Mikrophy'sikalische Vorgänge,die die Entstehung der Schnellen Schichtungswellen in der Neonglimmentladung bedingen

Zusammenfassung Im nachstehenden Artikel werden mikrophysikalische Vorgänge behandelt, die das Auftreten schneller Schichtungswellen in Neonglimmentladungen veranlassen können. Es werden sowohl die qualitativen Abhängigkeiten, als auch die ziffernmäigen Werte der Parameter der Schichtungswellen mit den charakteristischen Gröenwerten der in diesem Entladungstypus vor sich gehenden Vorgänge verglichen. Auf Grund der vorgenommenen Vergleiche kann gesagt werden, da die Relaxationszeiten der schnellen Wellen durch die Diffusionslebensdauer der atomaren, bzw. molekularen Ionen gegeben sind.

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Zum Schlu danken wir F. Kroupa und V. Krejí für die aufmerksame Lesung der Arbeit und wertvolle Hinweise.     

Three Types of Induced Tryptophan Optical Activity Compared in Model Dipeptides: Theory and Experiment

The tryptophan (Trp) aromatic residue in chiral matrices often exhibits a large optical activity and thus provides valuable structural information. However, it can also obscure spectral contributions from other peptide parts. To better understand the induced chirality, electronic circular dichroism (ECD), vibrational circular dichroism (VCD), and Raman optical activity (ROA) spectra of Trp‐containing cyclic dipeptides c‐(Trp‐X) (where X=Gly, Ala, Trp, Leu, nLeu, and Pro) are analyzed on the basis of experimental spectra and density functional theory (DFT) computations. The results provide valuable insight into the molecular conformational and spectroscopic behavior of Trp. Whereas the ECD is dominated by Trp π–π* transitions, VCD is dominated by the amide modes, well separated from minor Trp contributions. The ROA signal is the most complex. However, an ROA marker band at 1554 cm^?1 indicates the local χ₂ angle value in this residue, in accordance with previous theoretical predictions. The spectra and computations also indicate that the peptide ring is nonplanar, with a shallow potential so that the nonplanarity is primarily induced by the side chains. Dispersion‐corrected DFT calculations provide better results than plain DFT, but comparison with experiment suggests that they overestimate the stability of the folded conformers. Molecular dynamics simulations and NMR results also confirm a limited accuracy of the dispersion‐DFT model in nonaqueous solvents. Combination of chiral spectroscopies with theoretical analysis thus significantly enhances the information that can be obtained from the induced chirality of the Trp aromatic residue.     

The susceptibility of lead telluride PbTe

The results are given of measuring the temperature dependence of the susceptibility of samples of n- and p-type PbTe, containing either an excess of one or other of the components or ions Cl^–, or Ag⁺, as impurities. The conception of cation or anion vacancies, which can be occupied by a hole or electron, Ag⁺ or Cl^– ions, was employed, in addition to the constants taken from other measurements, to explain the dependences measured.     

An alternate version of Pirogov-Sinai theory

A new approach to the Pirogov-Sinai theory of phase transitions is developed, not employing the contour models with a parameter. The completeness of the phase diagram is proven.     

Solvent-free,catalyst-free aza-Michael addition of cyclohexylamine to diethyl maleate: Reaction mechanism and kinetics

The aza-Michael reaction is the addition of an amine to an electron deficient C=C double bond. This reaction is also used in the synthesis of precursors of polymeric networks. In this study, we paid attention to the kinetics and mechanism of the aza-Michael addition of cyclohexylamine (CHXA) to diethyl maleate (DEM) performed as a solvent-free, catalyst-free reaction and to concurrent reactions. In situ Raman spectroscopy, NMR spectroscopy and gas chromatography/mass spectrometry have shown the occurrence of three simultaneous reactions: (i) the aza-Michael addition of CHXA to DEM leading to diethyl 2-(cyclohexylamino)succinate, (ii) isomerization of DEM to diethyl fumarate (DEF), and (iii) the aza-Michael addition of CHXA to DEF formed by the reaction (ii). All of these reactions proceed with third order kinetics, first order in DEM or DEF and second order in CHXA. We propose a kinetic model that allows kinetic constants to be estimated. Furthermore, a numerical solution of the set of differential equations confirms the expected kinetic equations of reactions (i) and (ii) and gives values of rate constants comparable to the estimated ones. A DFT mechanistic study illustrates the structure of the reaction intermediates and transition states of all reactions and explains the contribution of the second amine molecule in the reaction mechanism.     

Preliminary study to prepare a reference material of toluene metabolite – o-cresol and benzene metabolite-phenol – in human urine

The candidate reference material (RM) was prepared by freeze-drying pooled urine samples obtained from healthy persons occupationally exposed to toluene. Homogeneity testing yielded no significant differences of urinary concentrations of o-cresol and phenol in 15 randomly selected units of RM. Stability testing showed no significant changes of concentrations of the above analytes over a period of 6 months. Property (pre-certified) values of phenol and o-cresol concentrations and their uncertainties (9.06±0.47 mg l⁻¹ and 1.03±0.06 mg l⁻¹, respectively) were estimated from results of a small-scale interlaboratory comparison in which two laboratories participated using four different analytical methods.     

