Study of Electron–Nuclear Interactions in Doped Calcium Phosphates by Various Pulsed EPR Spectroscopy Techniques

Abstract

Substituted calcium phosphates (CaPs) are vital materials for the treatment of bone diseases and repairing and replacement of defects in human hard tissues. In this paper, we present some applications of the rarely used pulsed electron paramagnetic resonance (EPR) and hyperfine interaction spectroscopy approaches [namely, electron spin-echo envelope modulation (ESEEM) and electron–electron double-resonance detected nuclear magnetic resonance (EDNMR)] to investigate synthetic CaPs (hydroxyapatite, tricalcium, and octacalcium phosphate) doped with various cations (Li+, Na+, Mn2+, Cu2+, Fe3+, and Ba2+). These resonance techniques provide reliable tools to obtain unique information about the presence and localization of impurity centers and values of hyperfine and quadrupole tensors. We show that revealed in CaPs by EPR techniques, radiation-induced stable nitrogen-containing species and carbonate radicals can serve as sensitive paramagnetic probes to follow CaPs’ structural changes caused by cation doping. The most pulsed EPR, ESEEM, and EDNMR spectra can be detected at room temperature, reducing the costs of the measurements and facilitating the usage of pulsed EPR techniques for CaP characterization.

Analysis of the Osseointegration Process of Dental Implants by Electron Paramagnetic Resonance: An In Vivo Study

“…This may be related to various atomic environments, the level of deformation in the crystal lattice, or the degree of delocalization with respect to the paramagnetic center [ 24 , 25 ]. The differences in the parameters of the spin Hamiltonian are useful for subsequent analysis of the crystal structures of samples doped with various cations [ 30 , 31 ].…”

“…Thus, these spectroscopic parameters are extremely important for revealing the nature (origin) and studying the behavior of free radicals (paramagnetic centers) in various types of samples. All these spectroscopic values will be discussed in the text of the article [ 31 ]. For a detailed description and quantum mechanical interpretation of the method, see articles [ 30 , 31 ].…”

“…All these spectroscopic values will be discussed in the text of the article [ 31 ]. For a detailed description and quantum mechanical interpretation of the method, see articles [ 30 , 31 ].…”

“…The high sensitivity and spectral resolution, along with the enhanced stability, of current EPR techniques has opened up new opportunities in the study of samples in the last ten years, such as in situ EPR imaging (EPRI) [ 29 ]. Traditional EPR can be used to control the impurity of samples or detect the presence of metal impurities [ 22 , 30 , 31 ]. The EPR method was successfully used to study the assimilation processes between tooth enamel and implant material (paramagnetic native and carbonate radicals with different natures localized in various bone tissue subsystems) and revealed the suitability of the present approach [ 32 ].…”

“…Since the EPR method is susceptible to detecting free radicals and has been proven to be useful in the study of biological objects, the authors of this work suggest the applicability of the EPR approach to the investigation of osseointegration processes. The research was prompted by the following hypotheses: first, that the processes of assimilation (osseointegration) between living bone tissue and the implant’s surface leads to the formation of stable free radicals (spin labels for the EPR technique [ 30 , 31 ]) under biochemical processes; and second, and most importantly, that the EPR method can track the dynamics of the formation of paramagnetic centers depending on the type of implant surface (morphology) and implantation system. Therefore, the purpose of this work is to describe the osseointegration (assimilation) processes and biochemical dynamics which take place during dental implantation using implants with different macro-microstructure surfaces at the level of stable free radicals by using the EPR method.…”