Lifetime prediction of ABS polymers based on thermoanalytical data

The service life of ABS polymer, stabilized by 2-(3,5-di-tert-butyl-4-hydroxyanilino)-4,6-bis(octylthio)-1,3,5-triazine and containing 50% of a modifying rubber component, was estimated from oxidative induction times measured by DSC in isothermal mode in the temperature interval 140–170°C. The lifetime of ABS powder at the actual temperature of drying was predicted by linear extrapolation according to Arrhenius. However, the extrapolated value was much longer than the real lifetime determined from the long-term oven aging tests at 70 and 90°C, simulating the industrial drying process. The effect of changes in the apparent activation energy of oxidation due to antioxidant consumption during polymer aging is discussed.     

4.50—Polarographic investigation of conformational changes of human serum albumin: Part I. Unfolding of human serum albumin by urea

The mechanism of the unfolding of human serum albumin by urea was studied using d.c. polarography. It was found that this reaction is a complex process which cannot be described in terms of a two-state transition model. As well as the Brdi?ka catalytic current we have also studied the reduction current of disulfide groups in native and denatured human serum albumin. The number of cystine residues accessible for electrode reduction in native and denatured protein was calculated. On the basis of these results a scheme for the unfolding of human serum albumin by urea is proposed.     

Synthesis and structure of the first dinuclear gold complex with the Au—Au bond containing no bridging ligands

Russian Chemical Bulletin -     

A comparison of the stochastic theory of the crystal growth and the Stefan problem

The stochastic theory of the crystal growth is compared with the solution of the Stefan problem in the case of Sn solidification. It is shown that the stochastic theory gives the same results as the solution of the Stefan problem if kinetic processes at the solidification front are very rapid.     

Transformations of epoxide derived from nopol over askanite-bentonite clay

Transformations of epoxide derived from nopol in the presence of natural askanite-bentonite clay were studied. The major products of the isomerization in the cold are diols possessing a p-menthane skeleton, which are readily converted into bicyclic ethers when the reaction is carried out at room temperature.Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 10, 2004, pp. 1483–1487.Original Russian Text Copyright © 2004 by Ilina, Volcho, Korchagina, Salakhutdinov, Barkhash.     

Intercalation of 1,2-Alkanediols into α-Zirconium Hydrogenphosphate

Intercalation compounds of α-Zr(HPO₄)₂ · H₂O with 1,2-alkanediols (from C3 to C16) have been prepared by replacing 1-propanol in α-Zr(HPO₄)₂ · 2C₃H₇OH with the desired 1,2-alkanediols by a treatment in a microwave field. It was found that the intercalates contain 1.5 molecules of diol per formula unit. The diol molecules are placed between the host layers in a bimolecular way with their aliphatic chains tilted at an angle of 51°. The diol molecules are anchored in the interlayer space by H-bonds. A mixed intercalate, containing 1,2-butanediol and 1,2-decanediol in a roughly equimolar ratio, is formed when the α-Zr(HPO₄)₂ · 2C₃H₇OH intercalate, suspended in a mixture of 1,2-butanediol and 1,2-decanediol, is exposed to microwave radiation. No new phase containing both types of the guest molecules was observed when the 1-propanol intercalate, suspended in a mixture of 1-propanol and 1,2-octanediol, is exposed to microwave radiation.     

Über die Wahl der Lösungsmittelsysteme bei der papierchromatographischen Trennung organischer Verbindungen

Zusammenfassung An praktischen Beispielen wurde gezeigt, in welcher Weise die Trennung organischer Verbindungen mittels Papierchromatographie erzielt werden kann. Man ist nicht auf einige bewährte Lösungsmittel systeme allein angewiesen, sondern kann von Fall zu Fall systematisch neue und geeignete Systeme benützen. Es hat sich bewährt, sich nach den elementaren Löslichkeitsregeln für organische Stoffe zu richten, unter der Voraussetzung, daß die zu chromatographierende Verbindung in der stationären Phase gut, in der mobilen Phase dagegen weniger löslich ist. Durch Änderung der stationären Phase (Wasser, nicht wäßriges, polares Lösungsmittel, nicht polares Lösungsmittel) oder der Polarität und Zusammensetzung der mobilen Phase kann man das Wandern der Flecke am Chromatogramm beeinflussen, beliebige R_fWerte erhalten und in vielen Fällen auch eine beliebige Reihenfolge der Verbindungen am Chromatogramm erzielen.Da die Löslichkeit organischer Verbindungen von intermolekularen Kräften abhängig ist, erscheint das Problem im Zusammenhang mit strukturellen Einflüssen sehr kompliziert und muß für jeden Fall auf eigene Weise gelöst werden. Die Löslichkeitseigenschaften können weiter durch Benutzung reaktiver Lösungsmittel beeinflußt werden, die z. B. die Verbindungen in wasserlösliche Salze überführen können. Dabei ist an die möglichen Komplikationen, die bei ionisierbaren Verbindungen durch Dissoziation und Hydrolyse entstehen können, zu achten.Von den Hauptfaktoren, die eine Trennung ermöglichen können, seien die folgenden erwähnt: funktionelle Gruppen, ihre Anzahl, Polarität, gegenseitige Stellung, bzw. ihre Basizität oder Azidität, C-Atomanzahl in homologen Verbindungen, inter- und intramolekulare Wasserstoffbindungen, sterische Faktoren u. a. Es ist dann von der Art des gewählten Lösungsmittelsystems abhängig, welche der genannten Faktoren im Vordergrund stehen und welche beseitigt werden.Wenn die Löslichkeitsunterschiede der zu trennenden Stoffe zu gering sind, um gute Trennungen zu ermöglichen, ist es zweckmäßig, die Verbindungen in solche Derivate zu überführen, deren Strukturunterschiede größer sind.

