A contribution to the understanding of the formation of calcium phosphates
1989; Elsevier BV; Volume: 94; Issue: 3 Linguagem: Inglês
10.1016/0022-0248(89)90102-4
ISSN1873-5002
AutoresJ. Christoffersen, Margaret R. Christoffersen, W. Kibalczyc, F. Allan Andersen,
Tópico(s)Bone and Dental Protein Studies
ResumoThe nature of the calcium phosphate precipitate formed when equal volumes of 20mM CaCl2 and 15mM or 12mM KPO4 with pH 7.4 are rapidly mixed at 15, 30 and 42°C has been investigated by chemical analysis, TEM, IR and by following the pH of the suspension as a function of time. At 30 and 42°C the final product is a deficient form of calcium hydroxyapatite, called d-HA. The formation of d-HA was preceded by an initial fast precipitation of a spherular amorphous form of calcium phosphate, called ACP1, which transformed into a floccular amorphous form, called ACP2, after which octacalcium phosphate, OCP, and d-HA crystallized. These transformations, which are considered to be solution-mediated, the one phase disappearing with the development of the next, occurred faster, the higher the temperature. The presence of MgCl2 slowed the ACP1-ACP2 transformation, but apparently not the crystallization of OCP and d-HA. At 15°C ACP1 was formed initially, but the product formed was calcium monohydrogen phosphate dihydrate, DCPD, which also nucleated soon after mixing. Filtering off ACP1 from a reaction mixture at 30°C also resulted in the formation of DCPD and not OCP and d-HA. The amorphous phase, ACP2, which has not previously been clearly identified as a separate phase, is thus considered necessary for the development of OCP and d-HA under the conditions studied.
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