Preparation of amorphous calcium-magnesium phosphates at pH 7 and characterization by x-ray absorption and fourier transform infrared spectroscopy

Abstract

Amorphous calcium-magnesium phosphates were prepared by precipitation from moderately supersaturated aqueous solutions at pH 7. Chemical analysis of the samples by ion chromatography showed that up to about 50% of the phosphate ions were protonated, the proportion increasing with the magnesium to calcium ion activity ratio in the solution. When left it contact with the supernatant, the amorphous precipitates matured to form the crystalline calcium phosphate brushite (CaHPO 4.2H20). The amorphous phases were characterized by X-ray absorption spectroscopy and by Fourier transform infrared spectroscopy and their properties compared with those of a basic amorphous tricalcium phosphate precipitated at pH 10. The X-ray absorption spectra near the K edge of calcium were very similar for all samples but there were differences in the infrared spectra between the basic and the more acidic salts. In the phosphate stretching region, the main band of the more acidic materials occurred at higher wavenumber and was broader. Also there was a broad band of medium intensity at about 890 cm 1 whereas there was virtually no absorption band in this region in the spectrum of the amorphous tricalcium phosphate. The acidic amorphous calcium phosphates may be useful as model compounds in describing some complex biological calcium phosphates that form near neutral pH.

Short-Range Structure of Amorphous Calcium Hydrogen Phosphate

“…38,39 The relative intensity of this main absorption feature corresponds well with the Ca-O scattering intensity in the EXAFS spectra (i.e., higher white line intensity will result from more Ca-O coordination, see the SI, Figure S11, Table S2, and section S2, for details).These results indicate that the short-range environments of the Ca atoms in the basic ACP and ACHP are very similar in regard to their Ca-O local structure (Ca-P or Ca-Ca are not visible for basic ACP and ACHP due to their amorphous character). The similarity of Ca environments between basic ACP and ACHP is consistent with previous EXAFS measurements, 29,30,40 although the "acidic" ACP studied therein had a Ca/P atomic ratio significantly larger than 1. For In order to investigate the structure of the possible building unit of ACHP, assuming a Ca:P ratio of 1:1, we monitored the stability of various clusters in an aqueous environment using computer simulations (Experimental Section for selection rules and simulation details; SI, Figure S12, S13, Table S3, and section S3 for detailed discussion).…”

Zn-Li alloy after extrusion and drawing: Structural, mechanical characterization, and biodegradation in abdominal aorta of rat

“…4b), a narrow and high intensity PO 4 3− band is observed at 1050–1180 cm −1 , which is related to the asymmetric stretching of the ν3 group [38]. The absorption band in the range of 920–1000 cm −1 is characteristic of the symmetrical stretching of the ν1 group [39]. The CO 3 2− bands from the ν3 apatitic substitution were detected at 1390–1500 and 1540–1620 cm −1 [40, 41].…”

Long-term surveillance of zinc implant in murine artery: Surprisingly steady biocorrosion rate

“…Since the cross sections of Zn wire were mounted in epoxy resin, which also absorbs FT-IR signals, the spectrum of the epoxy was first collected as a blank control. In the FT-IR spectrum of Zn wire cross sections, the PO 4 3− bands were present at 936 cm −1 , 943 cm −1 and 1134 cm −1 , which relates to the symmetrical stretching of the ν1 group (920–1000 cm −1 ) [48] and asymmetric stretching of the ν3 group (1050–1180 cm −1 ) [49,50], respectively. The CO 3 2− bands from the ν2 substitution were detected at 845 cm −1 , and CO 3 2− bands from the ν3 apatitic substitution were detected at 1395 cm −1 , 1431 cm −1 , and 1565 cm −1 [51,52].…”