β-Hairpin stabilization through an interstrand triazole bridge

β-Hairpin peptides were conformationally stabilized through a 1,4 disubstituted 1,2,3-triazole interstrand linkage. A NMR conformational analysis revealed that the β-hairpin content depends on the number and position of substituent methylene units of the 1,2,3-triazole ring. These results will allow the design of metabolically stable peptidomimetic analogs of bioactive β-hairpin peptides.     

New Cholesteric and Nematic Lyotropic Mesophases from Di-Sodium N-Lauroyl-Aspartate

Lyotropic liquid crystals are prepared from racemic and optically active di-sodium N-lauroyl aspartate (SNLA). The optically active levo enantiomer is a suitable amphiphile for obtaining cholesteric lyotropic mesophases. In the present work, different types of mesophases, including cholesteric and nematic, were prepared and their type I or II magnetic behavior characterized by deuterium and ²³Na NMR. The polarizing microscope textures were investigated, particularly with regards to magnetic field effects upon the samples. The usual chevron pattern was obtained for particular sample orientations and several characteristic effects were observed for the type I cholesteric lyomesophase in the first few minutes following removal of the sample from the magnetic field. Although the head group of di-sodium N-lauroyl aspartate possesses two negative charges, compositions are not too different from those reported for other amphiphile lyotropic systems.     

Unraveling the 13C NMR chemical shifts in single-walled carbon nanotubes: dependence on diameter and electronic structure

The atomic specificity afforded by nuclear magnetic resonance (NMR) spectroscopy could enable detailed mechanistic information about single-walled carbon nanotube (SWCNT) functionalization as well as the noncovalent molecular interactions that dictate ground-state charge transfer and separation by electronic structure and diameter. However, to date, the polydispersity present in as-synthesized SWCNT populations has obscured the dependence of the SWCNT (13)C chemical shift on intrinsic parameters such as diameter and electronic structure, meaning that no information is gleaned for specific SWCNTs with unique chiral indices. In this article, we utilize a combination of (13)C labeling and density gradient ultracentrifugation (DGU) to produce an array of (13)C-labeled SWCNT populations with varying diameter, electronic structure, and chiral angle. We find that the SWCNT isotropic (13)C chemical shift decreases systematically with increasing diameter for semiconducting SWCNTs, in agreement with recent theoretical predictions that have heretofore gone unaddressed. Furthermore, we find that the (13)C chemical shifts for small diameter metallic and semiconducting SWCNTs differ significantly, and that the full-width of the isotropic peak for metallic SWCNTs is much larger than that of semiconducting nanotubes, irrespective of diameter.     

Some remarks on systems of elliptic equations doubly critical in the whole $${\mathbb{R}^N}$$

We study the existence of different types of positive solutions to problem

Adsorption of cadmium and lead onto oxidized nitrogen-doped multiwall carbon nanotubes in aqueous solution: equilibrium and kinetics

Nitrogen-doped multiwall carbon nanotubes (CNx) were chemically oxidized and tested to adsorb cadmium and lead from aqueous solution. Physicochemical characterization of carbon nanotubes included morphological analysis, textural properties, and chemical composition. In addition, the cadmium adsorption capacity of oxidized-CNx was compared with commercially available activated carbon and single wall carbon nanotubes. Carboxylic and nitro groups on the surface of oxidized CNx shifted the point of zero charge from 6.6 to 3.1, enhancing their adsorption capacity for cadmium and lead to 0.083 and 0.139 mmol/g, respectively, at pH 5 and 25 °C. Moreover, oxidized-CNx had higher selectivity for lead when both metal ions were in solution. Kinetic experiments for adsorption of cadmium showed that the equilibrium was reached at about 4 min. Finally, the small size, geometry, and surface chemical composition of oxidized-CNx are the key factors for their higher adsorption capacity than activated carbon.     

High‐Throughput Metabolomics by 1D NMR

Metabolomics deals with the whole ensemble of metabolites (the metabolome). As one of the ‐omic sciences, it relates to biology, physiology, pathology and medicine; but metabolites are chemical entities, small organic molecules or inorganic ions. Therefore, their proper identification and quantitation in complex biological matrices requires a solid chemical ground. With respect to for example, DNA, metabolites are much more prone to oxidation or enzymatic degradation: we can reconstruct large parts of a mammoth's genome from a small specimen, but we are unable to do the same with its metabolome, which was probably largely degraded a few hours after the animal's death. Thus, we need standard operating procedures, good chemical skills in sample preparation for storage and subsequent analysis, accurate analytical procedures, a broad knowledge of chemometrics and advanced statistical tools, and a good knowledge of at least one of the two metabolomic techniques, MS or NMR. All these skills are traditionally cultivated by chemists. Here we focus on metabolomics from the chemical standpoint and restrict ourselves to NMR. From the analytical point of view, NMR has pros and cons but does provide a peculiar holistic perspective that may speak for its future adoption as a population‐wide health screening technique.     

