Multi-frequency electron paramagnetic resonance study of irradiated human finger phalanxes

Electron paramagnetic resonance (EPR) is often used in dosimetry using biological samples such as teeth and bones. It is generally assumed that the radicals, formed after irradiation, are similar in both tissues as the mineral part of bone and tooth is carbonated hydroxyapatite. However, there is a lack of experimental evidence to support this assumption. The aim of the present study was to contribute to that field by studying powder and block samples of human finger phalanxes that were irradiated and analyzed by multi-frequency EPR. The results obtained from bones are different from the ones obtained in enamel by several respects: the ordering of the apatite crystallites is much smaller in bone, complicating the assignment of the observed CO2- radicals to a specific location, and one type of CO3(3-) radical was only found in enamel. Moreover, a major difference was found in the non-CO2- and non-CO3(3-) signals. The elucidation of the nature of these native signals (in bone and tooth enamel) still represents a big challenge.     

Development of nickel-doped lithium formate as potential EPR dosimeter for low dose determination

EPR dosimetry employing L-alpha-alanine has been in vogue during the past few years, due to its tissue equivalence and linear dose response. However, L-alpha-alanine dosimetry has been improved during the past years, the sensitivity of this material is still too low for clinical applications. Polycrystalline lithium formate doped with NiCl2 was therefore examined for radiation response in the dose range of clinical interest (<5 Gy) using CW EPR and pulse EPR techniques. At equal and moderate settings of microwave power and modulation amplitude lithium formate doped with 1.6 wt% of NiCl2 was almost four times more sensitive compared to L-alpha-alanine, which is the most common EPR dosimeter standard. It was shown that the nickel-doped lithium formate has an excellent radiation response with a low limit of the measurable dose, and a linear dose response in the range 1-5 Gy. The relaxation and power saturation studies showed that high microwave power can be applied during measurements to improve the sensitivity of this material as an EPR dosimeter. These results show that lithium formate doped with Ni(II) exhibits promising properties required for further development of an EPR dosimeter in the dose range typical for clinical dosimetry.     

EPR evaluation of absorbed doses in γ-irradiated animal bone tissues

The accumulation of CO ₂ ^- radicals in γ-irradiated porcine, chicken, bovine, walleye pollack, and navaga bone tissues and chicken eggshells was studied by EPR spectroscopy for the purpose of detecting irradiated food and evaluating the dose absorbed during its radiation processing. It was found that, in the dose range 0–10 kGy, the concentration of radicals is a linear function of dose, and the variation coefficient of the radiationchemical yield of radicals is no higher than 30% for bone tissues from various biological species. The applicability of the additive dose method to the EPR dosimetry of irradiated beef was examined. A linear regression model used in the additive dose method was found to give overestimated results, as compared with an exponential fitting model.     

Solid state "self-calibrated" EPR-dosimeters-advantageous and shortcomings

EPR dosimetry method with alpha-alanine as radiation sensitive material (RSM) is widely used in high dose dosimetry laboratories. However, it is not suitable for routine industrial applications mainly because of difficult EPR measurement procedure. In order to simplify quantitative EPR dosimetry measurements Yordanov and Gancheva developed so-called "self-calibrated" (sc) dosimeters consists of RSM (alpha-alanine, sugar, other ones), Mn2+/MgO as internal EPR intensity standard (IES) and a binder. The aim of this work was to check dosimetric properties of two experimental batches of sc EPR dosimeters with alpha-alanine and sugar as RSM, Mn2+/MgO as IES and paraffin as a binder. The percentage content of the components was 60, 5 and 35% (w/w), respectively. It was established that the investigated alanine sc-dosimeters are about two times more sensitive than the sugar ones. The dose-response coefficient, K(dr) of sc-alanine dosimeters was stable in all investigated dose range from 1 to 23 kGy. The K(dr)-value of sugar sc-dosimeters decreased with the dose what was in a contradiction to the results pointed to the high stability of radiation generated sugar radicals. The observed effect arose probably from the special chemical procedure used for the sc-sugar dosimeters production. The results confirmed an expectation that the position of sc dosimeter in the cavity is not important factor for accurate dose evaluation. It allows to read-out dosimetric signals in shorter time, with lower uncertainty and on less sophisticate EPR-spectrometers than that commonly used till now. The main shortcomings of sc dosimeters are: (a) the limitation of RSM suitable for sc dosimeters to these ones having strictly linear signal to dose characteristic; (b) necessity to assure very good homogeneity of dosimeter material; and (c) the cost of IES present in the amount of some percent in each sc dosimeter.     

