SYNTHESIS AND AGGREGATION OF CALCIUM CARBONATE IN PHOSPHOLIPID VESICLES

这个子项目是许多利用资源的研究子项目之一 由NIH/NCRR资助的中心拨款提供。子项目的主要支持 而子项目的主要调查员可能是由其他来源提供的， 包括其它NIH来源。 列出的子项目总成本可能 代表子项目使用的中心基础设施的估计数量， 而不是由NCRR赠款提供给子项目或子项目工作人员的直接资金。 虽然有广泛的证据表明，使用无定形前体在合成成型的生物矿物，生物合成和稳定的机制仍然知之甚少。迄今为止的研究主要集中在添加剂和有机界面在提供瞬态稳定方面的作用。然而，最近的一项研究表明，大量形成的无定形碳酸钙（ACC）颗粒在直径低于70 nm时似乎是稳定的[1]。亚稳相与其多晶型物相比具有较低的表面能，可以想象，这会导致一个阈值尺寸，低于该尺寸，无定形形式实际上是最稳定的。在矿化细胞中，小泡很可能参与ACC的合成、运输和储存，增加了额外的复杂性。囊泡的小尺寸（30-300 nm）、脂质表面化学和高曲率半径可各自在通过调节表面相互作用实现稳定性方面发挥重要作用。在这里，我们使用一个体外系统，水钙盐封装在0.1 - 1微米直径单层囊泡，研究这个问题。通过加入碳酸铵引发沉淀。初步的小角和广角X射线散射（SAXS/WAXS）数据表明ACC纳米颗粒在10至300 nm范围内稳定至少13小时。为了扩展我们的分析，我们使用SAXS来研究封装ACC纳米颗粒的沉淀和聚集。与大量沉淀相反，在具有有限离子浓度的囊泡内分离沉淀物提供了对晶体生长的独特控制。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Although there is widespread evidence for the use of amorphous precursors in the synthesis of shaped biominerals, the mechanisms of biological synthesis and stabilization remain poorly understood. Research to date has focused largely on the role of additives and organic interfaces in providing transient stabilization. A recent study indicates, however, that amorphous calcium carbonate (ACC) particles formed in bulk appear to be stable below a diameter of 70 nm [1]. The lower surface energy of a meta-stable phase compared to itscrystalline polymorphs could conceivably lead to a threshold size below which the amorphous form is actually the most stable. In mineralizing cells, small vesicles are very likely involved in ACC synthesis, transport, and storage, adding an additional layer of complexity. The small size of the vesicles (30-300 nm), the lipid surface chemistry, and the high radius of curvature may each play an essential role in achieving stability by modulating surface interactions. Here we use an in vitro system, aqueous calcium salts encapsulated within 0.1 - 1 micron diameter unilamellar vesicles, to study this problem. Precipitation is initiated by addition of ammonium carbonate. Preliminary small and wide angle x-ray scattering (SAXS/WAXS) data indicate stabilization of ACC nanoparticles in the range from 10 to 300 nm for at least 13 hours. To extend our analysis, we use SAXS to study precipitation and aggregation of encapsulated ACC nanoparticles. In contrast to bulk precipitation, isolation of the precipitates inside vesicles with limited ion concentration offers a unique control over crystal growth.