Chromatographic determination of amino acid enantiomers in beers and raw materials used for their manufacture

Using gas chromatography (GC) on a chiral stationary phase, accompanied by high-performance liquid chromatography, beers and raw materials used for manufacturing (hops, barley grains, malts) were investigated for the pattern and quantities of amino acid enantiomers. Although L-amino acids were most abundant, certain D-amino acids were detected in all beers and most of the raw materials. Highest amounts of D-amino acids were detected in special beers such as Berliner Weisse that underwent bottle-conditioning with lactic cultures, and Belgian fruit beers produced by spontaneous fermentation. It is demonstrated that GC on chiral stationary phases is highly suitable for the quantitative determination of amino acid enantiomers in beers and raw materials used for their manufacture. Quantities, relative amounts and pattern of amino acid enantiomers can serve in particular as chiral markers for the authenticity of special beers.     

Yellowing and IR-changes of spruce wood as result of UV-irradiation

The yellowing and IR-changes of spruce wood as a result of UV-irradiation were studied using two different types of xenon lamps (lambda>300 nm; I(o)=50 mW cm(-2) and lambda>280 nm; I(o)=17.5 mW cm(-2)). Changes in the IR spectra as well as the yellowing of the irradiated wood surfaces show the influence of UV light on the wood modules. The UV-irradiation (72 h; lambda>300 nm; I(o)=50 mW cm(-2)) decreased the lignin content on the surface by up to 20% of the original values. The colour difference of yellowing (deltaE) exhibited a systematic trend to higher values with increasing irradiation time. Our results show that the photoyellowing (UV-Vis detection) correlates very well with lignin degradation (IR detection). This result is in agreement with the quinone formation as the chromophoric reaction product of lignin decay. The degradation, yellowing, and oxidation kinetics differed only little using different light sources. The absorbed light intensity, which depends on wavelength, the intensity distribution of the light source and the absorption spectrum of lignin, influenced the degradation rate. Under the current experimental conditions, the absorption spectrum of lignin was the most important factor. Therefore, irradiation with lambda>280 nm is useful for rapidly monitoring the UV-degradation of wood     

Heats of formation of [2.2]paracyclophane-1-ene and [2.2]paracyclophane-1,9-diene - an experimental study

The enthalpies of formation [Delta(g)] of tricyclo[8.2.2.2(4,7)]hexadeca-1(13),2,4(16),5,7(15),10(14),11-heptaene (2, 1,2-dehydro[2.2]paracyclophane or [2.2]paracyclophane-1-ene) and tricyclo[8.2.2.2(4,7)]hexadeca-1(13),2,4(16),5,7(15),8,10(14),11-octaene (3, 1,2,9,10-dehydro[2.2]paracyclophane or [2.2]paracyclophane-1,9-diene) have been determined by measuring their heats of combustion in a microcalorimeter and their heats of sublimation by the transpiration method. Values of the strain energies (SE) [SE(2) = 34.7 kcal mol(-)(1), SE(3) = 42.0 kcal mol(-)(1)] have been derived from the gas-phase heats of formation and are compared with those from MM3 and PM3 calculations and with the corresponding value SE(1) = 30.1 kcal mol(-)(1) for the parent tricyclo[8.2.2.2(4,7)]hexadeca-1(13),4(16),5,7(15),10(14),11-hexaene (1, [2.2]paracyclophane). The higher strain energies of 2 and 3 (by 4.6 and 11.9 kcal mol(-)(1)) are in accord with the well-known increased reactivities of their aromatic rings as a consequence of their increased bending. As revealed by an X-ray crystal structure analysis, the bending in the monoene 2 corresponds to that of 1 and 3 at one of two bridging corners.     

Extraction of gallium(III) and aluminium(III) with O,O-dialkyldithiophosphoric acids

The extraction of Ga³⁺ and Al³⁺ with the liquid cation-exchangers di-n-butyldithiophosphoric acid (DBTPA) and di-(2-ethylhexyl)dithiophosphoric acid (DETPA) in kerosene, in the presence and absence of alcohols and tri-n-butyl phosphate (TBP) has been studied. Both Ga³⁺ and Al³⁺ can be extracted in the form of a neutral complex, MA₃, but the distribution coefficient of Ga³⁺ is the higher by about two orders of magnitude, which can be the basis of the solvent extraction separation of gallium and aluminium. The differences can be explained by the interaction between the sulphur donor atoms of the extractants and the d¹⁰ electronic shell of Ga³⁺ as well as by the lower steric hindrance of ligands co-ordinated to Ga³⁺.     

