Amphiphilic and mesogenic carbohydrates. Part III: Synthesis and thermal behavior of di-O-(n-alkyl)-and tri-O-(n-alkyl)-D-glucose derivatives

The homologous series of the 2,3-di-O-(n-alkyl)-3a-e and 4,6-di-O-(n-alkyl)-D-glucopyranoses9a-e, as well as the 5,6-di-O-(n-hexadecyl)-D-glucofuranose15e, the 3,4,6-tri-O- and 1,4,6-tri-O-(n-octyl)-D-glucopyranoses10a and11a were prepared and their mesogenic properties studied. The derivatives3a-e and15e show enantiotropic but9a-e monotropic behavior. In contrast to this the bis single-tailed -D-glucosyl fluorides4e and7a and the tris single-tailed D-glucopyranoses10a and11a do not form any mesophase.     

Synthesis, Structure, and Superconductivity in Be1.09B3

The compound Be_1.09B₃ was prepared by arc-melting of the elemental constituents. The structure of single crystals taken from the arc-melted boule was determined from single-crystal X-ray data (T=120 K) and is hexagonal, having space group P6/mmm, and lattice parameters a=9.7738(7) Å and c=9.5467(6) Å, R=0.047. The structure consists of a hexagonal array of boronicosahedra, nonicosahedral B₁₂ cages, and B₁₈ cages. Stacked hexagonal layers of boron atoms, hexagons formed by B and Be, and equilateral triangles of boron atoms disordered by a 60° rotation exist along a 6-fold axis down the [001] direction. A superconducting transition at 0.72 K is clearly indicated by resistivity measurements.     

Amperometric enzyme electrode for the determination of aspartate aminotransferase and alanine aminotransferase in serum

Glutamate oxidase (E.C. 1.4.3.7) was immobilized at a platinized activated carbon electrode and the enzyme electrodes were used for the amperometric determination of L-glutamate in a stirred aqueous solution by the electrochemical detection of enzymically produced hydrogen peroxide at + 320 mV vs. Ag/AgCl. A linear calibration graph was obtained between 2 μM and 2 mM with a steady-state response time of 1 min. The glutamate oxidase electrode was subsequently applied to the measurement of aspartate aminotransferase (AST) (E.C. 2.6.1.1) and alanine aminotransferase (ALT) (E.C. 2.6.1.2) in serum. The performance of the electrode was compared with that of techniques used in the hospital diagnostic laboratory. The responses of the enzyme electrode to AST and ALT activities were linear over the clinically relevant range (5-500 U l ^?1), and correlated well (r=0.99) with the methods used for routine clinical analysis.     

Zur Komplexierung von enantiomerenreinen cis- und trans-3-Diphenylphosphino-4-hydroxy-tetrahydrofuranen mit [Rh(COD)2]BF4

The complexation behaviour of cis- und trans-3-diphenylphosphino-4-hydroxyl-tetrahydrofurans with [Rh(COD)₂]BF₄ is studied with the help of NMR and IR spectroscopy. In dependence of the spatial arrangement of hydroxyl and phosphino group the formation of different intra- and intermolecular bridged O-P complexes has been observed.

Zusammenfassung

Das Komplexierungsverhalten von cis- und trans-3-Diphenylphosphino-4-hydroxy-tetrahydrofuranen mit [Rh(COD)₂]BF₄ wird mit Hilfe von NMR- und IR-Spektroskopie studiert. In Abhängigkeit von der räumlichen Anordnung von Hydroxy- und Phosphinogruppe zueinander wird die Bildung von intra- bzw. intermolekular verbrückten O-P-Komplexen beobachtet.     

High-temperature ion transport in La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>FeO<Subscript>3−δ</Subscript>

The conductivity of the entire solid solution La_1–xSr_xFeO_3–, where x=0.2, 0.4, 0.5, 0.7 and 0.9, in the oxygen partial pressure range 10^–19 to 0.5 atm and temperatures between 750 and 950 °C is reported. The analysis of the isothermal pressure dependences of the conductivity reveal that the lanthanum-strontium ferrites can be characterized as mixed ion-electron conductors in the low-oxygen pressure/high-oxygen deficiency limit. The partial contribution to conductivity from oxygen ions increases with strontium content and attains a maximal value at x=0.5. Further increase in doping results in the development of oxygen vacancy ordering phenomena and deterioration of the conducting properties.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

Separate-local-field NMR spectroscopy on half-integer quadrupolar nuclei

New approaches to the characterization of resonances in the solid-state NMR spectroscopy of half-integer quadrupolar nuclei are explored, on the basis of the acquisition of heteronuclear separate-local-field spectra on rotating solids. In their two-dimensional version, these experiments correlate for each chemical site a second-order quadrupolar MAS powder pattern with the dipolar MAS sideband pattern to nearby heteronuclei. As 3D NMR sequences, such 2D anisotropic correlation spectra become separated for inequivalent chemical sites along a third, isotropic dimension. Extending in such manner separate-local-field NMR approaches to quadrupoles facilitates the assignment of inequivalent resonances to specific structural environments, and provides new tools for the investigation of dynamics in solids. Details about these 2D and 3D NMR experiments are given, and their application is illustrated with 1H-23Na recoupling experiments on mononucleotides possessing multiple bound cations.     

