An electron microscopic study of the archaeal feast/famine regulatory protein: 2. Crystal formation by a full length FFRP,pot0434017 (FL11)

In the crystal the archaeal feast/famine regulatory protein pot0434017 (FL11) forms helical cylinders, each extending along the c axis and densely packed with a hexagonal symmetry in the a/b plane. By applying cryo-electron microscopy to protein solutions yielding crystals, with selectively focussing zero-loss electrons accelerated at 200 KV, two types of regular objects were observed, hexagonal (i.e. projections of crystals to their a/b planes) or rectangular (i.e. projections onto planes perpendicular to a/b). The two types of images are different in the ranges of sizes, suggesting that the crystallization might initiate by forming a hexagonal sheet on the a/b plane, subsequently extending along the c axis. Some other images obtained were intermediate between regular and amorphous, suggesting that some crystals were growing inside amorphous precipitates by rearranging the protein molecules, and that some larger crystals were growing by absorbing smaller amorphous precipitates. Tubes running parallel to each other were also observed in pieces of thin films. These tubes have hollows in their centers, and their lateral arrangement with a periodicity of ~150 Å and the presence of a helical component ~50 Å suggest that they are projections of the helical cylinders, forming mono-layers on the a/c or b/c planes.     

An electron microscopic study of the archaeal feast/famine regulatory protein: 4. Estimation of the particle size

Using the method of Fourier transform, cryo-electron micrographs of two types of archaeal feast/famine regulatory proteins (FFRPs), pot0434017 (FL11) and pot1216151 (DM1), were analyzed. After correcting the Fourier power spectra by considering effects of the contrast transfer functions (CTFs), peaks were identified at frequencies, corresponding to the particle size of ~130 Å for FL11 in the complex with DNA, in addition, a smaller size, ~40 Å, for the same protein in the absence of DNA, the particle size of ~65 Å for DM1 when interacting with a ligand, and a smaller size of ~30 Å when the ligand was removed. These numbers are consistent with our previous observations that dimers of FL11 form octamers, i.e. tetrameric assemblies of the dimers, upon intercation with DNA, and that similar octamers of a smaller FFRP, DM1 of the molecular weight approximately half that of FL11, are stabilized by interaction with the ligand. Some aspects of CTF correction are discussed.     

An electron microscopic study of the archaeal feast/famine regulatory protein: 7. Single particles formed by pot0434017

Particles formed by a feast/famine regulatory protein (FFRP), pot0434017 (FL11), in solution in the absence of DNA were analyzed using electron microscopy (EM). By applying conventional (i.e. dry) EM to the protein negatively stained with uranyl acetate, top views of tetrameric assemblies of dimers were obtained, where four pairs each of N-domains were extending from C-domains assembled around the centers. In cryo-EM images of the protein embedded in 3D amorphous ice, sets of four densities were arranged around ellipsoids having similar lengths for their long axes but of different lengths for their short axes. These images were interpreted as projections with different tilts of four pairs of N-domains arranged inside flat assemblies: the positively charged N-domains only were stained with ammonium molybdate, but the negatively charged C-domains were unstained and thus unobservable. Using seventeen such cryo-images, in combination with a crystal structure equivalent to an assembly of C-domains, a disk-like 3D structure was reconstructed.     

An electron microscopic study of the archaeal feast/famine regulatory protein: 6. The cylindrical assembly form

Using a microcrystal of the feast/famine regulatory protein (FFRP) pot0434017 (FL11), a cryo-electron micrograph was taken, showing a projection of cylinder-like assemblies packed parallel to each other. This electron micrograph was processed in the Fourier space by selecting spots reflecting the packing and, in addition, those reflecting stacking of units inside the cylinders. Twenty seven subimages were selected, each containing three cylinders of 24 discs each, running nearly parallel to each other. By averaging these images and in combination with another average showing a different view [Ishijima, S. A., Clowney, L., and Suzuki, M. (2004) Proc. Jpn. Acad., Ser. B 80, 183–188], some details of the 3D structure of the cylindrical assembly form are discussed.     

Optical properties of the proton conductor (NH2(CH3)2)2CoCl4

Based on the data from optical-spectral studies of (NH₂(CH₃)₂)₂CoCl₄ crystals, the existence of high-temperature phase transitions at 419, 380, 352, and 313 K is confirmed. It was shown that with the exception of the first transition, they are related to a considerable extent to rearrangement of the network of hydrogen bonds and are not accompanied by, considerable deformation of the lattice. In this connection the character of the electron-phonon interaction remains unchanged in the entire temperature range of the measurements. The (NH₂(CH₃)₂)₂CoCl₄ structure at room temperature is close to that of the ordered low-temperature phases of such isomorphous crystals as β-K₂SO₄. I. Franko State University, L’vov, Ukraine, 8, Kirill and Mefodii St., UA-290005, L’vov. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 412–418, May–June, 1998.     

