Reviews of calcium phosphates have clearly established amorphous calcium phosphate (ACP) as a distinct, recognisable, non-crystalline phase, and ACP may be a key intermediate in the skeletal calcification process. Calcium phosphates are one of the major biomineral families, and are of crucial importance in humans. Work supported by National Institute of Health, NIDCR (grant # DE003223).īiomineralisation processes are extremely important for living organisms, and are studied for the insights they provide into synthesis routes for controlled crystallisation. The relative size of the inhibition window was dependent on the value of the supersaturation, σ HAP, used for the experiments. At aspartic acid concentrations outside this window, nucleation was promoted. At low aspartic acid concentrations (<1.50x10 -4 mol L -1), a window of concentration dependent inhibition of nucleation was discovered, in which aspartic acid prolonged the induction time by approximately 350 minutes. Investigations were made of Ca-P nucleation in the presence of aspartic acid (σ HAP= 19.5). The TEM and SEM data confirmed the formation of monodisperse amorphous Ca-P nano-particles (ca. At 2.0 μmol L -1, the hydrophobic rP148 segment promoted Ca-P nucleation to a greater degree than the full length rP172, 240±50 min (n=3) versus 375±45 min (n=3), respectively. At an equivalent molar concentration, the rP25 C-terminal polypeptide segment promoted Ca-P nucleation to a greater degree than rP12. In the presence of Amelogenin the induction time for Ca-P nucleation (σ HAP = 18.5) was markedly reduced from 820±55 min (n=3) for control experiments to 600±45 min (n=3) in the presence of 2.0 μmol L -1 rP12, and 535±45 min (n=3) with rP25, respectively. CC data indicate that polypeptides promoted Ca-P nucleation in a concentration dependent manner. The data are consistent with the formation of Posner’s Clusters, Ca 3(PO 4) 2. As the reaction progressed, these particles aggregated to larger amorphous calcium phosphate (Ca-P) spheres. Microscopic (SEM, TEM) analysis of samples removed at the induction time confirmed the formation of nano-particles. During the induction period, small increases in the solution pH and conductivity were observed these events preceded the sharp decrease in solution pH and specific conductance during crystal growth. CC mineralization experiments were made at pH 7.40 and 37.0☌, in the presence and absence of polypeptides and amino acids, at a relative supersaturation with respect to hydroxyapatite (σ HAP) of 20.9. A combination of macroscopic constant composition (CC) and conductimetry has provided new insights into the physical mechanisms of crystal growth and phase stability, and the influences of proteins, peptides and other small molecules. Our work focuses on the earliest events of homo/hetero-geneous nucleation from an initial supersaturated solution phase to the subsequent growth of nuclei. Although many studies of calcium phosphate crystallization have been made, most have focused only on the final structures and morphologies and have not emphasized the need to consider the molecular contacts between mineral and matrix that drive nucleation, nor the thermodynamic and kinetic controls imposed by matrix and soluble proteins during the nucleation stage.
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