Biomineralization nucleation control

Many heterogeneous processes such as dissolution of minerals, formation of the solid phase (precipitation, nucleation, crystal growth, and biomineralization), redox processes at the solid-water interface (including light-induced reactions), and reductive and oxidative dissolutions are rate-controlled at the surface (and not by transport) (10). Because surfaces can adsorb oxidants and reductants and modify redox intensity, the solid-solution interface can catalyze many redox reactions. Surfaces can accelerate many organic reactions such as ester hydrolysis (11). 

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. 

We must now consider the important question of the probability of these mechanisms taldng place in biomineralization. It is often implicitly assumed that the main function of the matrix is to act as a template for mineral development through the control of crystal orientation and structure, but as we have discussed previously this is not necessarily correct since the matrix may serve simply as an energetically favourable site for heterogeneous nucleation, or as a means of volume constraint, or as a framework for structural support. Thus the bulk mineral is often observed to be composed of crystallites interlaminated and virapped with organic sheets and it is often not at all clear what function the matrices serve. 

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. 

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