Mean configurational distribution function for the steady state and stern-volmer representation

A slight discrepancy appears between the treatment of the steady state of diffusion controlled bimolecular quenching of excited species either by the pair model or by the continuum model. A simplifying assumption is pointed out which helps to solve the steady state case but which is responsible for the discrepancy. The error involved is of small importance considering the experimental accuracy.

---

- , . , , . , .

     

Thermal and infrared spectrum analyses of natural and synthetic andersonites

The thermal decompositions of natural and synthetic andersonites were studied. Two partly overlapping dehydration steps and three partly overlapping decarbonation steps were observed. The second dehydration and the first decarbonation steps also partly overlap. During decarbonation, the gradual formation of sodium diuranate and monoclinic and hexagonal phases in the Na₂U₂O₇-CaUO_4–x system was proved. The results were correlated with measured infrared spectra using site and factor group analysis and X-ray structure analysis. The chemical formula inferred for natural andersonite, Na₂Ca[UO₂(CO₃)₃] 5.6H₂O, agrees with that proposed for its synthetic analogue.

---

Zusammenfassung Die thermische Zersetzung von natürlichem und synthetischem Andersonit wurde untersucht. Sie umfasst zwei teilweise überlappende Entwässerungs- und drei teilweise überlappende Decarboxylierungsstufen. Der zweite Entwässerungs- und der erste Decarboxylierungsschritt überlagern einander ebenfalls teilweise. Während der Decarboxylierung wird die allmähliche Bildung von Natriumdiuranat und monoklinen und hexagonalen Phasen des Systems Na₂U₂C₇-CaUO_4–x nachgewiesen. Die Ergebnisse wurden mit den gemessenen IR-Spektren unter Benutzung der site- und Faktor-Gruppenanalyse sowie Röntgenbeugungsuntersuchungen korreliert. Die für natürlichen Andersonit abgeleitete Formel Na₂Ca[UO₂(CO₃)₃].5,6H₂O stimmt mit der für synthetischen Andersonit vorgeschlagenen überein.

---

. . . , Na₂U₂O₇-CaUO_4–x. . Na₂Ca[UO₂(CO₃)₃] 5,6₂, ** , .

     

Thermal decompositions of (NH4)2WSe4 and (NH4)3VS4 under normal and reduced nitrogen pressures

A method is devised by modification of the author's previous method. Thermoanalytical data are transformed to equivalent isothermal ones, and linear relations are utilized to elucidate the mechanism and the pre-exponential factor, instead of curvefitting. Advantages are illustrated by applying this method to the decomposition of polycaprolactam.

---

Zusammenfassung Es wurde eine neue Methode durch Modifizierung der früheren Methode des Autors entwickelt. Bei der neuen Methode werden die thermoanalytischen Daten in isotherme umgewandelt und anstatt der Kurven-Anpassung der vorhergehenden Methode werden lineare Zusammenhänge zur Klärung des Mechanismus und des pre-exponentiellen Faktors eingesetzt. Die Vorteile der neuen Methode werden durch ihre Anwendung bei der Untersuchung der Zersetzung von Polycaprolactan veranschaulicht.

---

Résumé La méthode précédemment proposée par l'auteur est modifiée. La nouvelle méthode qui est présentée transforme les données thermoanalytiques en données isothermes équivalentes et utilise des relations linéaires pour établir le mécanisme et le facteur pré-exponentiel au lieu de la méthode antérieure avec ajustement des courbes. Les avantages de cette nouvelle méthode sont illustrés en l'appliquant à la décomposition du polycaprolactane.

---

, , , , , . .

     

TMA as a method of investigation of the phase structure of segmented polyurethanes

A complex of methodical approaches for investigating structural changes under the influence of temperature are presented on the basis of modern concepts of the domain structure of block copolymers. Effects of formation of structure due to phase segregation, crystallization processes and those of thermal homogenization have been considered in connection with the deformational properties of polymers. One and the same polymer appears to have quite different phase structures and properties when obtained by altering its thermal conditions. Thermomechanical analysis is shown to be a most efficient technique for investigating the changes in the phase structure of a wide series of polyether(ester)urethanes and -urethaneureas.

---

Zusammenfassung Ein Komplex methodischer Näherungen zur Untersuchung von Strukturänderungen unter dem Einfluss von Wärme werden vorgeführt, welche auf den modernen Konzepten der Gebietstruktur von Block-Kopolymeren beruhen. Die Effekte der Strukturbildung durch Phasensegregation, Kristallisationsvorgänge und thermische Homogenisierung wurden im Zusammenhang mit den Deformationseigenschaften der Polymeren in Betracht gezogen. Das gleiche Polymer scheint ganz verschiedene Phasenstrukturen und Eigenschaften zu haben, wenn es unter veränderten thermischen Bedingungen erhalten wird. Es wird gezeigt, dass die thermomechanische Analyse eine sehr wirksame Technik zur Untersuchung der Phasenstrukturänderungen einer ganzen Reihe von Polyäther(ester)urethanen und -urethankarbamiden ist.

