A DFT, X- and W-band EPR and ENDOR Study of Nitrogen-Centered Species in (Nano)Hydroxyapatite

Influence of Al on the Structure and in Vitro Behavior of Hydroxyapatite Nanopowders

“…The magnitudes of the superhyperfine splittings are given in Tables 3 and 4. They coincide with the data of ref 24, corresponding to the localization of the nitrogen-centered radical in the B position. It can be seen that the introduction of aluminum impurities does not affect 31 P ENDOR.…”

“…T 1e was extracted from an inversion-recovery experiment by applying the π − T delay − π/2 − τ − π pulse sequence, where both the π pulse duration and τ are fixed while T delay is varied. For Mims ENDOR, 24 the pulse sequence π/2 − τ − π/2 − T − π/2 with an additional RF pulse π RF = 18 μs (optimized for 1 H nuclei) inserted between the second and third microwave π/2 pulses was applied. The RF frequency in this setup could be swept in the range of 1−200 MHz.…”

“…The EPR spectra of the samples are described by the spin Hamiltonian of axial symmetry for S = 1/2 and I = 1. A detailed description of the EPR spectra of nitrogen-centered radicals with calculations in the framework of DFT models is given in ref 24. Figure 9 shows the corresponding spectra simulations for HA and 20Al-HA in both X-and W-bands with the parameters given in Table 2.…”

“…The nitrate molecule substituted the PO 4 position (B-type) as it was detected to be more experimentally relevant than the substitution of the OH − ion. 24 Comparing a number of positional combinations, it was argued that the remote location of NO 3 − was more energetically favorable than its positioning in the proximity of Al 3+ . This could be due to the larger polarity of the P−O bond than the N−O bond, which results in more favorable interactions of aluminum with the orthophosphate ion than with the nitrate ion.…”

Phonon Spectrum in Hydroxyapatite: Calculations and EPR Study at Low Temperatures

“…2 shows the ESE detected EPR spectrum of the NO 3 2radiation induced radicals due to the hyperfine interaction between the stable nitrogencontaining paramagnetic center with electronic spin with S = ½ and one nitrogen nuclear spin with I = 1 for 14 N isotope. From the previous EPR data analysis it was concluded that NO 3 2radiation induced radical substitutes PO 4 3position in the HAp structure while the carbonate ions could also replace OH group [15][16][17][18]. The T 1e measurements were done in the magnetic field B 0 = 343 mT (see Fig.…”