Gruppenuniversalität und Homogenisierbarkeit

Summary For a classC of structures there are two archetypical questions: 1) Is every group G the full automorphism group of some C C? and 2) May every C C embedded into some homogeneous H C, i.e. into a structure H enjoying some transitivity properties? Using model theoretic language and conditions on the existence of certain free constructions withinC, some rather general positive answers to these questions are obtained. These abstract results give some (methodical) unification to a variety of theorems for some very concrete classesC of combinatorial, geometrical or algebraic nature in the literature. To underline this point, the major part of the paper is devoted to a systematic survey of classesC of structures in which our general approach is applicable, included many classesC for which our type of questions has not yet been considered.

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Unserem lieben FreundeAdriano Barlotti zum 60. Geburtstag gewidmet.

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Die Autoren danken herzlich der Deutschen Forschungsgemeinschaft für die gewährte Unterstützung; der erstgenannte Autor bedankt sich darüber hinaus beim Consiglio Nazionale delle Ricerche für ein Stipendium an der Universität Bologna.     

Effect of evaporation temperature on the formation of particulate membranes from crystalline polymers by dry-cast process

The membrane formation of crystalline poly(ethylene-co-vinyl alcohol) (EVAL), poly(vinylidene fluoride) (PVDF), and polyamide (Nylon-66) membranes prepared by dry-cast process was studied. Membrane morphologies from crystalline polymers were found to be strongly dependent on the evaporation temperature. At low temperatures, all the casting solution evaporated into a particulate morphology that was governed by the polymer crystallization mechanism. The rise in the evaporation temperature changed EVAL membrane structure from a particulate to a dense morphology. However, as the temperature increased PVDF and Nylon-66 membranes still exhibited particulate morphologies. The membrane structures obtained were discussed in terms of the characteristics of polymer crystallization in the casting solution theoretically. At elevated temperatures the crystallization was restricted for the EVAL membrane because the increase rate in the polymer concentration was fast relative to the time necessary for growth of nuclei. Nonetheless, the time available for PVDF and Nylon-66 with stronger crystalline properties was large enough to form the crystallization-controlled particulate structure that differed in particle size only. In addition, particles in the PVDF membrane were driven together to disappear the boundary, but those in the Nylon-66 membrane exhibited features of linear grain boundary. The difference in particle morphology was attributed to the Nylon-66 with the most strongly crystalline property. Therefore, the kinetic difference in the crystallization rate of the polymer solution play an important role in dominating the membrane structure by dry-cast process.     

Die Bestimmung des Elastizitätsmoduls viskoelastischer Systeme aus rheologischen Messungen

Summary In this paper the best available inorganic insecticides were chosen as emulsifying agents. While preparing the emulsions it was kept in mind to take minimum of the substance as an economical measure. The ratio of water to oil was so kept, as to have the most stable and mobile emulsion, in order that it could be easily-used for practical purposes. It was found that the percentage of 0.5 and 0.25 of the emulsifying agent with a ratio of oil to water as 20∶80, best stable emulsions are produced. The substances taken were copper arsenate and arsenite, lead, calcium and aluminium arsenates. With the addition of natural colloids, the stability is increased to a great extent. The natural colloids easily formed a highly solvated membrane which envelops the oil globules, thereby making the emulsions very stable. The addition of soaps deteriorates or breaks the emulsions in all cases, but with aluminium arsenate. The addition of soaps instead of having an antagonistic effect, re-inforces aluminium arsenates. The aluminium arsenate is hydrolysed producing aluminium hydroxide. It has already been seen by previous workers that aluminium hydroxide and sodium or potassium oleate act as very good emulsifying agents.

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Zusammenfassung Die erreichbaren anorganischen Insektizide werden als emulgierende Agentien untersucht. Es wurde bei der Emulsion angestrebt, als m?gliches ?konomisches Ma? mit einem Minimum an Substanzen auszukommen. Das Verh?ltnis von Wasser zu ?l wurde so gew?hlt, da? m?glichst stabilste und flüssige Emulsionen erreicht wurden, so da? leichte Anwendbarkeit für praktische Zwecke besteht. Ein Gehalt an 0,5 und 0,25% und ein Verh?ltnis ?l zu Wasser wie 20 zu 80 ergab die stabilsten Emulsionen. Es wurden Kupferarsenat und -arsenit Blei-, Calzium- und Aluminiumarsenate verwendet. Zufügung von natürlichen Kolloiden verst?rkte die Stabilit?t au?erordentlich. Die natürlichen Kolloide bilden hochsolvatisierte Membranen, die die ?ltr?pfchen einhüllen und so die Stabilit?tserh?hung bedingen. Die Zufügung von Seifen zerst?rt oder bricht die Emulsionen, au?er im Falle von Aluminiumarsenat. In diesem Falle wird der Effekt statt dessen verst?rkt. Al-Arsenat wird hydrolysiert, es entsteht Al-Hydroxyd. Schon von anderer Seite wurde gezeigt, da? Al-Hydroxyd mit Na- oder K-Oleat sehr gut emulgierend wirkt.