A Raman spectroscopic study of the antimony mineral klebelsbergite Sb4O4(OH)2(SO4)

Many minerals based upon antimonite and antimonate anions remain to be studied. Most of the bands occur in the low wavenumber region, making the use of infrared spectroscopy difficult. This problem can be overcome by using Raman spectroscopy. The Raman spectra of the mineral klebelsbergite Sb₄O₄(OH)₂(SO₄) were studied and related to the structure of the mineral. The Raman band observed at 971 cm⁻¹ and a series of overlapping bands are observed at 1029, 1074, 1089, 1139 and 1142 cm⁻¹ are assigned to the SO₄²⁻ν₁ symmetric and ν₃ antisymmetric stretching modes, respectively. Two Raman bands are observed at 662 and 723 cm⁻¹, which are assigned to the Sb O ν₃ antisymmetric and ν₁ symmetric stretching modes, respectively. The intense Raman bands at 581, 604 and 611 cm⁻¹ are assigned to the ν₄ SO₄²⁻ bending modes. Two overlapping bands at 481 and 489 cm⁻¹ are assigned to the ν₂ SO₄²⁻ bending mode. Low‐intensity bands at 410, 435 and 446 cm⁻¹ may be attributed to O Sb O bending modes. The Raman band at 3435 cm⁻¹ is attributed to the O H stretching vibration of the OH units. Multiple Raman bands for both SO₄²⁻ and Sb O stretching vibrations support the concept of the non‐equivalence of these units in the klebelsbergite structure. It is proposed that the two sulfate anions are distorted to different extents in the klebelsbergite structure. Copyright © 2010 John Wiley & Sons, Ltd.     

1H NMR study of molecular dynamics and phase transition in (NH4)2ZnBr4

The proton second moment (M ₂) and spin-lattice relaxation time (T ₁) have been measured in (NH₄)₂ZnBr₄ in the range 77–300 K. The room-temperature spectrum shows a structure which disappears around 243 K. The signal is strong and narrow even at 77 K. Proton T ₁ shows a maximum at 263 K, caused by spin rotation interaction and decreases with decreasing temperature till 235 K, where it shows a sudden increase. Below 235 K, again it decreases and shows a slope change around 216.5 K (reported T_c ). From 216.5 K, T ₁ decreases continuously without exhibiting any minimum down to 77 K. The narrow line at 77 K, and absence of a T ₁ minimum down to 77 K indicate the possibility of quantum mechanical tunnelling in this system. Motional parameters such as activation energy and pre-exponential factor have been evaluated for the reorientational motion of the NH⁺ ₄ ion.     

有机材料(EDT-DSDTFVO)_2FeCl_4和(EDT-DSDTFVO)_2GaCl_4的磁电阻分析

有机材料(EDT-DSDTFVO)2FeCl4和(EDT-DSDTFVO)2GaCl4的输送实验结果,显示出这两类盐的电阻率对温度的依赖性以及压力效果十分相似,但是两种盐的磁电阻率却表现出很大的不同,FeCl4盐为负磁电阻,而GaCl4盐为正磁电阻。我们认为这种输送现象的差异性起源于π-d相互作用。我们用EDT-DSDTFVO表示ethylenedithiodiselenadithiafulvalenothioquinone-1,3-dithiole methide。     

A (27)Al MAS NMR study of a sol-gel produced alumina: Identification of the NMR parameters of the theta-Al(2)O(3) transition alumina phase

²⁷Al MAS NMR has been used to study a sol–gel prepared alumina annealed at various temperatures. Two-field simulation of the sample heated to 1200 °C confirmed the presence of corundum, as suggested by XRD, and also the presence of nanocrystalline θ-Al₂O₃. ²⁷Al MAS NMR chemical shifts, quadrupolar coupling constants and asymmetry parameters are reported for the tetrahedral and octahedral aluminium sites within θ-Al₂O₃.     

