Peroos, S. and du, Zhimei and de Leeuw, Nora Henriette (2006) A computer modelling study of the uptake, structure and distribution of carbonate defects in hydroxy-apatite. Biomaterials 27 (9), pp. 2150-2161. ISSN 0142-9612.Full text not available from this repository.
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 View the MathML source, followed by the combined A–B defect, where both a phosphate and a hydroxy group are replaced by two carbonate groups View the MathML source. 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 View the MathML source, 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 View the MathML source 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.
|Keyword(s) / Subject(s):||Hydroxyapatite, apatite structure, calcium carbonate, molecular modelling, carbonate defects|
|School or Research Centre:||Birkbeck Schools and Research Centres > School of Science > Biological Sciences|
|Date Deposited:||18 Aug 2011 10:34|
|Last Modified:||17 Apr 2013 12:21|
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