Synthesis and properties of Hg-based high-T c superconductors

Il Nuovo Cimento D - The formation of Hg-based HTSC materials was investigated through the development of non-conventional techniques. The former was based on a singlestep synthesis at temperatures...     

Native ethylene glycol in wine: Application of a dead volume free,very fast “deans heart-cut” system on-line with multi-chromatography

Data about the existence of native HO? CH₂? CH₂? OH (MEG) in natural wines and champagne has led to delicate questions because of legal decisions already made to declare wine or champagne illegal for sale if the MEG concentrations found are above 10 mg/liter. Action has been taken because of the DEG (diethylene glycol) disaster in European wines of 1985…86. An incorrect legal decision was made due to the belief that MEG cannot be produced biochemically by grape vines. A further reason may be lack of correct data on native MEG trace concentrations, as a result of the special behavior of this diol. As first member of a homologous series whose higher members (C₄) are normally found in all wines at quite high concentration levels, MEG shows extremely adsorptive behavior. The solution of the chromatographic problems is summarized in this paper. MEG concentrations in Riesling as example are in the range of 2 to 6 mg/liter and can easily be increased by biotechnological steps to a level of around 10 to 60 mg/liter. This is again due to the specific adsorptive behavior of MEG, which can be enriched on filter surfaces and displaced when the wine acidity changes with changing types. In order to control and guarantee the qualitative and quantitative results of MEG analyses we used a combination of Deans heart cutting on-line with Multi-Chromatography. It was easy to produce false data by many otherwise useful single column or two-dimensional separation processes, etc.     

40 GHz Mode-Locked Semiconductor Lasers: Theory, Simulations and Experiment

We study both theoretically and experimentally typical operation regimes of 40 GHz monolithic mode-locked lasers. The underlying Traveling Wave Equation model reveals quantitative agreement for characteristics of the fundamental mode-locking as pulse width and repetition frequency tuning, as well as qualitative agreement with the experiments for other dynamic regimes. Especially the appearance of stable harmonic mode-locking at 80 GHz has been predicted theoretically and confirmed by measurements. Furthermore, we derive and apply a simplified Delay-Differential-Equation model which guides us to a qualitative analysis of bifurcations responsible for the appearance and the breakup of different mode-locking regimes. Higher harmonics of mode-locking are predicted by this model as well.     

Coligand role in the NHC nickel catalyzed C–F bond activation: investigations on the insertion of bis(NHC) nickel into the C–F bond of hexafluorobenzene

The reaction of [Ni(Mes₂Im)₂] (1) (Mes₂Im = 1,3-dimesityl-imidazolin-2-ylidene) with polyfluorinated arenes as well as mechanistic investigations concerning the insertion of 1 and [Ni(ⁱPr₂Im)₂] (1ipr) (ⁱPr₂Im = 1,3-diisopropyl-imidazolin-2-ylidene) into the C–F bond of C₆F₆ is reported. The reaction of 1 with different fluoroaromatics leads to formation of the nickel fluoroaryl fluoride complexes trans-[Ni(Mes₂Im)₂(F)(Ar^F)] (Ar^F = 4-CF₃-C₆F₄2, C₆F₅3, 2,3,5,6-C₆F₄N 4, 2,3,5,6-C₆F₄H 5, 2,3,5-C₆F₃H₂6, 3,5-C₆F₂H₃7) in fair to good yields with the exception of the formation of the pentafluorophenyl complex 3 (less than 20%). Radical species and other diamagnetic side products were detected for the reaction of 1 with C₆F₆, in line with a radical pathway for the C–F bond activation step using 1. The difluoride complex trans-[Ni(Mes₂Im)₂(F)₂] (9), the bis(aryl) complex trans-[Ni(Mes₂Im)₂(C₆F₅)₂] (15), the structurally characterized nickel(i) complex trans-[Ni^I(Mes₂Im)₂(C₆F₅)] (11) and the metal radical trans-[Ni^I(Mes₂Im)₂(F)] (12) were identified. Complex 11, and related [Ni^I(Mes₂Im)₂(2,3,5,6-C₆F₄H)] (13) and [Ni^I(Mes₂Im)₂(2,3,5-C₆F₃H₂)] (14), were synthesized independently by reaction of trans-[Ni(Mes₂Im)₂(F)(Ar^F)] with PhSiH₃. Simple electron transfer from 1 to C₆F₆ was excluded, as the redox potentials of the reaction partners do not match and [Ni(Mes₂Im)₂]⁺, which was prepared independently, was not detected. DFT calculations were performed on the insertion of [Ni(ⁱPr₂Im)₂] (1ipr) and [Ni(Mes₂Im)₂] (1) into the C–F bond of C₆F₆. For 1ipr, concerted and NHC-assisted pathways were identified as having the lowest kinetic barriers, whereas for 1, a radical mechanism with fluoride abstraction and an NHC-assisted pathway are both associated with almost the same kinetic barrier.

