Biocatalytic and chemical routes to all the stereoisomers of methionine and ethionine sulfoxides

Biotransformations of the N-phthaloyl derivatives of d- and l-methionine and of d- and l-ethionine by Beauveria bassiana ATCC 7159 or Beauveria caledonica ATCC 64970 produce the corresponding (S_S) sulfoxides in good yield and diastereomeric excess. Pure (S_SS_C) diastereomers can be obtained from l-series substrates by crystallisation of the biotransformation extract, and the corresponding (S_SR_C) products obtained from d-series substrates by chromatography of the biotransformation extract. Hydrogen peroxide-catalysed oxidation of the N-phthaloyl derivatives of d- and l-methionine and of d- and l-ethionine gives diastereomeric mixtures from which the (S_SS_C) and (R_SR_C) diastereomers can be obtained by crystallisation, and the (S_SR_C) and (R_SS_C) diastereomers obtained by chromatography. N-Cbz- and N-t-Boc methionines are also converted to sulfoxides with predominant (S_S) configuration by both B. bassiana and B. caledonica, but the isolated yields and d.e. of products were generally lower than those obtained from the N-phthaloyl substrates.Removal of the N-phthaloyl group from diastereomerically pure methionine and ethionine sulfoxides gave the corresponding amino acid sulfoxides in high yield; removal of N-Cbz and N-t-Boc groups from protected methionine sulfoxides was also achieved without loss of configuration at sulfur.     

Adiabatic compressibility of critical binary mixtures of nitroethane/isooctane and nitroethane/3-methylpentane

The adiabatic compressibility β_S of nitroethane/isooctane is measured from 18 to 900 Hz at reduced temperatures ? ranging from 5 × 10^-5 to 5 × 10^-2. The zero-frequency compressibility extrapolated from the data is related with the specific heat at constant pressure c_p through the theory of Ferrell and Bhattacharjee (FB). The coupling constant g is evaluated from this relation as 0.38, which agrees with that from the thermodynamic definition of g. β_S at 900 Hz is observed for nitroethane/3-methylpentane at ? 5 × 10^-5-6 × 10^-2. A linear plot of the critical part of β_S against 1n? gives g = 0.34, which agrees with g from the thermodynamic definition and also with that from ultrasonic absorption. Numerical values of the critical and background components of β_S, the isothermal compressibility β_T, c_p, the specific heat at constant volume c_v, and the thermal expansion coefficient α_p are calculated for the two mixtures. The expression of β_S from Anisimov's theory is found to be consistent with that from the FB theory.     

A quantitative interpretation of the magnetic field effect on hyperfine-coupling-induced triplet fromation from radical ion pairs

Experimentally determined B_1/2 values characterizing the magnetic field dependence of molecular triplet production from radical ion pairs originating from photoinduced electron transfer are compared with semi-empirical values obtained according to B_1/2(hfi) = 2(B₁² + B₂²)/(B₁ + B₂) from the root-mean-square values for the hyperfine coupling of the two radicals, B₁ and B₂. The very good agreement is discussed.     

Thermodynamic quantities and defect equilibrium in La2−xSrxNiO4+δ

In order to elucidate the relation between thermodynamic quantities, the defect structure, and the defect equilibrium in La_2−xSr_xNiO_4+δ, statistical thermodynamic calculation is carried out and calculated results are compared to those obtained from experimental data. Partial molar enthalpy of oxygen and partial molar entropy of oxygen are obtained from δ-P(O₂)-T relation by using Gibbs-Helmholtz equation. Statistical thermodynamic model is derived from defect equilibrium models proposed before by authors, localized electron model and delocalized electron model which could well explain the variation of oxygen content of La_2−xSr_xNiO_4+δ. Although assumed defect species and their equilibrium are different, the results of thermodynamic calculation by localized electron model and delocalized electron model show minor difference. Calculated results by the both models agree with the thermodynamic quantities obtained from oxygen nonstoichiometry of La_2−xSr_xNiO_4+δ.     

Ultrasonic speed in compressed liquid by a sing-around method

A new apparatus for the measurement of ultrasonic speed in compressed liquid was constructed. The reliability of this instrument was confirmed by measuring the speeds in pure benzene in the ranges from 283.15 to 323.15 K and pressures up to near freezing pressure, and by comparing the results with literature values. The isentropic compressibilities κ_S were also determined using the experimental speeds and densities, and the results κ_S(u) were compared with those observed directly elsewhere κ_S(d) and those calculated thermodynamically κ_S(c) from (p, V_m, T). At atmospheric pressure, the present results, while agreeing with κ_S(u) reported in the literature, show differences from κ_S(d) and κ_S(c), while those for higher pressures close on a simple curve with κ_S(c).     

