Carbonate apatite

What determines the differenee in 5 C between eollagen and bone carbonate apatite (bioapatite) for animals with different diets or digestive systems ... 

Murphy, W.L. and Mooney, D.J. (2002) Bioinspired growth of crystalline carbonate apatite on biodegradable polymer substrata. Journal of the American Chemical Society, 124, 1910-1917. 

Inorganic Fractions Diagenetic or Secondary Carbonate Apatite... 

Bone and teeth in mammals and bony fishes all rely on calcium phosphates in the form of hydroxyapatite [Ca5(P04)30H]2, usually associated with around 5% carbonate (and referred to as carbonated apatite). The bones of the endoskeleton and the dentin and enamel of teeth have a high mineral content of carbonated apatite, and represent an extraordinary variety of structures with physical and mechanical properties exquisitely adapted to their particular function in the tissue where they are produced. We begin by discussing the formation of bone and then examine the biomineralization process leading to the hardest mineralized tissue known, the enamel of mammalian teeth. 

Apatites are complexes of cationic Ca " matched by HP04, COa ", OH , or F as anions. Depending on the counter-ion, apatite can occur in the forms carbonate apatite Caio(P04)6C03, as hydroxyapatite Caio(P04)e (0H)2, or fluoroapatite Caio(P04)6F2. In addition, alkaline earth carbonates also occur in bone. In adults, more than 1 kg calcium is stored in bone. 

Xu, G. Aksay, I. A. Groves, J. T. Continuous Crystalline Carbonate Apatite Thin Films. 

Fig. 3. Splitted view of atoms along the c axis of the hexagonal structure showing the two possible fluoride ion locations. In stoichiometric fluorapatite, fluoride ions locate in the equilateral triangle formed by Ca(ll) ions. In type B carbonate apatite, the replacement of P04 ions by ions creates an oxygen atom vacancy which may be occupied by a second kind of fluoride ion (adapted from Ref. [4]). (See Colour Plate Section at the end of this book.)...

The hydrolysis of Cap2 in solutions containing phosphates and carbonate ions results in the formation of fluor-, fluor-hydroxy- or fluor-carbonate-apatites. Fluor and fluor-hydroxy- apatites can also be formed by the hydrolysis of dicalcium phosphate (anhydrous or dihydrate), DCPAor DCPD, respectively, in solutions containing fluoride ions [121] or from the hydrolysis of any other calcium phosphate salt. 

R. M. Wilson, J.C. Elliott, S.E.P. Dowker, R.l. Smith, Rietveld structure refinement of precipitated carbonate apatite using neutron diffraction data. Biomaterials 25 (2004) 2205-2213. 

M. Vignoles, G. Bonel, Sur la localisation des ions fluorures dans les carbonate apatites de type B, C.R. Acad. Sci. (Paris) 287 (1978) 321-324. 

A. Barry, H. Zhuang, A.A. Baig, W.l. Higuchi, Effect of fluoride pretreatment on the solibility of synthetic carbonated apatite, Calcif. Tissue Int. 72 (2003) 236-242. 

The apatite group minerals are the most abundant phosphorus-bearing minerals on Earth, typically as accessory minerals in basic to acidic igneous rocks, pegmatites, hydrothermal veins and cavities, carbonates, contact and regionally metamorphosed rocks, and sedimentary rocks (Deer et al. 1996). The principal members of the apatite group include fluoroapa-tite (Ca5(P04)3F), chloroapatite (Ca5(P04)3Cl), hydroxyapatite, and carbonate apatite (Ca5(P04, C03)3(F,0H)) (Deer et al. 1996). 

Of the four prominent pure end-member phosphate species of the apatite group only dahllite (space group C63/m) is a common biomineral28. This carbonate apatite is a distinct variety of apatite rather than a mixture of CaC03 and hydroxyapatite. Expressed as oxides, the mineral content of bovine cortical bone (dry fat-free material) has the following chemical composition112 ... 

The nature of mineral phases present in bone, dentin, enamel and other phosphatic tissues, and their mode of formation have been subjects of lively discussions among health scientists and crystallographers. Bioscientists most commonly accept the viewpoint that the inorganic phase of bones or teeth is principally hydroxyapatite, Caio(P04)6(OH)2, and deviation in Ca/P ratio from common hydroxyapatite (Ca/P = 1.667) observed in mineralized tissues is explained by the presence of amorphous phosphates. In contrast, many crystallographers favor the idea of carbonate apatite, i.e. dahllite, as the major crystalline phase in biophosphates and they doubt the existence of amorphous phases. The topic has been reviewed14,15,22,28, 37,44,47,348-358) no common consent has yet been reached. In the following an attempt is made to at least coordinate the controversial findings. 

