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.     

Low energy electron diffraction and cyclic voltammetry studies of flame-annealed platinum single crystals

Low energy electron diffraction (LEED) and cyclic voltammetry were used to examine the surface structure of flame-annealed platinum (100), (110), and (111) electrodes. Well-defined LEED patterns were obtained for these surfaces but only after heat treatment in vacuo at 400°C in order to remove surface contaminants. The cyclic voltammograms correspond to those expected for these low index platinum surfaces from prior studies.     

Compounds with symmetrical tricobalt chains wrapped by dipyridylamide ligands and cyanide or isothiocyanate ions as terminal ligands

Three new linear compounds of the type Co(3)(dpa)(4)X(2), where dpa is the anion of di(2-pyridyl)amine and X is NCS(-) (5), CN(-) (6), and N(CN)(2)(-) (7), have been prepared, and their structures and magnetic behavior have been studied. In all of them, including three different solvates of 5, the Co(3) chains are symmetrical with Co-Co distances of ca. 2.31-2.32 A. The appearance of four lines in the (1)H NMR spectra of the three compounds is also consistent with a symmetrical structure in solution. For all compounds, the magnetic behavior is quite similar with mu(eff) of ca. 1.9-2.0 micro(B) at temperatures between 1.8 and 200 K. As the temperature increases, the effective moments increase gradually, but since saturation is not reached, even at 400 K, the high-spin state cannot be assigned.     

Study of the thermal decomposition of solids in a fluidized bed, III

The influence of the air humidity upon the thermal decomposition of diammonium hydrogen phosphate was studied in a fluidized bed, under isothermal conditions. It was found that the increase of the decomposition rate is influenced directly by the partial pressure of the water vapour in the air, and indirectly by the working temperature. The moisture effect is explained by the salt hydrolysis in the water condensed on the grain surface. The energy of activation of the thermal decomposition decreases when the air humidity increases.

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Zusammenfassung Der Einfluß der Luftfeuchtigkeit auf die thermische Zersetzung des Diammoniumhydrogenphosphats wurde in fluidisiertem Bett unter isothermen Verhältnissen studiert. Die Zunahme der Zersetzungsgeschwindigkeit war direkt proportional dem partialen Wasserdampfdruck in der Luft und indirekt proportional der Arbeitstemperatur. Diese Wirkung wird durch Salzhydrolyse in dem kondensierten Wasser an der Kernoberfläche erklärt. Die Aktivierungsenergie der thermischen Zersetzung nimmt mit zunehmendem Feuchtigkeitsgehalt ab.

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Résumé On a étudié l'influence de l'humidité atmosphérique sur la décomposition thermique de (NH₄)₂HPO₄ en lit fluidisé, en conditions isothermes. La pression partielle de la vapeur d'eau dans l'air intervient directement sur l'augmentation de la vitesse de décomposition et exerce une action indirecte sur la température de travail. On a expliqué l'effet de l'humidité par l'hydrolyse du sel dans l'eau condensée à la surface des grains. La valeur de l'énergie d'activation de la décomposition thermique diminue quand l'humidité atmosphérique augmente.

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