Biomineralization supersaturation control

Biomineralization. The processes controlling biomineralization are summarized in Fig. 6.1c. Organized biopolymers at the sites of mineralization are essential to these processes. In unicellular organisms these macromolecules act primarily as spatial boundaries through which ions are selectively transported to produce localized supersaturation within discrete cellular compartments. In many instances, particularity in organisms such as the diatoms that deposit shells of amorphous silica, the final shape of the mineral appears to be dictated by the ultrastrucure of the membrane-bound compartment. Thus, a diversity of mineral shapes can be biologi-... 

The regulation of supersaturation levels at the mineralization site by active ion transport can, in principle, control the rate of nucleation of the biomineral as indicated in Eq. (3) of Sect. 3.1. Also, the choice between pathways A and B in Fig. 3.9 will be determined to some degree by the structure of the critical nucleus initially formed. 

Problems caused by polymorphism appear in many fields such as fine chemicals in industries (pharmaceuticals(7,2), foods, etc.), optical electronic materials(i), clathrate compounds(4) and biominerals(5). In crystallizations of these materials the crystallization behavior of the polymorphs is controlled first by basic operational conditions such as temperature, supersaturation degree, stirring rates. In addition to these basic factors, solvents, additives and guest molecules (in clathrate compounds) should be also considered as the important factors((5,7). The crystallization process of the polymorphs is composed of comp)etitive nucleation, competitive growth of polymorphs and transformation from metastable to stable form. Accordingly individual step should be investigated to clarify the crystallization mechanism of polymorphs. 

Materials synthesis in biology is often conducted in compartments that delimit the extent of growth as well as provide a microenvironment in which parameters such as supersaturation of a precipitating phase can be delicately controlled by active transport of ions. This is how many biomineralization processes take place—for example, the formation of exquisitely patterned mineral plates in the soft tissues of coccolithophores. Mimesis of this principle... 

With the exception of urine whose composition can vary over wide ranges, physiological solutions are usually not highly supersaturated with respect to biominerals. A careful control of ion balance, which must be maintained for physiological function, including avoidance of undesirable precipitates, can... 

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