In search of 1,3-disila/germa/stannabicyclo[1.1.1]pentanes with short bridgehead-bridgehead distances and low ring strain energies

The strain energies and through-space distances between the two bridgehead E atoms of a selection of 1,3-dimethyl-1,3-ditetrelbicyclo[1.1.1]pentanes (tetrel E = Si, Ge or Sn) were examined by quantum chemical calculations at MP2 and B3LYP levels. The aim is to identify which bridges lead to short through-space E,E distances, and simultaneously, to as low strain as possible. A short E,E distance should improve through-space interaction, and a low strain should promote the thermal stability and possibly also facilitate their synthesis. The bridges examined included CH₂, CMe₂, CtBu₂, C(CH₂)n (n = 2–4), O, NMe, S, PMe, SiMe₂, GeMe₂, and SnMe₂. The calculations indicate that the phospha bridge is a good compromise providing reasonably low strain as well as E,E through-space distances which are only longer than normal E–E single bonds by factors of 1.06–1.10. This paper is dedicated to Professor Mitsuo Kira in recognition of his stimulating Si chemistry and his 2005 Wacker Award.     

Intercalation of Dyes Containing SO3H Groups into Zn–Al Layered Double Hydroxide

The intercalates of Naphthol Yellow S, Tropaeolin 000, and Tropaeolin 00 were prepared by heating [Zn_0.67Al_0.33(OH)₂](CO₃)_0.165 · 0.5H₂O with acidic forms of the dye solutions in an open reaction vessel. The intercalates were characterized by chemical and thermal analysis, X-ray powder diffraction and UV–VIS spectroscopy. A possible arrangement of the dye molecules in the intercalates was suggested on the basis of their chemical compositions and interlayer distances, by taking into account van der Waals dimensions of the guest molecules and by assuming that the structure of the host layers is not changed during the intercalation process.     

Z/E-photoisomerizations of olefins with 4npi- or (4n + 2)pi-electron substituents: zigzag variations in olefin properties along the T(1) state energy surfaces

[Figure: see text]. A quantum chemical study has been performed to assess changes in aromaticity along the T1 state Z/E-isomerization pathways of annulenyl-substituted olefins. It is argued that the point on the T1 energy surface with highest substituent aromaticity corresponds to the minimum. According to Baird (J. Am. Chem. Soc. 1972, 94, 4941), aromaticity and antiaromaticity are interchanged when going from S0 to T1. Thus, olefins with S0 aromatic substituents (set A olefins) will be partially antiaromatic in T1 and vice versa for olefins with S0 antiaromatic substituents (set B olefins). Twist of the C=C bond to a structure with a perpendicular orientation of the 2p(C) orbitals (3p*) in T1 should lead to regaining substituent aromaticity in set A and loss of aromaticity in set B olefins. This hypothesis is verified through quantum chemical calculations of T1 energies, geometries (bond lengths and harmonic oscillator measure of aromaticity), spin densities, and nucleus independent chemical shifts whose differences along the T1 PES display zigzag dependencies on the number of -electrons in the annulenyl substituent of the olefin. Aromaticity changes are reflected in the profiles of the T1 potential energy surfaces (T1 PESs) for Z/E-isomerizations because olefins in set A have minima at 3p* whereas those in set B have maxima at such structures. The proper combination (fusion) of the substituents of set A and B olefins could allow for design of novel optical switch compounds that isomerize adiabatically with high isomerization quantum yields.     

Dynamic imaging of single DNA-protein interactions using atomic force microscopy

Atomic force microscopy (AFM) imaging of static DNA-protein complexes, in air and in liquid, can be used to directly obtain quantitative and qualitative information on the structure of different complexes. For example, DNA length, the location of preferential binding sites for proteins and bending of DNA as a result of the complexation can all be measured. Recording consecutive AFM images of DNA and protein molecules under conditions that they are still able to move and interact, or dynamic AFM imaging, however, can reveal information on the dynamic aspects of the interactions between these molecules. Here, an overview is given of the technical challenges that need to be considered for successful dynamic AFM imaging studies of individual DNA-protein interactions. Necessary technical improvements to the AFM set-up and the development of new sample preparation methods are described in this paper.     

