Migration order of dipeptide and tripeptide enantiomers in the presence of single isomer and randomly sulfated cyclodextrins as a function of pH

The present study was conducted in order to evaluate the cyclodextrin (CD)-mediated chiral separation of peptide enantiomers as uncharged analytes at pH 5.3 using randomly sulfated beta-cyclodextrin, heptakis-6-sulfato-beta-CD and heptakis-(2,3-diacetyl-6-sulfato)-beta-CD as chiral selectors. Although less effective compared to stronger acidic conditions, the CDs proved to be suitable chiral selectors for the present set of peptides at pH 5.3. The carrier ability of the negatively charged CDs upon reversal of the applied voltage may also be exploited leading to a reversal of the migration order. In addition, reversal of the enantiomer migration order upon increasing the buffer pH from 2.5 to 5.3 was also observed for Ala-Tyr in the presence of randomly sulfated beta-CD, for Ala-Phe, Ala-Tyr, Phe-Phe, Asp-PheNH(2) and Gly-Ala-Phe in the presence of heptakis-6-sulfato-beta-CD, and for Phe-Phe and Ala-Leu in the presence of heptakis-(2,3-diacetyl-6-sulfato)-beta-CD. The migration behavior could be explained on the basis of the complexation constants and the mobilities of the peptide-CD complexes. While a change in the affinity pattern of the CDs upon increasing the pH was observed for some peptides, complex mobility was the primary factor for other peptide-CD combinations affecting the enantiomer migration order at the two pH values studied.     

Epitaxial growth of sexiphenyl on Al(111): from monolayer to crystalline films

A combination of in situ surface sensitive-techniques, UV photoemission and low energy electron diffraction, with ex situ bulk sensitive X-ray diffraction reveals the formation of epitaxial thin films of sexiphenyl on Al(111) starting from the first monolayer. For room temperature growth, highly ordered films are formed with a unique alignment of the sexiphenyl molecules with the long axes of all molecules aligned parallel to both the surface and the <10> azimuthal directions of Al(111). This is related to a densely packed highly commensurate first monolayer, which acts as a template for the unique (21) crystallite orientation observed.     

Kinetics of the adsorptional deformation of zeolites

Adsorptional deformation in the Xe-CaA system has been studied at 303 K; the kinetics of adsorption and deformation has been investigated. A kinetic model of deformation is proposed based on the principle of the instantaneous establishment of local deformational equilibrium. Kinetic deformation curves based on this model are plotted that have local extrema above equilibrium values or in the negative region. It is shown that when Xe is adsorbed by CaA zeolite and trans-2-butene is adsorbed by NaA zeolite, the time required for deformational equilibrium to be established is negligibly small, and that deformation at any point of time at any point in the crystal is in equilibrium with respect to adsorption and temperature.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1948–1951, September, 1990.     

Synthesis, structure and properties of SrAu3In3 and EuAu3In3—New indides with gold zig-zag chains

New indides SrAu₃In₃ and EuAu₃In₃ were synthesized by induction melting of the elements in sealed tantalum tubes. Both indides were characterized by X-ray diffraction on powders and single crystals. They crystallize with a new orthorhombic structure type: Pmmn, Z=2, a=455.26(9), b=775.9(2), c=904.9(2) pm, wR2=0.0425, 485 F² values for SrAu₃In₃ and a=454.2(2), b=768.1(6), c=907.3(6) pm, wR2=0.0495, 551 F² values for EuAu₃In₃ with 26 variables for each refinement. The gold and indium atoms build up three-dimensional [Au₃In₃] polyanionic networks, which leave distorted hexagonal channels for the strontium and europium atoms. Within the networks one observes Au2 atoms without Au-Au contacts and gold zig-zag chains (279 pm Au1-Au1 in EuAu₃In₃). The Au-In and In-In distances in EuAu₃In₃ range from 270 to 290 and from 305 to 355 pm. The europium atoms within the distorted hexagonal channels have coordination number 14 (8 Au+6 In). EuAu₃In₃ shows Curie-Weiss behavior above 50 K with an experimental magnetic moment of 8.1(1) μB/Eu atom. ¹⁵¹Eu Mössbauer spectra show a single signal at δ=−11.31(1) mm/s, compatible with divalent europium. No magnetic ordering was detected down to 3 K.     

Charaktere endlicher Gruppen mit vorgegebenen Schurschen Indizes

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Zur Schurgruppe eines lokalen Körpers

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