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.

中文翻译：

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磷酸钙成核过程中波斯纳团簇的检测：分子动力学研究

羟基磷灰石（HA）是哺乳动物牙齿珐琅质和骨骼的主要矿物质相，起源于体液中的无定形磷酸钙（ACP）。ACP以大小为0.9 nm的小畴和化学式Ca ₉（PO ₄）₆的小畴形式出现，称为Posner簇。在这项研究中，已经通过壳模型分子动力学模拟研究了水中钙和磷酸根离子的聚集和聚集。溶液中形成的磷酸钙聚集体具有与Posner簇中相似的组成和Ca配位，但这些物质的化学计量取决于溶液的离子组成：Ca含量低的溶液中缺乏钙的簇：P比 在中性溶液中含有质子化磷酸基团的簇；钠离子在含有钠和钙离子混合物的溶液中部分取代钙。这些类似Posner的簇可以通过磷酸酯基团连接，这些磷酸酯基团充当其中心钙离子之间的桥梁。磷酸钙团簇溶液中聚集的模拟是对波斯纳模型的公正无误的验证，并首次揭示了ACP成核早期阶段形成的物种的结构和组成，其规模尚无法进行实验。 。