Some recent multi-frequency electron paramagnetic resonance results on systems relevant for dosimetry and dating

Electron Paramagnetic Resonance (EPR) applications like e.g. EPR dosimetry and dating, are usually performed at X-band frequencies because of practical reasons (cost, sample size, etc.). However, it is increasingly recognized that the radiation-induced EPR signals are strongly composite, what might affect dose/age estimates. A few recent examples from both the dosimetry and dating field, illustrating the problems, will be presented. The involved spectra are mainly due to carbonate-derived radicals (CO2-, CO3(3-), etc.). Measurements at higher microwave frequencies are often recommended to improve the insight into the spectra and/or the practical signal quantification. Recent results at Q- and W-band frequencies will show that a multi-frequency approach indeed opens many interesting perspectives in this field but also that each frequency may have specific (dis)advantages depending on the EPR probe and application involved. The discussion will concern carbonate-containing apatite single crystals, shells, modern and fossil tooth enamel.     

Fluoride adsorption enhancement of Calcined-Kaolin/Hydroxyapatite composite

The use of waste or natural resources is an interesting approach to preparing adsorbent materials. Most adsorption materials are powder-based, making them impractical for a variety of applications. In this work, the natural kaolin clay and hydroxyapatite synthesized from biogenic waste were studied as defluoridation materials. The point of zero charge (pH_PZC), the fluoride adsorption capability and the adsorption isotherm of calcined kaolin and mixed calcined kaolin/hydroxyapatite in both powdered and moulded forms were investigated. The hardness of the moulded (post-formed) samples was tested before and after in immersion in a fluoride solution. The maximum hardness was 15.8 kilo-pounds for the post-formed calcined kaolin sample. Sample hardness values slightly decreased after immersion in a fluoride solution due to the formation of micro-cracks. Most samples presented high pH_PZC values, implying that these materials are suitable for the capture of fluoride anions. The adsorption properties varied with the ratio of calcined kaolin to hydroxyapatite. These properties for post-formed samples were different from those in powdered form. Post-formed samples showed higher fluoride adsorption. The maximum fluoride adsorption capacity and efficiency of the post-formed samples (calcined kaolin) at pH 3 were 1.74 F^? mg/g and 87%, respectively. The sorption of fluoride of hydroxyapatite and mixed calcined kaolin/hydroxyapatite powders was found to have the form of the Langmuir isotherm, which indicates a monolayer adsorption on the adsorbent surface. Isotherms of calcined kaolin powder, post-formed calcined kaolin and mixed calcined kaolin/hydroxyapatite samples followed the Freundlich isotherm, which indicates multilayer adsorption on a heterogenous adsorbent surface.     

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.     

Magnetic and spectroscopic investigation of partially reduced vanadium pentoxides. I. α-CuxV2O5

The electron paramagnetic resonance (EPR) and magnetic susceptibility of both powdered and crystalline α-Cu_xV₂O₅ near the compositional limit have been studied as a function of temperature. The EPR data indicate that the paramagnetic species are isolated V⁴⁺ centers in a nearly axially symmetric ligand field. It is demonstrated that reasonably precise EPR parameters can be derived from powdered spectra. The narrowness of the EPR line suggests that the spectra are motionally narrowed via thermally activated hopping of the paramagnetic electron of V⁴⁺. Expressions are derived for the temperature-dependent magnetic moments of the octahedral ²T_2g term under the combined perturbation of spin-orbit coupling and an axially symmetric ligand field, and the susceptibility data are interpreted in terms of this model. It is found that the sixfold degenerate ²T_2g level is split into three levels with the lowest and highest levels possessing a magnetic moment and the intermediate level having no moment. This model is also consistent with the g-tensor and can account for the temperature dependence of the EPR linewidth.     

Epr studies of copper(II) and oxovanadium(IV) dithiophosphate complexes in the solid state

A single crystal of Cu(dtp)₂ and numerous powdered copper(II) and oxovanadium(IV) dithiophosphate complexes magnetically diluted in the corresponding Ni and In complexes have been prepared and studied by EPR. It was shown that the values of A(³¹P) for all complexes are isotropic.Some assumptions about the origin of superhyperfine splitting in the EPR spectra of the complexes are discussed.     

