Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
Biomaterials. 2011 Mar;32(7):1826-37. doi: 10.1016/j.biomaterials.2010.11.017. Epub 2010 Dec 7.
The incorporation of Mg in hydroxyapatite (HA) was investigated using multinuclear solid state NMR, X-ray absorption spectroscopy (XAS) and computational modeling. High magnetic field (43)Ca solid state NMR and Ca K-edge XAS studies of a ∼10% Mg-substituted HA were performed, bringing direct evidence of the preferential substitution of Mg in the Ca(II) position. (1)H and (31)P solid state NMR show that the environment of the anions is disordered in this substituted apatite phase. Both Density Functional Theory (DFT) and interatomic potential computations of Mg-substituted HA structures are in agreement with these observations. Indeed, the incorporation of low levels of Mg in the Ca(II) site is found to be more favourable energetically, and the NMR parameters calculated from these optimized structures are consistent with the experimental data. Calculations provide direct insight in the structural modifications of the HA lattice, due to the strong contraction of the M⋯O distances around Mg. Finally, extensive interatomic potential calculations also suggest that a local clustering of Mg within the HA lattice is likely to occur. Such structural characterizations of Mg environments in apatites will favour a better understanding of the biological role of this cation.
采用多核固态 NMR、X 射线吸收光谱（XAS）和计算建模研究了 Mg 在羟基磷灰石（HA）中的掺入。对取代度约为 10%的 HA 进行了高磁场（43）Ca 固态 NMR 和 Ca K 边 XAS 研究，直接证明了 Mg 优先取代 Ca(II)位。（1）H 和（31）P 固态 NMR 表明，在这种取代的磷灰石相中，阴离子的环境是无序的。Mg 取代 HA 结构的密度泛函理论（DFT）和原子间势计算都与这些观察结果一致。实际上，发现低水平的 Mg 掺入 Ca(II)位在能量上更有利，并且从这些优化结构计算出的 NMR 参数与实验数据一致。这些计算提供了对 HA 晶格结构修饰的直接见解，这是由于 Mg 周围的 M⋯O 距离强烈收缩所致。最后，广泛的原子间势计算还表明，HA 晶格中 Mg 的局部聚集很可能发生。对磷灰石中 Mg 环境的这种结构特征研究将有助于更好地理解该阳离子的生物学作用。
