A local intercomparison study of ESR dosimetry using tooth enamel

Using electron spin resonance (ESR), tooth enamel is a possible dosimeter in case of a radiation accident. To check the present status of this technique, we conducted a local intercomparison study. We irradiated several samples of tooth enamel with a⁶⁰Co source. Three institutes in Belgium and The Netherlands recorded the ESR signal of the samples. The results of the measurements and the methods used are compared. It is concluded that ESR on tooth enamel can be a useful technique in accident dosimetry, provided further research is done.     

The effect of heating on background and radiation-induced EPR signals in tooth enamel

The presented study is a continuation of our work performed during participation in the Third International Intercomparison on EPR Tooth Dosimetry. During the process of samples preparation, all 22 enamel samples were accidentally exposed for about 30 min to 150 degrees C temperature. This considerably affected shape of their EPR spectra mainly due to substantial increase in the background signal, which approximately doubled its contribution to the spectra. These effects were studied closer under controlled conditions of the delivered dose and heating temperature using another enamel samples. The observed changes in the spectra shape partially faded within a few days after heating. The heating resulted also in a noticeable generation of a spectral component similar to the dosimetric signal induced in enamel by radiation. The temperature-induced dosimetric component in EPR spectra of the heated samples remained constant for 32 days. Deviations in calculated contributions of the dosimetric signal into total EPR spectra of irradiated sample varied from -12 to +15% of its initial contribution in the non-heated enamel, depending on type of the background spectrum applied in numerical processing of the spectra.     

Structural features of human tooth tissues affected by high dose of external ionizing radiation after nuclear catastrophe of Chernobyl plant

The application of micro-Raman spectroscopy is discussed for the analysis of structural features of human tooth tissues affected by high doses of external ionizing radiation (0.5–1.7 Gy) after the nuclear plant catastrophe in Chernobyl in 1986. The results have shown significant changes in the mineral matrix of dental enamel that lead to the decrease of tooth enamel hardness. Destruction of the collagen chain of the organic matrix has been observed for dentin and cementum.     

Radioactive labeling in the study of abrasion of hard tooth tissue

Labeling the surface of hard tooth tissue samples by the nuclear recoil effect in radioactive decay was applied to study abrasion caused by abrasive components of tooth-pastes.²²²Rn and its short-lived decay products were implanted into the surface in vacuum. For this purpose irradiation was applied to sample placed very close to thin²²⁶Ra source. Measuring the activity before and after abrasion was used to evaluate abrasion in the system toothbrush — various suspensions of the tooth-pastes — hard tooth tissue (enamel or dentine) in a specially designed device, dentoabrasionmeter VUS 2.     

Mechanical Motion of Chiral Azobenzene Crystals with Twisting upon Photoirradiation

The photomechanical motion of chiral crystals of trans‐azobenzene derivatives with an (S)‐ and (R)‐phenylethylamide group was investigated and compared with a racemic crystal. Changes in the UV/Vis absorption spectra of the powdered crystals before and after UV irradiation were measured by using an optical waveguide spectrometer, showing that the lifetime of the cis‐to‐trans thermal back‐isomerization of the chiral crystals was faster than that of the racemic crystals. Upon UV irradiation, a long plate‐like chiral microcrystal bent away from the light source with a twisting motion. A square‐like chiral microcrystal curled toward the light with some twisting. Reversible bending of a rod‐like chiral microcrystal was repeatable over twenty‐five cycles. In contrast, bending of a plate‐like racemic microcrystal was small. A possible mechanism for the bending and twisting motion was discussed based on the optimized cis conformer determined by using calculations, showing that the bending motion with twisting is caused by elongation along the b axis and shrinkage along the a axis.     

Multiblock copolymers composed of poly(butylene succinate) and poly(1,2-propylene succinate): Effect of molar ratio of diisocyanate to polyester-diols on crosslink densities, thermal properties, mechanical properties and biodegradability

In order to study the relationship between structure and properties, multiblock copolymers composed of poly(butylene succinate) (PBS) and poly (1,2-propylene succinate) (PPSu) have been synthesized by chain-extension at various molar ratios of hexamethylene diisocyanate (HDI) to polyester-diols, which have been abbreviated as R-values in this paper. Molecular weights of soluble fractions, gel fractions and crosslink densities have been determined. Thermal properties, mechanical properties and biodegradability have been studied and correlated with R-values. Crystallization of copolymers becomes difficult with increasing R-value. Tensile strength, flexural strength and flexural modulus tend to increase with increasing R-value up to 1.2, and vary little when R-value increases from 1.2 to 1.3, then decrease with further increase in R-value. Impact strength achieves a maximum value at R-value of 1.3. Biodegradation rate reaches a minimum value when R-value is 1.1. Biodegradation has been studied systematically by attenuated total reflectance Fourier transform infrared (ATR-FTIR), ¹H NMR and SEM.     

