X- and Q-band EPR of carbonate derived radicals in calcium apatites synthesized at high temperatures and heated tooth enamel

Abstract

The EPR spectra near g \ 2 of a few carbonated calcium apatites, synthesized at high temperatures are studied in X-and Q-band. Solid state reactions at high temperatures were used to prepare samples with carbonate substituting for OH~(A-type) and (B-type). In the present study the experience from previous X-band PO 4 3w ork on the same samples is combined with the higher resolution of Q-band experiments, to gain further insight into the composite nature of the spectra. X-Irradiation of carbonated calcium apatites gives rise to highly composite EPR spectra, due to the presence of di †erent paramagnetic centres. Except for A-type carbonated apatite, the contribution of several types of radicals dominate the spectra. The comparison CO 3 3b etween X-and Q-band results allows us to identify the di †erent types of (hydroxyl site, phosphate CO 3 3s ite, surface), together with a smaller component. Simulations of the experimental spectra support these CO 2 ãssignments. A-type carbonated apatite spectra are dominated by one or more contributions. In order CO 2 to elucidate the composite nature of the spectra, recent hydroxyapatite single crystal results are used to simulate the spectra, again in both frequency bands. Similar simulations of tooth enamel spectra and an evaluation of A-type carbonated apatite as a model system for tooth enamel are presented.

EPR study of radicals produced by gamma-irradiation in marine mollusc (Venussp.) fossils

“…The EPR signals at g x = 2.0030, g z = 2.0018 and g y = 1.9973 values can be attributed to the orthorhombicĊO − 2 free radical, which is often encountered in the spectra of natural carbonates especially of marine origin. The g y = 1.9973 component is characteristic of theĊO − 2 radical [44,45]. The more central isotropic signal at g iso = 2.0007 is attributed to the freely rotatingĊO − 2 free radical as it is reported in the literature [22,46].…”

Multi-frequency EPR study of radiation-induced radicals in tooth enamel

“…According to previous studies, the CO 3À 3 contributions would become more apparent after heating and at low microwave power [3,4]. The spectra from the unheated samples are dominated by CO À 2 lines, masking to a large extent the sharper CO 3À 3 lines.…”

“…In the past, several CO 3À 3 species have been isolated in synthetic apatite powders, with X-band [2] and Q-band EPR [3]. In total three different CO 3À 3 species have been observed in synthetic apatites and their g-values have been compared in Table I.…”