Through-shell alkyllithium additions and borane reductions

The through-shell borane reduction and methyllithium addition to benzaldehyde (1), benzocyclobutenone (2), and benzocyclobutenedione (3) incarcerated inside a hemicarcerand (4) with four tetramethylenedioxy bridges are reported. All guests could be reduced and methylated. Selective monoreduction and monomethylation were observed for 3. In the methyllithium addition to 4[symbol: see text]3, the initially formed lithium alcoholate underwent a Moore rearrangement. The reactivity of the incarcerated guests toward methyllithium increased in the order 1 < 2 < 3 and toward borane in the order 1 < 2 approximately equal 3. Guest reactivity was correlated with the inner-phase location of the reacting carbonyl group in the preferred guest inner-phase orientation. The latter was determined from the X-ray structures of 4[symbol: see text]1, 4[symbol: see text]2, and 4[symbol: see text]3, from molecular mechanical calculations, and from the hemicarcerand-induced upfield shift of the guest proton resonances. In the methyllithium and n-butyllithium addition to 4[symbol: see text]1 and 4[symbol: see text]3 at elevated temperatures, selective cleavage of a host's spanner or tetramethylenedioxy bridge, respectively, was observed. The cleavage of one spanner also took place in the methyllithium addition to the 1-methyl-2-pyrrolidinone hemicarceplex. These scission reactions are initiated by the initially formed lithium alcoholates, which show enhanced basicity and nucleophilicity in the inner phase as compared to the bulk phase. Mechanisms for the host scission reactions are discussed.     

Investigation of potential-sensitive fluorescent dyes for application in nitrate sensitive polymer membranes

The applicability of various potential-sensitive dyes (PSD) for optical sensing of anions is reported. Specifically, nitrate-responsive polymer membranes have been developed which are composed of a plasticized polymer, an anion exchange catalyst, and a fluorescent dye. On exposure to nitrate, the fluorescence intensity of such membranes increases, while the wavelengths of the excitation and emission maxima remain virtually unchanged. The membranes typically are 2–4 μm thick and exhibit highest sensitivity to nitrate in the 2 to 200 mgl^–1 range. Signal changes on exposure to 100 mmol/l nitrate can be as high as +300%. The detection limit is 0.2 mgl^–1. The cationic PSD octadecyl acridine organe was tested in combination with a tin-organic and an indium-organic anion carrier rather than with tridodecylmethylammonium chloride, but both carriers were found to display no improved selectivity. Received: 2 December 1995 / Revised: 28 March 1996 / Accepted: 5 April 1996     

Über die Tonneliertheit von lokalkonvexen Tensorprodukten

It is known that the inductive tensor product of two barrelled spaces is barrelled and that the projective tensor product of two barrelled metrizable spaces or barrelled (DF)-spaces is barrelled. In this note it will be shown by a counterexample that the projective tensor product EF of two barrelled spaces E and F in general is not barrelled, even if E is (DF)-Montel-space and F (F)-Montel-space. Furthermore we show that the -tensor product of two (B)-spaces in general is not barrelled. It follows from the fact that an (F)-space E is nuclear if and only if the -tensor product E l ⁴ is barrelled.     