Studies on the compounds in BaFeS system. III. Phase relation of Ba1+xFe2S4 with infinitely adaptive structure

Samples of the infinitely adaptive phase Ba_1+xFe₂S₄ (or Ba_p(Fe₂S₄)_q; p, q: integer) were carefully prepared by changing the nominal composition and annealing temperature T_a. The single-phase materials, defined in this paper as a member of the infinitely adaptive series Ba_p(Fe₂S₄)_q, were obtained by the addition of excess sulfur in the nominal composition range 0.05 ≤ x ≤ 0.20 at T_a ranging from 650 to 880°C. X-Ray powder diffraction showed the existence of many members of the Ba_p(Fe₂S₄)_q series. The supercell periodicity was markedly dependent on T_a. The composition of reaction products estimated from X-ray diffraction, the method proposed by Grey based on crystallographic considerations, deviated in practice from the nominal composition. This fact suggests random distribution of Ba and Fe vacancies.     

Une nouvelle famille structurale: Les titanoniobates et titanotantalates A2Nb6TiO18 et A2Ta6TiO18

New ternary oxides A₂M₆TiO₁₈ (A = Rb, Cs; M = Ta, Nb) have been synthesized by reaction between M₂O₅ and TiO₂ oxides and A₂CO₃ carbonates. They crystallize in the hexagonal system in a cell of dimensions a and c near 7.5 and 8.2 Å, respectively. There is one formula unit in the cell, in good agreement with the observed densities 4.38 and 4.78 for A₂Nb₆TiO₁₈, 6.62 and 6.93 for A₂Ta₆TiO₁₈. The structure has been determined from powder diffraction patterns, from the 64 first reflections (i.e., 190 hkl), and refined to R₁ values ranging from 0.06 and 0.08. It can be described from a basic unit of composition (M₆O₂₄) formed of 3 × 2 octahedra of oxygen atoms, sharing edges and corners, with MO distances ranging from 1.8 and 2.2 Å. Relations with the hexagonal tungsten bronze and pyrochlore-type structures are discussed.     

Multiple glass transitions in block copolymer films cast from cyclohexane solutions at two temperatures

Films of block copolymers of polystyrene + isoprene, cast from cyclohexane at temperatures above and below a conformational transition temperature (T_p) derived from the plot of [η] vs. T, have been examined for glass transition temperatures. In every case, two glass transitions were found, T_g1 (polyisoprene) and T_g2 (polystyrene) or T_g1 and T_g (an intermediate species). T_g is assumed to be characteristic of a mixed phase thus providing further evidence that T_p marks a conformational transition from a phase-separated to a phase-mixed form.     

Relative permittivities and refractive indices of binary mixtures of cyclohexanone with dichloromethane,trichloromethane, 1,2-dichloroethane,trichloroethene and cyclohexane at T=303.15 K

Relative permittivities, ϵ_r, and refractive indices, n_D, have been measured for binary liquid mixtures of cyclohexanone (C₆H₁₀O) with dichloromethane (CH₂Cl₂), trichloromethane (CHCl₃), 1,2-dichloroethane (CH₂ClCH₂Cl), trichloroethene (CHClCCl₂), and cyclohexane (c-C₆H₁₂) at T=303.15 K. The values of the deviations of ϵ_r and n_D from values arising from mole fraction average, which are represented respectively by Δϵ_r and Δn_D have been calculated. Values of ϵ_r and Δn_D have been fitted by the method of least squares to smoothing equations. Δϵ_r for the various mixtures has been discussed from the viewpoint of the existence of specific interactions between the components.     

Crystal structures of RPt3−xSi1−y(R=Y, Tb, Dy, Ho, Er, Tm, Yb) studied by single crystal X-ray diffraction

The crystal structures of ternary compounds RPt_3−xSi_1−y(R=Y, Tb, Dy, Ho, Er, Tm, Yb) have been elucidated from X-ray single crystal CCD data. All compounds are isotypic and crystallize in the tetragonal space group P4/mbm. The general formula RPt_3−xSi_1−y arises from defects: x≈0.20, y≈0.14. The crystal structure of RPt_3−xSi_1−y can be considered as a packing of four types of building blocks which derive from the CePt₃B-type unit cell by various degrees of distortion and Pt, Si-defects.     

