Characterization and carbohydrate specificity of pradimicin s

The pradimicin family of antibiotics is attracting attention due to its anti-infective properties and as a model for understanding the requirements for carbohydrate recognition by small molecules. Members of the pradimicin family are unique among natural products in their ability to bind sugars in a Ca(2+)-dependent manner, but the oligomerization to insoluble aggregates that occurs upon Ca(2+) binding has prevented detailed characterization of their carbohydrate specificity and biologically relevant form. Here we take advantage of the water solubility of pradimicin S (PRM-S), a sulfated glucose-containing analogue of pradimicin A (PRM-A), to show by NMR spectroscopy and analytical ultracentrifugation that at biologically relevant concentrations, PRM-S binds Ca(2+) to form a tetrameric species that selectively binds and engulfs the trisaccharide Manα1-3(Manα1-6)Man over mannose or mannobiose. In functional HIV-1 entry assays, IC(50) values of 2-4 μM for PRM-S corrrelate with the concentrations at which oligomerization occurs as well as the affinities with which PRM-S binds the HIV surface envelope glycoprotein gp120. Together these data reveal the biologically active form of PRM-S, provide an explanation for previous speculations that PRM-A may contain a second mannose binding site, and expand our understanding of the characteristics that can engender a small molecule with the ability to function as a carbohydrate receptor.     

Nanocomposites from biopolymer hydrogels: Blueprints for white biotechnology and green materials chemistry

Bionanocomposites based on the association between biological polymers and inorganic colloids are an emerging class of materials, with main applications in biotechnology and biomedicine. They combine the chemical diversity, hierarchical structure, and biocompatibility of natural biomacromolecules with the robustness and functionality of mineral phases. In particular, biopolymer hydrogels can act as templates and/or host matrices for nanoparticles to design bionanocomposites with tailored optical, conductive, magnetic, mechanical, and bioactive properties. This review presents the key concepts on which such materials are currently designed, in terms of chemistry and physics. Specific examples are provided to illustrate the importance of the bio‐organic/inorganic interface on the final properties of the composite structures. It is finally suggested that bionanocomposites have a major role to play for the development of green materials and bio‐responsive devices. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

A novel C-5' substituted cinchona alkaloid-derived catalyst promotes additions of alkyl thiols to nitroolefins with excellent enantioselectivity

A new bifunctional C-5' substituted cinchona alkaloid-based catalyst promotes the first highly enantioselective additions of alkyl thiols to nitrostyrenes.     

Analytical and Preparative Chiral Separation of β-Carboline Derivatives, LDL Oxidation Inhibitors, Using HPLC and CE Methodologies: Determination of Enantiomeric Purity

In the present study, baseline separation of the enantiomers of 16 β-carboline derivatives was successfully achieved using both capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) techniques in short run times (<15?min) and thus permit the determination of enantiomeric excess. In HPLC methodology, cellulose chiral stationary phase (Chiralcel OD-H) was used with a binary mobile phase constituted of n-hexane/ethanol 85/15 leading to a resolution factor of 12.6 in 15?min. Preparative HPLC allowed to obtain pure enantiomers of two compounds. In CE, chiral selectivity was developed with an in-capillary stacking strategy using anionic (highly sulfated-γ) cyclodextrins 5% (w/v) as chiral selectors and a 60?mM phosphate buffer (pH 2.5) resulting in a resolution of 10.26 in 14?min of analysis. The analytical characteristics of the two developed methods were studied in terms of repeatability, limits of detection and limits of quantification showing their suitability to be extended to all the other molecules.     

