Spectra hydroxyapatite

Another example is LIBS application for real-time identification of carious teeth (Samek et al. 2003). In the dental practice, usually more healthy tissue is removed than ultimately necessary. Carious and healthy tooth material can be identified through the decrease of matrix elements Ca and P in hydroxyapatite and/or the increase of non-matrix elements, typically Li, Sr, Ba, Na, Mg, Zn and C, using pattern recognition algorithms. A fiber-based LIBS assembly was successfully used for this task. As for the case of phosphate ores evaluation, the efforts aimed at normalizing the spectrum collection conditions and procedures, so that the spectra are sufficiently reproducible for precise quantitative... 

Mg contents (such as the studied Mg-substituted hydroxyapatites, with up to lOmol.% Mg with respect to the total cationic concentration), the authors reported a Mg MAS NMR spectrum containing a complex line-shape. This was tentatively attributed to the existence of several local environments around Mg sites, leading to a distribution of quadrupole parameters. DFT calculations (supported by H, and Ca NMR and other experimental results) yielded Mg NMR parameters (Cq, /q and 5iso) that differed depending on the t)rpe of Ca site substituted by Mg. The Cq values were particularly sensitive to the details of the local Mg environment in the substituted hydroxyapatites. Even with the observed preference for Mg substitution into Ca(II) sites, small deviations in Mg—O bond lengths could cause large Cq variations, which explains the complex and featureless lineshape observed in the Mg NMR spectrum. 

Raman spectroscopy is well suited for examining calcified tissues such as bones and teeth owing to its ability to probe both the inorganic and organic constituents of the tissue. The frequency and band shape of the symmetric and asymmetric phosphate stretching vibrations provide critical information on the crystallinity and orientation of the hydroxyapatite matrix. The analysis of a Raman spectrum of dental enamel provides features that are highly characteristic of the health and integrity of the tissue. 

The approach adopted for the interpretation of the spectra of poorly crystalline calcium phosphates was to take the shell model of the crystalline phase having the greatest chemical similarity and progressively simplify and refine the model while maintaining a good fit to the observed spectrum. For the amorphous calcium phosphates, however, it was found that virtually identical shell models resulted from simplification and refinement of either the hydroxyapatite or brushite shell models to give the structure depicted in Fig. 18. 

Crystalline Phosphate Studies. On the basis of the results with triethyl phosphate, a series of calcium phosphates was examined by infrared spectrophotometry. Pertinent properties of these materials are summarized in Table II, and their spectral characteristics are shown in Table III. None of the synthetic hydroxyapatites [Caio(P04)e(OH)2] had the stoichiometric Ca/P ratio of 1.667, although they showed the apatite lattice structure. A typical infrared transmission spectrum (between 1500 and 700 cm.-1) of a dry powder synthetic hydroxyapatite is shown in Figure 1. 

Table IV. Effect of Adsorbed Molecules upon the Infrared Spectrum of Synthetic Hydroxyapatites...

Figure 2.23 shows the diffraction spectrum of a powder sample of calcium phosphate after subtracting background. With assistance of a computer, we can identify the peak positions in the spectrum and search for a possible match between the spectrum and a PDF data file. Additional chemical information is often used to help in the search process. For example, this specimen contents Ca, P and O. The computer quickly searches for a compound containing Ca, P and O. It finds a match between the diffraction spectrum of a sample with data for hydroxyapatite (Figure 2.24). There are two important parameters in a standard data file shown in Figure 2.24 the position of diffraction (20) and relative intensities of peaks (j ), or int-f in the PDF. I is the peak intensity with the maximum value in a spectrum. The highest int-f value is 999 which should be read as 0.999 in the relative intensity. The PDF may also list the corresponding d-spacing of peaks, which are the true crystal properties.

Figure 2.25 shows a nearly perfect match between the pattern and diffraction data of hydroxyapatite. The powder sample shows 35 peak matches in the 20 range of 10-60°. Generally, the relative intensities of peaks also match well with the standard. For example, the highest intensity is at the peak of 20 = 31.77° and the second highest peak at 20 = 32.90° in the acquired spectrum. Both of their 20 values and relative intensities match those in the PDF for hydroxyapatite. The relative intensities of the peaks, however, do not exactly match all those in the PDF. The matches for lower intensity peaks between the spectrum and the standard file are relatively poorer, even though a sample of fine powder was examined. 

Left ESEEM spectrum of a solution containing triphosphate and vanadyl ions in the ratio 3 1, pH = 5, c(VO +) = 0.7mM, recorded at the nij = — V2 EPR transition and v- are the Zeeman frequencies for and H, respectively. The doublets at 5.3 and 6.7 MHz (superhyperfine coupling constants 1-1.5 MHz) are indicative of direct bonding of phosphate to VO, as represented by the proposed structure (inset).The presence of water/hydroxide in the coordination sphere of vanadium is inferred from the respective HYSCORE spectrum. Reproduced from S. A. Dikanov et at, J. Am. Chem. Soc. 124, 2969-2978. Copyright (2002), with permission from the American Chemical Society. Right section of the structure of hydroxyapatite, with two phosphorus sites arbitrarily replaced by vanadium (full circles). The drawing of the apatite structure was provided by Barbara Albert, Technical University of Darmstadt, Germany. 

Fig. 10.34 shows the INS spectrum of ox femur as the organic component is progressively removed [83]. Fig. 10.34a is very similar to that of the protein Staphylococcal nuclease. Fig 10.32, and emphasises one of the problems of working in this field because proteins are largely made of the same monomers (amino acids), the INS spectra of very different proteins tend to look very similar. Removal of the fat results in little change in the spectrum, Fig. 10.34b. It can be seen that elimination of the protein is highly effective, Fig. 10.34c the C-H stretching modes just below 3000 cm" and the C-H deformation modes at 1200-1500 cm have both disappeared. There is a weak, broad peak at 630 cm and its overtone near 1300 cm. For comparison, the INS spectrum of a highly crystalline reference hydroxyapatite is shown in Fig. 10.34d. The frequency match of the of the residual bone peak and that of the hydroxyapatite is exact, the width of the peak is attributed to heterogeneous broadening. The spectrum demonstrates that hydroxyl groups are still present in bone.

After plasma spraying, the IR spectrum of hydroxyapatite shows distinct changes (Table 7.1). Besides the expected loss of OH (see also Figures 7.8 and 6.16) and the associated weakening of the intensity of the band at 3571 cm-1 as well as the disappearance of the librational OH mode at 632 cm-1, the v4 band at... 

Figure 7.6 FUR spectrum of a hydroxyapatite coating deposited by electrophoresis (Aves et a ., 2007). The four principal vibrations of the P04 tetrahedron are visible at about 500cm-1 (v2), 600cm-1 (v4), 950cm-1 (v,) and 1040 and 1070cm-1 (v3). The OH stretching and librational vibrations are visible at 3575 and 630 cm-1, respectively.

Figure 7.7 (a) Laser-Raman spectrum of a plasma sprayed hydroxyapatite coating showing the four principal vibrational modes of the P043- tetrahedron, (b) The v-, Raman mode deconvoluted by a... 

Figure 7.13 H-MAS NMR spectrum of as-sprayed hydroxyapatite (Hartmann ef a ., 2001). The inset shows the spectrum of a completely ordered, highly crystalline hydroxyapatite (Hartmann ef a/., 2000). L highly...

The features of the 31P-M AS NMR spectrum of plasma-sprayed hydroxyapatite are even more complex and hence, open to discussion. Figure 7.14, inset shows the single band position A at 2.3 0.1 ppm of the P043- tetrahedra in well-ordered,... 

Figure 7.14 31P-MAS NMR spectrum of as- strongly distorted P043 environment with-sprayed hydroxyapatite (Hartmann et al out neighbouring OH (C) distorted P043 ...

Figure 7.15 2D-1H/31P-CP-HETCOR NMR spectrum of a plasma-sprayed hydroxyapatite coating (Tran, 2004).

Figure 7.16 2D-1 H/31 P-CP-HETCOR NMR spectrum (a) and a Lorentzian fit of the cross-section of the HETCOR spectrum at the proton frequency of band L (b) of a plasma-sprayed hydroxyapatite coating incubated in r-SBF for 12 weeks (Heimann, 2007). For details see text.

Fig. 19.13. Infrared absorption spectrum of hydroxyapatite before and after the reaction with dry carbon dioxide at 1000°C, bromoform mull. (Elliott, 1965.)...

Stability of hydroxyapatite phase depends on the partial pressure of the water in the atmosphere, so, in an environment with no presence of water, by addition of sufficient amount of energy, HAp will turn into more stable calcium phosphates in the waterless environment. After thermally treating the sample in vacuum, there is an absorption band detected at 948 cm-i in the FTIR spectrum already at 600 C. It ap>p)ears in the result of [PO4] group fluctuations and usually points onto TCP phase, however the literary sources mention that the absorption band at this wave length could also be characteristic to oxyapatite phase. In the result of thermal treatment, in vacuum at 1300 °C, HAp phase has completely decomposed and absorption bands, characteristic to TCP and TTCP phases, are visible in the FTIR spectrum (overlapping... 

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