Measurements of radiative vacancy transfer probabilities from L3 subshells to M,N and O shells and subshells in the atomic range 72⩽Z⩽92

The probabilities of vacancy transfer, η_L3M, ηL₃M₁, ηL₃M₄, ηL₃M₅, η_L3N, ηL₃N₁, ηL₃N₄, ηL₃N₅, ηL₃O₁ and ηL₃O_4,5 from L₃ subshell to M, N and O shells and subshells for the elements Hf, Ta, W, Re, Pt, Au, HgO, Tl, Pb, Bi, Th, U have been measured using L shell fluorescence yields and X-ray intensity ratios. These experimental values were obtained from samples excited by 59.5-keV γ-rays, which were emitted from an ²⁴¹Am radioisotope source. Also K and L X-rays emitted from samples were measured by means of Si(Li) detector with a resolution of 155 at 5.9 keV. The results obtained from this study are compared with the results of other studies.     

Quantum chemical calculations of intracell potential profile in superionic transition range in LaF3

The results of quantum chemical calculations of the potential profile in the LaF₃ crystal lattice in the range of superionic phase transition are presented for clusters containing 24 to 1200 ions. It is found that the values of formation energy E _a of vacancy-interstitial fluoride ion defects and potential barriers E _d hindering the movement of fluoride ions and determining the efficiency of charge transport in the lattice grow monotonously from the minimum values E _a = 0.12 eV and E _d = 0.22 eV for a 24-ion cluster to the maximum E _a = 0.16 eV and E _d = 0.26 eV for clusters of 576 and 1200 ions. It is shown that the values of E _a and E _d obtained for the dielectric phase (T < T _c) are several times the values of E _a and E _d for the superionic state (T ≥ T _c) of LaF₃. The values of E _a and E _d obtained by quantum chemical calculations from clusters of 576 and 1200 ions agree well with energies E _a and E _d obtained from the analysis of the data of the Raman and quasielastic light scattering.     

Further structural studies of membrane-bound IgM heavy chain of normal mouse B lymphocytes and partial amino acid sequence in its C-terminal hydrophobic tail

Comparative structural studies of membrane-bound (μ_m) and secretory μ chains (μ_s) obtained from normal mouse spleen B lymphocytes and plasma cells were performed on CNBr digests of biosynthetically labelled chains. The purified major CNBr fragments were further digested with trypsin or Staphylococcus aureus V8 protease, and analyzed by high pressure liquid chromatography. The data show that μ_m and μ_s chains exhibit a very similar if not identical polypeptide structure over most of the four constant domains (from position N151 through N551), but that, in contrast, the μ_m-C-terminal tail is different from μ_s and contains a very hydrophobic segment. A combination of proteolysis, hydrophobic adsorption and partial N-terminal sequencing of the hydrophobic fragment of μ_m revealed in this region of the molecule a portion of sequence in perfect agreement with the structure predicted from the nucleotide sequence of the corresponding cDNA. The sequence of the C-terminal residues of μ_m, which is different from that of μ_m could not be established, because of an apparent heterogeneity of μ_m chains probably due to a great susceptibility to proteolysis of their C-terminal extremity.     

The infrared spectrum of chd2cn and the ground state geometry of methyl cyanide

Analysis of the rovibration spectrum of CHD₂CN enables the rotation parameter (A_o—B?_o) to be determined, from which the value of A_o may be found using the microwave B_o and C_o constants. The use of A_o (CHD₂CN) in conjunction with all other available B_o and C_o constants for isotopes of methyl cyanide enables the ground state geometry to be defined within fairly narrow limits. The CH bond length is in agreement with the value predicted from the CH vibration frequency of CHD₂CN, and with the value calculated from the results of a recent analysis of the infrared spectrum of CD₃CN.     

Magnetic order and heavy fermion behavior in CePd1+xAl6−x: Synthesis, structure, and physical properties

The physical properties including magnetic susceptibility, specific heat, and electrical resistivity of single crystals are reported for the compound CePd_1+xAl_6−x (x=0.5) which crystallizes in the tetragonal SrAu₂Ga₅-type structure (space group P4/mmm). The compound was grown from an excess of molten Al flux from the respective elements and the crystal structure was established from single-crystal X-ray diffraction. Anomalies in the low temperature specific heat C_p(T) and electrical resistivity ρ(T) show that the compound undergoes ferromagnetic order at T_C=2.8 K. In the ordered state, CePd_1.5Al_5.5 displays heavy fermion behavior with a Sommerfeld coefficient of ca. 500 mJ/mol-K².     

