Zur Berechnung Stekloffscher Eigenwerte

Zusammenfassung Es wird ein neues Verfahren zur numerischen Berechnung des ersten nichttrivialen Stekloffschen Eigenwertes beschrieben. Dieses Verfahren arbeitet nur mit oberen Schranken.

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We describe a new procedure for the numerical evaluation of the first nontrivial Stekloff eigenvalue. This procedure works only with upper bounds.

     

Mechanism of the glutathione transferase-catalyzed conversion of antitumor 2-crotonyloxymethyl-2-cycloalkenones to GSH adducts

Human glutathione (GSH) transferase (hGSTP1-1) processes with similar kinetic efficiencies the antitumor agents 2-crotonyloxymethyl-2-cyclohexenone (COMC-6), 2-crotonyloxymethyl-2-cycloheptenone (COMC-7), and 2-crotonyloxymethyl-2-cyclopentenone (COMC-5) to 2-glutathionylmethyl-2-cyclohexenone, 2-glutathionylmethyl-3-glutathionyl-2-cycloheptenone, and 2-glutathionylmethyl-2-cyclopentenone, respectively. This process likely involves initial enzyme-catalyzed Michael addition of GSH to the COMC derivative to give a glutathionylated enol(ate), which undergoes nonstereospecific ketonization, either while bound to the active site or free in solution, to a glutathionylated exocyclic enone. Free in solution, GSH reacts at the exomethylene carbon of the exocyclic enone, displacing the first GSH to give the final product. This mechanism is supported by the observation of multiphasic kinetics in the presence of high concentrations of hGSTP1-1 and the ability to trap kinetically competent exocyclic enones in aqueous acid using COMC-6 and COMC-7 as substrates. That the exocyclic enone is formed by nonstereospecific ketonization of an enol(ate) species is indicated by the observation that COMC-6 (chirally labeled with deuterium at the exomethylene carbon) gives stereorandomly labeled exocyclic enone. The isozymes hGSTP1-1, hGSTA1-1, hGSTA4-4, and hGSTM2-2 catalyze the conversion of COMC-6 to final product with similar efficiencies (K(m) = 0.08-0.34 mM, k(cat) = 1.5-6.1 s(-)(1)); no activity was detected with the rat rGSTT2-2 isozyme. Molecular docking studies indicate that in hGSTP1-1, the hydroxyl group of Tyr108 might serve as a general acid catalyst during substrate turnover. The possible significance of these observations with respect to the metabolism of COMC derivatives in multidrug resistant tumors is discussed.     

Susceptibility to Effects of UVB Irradiation on Induction of Contact Sensitivity, Relevance of Number and Function of Langerhans Cells and Epidermal Macrophages

Sensitization on skin exposed to acute low-dose UVB irradiation separates normal humans into two phenotypically distinct groups: One group, following sensitization on UVB-irradiated skin, develops contact sensitivity, designated UVB resistant (UVB-R) and the second group, following sensitization on UVB-irradiated skin, fails to develop contact sensitivity, designated UVB susceptible (UVB-S). To investigate whether UVB susceptibility in humans is related to antigen-presenting activity in the skin we studied the effect of UVB irradiation on the number and function of the epidermal antigen-presenting cells in volunteers identified as UVB-R and UVB-S. Single cell suspensions of epidermal cells from control skin and skin exposed to 3 minimal erythema doses (MED) of UVB 3 days previously were stained for Langerhans cells (CD1a+HLA-DR+) and epidermal macrophages (CD1a-HLA-DR+). The UVB exposure of the skin significantly decreased the percentage of Langerhans cells (UVB-R: n = 7, P < 0.02, UVB-S: n = 6, P < 0.03) and increased the percentage of epidermal macrophages (UVB-R: n = 7, P < 0.03, UVB-S: n = 6, P < 0.03) however to the same degree in both the UVBR and the UVB-S group. To study the effect on Langerhans cell alloreactivity, epidermal cells were harvested immediately after UVB irradiation. However, in both UVB-R and UVB-S subjects the Langerhans cell alloreactivity was blocked to the same degree immediately after UVB irradiation compared to nonirradiated epidermal cells. To determine the effect of UVB irradiation on epidermal macrophages, epidermal cells were harvested 3 days after UVB irradiation. Irradiated epidermal cells from both UVB-R and UVB-S subjects demonstrated a strong antigen-presenting capacity compared to epidermal cells from control skin leading to activation of T cells that mainly secrete interferon (1FN)-γ and not interleukin (IL)-4. In conclusion we found that UVB susceptibility was not correlated with the number of Langerhans cells or epidermal macrophages in the skin at the same time of sensitization. Neither was it correlated with the capacity of Langerhans cells nor UVB-induced epidermal macrophages to activate T cells in vitro.     

Darstellung und Kristallstruktur von Cs2Sb4S7

Preparation and Crystal Structure of Cs₂Sb₄S₇ The first thioantimonite of Cesium has been synthesized and its crystal structure determined. The substance crystallizes monoclinic with spacegroup P2₁/_c. The lattice constants are a = 1111.2(5) pm, b = 1227.1(5) pm, c = 1163.7(5) pm and ß = 97.60(5)°. There are four formula units in the unit cell. Sb–S chains are formed by trigonal SbS₃ pyramids and ψ-trigonal SbS₄ bipyramids.     

The `cyclophene' [2.2.2](1,2,4)cyclophan‐9‐ene

In the title compound, C₁₈H₁₆, the [2.2]paracyclophane geometry is restrained to a considerable extent despite the introduction of the extra C=C bridge; typical paracyclophane features, such as the elongated C—C bridges, are still observed. However, the bridgehead atoms of the C=C bridge are forced into unusually close proximity [2.657 (3) Å], which in turn causes the rings to be rotated to an interplanar angle of 13.7 (2)°. The packing involves hexagonally close‐packed layers of molecules parallel to the xy plane, corresponding to the known `7,11' pattern of paracyclophanes, but without significant short intermolecular contacts.     

C—H...π interactions in five ethynyl‐substituted [2.2]paracyclophanes: further examples of the `7,11' packing pattern

The monosubstituted derivative 4‐ethynyl[2.2]paracyclophane, C₁₈H₁₆, (I), and the four disubstituted isomers, 4,12‐, (II), 4,13‐, (III), 4,15‐, (IV), and 4,16‐diethynyl[2.2]paracyclophane, (V), all C₂₀H₁₆, show the usual distortions of the [2.2]paracyclophane framework. The crystal packing is analyzed in terms of C—H...π interactions, some with H...π as short as 2.47 Å, in which the cyclophane rings and/or the triple‐bond systems may act as acceptors. For compounds (I) and (IV), the known `7,11'‐type cyclophane packing is observed, with a herring‐bone pattern of molecules in a layer structure.