Carbonate apatites from aqueous and non-aqueous media studied by ESR, IR, and X-ray diffraction: effect of NH4+ ions on crystallographic parameters.

Carbonate-containing apatites prepared from aqueous and non-aqueous media were investigated by ESR, IR, and X-ray diffraction. A typical asymmetric signal at g = 2.0, which many workers have observed in irradiated calcified tissues, is interpreted in terms of CO3(3)- and Co-2 and the trapped electron center, The CO3(3)- and CO2- ions originated from the carbonate which substitutes for the phosphate ion in the apatite crystalline structure. From the comparison of the data between the carbonate apatites prepared under the presence of Na+ and NH4+ ions, it is suggested that NH4+ ions contribute to the crystallographic parameters, either by substituting in the structure or by suppressing the CO3 incorporation into the structure, or by both. The production of the CO2- radical ion could be accounted for based on the concept of hydrogen bond between the oxygen atom of CO2(3)- and the hydrogen atom of NH4+.