A computer modelling study of the uptake, structure and distribution of carbonate defects in hydroxy-apatite.
A computer modelling study of the uptake, structure and distribution of carbonate defects in hydroxy-apatite.
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DOI：
10.1016/j.biomaterials.2005.09.025
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发表时间：
2006-03
期刊：
影响因子：
14
通讯作者：
Sherina Peroos;Z. Du;N. D. de Leeuw
中科院分区：
文献类型：
--
作者：
Sherina Peroos;Z. Du;N. D. de Leeuw
计算机模拟技术已被用来定性和定量研究的羟基磷灰石晶格中的碳酸根基团的吸收和分布。被认为是两个替代缺陷：A型缺陷，其中碳酸酯基团位于羟基通道，和B型缺陷，其中碳酸酯基团位于磷酸基团的位置。还考虑了组合型A-B缺陷，并考虑了不同的电荷补偿。A型碳酸盐的最低能量构型具有与磷灰石晶格的c方向上的通道对齐的O-C-O轴和位于a/B平面中的第三氧原子。B型缺陷的碳酸盐的取向受磷灰石材料的组成的强烈影响，从在a/B平面中（几乎）平坦的位置变化到其平面在B/c平面中的取向。然而，Ca-O相互作用总是最大化，并且电荷补偿离子位于碳酸根离子附近。当我们直接比较每个取代碳酸酯基团的能量时，不同缺陷模拟的结果表明，两个羟基被一个碳酸酯基团取代的A型缺陷在能量上是优先的（ΔH=-404kJmol-1），其次是磷酸根和羟基都被两个碳酸酯基团取代的A-B型缺陷（ΔH=-259kJmol-1）。在B型缺陷中，我们在同一位置用碳酸酯基团和另一个羟基基团取代了磷酸基团，这是能量中性的（ΔH=-1kJmol-1），但当用碳酸根取代磷酸根时，用钠离子或钾离子取代钙离子进行电荷补偿时，所产生的B型缺陷在能量上是有利的（ΔHNa=-71 kJmol-1，ΔHK=-6 kJmol-1），晶格中存在的A型缺陷也促进了它的形成。我们的模拟表明，它是积极的可能发生的所有取代，这是计算从水溶液中的离子交换反应。碳酸盐缺陷在生物羟基磷灰石中广泛存在，我们的模拟表明，从溶液中引入碳酸盐到羟基磷灰石晶格中在化学上是可行的，因此与实验一致。
Computer modelling techniques have been employed to qualitatively and quantitatively investigate the uptake and distribution of carbonate groups in the hydroxyapatite lattice. Two substitutional defects are considered: the type-A defect, where the carbonate group is located in the hydroxy channel, and the type-B defect, where the carbonate group is located at the position of a phosphate group. A combined type A–B defect is also considered and different charge compensations have been taken into account. The lowest energy configuration of the A-type carbonate has the O–C–O axis aligned with the channel in the c-direction of the apatite lattice and the third oxygen atom lying in the a/b plane. The orientation of the carbonate of the B-type defect is strongly affected by the composition of the apatite material, varying from a position (almost) flat in the a/b plane to being orientated with its plane in the b/c plane. However, Ca–O interactions are always maximised and charge compensating ions are located near the carbonate ion. When we make a direct comparison of the energies per substitutional carbonate group, the results of the different defect simulations show that the type-A defect where two hydroxy groups are replaced by one carbonate group is energetically preferred (ΔH=-404kJmol-1), followed by the combined A–B defect, where both a phosphate and a hydroxy group are replaced by two carbonate groups (ΔH=-259kJmol-1). The type-B defect, where we have replaced a phosphate group by both a carbonate group and another hydroxy group in the same location is energetically neutral (ΔH=-1kJmol-1), but when the replacement of the phosphate group by a carbonate is charge compensated by the substitution of a sodium or potassium ion for a calcium ion, the resulting type-B defect is energetically favourable (ΔHNa=-71kJmol-1,ΔHK=-6kJmol-1) and its formation is also promoted by A-type defects present in the lattice. Our simulations suggest that it is energetically possible for all substitutions to occur, which are calculated as ion-exchange reactions from aqueous solution. Carbonate defects are widely found in biological hydroxy-apatite and our simulations, showing that incorporation of carbonate from solution into the hydroxyapatite lattice is thermodynamically feasible, hence agree with experiment.