Wu Y, Glimcher M J, Rey C, Ackerman J L
Department of Radiology, Massachusetts General Hospital, Charlestown 02129.
J Mol Biol. 1994 Dec 9;244(4):423-35. doi: 10.1006/jmbi.1994.1740.
The detailed chemical composition and microstructure of freshly deposited bone mineral, and how these properties change with maturation of the mineral, have been studied intensively and still remain controversial. For example, current analytical technology is inadequate for the unambiguous characterization of the monohydrogen phosphate ions in bone mineral. Using a differential cross polarization/magic angle spinning solid state nuclear magnetic resonance spectroscopy technique, we suppress the dominant orthophosphate (PO4-3) signal to reveal the spectra of the minor phosphate constituents. This method depends upon differences in the cross polarization time constants for phosphorus-31 nuclei in protonated and non-protonated phosphate ions. It is now possible for the first time to directly measure both the proportion of acid phosphate (HPO4-2) as well as the parameters which characterize its isotropic and anisotropic chemical shift. In bone from three species at several developmental stages, we have found a single type of acid phosphate species, identical in all of the specimens examined. The phosphorus-31 isotropic chemical shift of this acid phosphate group in bone mineral corresponds precisely with that of acid phosphate in octacalcium phosphate, and not with that of brushite. In contrast, the bone acid phosphate anisotropic chemical shift parameters are close to those of brushite, and differ significantly from those of octacalcium phosphate. The orthophosphate resonances of bone mineral, synthetic hydroxyapatite and synthetic octacalcium phosphate share identical chemical isotropic shifts, and similar chemical shift anisotropies. The implication of these results is that the intimate structure of the acid phosphate group in bone mineral is unique, and that none of the common synthetic calcium phosphates accounts well for all of the observed solid state phosphorus-31 NMR properties of bone mineral.
新沉积骨矿物质的详细化学成分和微观结构，以及这些特性如何随矿物质成熟而变化，已得到深入研究，但仍存在争议。例如，目前的分析技术不足以明确表征骨矿物质中的磷酸氢根离子。我们使用差分交叉极化/魔角旋转固态核磁共振光谱技术，抑制主要的正磷酸盐（PO4-3）信号，以揭示次要磷酸盐成分的光谱。该方法取决于质子化和非质子化磷酸根离子中磷-31原子核的交叉极化时间常数差异。现在首次能够直接测量酸性磷酸盐（HPO4-2）的比例以及表征其各向同性和各向异性化学位移的参数。在来自三个物种不同发育阶段的骨骼中，我们发现了单一类型的酸性磷酸盐物种，在所检查的所有标本中都是相同的。骨矿物质中这种酸性磷酸盐基团的磷-31各向同性化学位移与磷酸八钙中的酸性磷酸盐精确对应，而与透钙磷石的不同。相比之下，骨酸性磷酸盐的各向异性化学位移参数接近透钙磷石的，与磷酸八钙的有显著差异。骨矿物质、合成羟基磷灰石和合成磷酸八钙的正磷酸盐共振具有相同的化学各向同性位移和相似的化学位移各向异性。这些结果表明，骨矿物质中酸性磷酸盐基团的紧密结构是独特的，并且没有一种常见的合成磷酸钙能很好地解释骨矿物质所有观察到的固态磷-31核磁共振特性。
