Reversible structural changes of octacalcium phosphate and labile acid phosphate.
Reversible structural changes of octacalcium phosphate and labile acid phosphate.
复制标题
磷酸八钙和不稳定酸式磷酸盐的可逆结构变化。
DOI：
10.1177/00220345950740110801
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发表时间：
1995
影响因子：
7.6
通讯作者：
Aoba,T
中科院分区：
文献类型：
--
作者：
Suzuki,O;Yagishita,H;Amano,T;Aoba,T
酸式磷酸盐是生物磷灰石中的主要杂质之一，其形成矿物的数量和环境已被用作诊断探针来寻找酸性前体。目前，人们对非化学计量磷酸八钙（OCP）的结构特征知之甚少，人们认为最有可能的是，它是在釉质形成过程中最初形成的矿物盐。在本报告中，我们尝试定义 OCP 晶体中酸式磷酸盐的状态，该晶体缺钙且含有 40% 的总磷酸盐作为酸式磷酸盐。我们通过在去离子水、10 mmol/L NaOH 溶液（初始 pH 11）或 pH 7.4 的 150 mmol/L Tris 缓冲液中提取晶体来评估离散环境中酸式磷酸盐的分数。通过化学分析和 X 射线衍射检查处理前后的固体样品。结果表明，使用碱性溶液的连续萃取使OCP的内部结构发生了可逆的变化（而不是水解），同时伴随着酸式磷酸盐的显着降低。在随后的中性 pH 值处理过程中，大部分丢失的酸式磷酸盐得到了恢复，有趣的是，这种恢复伴随着 OCP 结构的重新排序。数据表明，OCP 中的酸式磷酸盐分为三个池：(a) 稳定池，相当于总酸式磷酸盐的大约 50% 至 60%；(b) 可逆交换池，相当于酸式磷酸盐的 25% 至 30%，可能存在于水层或晶体表面上；(c) 不稳定（或不可逆损失）池，相当于酸式磷酸盐的 15% 至 20%，其中一部分可以解释OCP 中存在过量氢气。目前的工作支持这样的概念，即质子和较小程度的磷酸盐物质可以在 OCP 晶格开始水解转变为磷灰石之前扩散进出 OCP 晶格。
Acid phosphate is one of the major impurities incorporated into bioapatites, and its quantity and environment in forming mineral have been used as diagnostic probes to pursue acidic precursor(s). Currently, little is known about the structural feature of non-stoichiometric octacalcium phosphate (OCP), which has been advocated to be, most plausibly, mineral salt initially formed during amelogenesis. In the present report, we attempt to define the state of acid phosphate in OCP crystals which were Ca-deficient and contained 40% total phosphate as acid phosphate. We assessed fractions of acid phosphate in discrete environments by extracting the crystals in either deionized water, 10 mmol/L NaOH solution (initial pH 11), or 150 mmol/L Tris buffer at pH 7.4. Solid samples before and after the treatments were examined by chemical analyses and x-ray diffraction. The results indicated that successive extractions with use of the alkaline solution brought about a reversible change (not hydrolysis) in the interior structure of OCP, which accompanied a marked decrease in acid phosphate. A substantial part of the lost acid phosphate was restored during subsequent treatments at neutral pH, and, intriguingly, this restoration accompanied a re-ordering of OCP structure. The data suggested that the acid phosphate in OCP is separated into three pools: (a) a stable pool corresponding to roughly 50 to 60% of the total acid phosphate, (b) a reversibly exchangeable pool corresponding to 25 to 30% of the acid phosphate which may exist either in the water layer or on crystal surfaces, and (c) an unstable (or irreversibly lost) pool corresponding to 15 to 20% of the acid phosphate, a part of which might be explained by the presence of excess hydrogen in OCP. The present work supports the concept that protons and, to a lesser magnitude, phosphate species can diffuse into and out of the OCP lattice prior to initiation of its hydrolytic transition into apatite.