---

Résumé On présente un ensemble de méthodes d'approximation pour l'étude des variations structurales sous l'influence de la température, reposant sur des concepts modernes sur la structure en domaine des copolymères en bloc.Les effets de la ségrégation des phases, de la cristallisation et de l'homogénéisation thermique ont été examinés en connexion avec les propriétés de déformation des polymères. La même polymère semble avoir des structures de phases et des propriétés tout à fait différentes, quand il est obtenu sous différentes conditions thermiques. On montre sur une large série de polyéther (ester)uréthanes et -uréthane urées que l'analyse thermomécanique est une technique très efficace pour étudier les variations de la structure des phases.

---

- . , . , , . - .

     

Low-temperature oxidative chlorination of methane over supported platinum chloride catalyst

The Pt^II (catalyst)+Pt^IV (oxidant) system with a deficiency of Cl ligands is active in the oxidative chlorination of alkanes not only in aqueous solutions but also in the SiO₂-supported state. In heterogeneous as well as in homogeneous conditions, the reaction proceeds at 100°C through platinum-alkyl intermediates.

---

: Pt^II- Pt^IV- Cl-, , SiO₂. , , 100° - .

     

Reactions of Some Terpenoids with CH-Acids in the Presence of Cs-β Zeolite

Reactions of some ,-unsaturated ketones from terpenoid series with CH-acids in the presence of Cs- zeolite were studied under various conditions. The variation of reaction conditions (heating, ultrasonic irradiation) strongly affected the reaction products ratio, and the effect was singular in each case and gave different results.     

Modification of the face selectivity in asymmetric induction by cyclodextrins through the formation of three-component inclusion compounds

Stoichiometric amounts of triethylamine (TEA) were found to enhance the chiral induction by -cyclodextrin (-CD) in the reduction of acetophenone (ACPH) by aqueous NaBH₄. The enantioselectivity obtained depends upon the molar ratio -CD:ACPH:TEA. Evidence for the formation of a three-component inclusion compound was obtained from detailled¹H and²H NAM studies. The restriction of the molecular motion of the prochiral center probably accounts for the strong enhancement of the chiral induction observed.     

Dielectric properties of cleaned and monodisperse polystyrene latexes in microwaves

The dielectric behavior (, ) of three well-cleaned monodisperse polystyrene latexes having the same particle size and the same number of chemically-bound surface groups has been studied at a fixed microwave frequency (9.4 GHz), as a function of temperature and surface group (SO ₄ ^– , COO^–, OH).A large dielectric relaxation was observed in the sulfate-stabilized latex, which has the most polar surface end-group. The anomalous behavior in the thermal dependence of the hydroxyl and carboxyl-stabilized latexes (the OH latex being more pronounced than the COO^– latex) may originate from differences in the experimental conditions used for the preparation of such polymer colloids, or due to the presence of ionic species.On the basis of various dielectric models, the apparent volume fractions of the latexes were calculated. The amount of bound water around the latex particle was quantitatively correlated to the polarity of surface end-group (SO ₄ ^– > COO^– > OH). The differences between the calculated and actual values were not only a reflection of the thickness of vicinal water, but could also be indicative of the presence of oligomeric species in the suspension's medium (serum) of the latex. The permittivities of hydrated particle and of bound water were obtained with a non-linear iterative procedure.     

Two-dimensional model of a rough surface and spatial distribution of the desorbed species

We consider the angular distribution (AD) of species desorbed from a rough surface described by various distribution functions (DF) of the surface topography. It is shown that the width of the AD of the desorbed flow depends mainly on the roughness coefficient and is almost independent of the DF, except for the indirect dependence through . It is established that the secondary reflection of desorbed species from an uneven surface (with 1.2) has no appreciable effect on the form of the AD. Taking two models as examples, it is shown that anisotropy in the surface topology leads to anisotropy in the AD of the desorbed species.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2699–2704, December, 1990.     

Self-Consistent Calculation of Activity Coefficients and the Diffusion Layer Capacitance in Asymmetric Electrolytes

It is shown that substituting activities of individual ions for their concentrations in the equation for the ionic strength of solution substantially extends application of the first approximation of the Debye–Hückel theory for electrolytes of different valence. The obtained relationship predicts a changeover from the square root law in the charge region where the average distance between ions lis smaller than the ionic-atmosphere thickness 1/, to the cube root law, at l> 1/. The increasing deviation from experimental data upon going from LaCl₃solutions to La₂(SO₄)₃is attributed to the formation of ionic pairs LaSO₄ ⁺.     

