Ion-pair recognition of tetramethylammonium salts by halogenated resorcinarenes

The non-covalent interactions of different upper-rim-substituted C(2)-resorcinarenes with tetramethylammonium salts were analyzed in the gas phase in an Electrospray Ionization Fourier-transform ion-cyclotron-resonance (ESI-FTICR) mass spectrometer and by (1)H NMR titrations. The order of binding strengths of the hosts towards the tetramethylammonium cation in the gas phase reflects the electronic nature of the substituents on the upper rim of the resorcinarene. In solution, however, a different trend with particularly high binding constants for halogenated resorcinarenes has been observed. This trend can be explained by a synergetic effect originating from the interaction of the halogenated resorcinarenes with the counter anions through hydrogen bonding. This study highlights the importance of weak interactions in recognition processes and points out the benefits of comparing the gas-phase data with results obtained from solution experiments.     

Photoreflectance measurements in GaAs/AlGaAs asymmetric quantum wells

In this work we investigated the optical control of the bidimensional electron gas density in a single asymmetric quantum well using, for the first time, photoreflectance. We performed our measurements at 80 and 300 K as a function of the power density of the pump beam. Under strong illumination, the bidimensional electron gas density is washed out of the quantum well and under a dark condition, it reaches its maximum value. The variation of the optical transitions observed in our photoreflectance spectra was related to the induced changes of the band profile in between these two limiting cases.     

Numerical simulation of the growth of 2″ diameter GaAs crystals by the vertical gradient freeze technique

We present a global two-dimensional model of a multi-zone-furnace for the growth of GaAs using the bottom-seeded vertical gradient freeze (VGF) technique. The finite element code FIDAP was used to perform calculations of the heat transfer due to radiation and conduction in the whole furnace. The numerical results show a good agreement between measured and calculated temperature distributions in the furnace and calculated/measured power consumptions of the heaters. Quasi-steady-state calculations for a typical growth process were performed and the influence of different growth velocities on the interface shape was analyzed.     

Rational design of functional oxide thin films with embedded magnetic or plasmonic metallic nanoparticles

Getting into films: Semiconductor thin films containing magnetic or plasmonic metal nanoparticles are key materials for the development of high-efficiency solar cells, bright light-emitting diodes, and new magnetoelectric devices. The catalytically driven chemical vapor deposition offers a unique way to combine deposition of the metallic nanoparticles with that of functional oxides to produce such films.     

On-chip approach for traceable quantification of biomarkers based on isotope-dilution surface-enhanced Raman scattering (IDSERS)

We present an on-chip approach for the quantification of biomarkers based on isotope-dilution surface-enhanced Raman scattering (IDSERS). The full procedure was realized on a few square millimetres of a SERS-active substrate, covered with either lithographically engineered gold nanotriangles or silver nanospheres generated by galvanic displacement deposition. The use of certified reference materials combined with the ID principle ensures traceability of the quantitation to SI units. A series of substance spots was deposited onto the SERS active area and measured one by one in fast sequence. The SERS spectra were used to generate and validate a PLS model and also to predict the creatinine concentration of an unknown serum sample.     

A lifting and recombination algorithm for rational factorization of sparse polynomials

We propose a new lifting and recombination scheme for rational bivariate polynomial factorization that takes advantage of the Newton polytope geometry. We obtain a deterministic algorithm that can be seen as a sparse version of an algorithm of Lecerf, with a polynomial complexity in the volume of the Newton polytope. We adopt a geometrical point of view, the main tool being derived from some algebraic osculation criterion in toric varieties.     

Dependence of spin-asymmetry in the Shubnikov-de Haas resistance on back-gating, illumination and uniaxial stress

We present measurements of the Shubnikov-de Haas (SdH) resistivity on GaAs/AlGaAs heterojunctions. We compare measurements in which in the same sample the electron density was increased to the same value either by applying a back-gate voltage or illumination. We conclude that both the overlap of the electron wavefunctions in the two-dimensional electron gas with positive and negative scattering centers and the number of positive and negative scatterers determine the asymmetry in the SdH-peaks. The asymmetry in the SdH-peaks depends on the electron density because the scattering on remote and background impurities have a different electron density dependence. After illumination the neutralization rate of the acceptors in the GaAs determines whether the asymmetry increases or decreases. We show that the asymmetry of the SdH-peaks can also be modified by applying uniaxial stress.     

Cyclophosphate

Zusammenfassung Der second messenger Adenosin-3,5-monophosphat (A-3,5-MP) wird in den Organismen durch Phosphodiesterase abgebaut. Mit Hilfe einer Reihe verschiedener Cyclophosphate wurde die Abhängigkeit der Phosphodiesterase-Aktivität von der Struktur des Substrates untersucht. Das Enzym aus Herz spaltet Purinribosid-Cyclophosphate schneller als Pyrimidinribosid-Cyclophosphate. 6-Substitution am Purinring vermindert die Spaltgeschwindigkeit, dieser Effekt ist bei Substitution an der 8-Stelle noch stärker. Tritt ein Substituent an die 2O-Stellung, wird die Spaltrate in geringerem Maße wie bei 6-Substitution vermindert. Untersuchungen mit dem Enzym aus Fettgewebe brachten ähnliche Ergebnisse.

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CyclophosphatesIII. Splitting of various cyclophosphates by phosphodiesterase from heart and adipose tissue

In organisms, the second messenger adenosine-3,5-monophosphate (A-3,5-MP) is degraded by phosphodiesterase. Employing a series of different cyclophosphates, the structural requirements for phosphodiesterase activity are investigated. With the heart enzyme, purine riboside cyclophosphates are split faster than pyrimidine riboside cyclophosphates. 6-substitution of the purine moiety lessens the splitting rate. This effect is still more pronounced when substitution takes place in the 8-position. Substitution in the 2O-position has also a diminishing effect on the splitting rate, which is less than the effect achieved by 6-substitution. Studies with the enzyme from adipose tissue gave similar results.

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II. Mitteilung: Michal, G., du Plooy, M., Woschée, M., Nelböck, M., Weimann, G.: diese Z. 252, 183 (1970).

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Wir danken Frau Grudrun Kreutzer, Frl. Gisela Jurz und Herrn Rolf Kieffer für die geschickte und sorgfältige Ausführung der Untersuchungen, sowie Herrn Haid und Herrn Mühlegger für synthetische Arbeiten.