A Mössbauer spectroscopy study of the conformational dynamics of native membrane proteins

In a Mössbauer study of non-dehydrated membrane proteins from thermophilic green-blue algae we observed the behavior of the “narrow” and “broad” lines of their Mössbauer spectra during the heating from 80 to 270 K and found that the behavior of the full area S_F under the spectrum resembles that of the Debye-Waller factor and that quadrupole splitting decreases drastically, from Δ = 0.7 mm/s to Δ ≈ 0, as the temperature is increased from 220 to 270 K. The mathematical treatment of the spectra and decomposition into three components corresponding to thermal, diffusional and conformational motions enabled us to explain the temperature-dependent changes in the spectra.     

On the existence of “low/high spin transitions” in coupled spin-phonon models

We study the model used recently (Takahashi, K.: Z. Phys. B — Condensed Matter71, 205 (1988)) to perform Monte Carlo simulations of low/high spin transitions in certain transition metal complex materials. We show analytically that the model, a special Ising model on a harmonic square lattice with spring constants depending on local spin configurations, indeed shown a phase transition of the expected kind.     

Experimental study on the activation process of GaAs spin—polarized electron source

GaAs spin-polarized electron source is a new kind of electron source, where the GaAs semiconductor crystal is used as a photocathode under the irradiation of helicity light. In this paper the activation process of the GaAs spin-polarized electron source is unvestigated experimentally in detail, during which the negative electron affinity of the photo cathode should be achieved more carefully by absorbing the caesium and oxygen on the surface of the GaAs crystal under ultrahigh vacuum conditions. Besides the different activation processes, the important physical parameters are studied to achieve the optimum activation results. At the same time the stability and lifetime of the polarized electron beam are explored for future experiments. Some important experimental data have been acquired.     

Mössbauer study of spin structure transformation from an incommensurate to a commensurate state

We present crystallographic and magnetic properties of NiCr_1.98 ⁵⁷Fe_0.02O₄ by using X-ray diffractometry (XRD), vibrating sample magnetometry (VSM), and Mössbauer spectroscopy. The lattice constants a₀ were determined to be 8.318 Å. The ferrimagnetic Neel temperature (T _N) for NiCr_1.98 ⁵⁷Fe_0.02O₄ is determined to be 90 K. The Mössbauer absorption spectra for all chromites at 4.2 K show two well developed sextets superposed with small difference of hyperfine fields (H _hf) caused by Cr^3?+? ions in two different magnetic sites. The values of the isomer shifts show that the charge states of Fe are Fe^3?+? for all temperature range. Ni-chromites Mössbauer spectra below T _N present aline broadening due to a Jahn–Teller distortion and show that spin structure behavior of Cr ions change from an incommensurate to a commensurate state.     

Effect of nuclear structure on the single particle β− transitions in deformed nuclei

In the framework of the Nilsson model the calculations of the so called shape factor for the first forbidden ^– transitions 5/2^{+ 241}Pu 5/2^{– 241}Am and 7/2^{+ 177}Lu 7/2^{– 177}Hf are carried out. The dependence on the Nilsson potential parameters is studied. It turns out that for the transitions considered the calculated shape factor depends linearly on the electron energy and its slope is 10^–3 per 20 keV. This can affect the analysis of electron spectra if the endpoint energy is sufficiently large.     

EPR study of the high-TC superconductor YBa2Cu3O7−δ

EPR spectra of superconducting YBa₂Cu₃O_7-δ and insulating Y₂BaCuO₅ have been examined. The intensity of Cu²⁺ ions in YBa₂Cu₃O_7-δ is about 1/3000 of that in Y₂BaCuO₅ at room temperature. Owing to the Meissner effect in the superconducting state, the EPR signal of Cu²⁺ ions in YBa₂Cu₃O_7-δ disappears; moreover the EPR signal of DPPH deposited on the YBa₂Cu₃O_7-δ specimen is shifted. An additional EPR line is found for YBa₂(Cu_2.94Cr_0.06)O_7-δ at temperatures below 113K; this can be related to the phenomenon of superconductivity.     

EPR study of the [H−Ca+]0 defect in Tcr CaO

Abstract

A new hydrogen related low-temperature trap for the electrons released during the photoconversion of F→F⁺ centers is studied by EPR. The defects are stable up to 80 K. Below 20 K the spectrum corresponds to the static situation showing tetragonal symmetry. Above this temperature the spectrum is isotropic a consequence of the hopping among the six equivalent orientations. A model for the defect and the study of its reorientational motion are given.     

EPR and optical spectroscopy of the Yb3+ cubic center in β-PbF2

Optical spectroscopy and EPR are employed to study a β-PbF₂ crystal doped with Yb³⁺ ions. The presence of only one paramagnetic center, the Yb³⁺ ion with cubic symmetry, is established. Its optical lines are identified, the empirical system of energy levels is constructed, and the phenomenological crystal field potential is determined. The information on the phonon spectrum of the β-PbF₂ crystal is obtained from the electron-vibrational structure of the optical absorption and luminescence spectra.     

Possible Explanation of the Negative Values of m_ve~2Obtained from the β-Spectrum Shape Analyses

By comparing the results obtained using the same experimental data of CIAE but different theoretical formula fits it is pointed out that the negative value of mv2 is most likely stemmed from inaccuracy of the theoretical formula of the β-spectrum.     