Gitoxigenin glycosides

Summary Three cardiac glycosides have been synthesized from gitoxigenin and D-glucose: gitoxigenin 3-O--D-glucopyranoside, gitoxigenin 16 -O- -D-glucopyranoside, and gitoxigenin 3, 16-di-O- -D-glucoside. The first glycoside, obtained with a yield of 49% on the weight of the initial aglycone, possesses a fairly high biological activity (0.25 mg/kg), while the other two, formed in a yield of about 0.3%, do not possess the action on the heart that is specific for the cardenolides.Khar'kov Chemical and Pharmaceutical Scientific-Research Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 45–49, January, 1971.     

Chitosan–Carrageenan Gels

Phase behavior of the systems during the formation of polyelectrolyte complexes obtained by mixing of aqueous solutions of chitosan and -, -, or -carrageenan was studied. The gelation was shown to occur throughout the whole bulk solution at chitosan and -carrageenan concentrations higher than 0.1 and 0.3 wt %, respectively. At lower polysaccharide concentrations, the polyelectrolyte complexes precipitated. The study was performed at the polysaccharide concentrations not higher than 1 wt %. The gel systems were investigated by the dynamic rheology method. The mechanical characteristics of -carrageenan-containing gels were found to be mainly governed by the chitosan content; the viscosity of these gels was independent of temperature. Gels obtained with - and -carrageenans were sensitive to temperature because of the helix–coil conformational transitions in their molecules. The mechanical strength and stiffness of gels increase in the ––-carrageenan series. This effect was explained by the formation of additional crosslinks by double helixes of - and -carrageenan molecules.     

Colloid chemical studies of polystyrene latices polymerized without any surface-active agents

Summary The influence of secondary minimum for the stability of spherical colloid has been studied using a series of soap-free polystyrene latices from 350 m to 1400 m in diameter.The critical flocculation concentration (c. f. c.) and the zeta-potential at the c. f. c. for each latex were determined with several salts of different ionic valencies. The values of c. f. c. varied with the particle size, reaching a maximum value at 750 m and then decreasing gradually with the diameter.Another phenomenon detected in the experiment was the complete reversibility of coagulation which was observed only in the cases of large size latices, i. e., the coagulates of large size particles were fully redispersed in the solution by stirring. The time-dependence of their sedimentation curves was reproducible.These experimental results could not be explained by the simple theoretical consideration for stability of suspension. The satisfactory explanation is given only using the term of secondary minimum of interaction potential, i. e., the origin of coagulation was shifted from the ordinary primary minimum to the shallow secondary minimum at about 750 m of the particle diameter.

---

Zusammenfassung Der Einfluß des Sekundär-Minimum auf die Stabilität von Kolloiden wurde an seifenfreien Polystyrol-Latex-Suspensionen mit einem Durchmesser von 350 m bis 1400 m untersucht. Die kritische Flockungskonzentration (c. f. c.) und das Zeta-Potential bei c. f. c. wurde mit verschiedenen Salzen bestimmt.Der Wert von c. f. c. ändert sich mit der Teilchengröße.Ein weiterer wichtiger experimenteller Befund ist die vollständige Reversibilität der Flockung bei größeren Latices.Derartige Versuchsergebnisse können durch das Sekundär-Minimum befriedigend erklärt werden.

---

---

With 7 figures in 10 details and 2 tables     

Radiation-induced reactions of cholesterol in an aqueous medium

⁶⁰Co -ray radiolysis of cholesterol /3-hydroxy-5-cholestene/ /I/ in the two-phase system /water-ethyl acetate/ and in the presence of air has been studied using TLC and GC methods. The following products were observed in the irradiated mixture: 3, 7-dihydroxy-5-cholestene /II/, G O. 36, 3-hydroxy-7-keto-5-cholestene /III/, G 1.48, 3-hydroxy-7-keto-5-cholestane /IV/, G 0.22, 3,5,6-trihydroxy-5-cholestane /V/, G 0.83, 5,6-epoxy-3-hydroxy-5-cholestane /VIa/, G 0.26, 5,6-epoxy-3-hydroxy-5-cholestane /VIb/, G 0.24, and 2, 3-dihydroxy-5-cholestene /VII/, G 0.22. The dose dependence of the formation of these products shows that the cholesterol derivatives substituted in the position 7 /II–IV/ are formed from a common precursor — the radical Ia. On the other hand, the products of the 5–C=C double bond reactions /V and VI/ are formed independently. Also the product VII is formed independently. A reaction scheme that is in agreement with these results is proposed.     