Relationship between microhardness and fluorine contents on tooth enamel determined by PIGE analysis

The remineralization effect of fluoride has been measured by surface microhardness on tooth enamel. The purpose of this study was to investigate the relationship between microhardness and fluorine concentration on tooth enamel. Twelve sound bovine enamel specimens were prepared and immersed in 0.05% NaF solution for 1, 3, 6, 24 and 36 hours, respectively. The concentration of fluorine in specimens were measured by PIGE analysis and surface microhardness of each specimen was measured by surface microhardness tester. Fluorine concentration was increased by immersing time. There was no change in microhardness of each specimen by fluorine content. The results of this study suggest that there was no relationship between the fluorine concentration and surface microhardness in sound tooth enamel. PIGE analysis can be used effectively to assess the remineralization effect of fluorine content in tooth enamel.     

Superactive and stereospecific catalysts. III. Definitive identification of active sites by electron paramagnetic resonance

Superactive Ziegler–Natta catalysts have been prepared from a soluble MgCl₂·2-ethyl hexanol adduct in the presence of organic esters through reactions with TiCl₄ and activated with AlEt₃/phenyltriethoxy-silane. Electron paramagnetic spectra (EPR) were used to elucidate the nature and amount of those Ti⁺³ ions not bridged to another Ti⁺³ ion; the chlorine bridged Ti⁺³ ions are EPR silent. The EPR spectra were attributed to two rhombic Ti⁺³ sites with principal values for the g-tensors (1.967, 1.949, 1.915; and 1.979, 1.935, 1.887). The total amount of the EPR species, obtained by double integration of the EPR spectra, is in close agreement with the concentration of isospecific catalytic sites determined by radiotagging. This suggests that the nonspecific sites are EPR silent. When o-phthalic ester was present during the catalyst synthesis, there appears an EPR signal at the free electron g-value. This signal was attributed to a Ti⁺³ phthalate species with resonance stabilization and spin delocalization; it is absent in the catalysts made in the presence of monoesters such as ethyl benzoate. The effects of monomer, O₂, H₂O, and I₂ on the EPR spectra were investigated. The changes in the EPR spectral intensity and the total Ti⁺³ ions, the latter determined by redox titrations during a polymerization or catalyst aging, are described. The results were extensively compared with those observed for supported Ziegler–Natta catalyst prepared with crystalline MgCl₂.     

Some Physico-Technical Aspects of the New Generation of Self-Calibrated Alanine/EPR Dosimeter and Results from the International Intercomparison trial

Some physico-technical parameters of the self-calibrated alanine/EPR dosimeters are described. Principally, this new type of solid state/EPR dosimeter contains radiation sensitive diamagnetic material (in the present case, alanine), some quantity of EPR active, but radiation insensitive, substance (for example, Mn²⁺/MgO) playing roles of an internal standard and a binding material. Thus with this dosimeter the EPR spectra of alanine and the internal standard Mn²⁺ are recorded simultaneously and the dose response is represented as a ratio of EPR signal intensities of alanine versus Mn²⁺ as a function of absorbed dose. As a result, the data of the present study have shown that there is practically no interference of the dosimeter EPR response (expressed as the ratio I _alanine/I _Mn) from the way of preparation (homogeneity), behavior after irradiation (fading of EPR signals with time, influence of different meteorological conditions) as well as specific spectrometer setting conditions. These dosimeters show satisfactory reproducibility of preparation and reading as well as stability on keeping. Thus, fulfilling the described physico-technical data of this type of dosimeters, the reproducibility of the readings is significantly improved particularly when intercomparison among different laboratories is performed. This conclusion is confirmed by independent studies of the described self-calibrated alanine/EPR dosimeters in several laboratories in Europe. Results of which are also reported.     

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.     

Determination of strontium in human tooth enamel by flameless atomic-absorption spectrometry

The determination of strontium in human tooth enamel by flameless atomic-absorption spectrometry was found to be subject to interference from the calcium/phosphate matrix of the enamel. The standard addition method was used to compensate for this interference. Hydrochloric acid and nitric acid did not affect the strontium absorption, but perchloric acid caused a significant reduction in the absorption. The sensitivity of the flameless atomic-absorption enabled 1-mg samples of enamel to be analysed. Hence, the proposed method can be used to determine the distribution of strontium through the tooth. An average recovery of 100.4% for amounts of strontium added to enamel showed that the proposed method was reliable.     

