Anomalous Phases in Cavity-Free 240 GHz Pulsed ENDOR Spectra of 1.44 GeV Xe-Irradiated LiF

Paramagnetic centers generated by swift heavy ion irradiation of LiF crystals could be identified as electrons trapped at regular anion vacancy sites (F centers). Well-resolved electron-nuclear double resonance (ENDOR) spectra resulting from the hyperfine interaction with ⁷Li and ¹⁹F nuclei located in six different shells could be recorded. In order to preserve the millimeter-sized crystals, a cavity-free setup was used for the ENDOR experiments at an electronic Larmor frequency of 240 GHz. Apparently even under conditions of extremely high local energy loss in the ion track, the local density of persistent F centers is still sufficiently low to prevent distortions of the ionic crystal. The spread of hyperfine coupling constants was less than 5 %. Neither in electron paramagnetic resonance (EPR) nor in ENDOR spectra there was evidence for different types of paramagnetic centers. When performing ENDOR by applying the radiofrequency pulse directly after the 3-pulse Mims-type microwave sequence, an anomalous ENDOR effect was observed. The observed “positive” and “negative” ENDOR response can be attributed to efficient hole and anti-hole formation in the inhomogeneously broadened EPR spectrum and can be used to determine the sign of hyperfine coupling constants.     

Single channel recordings of alpha-hemolysin reconstituted in S-layer-supported lipid bilayers.

Previous studies demonstrated that lipid membranes attached to a proteinaceous crystalline surface-layer (S-layer) revealed a prolonged lifetime and showed a reduced tendency to rupture in the presence of membrane active molecules. In addition, comparative studies on folded and S-layer-supported lipid membranes (SsLM) revealed an uniform capacitance of 0.64 +/- 0.04 microF/cm(2) for both composite membranes. In the present study, the feasibility to reconstitute the channel-forming protein alpha-hemolysin (alpha HL) into SsLM at single channel resolution was investigated. Single alpha HL channels could be recorded and the intrinsic properties like unitary conductance, current-voltage characteristics, and closure was found to be similar at both membranes. Thus, the tightly attached S-layer allowed complete reconstitution of alpha HL channels in SsLM.     

Temperature-dependent surface X-ray diffraction on K/Ag(001)-(2 × 1)

Temperature-dependent surface X-ray diffraction experiments have been performed on the K/Ag(001)-(2 × 1) adsorption system. The structure is characterized by a missing-row geometry in which alternate Ag rows along [1 0] are missing. The K atoms reside within the large grooves coordinated by six Ag atoms at a distance of 3.44(5) Å, corresponding to an effective K-radius of 2.00(5) Å. Large anisotropic disorder is observed for both the K-atoms and the top-layer (“ridge”) Ag atoms. The K-atom displacements are largest in the direction along the grooves, whereas for the Ag atoms the vibrations along [110] are significantly larger. The temperature dependence of the Ag vibrations is in accordance with Debye theory for the [110] direction, but deviates from it for the [1 0] vibrations at high temperature. In contrast to the K-atoms, the out-of-plane vibrations of the top-layer Ag atoms are larger than the in-plane vibrations. The inclusion of anharmonic contributions to describe the Ag disorder significantly improves the fits. It is shown that if anharmonicity is neglected the interlayer contraction is overestimated (Δd₁₂/d₁₂ only −3.2%, instead of −12.7% if anharmonicity is neglected). Due to the anharmonicity, different definitions of the atomic position arise (mean, mode and equilibrium position), which are discussed on the basis of the results.     

Ternäre Verbindungen des Lithiums und Natriums mit Mangan und Elementen der 5. Hauptgruppe

Es wird über Darstellung und Kristallstruktur ternärer AMnX-Verbindungen (A ? Li, Na; X ? P, As, Sb, Bi) berichtet. Sie kristallisieren tetragonal in Raumgruppe P4/nmm-D_4h⁷, wobei sich LiMnX und NaMnX durch unterschiedliche Punktlagen der Alkaliatome unterscheiden. Die AMnX-Strukturen werden mit denen verwandter AMX-Verbindungen verglichen (A ? Li, Na, K, Rb; M ? Be, Mg, Zn, Cd; X ? 5b-Element). Ternary Compounds of Lithium and Sodium with Manganese and Elements of the Fifth Main Group Formation and crystal structure of ternary AMnX compounds (A ? Li, Na; X ? P, As, Sb, Bi) are reported. These compounds crystallize in the tetragonal space group P4/nmm-D. The structures of LiMnX and NaMnX differ by the positions of the alkali atoms. Structural relationship to AMX compounds (A ? Li, Na, K, Rb; M ? Be, Mg, Zn, Cd; X ? 5b element) are discussed.     

The cope rearrangement in substituted semibullvalenes as studied by dynamic 13C NMR

NMR-data for some substituted semibullvalenes are reported and the Cope rearrangement is analysed kinetically. Substituent effects on the activation barriers are discussed.