Study on the electroreduction of In(III) ions at gold from acidic bromide solutions by the rotating ring-disc electrode technique

The mechanism of the indium electrodeposition on gold from acidic KBr solutions has been investigated by means of the rotating ring-disc electrode technique. The measurements showed that the overall electrode reaction In(III) + 3 e In consists of two successive charge transfer steps, i.e. In(III) + 2 e In(I) and In(I) + e In, with soluble monovalent indium as an intermediate. The current efficiency for In(I) generation under steady-state conditions is 100% in the case of low disc current densities. The disproportionation of In(I) in the bulk of solution occurs in slightly acidified solutions,pH=2, in addition to the In(I) electrochemical reduction. Based on the ring current transients, it was established that the two-electron transfer step is preceded by the formation of a thin passive film of indium metal.

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Untersuchung der elektrochemischen Reduktion von In(III)-Ionen an Gold in sauren Bromidlösungen mit der rotierenden Ring-Scheiben-Elektrode

Zusammenfassung Mit Hilfe der rotierenden Ring-Scheiben-Elektrode wurde der Mechanismus der kathodischen Abscheidung von Indium auf Gold in sauren KBr-Lösungen untersucht. Aus den Messungen folgt, daß die Bruttoreaktion In(III) + 3e In über zwei aufeinanderfolgende Durchtrittsreaktionen, In(III) + 2 e In(I) und In(I) + e In, mit löslichem einwertigem Indium als Zwischenprodukt abläuft. Bei kleinen Stromdichten werden die In(I)-Ionen mit 100%iger Stromausbeute erzeugt. In schwächer sauren Lösungen (pH=2) konnte außer der elektrochemischen Reduktion von In(I) zusätzlich dessen Disproportionierung innerhalb der Lösung ermittelt werden. Auf Grund der Ringstrom-Zeit-Kurven wurde auch festgestellt, daß die Bildung von einer dünnen In-Metallschicht, die ein passives Verhalten aufweist, dem Zweielektronenübergang vorangegangen ist.

     

Disposable ionic liquid coating for headspace solid-phase microextraction of benzene, toluene, ethylbenzene, and xylenes in paints followed by gas chromatography-flame ionization detection

Solid-phase microextraction (SPME) with a disposable ionic liquid (IL) coating was developed for headspace extraction of benzene, toluene, ethylbenzene, and xylenes (BTEX) in paints. The SPME fiber was coated with IL prior to every extraction, then the analytes were extracted and desorbed on the injection port of gas chromatography, and finally the IL coating on the fiber was washed out with solvents. The coating and washing out of IL from the fiber can be finished in a few minutes. This disposable IL-coated fiber was applied to determine BTEX in water-soluble paints with results in good agreement with that obtained by using commercially available SPME fibers. For all the four studied paints samples, the benzene contents were under the detection limits, but relatively high contents of toluene, ethylbenzene and xylenes (56-271 microg g(-1)) were detected with spiked recoveries in the range of 70-114%. Compared to the widely used commercially available SPME fibers, this proposed disposable IL-coated fiber has much lower cost per determination, comparable reproducibility (RSD < 11%), and no carryover between each determination. Considering that IL possess good extractability for various organic compounds and metals ions, and that task-specific IL can be designed and synthesized for selective extraction of target analytes, this disposable IL coating SPME might has great potential in sample preparation.     

Møller was right

Direct calculation proves that the total energy-momentum vector derived from the Møller energy-momentum complex from 1958 does not transform like a free 4-vector with respect to the Lorentz transformation. This conforms with the conclusion formulated by Møller himself, but it contradicts the result of the critical analysis of Kovacs. Defects in Kovacs argumentation are found.