EPR of carbonate derived radicals: Applications in dosimetry, dating and detection of irradiated food

After exposure of biological (tooth enamel, bone, …) and synthetic apatites to ionizing radiation, the so-called “asymmetric EPR signal nearg = 2” is formed. Although this signal is being used in EPR dosimetry, dating and detection of irradiated food for many years already, its composite character and the precise nature of the radicals contributing to the spectrum are still insufficiently known and/or recognized. For some fifteen years already, the EPR group in Ghent is gaining extensive experience on the radicals present in calcified tissues and model systems like synthetic apatites, calcites and single crystals doped with carbonate. It will be shown that the majority of radicals in calcified tissues are carbonate derived, e.g., CO ₂ ^? , CO ₃ ^? , CO ₃ ^3? while also phosphate derived radicals like PO ₄ ^2? and oxygen species (O^?, O ₃ ^? ) have been identified with EPR and/or ENDOR. For the EPR applications mentioned above, the most important type of radicals is CO ₂ ^t- (g values ranging from 2.0035 to 1.9970). A second type of radicals which is very intriguing but still badly known, exhibits a spectrum atg values around 2.0045. It is very apparent in tooth enamel below doses of 1 Gy, it has been observed in certain fossil teeth in a very prominent way and also in irradiated food containing bone (e.g., frog legs). It will be shown that the organic origin of this signal can be questioned. The importance of other radicals like CO ₃ ^3t- and CO ₃ ^t- for EPR applications will also be discussed.     

Comparison of electron spin polarization of P 870 + Qa a − observed in Zn2+-containing and Fe2+-depleted bacterial reaction centers

Recently, a general model has been developed to explain electron spin polarized (ESP) electron paramagnetic resonance (EPR) signals found in systems where radical pairs are formed sequentially. The photosynthetic bacterial reaction center (RC) is such a system in which we can experimentally vary parameters (lifetime, structure, and magnetic interactions in the sequentially formed radical pairs) that affect ESP development in order to test this model. In Fe²⁺-depleted transfer step from intermediate radical pair, P ₈₇₀ ⁺ Q _a ^? which is produced in an electron transfer step from intermediate radical pair, P ₈₇₀ ⁺ I^?. (P ₈₇₀ ⁺ is the oxidized primary donor, a special pair of bacteriochlorophyll molecules, I^? is the reduced bacteriopheophytin acceptor, and Q _a ^? is the reduced primary quinone acceptor.) The lifetime of P ₈₇₀ ⁺ I^? can be shortened relative to the lifetime of P ₈₇₀ ⁺ I^? in Fe²⁺-depleted RCs by substitution of Zn²⁺. We report the first observation of X-band and Q-band ESP EPR signals due to P ₈₇₀ ⁺ Q^? from bacterial reaction centers that contain Zn²⁺. Comparison of these signals to those observed from Fe²⁺-depleted bacterial reaction centers shows intensity differences and g-factor shifts. The results are discussed in terms of the general sequential radical pair model.     

Structural analysis of three-spin systems of photosystem II by PELDOR

The pulsed electron electron double resonance (PELDOR) pulse sequence is applied to a three-spin system consisting of three radicals (Y _D ^· , Y _Z ^· and Q _A ^? ) generated in spinach PS II. The distance between Y_Z and Q_A has been determined to be 3.4 nm with the previously derived distances of the other radical pairs, 2.9 nm for Y _D ^· -Y _Z ^· and 3.9 nm for Y _D ^· -Q _A ^? . This distance has been derived from the Y _Z ^· -Q _A ^? radical pair trapped in Y_D-less mutants ofChlamydomonas reinhardtii. Furthermore the method was applied to the Y _D ^· -Q _A ^? -Chl _Z ⁺ system to find the unknown distance between Q_A and Chl_Z. The derived distance was 3.4 nm. A triangular configuration was found in the membrane system that gives the relative positions of the electron transfer components.     