     

Is there any three-center CBC bond in 1, 5-C2B3H5 and 1,5-C2B3H3?

Localized molecular orbitals, two- and three-center bond indices of 1,5-dicarba-closo-pentaborane ( 5 ) and 1,5-dicarba-closo-pentaborane ( 3 ) and their hydrocarbon analogs bicyclo [1,1,1]-pentane and [1,1,1] propellane, respectively, have been calculated using a suitable basis set. No previously reported three-center CBC bond has been found. However, a new three-center BCB bond has been observed in 1,5-dicarba-closo-pentaborane ( 5 ). © 1995 John Wiley & Sons, Inc.     

Beiträge zur Chemie der Pyrrolpigmente, 82. Mitt.: Wasserlösliche Polymere mit kovalent gebundenen violinoiden und 2,3-dihydro-verdinoiden Gallenfarbstoffen

Summary A violinoid and a 2,3-dihydrobilindione chromophore is attachedvia an appendix anchored at rings A of the pigments by means of reacting them with the polyacryl-N-acryloxysuccinimid copolymer to yield water-soluble chromopolymers. They are characterized by a molecular mass of about 4000 to 6000 and a relation of one chromophoric unit per 6 to 22 monomers. Their absorption spectra and circular dichroism recorded in water and dimethylsulfoxide as solvents are discussed with respect to structural aspects, and in comparison with monomeric chromophore derivatives.

Herrn Prof. Dr. K. Schlögl mit den besten Wünschen zum 65. Geburtstag gewidmet     

Enantiomerentrennung und chiroptische Eigenschaften eines 2,3-Dihydrobilatriens-abc

The enantiomers of the 2,3-dihydrobilatriene-abc1 have been separated by recycling chromatography on triacetylcellulose. Comparison of their chiroptical properties with those of amino acid substituted analogues, like3, reveals the chirality of center 3 to be of minor influence on the values. Stabilization of a definite helical conformation of these pigments seems to depend on this influence together with an appropriate dipole-dipole interaction.

     

An analysis of avidin, biotin and their interaction at attomole levels by voltammetric and chromatographic techniques

The electroanalytical determination of avidin in solution, in a carbon paste, and in a transgenic maize extract was performed in acidic medium at a carbon paste electrode (CPE). The oxidative voltammetric signal resulting from the presence of tyrosine and tryptophan in avidin was observed using square-wave voltammetry. The process could be used to determine avidin concentrations up to 3 fM (100 amol in 3 l drop) in solution, 700 fM (174 fmol in 250 l solution) in an avidin-modified electrode, and 174 nM in a maize seed extract. In the case of the avidin-modified CPE, several parameters were studied in order to optimize the measurements, such as electrode accumulation time, composition of the avidin-modified CPE, and the elution time of avidin. In addition, the avidin-modified electrode was used to detect biotin in solution (the detection limit was 7.6 pmol in a 6 l drop) and to detect biotin in a pharmaceutical drug after various solvent extraction procedures. Comparable studies for the detection of biotin were developed using HPLC with diode array detection (HPLC-DAD) and flow injection analysis with electrochemical detection, which allowed biotin to be detected at levels as low as 614 pM and 6.6 nM, respectively. The effects of applied potential, acetonitrile content, and flow rate of the mobile phase on the FIA-ED signal were also studied.     

Treatment of anions in SINDO1

The SINDO1 method is modified to include the calculation of molecular anions. Two versions of modifications are presented which are based on charge dependent orbital exponents. Calculated heats of formation and electron affinities are much improved compared to the standard version with fixed orbital exponents.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday     

Mechanistic investigation of the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes

The mechanism for the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes with electrophilic halogenation reagents has been investigated by using experimental and computational methods. These studies have led us to propose a mechanism for the reaction that proceeds through an initial N-chlorination of the chiral catalyst-substrate complex, followed by a 1,3-sigmatropic shift of the chlorine atom to the enamine carbon atom. The suggested reaction course is different from previously proposed mechanisms for organocatalytic enamine reactions, in which the carbon-electrophile bond is formed directly. Furthermore, the rate-determining step in the overall reaction was determined and the presence of nonlinear effects was probed.     

Komplexkatalyse : XI. Eine einfache synthese für chloro-nitrosyl-carbonyl-molybdän(0)-komplexe als neue hochaktive präkatalysatoren für die olefinmetathese

A simple preparation of the chloronitrosylcarbonylmolybdenum(0) complexes Mo(NO)(CO)₄(AlCl₄) and MoCl(NO)(CO)₂(PPh₃)₂ is described. The homogeneous system MoCl(NO)(CO)₂(PPh₃)₂/RAlCl₂ (R = Et, Me) represents a new highly active long-living catalyst for the metathesis of 2-pentene.