Nelson Adam, Papawassiliou Wassilios, Paul Subhradip, Hediger Sabine, Hung Ivan, Gan Zhehong, Venkatesh Amrit, Franks W Trent Trent, Smith Mark E, Gajan David, De Paëpe Gaël, Bonhomme Christian, Laurencin Danielle, Gervais Christel
LCMCP, UMR 7574, Sorbonne Université, CNRS, Paris, France.
ICGM, Univ Montpellier, CNRS, ENSCM, Montpellier, France.
Faraday Discuss. 2025 Jan 8;255(0):451-482. doi: 10.1039/d4fd00108g.
Octacalcium phosphate (OCP, Ca(PO)(HPO)·5HO) is a notable calcium phosphate due to its biocompatibility, making it a widely studied material for bone substitution. It is known to be a precursor of bone mineral, but its role in biomineralisation remains unclear. While the structure of OCP has been the subject of thorough investigations (including using Rietveld refinements of X-ray diffraction data, and NMR crystallography studies), important questions regarding the symmetry and H-bonding network in the material remain. In this study, it is shown that OCP undergoes a lowering of symmetry below 200 K, evidenced by H, O, P and Ca solid-state NMR experiments. Using molecular-dynamics (MD) simulations and gauge including projected augmented wave (GIPAW) DFT calculations of NMR parameters, the presence of rapid motions of the water molecules in the crystal cell at room temperature is proved. This information leads to an improved description of the OCP structure at both low and ambient temperatures, and helps explain long-standing issues of symmetry. Remaining challenges related to the understanding of the structure of OCP are then discussed.
磷酸八钙（OCP，Ca₈(HPO₄)₂(PO₄)₄·5H₂O）因其生物相容性而成为一种值得关注的磷酸钙，这使其成为一种被广泛研究的骨替代材料。已知它是骨矿物质的前体，但其在生物矿化中的作用仍不清楚。虽然OCP的结构已成为深入研究的对象（包括使用X射线衍射数据的Rietveld精修和核磁共振晶体学研究），但关于该材料的对称性和氢键网络仍存在重要问题。在本研究中，通过氢、氧、磷和钙的固态核磁共振实验证明，OCP在200 K以下会发生对称性降低。利用分子动力学（MD）模拟和包括投影增强波（GIPAW）密度泛函理论（DFT）计算核磁共振参数，证明了室温下晶胞中水分子的快速运动。这些信息有助于改进对OCP在低温和环境温度下结构的描述，并有助于解释长期存在的对称性问题。随后讨论了与理解OCP结构相关的剩余挑战。
