Zur Darstellung von Oxiden cyclischer,sekundärer Arsine

Hydrolysis of 1-chloro-arsolane, C₄H₈AsCl, and 1-chloro-arsenane, C₅H₁₀AsCl, leads to oxides C₈H₁₀As₂O and C₁₀H₂₀As₂O, respectively. On direct alkylation of arsenic trioxide with 1.4-butane- and 1.5-pentane-bis-magnesium bromide these oxides are formed only in trifling amounts. Better results are gained by alkylation of N,N-dimethylaminodichloroarsane into amino-arsolane and amino-arsenane, which are also transformed into these oxides by hydrolysis. By hydrolysis of 1.4-dichloro-diarsenane only a small amount of 1.4-epoxo-arsenane is formed, whereas mainly a dimer of this oxide results. Solvolysis of 2.6-dichloro-diarsa-[3.3.0]-bicyclooctane with water, hydrogen sulphide or methylamine leads to 7-oxa-, 7-thia- and 7-methylaza-2.5-diarsa-noradamantane, respectively.     

Quantitative goldbestimmung in filmmaterialien mittels flammenloser atomabsorption

A graphite rod electrothermal atomizer has been used for the AAS determination of traces of gold in hydrochloric and in hydrobromic acid solutions, and also after extraction into HBr-saturated methyl isobutyl ketone. Photographic film samples were decomposed first by enzyme action then by nitric acid/peroxide oxidation, and the gold was extracted into MIBK. For 10-μl aliquots of solution the 3s limits of detection were 3 × 10^?10g for aqueous solutions, 7 × 10^?10g for MIBK, and 7 × 10^?9 g/cm² for film.     

Die Analytik wasserl?slicher Cellulose?ther

Zusammenfassung Es werden allgemeine und qualitative Merkmale von Natrium-Carboxymethylcellulose, Methylcellulose und Hydroxyäthylcellulose sowie gravimetrische und titrimetrische Bestimmungsmöglichkeiten der wasserlöslichen Celluloseäther insbesondere im Zusammenhang mit dem Substitutionsgrad beschrieben.Verfahren zur Ermittlung der Viscosität von Lösungen, des Polymerisationsgrades und des Gelteilchengehaltes werden besprochen. Abschließend werden charakteristische Beispiele für das analytische Vorgehen bei Substanzgemischen gegeben, die nur einen geringen Anteil Celluloseäther enthalten.

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Analysis of water-soluble cellulose ethers

General and qualitative characteristics of sodium carboxymethylcellulose, methylcellulose and hydroxyethylcellulose are presented and gravimetric and titrimetric methods for the determination of water-soluble cellulose ethers are described, especially with regard to the degree of substitution. Procedures for the measurement of the viscosity of solutions, of the degree of polymerisation and of the content of gel particles are discussed. Characteristic examples are presented for the treatment of mixtures containing only a small percentage of cellulose ethers.

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Erweiterte und umgearbeitete Fassung eines Vortrages, gehalten am 28. 6. 1971 in Baden-Baden.

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Frau Dr. G. Bartelmus, Analyt. Laboratorium der Fa. Kalle AG, sprechen wir an dieser Stelle unseren herzlichen Dank für wertvolle Beratung aus.     

Organische Schwefelverbindungen—IV: Elektronenstossinduzierte Redoxreaktion von ortho-Nitrothiobenzoesäure-S-p-tolylester

The electron-impact fragmentation of S-p-tolylester of nitrothiobenzoic acid leads to a previously unknown rearrangement in the case of the ortho compound. This consists of an intra molecular redoxreaction with oxygen transfer from the o-nitro group onto the sulphur of the thiol ester group. The position of the nitro group is not only an essential influence on the fragmentation pattern, but also of dramatic importance in determining the lifetime of the molecular ion.     

Chemische Vitamin D<Subscript>3</Subscript>-Bestimmung in Lebertran

The different aspects of Vitamin D₃ determination and the data reported in the literature are discussed. The spectrophotometric determination of Vitamin D₃ in cod-liver oil is carried out after the alkaline saponification, extraction of unsaponified parts, precipitation of accompanying sterols and the column- and thin-layer chromatographic purification and separation of vitamin D₃ on 40 cm plates from other vitamins. The dyestuff α-naphtholbenzein is suited well as standard substance for the better location and identification of vitamin D₃ zone on the thin-layer plate. The results obtained from the chemical method were checked through the simultaneous biological determination.     