三角对称晶场中4A2(3d3)态离子EPR参量的SS和SOO机制

考虑了在以前工作中被忽略的自旋与自旋 (Spin spin(SS) )磁相互作用以及一个电子自旋与另外电子轨道 (Spin other orbit (SOO) )之间的磁相互作用 ,用VisualBasic6.0设计了新的CDM/EPR计算程序 .该程序不仅能计算 4 A2 (3d3)态离子在晶体中的EPR参量 ,而且能计算体系的光谱精细结构 .利用该程序研究了红宝石晶体与绿宝石晶体的EPR参量与光谱精细结构 ,理论与实验符合甚好 .在此基础上 ,研究了SS与SOO磁相互作用对EPR参量及其光谱的贡献 .发现在磁相互作用的三个部分中 ,EPR参量的主要来源是旋 轨 (Spin orbit (SO) )耦合相互作用 ;SS磁相互作用对零场分裂 (Zero fieldsplitting(ZFS) )参量D具有重要贡献 ,在研究中不能被忽略 ,而SOO磁相互作用对ZFS参量D的贡献较小 ;SS与SOO磁相互作用对Zeemang因子以及光谱的贡献甚微     

Proton N.M.R. study of the dynamics of the ammonium ion in ferroelectric langbeinite, (NH4)2Cd2(SO4)3

The proton N.M.R. lineshape of polycrystalline Langbeinite, (NH₄)₂Cd₂(SO₄)₃, has been studied in the temperature range 300 K to 1·8 K. The resonance line is motionally narrowed over the entire temperature range, and the low temperature proton line shows clear evidence for tunnelling motion of the ammonium ion between spin-symmetry states. From a computer simulation of the lineshape, we obtain an estimate for the tunnelling splitting parameter, J, of the torsional ground state of the ammonium ion, as 375 ± 125 gauss. For an undistorted tetrahedral crystal field this corresponds to a tunnelling splitting Δ = 4J = 6·3 ± 2·1 MHz.

Pulsed proton N.M.R. studies have also been carried out on the above compound at 30·8 MHz and 48·2 MHz and the spin-lattice relaxation time (T ₁) has been measured by the π - t - π/2 pulse sequence as a function of temperature down to 77 K. At 30·8 MHz, a T ₁ minimum of 13 ms occurs at 105·8 K, and is ascribed to random reorientations of the NH₄ ⁺ ion. An activational energy barrier of 0·74 ± 0·1 kcal/mole and an associated pre-exponential factor of 8·0 × 10^-13 s are calculated for the above motional process, and the value of the activation energy is correlated with the tunnelling splitting of the torsional ground state.

An anomaly in T ₁ has been observed at the ferroelectric Curie point (95 K), indicating the order-disorder nature of the transition. This is the first experimental evidence relating to the nature of the transition in Langbeinite.     

Pressure dependence of the Shubnikov-de Haas oscillation spectrum of \beta'-(BEDT-TTF)4(NH4)[ Cr(C2 O4)3] .DMF

The Shubnikov-de Haas (SdH) oscillation spectra of the -(BEDT-TTF)₄(NH₄)[ Cr(C₂O₄)₃] .DMF organic metal have been studied in pulsed magnetic fields of up to either 36 T at ambient pressure or 50 T under hydrostatic pressures of up to 1 GPa. The ambient pressure SdH oscillation spectra can be accounted for by up to six fundamental frequencies which points to a rather complex Fermi surface (FS). A noticeable pressure-induced modification of the FS topology is evidenced since the number of frequencies observed in the spectra progressively decreases as the pressure increases. Above 0.8 GPa, only three compensated orbits are observed, as it is the case for several other isostructural salts of the same family at ambient pressure. Contrary to other organic metals, of which the FS can be regarded as a network of orbits, no frequency combinations are observed for the studied salt, likely due to high magnetic breakdown gap values or (and) high disorder level evidenced by Dingle temperatures as large as ≃7 K.     

Phase transitions and temperature changes of the optical absorption edge in (NH2(C2H5)2)2CoCl4 layered crystal

This work was devoted to X-ray diffraction study and investigations of temperature changes of the optical absorption edge of (NH₂(C₂H₅)₂)₂CoCl₄ crystals in the region of possible phase transitions. The X-ray powder diffraction data revealed the monoclinic phase at room temperature – space group P2/n. The cobalt atom was found to be square-plane coordinated by four chlorine atoms resulting [CoCl₄]^2– anion, which is surrounded by two DEA⁺ cations. It was shown that the low-energy tail of the absorption edge in these materials possesses an exponential shape. In the temperature range above 255?K it follows the empirical Urbach’s rule. The obtained experimental data confirmed the existence of the ferroelastic phase in (NH₂(C₂H₅)₂)₂CoCl₄ in the temperature range between 255 and 326?K. The anomalous behaviour of the investigated parameters observed at the temperatures below 255?K would be related to earlier unknown phase transitions.     