The principal mineral species is an apatite which is best defined as an isomorphous mixture consisting of two endmembers hydroxyapatite and carbonate apatite, i.e. Ca10(P04)6(OH)2 and (Na, Ca)io(P04, C03)6(0H)2. Because of the isomorphous nature of the material the proportions of C03 that substitute for P04 most certainly vary from one unit cell of bone mineral to another and no uniform composition should actually exist. The extent to which carbonate groups proxy for phosphate groups in the crystal lattice is in the order of a few to a maximal of 10% by weight. 

A topic of considerable controversy is the question of carbonate incorporation in the apatite lattice since carbonate apatite does not precipitate from aqueous solutions28, 395 398 Carbonate apatites (phosphorites) forming in marine environments134 are considered metasomatic alteration products of calcium carbonate, and as a result carbonate content decreases and phosphate content increases with time399. In biophosphates, the situation appears to be just reversed in that carbonate content increases with bone maturation and it was argued that the similarity between bone mineral and naturally occuring C03-apatite ends before it begins 397. ... 

In invertebrates, collagen is uncalcified, whereas in vertebrates it occurs in the form of soft and hard tissue. Remains of the earliest vertebrates — bony armour — are found in sediments of the Ordovician (ca. 500 million years). At about that time, conodonts appeared in the stratigraphic column mineralogically they are carbonate apatite. Conodonts are small tooth-shaped fossils 0.2 to 3 mm in size whose origin is in doubt they are most likely remains of some unknown chordata that became extinct in Triassic time516. ... 

McConnell, D. Crystal chemistry of bone mineral Hydrated carbonate apatites. Amer. Mineralog. 55, 1659-1669 (1970). 

Newesely, H. Conditions for the existence of octacalcium phosphate, withlockit and carbonate apatite. A contribution to the crystal chemistry of biological hard substances. Dtsch. zahnarztl. Ztschr. 20, 754-766 (1965). 

Carbonate band assignment has been more difficult in Raman spectra than in the infrared [15] because of near overlap of the major carbonate Vi mode at 1070cm-1 with a component of phosphate V3 at 1076cm-1 in carbonated apatites [16]. These bands have earlier been reported as coincident [17] or have been assumed to be a single broad carbonate band [18]. Most investigators have used the ratio of the carbonate Vi band/phosphate Vi band as a measure of the carbonate/phosphate ratio. It is likely that in many cases this error is small, but for lightly carbonated mineral, typically freshly precipitated mineral, the error may be important. Remeasurement or reinterpretation of some Raman spectroscopic data may be needed. 

The methods of synthesis of fluorapatite have been widely dis cussed (J ). It is for example possible to obtain fluorapatite by substituting the hydroxyl ion for the fluoride ion, either in a-queous solution at room temperature, or through a solid state reaction at 800°C. It can also be prepared by the action of 6-tricalcium phosphate on calcium fluoride at about 800°C. Its solubility and thermal stability have already been established. While much is known about fluorapatite, many questions still exist concerning the mechanism of their formation, their composition and the structure of some of them. Two of these problems are dealt with here. First, we discuss the formation mechanism of fluorapatite by a solid state reaction between calcium fluoride and apa-titic tricalcium phosphate. Then we present the preparation and the structure of a carbonated apatite rich in fluoride ions. 

The X-band E.S.R. results (6) obtained with the carbonated apatites support the proposed model. Indeed, in X-irradiated samples we have observed the resonance of a defect in which an electron is trapped by an oxygen vacancy. The number of such defects is greater in the compounds prepared from an aqueous medium poor in F ions than in the apatites prepared from an aqueous medium rich in fluoride ions. Moreover there exists a close correlation between the spectral intensity and the number of oxygen vacancies calculated from the model we propose. 

Figure 14 43Ca 3QMAS spectrum of 43Ca-enriched carbonated apatite powder sample, to which bovine osteocalcin was physically adsorbed. (Reprinted with permission from Ref. 186. 2010 American Chemical Society.)... 

Protein comprises about 10% by weight of the organic matrix. The proteins are phosphorylated, and are enriched in aspartic acid, glutamic acid and glycine. Some of the proteins and the chitin are intimately associated. The carbonated apatite layer contains much more protein than the magnetite layer [22]. To date, nothing is known about the individual proteins within the framework. 

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