Conformational flexibility of a synthetic glycosylaminoglycan bound to a fibroblast growth factor. FGF-1 recognizes both the (1)C(4) and (2)S(O) conformations of a bioactive heparin-like hexasaccharide

The first direct NMR determination of the conformation of a conformationally flexible heparin-like hexasaccharide bound to a key receptor, FGF-1, is described. The determination has been based on the use of a 13C-labeled protein and a regular 12C sugar. FGF-1 recognizes several conformations of the iduronic moieties of the hexasaccharide. Therefore, this case is different than that described for the controversial recognition of heparin-like saccharides by AT-III, which seems to recognize just one conformation of the iduronic acid residues.     

B-allyl-10-Ph-9-borabicyclo[3.3.2]decanes: strategically designed for the asymmetric allylboration of ketones

The simple and efficient syntheses of B-allyl-10-(phenyl)-9-borabicyclo[3.3.2]decane (1) in both enantiomeric forms are reported. The remarkable enantioselectivity (81-99% ee) of these reagents in the allylboration process at -78 degrees C is only modestly diminished when the process is conducted at 0 degrees C, a phenomenon attributable to its rigid bicyclic structure. In addition to providing the homoallylic alcohols 6 efficiently (70-92%), the procedure also permits the efficient recovery of the chiral boron moiety (67-82%) as an air-stable crystalline N-methylpseudoephedrine complex 4 for the direct regeneration of 1 with allylmagnesium bromide in ether (98%). The reagent gives predictable stereochemistry, providing a strategically designed "chiral pocket" which is particularly receptive to leading methyl groups (e.g., methyl ethyl ketone, 87% ee).     

Antisymmetry of solutions for some weighted elliptic problems

This article concerns the antisymmetry, uniqueness, and monotonicity properties of solutions to some elliptic functionals involving weights and a double well potential. In the one-dimensional case, we introduce the continuous odd rearrangement of an increasing function and we show that it decreases the energy functional when the weights satisfy a certain convexity-type hypothesis. This leads to the antisymmetry or oddness of increasing solutions (and not only of minimizers). We also prove a uniqueness result (which leads to antisymmetry) where a convexity-type condition by Berestycki and Nirenberg on the weights is improved to a monotonicity condition. In addition, we provide with a large class of problems where antisymmetry does not hold. Finally, some rather partial extensions in higher dimensions are also given.     

Voltammetric Electronic Tongue Based on Carbon Paste Electrodes Modified with Biochar for Phenolic Compounds Stripping Detection

Biochar is a charcoal produced from the biomass pyrolysis process that presents a highly porous and functionalized surface. In the present work an array of carbon paste electrodes (CPE) made of different forms of carbon (graphite, carbon nanotubes and activated biochar) was evaluated in the development of an electronic tongue for discrimination and stripping voltammetric determination of catechol (CAT), 4‐ethylcatechol (4‐EC) and 4‐ethylguaiacol (4‐EG) phenolic compounds. Morphological characterization of carbon materials and electrodes surfaces was performed by scanning electron microscopy (SEM) and semi‐quantitative elemental composition by energy dispersive spectroscopy (EDS). Electrochemical Impedance Spectroscopy (EIS) measurements were used for electrochemical characterization of electrodes. Cyclic voltammetry measurements were performed for the phenolic compounds evaluated using different concentrations. Principal component analysis (PCA) was performed to evaluate the qualitative analysis. Quantitative data modeling was done using artificial neural networks (ANN). The proposed sensor array presented analytical potentiality allowing the distinction and determination of CAT, 4‐EC and 4‐EG by using chemometric processing. The method showed sensibility, reproducibility and a good linearity (R²>0.9940) for three compounds evaluated. Spontaneous preconcentration of three compounds was possible using all three sensors, which can allow the application of these as passive samplers for remote determinations of phenolic compounds in wine and food samples.     

Speckle statistics in partially corrected wave fronts

Wave fronts distorted by the atmosphere preserve high-spatial-frequency information. This information can be retrieved by use of adaptive optics systems to correct the incoming wave front. This correction should be as nearly complete as possible. In experiments performed in the visible, only partial compensation is attainable. We provide a theoretical model to predict the intensity statistics of the light in the image center as a function of the number of Zernike polynomials corrected.     

Highly enantioselective [4 + 2] cycloaddition reactions catalyzed by a chiral N-methyl-oxazaborolidinium cation

The reaction of lithium aryl borohydrides with salts of beta-amino alcohols provides a new route for the synthesis of oxazaborolidines. This method also leads to the first synthesis of hitherto elusive N-methyl oxazaborolidine cations, specifically the cationic proline derivative 3. Compound 3 is a strong chiral Lewis acid which is very effective for catalysis of [4 + 2]-cycloaddition reactions in good yield and with high enantioselectivity. Several diverse examples illustrate the scope of these catalytic reactions.     

Synthesis of tetracyclic dioxygenated isoquinolines and their cytotoxic activity

An efficient synthesis of new dioxygenated isoquinolines is reported. The novelty of this approach derives from its use of tricyclic-nitril (3) as a building block in a synthetic sequence of seven steps for the preparation of the tetracyclic isoquinoline (14) and its derivatives. The isoquinoline 16 was 10-fold more active against leukemia L₁₂₁₀ than the corresponding tetrahydroisoquinoline 14.