Structures based on the 3-connected net 103-b

The net 10³-b, one of the two simplest 3D 3-connected nets, is a periodic network of 3-connected points in which all the shortest circuits are 10-gons. Some configurations of this net are described, and examples are given of structures based on the net, in particular those formed from tetrahedral or octahedral coordination groups each joined to three other similar groups by sharing appropriate numbers of X atoms. Structures in which each X atom is 2-connected may be constructed from tetrahedral AX₄ groups (AX₂ and A₂X₅) and from octahedral AX₆ groups (AX₃, A₂X₇, AX₄, and A₂X₉). At present, however, examples are known only of A₂X₅ structures.     

Preparation and crystallographic investigation of the spinel series: Mn1 + 2sCr2 − 3sSbsO4 (0.05 ⩽ , s ⩽ 0.30)

Mn_{1 + 2s}Cr_{2 ? 3s}Sb_sO₄, a new series of spinels, have been prepared and studied using X-ray powder data. For s going from 0.05 to 0.30, a gradually increases from 8.441(1) to 8.472(1) Å, and u slightly decreases, from 0.262 to 0.258. Interatomic distances are given. The Mn_{1 + 2s}Cr_{2 ? 3s}Sb_sO₄ (0.05 < s < 0.30) series may be conceived as the result of partial substitution of Cr^{3 +} by 2/3Mn^{2 +} + 1/3Sb^{5 +} in the normal spinel, MnCr₂O ₄.     

New Molybdenyl Iodates: Hydrothermal Preparation and Structures of Molecular K2MoO2(IO3)4 and Two-Dimensional β-KMoO3(IO3)

Two new molybdenyl iodates, K₂MoO₂(IO₃)₄ (1) and β-KMoO₃(IO₃) (2), have been prepared from the reactions of MoO₃ with KIO₄ and NH₄Cl at 180°C in aqueous media. The structure of 1 consists of molecular [MoO₂(IO₃)₄]²⁻ anions separated by K⁺ cations. The Mo(VI) centers are ligated by two cis-oxo ligands and four monodentate iodate anions. Both terminal and bridging oxygen atoms of the iodate anions form long ionic contacts with the K⁺ cations. β-KMoO₃(IO₃) (2) displays a two-dimensional layered structure constructed from ²_∞[(MoO₃(IO₃)]¹⁻ anionic sheets separated by K⁺ cations. These sheets are built from one-dimensional chains formed from corner-sharing MoO₆ octahedra that run along the b-axis that are linked together through bridging iodate groups. K⁺ cations separate the layers from one another and form long contacts with oxygen atoms from both the iodate anions and molybdenyl moieties. Crystallographic data: 1, monoclinic, space group C2/c, a=12.8973(9) Å, b=6.0587(4) Å, c=17.694(1) Å, β=102.451(1)°, Z=4, MoKα, λ=0.71073, R(F)=2.64% for 97 parameters with 1584 reflections with I>2σ(I); 2, monoclinic, space group P2₁/n, a=7.4999(6) Å, b=7.4737(6) Å, c=10.5269(8) Å, β=109.023(1)°, Z=4, MoKα, λ=0.71073, R(F)=2.73% for 83 parameters with 1334 reflections with I>2σ(I).     

Synthesis and properties of the Co7Se8−xSx and Ni7Se8−xSx solid solutions

We report the synthesis and elementary properties of the Co₇Se_8−xS_x (x=0-8) and Ni₇Se_8−xS_x (x=0-7) solid solutions. Both systems form a NiAs-type structure with metal vacancies. In general, the lattice parameters decrease with increasing x, but in the Ni₇Se_8−xS_x system c increases on going from x=5 to 7. Magnetic susceptibility measurements show that all samples exhibit temperature-independent paramagnetism from 25-250 K. Samples within the Co₇Se_8−xS_x system, as well as Ni₇Se₈ and Ni₇SeS₇, were found to be poor metals with resistivities of ∼0.20 and ∼0.06 mΩ cm at 300 K, respectively. The Sommerfeld constant (γ) was determined from specific heat measurements to be ∼13 mJ/mol_CoK² and ∼7 mJ/mol_NiK² for Co₇Se_8−xS_x and Ni₇Se_8−xS_x, respectively.