2-Benzoylamino-6,7-dimethoxy-4H-3,1-benzoxazin-4-one: Synthesis and investigation of serine protease inactivation

Summary 2-Benzoylamino-6,7-dimethoxy-4H-3,1-benzoxazin-4-one was prepared by thermal treatment of 2-(3-benzoylthioureido)-4,5-dimethoxybenzoic acid and by benzoylation of 2-amino-6,7-dimethoxy-4H-3,1-benzoxazin-4-one. The inactivation of chymotrypsin and human leukozyte elastase by the title compound and 2-benzoylamino-4H-3,1-benzoxazin-4-one is reported.

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2-Benzoylamino-6,7-dimethoxy-4H-3,1-benzoxazin-4-on: Synthese und Untersuchung der Inaktivierung von Serin-Proteasen

Zusammenfassung 2-Benzoylamino-6,7-dimethoxy-4H-3,1-benzoxazin-4-on wurde durch thermische Behandlung von 2-(3-Benzoylthioureido)-4,5-dimethoxybenzoesäure und durch Benzoylierung von 2-Amino-6,7-dimethoxy-4H-3,1-benzoxazin-4-on hergestellt. Über die Inaktivierung von Chymotrypsin und humaner Leukozyten-Elastase durch die Titelverbindung und 2-Benzoylamino-4H-3,1-benzoxazin-4-on wird berichtet.

     

In-situ HEED structure analysis of AlNx films grown by the simultaneous use of a radical beam source and ICB technique

A reactive ionized cluster beam technique (RICB) which was composed of a conventional ICB source and a radical beam source has been used to deposit stable and metastable polycrystalline AlN_x (0≤x≤1) films. Using in-situ high energy electron diffraction (HEED) at grazing incidence geometry, crystallographic properties such as structure, preferred orientation and interplanar dspacing values were determined and the relation to deposition parameters investigated. It could be shown that the simultaneous use of the ICB technique and a radical beam source to separately control the kinetic energy of the Al ions and the dissociation rate of molecular nitrogen, allows AlN films to be deposited with variable composition and crystal structures. In-situ HEED used in the transmission mode is an effective tool to investigate the crystallography of growing compound films such as AlN_x.     

On using the adjacency matrix power method for perception of symmetry and for isomorphism testing of highly intricate graphs

A modification of the adjacency matrix power method described recently for the perception of symmetry in graphs is introduced, which expands the limits of the method far beyond the realm of chemically interesting graphs. The procedure finds the automorphism partition even for intricate graphs without performing a tree search. The calculation effort increases with the problem size polynomially for all tested cases, including strongly regular graphs, two-level regular graphs, and graphs corresponding to balanced incomplete block designs (BIBD). An equally powerful computer program for testing isomorphism of graphs based on the adjacency matrix power method is introduced.     

A new tandem route to angular tetraquinanes. Synthesis of the Waihoensene ring system

[formula: see text] This paper describes a new tandem reaction sequence leading to angularly fused polyquinanes from squaric acid-derived bicyclo[6.3.0]-undecadienediones. Such compounds undergo a dual Michael addition. The enolate form in the first intermolecular addition undergoes the second intramolecular transannular addition to give the angular polyquinanes. A particularly interesting example is a catalytic transformation of cis-13-methylyricyclo[10.3.0.0]pentadeca-4(5),12(13)-diene-3 ,14-dione to (3R*,3aS*,5aR*,9aR*,11aR*)-3-methyl-1,2,3,5,5a,6 ,7,10,11,11a-decahydro-4H- pentaleno[6a,1-c]indene-2,10-dione, a compound having the tetracyclic ring system found in the natural product waihoensene. The mechanism and synthetic scope of these reactions are discussed.     

Optimization of the electrophoretic deposition of YBa2Cu3O7−x superconducting large area coatings

Large area coatings (>10cm²) of the high temperature superconductor YBa₂Cu₃O_7–x (x = 0.1 – 0.2) (YBCO) have been prepared by scale up an electrophoretic deposition technique using silver sheets and Si-wafers coated with Ag or Au as substrates. Several parameters, like the kind of the solvent, the applied voltage, the distance between the electrodes, the initial concentration of the suspension and the temperature during the electrophoresis were investigated in order to attain high deposition rates, as well as uniform YBCO coatings with the proper stoichiometry. To obtain a strongly adherent and dense coating a subsequent appropriate sintering and annealing procedure has been developed. The coatings obtained were characterized for their stoichiometry and superconducting properties by X-ray diffraction (XRD), Raman spectroscopy and magnetic measurements. The homogeneity and thickness of the films and the average grain size of the deposited particles have been investigated by optical and scanning electron microscopy (SEM).