Screening of north-east Mexico medicinal plants with activities against herpes simplex virus and human cancer cell line

The plants examined in this study have previous biological activity reports indicating the possibility of found activity against herpes and cancer cell. The aim of this contribution was to carry out a screening of Juglans mollis (Juglandaceae), Persea americana (Lauraceae), Hamelia patens (Rubiaceae), Salvia texana (Lamiaceae), Salvia ballotaeflora (Lamiaceae), Ceanothus coeruleus (Rhamnaceae), Chrysactinia mexicana (Asteraceae) y Clematis drummondii (Ranunculaceae), against HeLa cells, VHS-1 and VHS-2. The method MTT was used to determine the 50% cytotoxic concentration (CC₅₀), in Vero and HeLa cell lines. To determine the 50% inhibitory concentration (IC₅₀) against herpes, the plaque reduction method was used. Results showed that none of the plants exhibited activity against HeLa cells. About antiherpetic activity, J. mollis and S. ballotaeflora extracts present antiherpetic activity in terms of their SI, increasingly interest for further studies on the isolation of compounds with antiherpetic activity and about the mechanisms of action that produce this activity.     

Sr<Subscript>4</Subscript>Al<Subscript>14</Subscript>O<Subscript>25</Subscript>: Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript>/silica core–shell particles synthesized via urea combustion method for carbon dioxide reduction in plants

Strontium Aluminate doped with Europium and Dysprosium is one of the most widely studied phosphors because of its high intensity and long persistence time. In this study, the unique characteristics of strontium aluminate based phosphors, specifically Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺, was utilized as light source for plants for enhanced carbon dioxide reduction in dark field conditions. The Sr₄Al₁₄O₂₅: Eu²⁺, Dy³⁺ phosphor was synthesized using the combustion method. Stoichiometric amounts of aqueous precursors were dissolved in water, then placed in a high temperature furnace at 600 °C to obtain a foamy, amorphous precursor powder. The powders were cooled to room temperature and then grinded. After grinding, the powders were calcined for 8 h at 1300 °C. The powders were then encapsulated with silica particles using the Stöber process to prevent the oxidation of Eu²⁺ without a reducing atmosphere during calcination. The obtained coated and uncoated particles were then characterized using SEM, TEM–EDX, XRD and photoluminescence analysis to determine the effect of the core–shell structure on the luminescence properties of the phosphors. Finally, the obtained phosphor-silica core–shell particles will be attached to the surface of four different plant species commonly grown indoors using a mixture of natural oils and waxes as adhesive. The effect of the addition of phosphor as an external light source on the amount of carbon dioxide production of the plants will be monitored and compared to a control specimen without the phosphor as well as with other artificial light sources.     

Gas phase hydrogen/deuterium exchange reactions of fluorophenyl anions

Hydrogen/deuterium (H/D) exchange reactions of fluorophenyl and difluorophenyl anions (C₆H₄F^?, o-C₆H₃F ₂ ^? , m-C₆H₃F ₂ ^? , p-C₆H₃F ₂ ^? ) have been studied using the flowing afterglow-selected ion flow tube technique. The C₆H₄F^? anion exchanges all hydrogens for deuterium upon reaction with D₂O. The difluorophenyl anions o-, m-, and p-C₆H₃F ₂ ^? exchange three, two, and one hydrogen, respectively, with D₂O, whereas they undergo one, two, and three H/D exchanges, respectively, with CH₃OD. The structures of the anions and the isotope exchange dynamics within the intermediate ion-dipole complexes are discussed using ab initio molecular orbital calculations. Calculated values for the proton affinities of the most stable anions are 385.2, 378.0, 371.9, and 378.2 kcal/mol for C₆H₄F^?, o-C₆H₃F ₂ ^? , m-C₆H₃F ₂ ^? , and p-C₆H₃F ₂ ^? , respectively, in excellent agreement (within 2 kcal/mol) with the previous experimental values for the acidities of the corresponding fluorobenzenes. The H/D exchange results are explained by the energy differences of the intermediate DO^? and CH₃O^? species within the ion-dipole complexes; CH₃O^? is mobile within the “hot” intermediate complex, whereas DO^? is nearly “frozen” within the complex and cannot migrate across the barriers caused by the fluorine atoms or by the π electrons.