Radiation-Induced Stable Radicals in Calcium Phosphates: Results of Multifrequency EPR, EDNMR, ESEEM, and ENDOR Studies

Abstract

This article presents the results of a study of radiation-induced defects in various synthetic calcium phosphate (CP) powder materials (hydroxyapatite—HA and octacalcium phosphate—OCP) by electron paramagnetic resonance (EPR) spectroscopy at the X, Q, and W-bands (9, 34, 95 GHz for the microwave frequencies, respectively). Currently, CP materials are widely used in orthopedics and dentistry owing to their high biocompatibility and physico-chemical similarity with human hard tissue. It is shown that in addition to the classical EPR techniques, other experimental approaches such as ELDOR-detected NMR (EDNMR), electron spin echo envelope modulation (ESEEM), and electron-nuclear double resonance (ENDOR) can be used to analyze the electron–nuclear interactions of CP powders. We demonstrated that the value and angular dependence of the quadrupole interaction for 14N nuclei of a nitrate radical can be determined by the EDNMR method at room temperature. The ESEEM technique has allowed for a rapid analysis of the nuclear environment and estimation of the structural positions of radiation-induced centers in various crystal matrices. ENDOR spectra can provide information about the distribution of the nitrate radicals in the OCP structure.

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

“…PCs are atoms, ions, or free radicals (the case for our article) that have their magnetic moment due to the spin (S) or orbital (L) contribution. The main condition of EPR absorption is determined by the expression [ 30 ]: where h is Planck’s constant, ν is the microwave frequency, β is the Boron magneton, g is the spectroscopic splitting factor, and B 0 is the value of the induction of the magnetic field. The magnetic field is necessary to cause the quantization of PCs along the B 0 force lines.…”

“…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.…”

Using DFT to Calculate the Parameters of the Crystal Field in Mn2+ Doped Hydroxyapatite Crystals

“…Electron paramagnetic resonance (EPR) is known as one of the analytical, nondestructive methods for determining the type and concentration of paramagnetic impurities in liquids and solids including HAp [16]. To calculate the concentration, the integral signal Crystals 2021, 11, 1050 2 of 7 intensity should be known [17].…”