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.