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.     

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.     

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.     

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).     

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.     

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.     

Order-disorder transition in Nd2−yGdyZr2O7 pyrochlore solid solution: An X-ray diffraction and Raman spectroscopic study

Powder X-ray diffraction (XRD) and Raman spectroscopic study of order-disorder-phase transition with increase in the content of Gd in Nd_2−yGd_yZr₂O₇ solid solution is being reported. It has been observed from Rietveld analysis that with increase in concentration of Gd in Nd_2−yGd_yZr₂O₇, the value of the x parameter of the 48f oxygen changes from 0.332(1) to 0.343(1) with a sudden change in the slope for y=1.8, which indicates that the structure is transforming from ordered pyrochlore to disordered pyrochlore. In addition to that a sudden and drastic change in the Raman spectra including changes in the position and width of several Raman modes beyond y?1.8 has also been observed which has been correlated with increasing disorder. Based on these studies, it is suggested that there is a discontinuous order-disorder transition from ‘perfect pyrochlore’ to ‘defect pyrochlore’ phase in Nd_2−yGd_yZr₂O₇ solid solution.     

Crystal structure and magnetic properties of Ce7Ni5±xGe3±xIn6 and Pr7Ni5±xGe3±xIn6

The indides Ce₇Ni_5±xGe_3±xIn₆ and Pr₇Ni_5±xGe_3±xIn₆ were synthesized from the elements by arc-melting of the components. Single crystals were grown via special annealing sequences. Both structures were solved from X-ray single crystal diffraction data: new structure type, P6/m, Z=1, a=11.385(2), c=4.212(1) Å, wR₂=0.0640, 634F² values, 25 variables for Ce₇Ni_4.73Ge_3.27In₆ and a=11.355(6), c=4.183(2) Å, wR₂=0.0539, 563F² values, 25 variables for Pr₇Ni_4.96Ge_3.04In₆. Both indides show homogeneity ranges through Ni/Ge mixing (M sites). This new structure type can be derived from the AlB₂ structure type by a substitution of the Al and B atoms by CeM₁₂ and NiIn₆Ce₃ polyhedra (tricapped trigonal prism). Magnetic susceptibility measurements on a polycrystalline sample of Ce₇Ni₅Ge₃In₆ indicated Curie-Weiss like paramagnetic behavior down to 1.71 K with the effective magnetic moment slightly reduced in relation to the value expected for trivalent cerium ions. No magnetic ordering is evident.     

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 polymerization of fluorinated monomers bearing a reactive lateral group 13. Copolymerization of vinylidene fluoride with 2-benzoyloxypentafluoropropene

The synthesis of 2-benzoyloxypentafluoropropene (BPFP) and its radical copolymerization with vinylidene fluoride (VDF), initiated by tert-butyl peroxypivalate is presented. In a first step, the preparation of two monomers [F₂CC(CF₃)OCOR were R stands for CH₃ or C₆H₅] was attempted. In contrast to the acetoxy derivative that could not be isolated, the benzoyl monomer was purified and then copolymerized with VDF. A series of 11 copolymerization reactions was achieved starting from initial [VDF]₀/([BPFP]₀+[VDF]₀) molar ratios ranging from 19 to 99 mol%. The molar compositions of the obtained copolymers were assessed by means of ¹⁹F nuclear magnetic resonance spectroscopy. From the Tidwell and Mortimer method, this kinetics of copolymerization led to the determination of the reactivity ratios, r_i, of both comonomers (r_VDF=0.77±0.40 and r_BPFP=0.11±0.32). Hence, the Alfrey and Price equation enabled one to assess the Q and e parameters of BPFP as follows: 0.019 (from Q_VDF=0.008), 0.043 (from Q_VDF=0.015) or 0.182 (from Q_VDF=0.036) and 1.97 (vs e_VDF=0.40), 2.07 (vs e_VDF=0.50) or 2.77 (vs e_VDF=1.20), respectively. These Q-e parameters and r_i were compared to those of other fluoroalkenes and 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.     

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.     

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.     

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.     

Concentration dependence of critical exponents for gelation in gellan gum aqueous solutions upon cooling

The sol-gel transition in aqueous gellan gum solutions induced upon cooling was investigated by rheology measurements. The gelation temperature was determined from the crossover point of storage and loss moduli, i.e., G′ = G′′ (T_c) and from the Winter’s criterion (T_gel), respectively, which increased with gellan concentration. T_gel was higher than T_c and the difference became larger as the gellan concentration got higher. The relaxation critical exponent n was estimated with the Winter’s method and the self-similarity was observed from the critical gel. The scaling for the zero-shear viscosity η₀ before the gel point and the equilibrium modulus G_e after the gel point was established against the relative distance ε from the gel point over the gellan concentration C_g of 1.0-2.5 wt%, giving the critical exponents k and z. The critical exponent n calculated from k and z agrees well with n from the Winter’s criterion. However, no universal n was found for the gelation in aqueous gellan gum solutions, indicating that this gelation should be classified into the cross-linking category for the physical gelation. The critical exponent n decreased with increasing C_g for the gellan gum solution. The fractal dimension d_f calculated from n with the screened hydrodynamic interaction and the excluded volume effect suggested a denser structure in the critical gel with higher C_g.     

Spectroscopy and dynamics of 9,10-dichloroanthracene-Arn van der Waals complexes

In this paper we report on the measurements of the absorption spectra of large van der Waals complexes in planar supersonic jets. The absorption spectra and the fluorescence excitation spectra of the complexes of 9,10-dichloroanthracene (DCA) with Ar atoms are reported for the S₀ → S₁(0) vibrationless transition of DCA·Ar_n (n = 1?6), and from the S₀ → S₁ (1390 cm^?1) transition of DCA·Ar_n (n = 1?4). Information on the structure of these complexes was inferred from the additivity of the spectral shifts per added rare-gas atom (ASSRA) for DCA·AR_n (n = 1.2) and from deviations from the ASSRA for CDA-Ar_n (n = 3?6). The vibrational predissociation (VP) dynamics of DCA-Ar_n (n = 1?3) complexes was interrogated by fluorescence quantum yield, Y, measurements. The value of the S₁ (1390 cm^?1) state of DCA·Ar_n (n = 1?3) exhibits a dramatic enhancement relative to that of DCA. Utilizing the dependence of Y on the excess vibrational energy of bare DCA, we were able to estimate the internal energy of the fragments resulting from VP of DCA·Ar_n of DCA·Ar_n (n = 1?3). An upper limit of ? 100 ps was estimated for the VP (and/or vibrational energy redistribution) lifetime from the S₁ (1390 cm^?1) state of DCA·Ar₃.     

High-temperature heat capacity of YbAl3(BO3)4

The isobaric heat capacity C _p (T) of YbAl₃(BO₃)₄ grown by spontaneous crystallization from solution (100 ? n) wt % (Bi₂Mo₃O₁₂ + 2.5% B₂O₃ + 0.75% Li₂MoO₄) + n wt % YbAl₃(BO₃)₄ is studied experimentally in the region of 344–1016 K. It is established that there are no extrema on the C _p (T) dependence, and the obtained data can be described using the Berman-Brown polynomial. The temperature variations of enthalpy and entropy are calculated from the C _p (T) dependence.