Condensed systems based on 4-amino-3-mercapto-1,2,4-triazole

1,2,4-Triazolo[3,4-b]-1,3,4-thiadiazines, hydrazones, and -thio adducts were obtained by reactions of 4-amino-3-mercapto-1,2,4-triazole with -bromoacetophenones, aldehydes, and ,-unsaturated ketones. Conditions that promote the cyclocondensation of the -thio adducts to the previously undescribed 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazepines were found. The chemical and spectral properties of the compounds obtained are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 267–272, February, 1992.     

Performance,data and results with various chromatographic systems and various detection patterns in high-performance thin-layer chromatography

Summary A knowledge of the relationships between particle size and layer thickness on the one hand and migration distance and plate height on the other has prompted the development of the pre-coated HPTLC plate for nano-TLC. A separation performance which is very high with respect to time is achieved with a migration distance of 3–7 cm with a plate height of about 12 m and several thousand theoretical plates, thanks to the possibility of simultaneous chromatography. In HPTLC quantitative evaluation, standardised chromatographic conditions are essential. In this context the complex influences of different types of chamber and solvents on linear and circular chromatography are described. Various methods of conditioning the adsorbent by immersion impregnation, as well as detection procedures are discussed. The scope for varying TLC procedures and the advantages of TLC in general are listed.     

Formation of hexagonal MoO3 upon the decomposition of silica-supported ammonium paramolybdate

Upon the decomposition of silica-supported ammonium paramolybdate, hexagonal MoO₃ is formed at 300–350 °C. Irreversible transformation of hexagonal to rhombic MoO₃ is observed with increasing calcination temperature. The hexagonal MoO₃ structure is probably stabilized by the insertion of ammonium and silicon ions into the lattice of molybdenum trioxide.

---

, , 300–359 °C . MoO₃ . MoO₃, , MoO₃.

     

Oxidation of ethylene to ethylene oxide: A tpr study on fresh and aged catalysts

The deactivation of a silver catalyst was investigated after six years of industrial production of ethylene oxide. Temperature-programmed reduction was used to characterize the chemical nature of the silver and its reactivity towards oxygen. The fresh and some aged catalysts were examined, also after different thermal treatments.During the industrial run, the surface species were modified and some oxygen diffused into the bulk of the metal. Aging caused permanent changes in the characteristics of the silver, resulting in a different interaction with oxygen. The TPR spectra exhibited a trend along the reactor axis, suggesting a correlation with the degree of deactivation of the catalyst.

---

Zusammenfassung Die Desaktivierung eines Silberkatalysators wurde nach 6-jährigem Einsatz zur industriellen Produktion untersucht. Temperaturprogrammierte Reduktion wurde angewandt, um die chemische Natur des Silbers und dessen Reaktivität gegenüber Sauerstoff zu charakterisieren. Frische und einige gealterte Katalysatoren wurden nach verschiedenen thermischen Vorbehandlungen untersucht. Die Alterung verursachte bleibende Veränderungen in charakteristischen Eigenschaften des Silbers, was in der unterschiedlichen Wechselwirkung mit Sauerstoff zum Ausdruck kommt. Die TPR-Resultate zeigen einen Trend entlang der Reaktorachse, was auf eine Korrelation mit dem Grad der Desaktivierung des Katalysators hindeutet.

---

. () . , , . . , , . , .

---

---

The experimental contributions by F. Genoni and G. Valassina are gratefully acknowledged.     

Concentrated electrolyte solutions at high temperatures and pressures

A survey is given of recent experimental results obtained from high-temperature, high-pressure investigations with water, aqueous solutions, and ionic fluids. Data on the static dielectric constant of water to 550°C and 5 kbar are given and discussed with respect to their relation to water structure. Infrared and Raman spectra of HDO in pure water have been obtained to 400°C and 4 kbar, which give information on hydrogen bonding. Xe–H₂O and CO₂–H₂O mixtures were investigated in the infrared. Ni(II) and Cu(II) complexes were investigated by absorption spectroscopy in aqueous solutions of high chloride content to 350°C and 2–6 kbar. The gas-liquid critical point of ammonium chloride was found at 880°C and 1635 bars. This fluid appears to be predominantly ionic even in the critical region. The possibility of converting pure polar fluids such as ammonia and water into concentrated ionic solutions by self-ionization at very high pressures is mentioned.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.     

Adsorption and hydrogenation of unsaturated aldehydes over rhodium black

Hydrogenation selectivity of conjugated ethylenic bonds of unsaturated aldehydes over rhodium black is shown to be determined by intramolecular interactions in surface complexes due to the electronic structure of the initial unsaturated aldehydes.

---

- , .