One-pot synthesis of orthogonally protected sugars through sequential base-promoted/acid-catalyzed steps: A solvent-free approach with self-generation of a catalytic species

A varied set of solvent-free, one-pot synthetic sequences were developed to carry out the orthogonal protection of saccharide polyols. These sequences are composed of an initial regioselective benzylation, silylation or iodination (under mildly basic conditions), followed by an acid catalyzed protection of two further hydroxyl sites via the generation of a cyclic acetal. These processes allow recycling of the ammonium or pyridinium side products generated in the former step as effective catalytic species for the latter step.     

Kβ X-Ray Emission Spectroscopic Study of a Second-Row Transition Metal (Mo) and Its Application to Nitrogenase-Related Model Complexes

In recent years, X-ray emission spectroscopy (XES) in the Kβ (3p-1s) and valence-to-core (valence-1s) regions has been increasingly used to study metal active sites in (bio)inorganic chemistry and catalysis, providing information about the metal spin state, oxidation state and the identity of coordinated ligands. However, to date this technique has been limited almost exclusively to first-row transition metals. In this work, we present an extension of Kβ XES (in both the 4p-1s and valence-to-1s [or VtC] regions) to the second transition row by performing a detailed experimental and theoretical analysis of the molybdenum emission lines. It is demonstrated in this work that Kβ₂ lines are dominated by spin state effects, while VtC XES of a 4d transition metal provides access to metal oxidation state and ligand identity. An extension of Mo Kβ XES to nitrogenase-relevant model complexes shows that the method is sufficiently sensitive to act as a spectator probe for redox events that are localized at the Fe atoms. Mo VtC XES thus has promise for future applications to nitrogenase, as well as a range of other Mo-containing biological cofactors. Further, the clear assignment of the origins of Mo VtC XES features opens up the possibility of applying this method to a wide range of second-row transition metals, thus providing chemists with a site-specific tool for the elucidation of 4d transition metal electronic structure.     

Interplay of Hole Transfer and Host–Guest Interaction in a Molecular Dyad and Triad: Ensemble and Single‐Molecule Spectroscopy and Sensing Applications

A new molecular dyad consisting of a Cy5 chromophore and ferrocene (Fc) and a triad consisting of Cy5, Fc, and β‐cyclodextrin (CD) are synthesized and their photophysical properties investigated at both the ensemble and single‐molecule levels. Hole transfer efficiency from Cy5 to Fc in the dyad is reduced upon addition of CD. This is due to an increase in the Cy5‐Fc separation (r) when the Fc is encapsulated in the macrocyclic host. On the other hand, the triad adopts either a Fc‐CD inclusion complex conformation in which hole transfer quenching of the Cy5 by Fc is minimal or a quasi‐static conformation with short r and rapid charge transfer. Single‐molecule fluorescence measurements reveal that r is lengthened when the triad molecules are deposited on a glass substrate. By combining intramolecular charge transfer and competitive supramolecular interaction, the triad acts as an efficient chemical sensor to detect different bioactive analytes such as amantadine hydrochloride and sodium lithocholate in aqueous solution and synthetic urine.     

High refractive index hyperbranched polyvinylsulfides for planar one‐dimensional all‐polymer photonic crystals

We report on the growth and characterization of one‐dimensional (1D) planar all‐polymer photonic crystals (PhC) with high dielectric contrast (Δn = 0.3) prepared by spin coating using hyperbranched polyvinylsulfide polymers (HB‐PVS) as high refractive index material and cellulose acetate as low refractive index material. Solution processable HB‐PVS show a near ultraviolet absorption inducing an increased refractive index in the visible‐near infrared (n = 1.68, λ = 1000 nm). HBPVS:Cellulose Acetate Distributed Bragg Reflectors show a very clear fingerprint of the photonic band gap possessing the expected polarized dispersion properties as a function of the incidence angle. Moreover, engineered microcavities tuned on the weak fluorescence spectrum of the HB‐PVS show directional fluorescence enhancement effects due to spectral redistribution of the emission oscillator strength. The combination of all these properties testifies the high optical quality of the obtained photonic structures thus indicating HB‐PVS as an interesting material for the preparation of such PhC. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 73–80     

Singularity Formation in Fractional Burgers’ Equations

The formation of singularities in finite time in nonlocal Burgers’ equations, with time-fractional derivative, is studied in detail. The occurrence of finite-time singularity is proved, revealing the underlying mechanism, and precise estimates on the blowup time are provided. The employment of the present equation to model a problem arising in job market is also analyzed.

     

Crystal structure of the new FeSe(1-x) superconductor

The newly discovered superconductor FeSe(1-x) (x approximately 0.08, T(c)(onset) approximately 13.5 K at ambient pressure rising to 27 K at 1.48 GPa) exhibits a structural phase transition from tetragonal to orthorhombic below 70 K at ambient pressure-the crystal structure in the superconducting state shows remarkable similarities to that of the REFeAsO(1-x)F(x) (RE = rare earth) superconductors.     

Rapid microchip-based electrophoretic immunoassays for the detection of swine influenza virus

Towards developing rapid and portable diagnostics for detecting zoonotic diseases, we have developed microchip-based electrophoretic immunoassays for sensitive and rapid detection of viruses. Two types of microchip-based electrophoretic immunoassays were developed. The initial assay used open channel electrophoresis and laser-induced fluorescence detection with a labeled antibody to detect influenza virus. However, this assay did not have adequate sensitivity to detect viruses at relevant concentrations for diagnostic applications. Hence, a novel assay was developed that allows simultaneous concentration and detection of viruses using a microfluidic chip with an integrated nanoporous membrane. The size-exclusion properties of the in situ polymerized polyacrylamide membrane are exploited to simultaneously concentrate viral particles and separate the virus/fluorescent antibody complex from the unbound antibody. The assay is performed in two simple steps--addition of fluorescently labeled antibodies to the sample, followed by concentration of antibody-virus complexes on a porous membrane. Excess antibodies are removed by electrophoresis through the membrane and the complex is then detected downstream of the membrane. This new assay detected inactivated swine influenza virus at a concentration four times lower than that of the open-channel electrophoresis assay. The total assay time, including device regeneration, is six minutes and requires <50 microl of sample. The filtration effect of the polymer membrane eliminates the need for washing, commonly required with surface-based immunoassays, increasing the speed of the assay. This assay is intended to form the core of a portable device for the diagnosis of high-consequence animal pathogens such as foot-and-mouth disease. The electrophoretic immunoassay format is rapid and simple while providing the necessary sensitivity for diagnosis of the illness state. This would allow the development of a portable, cost-effective, on-site diagnostic system for rapid screening of large populations of livestock, including sheep, pigs, cattle, and potentially birds.