Toward understanding reactive adsorption of ammonia on Cu-MOF/graphite oxide nanocomposites

The adsorption of ammonia on HKUST-1 (a metal-organic framework, MOF) and HKUST-1/graphite oxide (GO) composites was investigated in two different experimental conditions. From the isotherms, the isosteric heats of adsorption were calculated from the Clausius-Clapeyron equation following the virial approach. The results on HKUST-1 were compared with those obtained using molecular simulation studies. All materials exhibit higher ammonia adsorption capacities than those reported in the literature. The ammonia adsorption on the composites is higher than that measured separately on the MOF component and on GO. The strong adsorption of ammonia caused by chemical interactions on different adsorption sites is evidenced by the trends in the isosteric heats of adsorption. The molecular simulations conducted on HKUST-1 support the trends observed experimentally. In particular, the strong chemisorption of ammonia on the metallic centers of HKUST-1 is confirmed. Nevertheless, higher adsorption capacities are predicted compared with the experimental results. This discrepancy is mainly assigned to the partial collapse of the MOF structure upon exposure to ammonia, which is not accounted for in the simulation study.     

The multivalent effect in glycosidase inhibition: probing the influence of architectural parameters with cyclodextrin-based iminosugar click clusters

In contrast to most lectins, glycosidases may appear to be unpromising targets for multivalent binding because they display only a single active site. To explore the potential of multivalency on glycosidase inhibition, unprecedented cyclodextrin-based iminosugar conjugates have been designed and prepared. The synthesis was performed by way of Cu(I) -catalyzed azide-alkyne cycloaddition reaction under microwave activation between propargylated multivalent β-cyclodextrins and an azide-armed N-alkyl 1-deoxynojirimycin derivative. Evaluation with a panel of glycosidases of this new class of glycomimetic clusters revealed the strongest affinity enhancement observed to date for a multivalent glycosidase inhibitor, with binding enhancement up to four orders of magnitude over the corresponding monovalent ligand for α-mannosidase. These results demonstrate that the multivalency concept extends beyond carbohydrate-lectin recognition processes to glycomimetic-enzyme inhibition.     

Palladium-catalyzed Minisci reaction with simple alcohols

A palladium-catalyzed coupling of N-heterocycles with simple alcohols was achieved. The reaction is initiated by peroxide and does not require the use of stoichiometric acid for activation of the heterocycle.     

Chemo- and Magnetotaxis of Self-Propelled Light-Emitting Chemo-electronic Swimmers

Miniaturized autonomous chemo-electronic swimmers, based on the coupling of spontaneous oxidation and reduction reactions at the two poles of light-emitting diodes (LEDs), are presented as chemotactic and magnetotactic devices. In homogeneous aqueous media, random motion caused by a bubble-induced propulsion mechanism is observed. However, in an inhomogeneous environment, the self-propelled devices exhibit positive chemotactic behavior, propelling themselves along a pH or ionic strength gradient (∇pH and ∇I, respectively) in order to reach a thermodynamically higher active state. In addition, the intrinsic permanent magnetic moment of the LED allows self-orientation in the terrestrial magnetic field or following other external magnetic perturbations, which enables a directional motion control coupled with light emission. The interplay between chemotaxis and magnetotaxis allows fine-tuning of the dynamic behavior of these swimmers.     

Effect of graphite features on the properties of metal-organic framework/graphite hybrid materials prepared using an in situ process

Metal-organic framework (MOF)/graphite hybrid materials were prepared using an in situ process. Graphites with various chemical and physical features were used, and HKUST-1 was selected as the MOF component. The samples (parent materials and hybrid materials) were characterized by X-ray diffraction, nitrogen sorption, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Then they were tested as ammonia adsorbents in dynamic conditions. The results indicate that the functionalization of graphite is important to build the hybrid materials with synergistic properties. The lack of functional groups on graphite results in the formation of a simple physical mixture. Besides the surface chemistry of the graphitic component, the physical parameters (porosity and size of flakes) also seem to influence the formation of the hybrid materials. It is observed that the graphite particles disturb the formation of HKUST-1 and induce a different crystal morphology (more defects and increased surface roughness) than the one observed when MOF is formed in the absence of a substrate. The latter behavior causes less ammonia to be adsorbed on the hybrid materials than is expected for the simple physical mixture of HKUST-1 and graphite. The MOF structure collapses (in HKUST-1 and the hybrid materials) upon ammonia adsorption and leads to the formation of new species.     

Observation of Reform Teaching in Undergraduate Level Mathematics and Science Courses

This paper reports on initial results from an ongoing evaluation study of a National Science Foundation project to implement reform‐oriented teaching practices in college science and mathematics courses. The purpose of this study was to determine what elements of reform teaching are being utilized by college faculty members teaching undergraduate science and mathematics courses, including a qualitative estimate of the frequency with which they are used. Participating instructors attended summer institutes that modeled reform‐based practices and fostered reflection on current issues in science, mathematics, and technological literacy for K‐16 teaching, with an explicit emphasis on the importance of creating the best possible learning experience for prospective K‐12 science and mathematics teachers. Utilizing a unique classroom observation protocol (the Oregon‐Teacher Observation Protocol) and interviews, the authors (a) conclude that some reform‐oriented teaching strategies are evident in undergraduate mathematics and science instruction and (b) suggest areas in which additional support and feedback are needed in order for higher education faculty members to adopt reform‐based instructional methodology.     

