Chemo- and regioselective synthesis of 2-alkylidenetetrahydrofurans bearing a chiral sulfur atom by domino reactions of sulfoximines

The addition of the dianion of Johnson’s sulfoximine to α,ω-halogenoesters evolves by an intramolecular heterocyclization to provide a direct access to 2-alkylidenetetrahydrofurans bearing a chiral sulfur atom via domino addition-elimination/S_N reactions.     

Calculation of cross sections for positron-Ar collisions

The three-body classical trajectory Monte-Carlo (CTMC) method is used to investigate positron-argon atom collisions. The total ionization cross sections are presented along with singly and doubly differential cross sections. The existence of the cusp-like peak in the triply differential electron and positron spectra at positron impact is predicted.     

Investigations of copper,silver and bismuth deposition on palladium in perchloric acid media

Investigations have shown that copper and silver ions deposited at more positive potentials than the Nernst potential—similarly to bismuth ions—are not adsorbed but form alloys with palladium. Similarly, in the case of metal deposition via the ionization of sorbed hydrogen, the same alloys were formed as observed by the potentiostatic method.     

Rapid and simple chromatographic separation of V(V) and V(IV) using KH-phthalate and their determination by flame atomic absorption spectrometry

A method was developed for the chromatographic separation of V(V) and V(IV) based on the different sorption forces of these vanadium species in C18 columns in presence of KH-phthalate. The vanadium species were detected with a flame atomic absorption spectrometer with acetylene/N₂O flame. The detection limits (3σ) of V(V) and V(IV) were 0.18 μg/mL and 0.15 μg/mL, respectively. The relative standard deviations (N = 5) are 4.2% and 3.4% for 20–20 μg/mL V(V) and V(IV), respectively. The sampling frequency is 75/h. Because of the special interaction occurring between phthalate and V(IV) on the C18 column and the acetylene/N₂O flame atomic absorption detection, practically no interferences can be detected even in large inorganic matrix.     

Etudes sur les fibres naturelles et de synthèse

Résumé Nous avons mesuré, en fonction de la température, le degré de gonflement dans l'eau de fibres de collagène amorphes qui ont été tannées différemment, ceci dans le but de pouvoir déterminer, pour chaque degré de tannage (pontage chimique) la chaleur de mélange du collagène amorphe sec avec l'eau de gonflement. En utilisant la théorie relative au gonflement des réseaux polymériques amorphes dans un excès de diluant, on a pu montrer que le paramètre thermodynamiqueχ ₁ caractéristique du système collagène-eau (paramètre deFlory-Huggins) varie avec la composition du réseau gonflé. Par contre, le paramètre ?enthalpique? correspondantϰ ₁=− =−0,34 est indépendant de cette composition. La chaleur de mélangeΔH _mél/V ₀ d'un cm³ de collagène amorphe sec avec l'eau de gonflement peut être calculée pour les différents degrées de tannage. Elle a le signe deϰ ₁, i. e. elle est négative et est donnée par:ΔH _mél/V ₀=RT gK₁(1−v₂ ^éq). Sa valeur absolue est donc d'autant moins importante que le degré de tannage des fibres est poussé; v₂ ^éq augmente en effet avec la concentration en liens intermoléculaires introduits dans les échantillons. La variation d'enthalpie accompagnant la transformation d'une fibre de collagène cristalline sèche en fibre amorphe gonflée (enthalpie de rétraction dans l'eau) diminuée de la chaleur de mélange correspondant au gonflement de la fibre amorphe sèche dans l'eau donne la chaleur de fusion du collagène sec. Cette quantité est égale à:ΔH/V ₀=28±1,5 cal./cm³ et est indépendante du degré de tannage comme on doit s'y attendre.

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Summary We have measured the temperature dependence of the swelling of amorphous collagen fibres of different degrees of tanning in an excess of water. This was done for the purpose of determining the heat of mixing of amorphous dry collagen with the equilibrium swelling water for each degree of tanning (chemical crosslinking). Using the theory of swelling of polymeric networks in an excess of diluent we were able to show that the parameterχ ₁ of the system collagen-water (Flory-Huggins parameter) is a function of the composition of the swollen network. On the other hand, the energy parameterϰ ₁=− =−0,34 is found to be concentration independent. The heat of mixingΔH _mél/V ₀ of 1 cm³ of dry amorphous collagen with the equilibrium swelling water can be calculated for the different degrees of tanning. It has the same sign asϰ ₁, i. e. is negative, and is given byΔH _mél/V ₀=RTϰ ₁ (1−v₂ ^éq). Its absolute value decreases therefore with increasing degrees of tanning, sincev ₂ ^éq increases with the density of the cross-links in the sample. The change in heat content on transforming 1 cm³ of dry crystalline collagen fibre into amorphous swollen fibre (heat of shrinking in water), decreased by the heat of swelling of the dry amorphous fibre in water, gives the heat of fusion of dry collagen. This latter equalsΔH/V ₀=28±1.5 cal/cm³ and is, as expected, independent of the degree of tanning.

