Cheng P T
Calcif Tissue Int. 1987 Jun;40(6):339-43. doi: 10.1007/BF02556696.
By means of X-ray powder diffraction (XRD), octacalcium phosphate (OCP, Ca8H2(PO4)6 X 5H2O, Ca/P = 1.33) has been shown to be a metastable precursor of hydroxyapatite (HA, Ca10(PO4)6(OH)2, Ca/P = 1.67) during de novo HA formation in aqueous solutions containing [CaCl2] = 1.0-2.0 mM and [Na2HPO4] less than or equal to 3 mM, kept at 37 degrees C, 300 mosM and stirred gently at 150 rpm. At the precipitation boundary with initial pH = 7.4, OCP is stable for at least 24 hours when [Ca] = 1.0 mM, and is less stable when [Ca] = 2.0 mM, transforming into a mixture of OCP and HA within 24 hours. Almost complete transformation to HA within 24 hours takes place with high [Ca] and high [Pi]. Statistical analysis of the pH 7.4 precipitation boundary data supports the XRD findings: although [Ca][Pi] values vary significantly (P less than 0.001) with [Ca] (2.70 +/- 0.05 mM2 for [Ca] = 1.0 mM and 2.00 +/- 0.10 mM2 for [Ca] = 2.0 mM), [Ca]1.33[Pi] values do not vary with [Ca] suggesting that the initial precipitation process is 6(1.33 Ca + Pi)----OCP. With initial pH = 7.6, a different precipitation boundary with lower [Ca][Pi] values has been determined. These findings strongly support the fact that rat epiphyseal cartilage fluid which has [CaUF][PiUF] = 2.6 mM2 (UF = ultrafiltrate) and pH 7.6 [2] should be able to support de novo calcification.
通过X射线粉末衍射（XRD）表明，在含有[CaCl₂]=1.0 - 2.0 mM且[Na₂HPO₄]≤3 mM的水溶液中，于37℃、300 mosM下并以150 rpm轻轻搅拌时，八钙磷酸钙（OCP，Ca₈H₂(PO₄)₆·5H₂O，Ca/P = 1.33）是羟基磷灰石（HA，Ca₁₀(PO₄)₆(OH)₂，Ca/P = 1.67）从头形成过程中的亚稳前体。在初始pH = 7.4的沉淀边界处，当[Ca]=1.0 mM时，OCP至少稳定24小时；当[Ca]=2.0 mM时，稳定性较差，在24小时内转化为OCP和HA的混合物。在高[Ca]和高[Pi]的情况下，24小时内几乎完全转化为HA。对pH 7.4沉淀边界数据的统计分析支持了XRD的结果：尽管[Ca][Pi]值随[Ca]显著变化（P＜0.001）（[Ca]=1.0 mM时为2.70±0.05 mM²，[Ca]=2.0 mM时为2.00±0.10 mM²），但[Ca]¹·³³[Pi]值不随[Ca]变化，这表明初始沉淀过程为6(1.33 Ca + Pi)→OCP。当初始pH = 7.6时，已确定了具有较低[Ca][Pi]值的不同沉淀边界。这些发现有力地支持了以下事实：大鼠骺软骨液的[CaUF][PiUF]=2.6 mM²（UF = 超滤物）且pH为7.6[2]，应该能够支持从头钙化。