Infrared spectroscopy of acetone-hexane liquid mixtures

Acetone and hexane mixtures covering the whole solubility range were studied by Fourier transform infrared attenuated total reflectance spectroscopy. Factor analysis separates the spectra into four principal factor spectra and multiplying factors. Those containing negative factors are abstract, but the spectra are real. A statistical distribution model of the molecules in the solutions rendered the factors real. From these we define the intermediate species that occur in a 1:2 molar ratio of acetone in hexane, present principally in the low acetone concentration regions, and in a 2:1 molar ratio of acetone in hexane, present principally in the higher acetone concentration region. However, except at the concentration range limits where only pure acetone and pure hexane are present, the four species are present over the whole solubility range. The IR spectra of the species indicated very little displacement of the CH stretch bands, HCH deformation bands, and CC stretch bands, although there are some small intensity variations. Most of the modifications are observed on the acetone C=O stretch band. From the gas phase position, a strong bathochromic shift of 19 cm(-1) of the pure liquid is assigned to dipole-dipole interactions. In the 2:1 groupings, the shift that decreases to 15 cm(-1) is due to the diminished dipole-dipole interactions. In the 1:2 groupings, no dipole-dipole interaction can exist, and the bathochromic displacement of 9 cm(-1) is attributed to van der Waals interactions. In the one acetone to two hexanes grouping, no dipole-dipole interaction can exist, and the bathochromic displacement of 9 cm(-1) is attributed to van der Waals interactions. From the statistical distribution of the molecules, we determine that mixtures of hexane and acetone form a random organization with no preferred association or complex.     

Infrared spectroscopy of aqueous ionic salt mixtures at low concentrations: ion pairing in water

The analysis by infrared spectroscopy of aqueous mixtures of NaI and CsCl was made in order to obtain information at the molecular level of the mixing of these two salts taken as model systems of strong electrolytes in water. In previous papers [J.-J. Max and C. Chapados, J. Chem. Phys. 115, 2664 (2001) and J.-J. Max et al., ibid. 126, 184507 (2007)] it was reported that a pure salt in water forms pairs of monoions to which are attached a fixed number of water molecules, giving solvated water species. Due to their interaction with the ion pairs, the solvated water molecules are strongly perturbed, modifying the IR water spectrum being monitored. After taking the IR spectrum of pure water, a small volume of NaI 2M was added and the IR spectrum taken. Then a small volume of CsCl 2M was added and a new IR spectrum taken. This procedure was repeated to obtain a series of 38 spectra in the 0.05M-0.83M concentration range. Factor analysis made on the series revealed the presence of three types of water: pure water and two salt solvated waters. The number of solvated water molecules on the two salts taken together is ten. Since NaI and CsCl have, respectively, 3.5 and 3.0 solvated water molecules, it was concluded that a reaction occurred in the solutions forming NaCl and CsI that have, respectively, five water molecules each for a total of ten. The analysis of the spectra of the orthogonal factors supports this attribution. These results provide additional proof of ion pairing in water. Furthermore, comparing the band displacements and intensity variations observed on the solvated water species to that of pure water indicates that the dielectric milieu surrounding the ion pairs is not constant. These results do not support the classical view of Debye-Huckel that considers that the ions are independent and the dielectric milieu constant. The present results give some in situ information on the reaction that goes on in "simple" electrolyte systems whose reactivity and molecular organization are still not completely mastered.     

Chern–Weil map for principal bundles over groupoids

The theory of principal G-bundles over a Lie groupoid is an important one unifying various types of principal G-bundles, including those over manifolds, those over orbifolds, as well as equivariant principal G-bundles. In this paper, we study differential geometry of these objects, including connections and holonomy maps. We also introduce a Chern–Weil map for these principal bundles and prove that the characteristic classes obtained coincide with the universal characteristic classes. As an application, we recover the equivariant Chern–Weil map of Bott–Tu. We also obtain an explicit chain map between the Weil model and the simplicial model of equivariant cohomology which reduces to the Bott–Shulman map when the manifold is a point. P. Xu Research partially supported by NSF grant DMS-03-06665.     

Synthesis,Discovery, and Quantitation of Dihomo‐Isofurans: Biomarkers for In Vivo Adrenic Acid Peroxidation

The growing importance of lipidomics, and the interest of non‐enzymatic metabolites of polyunsaturated fatty acids (PUFAs) prompted us to initiate the synthesis of novel dihomo‐IsoF compounds. Such metabolites of adrenic acid, the main PUFA in white matter, were synthesized using a divergent approach based on an orthoester cyclization. LC‐MS/MS investigation on pig brains showed the potential of this novel biomarker for the first time, as a powerful new tool for brain lipid peroxidation assessment.