Electric field-induced isomerization of azobenzene by STM

The electric field applied between the tip of a scanning tunneling microscope and a metallic surface is shown to induce the reversible trans-cis isomerization of single azobenzene derivatives adsorbed on a Au(111) surface. The investigated molecule is symmetrically equipped with four tert-butyl groups, which decouple the azobenzene core from the metallic surface, facilitating the formation of highly ordered islands. Due to the spatial extension of the electric field, it is possible to switch many molecules within the same island simultaneously.     

On the illusive nature of o-formylazobenzenes: exploiting the nucleophilicity of the azo group for cyclization to indazole derivatives

Facile rearrangement of azobenzenes is shown to occur in cases where the azo group is placed in the ortho position to carbonyl electrophiles to furnish the indazole skeleton. While this study demonstrates the illusive nature of o-formylazobenzenes, it offers potential for the synthesis of indazoles and related heterocycles.     

Amphiphilic folded dendrimer discs and their thermosensitive self-assembly in water

Folded dendrimers with peripheral ether side chains show a thermally induced hierarchical aggregation process, in which the transition temperature and the dimensions of the aggregates can readily be tuned via the generation number (see figure).     

Comparative Study of Scattering and Osmotic Properties of Synthetic and Biopolymer Gels

Summary: The effect of monovalent/divalent cation exchange on the structure and osmotic properties of chemically cross-linked polyacrylate and DNA gels swollen in near physiological salt solutions has been investigated. Both systems exhibit a reversible volume phase transition in the presence of calcium ions. The small-angle neutron scattering spectra of these gels display qualitatively similar features. At low values of q surface scattering is observed, while in the intermediate q range the signal is characteristic of scattering from rod-like elements. At high values of q the scattering intensity is governed by the local (short-range) geometry of the polymer chains. The competition between monovalent and divalent cations has been studied by anomalous small-angle X-ray scattering (ASAXS). The ASAXS results reveal that the local concentration of the divalent counter-ions in the vicinity of the polymer chains significantly exceeds that of the monovalent counter-ions.     

Synthesis and Strong Solvatochromism of Push-Pull Thienylthiazole Boron Complexes

The solvatochromic behavior of two donor-π bridge-acceptor (D-π-A) compounds based on the 2-(3-boryl-2-thienyl)thiazole π-linker and indandione acceptor moiety are investigated. DFT/TD-DFT calculations were performed in combination with steady-state absorption and emission measurements, along with electrochemical studies, to elucidate the effect of two different strongly electron-donating hydrazonyl units on the solvatochromic and fluorescence behavior of these compounds. The Lippert–Mataga equation was used to estimate the change in dipole moments (Δµ) between ground and excited states based on the measured spectroscopic properties in solvents of varying polarity with the data being supported by theoretical studies. The two asymmetrical D-π-A molecules feature strong solvatochromic shifts in fluorescence of up to ~4300 cm⁻¹ and a concomitant change of the emission color from yellow to red. These changes were accompanied by an increase in Stokes shift to reach values as large as ~5700–5800 cm⁻¹. Quantum yields of ca. 0.75 could be observed for the N,N-dimethylhydrazonyl derivative in nonpolar solvents, which gradually decreased along with increasing solvent polarity, as opposed to the consistently reduced values obtained for the N,N-diphenylhydrazonyl derivative of up to ca. 0.20 in nonpolar solvents. These two push–pull molecules are contrasted with a structurally similar acceptor-π bridge-acceptor (A-π-A) compound.     

Dünnschichtchromatographie anorganischer Ionen. I. Trennung von Kationen

Zusammenfassung An Hand einer Reihe von Modellversuchen konnte gezeigt werden, daß man mit Tri-iso-octylamin als Laufmittel dünnschichtchromatographische Trennungen durchführen kann. Ein Ion mit einem hohen Verteilungskoeffizienten kann aus einer Mischung von Ionen mit geringem Verteilungskoeffizienten selektiv abgetrennt werden. Beispiele dafür sind die selektive Abtrennung von U⁶⁺ oder Mo⁶⁺ aus einem Gemisch von Fe, Ni, Co, Zn in salpetersaurer Lösung oder dei Abtrennung von Fe³⁺ aus (Ni²⁺, Mn²⁺, Fe³⁺)-Mischungen.

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Summary By means of a number of model trials it was shown that thin layer chromatographic separations can be made by means of tri-iso-octylamine as carrier. An ion with a high distribution coefficient can be selectively isolated from a mixture of ions with low distribution coefficients. Illustrative examples include the selective separation of U⁶⁺ or Mo⁶⁺ from a mixture with Fe, Ni, Co, Zn, in nitric acid solution or of Fe³⁺ from a mixture of Ni²⁺, Mn²⁺, Fe³⁺.

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Résumé On montre, en se servant d'une série d'expériences types, que l'on peut effectuer des séparations chromatographiques en couche mince avec la tri-isooctylanaine comme éluant. On peut séparer sélectivement un ion dont le coefficient de partage est élevé, à partir d'un mélange d'ions possédant des coefficients de partage faibles. On cite comme exemple la séparation sélective de U⁶⁺ ou de Mo⁶⁺ à partir d'un mélange de Fe, Ni, Co, Zn en solution nitrique ou la séparation de Fe³⁺ à partir de mélanges (Ni²⁺, Mn²⁺, Fe³⁺).

     

Eine Methode zur Analyse sehr kleiner Monazitmengen

Zusammenfassung An natürlichen Monaziten wurde eine Methode für die MikroGesamtanalyse dieser Mineralien entwickelt. Dieser Analysengang wurde sodann, an einem künstlichen Gemenge, welches ähnlich den natürlich vorkommenden Monaziten zusammengesetzt war und lediglich von den Nebenbestandteilen etwas größere Mengen enthielt, überprüft und für ausreichend genau befunden. Für Blei jedoch wurde eine Spezialmethode ausgearbeitet, da es nicht möglich war, innerhalb des beschriebenen Gesamtanalysenganges befriedigende Bleiwerte zu erhalten.Es ist uns eine angenehme Pflicht, dem Vorstand des Instituts, Herrn Professor Dr. A. Franke, für seine wirksame Förderung unserer Arbeit unseren wärmsten Dank auszusprechen.     

Die quantitative Mikro-Mineralanalyse und ihre Ergebnisse

Ohne Zusammenfassung