Non-oxo vanadium(IV) complexes with acetylacetone 4-R-benzoylhydrazones

Vanadium(IV) complexes of formula [V(acRbh)₂] with acetylacetone 4-R-benzoylhydrazones (H₂acRbh, R=H, Cl, OMe and NO₂) have been synthesized and characterized by elemental analysis, IR, UV–vis, and electron paramagnetic resonance (EPR) spectroscopic measurements. All the complexes are one-electron paramagnetic and show very similar axial EPR spectra in frozen solution. In dimethylformamide, the complexes display a V(IV)?V(III) redox couple in the E _1/2 range ?0.16–?0.25?V (versus Ag/AgCl). Single crystal X-ray structures of [V(acHbh)₂] and [V(acClbh)₂] have been determined. The metal center in each complex is in a distorted trigonal prismatic N₂O₄ coordination sphere assembled by the enolate-O, the imine-N, and the iminolate-O donor acRbh^2?.     

Selfcalibrated alanine/EPR dosimeters: A new generation of solid state/EPR dosimeters

Alanine/EPR dosimeters are well established as secondary, reference dosimeters for high-energy radiation. However, there are various sources of uncertainty in the evaluation of absorbed dose. This arises primarily from the necessity to calibrate each EPR spectrometer and each batch of dosimeters before their use. In order to overcome this disadvantage, a new generation alanine/EPR dosimeter has been developed, and its possibilities as a radiation detector are reported. Principally, it is a mixture of alanine, some quantity of EPR active substance, and a binding material. The EPR active substance, acting as an internal EPR standard, is chosen to have EPR parameters which are independent of the irradiation dose. The simultaneous recording of the spectra of both the sample and the standard under the same experimental conditions and the estimation of the ratioI _alanine/I _Mn as a function of the absorbed dose strongly reduces the uncertainties. The response of these dosimeters for⁶⁰Co γ-radiation exhibits excellent linearity and reproducibility in the range of absorbed dose, 10²−5·10⁴ Gy.     

Crystal and molecular structure ofN,N′,N″-tritosyl-5,8,14,17,23,26-hexamethyl-2,11,20-triaza[3.3.3]-paracyclophane 1 : 1 dichloromethane clathrate

The crystal and molecular structure of the title compound, C₅₁H₅₇N₃O₆S₃·CH₂Cl₂ has been determined by single crystal X-ray analysis and refined to anR-value of 0.069 for 1032 reflections. The crystal is trigonal, space groupR3, witha = 21.255(7),c = 11.317(4), andZ = 3. One molecule of dichloromethane used as solvent is enclathrated in the crystal lattice.     

Comparative identification of irradiated herbs by the methods of electron paramagnetic resonance and thermoluminescence

Non irradiated and γ-irradiated dry herbs savoury (Savoury), wild thyme (Thymus serpollorium) and marjoram (Origanum) with absorbed dose of 8 kGy have been investigated by the methods of elecrtron paramagnetic resonance (EPR) and thermoluminescence (TL). Non-irradiated herbs exhibit only one weak siglet EPR signal whereas in irradiated samples its intensity increase and in addition two satelite lines are recorded. This triplet EPR spectrum is attributed to cellulose free radical generated by irradiation. It has been found that upon keeping the samples under the normal stock conditions the life-time of the cellulose free radical in the examined samples is ∼60–80 days. Thus the conclusion has been made that the presence of the EPR signal of cellulose free radical is unambiguous indication that the sample under study has been irradiated but its absence can not be considered as the opposite evidence. In the case when EPR signal was absent the method of TL has been used to give the final decision about the previous radiation treatment of the sample.     

Übergangsmetallkomplexe mit Nitronylnitroxylradikalliganden

The stable free radicals, the isomers of 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide with the 2-substituentR (R=para-,meta-,ortho-pyridyl), have been prepared and used as ligands in copper(II), palladium(II) and platinum(II) complexes. The magnetic moments and the EPR spectra of the complexes and the free radicals have been investigated. Most of the complexes show a considerable intramolecular interaction between the radicalic groups of the ligands. No intramolecular interaction was found, however, between the transition metal ions and the unpaired electrons of the ligands. But by analysis of the EPR spectra in the solid state there was found in some cases an intermolecular interaction between the metal ion [copper(II)] and the unpaired electrons of the ligands.

