2-Phospha-Allylic Systems

Abstract

Phosphamethincyanines prepared in 1964 by Dimroth and Hoffmann were among the first compounds with two-coordinate phosphorus. They are special cases of 2-phospha-allylic cations. Simple representatives of this type become available from the reaction of imidoyl chlorides with tris(trimethylsily1)phosphane.     

Time‐Resolved,In Situ DRIFTS/EDE/MS Studies on Alumina‐Supported Rhodium Catalysts: Effects of Ceriation and Zirconiation on Rhodium–CO Interactions

The effects of ceria and zirconia on the structure–function properties of supported rhodium catalysts (1.6 and 4 wt % Rh/γ‐Al₂O₃) during CO exposure are described. Ceria and zirconia are introduced through two preparation methods: 1) ceria is deposited on γ‐Al₂O₃ from [Ce(acac)₃] and rhodium metal is subsequently added, and 2) through the controlled surface modification (CSM) technique, which involves the decomposition of [M(acac)_x] (M=Ce, x=3; M=Zr, x=4) on Rh/γ‐Al₂O₃. The structure–function correlations of ceria and/or zirconia‐doped rhodium catalysts are investigated by diffuse reflectance infrared Fourier‐transform spectroscopy/energy‐dispersive extended X‐ray absorption spectroscopy/mass spectrometry (DRIFTS/EDE/MS) under time‐resolved, in situ conditions. CeO_x and ZrO₂ facilitate the protection of Rh particles against extensive oxidation in air and CO. Larger Rh core particles of ceriated and zirconiated Rh catalysts prepared by CSM are observed and compared with Rh/γ‐Al₂O₃ samples, whereas supported Rh particles are easily disrupted by CO forming mononuclear Rh geminal dicarbonyl species. DRIFTS results indicate that, through the interaction of CO with ceriated Rh particles, a significantly larger amount of linear CO species form; this suggests the predominance of a metallic Rh phase.     

High-performance AlGaAs-based VCSELs emitting in the 760 nm wavelength range

Vertical-cavity surface-emitting lasers (VCSELs) showing continuous-wave operation with emission wavelengths ranging between 717 and 790 nm have been fabricated. The samples are grown by solid source molecular beam epitaxy on GaAs substrates and are entirely based on the AlGaAs material system. A maximum single-mode output power of 2.0 mW is obtained at 754 nm wavelength by using the inverted surface relief technique.     

Determination of Soot Particle Size in a Premixed Flame: a Static and Dynamic Light Scattering Study

In this contribution we report upon our static and dynamic light scattering experiments to characterize soot particles in flames. We studied sooting laminar premixed flame with acetylene as fuel mixed with air as oxidizer. The air equivalence ratio of the combustion was larger than one. We used a Kaskan type burner with circular geometry and a stabilizing flow of nitrogen around the flame. We focused on the determination of the size of the soot particles in the center of the flame as a function of height above burner. In addition we investigated the influence of the mixing ratio of the gases on the size of the particles. Our results show that static light scattering is better suited than dynamic light scattering for a fast and reliable characterization of soot particles in flames. The latter needs detailed a priori information about the flame to allow the unique determination of sizes from the diffusion measurements. The soot particles grow monotonously with height above burner and with decreasing air equivalence ratio. The aggregates have a fractal dimension lower than two.     

On-line measurement of extracellular enzymes during fermentation by using membrane techniques

The measurement of enzymes during fermentation is of general interest for process control in industrial biotechnology. Studies are presented to develop an on-line measurement for extracellular hydrolases by using membrane separations as the main unit operation, first for achieving continuous sampling from the bioreactor prior to analysis, and secondly for measuring hydrolytic activities, by separating the cleavage products during reaction of enzymes with high-molecular-weight substrates by an ultrafiltration membrane. The evaluation of batchwise and continuous flow analysis for an alkaline protease and pullulanase are described, and the feasibility of on-line measurement during fermentation of Bacillus licheniformis and Klebsiella pneumoniae on a 30- and 70-l pilot scale is demonstrated, including aseptic continuous sampling.     

Beiträge von direkten und Compoundprozessen zur Reaktion40Ca(d, α)38K beiE d =5–10 MeV

For the reaction⁴⁰Ca(d,α)³⁸K differential cross sections for the excitation of the low lying states in³⁸K have been measured at bombarding energies between 5 and 10 MeV. Total cross sections have been calculated using the statistical theory. It was found, that in the whole energy region the isotropic background of the angular distributions gives a good estimation of the compound contribution to the reaction cross section.     

Nonlinear optical properties of dicyanomethylene‐derived heteroaromatic dyes: Semiempirical molecular orbital calculations and experimental investigations

The effect of conformation (E/Z isomerism), nature (donor/acceptor) of substituents, and endgroups (indandione, pyrazolone, pyrazoledione) on the molecular hyperpolarizability β_vec of dicyanomethylene (hetero)aromatic dyes is investigated by means of semiempirical (AM1, ZINDO) molecular orbital calculations. Unless Z isomers are stabilized by intramolecular hydrogen bonding, generally E conformers have larger β_vec's. Replacement of one nitrile group of the dicyanomethylene moiety by p‐aminoaryl rather than p‐R‐arylamino (R=NMe₂, MeO, H, NO₂) is found to be advantageous. Increasing the acceptor strength of 29 by successively replacing the carbonyl with dicyanovinyl groups leads to a maximum of β_vec for the derivative with one rather than two C(CN)₂ groups. With respect to endgroups, the indandione moiety generally is the least active group. Solvent effects are treated within the framework of the self‐consistent reaction field approximation. In most cases gas‐phase tendencies are either parallel or even reinforced if solvent effects are taken into account. The calculated results are compared with electric field induced second harmonic generation (EFISH) measurements. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 253–266, 2000     

Surface-modified membranes as a matrix for protein purification.

Recently introduced membrane-based chromatographic supports for protein separation are available either with a coupled ligand, e.g., protein A, protein G or ion-exchange groups, or as activated matrices for coupling a desired ligand. The coupling conditions for protein A and immunoglobulin G to an epoxy-activated membrane were determined. The performance of the prepared affinity membranes was investigated using pure rabbit immunoglobulin G and protein A as a model system. For practical application monoclonal antibodies from cell culture supernatant were purified with a prepared protein A membrane and for comparison with a sulphonic acid ion exchange membrane.     

Tuning the cross-gap transition energy of a quantum dot by uniaxial stress

We show that a piezoelectric actuator can be used to apply uniaxial stress to a layer of self-assembled quantum dots. The applied stress leads to a change of the quantum dot's ground state exciton energy by up to a few hundred μeV. This approach allows the possibility of an in situ and continuous tuning of the stress at temperatures down to 4 K and offers an alternative to tuning by temperature and Stark effect. We measure the relative change in the charging energy to the n-doped back contact by capacitance and the change in the exciton energy by photoluminescence. By tuning the uniaxial stress we are able to perform reflection spectroscopy on a single dot.     

High-performance single fundamental mode AlGaAs VCSELs with mode-selective mirror reflectivities

We present inverted surface relief vertical-cavity surface-emitting lasers (VCSELs) showing a side-mode suppression ratio above 30 dB up to maximum optical output powers of 6.3 mW and differential quantum efficiencies exceeding 90%. An evaluation of 160 relief devices on a sample incorporating graded layers yields 157 lasers with single-mode output powers of at least 2.9 mW, proving the high effectiveness of the technique despite the comparatively simple manufacture.