自然界中发现的生物矿物的多样性,每个都有自己的形态,机械性能和成分,是非凡的。为了生产适合其功能的最佳矿物质,生物矿化通常发生在严格的细胞控制下。这种控制是由组装成三维有机基质框架的特殊蛋白质和多糖施加的。形成矿物沉积发生的微环境。软体动物的独特之处在于它们使用各种惊人的结构图案来建造贝壳,每个晶体具有不同的形态和不同的碳酸钙多晶型物。关于软体动物壳形成的许多知识都来自对珍珠层的研究,或者珍珠母.在这次审查中,我们讨论了珍珠质形成过程中文石晶体成核的两种现有模型:异质外延成核和矿物桥。异质外延成核模型基于对晶体印记中心的化学官能团和文石成核蛋白的识别。它建议在珍珠层形成期间,每个文石片独立地在成核位点上成核,所述成核位点由吸附在几丁质支架上的酸性蛋白和/或糖蛋白形成。矿物桥模型基于对堆栈中晶体之间物理连接的识别,这导致跨若干层的大量晶体共享相同的晶体学取向。这些观察表明,每堆片剂存在一个成核事件。一旦第一个晶体成核并到达顶部的层间基质,它继续通过毛孔生长,产生下一层珍珠层,随后传播到堆栈中。我们比较了这两种模型,并建议它们协同工作以控制珍珠母中的晶体成核。每堆排列的晶体必须至少发生一次从头晶体成核,并由成核位点诱导。我们建议进一步的生长受矿物桥和成核位点的控制。最后,我们讨论了无定形碳酸钙前体在珍珠层形成中的作用。
The wide diversity of biogenic minerals that is found in nature, each with its own morphology, mechanical properties and composition, is remarkable. In order to produce minerals that are optimally adapted for their function, biomineralisation usually occurs under strict cellular control. This control is exerted by specialised proteins and polysaccharides that assemble into a 3-dimensional organic matrix framework, forming a microenvironment where mineral deposition takes place. Molluscs are unique in that they use a striking variety of structural motifs to build their shells, each made of crystals with different morphologies and different calcium carbonate polymorphs. Much of want is known about mollusc shell formation comes from studies on the nacreous layer, or mother-of-pearl. In this
review, we discuss two existing models on the nucleation of aragonite crystals during
nacre formation: heteroepitaxial nucleation and mineral bridges. The heteroepitaxial nucleation model is based on the identification of chemical functional groups and aragonite-nucleating proteins at the centre of crystal imprints. It proposes that during
nacre formation, each aragonite tablet nucleates independently on a nucleation site that is formed by acidic proteins and/or glycoproteins adsorbed on the chitin scaffold. The mineral bridges model is based on the identification of physical connections between the crystals in a stack, which results in a large number of crystals across several layers sharing the same crystallographic orientation. These observations suggest that there is one nucleation event per stack of tablets. Once the first crystal nucleates and reaches the top interlamellar matrix, it continues growing through pores, giving rise to the next layer of
nacre, subsequently propagating into a stack. We compare both models and propose that they work in concert to control crystal nucleation in
nacre. De novo crystal nucleation has to occur at least once per stack of aligned crystals, and is induced by nucleation sites. We suggest that further growth is controlled both by mineral bridges and nucleation sites. Finally, we discuss the role of amorphous calcium carbonate precursor in
nacre formation.