PFGSE-NMR study of the self-diffusion of sucrose fatty acid monoesters in water

The micellization of pure monosubstituted sucrose fatty acid esters in water, namely sucrose octanoate, sucrose decanoate, sucrose laurate, sucrose dodec-5-cis-enoate, sucrose myristate, and sucrose palmitate, has been investigated by means of two NMR methods, pulsed field gradient spin-echo NMR (PFGSE-NMR), giving access to the self-diffusion coefficients of free molecules and micelles in solution, and the ERETIC method (electronic reference to access in vivo concentrations) for the measurement of concentrations by external calibration of a synthetic NMR signal. The early micellar regions and, when possible, the premicellar regions were investigated. By this method, we obtained the hydrodynamic radii of micelles, displaying a linear progression in relation to the chain length and an accurate determination of critical micellar concentration (CMC) for each sucrose ester. The effect of the regiochemistry of fatty chain grafting has been investigated, showing special behavior for 1'-O-sucrose palmitate.     

19F NMR chemical shifts of n-F-alkyl compounds

The examination of ¹⁹F chemical shifts for ca. 650 F-alkylated compounds of general formula CF₃(CF₂)_nCF₂X led to the following conclusions: the CF₂ groups α to X are very sensitive to the nature of X, and are spread over a range of 85 ppm. The effect of the length of the F-alkyl chain decreases rapidly, so that δCF₂(α) can already be considered as characteristic of X for n = 1 or 2 for most practical purposes. Solvent effects (in 9 different solvents having ε = 1.8 to 52.1) were found to be rather small except for the F-alkyl iodides. A chart which indicates the domain in which the CF₂(α) resonance signal is to be expected is given for 42 different series of F-alkylated compounds; it is expected to provide the synthetic chemist with a useful tool for the identification and characterization of such compounds.     

Dilute solution properties of a polyurethane. I. Linear polymers

A linear polyurethane of high molecular weight was prepared in solution by the polyaddition of equimolar amounts of ethylene glycol and methylene bis(4-phenyl isocyanate). The polymer was fractionated by using a direct sequential extraction procedure, with a solvent–nonsolvent system consisting of N,N′-dimethylformamide (DMF) and acetone (A). The resulting fractions were characterized by viscosity and lightscattering measurements. The relationship between the intrinsic viscosity and molecular weight was found in DMF at 25°C. to be [η] = 3.64 × 10^?4M^0.71. The unperturbed polymer chain dimensions were determined from intrinsic viscosity measurements carried out under experimentally determined theta conditions.     

k-spaces and Borel filters on the set of integers

We say that a countable, Hausdorff, topological space with one and only one accumulation point is a point-space. For such a space, we give several properties which are equivalent to the property of being a k-space. We study some free filters on the set of integers and we determine if the associated point-spaces are k-spaces or not. We show that the filters of Lutzer-van Mill-Pol are k-filters. We deduce that, for each countable ordinal , there exists a free filter of true additive class (Baire's classification) and a free filter of true multiplicative class for which the associated point-spaces are k-spaces but not , the existence being true in the additive case for . In particular, we answer negatively a question raised in J. Calbrix, C. R. Acad. Sci. Paris 305 (1987), 109--111.

     

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.     

Recherches sur la structure électronique de composés soufrés (méthode L.C.A.O. améliorée)

Improved L.C.A.O. method primitively built for conjugated molecules holding only atoms of second row in the periodic classification is extended to molecules holding atoms of the third row. The application is done for thiophen, thioketones, SO₂ and SO₃. d orbitals are not introduced in this study. Discussion about results shows that d orbitals must be introduced when the sulphur atom is strongly positively charged like in sulphur oxides.     

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).     

Mild cleavage of methoxymethyl (MOM) ethers with trimethylsilyl bromide

Trimethylsilyl bromide is an effective reagent for the deprotection of methoxymethyl ethers under mild conditions.     

Synthèse de nouveaux types de dérivés C-glycosyliques à partir de sucres acétyléniques ou de leurs équivalents synthétiques partiels

Synthesis of Novel Types of C-Glycosyl-derivatives from Acetylenic Sugars or Partial Synthetic Equivalents thereof The concept of synthetic equivalent is not unequivocal and, for example, α-fluoroenamines may behave in some cases as synthetic equivalents of ynamines and, in other situations, quite differently. Some uses of these α-fluoroenamines, ‘partial synthetic equivalents’ of ynamines, for the synthesis of C-glycosyl derivatives of coumarins, chromones, quinolines, quinolones, thietenes and isoxazoles are described. We also report the preparation of a series of mono- and diglycosylthiophenes by reacting HS^? with mono- and diglycosylbutadiynes. Acetylenic sugar derivatives have also been used for the synthesis of a diglycosylazaphosphorine and a spirooxolenone.