Electronegativity force of cations and thermal decomposition of complex fluorides

The thermal decomposition of anhydrous fluoroborates MBF₄ (M=Li, Na, K, Rb, Cs) and M(BF₄)₂ (M=Ca, Sr, Ba) was investigated. The decomposition proceeds according to a simple acid-base mechanism with evolution of BF₃. The influence of the acidity of cationic counterions, expressed by the electronegativity force on the course of thermal decomposition was estimated quantitatively.     

Head-to-tail connected double calix[4]arenes

Summary New macrotricyclic compounds consisting of two calix[4]arene substructures connected by aliphatic chains of various length (three to five carbon atoms) between two oppositep-positions and two distal phenolic oxygens have been synthesized. Starting withp-tert-butyl-calix[4]arene, two O-protected phenolic units are attachedvia ether links in 1,3-position by reaction with the corresponding tosylates. After deprotection, the new calix[4]arene is formed by fragment condensation with 2,6-bisbromomethylated 4-alkylphenols. The structure of one example (8c) has been confirmed by single crystal X-ray analysis. Both calixarene parts assume the cone conformation, a molecule of acetonitrile being included in both cavities.

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Doppelte Calix[4]arene in Kopf-Schwanz-Verknüpfung

Zusammenfassung Neue makrotricyclische Verbindungen, in denen zwei Calix[4]aren-Einheiten durch aliphatische Ketten unterschiedlicher Länge (drei bis fünf C-Atome) zwischen zwei gegenüberliegendenp-Positionen und zwei gegenüberliegenden Phenolsauerstoffen verknüpft sind, wurden hergestellt. Ausgehend vonp-tert-Butyl-calix[4]aren werden zunächst zwei O-geschützte Phenolbausteine in 1,3-Stellung durch Umsetzung mit den entsprechenden Tosylaten etherartig gebunden. Nach Abspaltung der Benzylether-Schutzgruppe wird durch Fragmentkondensation mit 2,6-bisbrommethylierten 4-Alkylphenolen das neue Calix[4]aren gebildet. Für8c wurde die Struktur durch Einkristallröntgenstrukturanalyse bestätigt. Beide Calixarenteile nehmen diecone-Konformation ein, wobei in die beiden Hohlräume je ein Molekül Acetonitril eingeschlossen wird.

     

Medium Effect on the Rotational Isomerism in 1,3,5-Triacetylbenzene

Summary. The optimal geometries, energies, polarities, infrared frequencies, and intensities of the non-polar and polar conformers of 1,3,5-triacetylbenzene were calculated using DFT/B3LYP/6-311G** and semi-empirical (AM1 and PM3) methods. All the methods revealed that the non-polar conformer prevails in vacuum. The infrared spectra in the solid state, in Ar matrix, and in liquid solutions as well as the dipole moments of 1,3,5-triacetylbenzene in many solvents show the distinct influence of the environment on the non-polar conformer ⇌ polar conformer equilibrium. The effect of solvent polarity on the standard Gibbs energy of this conformational equilibrium is quantitatively discussed in terms of the continuum-homogenous dielectric model.     

Reversed-phase porous silica rods, an alternative approach to high-performance liquid chromatographic separation using the sequential injection chromatography technique

A commercially available porous silica rod column was used as a separation tool for the sequential injection analysis (SIA). A porous solid monolithic column showed high performance at a low pressure, allowing sequential injection analysis to be used for the first time for separation in HPLC fashion. In this contribution, we tried to demonstrate a new separation concept with SIA manifold for the simultaneous determination of four different compounds (methylparaben (MP), propylparaben (PP), triamcinolone acetonide (TCA) and internal standard ketoprofen (KP)) in a pharmaceutical triamcinolon cream 0.1% formulation. A Chromolith Flash RP-18e, 25 mm x 4.6 mm column with a 10 mm pre-column (Merck, Germany) and a FIAlab 3000 system (USA) with an 8-port selection valve and 10 ml syringe were used for sequential injection chromatographic separations in our study. The mobile phase used was acetonitrile-methanol-water (35:5:65, v/v/v) + 0.05% nonylamine, pH 2.5, flow rate 0.6 ml min(-1). The analysis time was <6 min. A novel sequential injection chromatography (SIC) technique with UV spectrophotometric detection was optimised and validated.     