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Summary Practical examples are given to show how organic compounds can be separated by means of paper chromatography. The operator is not limited to tested solvent systems, but can use new suitable systems as the occasion demands. It has been found best to abide by the elementary rules of solubility of organic compounds, provided the compound to be chromatographed is quite soluble in the stationary phase but less soluble in the mobile phase. By altering the stationary phase (water, nonaqueous, polar solvent, non-polar solvent) or the polarity and composition of the mobile phase, the migration of the stains in the chromatogram can be influenced, selectedR _f -values can be obtained, and in many cases it is also possible to secure a desired succession of the compounds on the chromatogram.Since the solubility of organic compounds depends on intermolecular forces, the problem in connection with structural influences appears very complicated and must be solved individually for each case. Moreover, the solubility characteristics can be affected by using reactive solvents; for instance, the compounds can be converted into water soluble salts. Under such circumstances, sight must not be lost of the complications which may arise because of the dissociation and hydrolysis of ionizable compounds. The following are among the chief factors, which may make a separation possible: functional groups, their number, polarity, relative position, their basicity or acidity, C-atom number in homologous compounds, inter- and intramolecular hydrogen bonds, steric factors, etc. It then depends on the type of solvent system selected, which of these factors are predominant and which can be neglected or eliminated.If the solubility differences are too slight to permit good separations, the compounds to be separated should, if possible, be converted into derivatives whose structural differences are more pronounced.

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Résumé Des exemples pratiques montrent comment il est possible d'effectuer la séparation de combinaisons organiques par Chromatographie sur papier. Il n'est pas uniquement fait appel à des systèmes de solvants éprouvés mais, dans certains cas, de nouveaux systèmes appropriés sont systématiquement utilisés.Il s'est avéré satisfaisant de faire appel aux règles élémentaires de solubilité des substances organiques sous réserve que la combinaison à chromatographier soit suffisamment soluble dans la phase stationnaire et moins soluble dans la phase mobile. En faisant varier la phase stationnaire (eau, solvant non aqueux, solvant polaire, solvant non polaire) ou la polarité et la composition de la phase mobile, il est possible d'influencer la migration des taches du chromatogramme, d'obtenir des valeurs deR _f désirées et, dans de nombreux cas, d'obtenir les combinaisons dans un ordre déterminé sur le chromatogramme.La solubilité des combinaisons organiques étant fonction des forces intermoléculaires il en résulte que le problème se complique considérablement dans la mesure où l'on considère les influences structurelles et que chaque cas particulier doit recevoir une solution qui lui est propre. Les propriétés de solubilité peuvent en outre être influencées par l'emploi de solvants réactifs qui peuvent transformer, par exemple les combinaisons en sels solubles dans l'eau. Il faut alors tenir compte des possibilités de complications qui peuvent apparaître par dissociation et hydrolyse des combinaisons ionisables.Parmi les principaux facteurs qui permettent une séparation, il convient de mentionner les suivants: les groupes fonctionnels, leur nombre, leur polarité, leur position relative, ou encore leur acidité ou leur basicité, le nombre d'atomes de carbone de combinaisons homologues, les liaisons hydrogène inter- et intramoléculaires, les facteurs stériques, etc. Suivant la nature du système solvant choisi pourront alors varier les facteurs dont l'effet est prépondérant et ceux dont l'effet est nul. Lorsque les différences de solubilité des substances à séparer sont trop faibles pour permettre des séparations satisfaisantes, il est commode de transformer les combinaisons en dérivés dont les différences de structure soient plus importantes.

     

Neurosteroid analogues: synthesis of 6-aza-allopregnanolone

An efficient synthesis of 6-azapregnane derivatives and their biological activity is described. The nitrogen was introduced into the B ring using Beckmann rearrangement of the (E)-oxime of 6-oxo-B-nor-5α-pregnane derivatives. The required 3α-hydroxyl was produced either by solvolysis of the corresponding 3β-mesyloxy group or by the Meerwein-Ponndorf-Verley reduction of the 3-oxo group; this reduction could be carried out selectively with an unprotected 3,20-dioxo derivative. The binding of the 6-aza-steroids to the γ-aminobutyric acid receptor (GABA_A) was measured using [³⁵S]-tert-butyl-bicyclo[2.2.2]phosphorothionate (TBPS) and [³H]flunitrazepam. The only analogue to be slightly active was that lacking any oxygen function in position 3.