Mineralization nucleation

Bacterial cell walls contain different types of negatively charged (proton-active) functional groups, such as carboxyl, hydroxyl and phosphoryl that can adsorb metal cations, and retain them by mineral nucleation. Reversed titration studies on live, inactive Shewanella putrefaciens indicate that the pH-buffering properties of these bacteria arise from the equilibrium ionization of three discrete populations of carboxyl (pKa = 5.16 0.04), phosphoryl (oKa = 7.22 0.15), and amine (/ Ka = 10.04 0.67) groups (Haas et al. 2001). These functional groups control the sorption and binding of toxic metals on bacterial cell surfaces. 

Calcite crystals grow at the expense of aragonite Crystals grow Other minerals nucleate and grow Bubbles grow volume of bubbly magma expands rapidly... 

Hohling, H. J., Ashton, B. A., Roster, H. D. Quantitative electron microscope investigations of mineral nucleation in collagen. Cell. Tiss. Res. 148, 11 (1974)... 

KINETICS AT THE SOLID-WATER INTERFACE ADSORPTION, DISSOLUTION OF MINERALS, NUCLEATION, AND CRYSTAL GROWTH... 

Filmon et al. initiated calcium phosphate mineralization by immobilizing alkaline phosphatases (AlkP) on PHEMA [192], The authors also modified the neutral surface of PHEMA by carboxymethylation and further investigated the mineralization process in an in vitro assay that compared the effect of additional carboxylic acid groups and the effect of AlkP/PHEMA hybrid. In both systems, the formation of globular calcospherites could be observed. These findings confirm the assumption that molecules containing carboxylic residues act as mineralization nucleators [193]. 

In practice, both in industrial systems and in biological and pathological mineralization, nucleation is usually induced at much lower supersaturations by heterogeneous nuclei that lower the activation energy, i.e., AGhet < AG . These can be nonspecific impurities, which are always present in solution, or templates, which are specifically added with the purpose of producing a certain kind of precipitate. The number of particles formed by heterogeneous nucleation cannot exceed the number of seeds or impurity particles, which, in aqueous solutions, is estimated to be A 10 -10 particles per cubic centimeter. 

Lipid content In biological hard tissues, lipids have been reported to be mineral nucleators [24-26]. As is the case with proteoglycans, their content is rather easily established in Raman spectra through the integrated area of the characteristic band at 1298cm [27]. 

---