Raman study of (NH4)2CuCl4 · 2H2O—II: Order-disorder transition

Thc results of a Raman scattering study of the order-disorder phase transition in (NH₄)₂CuCL₄ · 2H₂O are presented. From the variation of intensity of some selected modes in the temperature range 300-100°K, we have established the temperature dependence of the long range order parameter m, defined as the difference between the fractional number of NH₄ ions in the two possible orientations. Since the ammonium network in (NH₄)₂CuCL₄ · 2H₂O is “quasi one-dimensional”, in contrast to the three-dimensional network in NH₄Cl, we discuss the consequence of this feature on the evolution of m.     

A photoemission study of 4H---SiC(0001)

A photoemission study using synchrotron radiation of the (0001) surface of 4H-SiC is reported. The investigations were concentrated on the (√3 × √3)-R30° and (6√3 × 6√3)-R30° reconstructed surfaces, prepared by resistive heating at a temperature of about 1000°C and 1250°C, respectively. Results from surfaces heated at intermediate temperatures, exhibiting a mixture of these reconstructions, and after heating at a higher temperature, when graphitisation is clearly observed, are also presented. The √3 and 6√3 reconstructed surfaces exhibit characteristic core level and valence band spectra. High resolution core level spectra show unambiguously the presence of surface shifted components in both the Si 2p and C 1s core levels. For the √3 reconstruction, two surface shifted components are observed both in the Si 2p and C 1s level. For the 6√3 reconstruction, the surface region is found to contain a considerably larger amount of carbon. This carbon is found not to be graphitic since surface C 1s components with binding energies different from a graphitic C 1s peak are observed. Graphitisation, as revealed by the appearance of a graphitic C 1s peak, is observed only after heating to a higher temperature than that required for obtaining a well developed 6√3 diffraction pattern.     

A new quaternary semiconductor compound (Ba2Sb4GeS10): Ab initio study

Abstract

The newly synthesised Ba₂Sb₄GeS₁₀ compound is notable because of the interesting features of the quaternary Sb-containing materials. The first principle method has been used to determine the physical properties of this compound. In particular, the electronic structure has been analysed using both conventional GGA-PBE and HSE06 functional. The values of the band gap for PBE and HSE06 calculations were 1.324 and 1.84 eV, respectively. The calculated elastic constants were used to predict polycrystalline mechanical properties. The estimated Vickers hardness (2.7 GPa) values show that Ba₂Sb₄GeS₁₀ is soft matter. Moreover, the vibrational properties of the compound have been studied. The calculation of the elastic constants and phonon dispersion curves indicates that the Ba₂Sb₄GeS₁₀ compound is stable both mechanically and dynamically. Furthermore, the minimum thermal conductivity and optical properties, such as dielectric functions and energy loss function, have also been discussed in detail in this paper.     

低能电子离化H初通道库仑作用过程的理论研究

基于CDS3C模型,研究了初通道库仑场对低能电子碰撞H(e,2e)反应三重微分截面(TDCS)的影响,计算了在共面对称几何条件下,两个出射电子相对角取不同固定值时,能量近阈值(E0=30、20和17.6eV)的入射电子碰撞H(e,2e)反应的TDCS,将其计算结果与3C、DS3C模型所得结果与实验结果进行了比较.结果表明,初通道库仑场对低入射能,两个出射电子相对角较小时的TDCS有一定影响.     

The infrared spectra of tutton salts 1. A comparative study of (NH4)2 M″(SO4)2·6H2O (M″=Ni,Co or Mg)

The infrared spectra of (NH₄)₂M″(SO₄)₂.6H₂O has been analysed in the region 4000–250 cm⁻¹. The dynamics of each crystal has been discussed in terms of 234 phonon modes, including 3 acoustical ones, using the unit cell approximation. The ambiguity in the assignments of the bands in the region 900–500 cm⁻¹ has been removed by assigning the bands in this region to the libratory modes of H₂O molecules. It has been concluded that the NH ₄ ⁺ and SO ₄ ²⁻ ions have a symmetry lower thanT _dand also the complex [M″(H₂O)₆]²⁺ has a symmetry lower than O _h . The hydrogen bonding is the strongest in the Ni-salt and the weakest in the Mg-salt.     

Dirty superconductivity in the electron-doped cuprate Pr(2-x)Ce(x)CuO(4-delta): tunneling study

We report a tunneling study between Pr(2-x)Ce(x)CuO(4-delta) and lead as a function of doping, temperature, and magnetic field. The temperature dependence of the gap follows the BCS prediction. Our data fit a nonmonotonic d-wave order parameter for the whole doping range studied. From our data we are able to conclude that the electron-doped cuprate Pr(2-x)Ce(x)CuO(4-delta) is a weak-coupling BCS dirty superconductor.