Detection of Posner's clusters during calcium phosphate nucleation: a molecular dynamics study.
Detection of Posner's clusters during calcium phosphate nucleation: a molecular dynamics study.
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DOI：
10.1039/c7tb01199g
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发表时间：
2017-09
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影响因子：
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通讯作者：
G. Mancardi;Carlos Hernandez Tamargo;D. Di Tommaso;N. D. de Leeuw
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作者：
G. Mancardi;Carlos Hernandez Tamargo;D. Di Tommaso;N. D. de Leeuw
羟基磷灰石（HA）是哺乳动物牙釉质和骨骼的主要矿物相，来源于体液中的无定形磷酸钙（ACP）。ACP以0.9 nm的小结构域形式呈现出短范围有序，化学式为Ca9(PO4)6，称为Posner簇。本研究采用壳模型分子动力学模拟的方法研究了钙和磷酸盐离子在水中的聚集和聚类。磷酸钙聚集体在溶液中形成，其组成和钙配位与波斯纳团簇中发现的相似，但这些物种的化学计量取决于溶液的离子组成：钙磷比低的溶液中缺钙团簇；中性溶液中含有质子化磷酸基团的团簇；钠离子在含有钠离子和钙离子的混合物的溶液中部分取代钙离子。这些类似波斯纳的簇可以通过磷酸基团连接起来，磷酸基团在它们的中心钙离子之间起着桥梁的作用。磷酸钙簇在溶液中聚集的模拟是对Posner模型的无偏和明确的验证，并首次揭示了在ACP成核早期阶段形成的物种的结构和组成，其规模仍然无法进行实验。
Hydroxyapatite (HA), the main mineral phase of mammalian tooth enamel and bone, originates in body fluids from amorphous calcium phosphate (ACP). ACP presents short-range order in the form of small domains with size of 0.9 nm and chemical formula Ca9(PO4)6, known as Posner's clusters. In this study, the aggregation and clustering of calcium and phosphate ions in water has been investigated by means of shell-model molecular dynamics simulations. Calcium phosphate aggregates form in solution with compositions and Ca coordination that are similar to those found in Posner's cluster, but the stoichiometry of these species is dependent on the ionic composition of the solution: calcium-deficient clusters in solutions with low Ca : P ratio; cluster containing protonated phosphate groups in neutral solutions; sodium ions partially substituting calcium in solutions containing a mixture of sodium and calcium ions. These Posner-like clusters can be connected by phosphate groups, which act as a bridge between their central calcium ions. The simulations of the aggregation in solution of calcium phosphate clusters are an unbiased and unequivocal validation of Posner's model, and reveal for the first time the structure and composition of the species that form during the early stages of ACP nucleation at a scale still inaccessible to experiment.