A microelectrochemical scanning flow cell with downstream analytics

The combination of a capillary based microelectrochemical flow cell system and downstream UV–vis analytics allows obtaining synchronized electrochemical and spectroscopic data in a fully automated mode. This method combination can be generally applied to microelectrochemical studies in which an electrochemical species is released or consumed during the electrochemical reaction. For the example of pure zinc surfaces, the characterization of the integrated spectroscopic system is presented with a Zn²⁺ detection limit below 0.1 μmol l⁻¹ using Zincon as complexing agent. A parameter screening of the effect of pH in the range of 6.6–9.0 in borate buffer reveals a linear increase in zinc dissolution with proton concentration but a distinct step in the open circuit potential from the active state (around −700 mV SHE, pH 6.6–7.1) to the passive state (around −300 mV SHE, pH 7.4–9.0) indicating the formation of a closed passive layer. This mechanism is strongly influenced by sulfate anions which increase the dissolution rate of the passive film and promote the active state as monitored by the dissolution profile and OCP (open circuit potential) values. Within the scope of this parameter variation, the congruency between OCP transients, potentiodynamic sweeps and time resolved dissolution profiles is discussed.     

Coagulated concentrated anatase slurry leads to improved strength of ceramic TiO2 bone scaffolds

Slurry behaviour has an important influence on the properties of ceramic scaffolds produced by the polymer sponge method. By adding chloride salts to the TiO₂ slurry, the viscosity was increased depending on the chloride concentration at low pH and high particle concentration. Slurries with higher viscosity led to closed and dense scaffold struts combined with high porosity, resulting in a compressive strength over 1.6 MPa. Furthermore, scaffold prepared with 0.1 M CaCl₂ and SrCl₂ showed the formation of Ca- and Sr-rich phases at the grain boundaries. These ions were also shown to reduce the activation energy for grain growth in the TiO₂ scaffold as indicated by the significantly larger grain size. Ca²⁺-doped scaffolds had the highest compressive strength, while the strength of Sr²⁺-doped scaffolds was reduced by the formation of a solid solution phase below the sintering temperature.     

2,2′-Bipyridine chelates substituted with alkyne groups,and their Ru(II) complexes

The palladium-catalyzed cross-coupling of 5-bromo-2,2′-bipyridine and 5,5′-dibromo-2,2′-bipyridine with phenylacetylene leads to 2 and 3 , and the reaction of 5-ethinyl-2,2′-ethinyl-2,2′-bipyridine with 1,4-diiodo-2,5-dibutyloxybenzene provides 4 . Ruthenium complexes were prepared by reaction of the ligands 2 – 4 with [Ru(bpy)₂Cl₂].The ligands 2 and 4 show a fluorescence quantum yield near 100%. Further photophysical properties of the ligands and their ruthenium complexes were given     

Novel small-size directional antenna for UWB WBAN/WPAN applications

This paper presents a novel small-size directional antenna design for ultrawide-band wireless body area networks/wireless personal area networks applications. The design is based on a typical slot antenna structure with an added reflector in order to achieve directionality. The effects of different antenna parameters and human body proximity on the radiation characteristics are analyzed. Antenna measurements with an optic RF setup were performed in order to characterize the small-size antenna far field radiation pattern. The different structural antenna parameters were optimized via extensive numerical simulations. Results show that for frequencies above 3.5 GHz, where the power front-to-back ratio of the directional antenna is greater than 10 dB, its impedance is nearly the same as in the free space. It is not the case neither for the omnidirectional slot antenna nor the monopole antenna next to the body. Between 3 and 6 GHz performance of the novel directional antenna, in terms of radiation efficiency and SAR values, is significantly improved compared to omnidirectional antenna designs.     