Darstellung neuer Indandion-Analoga, 6. Mitt.: Sulfonierung des Indandion-Analogons aus Diphensäureanhydrid und Phenylessigsäure

Zusammenfassung Durch Behandlung des aus Phenylessigsäure und Diphensäureanhydrid synthetisierten Indandion-Analogons1 mit Oleum wurden Salze von zwei Monosulfosäuren (4 a und5 a) hergestellt. Die IR- und UV-Spektralanalyse sowie einige chemische Umwandlungen deuten darauf hin, daß die Sulfogruppe in4 a die 6- und in5 a die 6'-Stellung einnimmt. Aus der Sulfosäure4 erhielt man nach Behandlung mit SOCl₂ das Sulfochlorid (7), das mit Ammoniak leicht in das entsprechende Sulfonamid (8) übergeht.

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Preparation of new indandione analogues, VI.: Sulfonation of the indandione analogue from diphenic anhydride and phenylacetic acid

After treatment with oleum of the indandion analogues1 obtained from phenylacetic acid and diphenic anhydrid, the salts of two monosulfo derivates (4 a and5 a) were isolated. The UV and IR spectra, as well as some chemical conversions point out that the sulfo group in4 a is at the 6 position and at 6' position in5 a.From the sulfonic acid4 and SOCl₂ the sulfochloride7 was obtained, which at the action of NH₃ gave easily the corresponding sulfonamide (8).

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5. Mitt: Mh. Chem.100, 2024 (1969).     

Beitrag zur ascorbinometrischen Cer(IV)-Bestimmung

Zusammenfassung Es wird ein Verfahren zur Titration von Cer(IV)-salz mit Ascorbinsäuremaßlösung unter Verwendung von Variaminblau B als Indicator beschrieben. Die erhaltenen Werte stimmen mit den Ergebnissen der Titration mit Eisen(II)-ammoniumsulfatmaßlösung überein. Ein Nachteil der ascorbinometrischen Methode liegt in der leichten Oxydierbarkeit (Titerunbeständigkeit) der Ascorbinsäuremaßlösung.Es ist uns eine angenehme Pflicht, Herrn Prof. Dr. Erdey für die Überlassung von Variaminblau B zu danken.     

Ein neues Verfahren zur Darstellung von Dibenzo [c,e] azocinen

Zusammenfassung Unter der Einwirkung von Polyphosphorsäure gehen Monoxime von Di- und Triketonen mit einem 7gliedrigen Ring (3 und8) in die Dibenzo[c, e]azocine4 bzw.9 über. Die Struktur der neuen Azocine wurde durch Elementar-, IR- und NMR-Analyse und einige chemische Umwandlungen bestätigt.

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A new method for preparation of dibenzo [c, e]azocines

Monoximes of di- and triketones containing a 7membered ring (3 and8) gave upon treatment with polyphosphoric acid the corresponding dibenzo[c, e]azocines (4, 9). The structure of the new azocines was confirmed by elementary analyses, IR-and NMR-spectrometry as well as by some chemical transformations.

     

Enantioseparation of solriamfetol and its major impurity phenylalaninol by capillary electrophoresis using sulfated gamma cyclodextrin

R-solriamfetol is a recently approved drug used for the treatment of excessive sleepiness associated with narcolepsy and sleep apnea. Herein, a capillary electrophoretic method was developed, enabling the simultaneous analysis of the API and its S-enantiomer in addition to the enantiomers of its major impurity phenylalaninol. Twenty-nine different cyclodextrins (CDs), including native, neutral, and charged ones were screened as potential chiral selectors, and the best results were obtained with sulfated CDs. Randomly sulfated-β-CD exhibited outstanding enantioresolution, the peaks of phenylalaninol enantiomers inserted between the two peaks of solriamfetol enantiomers, while sulfated-γ-CD (S-γ-CD) showed remarkable resolution values in a much shorter analysis time with the optimal enantiomer migration order. Among the single isomer sulfated CD derivatives, substituent dependent enantiomer migration order reversal could also be observed in the case of heptakis(6-O-sulfo)-β-CD (HS-β-CD) or heptakis(2,3-O-dimethyl-6-O-sulfo)-β-CD (HDMS-β-CD) with R-,S-solriamfetol, and heptakis(2,3-O-diacetyl-6-O-sulfo)-β-CD (HDAS-β-CD) resulting S-,R-solriamfetol migration order. The sulfated-γ-CD system was chosen for method optimization applying orthogonal experimental design. The optimized method (45 mM Tris-acetate buffer, pH 4.5, 4 mM S-γ-CD, 21°C, +19.5 kV) was capable for the baseline separation of solriamfetol and phenylalaninol enantiomers within 7 min. The optimized method was validated according to the ICH guidelines and successfully applied for the analysis of pharmaceutical preparation (Sunosi^® 75 mg tablet), thus it may serve as a routine procedure for the laboratories of regulatory authorities as well as in Pharmacopoeias.