Calcium phosphate transformation

Mahamid J, Aichmayer B, Shimoni E, Ziblat R, Li C, Siegel S et al (2010) Mapping amorphous calcium phosphate transformation into crystalline mineral liom the eell to the bone in zebrafish fin rays. Pioc Natl Acad Sci 107(14) 6316-6321... 

Fluorhydroxyapatite solid solutions can be prepared by the sol-gel method [134,135]. Cheng et al. reported the control of fluoride content in fluorhydroxyapatite solid solutions by the amounts of triethanolamine (N(CH2CH20H)3) and trifluoroacetic acid (CF3COOH) in the mixed ethanol solutions of Ca(N03)2 and P0(CH2CH20H)x(0H)3 x with a Ca/P ratio of 1.67 [134]. After evaporation of the mixed ethanol solution at 150°C on a hot plate, the powder obtained, comprising a homogeneous mixture of calcium nitrate crystallites and amorphous calcium phosphates, is then heated at 500 or 900°C for 1 h to be transformed into the pure apatitic phase. 

When calcium phosphate is precipitated from aqueous solutions of high supersaturation and pH values above 7, the solid phase appearing initially is an ACP with the formula Ca9(P04)61U u2 - If this amorphous precipitate is allowed to remain in contact with the solution, it transforms to crystalline HA through a process of dissolution, nucleation and crystal growth77, unless stabilized in some manner. 

Brecevic, Lj., Fiiredi-Milhofer, H. Precipitation of calcium phosphates from electrolyte solutions. II. The formation and transformation of the precipitates. Calc. Tiss. Res. 10, 82 (1972)... 

Termine, J. D., Peckauskas, R. A., Posner, A. S. Calcium phosphate in vitro. II. Effects of environment of amorphous-crystalline transformation. Arch. Biochem, Biophys. 140, 318 (1970)... 

Eanes, E. D., Termine, J. D., Nylen, M. U. An electron microscope study of the formation of amorphous calcium phosphate and its transformation to crystalline apatite. Calc. Tiss. Res. 12, 144 (1973)... 

SS) West, V. C. Observations on phase transformation of a precipitated calcium phosphate. Calc. Tiss. Res. 7, 212-219 (1971). 

Transfection, DNA uptake in eukaryotic systems, often is more problematic then bacterial transformation the mode of DNA uptake is poorly understood and efficiency is much lower. In yeast, cell walls can be digested with degradative enzymes to yield fragile protoplasts, which are then able to take up DNA. Cell walls are resynthesized after removal of the degrading enzymes. Mammalian cells take up DNA after precipitation onto their surface with calcium phosphate [Fugene 6 (Roche) Lipofectin (Life Technologies) Effectene (Qiagen)]. Electroporation is often more efficient for transfection in eukaryotic cell systems, especially in yeasts. 

The ratio of DOTMA to DNA is critical but efficiency in immediate expression assays and in transformation is reported to be from 6-80-fold greater than with calcium phosphate or DEAE dextran (Feigner et al., 1987). Furthermore, the reagent can be used to transfect some cells which are refractory to other methods. 

Another means of assessing the nature of the medium/solution from which the mineral forms is to analyse the very first mineral deposits precipitated. These must reflect the chemistry of the medium in which they formed. In most chiton teeth a poorly crystalline ferrihydrite is the first mineral deposited and it subsequently transforms into magnetite. In the anterior layer, amorphous calcium phosphate is first deposited, and only after several weeks does it begin... 

The phosphates of lime which occur in nature or are produced during the course of manufacture of phosphorus compounds are salts of orthophosphoric acid. The hydrogen is replaced by calcium in stages giving successively mono-, di- and tri-calcium phosphate. Of these the mono-calcium salt alone is freely soluble. The solids deposited on evaporation, or obtained by double decomposition, are generally mixtures of the di-, tri- or more basic compounds, but pure crystalline forms have been prepared, especially of the more acid phosphates. The more basic phosphates are very sparingly soluble, and the solubilities are not definite. The solids are not in equilibrium with solutions of their own composition, but are in process of transformation which is so slow that equilibrium is not attained in most operations. 

Eanes, E.D., Gillessen, I.H., and Posner, A.S. Mechanism of conversion of non-crystalline calcium phosphates to crystalline hydroxyapatite, p 373-375, "Proc. Int. Cong, on Crystal Growth, Boston, 1966. Pergamon Press, Oxford, 1967. Termine, J.D., Peckauskas, R.A., and Posner, A.S. Calcium phosphate formation in vitro. II. Effect of environment on amorphous crystalline transformation. Arch. Biochem. Bio-phys. 140. 318-325 (1970). 

Various tiny structures, so-called organelles, are embedded in the cytoplasm where they make numerous cell functions possible, (s. fig. 2.9) (s. tab. 2.1) The enzyme-rich mitochondria have an outer and an inner membrane, with the latter forming creases (cristae). The outer membrane is relatively permeable for small molecules. However, the inner membrane (which surrounds the matrix) must use specific transport proteins to enable protons, calcium, phosphate and so on to pass. Energy-rich substrates are transformed into ATP in the mitochondria. The enzymes which are responsible for fatty-acid degradation and the citric-acid cycle can be found in the matrix. The inner membrane also contains the enzymes of the so-called respiratory cycle. An enormous number of energy-providing reactions and metabolic processes take effect at this site. They have a round-to-oval shape with a diameter of about 1 im. There are 1,400-2,200 mitochondria per liver cell (18-22% of the liver cell volume). They generally lie in... 

Rey G, Shimizu M, GoUins B, Glimcher MJ (1990) Resolution-enhanced Fourier transform infrared spectroscopy study of the environment of phosphate ion in the early deposits of a solid phase of calcium phosphate in bone and enamel and their evolution with age. 1. Investigations in the V4-PO domain. Galcif Tissue Int 46 384-394... 

Other reports (27-29) have focused on the role of citric acid, as a source of carboxylate anions, during precipitation of calcium phosphates from electrolyte solutions. It has been found that citrate anions inhibit the ciystal growth of calcium phosphates and hinder their transformation into hydroxyapatites. This was attributed to the adsorption of citrate anions into the crystals and the displacement of an equivalent amount of phosphate anions. Interestingly, Rhee and Tanaka (30) found that the presence of a collagen membrane in the medium changed the behavior of citrate anions from being an inhibitor to becoming a promoter of calcification, provided that the molar ratios of calcium to citric acid were between 2 and 12. 

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