Crystal growth, characterization and physical properties of PrNiSb3, NdNiSb3 and SmNiSb3

The crystal structures of three new intermetallic ternary compounds in the LnNiSb₃ (Ln=Pr, Nd and Sm) family have been characterized by single crystal X-ray diffraction. PrNiSb₃, NdNiSb₃ and SmNiSb₃ all crystallize in an orthorhombic space group, Pbcm (No. 57), Z=12, with , , , and ; , , , and ; and , , , and , for Ln=Pr, Nd and Sm, respectively. These compounds consist of rare-earth atoms located above and below layers of nearly square, buckled Sb nets, along with layers of highly distorted edge- and face-sharing NiSb₆ octahedra. Resistivity data indicate metallic behavior for all three compounds. Magnetization measurements show antiferromagnetic behavior with (PrNiSb₃), 4.6 K (NdNiSb₃), and 2.9 K (SmNiSb₃). Effective moments of 3.62 μ_B, 3.90 μ_B and 0.80 μ_B are found for PrNiSb₃, NdNiSb₃ and SmNiSb₃, respectively, and are consistent with Pr³⁺ (f ²), Nd³⁺ (f ³), and Sm³⁺ (f ⁴).     

Improved determination of selenium in plant and peat samples using hydride generation-atomic fluorescence spectrometry (HG-AFS)

A robust, accurate and sensitive analytical procedure for the determination of Se in plant and peat samples by hydride generation-atomic fluorescence spectrometry (HG-AFS) was developed. Aliquots (200 mg) of dried samples were digested with 3 mL nitric acid and 0.5 mL hydrogen peroxide in closed, pressurized PTFE vessels in a microwave oven at 220 °C. Addition of HBF₄ or HF to the digestion mixture was not required because experiments demonstrated that Se was not hosted in the silicate fraction of the investigated sample matrices. Selenium(VI) was directly reduced to Se(IV) in the undiluted digestion solutions after addition of 3.8 mL of 4 M HCl in a microwave oven at 103 °C for 3 min. Other reduction reagents, such as hydroxylamine hydrochloride or urea, were not necessary to cope with potential interferences from nitrogen oxides that could hamper the reliable determination of Se by HG-AFS. Optimum hydride generation of Se was achieved by using 0.9% NaBH₄ and 4.5 M HCl. A solution detection limit of 11 ng L⁻¹ was obtained under the optimized experimental conditions which corresponds to a method detection limit of 2.8 ng g⁻¹ in solid peat and plant materials. The precision of replicate measurements was better than 3% at Se concentrations of 50 ng L⁻¹. The analytical procedure was critically evaluated by analysing two certified plant reference materials (SRM 1515 Apple Leaves and SRM 1547 Peach Leaves) as well as three peat reference materials. Excellent agreement between the experimental values ranging from 50 ng g⁻¹ to ∼2 μg g⁻¹ and the certified concentrations was obtained.     

Cyclodextrin Complexation of the Stilbene 4-(2-(4-Tert-butylphenyl)ethen-1-yl)- benzoate and the Self-assembly of Molecular Devices

E-4-(2-(4- tert - butylphenyl) ethen-1- yl)benzoate, E-1^–, photoisomerizes to the Z-1^– isomer and vice versa in the free state and in the binary complexes 2·E-1^–, 2·Z-1^–, 3·E-1^– and 3·Z-1^– where 2 is the urea-linked cyclodextrin N-(6 ^A -deoxy--cyclodextrin-6 ^A - yl)-N-(6 ^A -deoxy--cyclodextrin-6 ^A - yl)urea and 3 is N,N- bis(6 ^A -deoxy--cyclodextrin-6 ^A - yl)urea. In 2·E-1^–and 3·E-1^– the stilbene occupies both cyclodextrin (CD) components of 2 and 3, whereas in 2·Z-1^– and 3·Z-1^– it only occupies one CD component while the other CD component is unoccupied. 4- tert - Butylphenolate, 4^–, and its carboxylate, 5^–, and sulfonate, 6^–, analogues form the ternary complex 2·Z-1^–·4^– and its analogues and also 3·Z-1^–·4^– and its analogues. These photoisomerize to 2·E-1^–and 3·E-1^– and either free 4^–, 57^– or 6^– and thereby function as molecular devices.     

Half-sandwich dibenzyl complexes of scandium: Synthesis, structure, and styrene polymerization activity

Half-sandwich dibenzyl complexes of scandium have been prepared by stepwise treatment of scandium trichloride with lithium derivatives of silyl-functionalized tetramethylcyclopentadienes (C₅Me₄H)SiMe₂R (R = Me, Ph) and benzyl magnesium chloride. The resulting complexes [Sc(η⁵-C₅Me₄SiMe₃)(CH₂Ph)₂(THF)] and [Sc(η⁵-C₅Me₄SiMe₂Ph)(CH₂Ph)₂(1,4-dioxane)] show structure related to that of the corresponding bis(trimethylsilylmethyl) compounds [Sc(η⁵-C₅Me₄SiMe₂R)(CH₂SiMe₃)₂(THF)]. The four-coordinate complexes display η¹-coordinated benzyl ligands without significant interaction of the ipso-carbon of the phenyl moiety. Conversion of [Sc(η⁵-C₅Me₄SiMe₃)(CH₂Ph)₂(THF)] into the cationic species by treatment with triphenylborane in THF led to the formation of a stable charge separated complex [Sc(η⁵-C₅Me₄SiMe₃)(CH₂Ph)(THF)_x][BPh₃(CH₂Ph)]. Benzyl cation formed using [Ph₃C][B(C₆F₅)₄] in toluene resulted in a moderately active syndiospecific styrene polymerization catalyst.