Resolution-enhanced fourier transform infrared spectroscopy study of the environment of phosphate ions in the early deposits of a solid phase of calcium-phosphate in bone and enamel, and their evolution with age. I: Investigations in thev 4 PO4 domain

Abstract

In order to investigate the possible existence in biological and poorly crystalline synthetic apatites of local atomic organizations different from that of apatite, resolution-enhanced, Fourier transform infrared spectroscopy studies were carried out on chicken bone, pig enamel, and poorly crystalline synthetic apatites containing carbonate and HPO4(2-) groups. The spectra obtained were compared to those of synthetic well crystallized apatites (stoichiometric hydroxyapatite, HPO4(2-)-containing apatite, type B carbonate apatite) and nonapatitic calcium phosphates which have been suggested as precursors of the apatitic phase [octacalcium phosphate (OCP), brushite, and beta tricalcium phosphate and whitlockite]. The spectra of bone and enamel, as well as poorly crystalline, synthetic apatite in the upsilon 4 PO4 domain, exhibit, in addition to the three apatitic bands, three absorption bands that were shown to be independent of the organic matrix. Two low-wave number bands at 520-530 and 540-550 cm-1 are assigned to HPO4(2-). Reference to known calcium phosphates shows that bands in this domain also exist in HPO4(2-)-containing apatite, brushite, and OCP. However, the lack of specific absorption bands prevents a clear identification of these HPO4(2-) environments. The third absorption band (610-615 cm-1) is not related to HPO4(2-) or OH- ions. It appears to be due to a labile PO4(3-) environment which could not be identified with any phosphate environment existing in our reference samples, and thus seems specific of poorly crystalline apatites. Correlation of the variations in band intensities show that 610-615 cm-1 band is related to an absorption band at 560 cm-1 superimposed on an apatite band. All the nonapatitic phosphate environments were shown to decrease during aging of enamel, bone, and synthetic apatites. Moreover, EDTA etching show that the labile PO4(3-) environment exhibited a heterogeneous distribution in the insoluble precipitate.

Apatite Deposition on Serum Protein-Adsorbed Polystyrene Surfaces under Body Fluid Conditions

“…The former of the newly appeared peak (1150-900 cm -1 ) was assignable to the stretching vibration (n 3 ) of the phosphate (PO 4 3-) groups and the latter (650-500 cm -1 ) represented the bending vibration (n 4 ) of the phosphate (PO 4 3-) groups [16]. In the case of standard HAp samples having stoichiometric chemical composition and relatively high crystallinity, both of these two peaks split into a number of distinct peaks (data not shown), same as the case that reported in literatures [16][17][18]. The broad shape of these peaks indicated that the obtained HAp deposits had low crystallinity or other crystal phase of calcium phosphates co-existed.…”

Design of graded biomimetic osteochondral composite scaffolds

“…In addition, the broad band centered between 550 and 560 cm -1 , assigned to acid phosphate (HPO 4 2-) in the mineral lattice, was much more intense in Mg doped HA nucleated on Collagen. These peculiarities of MgHA/Coll can be similarly observed in the FTIR spectrum of young bone; while they tend to disappear in mature bone and in highly crystalline synthetic apatite [28][29][30]. Correlation was noted between the fractional intensity of ~1050 cm -1 band related to PO 4 3-group and the crystal size of the apatite: a reduction of the apatitic crystal size induced an increase of the percentage area of this component [31,32].…”

Apatite Biominerals

“…Another specificity of biological apatites, which was more recently established, is the presence of hydrogen phosphate (HPO 4 2´) ions in PO 4 3´s ites [21][22][23]. These two types of bivalent ions substituting for PO 4 3´( type B CO 3 2´a nd HPO 4 2´) have been shown to correspond to the formation of calcium deficient apatites, the chemical formulas of which have been the subject of several works, essentially based on the composition of model minerals proposed by mineralogists or synthetic analogues.…”

“…More recently, these models, which are based on well-crystallized apatites, were re-examined due to the discovery, using mostly spectroscopic techniques (Fourier transform infrared (FTIR), Raman and solid-state nuclear magnetic resonance (NMR) spectroscopies), of the existence of specific spectral lines in the spectra of biological nanocrystalline apatites which do not appear for well-crystallized apatites and which have been designated as "non-apatitic environments" of the mineral ions [22,23,27,28]. These "non-apatitic" phosphate and carbonate environments have been shown to appear more clearly in the ν 4 PO 4 and ν 2 CO 3 domains of FTIR spectra.…”