The infrared (IR) spectra of KBr pellet preparations of tetracycline (TC) complexes with hydroxyapatite (HA) indicated that the binding of the antibiotic to bone mineral can occur independently at each of two ligands. The shifts in the IR spectrum occur for the keto-enol ligand of rings B and C and for the tricarbonylmethane grouping of ring A. Analogs that lack one or the other of these groups are able to form complexes with HA in which the common portion resembles that of the parent molecule.

Hydroxyapatite is used as a model for studying radical formation in the mineral compartment of irradiated calcified tissues. Treating this material with 13C-enriched CO2 confirms that radiogenic long-lived radicals correspond to carbon centred species. It is shown, however, that these radicals are not located on the carbonate ions which substitute either the phosphate or the hydroxyl groups. The conditions which allow the formation and the trapping of these radicals are investigated (role of humidity, CO2 and temperature) and this paramagnetic species is identified as CO-2 adsorbed at the surface of apatite crystallites.

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Low temperature ashing by excited gas (LTA) causes crystallographic and paramagnetic alterations of the human bone and tooth enamel mineral. On the one hand, LTA induces variations of the alpha lattice parameter. These variations depend upon the nature of the gas used, but are little affected by its degree of excitation. Trapping of gas molecules in the crystal structure is demonstrated. On the other hand, LTA produces two preponderant paramagnetic centers in bone and enamel samples at 20 degrees C. Their inorganic origin clearly indicated. One of the two radicals has been identified as O3- (g1 = 2.002, g2 = 2.010, g3 = 2.016) and the other as (CO3-3 (parallel = 1.996, g = perpendicular 2.003). Variations of the alpha lattice parameter and trapping of paramagnetic gas species do not seem to be directly related.

The evolution of the mineral constituents of subcutaneous calcinosis induced in rats by topical calciphylaxis was studied by the method of quantitative chemical analysis, and after treatment with excited gases by electron spin resonance (ESR) analysis. Chemical data show that the genesis of the subcutaneous calcinosis does not significantly alter the concentration of Ca, P, F, CO3, Mg, and Fe in the mineral phase of the femoral bone of calciphylactic rats. In the calcinosis an important increase of the fluoride concentration is noticed in function of the time after challenging. There is also a high concentration of Mg2+ ions in the early stages of the experimental calcification. Iron injected for the challenging is continuously present in the calciphylactic tissue after this treatment. This suggests that subcutaneous calcinosis might be a means of fixing certain heavy metal ions. After treatment with excited gases, the proportions of the trapped CO33- and O3- radicals are of the same order of magnitude in calciphylactic tissue after 12 days and observations in bone mineral. These suggest that after 12 days the mineral of the calciphylactic tissue has a crystalline state close to that of bone.