The influence of cosolvent polarity on the flow properties of hydroalcoholic gels: empirical models

The aim of this study was to investigate the influence of cosolvent polarity on the rheological flow properties of aqueous and hydroalcoholic gels obtained from the Carbopol Ultrez 10 base and used for topical applications. Specifically, we have examined the effect of pH (range 4.0--7.0) on the consistency and flow properties of dispersed systems in water and mixtures--15 : 85% v/v of methanol : water, ethanol : water, n-propanol : water and n-butanol : water--at a constant polymer concentration of 0.3% w/w. The gels, which had decreasing polarity values in the jellifying medium, showed qualitatively similar flow behavior, characteristic of pseudoplastic systems, and all of the flow curves were adjusted to the Ostwald model. Sigmoidal dose response functions were calculated to describe the flow and consistency indexes as a function of pH. As a result, the influence of alcohol polarity on the polymer network has been assessed meaningfully using the empirical parameters obtained: maximum consistency index value (k(max)), pH value required for 50% development of polymer network (pH(50)), and asymptotic flow index value (n(min)) for the fully structured gels.     

Synthesis of gamma,delta-unsaturated and delta,epsilon-unsaturated alpha-amino acids from fragmentation of gamma- and delta-lactones

A noncoded amino acid of cyclomarin A (1) was synthesized in a racemic fashion. The method employs a six-membered ring template to control the relative stereochemistry and introduction of the functional groups. Ultimately, Pd-catalyzed fragmentation of the lactone provided gamma,delta-unsaturated and delta,epsilon-unsaturated alpha-amino acids. A Pd-catalyzed ring opening of a gamma-lactone is also reported.     

Alpha-sulfinyl carbanions as a new source of olefins

[reaction: see text] Secondary alpha-lithiosulfinyl carbanions react either intermolecularly, after transmetalation into an organocopper derivative in an S(N)2-type process with zinc carbenoid, or intramolecularly via higher-order zincate to give, through a tandem zinc homologation-beta-elimination reaction the corresponding alkenes. alpha,alpha-Disubstituted alkenes are only formed from tertiary alpha-lithiosulfinyl carbanions via the 1,2-metalate rearrangement.     

Le problème de la réduction des intégrales électroniques dans la méthode L.C.A.O. améliorée

Résumé L'auteur reprend les principes de la méthode L.C.A.O. améliorée en vue d'une justification plus complète des procédés employés. La théorie des perturbations permet d'une façon simple de tenir compte de la corrélation entre les électrons grâce à l'introduction d'une fonction universelle de la distance entre deux électrons. Le problème est ainsi ramené de l'échelle moléculaire à l'échelle atomique. On montre que la corrélation entre les électrons entraîne la réduction des intégrales atomiques. Le problème de la réduction des intégrales coulombiennes est traité en détail. La possibilité de négliger les autres intégrales biélectroniques est ensuite examiné. Enfin est étudié le problème de la réduction des intégrales de coeur.

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The principles of the improved LCAO theory are investigated to give a better justification for its methods. Perturbation theory allows a simple account for electronic correlation, when a universal function of interelectronic distance is introduced. The problem is hereby reduced from molecular to atomic scale. The reduction of electronic energy integrals by correlation is shown, especially for Coulomb integrals. The possibility of neglecting the other bielectronic integrals is examined. Finally the problem of core integral reduction is studied.

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Zusammenfassung Die Grundlagen der verbesserten LCAO-Methode werden untersucht, um dieses Verfahren besser zu rechtfertigen. Mit einer allgemeinen Funktion des Abstandes je zweier Elektronen und der Störungstheorie läßt sich die Elektronenkorrelation auf einfache Weise berücksichtigen. Damit wird das Problem vom molekularen auf den atomaren Maßstab zurückgeführt. Die Elektronenkorrelation bringt eine Reduktion der Elektronenenergieintegrale mit sich; die Coulombintegrale werden im einzelnen behandelt. Anschließend wird die Möglichkeit untersucht, die übrigen Zweielektronenintegrale zu vernachlässigen. Schließlich wird die Reduktion der Rumpfintegrale behandelt.

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Nous tenons à remercier très vivement le Docteur Chr. K. Jørgensen (Cyanamid European Research Institut, Genève) pour les intéressants échanges de vue que nous avons eu sur les divers problèmes évoqués dans cet article ainsi que le Docteur G. Berthier (Institut de Biochimie théorique, Paris) et Monsieur H. v. Hirschhausen.     