Profiling of cyclic hexadepsipeptides roseotoxins synthesized in vitro and in vivo: a combined tandem mass spectrometry and quantum chemical study

High-performance liquid chromatography and tandem mass spectrometry (HPLC/MS/MS) was used for the detection of cyclic hexadepsipeptides roseotoxins produced by Trichothecium roseum. Roseotoxins were found in both submerged standard cultivation on CzapekDox medium and in vivo cultivation extract obtained from an apple. Roseotoxin chromatographic profiles from these two experiments were compared. Product-ion collision-induced dissociation (CID) spectra obtained on an ion trap (electrospray ionisation, ESI) were used for the identification of natural roseotoxins A, B, C and of minor destruxins A and B. The dissociation behavior of roseotoxins is discussed in terms of a fragmentation scheme proposed for describing the dissociation pathways of cyclic peptides. This scheme involves opening of the cyclopeptide ring via formation of oxazolone derivatives and fragmentation of the resulting linear species, which have a free N-terminus and an oxazolone ring at the C-terminus. Some aspects of this fragmentation scheme are underlined by modeling the dissociation channels of roseotoxin A using quantum chemical calculations. The structures of roseotoxin A and destruxin B were verified by nuclear magnetic resonance (NMR) spectroscopy. Structures of three new minor natural roseotoxins [Val(4)]RosA, [MeLxx(4)]RosA and [MeLxx(4)]RosB were deduced by ion cyclotron resonance Fourier transform mass spectrometry (ICR-FT-MS) and ion trap tandem mass spectrometry by examining the pre-separated roseotoxin fraction.     

Solvent influence on the rotational isomerism in terephthalaldehyde

Experimental and theoretical studies were carried out in order to investigate the rotational isomerism of terephthalaldehyde. The dipole moment measurements and infrared spectroscopy in Ar matrix and using various solvents were performed experimentally. In order to supplement the experimental study, both static and dynamical theoretical calculations were performed. IR spectra and potential energy distribution (PED) were calculated for both cis and trans isomers of terephthalaldehyde in gas phase using B3LYP/6-31G(d,p) level of theory. Further calculations consisted of conformational analysis were performed in order to estimate the rotational barrier and relative stabilities of isomers. The DFT theory with B3LYP functional and four double-zeta and triple-zeta basis sets served as framework for this part of calculations. Semiempirical AM1 and PM3 methods were also used for gas-phase modeling. Molecular dynamics using MM3 force field was applied to study the preferences of solvent molecules’ orientation around the studied molecule. Additionally, the effect of solvent polarity on the Gibbs energy of the trans ⇌ cis equilibrium was analyzed in terms of the continuum dielectric medium models.     

An isotherm equation for adsorption from binary liquid mixtures on solids involving surface heterogeneity and differences in molecular sizes of components and its numerical verification

An equation derived previously¹⁴ for adsorption from binary liquid mixtures composed of molecules of different sizes on heterogeneous solids has been reexamined. Verification of this equation by means of numerical simulation showed its applicability for describing the liquid adsorption onto weakly and strongly heterogeneous surfaces.

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Eine Isothermen-Gleichung für die Adsorption aus binären flüssigen Gemischen an heterogenen Oberflächen fester Körper unter Berücksichtigung der Differenzen in den Molekülgröen der Komponenten und ihre numerische Verifikation

Zusammenfassung Es wurde die früher¹⁴ abgeleitete Isothermen-Gleichung der Adsorption aus binären flüssigen Gemischen an heterogenen Oberflächen fester Körper abermals untersucht. Durch Computersimulation wurde gezeigt, daß diese Gleichung den obengenannten Prozeß, der sich sowohl an schwach wie auch an stark heterogenen Oberflächen vollzieht, gut beschreibt.

     

Spectrophotometric determination of vitamins D2 and K1 in presence of rutin

Summary Methods are given for determination of vitamin D₂ and K₁ in presence of rutin added as stabilizer, and applied to assessment of the rate of breakdown of these vitamins when exposed to ultraviolet light. Because the absorption maxima of these vitamins, rutin and some of the decomposition products are very near to each other a preliminary separation is necessary. Thin layer chromatography with chloroform on silica gel H is suitable.

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Spektropbotometrische Bestimmung von Vitamin D₂ und K₁ in Gegenwart von Rutin

Zusammenfassung Für die Bestimmung von Vitamin D₂ und Vitamin K₁ in Gegenwart von Rutin, das als Stabilisator zugegeben wird, wurden Methoden angegeben und zur Bestimmung der bei UV-Bestrahlung eintretenden Zersetzung dieser Vitamine angewendet. Da deren Absorptionsmaxima alle sehr nahe beieinander liegen, ist eine vorherige Trennung nötig. Dazu hat sich die Dünnschichtchromatographie mit Chloroform auf Silicagel H als geeignet erwiesen.

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Presented at the 8th International Microchemical Symposiums Graz, August 25–30, 1980.     

Spinors and diffeomorphisms

We discuss the action of diffeomorphisms on spinors on an oriented manifoldM. To do this, we first describe the action of the diffeomorphism groupD(M) on the set =H ¹ (M,Z ₂) of inequivalent spin structures and show that it is affine. We argue that in the presence of spinors the gauge group of gravity is a certain double cover ofD(M) which depends on the spin structure. We explicitly compute the action ofD(M) on whenM is a closed Riemann surface; is seen to consist of exactly two orbits, corresponding to even and odd spin structures.On leave of absence from I.F.T., University of Wrocaw, Poland