Pulse ENDOR studies on the radical pair P 700 +· A 1 ·− and the photoaccumulated quinone acceptor A 1 ·− of photosystem I

The secondary acceptor A₁ of the electron transport chain(s) of photosystem (PS) I is a phylloquinone (vitamin K₁, VK₁). Pulse electron paramagnetic resonance and electron nuclear double resonance (ENDOR) experiments at X-band frequencies were performed on the photoaccumulated acceptor radical A ₁ ^·? and the radical pair state P ₇₀₀ ^·+ A ₁ ^·? in PS I ofThermosynechococcus elongatus. The data obtained were compared with data from the respective radical anion of VK₁ in organic solvents. The unusualg tensor magnitude of A ₁ ^·? is explained by the hydrophobic binding pocket of this radical. The hyperfine couplings and the spin (and charge) density distribution is very different for A ₁ ^.? in PS I and VK ₁ ^·? in frozen alcoholic solution. This is attributed to a rather strong one-sided hydrogen bond to A ₁ ^·? . The presence of a hydrogen bond to A ₁ ^·? has only a minor effect ong. The hyperfine coupling constants of A ₁ ^·? determined from the radical pair spectra deviate only slightly from those derived from photoaccumulated A ₁ ^·? in PS I treated with dithionite at high pH. ENDOR resonances of the proton in a H bond were detected and an estimate of the strength and geometry of this bond to A ₁ ^·? was obtained. The significance of the hydrogen bond and other (hydrophobic) interactions of A₁ with the surrounding are briefly discussed.     

Studying track electrons in frozen aqueous solutions by means of emission Mössbauer spectroscopy

It is shown by means of emission Mössbauer spectroscopy that the reactivity of NO ₃ ^? cations with quasi-free track electrons exceeds those of H₃O⁺, ClO ₄ ^? , and HSO ₄ ^? ions by a factor of only three. This is in drastic contradiction to published assertions that these values differ by two orders of magnitude. An explanation for this discrepancy is proposed.     

Statistical mechanism of the formation of the energy spectra of sputtered molecular clusters

The energy spectra of Si _n O _m ^? clusters sputtered from Si targets by Xe⁺ ions with O₂ pumping onto a bombarded surface, as well as by O ₂ ⁺ ions, are studied. It is shown that the form of the Si _n O _2n+1 ^? energy distributions does not depend on the experimental conditions. Significant differences in the energy spectra of O and Si monomers as compared to Si _n O _2n+1 ^? clusters are revealed. The mentioned features of the energy distribution of Si _n O _m ^? clusters are explained within the framework of the statistical recombination mechanism of their formation in combinatorial synthesis processes.     

EPR study of carbonate derived and ozonide radicals in carbonated apatites synthesized from aqueous solutions

In this study, a series of Na⁺ and¹²CO ₃ ^2? containing apatites synthesized by a hydrolysis of octo-calciumphosphate (OCP) and dried at 25°C until constant weight, were examined with EPR after X-irradiation. A variety of different paramagnetic radicals was formed, giving rise to composite and hence complex EPR powder spectra. The spectra were successfully decomposed into their basic components using a multivariate statistical technique. The different components could be identified unambiguously. In this way, it was found that an O^?, an O ₃ ^? , a CO ₃ ^? , two types of CO ₂ ^? and two types of CO ₃ ^3? ions were formed upon X-irradiation. Also resonances from atomic hydrogen were observed. The most striking feature is the presence of the ozonide ion, which is only rarely observed in irradiated hydroxyapatites. A comparison is made between the EPR spectra of apatite samples prepared by hydrolysis of OCP on the one hand, and those of samples prepared by hydrolyzing monetite, and the tooth enamel spectrum on the other hand.     

Elektronenspinresonanz von elektronenbestrahlten Ammoniakschichten

Ammonia, NH₃ or ND₃, is vaporized upon a cold substrate (20–100 K) and irradiated with electrons of energies from 0.2 to 6 keV. The different EPR spectra show hyperfinestructure and may be ascribed to centers of the type H ₂ ^? , D ₂ ^? , (NH ₂ ^? )^?, (ND ₂ ^? )^?. With respect to electrostatic charge a chemical decomposition of ammonia must be assumed. No electronic centers are found, which could be compared with the solvated electrons known in liquid metal-ammonia-solutions or quenched solid metal-ammonia-layers.     

Luminescence of Sc3+ and La3+ isoelectronic impurities in Lu3Al5O12 single-crystal films

