Convolution voltammetry of metal complexes

The application of convolution potential voltammetry to questions of metal complexation is described. Theoretical relations are derived to show that the stability constants may be directly related to the shift in the peak potential of the semiderivative wave, provided the complexes are labile. Equations are also given for inert and quasilabile complexes. Stability constants for the PbCl_x and CdCl_x systems are reported, illustrating the use of convolution techniques with linear scan voltammetry and with linear scan anodic stripping voltammetry. Advantages of convolution techniques are discussed.     

Low-temperature infrared and raman studies: XI. The vibrational behaviour of ammonium perchlorate- its phase changes and the rotational freedom of its ions

An infrared, Raman and X-ray diffraction study on NH₄CIO₄. was conducted in the temperature ranges 300 to 17 °K, 300 to 130 °K and 300 to 120 °K respectively. The infrared studies also included the deuterated salt. The spectra are discussed and vibrational assignments made. Changes in the infrared spectra, as well as intensity measurements of the vibrational bands indicate anomalous behaviour in the region 100–110 °K as well as 17–50 °K. Possible reasons for these changes are proposed. The rotational behaviour of the ammonium ion upon cooling and hydrogen bonding are discussed.     

Koordinationschemische Untersuchungen an Zinkdialkylen. X. Über die Reaktion von Zinkdimethyl mit sekundären Aminen

Dimethyl zinc reacts with diethyl amine, piperidine and morpholine forming definite 1:2- or 1:1-complexes. The weaker basic secondary amines pyrroline, pyrazolidine and imidazoline cause the evolution of methane and the formation of the corresponding zinc amides. In this way zinc pyrrolide, zinc pyrazolide and zinc imidazolide were obtained in form of pure substances.     

Electronic and vibrational second-order nonlinear optical properties of protein secondary structural motifs

A perturbation theory approach was developed for predicting the vibrational and electronic second-order nonlinear optical (NLO) polarizabilities of materials and macromolecules comprised of many coupled chromophores, with an emphasis on common protein secondary structural motifs. The polarization-dependent NLO properties of electronic and vibrational transitions in assemblies of amide chromophores comprising the polypeptide backbones of proteins were found to be accurately recovered in quantum chemical calculations by treating the coupling between adjacent oscillators perturbatively. A novel diagrammatic approach was developed to provide an intuitive visual means of interpreting the results of the perturbation theory calculations. Using this approach, the chiral and achiral polarization-dependent electronic SHG, isotropic SFG, and vibrational SFG nonlinear optical activities of protein structures were predicted and interpreted within the context of simple orientational models.     

Thermal resistance of ridge-waveguide laser diodes based on GaAs,GaSb or InP

The effects of different substrates (GaAs, GaSb and InP) on the thermal properties of laser diodes with a ridge-waveguide structure are presented. Laser diodes with the same basic geometry exhibit different thermal resistances. The reason is therefore the difference in thermal conductivity of the substrates and the active layer compounds. This leads to different temperature distributions in the structures. The theoretical results were supported by experimental data.

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Zusammenfassung Es wurde der Einfluß verschiedener Substrate (GaAs, GaSb und InP) auf die thermischen Eigenschaften von Laserdioden mit gefurchter Hohlleiterstruktur untersucht. Laserdioden mit dem gleichen geometrischen Grundaufbau zeigen verschiedene Wärmewiderstände. Die Ursache ist folglich der Unterschied in der Wärmeleitfähigkeit der Substrate und der Verbindungen der aktiven Schicht. Dies führt zu einer unterschiedlichen Temperaturverteilung in der Strukturen. Theoretische Ergebnisse werden durch experimentelle Daten bekräftigt.

     

Large clusters of cesium from pure vapor expansions

The generation of cesium clusters with up to 2500 atoms per cluster by nozzle expansion of pure metal vapor without carrier gas is reported. Electron impact is found to lead to positively or negatively charged clusters with comparable probability.     

Laser-induced breakdown spectroscopy of silicate, vanadate and sulfide rocks

Laser-induced breakdown spectroscopy (LIBS) in air at atmospheric pressure has been used to study four geological samples belonging to different structural families. Atomic emission spectra of vanadinite, pyrite, garnet and a type of quartz (compostela's quartz) are shown. The 532 nm line of a Nd:YAG laser at an irradiance of 18 x 10(11) W cm(-2) was used. The precise focus of the beam allowed microanalysis of a 0.02 mm(2) surface area working in single-laser shot mode. The use of an intensified gateable charge-coupled-device (CCD) detector permitted time-resolved studies. The spectral lines have been assigned to transitions in the neutral charge state of the corresponding atom of the material under investigation. The behavior of different transitions with time delay are shown. In experiments, minor components contained in several minerals have been detected. This fact has been used to demonstrate the applicability of the technique to characterize and identify similar minerals.     

Enantioselective synthesis of imperanene, a platelet aggregation inhibitor

Both enantiomers of imperanene, a platelet aggregation inhibitor, have been synthesized in 82-90% ee. The key step of establishing the chiral center was achieved through stereoselective alkylation with benzyl chloromethyl ether using Enders' RAMP/SAMP chiral auxiliary method. The natural product was determined to be the (S)-enantiomer through comparison of optical rotation data. Reaction: see text.     

Zum mechanismus des strahlenchemischen abbaus von polytetrafluorethylen

The present work studies the changes in polymer structure and the mechanism of the decomposition of polytetrafluoroethylene resin (PTFE) exposed to high energy radiation (electron beam). Spectroscopic and kinetic observations are used to interpret the degradation process. For the first time the decomposition of PTFE has been carried out on a preparative scale and new results obtained by analysing the degradation products. The radiation-induced degradation of PTFE is accompanied by thermal degradation under certain irradiation conditions. This is due to an increase in temperature of the polymer caused by retardation of highly accelerated electrons (heat accumulation effect).The kinetics are discussed in terms of the reactions and recombination of radicals produced by high-energy radiation both in the polymer melt and the polymer surface. These are related to the overall rate of decomposition.The primary radicals formed by decomposition of PTFE in an inert atmosphere (N₂, Ar) react to produce perfluorinated alkanes and alkenes. In the presence of reactive gases the decomposition fragments originated will react rapidly; e.g. if oxygen is present in the reactive area the radicals form perflourinated peroxyl and oxyl radicals which finally stabilize themselves by CC-scission to perfluorocarbon acid fluorides and carbonyldifluorides.     

High-performance liquid chromatography – atmospheric pressure negative chemical ionisation – mass spectrometry of 2,4-dinitrophenyl derivatives of amines

High-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) is used to detect 2,4-dinitrophenyl (DNP) derivatives of amines by means of negative chemical ionisation at atmospheric pressure. The high sensitivity and good comparability of UV- and MS-detection of DNP-derivatives of amines is shown by several examples. The high selectivity of the derivatisation and the detection method (UV and MS) is used for the analysis of unknown amines in aqueous phases after hydrolytic degradation of polyamide-amine- or polyamine-epoxide-adducts as well as for the characterisation of commercial products.