Adsorption and conformational change of myoglobin on biomimetic hydroxyapatite nanocrystals functionalized with alendronate

The chemical conjugation of bisphosphonates (BPs), specifically alendronate, to hydroxyapatite could be an effective means to impart to it fine-tuned bioactivity. Horse heart myoglobin (Mb), a well-characterized protein, has been adsorbed onto biomimetic hydroxyapatite nanocrystals (nHA) and onto the nHA/alendronate conjugate powdered samples. The obtained materials have potential use in bone implantation and as prospective drug-delivery devices. The kinetic absorption of Mb onto nHA is dramatically affected by its functionalization with alendronate. The covering of the nHA surface by alendronate inhibits the adsorption of myoglobin. The adsorption mechanisms of the protein were studied by spectroscopic techniques (UV-vis and surface-enhanced Raman spectroscopy). The results indicate that the protein changes conformation upon adsorption on the inorganic substrate. In particular, the interaction with nHA alters the coordination state of the iron in the heme through the formation of a hexacoordinated low-spin Mb heme, possibly involving the distal histidine. Instead, the covering of the nHA surface by alendronate does not adsorb the protein but preserves the coordination state of the heme moiety. This study could be of significance either in the field of biomaterials science, in particular, to fine tune a bone-specific drug delivery device and to test nHA as a new support for heterogeneous catalysis, improving the understating of enzyme immobilization.     

EPR spectroscopy of tooth enamel: the tooth radicals and the microcrystal alignment

The paramagnetic radicals induced by radiation in dental enamel are very important because they can be related to the crystalline structure of hydroxyapatite. The R-value, that is, the ratio of the amplitude of the lines of the EPR signal due to radiation, is a measure of the degree of microcrystal alignment in human tooth enamel. The aim of this study is to underline the importance of a correct evaluation of the R-value, by using the current method to increase reproducibility in EPR spectroscopy of tooth enamel. Data with and without correction show a significant difference and, consequently, they give rise to a different valuation of microcrystal alignment.     

原位沉析法制备磁性氧化铁羟基磷灰石/壳聚糖棒材

首先通过化学沉淀法制备磁性氧化铁羟基磷灰石(Fe3O4/HA),然后以壳聚糖(CS)为基体,利用原位沉析法将Fe3O4/HA与CS复合,制得磁性Fe3O4/HA/CS复合材料.经XRD、粒径分布和PPMS测试,结果表明了Fe3O4/HA复合物的生成.系统研究了磁性Fe3O4/HA/CS棒材力学性能的影响因素,最终确定Fe3O4与HA质量比为3∶17,磁性Fe3O4/HA与CS质量比为9∶91时,棒材的力学性能最优,弯曲强度可达到87.0 MPa,弯曲模量1.57 GPa.     

Electron paramagnetic resonance, NIR studies on zoisite, clinozoisite and chrom-zoisite minerals

A zoisite group of mineral samples from different localities are used in the present study. An EPR study on powdered samples confirms the presence of Mn(II), Fe(III) and Cr(III) in the minerals. NIR studies confirm the presence of these ions in the minerals.     

Valorization of Bone Waste of Saudi Arabia by Synthesizing Hydroxyapatite

At present, hydroxyapatite is being frequently used for diverse biomedical applications as it possesses excellent biocompatibility, osteoconductivity, and non-immunogenic characteristics. The aim of the present work was to recycle bone waste for synthesis of hydroxyapatite nanoparticles to be used as bone extracellular matrix. For this reason, we for the first time utilized bio-waste of cow bones of Albaha city. The residual bones were utilized for the extraction of natural bone precursor hydroxyapatite. A facile scientific technique has been used to synthesize hydroxyapatite nanoparticles through calcinations of wasted cow bones without further supplementation of chemicals/compounds. The obtained hydroxyapatite powder was ascertained using physicochemical techniques such as XRD, SEM, FTIR, and EDX. These analyses clearly show that hydroxyapatite from native cow bone wastes is biologically and physicochemically comparable to standard hydroxyapatite, commonly used for biomedical functions. The cell viability and proliferation over the prepared hydroxyapatite was confirmed with CCk-8 colorimetric assay. The morphology of the cells growing over the nano-hydroxyapatite shows that natural hydroxyapatite promotes cellular attachment and proliferation. Hence, the as-prepared nano-hydroxyapatite can be considered as cost-effective source of bone precursor hydroxyapatite for bone tissue engineering. Taking into account the projected demand for reliable bone implants, the present research work suggested using environment friendly methods to convert waste of Albaha city into nano-hydroxyapatite scaffolds. Therefore, besides being an initial step towards accomplishment of projected demands of bone implants in Saudi Arabia, our study will also help in reducing the environmental burden by recycling of bone wastes of Albaha city.     