The time-resolved luminescence and luminescence excitation spectra, and luminescence decay kinetics at 8 and 300 K of Lu₃A₁₅O₁₂ (LuAG) single-crystal films doped with Sc³⁺ and La³⁺ isoelectronic impurities and excited by synchrotron radiation are investigated. It is established that the La³⁺ isoelectronic impurity in the ?ub;c?ub; positions of the garnet lattice forms La _Lu ³⁺ luminescence centers emitting in the band with λ_max = 280 nm and the decay time of the main component τ = 300 ns at 300 K. The Sc³⁺ isoelectronic impurity located in the ?ub;c?ub; and (a) positions of the LuAG lattice forms two luminescence centers, Sc _Lu ³⁺ and Sc _Al ³⁺ , emitting in the bands with λ_max = 290 nm and τ = 240 ns and λ_max = 335 nm and τ = 375 ns, respectively, at 300 K. It is shown that the luminescence excitation of the La³⁺ and Sc³⁺ isoelectronic impurities in LuAG single-crystal films occurs through radiative decay of excitons localized near La _Lu ³⁺ , Sc _Lu ³⁺ , and Sc _Al ³⁺ centers. The energies of formation of these excitons are determined to be 6.8, 6.88, and 7.3 eV, respectively. It was found that the excited state of the excitons genetically related to the La _Lu ³⁺ , Sc _Lu ³⁺ , and Sc _Al ³⁺ enters has two radiative levels with different transition probabilities. This configuration leads to the presence of fast (2.3–8.4 ns) and slow (150–375 ns) main components in the luminescence of the centers formed by isoelectronic impurities in garnets.     

Ionization and dissociative ionization of methane molecules

A technique for mass-spectrometric investigation of the yield of positive ions produced by direct and electron-impact dissociative ionization of methane molecules is described, and respective experimental data are presented. Doubly charged C ₂ ⁺ , CH ₃ ²⁺ , and CH ₄ ²⁺ ions, as well as singly charged D ₂ ⁺ , CD ₃ ⁺ , and CD ₄ ⁺ ions, are detected in the mass spectrum of a methane molecule at electron energy U _e = 90 eV for the first time. From ionization efficiency curves, the ionization energy of the parent molecule and the appearance energy of fragment ions are determined. The ionization energy of the CH₄ molecule is found to be 12.62 ± 0.20 eV. Electron-molecular reactions that may take place when a low-energy electron beam interacts with a methane molecule are analyzed. The ionization process and the formation of methane molecule fragments are studied.     

X-ray study of some spinels containing gallium and manganese

The ternary oxides CrMnGaO₄, NiMnGaO₄, CuMnGaO₄ and ZnMnGaO₄, crystallize in the cubic spinel structure with lattice parametera=8.41±0.02 Å, 8.34±0.02 Å, 8.36±0.02 Å and 8.32±0.02 Å, respectively. The oxidation state of manganese in these spinels was determined x-ray spectroscopically. The site distribution was determined from the structural properties and calculated site preference energies of cations in the lattice. The ionic structures were found to be Ga³⁺ [Mn²⁺ Cr³⁺] O ₄ ^2? . Ga³⁺ [Cu²⁺ Mn³⁺] O ₄ ^2? , Mn²⁺ [Ga³⁺ Ni³⁺] O ₄ ^2? and Zn²⁺ [Mn³⁺ Ga³⁺] O ₄ ^2? .     

The predissociation of the 2σ u −1 (c 4Σ u − , v states of the oxygen molecular ion

The dynamics of predissociation of the 2σ _u ^?1 (c ⁴Σ _u ^? ), v vibrational states of the O ₂ ⁺ ion was studied theoretically using the method of coupled differential equations. The main equations describing the vibrational motions of nuclei in the adiabatic and diabatic approximations are given. The applicability scope of approximate methods for solving these equations was studied. The predissociation widths for the v = 0 and 1 vibrational levels were found to be Γ₀ = 0.054 meV and Γ₁ = 9.71 meV. This substantiated the results of recent observations of neutral fragments formed after the dissociation of the O₂ molecule. About 99% of the O ₂ ⁺ ions in the 2σ _u ^?1 (c ⁴Σ _u ^? ), v states were found to decompose to the O(¹ D) + O⁺(⁴ S) dissociation products.     

Correlation femtoscopy of Kaons in the SELEX experiment

Preliminary results from the correlation femtoscopy of identical kaons in the SELEX experiment (Fermilab E781) are presented. Kaons are selected in inclusive reactions of Σ^?C(Cu) interactions at an initial energy of 610 GeV. Kaon pairs are studied in all possible charged states: K _s ⁰ K _s ⁰ , K _s ⁰ K⁺, K _s ⁰ K^?, K⁺K⁺, K⁺K^? and K^?K^?. The source sizes of the hadronization region of neutral and charged kaon pairs are measured.     

The role of additional anions in microporous aluminosilicates with cancrinite-type framework

Microporous framework aluminosilicates with the cancrinite- and sodalite-type structures containing NO ₃ ^? , CO ₃ ^2? , SO ₄ ^2? and PO ₄ ^3? , as extra-framework anions were synthesized under hydrothermal conditions at temperatures from 160 to 200°C. SO ₄ ^2? exhibits the highest affinity to cancrinite structure at the competition of various X anions. Chemical composition, X-ray diffractometry characteristics, and IR spectra of the compounds obtained, as well as kinetics and mechanism of thermal transformations of nitrate counterpart of cancrinite, were studied.     

