Synthesis and properties of macrocyclic diazene switch with binaphthalene unit attached via acrylamide linkers

2,2′-Diiodo-1,1′-binaphthalene undergoes a tandem Heck reaction with methyl acrylate to afford methyl 2-(7H-dibenzo[c,g]fluoren-7-ylidene)acetate. As a consequence, the target macrocyclic diazene with binaphthalene unit attached via acrylamide linker was prepared by the stepwise building of acrylamide at a binaphthalene moiety, including the Doebner modification of the Knoevenagel condensation, and completed by oxidative macrocyclisation of aniline end-groups. Despite being an equimolar mixture of monomer and dimer, it exhibited remarkable changes in CD spectra due to reversible (E/Z) isomerisation of N=N diazene bonds upon irradiation at 365/465 nm. Although the dimer isomerises from (E) to (Z) isomer 7.4 times faster than the monomer, the latter’s contribution to the change in ellipticity at 307 nm in the photostationary state is 2.4 times greater.     

Spectral characterisation of new organic fluorescent dyes with an alkoxysilane moiety and their utilisation for the labelling of layered silicates

New fluorescence dyes with an alkoxysilane moiety were synthesised by the condensation of 3-(triethoxysilyl)-1-propanamine (3-aminopropyltriethoxysilane) with 4,10-benzothioxanthene-3,1′-dicarboxylic acid anhydride (BTXA) and N,N-dimethylaminonaphthalene-1,8-dicarboxylic acid anhydride (DMANA), which was accompanied by the formation of an imidic bridge. The compounds N-(3-(triethoxysilyl)propyl)-thioxantheno[2,1,9-dej]isoquinoline-1,3-dione (BTX-S) and 4-(N′, N′-dimethyl)-N-(triethoxysilyl)propyl-1,8-naphthalene dicarboxylic acid imide (DMAN-S) were characterised by steady-state and time-resolved fluorescence spectroscopy in chloroform and ethanol. Both conjugates (BTX-S and DMAN-S) exhibited absorption and emission bands in the same region as the un-substituted BTXA and DMANA. An important Stokes shift was observed for DMAN-S in ethanol. A high fluorescence quantum yield was observed for BTX-S in both solvents and for DMAN-S in chloroform. In addition, the newly developed fluorescent silane dyes were covalently attached to the microscopic particles of layered silicates and on the surface of SiO₂ wafers as a proof of concept for fluorescence particle (surface) visualisation. The surface wafer modification was precisely characterised by X-ray photoelectron spectroscopy (XPS). Successful covalent linkage onto the particles of layered silicates was proved by confocal laser scanning microscopy technique.     

Catalytic behavior of decomposed molybdophosphoric acid supported on alumina for oxidative dehydrogenation of ethane to ethylene

Oxidative dehydrogenation of ethane (ODHE) to ethylene was investigated over a series of alumina supported molybdophosphoric acid (MPA) catalysts. The MPA was transformed into surface Mo oxides on Al₂O₃ when subjected to calcination at 600°C. The catalysts were characterized by N₂-adsorption, XRD, FT-IR spectroscopy and TPR techniques. The results showed that MPA loading and the source of Mo precursor had a clear influence on the catalytic performance. The evaluation of the catalysts for ODHE at temperatures between 450 and 550°C revealed superior ethane conversion (X～24%) and ethylene selectivity (S = ca. 65%) over 20 wt % MPA/Al₂O₃ catalyst. The transformation of MPA into finely dispersed Mo oxides on Al₂O₃ appeared to be responsible for this improved performance.     

Influence of the aluminum alkyl co-catalyst type in Ziegler-Natta ethene polymerization on the formation of active sites, polymerization rate, and molecular weight

The influence of the concentration of the co-catalysts triethylaluminium (TEAL), tri-iso-butylaluminium (TIBAL), tri-n-octylaluminium on the polymerization rate for standard Ziegler-Natta catalyst systems was studied. By comparing the influence of monomeric TIBAL with TEAL co-catalyst on the polymerization activity, the effect of TEAL dimerization was described. The use of the Eley-Ridealadsorption model instead of Langmuir-Hinselwood model is proposed for the absorption of monomeric aluminiumalkyl species and for the formation of active centers C*. It is further proposed that steric hindrance from different co-catalysts, which results in a higher molecular weight (MW) of polymers, is caused by active centers with reduced space for chain transfer reactions.     

Analysis of Early Medieval Glass Beads – The Raw Materials to Produce Green, Orange and Brown Colours

 Monochrome coloured glass beads of the Merovingians (5^th–7^th cent. AD) have been examined by different analytical methods. The elemental composition of a large number of mostly unprepared beads have been measured non-destructively by X-ray fluorescence analysis. After subtracting the content of the colouring oxides of the glass beads and normalising the residual values to 100% an identical soda-lime-glass matrix was obtained. X-ray diffraction was used for the identification of the crystalline colouring and opacifying pigments (SnO₂, Cu, Cu₂O, PbSnO₃), and scanning electron microscopy as well as electron probe microanalysis were applied to study the microstructure and the composition of white, brown, green, orange and yellow coloured glass beads. Oxidised metals, alloys (lead, copper, bronze, brass and mixtures of them) and iron smelting slag have been identified as raw materials to colour the soda-lime-glass.     

Non‐Planar Lithium‐Phthalocyanine in the Double Salt (nBu4N)2[Lipc]PF6

We report the synthesis of the diamagnetic double salt bis(tetra(n‐butyl)ammonium) phthalocyanato(2‐)lithate hexafluorophosphate (nBu₄N)₂[Lipc]PF₆ [pc = phthalocyanine, nBu₄N⁺ = tetra(n‐butyl)ammonium] in dme (dme = dimethoxyethane). According to single‐crystal X‐ray diffraction structure analysis [P$\bar{1}$ , a = 8.642(2) Å, b = 12.820(3) Å, c = 15.019(3) Å, α = 83.01(3)°, β = 87.87(3)°, γ = 74.45(3)°, Z = 1, R₁ = 6.4 %], the phthalocyanine building bloc shows a substantial distortion of the macrocyclic ring from planarity. The deviation from D_4h symmetry originates from packing effects induced by the two tetra(n‐butyl)ammonium cations located above and below the macrocycle. DFT structure optimization starting from the experimental non‐planar configuration produces a fully planar complex anion [Lipc]^–.     

Predicting the selectivity of imprinted polymers

Summary Imprinted polymers as stationary phases for HPLC separations have been the subject of extensive investigations in recent years. In order to aid the rational design of synthetic protocols for the preparation of imprinted polymers, a series of calculations were made to assess the equilibrium concentration of templatemonomer complexes as a function of association constant (K) for the functional groups involved in the interactions and initial concentrations of reactants. This data was then used to predict the selectivity of polymers prepared under different reaction conditions and the model was tested using an experimentally determined value ofK and separation factors taken from the literature.