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Zusammenfassung Um die Mischungsw?rme des amorphen trockenen Kollagens mit dem Quellungswasser zu bestimmen, wurde die Temperaturabh?ngigkeit des Quellungsgrades von verschieden stark gegerbten amorphen Kollagenfasern gemessen. Auf Grund der Theorie der Quellung von amorphen polymeren Netzwerken in einem überschu? von Quellungsmittel konnte gezeigt werden, da? der thermodynamische (Flory- Huggins) Parameterχ ₁ für das System Kollagen-Wasser vom Quellungsgrad des Netzwerkes abh?ngt. Hingegen ist der Enthalpieparameterϰ ₁=− =−0,34 davon unabh?ngig. Die Mischungsw?rmeΔH _mél/V₀ eines cm³ trockenen amorphen Kollagens mit dem Quellungswasser kann für verschiedene Gerbungsgrade (Vernetzungsgrade) berechnet werden. Sie hat das gleiche Vorzeichen wieϰ ₁ d. h. ist negativ, und gehorcht der Gleichung:ΔH _mél/V ₀=RTϰ ₁ (1−v₂ ^éq). Der Betrag der Mischungsw?rme ist um so kleiner, je h?her der Gerbungsgrad der Faser ist; in der Tat w?chstv ₂ ^éq mit der Konzentration der Vernetzungspunkte an. Wenn von der Enthalpie?nderung, welche mit dem übergang von einer trockenen kristallinen Faser zu einer gequollenen amorphen verbunden ist, (Schrumfungsenthalpie im Wasser), die oben definierte QuellungsenthalpieΔH _mél/V ₀ abgezogen wird, so bleibt die Schmelzw?rme des trockenen Kollagens übrig. Diese Schmelzw?rme betr?gt:ΔH/V ₀=28±1,5 cal./cm³ und ist, wie zu erwarten, vom Vernetzungsgrad (Gerbungsgrad) des Fadens unabh?ngig.

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Travail effectué au Laboratoire de Chimie-Physique de l'Université de Liège, Liège (Belgique).     

The algorithm of substructure recognition in organic compounds by the artificial intelligence method on the basis of IR-spectra

An algorithm for identification of the IR-active substructures has been developed. In the algorithm, which recognizes about 100 substructures, the analysis is based on three parameters for a set of characteristic bands: position, intensity and arbitrarily chosen diagnostics. The algorithm provides two ways of identification: a. standard method, which compares an IR spectrum with the correlation tables contained in the algorithm, b. dynamic method advanced here which consists in that the recognized substructures cause blocking of their characteristic bands making them almost inaccessible for further analysis.     

Na-montmorillonite hydrates under ethane rich reservoirs: NPzzT and muPzzT simulations

Na-montmorillonite hydrates in presence of ethane molecules are studied by means of hybrid Monte Carlo simulations in the NP(zz)T and muP(zz)T ensembles. The NP(zz)T ensemble allows us to study the interlaminar distance as a function of water and ethane content. These data show clear plateaus for lower ethane contents and mainly for water contents consistent with the formation of a single water layer. In addition, from this ensemble the structure for some of these interlaminar compositions were analyzed. For systems containing few ethane molecules and water enough to complete a single layer, it was observed that ethane mainly situates close to the interlayer midplane and adopts a nearly parallel arrangement to the clay surface. On the other hand, the muP(zz)T ensemble allows us to determine the interlaminar distance and water-ethane content for any specific reservoir. Here, some important findings are the following: the partial exchange of water by ethane molecules that enhances for decreasing the water vapor pressure; the obtention of a practically constant interlaminar space distance as a function of the water vapor pressure; the conservation of ion solvation shells; the enhancement of the water-ethane exchange for burial conditions; and finally, the incapability for a dehydrated clay mineral to swell in a dry and rich ethane atmosphere.     

Temperature induced structural changes of Cu(II) and Ni(II) complexes and their thermal decomposition

The paper discusses the structural changes of some Cu(II) and Ni(II) complexes during the heating and their influence upon the decomposition stoichiometry. The influence of the interactions inside of coordination polyhedra, bonding and stereochemical properties of the counter ions or molecules are discussed in this connection as well. The expressive influence of the plasticity or rigidity of the Cu(II) and Ni(II) coordination polyhedra, respectively, is emphasized.

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Zusammenfassung Es werden wÄrmebedingte StrukturverÄnderungen einiger Cu(II) bzw. Ni(II)-Komplexe sowie deren Einflu\ auf die Stöchiometrie der Zersetzung beschrieben. In diesem Zusammenhang wird auch ebenso der Einflu\ von Wechselwirkungen innerhalb des Koordinationspolyeders sowie von Bindungs- und stereochemischen Eigenschaften der Gegenionen oder -moleküle beleuchtet. Es wird der ausdrucksvolle Einflu\ der PlastizitÄt und HÄrte von Cu(II)- und Ni(II)-Koordinationspolyedern hervorgehoben.

     

Investigation on the chemistry of berbans—VII: Synthesis of 10,11-dimethoxy(depyrrolo)raunescine stereoisomers

Acyloxy-ketone rearrangement, proceeding by the action of base, has been observed in the case of ketone 2. By the reduction of ketones 2 and 3 with sodium boron hydride, new 10, 11-dimethoxy(depyrrolo)raunescine stereoisomers (5a–7a) have been prepared. Previously known alcohols with alloberban skeleton (12,13) have been similarly converted into tetracyclic raunescine stereoisomers (8a,9) by the oxido-reductive method. The stereochemistry of these compounds has been investigated by physical (¹H NMR, IR) and by chemical methods.     

Potentiometric studies of dithiooxamide with a sulphide-selective membrane electrode

The sulphide-selective electrode is applicable to the determination of dithiooxamide by titration with silver nitrate. The effect of the alkali content of the solutions on the reaction has been studied. The reaction products are silver sulphide, oxalic acid, and nitric acid. If the alkali concentration of the solution is lower than that equivalent to the acid formed during the titration, the amount of sulphide produced by hydrolysis decreases and the equilibrium potential is established more slowly.The determination is rapid and accurate in the presence of 1 M sodium hydroxide.