Impacts of Initial Ca/P on Amorphous Calcium Phosphate
Impacts of Initial Ca/P on Amorphous Calcium Phosphate
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DOI：
10.1021/acs.cgd.1c00058
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发表时间：
2021-06-03
影响因子：
3.8
通讯作者：
Michel, F. Marc
中科院分区：
文献类型：
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作者：
Hoeher, Alexandria J.;Mergelsberg, Sebastian T.;Michel, F. Marc
无定形磷酸钙（ACP）是磷酸钙结晶途径中的亚稳态相。了解其化学和结构特性可以为生物矿化机制提供重要的见解。特别令人感兴趣的是初始 Ca/P 对 ACP 结构的影响。此外，Ca/P 对 ACP 的尺寸、沉淀化学和转化的影响对于理解无定形磷酸盐的亚稳定性至关重要。混合后 5 分钟的原位对分布函数 (PDF) 分析结果表明，随着 Ca/P 从 0.2 增加到 5.0，Ca-P 键合几何形状从主要单齿，到混合单齿和双齿，再到主要双齿。这种关系在 6-11 的 pH 范围内是一致的。仅具有单齿 Ca-P 几何形状的样品直接转变为羟基磷灰石，而部分或全部双齿几何形状的样品形成透钙磷石。无论初始比率如何，沉淀物的 Ca/P 都接近 1.0。原位小角 X 射线散射显示颗粒尺寸随着 Ca/P 的增加而增加。这是 ACP 结构变化的第一个证据，并且与系统化学直接相关。合成具有单齿 Ca-P 几何形状的 ACP 是一种有前途的方法，可以控制结晶途径，在中性 pH 值左右形成羟基磷灰石，无需稳定离子。
Amorphous calcium phosphate (ACP) is a metastable phase in the crystallization pathway of calcium phosphates. Understanding its chemical and structural properties could provide critical insights into biomineralization mechanisms. Of particular interest is the impact of the initial Ca/P on the structure of ACP. Further, the influence of Ca/P on the size, precipitate chemistry, and transformation of ACP is crucial to understanding the metastability of amorphous phosphates. In situ pair distribution function (PDF) analysis results 5 min after mixing show that the Ca-P bonding geometry varies from predominantly monodentate, to mixed monodentate and bidentate, to predominantly bidentate as Ca/P increases from 0.2 to 5.0. This relationship is consistent across a pH range of 6-11. Samples with only monodentate Ca-P geometries transform directly to hydroxylapatite, while samples some or all bidentate geometries form brushite. Regardless of the initial ratio, the Ca/P of precipitates is close to 1.0. In situ small-angle X-ray scattering shows particle size increases with increasing Ca/P. This is the first evidence of structural variations in ACP and is directly linked to system chemistry. Synthesis of ACP with monodentate Ca-P geometries is a promising method to control the crystallization pathway to form hydroxylapatite at circumneutral pH without stabilizing ions.