M. R. Gafurov

Pb3+ radiation defects in Ca9Pb(PO4)6(OH)2 hydroxyapatite nanoparticles studied by high-field (W-band) EPR and ENDOR

W-band pulsed EPR and ENDOR investigations of X-ray irradiated nanoparticles of synthetic hydroxyapatite Ca(9)Pb(PO(4))(6)(OH)(2) are performed. It is shown that in the investigated species lead ions probably replace the Ca(1) position in the hydroxyapatite structure.

Combination of EPR measurements and DFT calculations to study nitrate impurities in the carbonated nanohydroxyapatite.

We demonstrate the application of the combined experimental-computational approach for studying the anionic impurities in hydroxyapatite (HAp). Influence of the carbonation level (x) on the concentration of the NO3(2-) radicals in the HAp nanocrystals of Ca10-xNax(PO4)6-x(CO3)x(OH)2 with x in the range 0 < x < 2 and average sizes of 30 nm is investigated by different analytical methods including electron paramagnetic resonance (EPR). Stable NO3(2-) radicals are formed under X-ray irradiation of nano-HAp samples from NO3(-) ions incorporated in trace amounts during the wet synthesis process. Density functional theory (DFT) based calculations show energetic preference for the PO4 group substitution by NO3(-) ions. Comparison of the calculated and experimental spectroscopic parameters (g and hyperfine tensors) reveals that EPR detects the NO3(2-) radicals located in the positions of the PO4 group only. It is shown that with the increase in x, the carbonate ions substitute the NO3(2-)/NO3(-) ions. DFT calculations confirm that carbonate incorporation in HAp structure is energetically more favorable than the formation of the nitrate defect.

Nitrogen-containing species in the structure of the synthesized nano-hydroxyapatite

Synthesized by the wet chemical precipitation technique, hydroxyapatite (HAp) powders with the sizes of the crystallites of 20–50 nm and 1 μm were analyzed by different analytical methods. By means of electron paramagnetic resonance (EPR) it is shown that during the synthesis process nitrate anions from the reagents (byproducts) could incorporate into the HAp structure. The relaxation times and EPR parameters of the stable axially symmetric NO32− paramagnetic centers detected after X-ray irradiation are measured with high accuracy. Analyses of high-frequency (95 GHz) electron-nuclear double resonance spectra from 1H and 31P nuclei and ab initio density functional theory calculations allow suggesting that the paramagnetic centers and nitrate anions as the precursors of NO32− radicals preferably occupy PO43− site in the HAp structure.

Changes in mitochondrial functioning with electromagnetic radiation of ultra high frequency as revealed by electron paramagnetic resonance methods

Abstract Purpose: To study the effects of electromagnetic radiation (EMR) of ultra high frequency (UHF) in the doses equivalent to the maximal permitted energy load for the staffs of the radar stations on the biochemical processes that occur in the cell organelles. Materials and methods: Liver, cardiac and aorta tissues from the male rats exposed to non-thermal UHF EMR in pulsed and continuous modes were studied during 28 days after the irradiation by the electron paramagnetic resonance (EPR) methods including a spin trapping of superoxide radicals. Results: The qualitative and quantitative disturbances in electron transport chain (ETC) of mitochondria are registered. A formation of the iron-nitrosyl complexes of nitric oxide (NO) radicals with the iron-sulphide (FeS) proteins, the decreased activity of FeS-protein N2 of NADH-ubiquinone oxidoreductase complex and flavo-ubisemiquinone growth combined with the increased rates of superoxide production are obtained. Conclusions: (i) Abnormalities in the mitochondrial ETC of liver and aorta cells are more pronounced for animals radiated in a pulsed mode; (ii) the alterations in the functioning of the mitochondrial ETC cause increase of superoxide radicals generation rate in all samples, formation of cellular hypoxia, and intensification of the oxide-initiated metabolic changes; and (iii) electron paramagnetic resonance methods could be used to track the qualitative and quantitative changes in the mitochondrial ETC caused by the UHF EMR.

