NMR experiments on acetals—XXXVII: NMR spectral study of cis-, and trans-6-methyl-4-r-1,3-oxaselenans

The NMR spectral parameters are reported for cis-, and trans-6-Me-4-alkyl-1,3-oxaselenans with the aid of the INDOR- technique. Low temperature studies show the conformational equilibrium in the trans series to be pronouncedly one-sided and a value for the inversion barrier has been obtained.     

Ladder polymers from tetraaminodiquinoxalpyrene

A new fused aromatic heterocyclic tetraamine 2,3,11,12-tetraaminodiquinoxal [2,3-e,2′,3′-1] pyrene has been prepared and polymerized with 1,4,5,8-naphthalenetetracarboxylic acid and pyromellitic dianhydride. The resulting ladder polymers with inherent viscosities ranging from 0.5 to 1.0 dl/g in methanesulfonic acid exhibited thermal stabilities near 600°C in nitrogen and near 450°C in air.     

Chemistry of acetals

Summary Optimum conditions were developed for the preparation of 3-ethoxyacrolein, 3,3-diethoxypropionaldehyde, and 3,3-diethoxy~2-methylpropionaldehyde by the hydrolysis of the diacetals of malonaldehyde and methylmalonal dehyde in presence of p-toluenesulfonic acid and phosphoric acid.     

Über die dilatometrisch indizierten Titrationen

With the help of a dilatometer which permits the continuous determination of volume changes occuring in chemical reactions in aqueous solutions, the volume change during the precipitation of BaSO₄ was followed and applied to the determination of the endpoint of the precipitation. In the case of precipitations of 1 mM BaSO₄ the end-point determination can be reproduced with a standard deviation of less than 0.2%. A strict linearity between the amount of Na₂SO₄ applied and the position of the end-point does not exist. However, a correction factor could be established, so that the absolute determination of sulphate is possible (standard deviation 0.2%). The time required to carry out a single measurement is about 1.5 min. The acid concentration does not influence the composition. On the other hand, the composition was shown to be considerably dependent on Na⁺ and NH₄ ⁺ ions. The presence of the cation N(CH₃)₄ ⁺ does not alter the composition of the precipitate. It is obviously too big to substitute the Ba²⁺ ion.     

Plasma Modification of Elastomers

The treatment of elastomer articles in a low-temperature glow-discharge plasma in fluorinated organics is an effective method for the enhancement of their wear resistance without changing the formulation of rubbers. As a result of plasma-assisted deposition on an elastomer of a fluorinated antifriction film chemically bound to the substrate, the elastomer friction coefficient is considerably decreased, sticking to a counterface is prevented, and the wear resistance of the elastomer is enhanced, retaining their bulk properties. Based on the study of the structure of the antifriction film at different modification stages and its transformation during friction, a conclusion on the mechanism of elastomer surface failure under dynamic friction conditions was made.     

Inactivation of nitroalkane oxidase upon mutation of the active site base and rescue with a deprotonated substrate

Mutation of Asp402 in nitroalkane oxidase to Asn or Ala inactivates the enzyme with neutral nitroethane as substrate, but the activity can be rescued with the nitroethane anion. The V/K values of the D402N and D402A enzymes with the nitroethane anion are independent of pH, whereas the V/K values of the wild-type and D402E enzymes are pH dependent with both the protonated and the deprotonated forms of nitroethane. Moreover, although the V/K value of the D402E enzyme with neutral nitroethane is 20-fold less than that of the wild-type enzyme, there is only a 2-fold difference in the V/K values with the nitroethane anion. These results are fully consistent with a primary role for Asp402 as the active site base in nitroalkane oxidase which abstracts the substrate alpha-proton.     

The question of thermal decomposition of pyrite

The thermal decomposition of monomineral pyrite was studied in an inert atmostphere. From an analysis of the values of the thermal effects, an interpretation of the hree physicochemical processes recorded in the thermoanalytical curves is proposed.

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Zusammenfassung Die thermische Zersetzung von monomineralem Pyrit wurde in inerter Atmosphäre untersucht. An Hand der Analyse der Werte der thermischen Effekte wird eine Beschreibung dreier, in den thermoanalytischen Kurven festgehaltener physikalischchemischer Vorgänge vorgeschlagen.

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Résumé On a étudié la décomposition thermique de la pyrite, en atmosphère inerte. On propose une interprétation des trois processus physicochimiques enregistrés sur les courbes thermoanalytiques, qui repose sur l'analyse des effects thermiques.

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The different steric environments of the 5-exo- and 5-endo- substituent for a pair of isomeric tricarbonyl(methoxycyclohexa-1,-diene)irons

A shift reagent has been employed to demonstrate the sterically-hindered environment of the methoxy group in tricarbonyl(5-endo-methoxycyclohexa-1,-diene)iron relative to that of the methoxy group in the 5-exo analogue.     

Calorimetric determination of solubility of water in pectin and physical state diagram of a pectin-water system

For the mixtures of pectin of different esterification degrees and water, heat capacities in the range of 80–320 K have been measured, and DTA measurements have been carried out in the range 80–450 K. The effect of water on the physical transitions of pectin has been studied, and the solubility of water in pectins of different esterification degrees at the temperature of melting of a liquid component has been determined. On the basis on the experimental data, the physical state diagram of the pectin-water system has been constructed and analyzed for the whole range of component concentrations within a wide temperature interval.     

Pyrimido[4,5‐c]pyridazine‐5,7(6H, 8H)‐diones: Marvelous substrates for study of nucleophilic substitution of hydrogen

The data on nucleophilic substitution reactions of hydrogen in 6,8‐dimethylpyrimido[4,5‐c]pyridazine‐5,7(6H,8H)‐dione, its 3‐chloride, N₂‐oxide and some other derivatives are reviewed. All these compounds possess a remarkable ability to undergo not only simple functionalizations but also tandem and cascade transformations leading to annelation of various heterocyclic rings.