Comparison of Singer's Formant, Speaker's Ring, and LTA Spectrum Among Classical Singers and Untrained Normal Speakers

Many studies have described and analyzed the singer's formant. A similar phenomenon produced by trained speakers led some authors to examine the speaker's ring. If we consider these phenomena as resonance effects associated with vocal tract adjustments and training, can we hypothesize that trained singers can carry over their singing formant ability into speech, also obtaining a speaker's ring? Can we find similar differences for energy distribution in continuous speech? Forty classically trained singers and forty untrained normal speakers performed an all-voiced reading task and produced a sample of a sustained spoken vowel /a/. The singers were also requested to perform a sustained sung vowel /a/ at a comfortable pitch. The reading was analyzed by the long-term average spectrum (LTAS) method. The sustained vowels were analyzed through power spectrum analysis. The data suggest that singers show more energy concentration in the singer's formant/speaker's ring region in both sung and spoken vowels. The singers' spoken vowel energy in the speaker's ring area was found to be significantly larger than that of the untrained speakers. The LTAS showed similar findings suggesting that those differences also occur in continuous speech. This finding supports the value of further research on the effect of singing training on the resonance of the speaking voice.     

Direct evidence for distinct colour origins in ROY polymorphs

ROY is one of the most well-studied families of crystal structures owing to it being the most polymorphic organic material on record. The various red, orange, and yellow colours of its crystal structures are widely-believed to originate from molecular conformation, though the orange needle (ON) polymorph is thought to be an exception. We report high-pressure, single-crystal X-ray measurements which provide direct experimental evidence that the colour origin in ON is intermolecular, revealing that the molecule undergoes minimal deformation but still exhibits a pronounced, reversible, pale orange → dark red colour change between ambient pressure and 4.18 GPa. Our experimental data are rationalised with band structures, calculated using an accurate hybrid DFT approach, where we are able to account for the variation in colour for five polymorphs of ROY. We highlight the outlier behaviour of ON which shows marked π⋯π stacking interactions that are directly modified through application of pressure. Band structure calculations confirm these intermolecular interactions as the origin of the colour change.

Alternative colour origins in ROY polymorphs are conclusively determined for the first time, using high-pressure diffraction and hybrid DFT.     

A submersible flow analysis system

A submersible chemical analyzer (SCANNER) has been developed which can perform analyses in situ in the ocean. The SCANNER is based on a modified flow-injection system and can be used to automate virtually any spectrophotometric determination that can be done by flow injection analysis. The SCANNER consists of a multichannel peristaltic pump, solid-state colorimeters, manifold tubing, valves, and an electronic module. All of the components are pressure-tolerant, except the electronics module, which is placed in a pressure housing. Typical detection limits are of the order of 0.1 μM. Sample introduction is continuous. The SCANNER has been tested successfully to pressures of 3300 dbar in the laboratory and to depths of 2500 m in the ocean. Examples of silicate and sulfide determinations around animal communities in a deep-sea hydrothermal vent field are presented.     

Two tris(oxalato)ferrate(III) hybrid salts with pyridinium derivative isomers as counter cations: synthesis,crystal structures,thermal analyses,and magnetic properties

Two organic–inorganic hybrid salts, tris(2-amino-4,6-dimethylpyridinium) tris(oxalato)ferrate(III), (C₇H₁₁N₂)₃[Fe(C₂O₄)₃] (1), and tris(4-dimethylaminopyridinium) tris(oxalato)ferrate(III) tetrahydrate, (C₇H₁₁N₂)₃[Fe(C₂O₄)₃]·4H₂O (2), have been synthesized and characterized by elemental and thermal analyses, IR spectroscopy, single-crystal X-ray diffraction, and SQUID magnetometry. Compounds 1 and 2 crystallize in triclinic P-1 and monoclinic C2/c space groups, respectively. Each compound contains the anionic complex [Fe(C₂O₄)₃]^3- in which the central metal is six-coordinate in a slightly distorted octahedron defined by three chelating oxalate(2-) ligands. The two substituted pyridinium cations are isomers. However, due to the great steric hindrance provided by the bulky cation, 2-amino-4,6-dimethylpyridinium, only the 4-dimethylaminopyridinium cation, the smallest of this series, led to formation of 2 with enough vacant spaces to be occupied by four solvent water molecules. In the crystals, cations and anions are connected via hydrogen-bonds of the types N–H?O in 1 and N–H?O and O–H?O in 2, with π–π stacking interactions between the pyridine rings stabilizing the 3-D framework. The thermal studies confirmed the anhydrous character of salt 1 and the presence of water molecules in salt 2. The magnetic susceptibility measurements in the 2–300 K temperature range revealed weak antiferromagnetic coupling in the two salts.