Estimation of the sources of pelagic sediments from the South Pacific Ocean to the Antarctic Ocean

Gamma-irradiated L-α-alanine used in EPR-coupled dosimetry has a complex EPR spectrum at room temperature. Changing the temperature or other conditions of the irradiated samples leads to varied EPR spectrum, i.e., some components disappear and/or new ones are formed. We used both molecular mechanics (MM+) and semiempirical (AM1) methods to perform a theoretical investigation of the seven radical species that have been experimentally detected. We established their order of priority in the given simulation conditions (at 0 K, in vacuo). The formation stages advanced for these long-lived radical species were characterized by a theoretical determination of the reaction enthalpies.     

Physical and chemical aspects of a new porous hydroxyapatite

The new engineered porous hydroxyapatite (EP-HA) described in this paper seems to be suitable as a bone substitute. Its physico-chemical characteristics and morphology are similar to those of natural bone. Study of its histological behaviour in humans revealed bone formation within and around the porous hydroxyapatite that is markedly resorbed.     

Electron paramagnetic resonance and optical absorption spectral studies on chalcocite

A chalcocite mineral sample of Shaha, Congo is used in the present study. An electron paramagnetic resonance (EPR) study on powdered sample confirms the presence of Mn(II), Fe(III) and Cu(II). Optical absorption spectrum indicates that Fe(III) impurity is present in octahedral structure whereas Cu(II) is present in rhombically distorted octahedral environment. Mid-infrared results are due to water and sulphate fundamentals.     

Apparent solubility distributions of hydroxyapatite and enamel apatite

Samples of human dental enamel and hydroxyapatite were equilibrated at 5 mg/40 ml for 9 days at 37 degrees C with acetate buffers adjusted to a range of saturations with respect to hydroxyapatite. Sigmoidal apparent solubility distributions, in which the fraction dissolved was plotted against--log(ion activity product for hydroxyapatite) (pIHA), were constructed. About 10% of the hydroxyapatite and 14% of the enamel was very soluble, dissolving even at pIHA 55. The apparent solubility distributions for both solids were invariant with pH (4.5, 5.0, 5.5), within experimental error, showing that solubility was controlled by a phase with the stoichiometry of hydroxyapatite, probably in the form of a surface layer or complex on the crystals, in agreement with other studies on carbonate-apatites and bone mineral. The pIHA at 50% dissolution was employed as an average value. The pIHA (50%) values for pooled data (58.76 for enamel and 60.17 for hydroxyapatite) were lower than the respective pIHA previously measured by conventional equilibration techniques. However, the average pIHA measured for enamel was higher than that obtained by the same technique in another study, possibly because of differences in specimen preparation and equilibration time. The possible implications of the findings for understanding the process of dental caries are discussed.     

Electron paramagnetic resonance and optical absorption spectral studies on covellite mineral

A covellite mineral sample from Coquimbo region, Chile is used in the present study. An electron paramagnetic resonance (EPR) study on powdered sample confirms the presence of Mn(II) and Cu(II). Optical absorption spectrum indicates that Fe(II) and Cu(II) impurities are present in octahedral structure. Bands in the near-infrared from 7,000 to 5,000 cm(-1) result from the overtones of the first fundamental OH-stretching modes.     

EPR of Radiation-Induced Nitrogen Centers in Hydroxyapatite: New Approaches to the Study of Electron-Nuclear Interactions

Russian Journal of Coordination Chemistry - Radiation-induced impurity nitrogen centers ( $${\text{NO}}_{3}^{{2 - }}$$ ) in nanosized powders of synthetic hydroxyapatite are studied by pulse EPR...