Gamma transitions in 60Ni following the β+ decay of 60Cu (II)

Gamma-ray spectra following the decay of ⁶⁰Cu have been re-examined on the basis of recent new information concerning the properties of ⁶⁰Ni levels. Additional direct β⁺ branches to the 3871.4(2⁺), 3925.6(3⁺) and 4535.9 keV states of ⁶⁰Ni have been identified with log ft values of 6.9, 6.4 and 6.1 respectively. Log ft values have been revised for some previously established branches, and limits for direct population of several other energetically available states are presented. It is noted that the 3194.1 keV 1₁⁺ and 3735.5 keV 1₂⁺ states prefer to decay much more strongly to the O₂⁺ rather than the O₁⁺ state, while the 4020.4 keV 1₃⁺ state shows no such preference.     

Mössbauer study of the inorganic sulfur removal from coals

Mössbauer Spectroscopy (MS) was applied to study the occurrence and behavior of the iron-sulfur-containing minerals in coal and coal fractions obtained by different separation methods: hydrocyclonic, flotation and chemical removal process. Samples of one high sulfur coal from Guachinte mine (Valle, Colombia) and three low sulfur coals from the El Salitre zone (Paipa-Boyacá, Colombia) were analyzed. MS evidenced only the presence of pyrite in Esmeralda and Las Casitas coals, while it identified pyrite and siderite on Cerezo coal. MS and SEM- EDX confirm the inorganic sulfur removal on Guachinte coal submitted to hydrocyclonic removal process. MS of the precipitated coal fraction from Las Casitas mine obtained by flotation in water showed the presence of ferrous sulfate because of coal-weathering process. Treatment with hot diluted HNO3 equal to 27 acid on raw coal sample from Las Casitas mine showed that almost all of the pyrite in raw coal was removed.     

Mössbauer study of products from the arc synthesis of Fe-carbon nanoclusters

This paper presents the results of research into the phase and magnetic state of products of the arc synthesis of Fe-carbon nanoclusters by Mössbauer spectroscopy. These nanoclusters are prepared by the burning of iron-graphite electrodes and carbon-condensate extraction in organic solvents of varying polarity. The local inhomogeneity of the distribution of iron atoms is revealed in the studied samples. It is found that iron atoms are distributed between four iron-containing phases: α-Fe, γ-Fe, FeC _n and iron carbide FeC₂ at different ratios with an accuracy to the resonant absorption factor f. It is shown that the singlet line with a negative chemical shift observed in the Mössbauer spectra of the samples corresponds to the γ-Fe phase and not to iron metallofullerene.     

Reinvestigation of the high spin states in ^（161）Er and enhanced E1 transitions in the N=93 isotones

High-spin states in ¹⁶¹Er have been studied experimentally using the ¹⁵⁰Nd(¹⁶O, 5n) reaction at a beam energy of 86 MeV. The relatively enhanced E1 transitions between the 5/2⁺[642] and 3/2^-[521] bands are observed in ¹⁶¹Er, and the B(E1) values are extracted experimentally. The systematics of the R(E1) values in the N=93 isotones are presented. It is found that the strength of the E1 transitions obviously exhibits angular momentum dependence, and the occurrence of the relatively enhanced E1 transitions could be attributed to octupole softness.     

β-decay matrix elements from the study of asymmetric emission from polarised nuclei: γ-tagging – a new method for complex β-decay

A new method is introduced designed to facilitate study of matrix elements in complex β-decay through the measurement of asymmetric β-emission from a low-temperature polarised source. The method involves coincident detection of the β-emission with subsequent γ-transitions to tag the β-spectrum component. The method is demonstrated by application to the decay of ¹⁴⁰La. This revised version was published online in August 2006 with corrections to the Cover Date.     

Description of the gamov-teller β+-decays and (n,p) transitions in spherical nuclei

The results of calculations of the total log (t)-quantities for decays of neutron-deficit nuclei and strength functions of (n, p) transitions are presented. It is shown that in spherical nuclei the ¦g _A/g _V¦1·0 conditions hold for the constants of a weak interaction.Dedicated to the memory of M. Gmitro.     

Relationships for the computation of long-range proton hyperfine coupling constants derived from π-electron spin labels

Long-range proton hyperfine coupling constants derived from both cationic and anionic spin labels are calculated. The relationships employed are based on a non-empirical CI treatment of the σ-π interactions. Both positive and negative γ-proton coupling constants may be obtained.     

Determination of vicinal HH couplings of the two rotational isomers of β-bromopropionitrile from the solvent dependence of the NMR spectrum

Studies of the NMR spectra of β-bromopropionitrile over a range of concentrations in nine suitable solvents indicate that both the rotationally averaged values of the vicinal coupling parameters and the corresponding chemical shift vary with both solvent and concentration, while the two geminal coupling parameters resonably appear to be constant within experimental error. The CN dipole-dipole interaction appearing in the solvents of low dielectric constants has been indicated as the prominent factor causing the concentration dependence of the spectral parameters in the said solvents. General dielectric effects alone can provide a complete explanation for the combination of factors including solute-solute and solute-solvent interactions in the solutions.The calculation of the solvent dependence of the NMR spectrum of β-bromopropionitrile, gave results in good agreement with the experiment for the energy difference between the two rotational isomers in the liquid state and the results have been used to derive the HH couplings of the two individual isomers of the compound. The values of the HH trans and gauche couplings thus obtained have been shown to be critically dependent on the orientations and nature of the substituents attached to the C-atom.