Biomineral precursor

Navrotsky, A. (2004) Energetic clues to pathways to biomineralization precursors, clusters, and nanoparticles. Proceedings of the National Academy of Sciences of the USA, 101, 12096-12101. 

The detection of a peroxodiferric intermediate in the ferritin ferroxidase reaction establishes the ferritin ferroxidase site as being very similar to the sites in the 02-activating (/x-carboxylato)diiron enzymes. However, in ferritins, the peroxodiferric intermediate forms diferric oxo or hydroxo precursors, which are transferred to biomineralization sites with release of hydrogen peroxide. 

In biomineralization, ACP always refers to the disordered phase of calcium orthophosphate. Because ACP has been considered as a possible precursor of bone minerals in vertebrates, it serves as an important model compound for the study of biominerals. The P MAS spectrum of ACP contains a single broad peak at about 3 ppm.31 The 31P CSA of ACP is intermediate between those of HAp and protonated phosphates. On the basis of low temperature measurements, it has been suggested that ACP does not contain HP042 groups undergoing rapid reorientation.109 The 31P CSA of the dried ACP sample (vacuum dried at 400 °C) is very similar to that of ACP, but the 31P 1H CP efficiency is dramatically reduced for the dried sample. It indicates that most of the orthophosphate groups in ACP are not protonated.109... 

As a close relative to the brome mosaic virus the cowpea chlorotic mottle vims (CCMV) possesses an outer diameter of 28 nm, is assembled from 180 subunits that create an icosahedral type structure, and contains an RNA core. " Another similarity is the cationic interior surface of the viral capsid which is formed from subunits with highly basic N-termini (6 positively charged arginine and 3 lysine residues) that project into the cavity and stabilize the RNA core. However as a potential biomineralization template, the electrostatic environment of the virion cavity precludes any cationic metal precursors and thus limits its applicability for nanoparticle synthesis. 

The synthesis of molecular precursors responsible for tailored nucle-ation and growth is a key feature in the chemical control of biomineralization. Here we highlight recent studies using simplified model systems that aim to identify aspects of solution chemistry important in (1) silica polymerization and aggregation and (2) the morphological design of calcite crystals. 

An obvious case where organic matrices can not possibly act as templates for oriented growth is in the formation of amorphous biominerals. Since the number of amorphous precursors observed in biomineralization has increased markedly in recent years (Table 1.1) (the difficulty in isolating these phases as precursors may be due to their rapid transformation to crystalline phases in vivo) there appears to be some evidence that the control of mineral orientation and structure by atomic relationships between matrix and crystal is not a major role of organic frameworks. 

Keywords Biomineralization Calcium carbonate Stearic acid Thin film Amorphous precursor Monolayer Interface... 

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