A combined experimental and theoretical study on the mechanism of the C–F bond activation of C₆F₆ with [Ni(NHC)₂] is provided.     

Determination of ammonia, ethanol and acetic acid in solution using membrane introduction mass spectrometry

Methods have been developed to allow applications of membrane introduction mass spectrometry (MIMS) to monitor solution phase components of fermentation broths using electron ionization. The solutions are transported by flow injection analysis (FIA) through a direct insertion membrane probe, fitted with a silicone membrane in the sheet configuration. Analytes of interest pass through the membrane and are ionized by electron implant ionization. The compounds monitored are ammonia, acetic acid, and ethanol, with ammonia being detected as the monochloramine derivative which is generated at pH 10 upon addition of hypochlorite. Quantitation is achieved using external standard solutions. The dynamic range for the quantification of ammonia is 2-8000 ppm, and for ethanol and acetic acid 10-1000 ppm. This method provides rapid detection of analytes of interest, on-line monitoring capabilities, and the advantage of electron ionization. The introduction of samples into the mass spectrometer is achieved readily and automatically, the response time is a few seconds, and there are no memory effects.     

40Ar/39Ar — Alter eines Basits der Ostantarktis

The⁴⁰Ar/³⁹Ar technique is an analytical variation of the K–Ar dating method. A known fraction of the³⁹K in a sample is converted to³⁹Ar by irradiation with fast neutrons. In an incremental heating experiment, the argon is released from the sample fractionally by stepwise heating. The result is a series of apparent ages.⁴⁰Ar/³⁹Ar age spectrum was determined for the sample Oase Vestfold. The minimum of the saddle-shaped age spectrum gives 1.0 billion years.     

Characterization of SiO2 protective coatings on polycarbonate

SiO₂ protective coatings have been deposited on polycarbonate substrates by plasma ion assisted deposition. The influence of ion energy on the water permeability and the surface topography of the coatings was studied by infrared spectroscopy and atomic force microscopy. Coatings deposited at sufficiently high ion energies show a barrier effect against moisture uptake and considerably reduced film roughness. Both effects are attributed to an increase of the packing densities of the coatings.     

Hydrazones and new Oximes of 4-Aminobicyclo[2.2.2]octanones and their Antiprotozoal Activities

Summary. 4-Aminobicyclo[2.2.2]octan-2-ones and -ols showed activity against the causative organisms of East African sleeping sickness and Malaria tropica. Several imino derivatives of the ketones were more active. Now hydrazono analogues and 3-hydroximino derivatives of the ketones and alcohols were synthesized. The structures of the obtained isomers were elucidated by NMR spectroscopy. A single phenylhydrazone exhibited quite good antitrypanosomal activity in the range of already known imino analogues.     

Electron Impact Induced Fragmentation of Aromatic Alkoxyimines II [5]. Formation and Transformation of Heterocyclic Radical Cations in the Gas Phasea

 The molecular ion 1 of N-(n-propoxy)benzaldimine I rearranges by an 1,5-H-shift to the δ-distonic ion 2 which subsequently cyclizes to the α-distonic ion 3. Homolytic cleavage of the N–O bond in 3 results in the δ-distonic ion 4 which expels CH₂O leading to the β-distonic ion 5. Ion 5 is also formed from the molecular ions of tetrahydrooxazines II and III and from M^+• of phenylazetidine IVa. In a subsequent step, ion 5 cyclizes to the N-protonated 3,4-dihydroisoquinolinium ion 6. The syntheses of II–IV and their derivatives are described.