Silver nanoparticles/montmorillonite composites prepared using nitrating reagent at water and glycerol

Three procedures (P) were applied to prepare silver nanoparticles on natural Ca-montmorillonite (MT). The intercalation of the montmorillonite with silver nitrate in aqueous solution (P1), the intercalation of the montmorillonite with silver nitrate in glycerol (P2) and the successive combination of both P1 and P2 methods resulted to P3 method. X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and Fourier Transform Infrared (FTIR) spectroscopy and the molecular modeling were employed to characterize silver nanoparticles and montmorillonite nanocomposite. The P1 produced MT-1 composite with 2.3 wt% Ag and the partially collapsed layered structure. Nanoparticles of silver larger than 20 nm with a lot of planar defects were randomly distributed on the MT-1 surface; nanoparticles smaller than 20 nm were oriented to the montmorillonite substrate. The MT-2 composite from P2 contained only 1 wt% of Ag. The molecular simulation model of MT-2 showed the interlayer space with the exchangeable cations and metallic silver atoms arrangement within the glycerol bilayer. The P3 produced composite MT-3 that contained 2.4 wt% Ag. The nanoparticles > 20 nm size had a well-defined geometry, very small nanoparticles were amorphous. The modeled structure showed the exchangeable cations, Ag+ and Ag0 located close to the silicate layers and monolayer of glycerol molecules in the interlayer space.     

Untersuchungen zur thioladdition an polybutadiene

The free-radical addition of 1-octanediol (RSH) on polybutadienes with different molecular weights and configuration of the C? C double bonds occurs selectively to the 1,2-vinyl and 1,4-cis double bond, while the 1,4-trans double bond remains unchanged. The reactivity order 1,2- > cis > trans is confirmed by the model experiments with the isomers of pentene. The addition is favoured by the formation of an olefin/RSH charge-transfer complex as preinitiation step.     

Maximum safe diameters of microcapillaries for a stoichiometric ethene/oxygen mixture

A method and its corresponding first results are presented for the determination of maximum safe capillary diameters, which may be used to describe the extended safety range of operation conditions for partial gas phase oxidation reactions in microreactor devices. Sections of stainless steel microcapillaries of different inner diameters were mounted between a primary and a secondary chamber. A detonation was ignited in the primary chamber and the propagation of the detonation through the stainless steel microcapillaries was monitored by pressure transducers located between the sections of the microcapillaries. This set-up was used in order to determine explosion velocities inside the capillaries, maximum safe initial pressures, and corresponding maximum safe capillary diameters. Initial investigations were performed with an ideal stoichiometric mixture necessary for complete combustion of ethene with oxygen at room temperature. The measured maximum safe capillary diameters obey an indirect proportionality to the initial pressures. The maximum safe capillary diameter can be estimated on the basis of the λ/3-rule.     

Ermüdungsprodukte des photochromen 2-(2′,4′-Dinitrobenzyl)-pyridins

Fatigue Products of Photochromic 2-(2′,4′-Dinitrobenzyl)-pyridine Under prolonged irradiation or frequent repetitions of its photochromic cycle, 2-(2′,4′-dinitrobenzyl)-pyridine 1 shows fatigue phenomena both in solid state and in solution. These phenomens — yellow discoloration, depression of the melting point, decrease of band intensity of the coloured form, shorter lifetime of the coloured form — are caused by irreversible redox processes and subsequent reactions at the methylene and ortho-nitro groups which are essential for photochromism. Azomethine 2 , ketone 3 and amine 4 are isolated as the major fatigue products.     

Synthese und Charakterisierung photochromer 2,2′-Dinitro-diphenylmethane

Synthesis and Characterization of Photochromic 2,2′-Dinitrodiphenylmethanes Photochromic methyl-, amino-, nitro- and formyl-derivatives of 2,2′-dinitro-diphenylmethane 1 are synthesized by nitration of the substituted diphenylmethanes. They react with aromatic aldehydes or activated benzylcompounds respectively to the photochromic compounds 6a, 6b and 5c–5f containing phenyl-vinylen and phenyl-azavinylen units. Condensations with corresponding bifunctional compounds yield oligomers, the Knoevenagel-product is soluble and photochromic. The synthesized 2,2′-dinitro-diphenylmethanes are photochromic in solution. The thermal back reaction is described by first order kinetics. Methyl groups decrease and, on the other hand, nitro functions increase the lifetime of the coloured polymethinform.