Rhodopsin exhibits a preference for solvation by polyunsaturated docosohexaenoic acid

An all-atom molecular dynamics simulation of rhodopsin in a membrane environment has been carried out with lipid composition similar to that of the retinal membrane. The initial conformation of the protein was taken from the X-ray crystallographic structure (1F88), while those of the lipids came from a previous molecular dynamics simulation. During the course of the 12.5 ns simulation, the initially randomly placed lipids adopt an anisotropic solvation structure around the protein. The lipids, having one saturated stearic acid chain and one polyunsaturated docosohexaenoic acid chain with a zwitterionic phosphatidylcholine headgroup, arrange themselves to maximize contact between the polyunsaturated chain and the protein surface. This organization is driven by energetically favorable interactions between the transmembrance helices and the docosohexaenoyl chains that are largely of the van der Waals type. These observations are consistent with various experimental studies on rhodopsin and other G-protein coupled receptors and with the picture of extreme flexibility in polyunsaturated fatty acid chains that has arisen from recent NMR and computational work.     

Photon-induced dissociation with a four-sector tandem mass spectrometer

The feasibility of using photodissociation of protonated peptide molecules to sequence specific fragment ions with a 193-nm pulsed laser beam in a magnetic deflection tandem mass spectrometer of EBEB configuration was demonstrated. Although the short pulse (15 ns) and low repetition rate (100 Hz) of the excimer laser permitted the irradiation of only ～ 0.02% of the (M + H)⁺ ions exiting MS-1, a photon-induced decomposition spectrum of the heptapeptide angiotensio III (M _r 930.5) was produced that was practically the same (but with better signal-to-noise ratio) as that generated by collision-activated dissociation at the same low duty cycle. Because of the low and pulsed fragment ion currents, an array detector was used to record the spectra. A dependence between laser power and abundance of fragment ions was observed (increased power increases the relative abundance of ions of low mass). Laser power was varied from 6 to 80 mJ. Formation of fragment ions from a large peptide (melittin, M, 2844.75) was also observed. The results permit the design of modifications that may increase the fragment ion yield to 10% or higher, which would make photon-induced decomposition a useful method for magnetic deflection mass spectrometers.     

Notiz zur quantitativen Bestimmung von Si-H- und Si-Si-Gruppen

Zusammenfassung Eine einfache und genaue Methode zur Bestimmung von Si-H- und Si-Si-Gruppen wird vorgeschlagen, die auf alkalischer Hydrolyse der Substanz in einem verschlossenen und evakuierten Kolben und AuswÄgen des dem entwickelten Wasserstoff entsprechenden Wasservolumens beruht. Bei H-Gehalten von 1–2% betrÄgt die Genauigkeit ± 0,03% (abs.).

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Note on the quantitative determination of Si-H- and Si-Si-groups

A simple, robust and surprisingly exact method for the quantitative determination of Si-H- or Si-Si-groups is based on alkaline hydrolysis of the Si-H- or Si-Si-containing substances in a sealed and evacuated vessel and weighing of the volume of water equivalent to the developed volume of hydrogen. The accuracy is ± 0.03% (abs.) with H contents of 1–2%.

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Herrn Prof. Dr. E. Asmus zum 60. Geburtstag gewidmet.     

2d-CUSUM for the detection of tendencies inherent in noisy bivariate data

Noisy analytical data dependent on 2 different variables (bivariate data) can be evaluated by an extended (2-dimensional) CUSUM-algorithm. Even at very high random fluctuations this 2d-CUSUM allows to detect long-term instationarities even from short series of measurements. The model of 2d-CUSUM as well as examples (distribution analysis, time-series analysis, treatment of calibration functions) are shown in this paper.Dedicated to Professor Dr. R. Geyer (Naumburg/Saale) on the occasion of his 80th birthday on April 14, 1994     

Periodic solutions of dry friction problems

Dry friction problems lead to discontinuous differential equations, e.g. to