The effect of Mg2+ incorporation on the structure of calcium carbonate clusters: investigation by the anharmonic downward distortion following method
The effect of Mg2+ incorporation on the structure of calcium carbonate clusters: investigation by the anharmonic downward distortion following method
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DOI：
10.1039/c5cp05139h
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发表时间：
2016-01-28
影响因子：
3.3
通讯作者：
Nagai, Takaya
中科院分区：
文献类型：
--
作者：
Kawano, Jun;Maeda, Satoshi;Nagai, Takaya
Mg 2+被认为在碳酸钙多晶型物的形成中起着重要作用;然而，在碳酸钙形成的早期阶段，它如何影响多晶型物的选择尚未得到很好的理解。在本研究中，为了阐明Mg 2+对碳酸钙多晶型物成核的影响，无水无添加剂和含Mg的碳酸钙簇的稳定结构推导使用非谐向下失真以下的方法，基于量子化学计算。在B3 LYP/6-31+G（d）水平上进行优化，采用自洽反应场方法，采用类导体极化连续计算模型，引入溶剂效应.计算结果表明，Mg ~（2+）的引入改变了团簇的稳定构型。在二聚体和三聚体的情况下，Mg离子强烈倾向于位于簇的中心，这表明一旦Mg从其紧密的水合壳释放，它就容易并入簇中。值得注意的是，当只有四个CaCO 3单元聚集成簇时，出现类似于结晶相的结构：在无添加剂的CaCO 3四聚体的稳定结构中，Ca和CO 3离子的排列几乎与方解石结构相同，而含Mg的CaCO 3四聚体的结构在CO 3离子堆叠的方式上类似于文石结构。这些结果表明，镁可以在文石的形成中发挥关键作用，不仅通过抑制方解石的生长，但也直接促进文石成核的早期阶段的碳酸钙形成。
Mg2+ is considered to play an important role in the formation of calcium carbonate polymorphs; however, how it affects polymorph selection during the early stages of CaCO3 formation is not yet well understood. In the present study, in order to clarify the effect of Mg2+ on the nucleation of calcium carbonate polymorphs, the stable structures of anhydrous additive-free and Mg-containing calcium carbonate clusters are derived using the anharmonic downward distortion following method, based on quantum chemical calculations. Optimization is performed at the B3LYP/6-31+G(d) level and the solvent effect is induced by the self-consistent reaction field method using the conductor-like polarized continuum calculation model. Calculation results show that incorporating Mg2+ into clusters can change the clusters' stable configuration. In the case of dimers and trimers, a Mg ion strongly prefers to locate at the centre of the clusters, which suggests that Mg is easy to incorporate into the clusters once it is released from its tight hydration shell. Notably, structures similar to the crystalline phase appear when only four CaCO3 units aggregate into the cluster: in the stable structure of the additive-free CaCO3 tetramer, the arrangement of Ca and CO3 ions is almost the same as that of the calcite structure, while the structure of the Mg-containing CaCO3 tetramer resembles the aragonite structure in the way that CO3 ions are stacked. These results indicate that Mg can play a key role in aragonite formation not only by inhibiting calcite growth but also by directly promoting aragonite nucleation in the early stages of CaCO3 formation.