC在这些大的分离度下不是热力学稳定的，其稳定性归因于动力学因素。因此，这项研究表明，矿物形成的环境对其稳定性有显著影响，并证明仅通过限制，ACC就可以相对于CaCO3的晶型稳定下来。ACC稳定在如此大的(微米)分离是惊人的，并证明了这一策略的多功能性及其在生物系统中的潜在价值。
Biominerals typically form within localized volumes, affording organisms great control over the mineralization process. The influence of such confinement on crystallization is studied here by precipitating CaCO3 within the confines of an annular wedge, formed around the contact point of two crossed half-cylinders. The cylinders are functionalized with self-assembled monolayers of mercaptohexadecanoic acid on gold. This configuration enables a systematic study of the effects of confinement since the surface separation increases continuously from zero at the contact point to macroscopic (mm) separations. While oriented rhombohedral calcite crystals form at large (>10 mu m) separations, particles with irregular morphologies and partial crystallinity are observed as the surface separation approaches the dimensions of the unconfined crystals (5-10 mu m). Further increase in the confinement has a significant effect on the crystallization process with flattened amorphous CaCO3 (ACC) particles being formed at micrometer separations. These ACC particles show remarkable stability when maintained within the wedge but rapidly crystallize on separation of the cylinders. A comparison of bulk and surface free-energy terms shows that ACC cannot be thermodynamically stable at these large separations, and the stability is attributed to kinetic factors. This study therefore shows that the environment in which minerals form can have a significant effect on their stability and demonstrates that ACC can be stabilized with respect to the crystalline polymorphs of CaCO3 by confinement alone. That ACC was stabilized at such large (micrometer) separations is striking, and demonstrates the versatility of this strategy, and its potential value in biological systems.