Cation distribution of the system Zn1−xCoxFeMnO4 by x-ray,electrical conductivity and Mössbauer studies

Structural, electrical and Mössbauer studies were carried out for the system Zn_1?xCo _x Fe MnO₄. It is observed that forx?0.6, the ionic configuration of the system is Zn _1?x ²⁺ Mn _x ²⁺ [Co _x ³⁺ Mn _1?x ³⁺ Fe³⁺]O ₄ ^2? and forx?0.8 Fe³⁺ ions occupy tetrahedral site also. On the basis of electrical and Mössbauer studies a probable valence distribution of CoMnFeO₄ has been suggested. All the compounds showed positive values of thermoelectric coefficient and electrical conduction takes place by a hopping mechanism. Activation energy and thermoelectric coefficient values decreased with decrease in concentration of Zn²⁺ ions. The compounds possess low mobility values varying between 10^?7 and 10^?9 cm²/V sec.     

An ESR study of NH 3 + , al center and HO2 · radical in alkali feldspars

Paramagnetic centers of NH ₃ ⁺ , Al, and HO₂ · have been observed in alkali feldspars from Aichi prefecture, Japan. The quartet signal has been tentatively ascribed to NH ₃ ⁺ rather than to ·CH₃, although the hyperfine splitting by¹⁴N (I=1) was not observed. The averageg- andA-valuesg _av=2.0033 andA _av ^H =2.45 mT, respectively, were attributed to hydrogen. The powder spectra of Al centers stable up to 400 K were simulated by the anisotropicg factors ofg _zz =2.060,g _xx =2.0014,g _yy=2.0021 andA=0.9 mT. Newly discovered HO₂ · is stable up to 570 K. The intensities of the spectra from NH ₃ ⁺ and Al centers were enhanced by gamma-ray irradiation, while that of HO₂ · was not enhanced. Production efficiency,G-value (radical/100 eV) of NH ₃ ⁺ has been obtained to beG=0.01. These results suggest that ESR dating of feldspars is possible.     

High spin shell model excitations in149Gd

The high spin level structure of the three-neutron nucleus¹⁴⁹Gd has been investigated by in-beamγ-ray and electron spectroscopy with (α, xn) reactions. The observed levels are characterized as members of the shell model multipletsνf ₇ ^2/3 ,νh _9/2 f ₇ ^2/2 ,νf ₇ ^2/3 ×3^?,νh _9/2 f ₇ ^2/2 ×3^?, and tentativelyνf ₇ ^2/3 ×(3^?)². The energies of theν f ₇ ^2/3 states agree only moderately with those calculated using empirical two-nucleon interactions taken from¹⁴⁸Gd, which indicates the importance of long range contributions already atN=85.     

Search for Θ+(1540) in exclusive proton-induced reaction p + C(N) \to \Theta ^ + \bar \kappa ^0 + C(N) at the energy of 70 GeV

A search for narrow Θ⁺(1540), a candidate for a pentaquark baryon with positive strangeness, has been performed in an exclusive proton-induced reaction $p + C(N) \to \Theta ^ + \bar \kappa ^0 + C(N)$ on carbon nuclei or quasifree nucleons at $E_{beam} = 70GeV(\sqrt s = 11.5GeV)$ studying nK ⁺, pK _S ⁰ , and pK _L ⁰ decay channels of Θ⁺(1540) in four different final states of the $\Theta ^ + \bar K^0 $ system. In order to assess the quality of the identification of the final states with neutron or K _L ⁰ , we reconstructed Λ(1520) → nK _S ⁰ and ? → K _L ⁰ K _S ⁰ decays in the calibration reactions p + C(N) → Λ (1520)K ⁺+C(N) and p+C(N) → p?+C(N). We found no evidence for a narrow pentaquark peak in any of the studied final states and decay channels. Assuming that the production characteristics of the $\Theta ^ + \bar K^0 $ system are not drastically different from those of the Λ(1520)K ⁺ and p? systems, we established upper limits on the cross-section ratios $\sigma (\Theta ^ + \bar K^0 )/\sigma (\Lambda (1520)K^ + ) < 0.02$ and $\sigma (\Theta ^ + \bar K^0 )/\sigma (p\phi ) < 0.15$ at 90% C.L. and a preliminary upper limit for the forward-hemisphere cross section $\sigma (\Theta ^ + \bar K^0 )$ nb/nucleon.