CaCO3生物矿化的研究进展——有机质的控制作用

生物CaCO₃是自然界分布最广泛的一类生物矿物,其组成除了无机相的CaCO₃外,还含有少量的有机质,包括水可溶(SM)和水不可溶有机质(IM),SM富含阴离子基团,是控制CaCO₃结晶的重要因素之一。通过有机—无机界面分子识别,有机质选择性地与CaCO₃晶体特定方向的面网相互作用,从而对CaCO₃的生长、形貌、多型及结晶学定向等产生明显的控制作用。有机—无机界面的分子识别机制包括静电、晶格几何匹配和立体化学互补等。仿生矿化的研究为进一步深入了解生物矿化的机理及制造高级复合材料提供了新的方法。

ADVANCES IN BIOMINERALIZATION STUDY OF BIOGENIC CALCIUM CARBONATES: CONTROL OF CRYSTALLIZATION BY ORGANIC MATRIX

Among biominerals, calcium carbonates are most widespread in nature, the compositions of which include minor organic matrix in addition to inorganic materials. The organic matrix can be divided into two classes: water-soluble(SM) and water-insoluble(IM) matrix. SM is often rich in anionic groups such as carboxylate, phosphonate and sulphate groups and plays important role in regulating the crystallization of calcium carbonates. The mineralization experiments, when using the organic matrix directly extracted from organisms to induce carbonates crystallization , show that: (1) with respect to morphology and orientation control, SM from mollusk bivalve shells is susceptible to interacting with (001) face of calcite, whereas SM from echinoderm or sponge spicules tends to interact with (01l)(l=1～1.5) face of calcite; (2) with respect to polymorphism modification, SM from biogenic calcite can always induce calcite nucleation, but SM from biogenic aragonite is not always inducing aragonite nucleation.In addition, the synthetic micromolecules are also used to study biomineralization. The results show that: (1) with respect to morphology and orientation control, the monolayers of n-eicosyl sulphate and n-eicosyl phosphonate tend to interact with (001) face of calcite, the monolayer of n-octadecanoic acid to interact with of (110) face calcite, and film of 10,12-pentacosadiynoic acid to interact with (012) face of calcite; (2) with respect to polymorphism modification, up to date, monolayers of micromolecules generally induce calcite nucleation except for film of 5-hexadecyloxyisophthalic(C16ISA) which promotes aragonite formation.
It is generally accepted that the control of organic matrix over CaCO₃ morphology and polymorphism is due to the molecular recognition between organic-inorganic interface such as electrostatic attraction, lattice geometry matching and stereochemical complimentary. At the negative charged interface between organic monolayer and inorganic phase, the electrostatic attraction results in the composition departure from lattice ion stoichiometry and pH lowering which are considered as the main factors to promote inorganic mineral nucleation. Lattice geometry matching and stereochemical complimentary between organic matrix and calcium carbonate effectively reduce the activation energy of nucleation of minerals along such matching faces to result in the oriented nucleation and growth of minerals. Though there is little understanding of detailed control mechanism of biogenic calcium carbonate by matrix, the research will shed lights on material science and provide new pathways to fabricate advanced organic-inorganic composite materials.