Sample preparation improvement in polycyclic aromatic hydrocarbons determination in olive oils by gel permeation chromatography and liquid chromatography with fluorescence detection

The determination of 15 polycyclic aromatic hydrocarbons (PAHs) in olive oil samples has been improved in order to obtain a fast methodology with a low limit of detection through the combination of liquid-liquid extraction with acetonitrile and preparative gel permeation chromatography (GPC) prior to the injection of purified extracts into a C18 column. Acetonitrile-water was used as the mobile phase with a gradient from 50 to 95%, w/w, acetonitrile in 30 min. The oven temperature was maintained at 15 degrees C, and fluorometric detection was made at a fixed excitation wavelength of 264 nm and variable, optimal emission wavelength for each analyte ranging from 352 nm for 11-H-benzo(b)fluorene to 500 nm for indeno(1,2,3-cd)pyrene. Recovery for all the compounds studied varied from 75 to 111%, and limit of detection values from 0.05 ng/g for benzo(k)fluoranthene to 0.48 ng/g for indeno(1,2,3-cd)pyrene, corresponding to 0.09 ng/g benzo(a)pyrene. Results were compared with those obtained by liquid-liquid extraction followed by a cleanup on silica and a direct GPC treatment of oil samples diluted in dichloromethane, 2 other methodologies that are appropriate for quantifying PAHs in olive oils. However, the proposed method improves the determination limits, reduces the time of analysis, and provides a highly stable baseline for sample chromatograms.     

Spontaneous dissolution of a single-wall carbon nanotube salt

Upon reduction with alkali metals, single-wall carbon nanotubes (SWNTS) are shown to form polyelectrolyte salts that are soluble in polar organic solvents without any sonication, use of surfactants, or functionalization whatsoever, thus forming true thermodynamically stable solutions of naked SWNTs.     

Fitting complex potential energy surfaces to simple model potentials: application of the simplex-annealing method

A stochastic method of optimization, which combines simulated annealing with simplex, is implemented to fit the parameters of a simple model potential. The main characteristic of the method is that it explores the whole space of the parameters of the model potential, and therefore it is very efficient in locating the global minimum of the cost function, in addition to being independent of the initial guess of the parameters. The method is employed to fit the complex intermolecular potential energy surface of the dimer of water, using as a reference the spectroscopic quality anisotropic site-site potential of Feller et al. The simple model potential chosen for its reparameterization is the MCY model potential of Clementi et al. The quality of the fit is assessed by comparing the geometry of the minimum, the harmonic frequencies, and the second virial coefficients of the parameterized potential with the reference one. Finally, to prove more rigorously the robustness of this method, it is compared with standard nonstochastic methods of optimization.     

UV index experimental values during the years 2000 and 2001 from the Spanish broadband UV-B radiometric network

An analysis is made of experimental ultraviolet erythemal solar radiation data measured during the years 2000 and 2001 by the Spanish UV-B radiation evaluation and prediction network. This network consists of 16 Robertson-Berger type pyranometers for evaluating solar erythemal radiation and five Brewer spectroradiometers for evaluating the stratospheric ozone. On the basis of these data the Ultraviolet Index (UVI) was evaluated for the measuring stations that are located either in coastal regions or in the more densely populated regions inland on the Iberian Peninsula. It has been checked that in most cases the maximum irradiance values corresponded to solar noon, although there were exceptions that could be explained by cloudiness. The maximum experimental values of the UVI were around 9 during the summer, though frequently passing this value at the inland measurement stations. The annual accumulated dose of irradiation on a horizontal plane has also been studied, as well as the evolution through the year in units of energy, standard erythemal doses and minimum erythemal doses, according to different phototypes.     

Conformational behaviour of 2,2′-bipyrrole

The rotational potential around the interannular bond in 2,2-bipyrrole has been calculated making use of standard minimal STO-3G and split valence 4-31G basis sets. Geometrical optimization concerning the most significant interannular internal parameters has been performed with both basis sets. The trans conformer is predicted to be more stable than the cis. The minimal basis set predicts the existence of a cisoid-gauche minimum which after limited optimization becomes very shallow and it seems to be an artifact of the rigid rotor approximation. At 4-31G level, both the trans and cis conformers represent maxima in the potential curve and two gauche minima appear at =46.0° and =147.6°, the latter being the absolute minimum. The absolute maximum of the potential curve corresponds to the cis conformer.     

Cover Picture

The cover picture shows the structure, determined crystallographically, of the tetrakis(trimethylstannyl)phosphonium cation that is formed with surprising ease from the reaction of P(SnMe(3))(3) with Me(3)SnOTf (OTf=OSO(2)CF(3)) and is isolated as the OTf salt. It is the first completely substituted main group organometallic phosphonium derivative, and, in contrast to the more common tetraorganic-substituted phosphonium cations is only stable in the solid state; in solution it functions as a masked Me(3)Sn(+) reagent. More about this chameleonlike ion and the N(SnMe(3))(4) cation homologue, which is equally dynamic in solution and has unusual long Sn-N bond lengths, is reported by M. Driess et al. on p. 3684 ff.