Hydrogen effects on the catalytic activity and selectivity of the zeolites H?NaY and PtH?NaY

The decomposition of methylcyclohexane on H–NaY and PtH–NaY zeolites has been studied. It has been found that the presence or abscence of H₂ affects not only the activity of these catalysts but also their selectivity to dehydrogenation and isomerization products.

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H–NaY PtH–NaY. , H₂ , .

     

Near-Wake Turbulence Properties in the High Reynolds Number Incompressible Flow Around a Circular Cylinder Measured by Two- and Three-Component PIV

The main objective of the present experimental study is to analyse the turbulence properties in unsteady flows around bluff body wakes and to provide a database for improvement and validation of turbulence models, concerning the present class of non-equilibrium flows. The flow around a circular cylinder with a low aspect ratio () and a high blockage coefficient () is investigated. This confined environment is used in order to allow direct comparisons with realisable 3D Navier–Stokes computations avoiding ‘infinite’ conditions. The flow is investigated in the critical regime at Reynolds number 140,000. A cartography of the velocity fields in the near wake of the cylinder is obtained by PIV and Stereoscopic PIV techniques. Statistical means and phase-averaged quantities are determined. Furthermore, POD analysis is performed on the data set in order to extract coherent structures of the flow and to compare the results with those obtained by the conditional sampling technique. The Reynolds stresses, the strain-rate and vorticity fields as well as the turbulence production terms are determined.     

Absolute Configuration of 2-Substituted 2-Azabicyclo[2.2.1]hept-5-enes

The diastereoisomeric 2-substituted 2-azabicyclo[2.2.1]hept-5-enes 2 – 4 were prepared by aza-Diels-Alder reaction of cyclopentadiene with the corresponding methaniminium ions. Their relative configurations were deduced using ¹H, ¹H-ROESY experiments, and their absolute configurations were assigned from the crystal structure of the aziridinium derivative (?)- 5 . The absolute configuration of (+)- 1 , i.e. (1R), was assigned by CD spectroscopy.     

Nonlinear absorption of new mesoionic compounds

The nonlinear absorption of new mesoionic compounds (MIC) was investigated using nanosecond laser pulses with wavelengths at 570, 605 and 618 nm. Nonlinear absorption cross-sections, σ₂ ≈ 10⁻⁴⁵ cm⁴ s/photon, larger than any recorded in the literature, were obtained due to the introduction of p-CF₃-C₆H₄ electron-acceptor and p-CH₃-C₆H₄ or p-CH(CH₃)₂-C₆H₄ electron-donor groups in the MIC ring. The large values of σ₂, the ease of synthesis of these compounds and their marked stability, make them promising candidates for photonic applications.     

A Clear‐Cut Example of Selective BpinBdan Activation and Precise Bdan Transfer on Boron Conjugate Addition

Activating the non‐symmetrical Bpin?Bdan diboron reagent with alkoxide leads to the formation of two possible adducts: MeO^?→Bpin?Bdan or MeO^?→Bdan?Bpin. Experimental and theoretical investigation confirms that the MeO^?→Bpin interaction is preferred and thus selective formation of a C?Bdan bond upon reaction with an activated C?C bond.     

Effect of coadsorbent on the photovoltaic performance of zinc pthalocyanine-sensitized solar cells

The effect of chenodeoxycholic acid as a coadsorbent on TiO 2 nanocrystalline solar cells incorporating phthalocyanine sensitizers was studied under various conditions. Adding chenodeoxycholic acid onto TiO 2 nanoparticles not only reduces the adsorption of phthalocyanine sensitizers but also prevents sensitizer aggregation, leading to different photovoltaic performance. The inspection of IPCE and absorption spectra showed that the load of phthalocyanine sensitizers is strongly dependent on the molar concentration of chenodeoxycholic acid coadsorbent. The open circuit voltage of the solar cells with chenodeoxycholic acid coadsorbent increases due to the enhanced electron lifetime in TiO 2 nanoparticles coupled with the band edge shift of TiO 2 to negative potentials.     

Fluorescence intensity ratio technique for Sm3+ doped calibo glass

The most promising fluorescence based temperature sensing technique has been employed. The effect of variation of the temperature on the fluorescence intensity of the two bands, specially coming from the two closed levels to a common lower level in Sm3+ doped calibo glass monitored using 476.5nm line of Ar+ laser and inferred that the present system can be used as a temperature sensor.     

Single-particle electrophoresis for studying the adsorption of cationic polymers onto anionic particles

Understanding the adsorption of polymers onto particles is crucial for many technological and biomedical applications. Even though polymer adsorption on particles is a dynamic process, most experimental techniques can only study the adsorption indirectly, in equilibrium and on the ensemble level. New analysis methods are required to overcome these limitations. We investigated the use of single-particle electrophoresis to study the adsorption kinetics of cationic polymers onto anionic particles and compared the resulting data to a theoretical model. In this approach, the electrophoretic mobility of single polystyrene (PS) particles, exposed to different concentrations of poly(2-guanidinoethyl methacrylate), was measured as a function of time. The polymer adsorption leads to an electrophoretic mobility change of the PS particle over time, from the initial negative value to a positive value at equilibrium. By fitting the kinetics data to the Langmuir model, the adsorption rate, desorption rate and equilibrium constant were determined. Finally, the adsorption kinetics of several other polymers was investigated. This showed that the presented technique enables direct analysis and comparison of the kinetics of polymer adsorption on the single-particle level.     

Carbon nanotube field effect transistors for the fast and selective detection of human immunoglobulin G

We report a field effect transistor (FET) based on a network of single-walled carbon nanotubes (SWCNTs) which can selectively detect human immunoglobulin G (HIgG). HIgG antibodies, which are strongly adsorbed onto the walls of the SWCNTs, are the basic elements of the recognition layer. The non-specific binding of proteins and the effects of other interferences are avoided by covering the non-adsorbed areas of the SWCNTs with Tween 20. The selectivity of the sensor has been tested against bovine serum albumin (BSA), the most abundant protein in plasma. HIgG in aqueous solution with concentrations from 1.25 mg L(-1) (8 nM) can be readily detected with response times of about 10 min. The SWCNT networks that form the basis of the sensor are easily grown by chemical vapour deposition. Silver screen-printed electrodes make the sensor quick to build. The sensitivity obtained with this sensor is similar to other FET devices based on SWCNTs built using much more complicated lithography processes. Moreover, the sensor is a reagentless device that does not need labels to detect HIgG.