Ternäre Thallium-Indium-Sulfide: Eine Zusammenfassung

Ternary Thallium Indium Sulfides: A Summary Combined thermal and X-Ray analyses in the ternary system Thallium—Indium—Sulfur show, that the two binary sections Tl₂S? In₂S₃ and TlS? InS contain ternary compounds with unique crystal structures. The chemical formulas of these ternary solids are TlIn₅S₈, TlIn₃S₅, TlInS₂ and Tl₃InS₃ for the section Tl₂S? In₂S₃ and TlIn₅S₆ as well as Tl₃In₅S₈ (metastable high temperature phase) for the section TlS? InS respectively. With TlIn₅S₇ an additional ternary solid could be detected, which is located outside the two sections. It is derived from the binary mixed valence compound In₆S₇ by complete substitution of In⁺ by Tl⁺. The following ionic formulations make the mixed valence character of the ternary Thallium—Indium-Sulfides reasonable: TlIn₅S₈ = Tl⁺(In³⁺)₅(S^2?)₈, TlIn₃S₅ = Tl⁺ (In³⁺)₃(S^2?)₅, TlInS₂ = Tl⁺In³⁺(S^2?)₂, Tl₃InS₃ = (Tl⁺)₃In³⁺ · (S^2?)₃, TlIn₅S₆ = Tl⁺([In₂]⁴⁺)₂In³⁺ (S^2?)₆, Tl₃In₅S₈ = 4 × [(Tl⁺)_0,75 · (In⁺)_0,25In³⁺(S^2?)₂], TlIn₅S₇ = Tl⁺[In₂]⁴⁺ (In³⁺)₃(S^2?)₇. All compounds contain Tl⁺-ions in a characteristic “lone pair coordination” of S^2? ions. Indium atoms however occur with the oxidation numbers +2 (formal, In₂ dumb bells with covalent In? In bonding) and +3 (with In³⁺ in tetrahedral and octahedral coordination of S^2?). Chemical preparation, crystal chemistry and general properties of the ternary solids are discussed, summarized and compared to each other.     

In Situ Study of the Surface Oxidation of FeCr Alloys Using Grazing Incidence X‐ray Absorption Spectroscopy (GIXAS)

The surface oxidation of FeCr alloys with 18, 28, and 43 mass‐% Cr was investigated in situ using grazing‐incidence X‐ray absorption spectroscopy (GIXAS) at the chromium and iron K‐edges. Oxidation in air was monitored in situ in the temperature range from 290 K to 680 K. The standard GIXAS data analysis is extended for the treatment of a single layer model in order to estimate the chromium concentrations of the oxide layer and of the near‐interface substrate as well as the oxide layer thickness. XANES analysis shows transitions from b.c.c. Fe to corundum type Fe₂O₃ and from b.c.c. Cr to corundum type Cr₂O₃. The initial oxide layers are 1.1‐1.4 nm thick and contain 60‐90 mass‐% chromium, while the near‐interface substrate is depleted in Cr. During heating, iron oxide growth dominates up to 560‐600 K. Then the chromium oxide layer loses its passivation effect and Cr oxidation sets in.     

Channel activity of a viral transmembrane peptide in micro-BLMs: Vpu(1-32) from HIV-1

We report for the first time on pore-suspending lipid bilayers, which we call micro-black lipid membranes (micro-BLMs), based on a highly ordered macroporous silicon array. Micro-BLMs were established by first functionalizing the backside porous silicon surface with gold and then chemisorbing 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol followed by spreading 1,2-diphytanoyl-sn-glycero-3-phosphocholine dissolved in n-decane. Impedance spectroscopy revealed the formation of single lipid bilayers confirmed by a mean specific capacitance of 0.6 +/- 0.2 microF/cm2. Membrane resistances were in the G omega-regime and beyond. The potential of the system for single channel recordings was demonstrated by inserting the transmembrane domain of the HIV-1 accessory peptide Vpu(1-32), which forms helix bundles with characteristic opening states. We elucidated different amilorides as potential drugs to inhibit channel activity of Vpu.     

AES investigations on starting powders for high performance ceramics

AES depth profiles on ceramic powders (untreated/hydrolyzed/oxidized/ (Al, Y)₂O₃ coated Si₃N₄, [BaO, SiO₂] coated Al₂O₃) are feasible on thin, homogeneous layers or m sized agglomerations prepared on an Au foil. By means of the depth profiles one can qualitatively characterize the coating around the particles. Factor analysis of the depth profiles on the differently treated Si₃N₄ powders suggests the existence of an Si₂N₂O phase on the oxidized sample.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday