Fourier transform infrared spectroscopy of the solution-mediated conversion of amorphous calcium phosphate to hydroxyapatite: New correlations between X-ray diffraction and infrared data

Abstract

Fourier Transform infrared spectroscopic analysis of maturing, poorly crystalline hydroxyapatite (HA) formed from the conversion of amorphous calcium phosphate (ACP) at constant pH or variable pH show only subtle changes in the v1, v3 phosphate absorption region (900 cm-1-1200 cm-1). This region is of interest because it can be detected by analysis of mineralized tissue sections using FT-IR microscopy. To evaluate the subtle spectral changes occurring during the maturation, second derivatives of the spectra were calculated. HA formed at constant pH showed little or no variation in the second derivative peak positions with bands occurring at 960 cm-1, 985 cm-1, 1030 cm-1, 1055 cm-1, 1075 cm-1, 1096 cm-1, 1116 cm-1, and 1145 cm-1. These bands can be assigned to molecular vibrations of the phosphate (PO4(3-)) moiety in an apatitic/stoichiometric environment of HA. In contrast, during the early stages of maturation of the HA formed at variable pH, second derivative peak positions occurring at 958 cm-1, 985 cm-1, 1020 cm-1, 1038 cm-1, 1112 cm-1, and 1127 cm-1 shifted in position with maturation, indicating that the environment of the phosphate species is changing as the crystals mature. Peaks at 1020 cm-1, 1038 cm-1, 1112 cm-1, and 1127 cm-1 were attributable to nonstoichiometry and/or the presence of acid phosphate-containing species. This concept was supported by the lower Ca:P molar ratios measured by chemical analysis of the synthetic material made at variable pH. Using the second derivative peak positions as initial input parameters, the v1, v3 phosphate region of the synthetic HAs prepared at constant pH were curve fit. X-ray diffraction patterns of these same materials were also curve fit to calculate the changes in crystallinty (size/perfection) in the c-axis 002 reflection as well as the 102, 210, 211, 112, 300, 202, and 301 planes. Linear regression analysis showed that the changes in the percent area of the underlying bands at 982 cm-1, 999 cm-1, 1030 cm-1, 1075 cm-1, 1096 cm-1, 1116 cm-1, and 1145 cm-1 were correlated with changes in crystallinity in one or more of the reflection planes. It is suggested that a combination of second-derivative and curve-fitting analysis of the v1, v3 phosphate contour allows the most reproducible evaluation of these spectra.

Novel poly(butylene succinate) nanocomposites containing strontium hydroxyapatite nanorods with enhanced osteoconductivity for tissue engineering applications

“…PBSu is a typical semicrystalline polymer with two characteristic peaks at 2& 19.8 and 22.6° while the features of interest consists of a broad contour between 2& = 27-37° resulting from the 002 reflection of hydroxyapatite. New peaks are observed at 2& 32,4 36,45 and 46° after immersion in SBF which confirm that partially crystallized apatite layer formed on the surfaces of PBSu film as well as on its nanocomposites [33,37,38].…”

Infrared microspectroscopic imaging as a probing tool to fast distinguish chemical compositions in calcified deposits of prostatic calculi and calcific tendonitis

“…6). It has been reported that a peak near 1020 cm −1 is attributed to the ν 3 vibration of PO 4 3− in non-stoichiometric apatites but a peak at 1030 cm −1 is indicative of the ν 3 vibration of PO 4 3− in stoichiometric apatites [14,15]. Both peaks appeared in the second-derivative IR spectra of the calcified sample of tendon, suggesting the mineralization is still in progress.…”

“…Figure 5b shows several unique peaks at 1153, 1012, 989, 956 and 873 cm −1 in the IR spectrum of sample b. The IR peaks at 1153, 1012 and 989 cm −1 were assigned to the brushite (CaHPO 4 · 2H 2 O), which was believed to be a precursor of apatite [15,42]. The peaks at 956 and 873 cm −1 corresponded to the ν 1 PO 4 3− of HA and carbonate ions located in PO 4 3− sites of HA [14,15,19,42].…”

Characterising Bone Material Composition and Structure in the Ovariectomized (OVX) Rat Model of Osteoporosis

“…[18], carbonate-phosphate ratio (890 -850 cm -1 / 1200 -900 cm -1 ) [19], crystallinity (1030/1020 cm -1 ) [20,21], collagen maturity (1660/1690 cm -1 ) [22] and acid phosphate (1127/1096 cm -1 ) [23]. Furthermore, the spatial heterogeneity of each parameter was determined from the full width of half maximum (FWHM) of the Gaussian curve fitted to the pixel histogram of the measured area [24].…”