One-pot microwave-assisted substitution of a glucuronan trisaccharide

Substitution of a glucuronic acid trisaccharide was easily performed in one step under microwave irradiation, affording a product resulting from simultaneous glycosylation, esterification and a butyl ether formation.     

Détermination de l'énergie de conjugaison des acides naphtoǐques

The present paper deals with the experimental and theoretical determination of energies of conjugation of organic molecules.A computation process has been applied, first to simple molecules comprising an hydrocarbon (styrene), an oxygen function (benzaldehyde) and a nitrogen function (aniline). The results are compared with those obtained from the literature.The application of this computation process to naphthoic acids permits the determination of energies of conjugation and isomerization of these molecules.     

Structure électronique et spectres de resonance paramagnétique électronique des radicaux vinyle et cyclopropyle

Résumé Une méthode de calcul dérivant des théories de champ self-consistant est utilisé pour l'étude des radicaux vinyle et cyclopropyle. L'énergie électronique et les écarts hyperfins dûs aux hydrogènes et au ¹³C ont été évalués en fonction de la géométrie du carbone radicalaire. L'angle C=-H du radical vinyle a été trouvé de l'ordre de 150°. Il est montré que les radicaux vinyle et cyclopropyle ont une structure électronique similaire qui ne peut être totalement expliquée ni par un modèle ni par un modèle classique, chaque radical présentant à la fois les deux caractères.

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A method of calculation derived from self-consistent field theories is used for a study of vinyl and cyclopropyl radicals. Electronic energy, hydrogens and ¹³C hyperfine splittings are evaluated as a function of the carbon geometry. The C=-H bond angle is found to be about 150°. It is shown that vinyl and cyclopropyl radicals have a similar electronic structure which cannot be completely interpreted neither by a classical model nor by a one, each radical presenting both and character.

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Zusammenfassung Nach einer auf dem SCF-Verfahren basierenden Methode werden Elektronenenergie, H- und ¹³C-Hyperfeinaufspaltung in Vinyl- und Cyclopropylradikalen in Abhängigkeit vom Bindungswinkel am berechnet, der sich im ersten Fall zu 150° ergibt. Es zeigt sich, daß die Elektronenstruktur der beiden behandelten Radikale ähnlich ist und daß sie weder durch ein reines - noch ein reines -Modell zu beschreiben ist.

     

Usefulness of the direct coupling headspace-mass spectrometry for sensory quality characterization of virgin olive oil samples

The applicability of the headspace coupled to mass spectrometry for evaluation of the sensory quality of virgin olive oil samples is presented. The volatiles of the oil are directly transferred from the sample vial to the detector without chromatographic separation. The mass spectrum obtained can be considered as a fingerprint of the oil sample and can be used for classification purposes. After a training step with samples previously qualified following the official method, a classification model was created using the supervised technique soft independent modeling of class analogy (SIMCA). Eight negative (rancid, winey-vinegary, muddy sediment, hay-wood, vegetable water, earthy, fusty and musty-humidity) and three principal positive attributes (fruity, bitter and pungent) have been included in this study. With them, a classification model consisting of two main classes (extra- and lampante-virgin olive oil) was constructed. In addition, the unsupervised technique cluster analysis permited the discrimination among oils with different negative attributes. The proposed procedure has been applied to the classification of commercial samples (as extra- or lampante-virgin olive oils) and the results were compared with those provided by the expert's panel with acceptable correlation.     

Changes in silicon elastomeric surface properties under stretching induced by three surface treatments

Poly(dimethylsiloxane) (PDMS) substrates are used in many applications where the substrates need to be elongated and various treatments are used to regulate their surface properties. In this article, we compare the effect of three of such treatments, namely, UV irradiation, water plasma, and plasma polymerization, both from a molecular and from a macroscopic point of view. We focus our attention in particular on the behavior of the treated surfaces under mechanical stretching. UV irradiation induces the substitution of methyl groups by hydroxyl and acid groups, water plasma leads to a silicate-like layer, and plasma polymerization causes the formation of an organic thin film with a major content of anhydride and acid groups. Stretching induces cracks on the surface both for silicate-like layers and for plasma polymer thin coatings. This is not the case for the UV irradiated PDMS substrates. We then analyzed the chemical composition of these cracks. In the case of water plasma, the cracks reveal native PDMS. In the case of plasma polymerization, the cracks reveal modified PDMS. The contact angles of plasma polymer and UV treated surfaces vary only very slightly under stretching, whereas large variations are observed for water plasma treatments. The small variation in the contact angle values observed on the plasma polymer thin film under stretching even when cracks appear on the surface are explained by the specific chemistry of the PDMS in the cracks. We find that it is very different from native PDMS and that its structure is somewhere between Si(O2) and Si(O3). This is, to our knowledge, the first study where different surface treatments of PDMS are compared for films under stretching.     

Inverse gas chromatography study on the effect of humidity on the mass transport of alcohols in an ethylene-vinyl alcohol copolymer near the glass transition temperature

Inverse gas chromatography (IGC) was used to study the effect of moisture on transport properties of three low molecular weight alcohols (methanol, ethanol, and 1-butanol) through high barrier copolymers of ethylene-vinyl alcohol with an ethylene content of 38%mol (EVOH38) at 40 degrees C. The value of the partition coefficient (K) was obtained by using two approaches: (a) the fit of the slope of sorption isotherms obtained through the method of Kiselev and Yashin; and (b) the solution to the model of Romdhane and Danner obtained by using the law of moments. The second method also allowed the estimation of the diffusion coefficient (D(p)) at the different humidity conditions. None of these two methods were applicable at low values of relative humidity. With the first method, the diffusion of the permeants through the copolymer was not fast enough to allow them to reach the core of the EVOH particles used as stationary phase resulting in sorption values unrealistically low. The fit of the chromatograms obtained by using the second method also suggested questionable values of the mass transport parameters. Although the theoretical curve perfectly described the chromatogram, the low extent of the interaction and the slow diffusion resulted in interdependent values of the coefficients K and D(p), with infinite pairs of values providing the same curve profile. As the relative humidity of the carrier gas increased, the diffusivity and the sorption of the alcohols also increased, making both methods applicable. In the case of the partition coefficient, the sorption of the biggest molecules (ethanol and 1-butanol) was the most affected, the increment of K for methanol being moderate. As regards the D(p) value, methanol was the most influenced compound and 1-butanol the least. Finally, a sharp increment of the D(p) of the three alcohols was observed between 35 and 47% RH and attributed to the plasticization of the copolymer.     

From simple amphiphilic to surfactant behavior: analysis of (1)H NMR chemical shift variations

Analysis of the (1)H NMR chemical shift variations for the methyl protons of sodium decanoate and decanoic acid in D(2)O solutions using reduced variables is consonant with a narrow distribution of sizes about the mean aggregation number for decanoate ion micelles, in contrast with decanoic acid polydisperse aggregates which increase their size with concentration, until phase separation is reached. At defined temperatures between 10 and 50 degrees C, the chemical shift coefficients for the methyl group protons exhibit a negative temperature slope (shielding) for decanoate ion micelles and a positive temperature slope (deshielding) for decanoic acid aggregates. These results suggest that an increase of temperature improves the mobility of the decanoate ion chains in the micelles, thus inducing the methyl groups of the decanoate ion micelles to spend more time near the micelle-water interfaces. In turn, the size of polydisperse decanoic acid aggregates increases with temperature.