Stomach Cancer: Interconnection between the Redox State, Activity of MMP-2, MMP-9 and Stage of Tumor Growth

High levels of reactive oxygen (ROS) and nitrogen (RNS) species can lead to the destruction of extracellular matrix facilitating tumor progression. ROS can activate matrix metalloproteinases (MMP), damage DNA and RNA. Therefore, the levels of MMP, ROS and RNS can serve as additional prognostic markers and for the estimation of the effectiveness of tumor therapy. Concerning gastric cancer, the prognostic role of MMP, its connection with the cancer staging remains controversial and correlations between the activity of MMP with the ROS and RNS levels are insufficiently confirmed. Superoxide generation rates, nitric oxide (NO) levels, concentrations of active forms of matrix metalloproteinases MMP-2 and MMP-9 in tumor and adjacent tissues of patients with stomach cancer at different disease stages were measured by electron spin resonance (ESR) including spin-trapping and polyacrylamide gel zymography. It is shown that the activity of MMP-2 and MMP-9 in tumor tissue correlate with the superoxide radicals generation rate and NO levels (r = 0.48÷0.67, p < 0.05). The activity of MMP-2 and MMP-9 in tumor tissues and superoxide radical generation rates correlate positively with the stage of regional dissemination (r = 0.45 and 0.37, correspondingly, p < 0.05), but MMP-2 and MMP-9 activity inversely depends on distant metastatic degree of stomach cancer (r = 0.58; p < 0.05). Additionally, the feasibility of ESR to locally determine oxidative stress is demonstrated.

Study of the effects of hydroxyapatite nanocrystal codoping by pulsed electron paramagnetic resonance methods

The effect of codoping of hydroxyapatite (HAP) nanocrystals with average sizes of 35 ± 15 nm during “wet” synthesis by CO32− carbonate anions and Mn2+ cations on relaxation characteristics (for the times of electron spin–spin relaxation) of the NO32− nitrate radical anion has been studied. By the example of HAP, it has been demonstrated that the electron paramagnetic resonance (EPR) is an efficient method for studying anion–cation (co)doping of nanoscale particles. It has been shown experimentally and by quantummechanical calculations that simultaneous introduction of several ions can be energetically more favorable than their separate inclusion. Possible codoping models have been proposed, and their energy parameters have been calculated.

A study of hydroxyapatite nanocrystals by the multifrequency EPR and ENDOR spectroscopy methods

Specimens of powders of hydroxyapatite (Ca10(PO4)6(OH)2) with average crystallite sizes in the range of 20–50 nm synthesized by the wet precipitation method have been investigated by the multifrequency (9 and 94 GHz) electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) methods. In specimens subjected to X-ray irradiation at room temperature, EPR signals that are caused by nitrogen compounds have been observed. Numerical calculations performed in terms of the density functional theory show that the observed EPR signal is caused by the occurrence of paramagnetic centers, the structure of which is NO32− and which replace the positions of PO43− in the hydroxyapatite structure.

Superhyperfine structure of the EPR spectra of impurity ions in the LiYF4 : Nd3+ system doped by 143Nd isotopes

Results of measuring the EPR spectra in the LiYF4: Nd3+ system doped by 143Nd isotopes with the nuclear spin I = 7/2 have been presented. We have succeeded to observe superhyperfine splitting of the EPR spectra of the samples under investigation at the orientation of the magnetic field B along the symmetry axis c of the crystal and at B ⊥ c on the lines corresponding to both even neodymium isotopes and 143Nd.

Perspective of zero-field ODMR to study nano-biological systems

This work presents an introduction, a short literature review as well as our recent optical and high field magnetic resonance experiments with regard to the applications of nitrogen paramagnetic defects in (nano)diamonds for biomedical related research. The perspectives of combination of optical and magnetic resonance (high field electron paramagnetic resonance) spectroscopic methods for the sensitive spatially resolved screening of electrical and magnetic gradients in biological tissues on the nanoscale level are discussed.

Investigation of atherosclerotic plaque by high-frequency EPR

We present a comparative study of samples of aorta walls from male patients with atherosclerosis and hydroxyapatite powders with the average size of crystallites of 30 nm synthesized by the wet precipitation technique by using 94 GHz pulsed EPR. Origin of the observed paramagnetic centers is discussed. Supported by the electron microscopy and microanalysis, it is shown that EPR spectra from the calcified biological tissues correlates with those obtained in inorganic hydroxyapatites. The hypothesis about the important role of (nano)hydroxyapatite in formation of the mineral deposits and atherosclerotic plaque instability is further sustained.