     

Influence of the nature of ligands in iridium complexes with C60 fullerene and ·P(O)(OPri)2, ·CMe3, and ·CCl3 radicals on regioselectivity of addition and stability of spin-adducts formed: an EPR study

The addition of ^·P(O)(OPrⁱ)₂ (R¹), ^·CMe₃ (R²), and ^·CCl₃ (R³) radicals to metallofullerenes (η²-C₆₀)IrH(CO)(CNBu^t)₂(o-HCB₁₀H₉CCH₂PPh₂-B,P) (1), (η²-C₆₀)IrH(CO)(DIOP) (DIOP is (4R,5R)-(+)-4,5-bis(diphenylphosphinomethyl)-2,2-dimethyl-1,3-dioxolane, 2), and (η²-C₆₀)IrH(CO)(PPh₃)₂ (3) was studied by EPR spectroscopy. A stability study of spin adducts (SAs) of R¹ radicals with complexes 1 and 2 showed that when the reactions are initiated by illumination with 366-nm light, the EPR spectra exhibit only signals of those isomers that are formed upon attack of the R¹ radicals on the carbon atoms of the cis-1 and cis-2 bonds (i.e., carbon atoms of the fullerene hemisphere to which the metallofragment is attached). Investigations of the reactions of R² and R³ radicals with complexes 1–3 initiated with 366-nm light made it possible to detect (i) regioisomers formed by adding these radicals to carbon atoms of the cis-n bonds and (ii) SAs formed by adding the radicals to carbon atoms of other bonds in complexes 1–3. The hyperfine structure of the EPR spectrum essentially depends on the spatial structure of substituents at the metal atom and allows individual regioisomers of not only phosphoryl radicals, but also carbon-centered radicals R² and R³ with metallofullerenes 1–3 to be identified. The rate constants for addition of R² and R³ radicals to complexes 2 and 3 were determined. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1302–1309, July, 2007.     

Multifrequency electron paramagnetic resonance study on deproteinized human bone

Irradiated samples of deproteinized powdered human bone (femur) have been examined by electron paramagnetic resonance (EPR) spectroscopy in X, Q and W bands. In the bone powder sample only one type of CO2- radical ion is stabilized in the hydroxyapatite structure in contrast to powdered human tooth enamel, a material also containing hydroxyapatite, widely used for EPR dosimetry and in which a few radicals are stable at room temperature. It is suggested that the use of deproteinized bone for EPR dosimetry could improve the accuracy of dose determination.     

Self‐Association of an Enantiopure β‐Pentapeptide in Nematic Liquid Crystals

Herein, we report for the first time that nematic liquid‐crystalline environments drive the reversible self‐aggregation of an enantiopure β‐pentapeptide into oligomers with a well‐defined structure. The peptide contains four (1S,2S)‐2‐aminocyclopentane carboxylic acid (ACPC) residues and the paramagnetic β‐amino acid (3R,4R)‐4‐amino‐1‐oxyl‐2,2,5,5‐tetramethylpyrrolidine‐3‐carboxylic acid (POAC). The structure of the oligomers was investigated by electron paramagnetic resonance (EPR) spectroscopy, which allowed us to obtain the intermonomer distance distribution in the aggregates as a function of peptide concentration in two nematic liquid crystals, E7 and ZLI‐4792. The aggregates were modeled on the basis of the EPR data, and their orientation and order in the nematic phase were studied by the surface tensor method.     

Correlation between Luminescence and EPR Spectroscopy as Evidence of Ytterbium Pair Formation in Li6Ln(BO3)3:Yb3+ (Ln=Gd,Y) Borate Single Crystals

Synthesized powders and grown single crystals of nominal compositions Li₆Ln(BO₃)₃:Yb³⁺ (Ln=Y, Gd) were investigated by means of powder and single‐crystal X‐ray diffraction (XRD), as well as optical near‐IR spectroscopy in conjunction with electron paramagnetic resonance (EPR) spectroscopy. The appearance of two distinct zero‐phonon lines suggests the existence of two kinds of Yb³⁺ ions in the single crystals. The XRD results exclude the possibility of a phase transition occurring between room and low temperatures. EPR spectra of single crystals show the presence of both isolated ions and pairs of ytterbium ions substituted for Y³⁺. A strong temperature dependence of the intensity of Yb–Yb pairs resonance lines coincides with temperature dependence of emission peak at 978 nm, confirming a common origin of the defect giving rise to these spectra. Calculated from EPR spectra, the distance between pairs of Yb³⁺ is in good agreement with crystallographic ones: R=3.856 Å, R_cryst=3.849 Å.