Work functions of the (001) face of the hexaborides of Ba,La, Ce and Sm

From thermonic and field emission retarding potential methods the following order of increasing work function for RB₆-type single crystals was determined: CeB₆(001) ? LaB₆(001) < BaB₆(001) < SmB₆(001) Auger electron spectroscopy indicated that low work function surfaces correlated with low B/R ratios; however, energy dependence of the electron reflection coefficient maxima suggests that a conduction band edge shift relative to the Fermi level among the various RB₆(001) crystals largely accounts for the work function variation. Mass spectrometric studies showed only atomic species vaporizing from all the RB₆ crystals investigated. Large variations in the vapor phase B/R ratios and vaporization energies for crystals of the same material were believed to be due to small variations in bulk stoichiometry.     

Detection of intact influenza viruses using biotinylated biantennary S-sialosides

We report the modular synthesis of robust, biotinylated biantennary sialylglycoconjugates and their ability to differentiate between two type A influenza strains. This is the first demonstration of glycoconjugate-based discriminatory capture and detection of two strains of intact influenza virus, in the presence of the innate enzymatic activity of viral neuraminidases. We also demonstrate a "carboassay" using glycoconjugates as capture and reporter elements, which therefore, does not require antibodies. The capture of intact influenza viruses is of potential benefit for clinical diagnostics.     

Antimony oxide hydroxide ethanedisulfonate: a cationic layered metal oxide for Lewis acid applications

We have discovered a rare example of a cationically charged inorganic material. The layered structure is an example outside the extensively studied isostructural set of anionic clays/layered double hydroxides and our previously reported lead fluoride nitrate. For the present compound, the antimony oxide hydroxide layers are positively charged and are templated by anionic alkylenedisulfonate. The organic molecules are only bonded electrostatically to the layers with sulfonate oxygen to antimony distances beyond the covalent range. The material catalyzes a ketal formation reaction as a Lewis acid without the need for drying the solvent before the reaction or a nonaqueous medium such as toluene. The catalyst is heterogeneous and is completely recovered after the catalysis for reapplication.     

A Far-Red Molecular Rotor Fluorogenic Trehalose Probe for Live Mycobacteria Detection and Drug-Susceptibility Testing

Increasing the speed, specificity, sensitivity, and accessibility of mycobacteria detection tools are important challenges for tuberculosis (TB) research and diagnosis. In this regard, previously reported fluorogenic trehalose analogues have shown potential, but their green-emitting dyes may limit sensitivity and applications in complex settings. Here, we describe a trehalose-based fluorogenic probe featuring a molecular rotor turn-on fluorophore with bright far-red emission (RMR-Tre). RMR-Tre, which exploits the unique biosynthetic enzymes and environment of the mycobacterial outer membrane to achieve fluorescence activation, enables fast, no-wash, low-background fluorescence detection of live mycobacteria. Aided by the red-shifted molecular rotor fluorophore, RMR-Tre exhibited up to a 100-fold enhancement in M. tuberculosis labeling compared to existing fluorogenic trehalose probes. We show that RMR-Tre reports on M. tuberculosis drug resistance in a facile assay, demonstrating its potential as a TB diagnostic tool.     

Charting the landscape of supercritical string theory

Special solutions of string theory in supercritical dimensions can interpolate in time between theories with different numbers of spacetime dimensions and different amounts of world sheet supersymmetry. These solutions connect supercritical string theories to the more familiar string duality web in ten dimensions and provide a precise link between supersymmetric and purely bosonic string theories. Dimension quenching and c duality appear to be natural concepts in string theory, giving rise to large networks of interconnected theories.     

Local conformational dynamics regulating transport properties of a Cl−/H+ antiporter

ClC-ec1 is a Cl⁻/H⁺ antiporter that exchanges Cl⁻ and H⁺ ions across the membrane. Experiments have demonstrated that several mutations, including I109F, decrease the Cl⁻ and H⁺ transport rates by an order of magnitude. Using reactive molecular dynamics simulations of explicit proton transport across the central region in the I109F mutant, a two-dimensional free energy profile has been constructed that is consistent with the experimental transport rates. The importance of a phenylalanine gate formed by F109 and F357 and its influence on hydration connectivity through the central proton transport pathway is revealed. This work demonstrates how seemingly subtle changes in local conformational dynamics can dictate hydration changes and thus transport properties. © 2019 Wiley Periodicals, Inc.     

Using force-matching to reveal essential differences between density functionals in ab initio molecular dynamics simulations

The exchange-correlation (XC) functional and value of the electronic fictitious mass μ can be two major sources of systematic errors in ab initio Car-Parrinello Molecular Dynamics (CPMD) simulations, and have a significant impact on the structural and dynamic properties of condensed-phase systems. In this work, an attempt is made to identify the origin of differences in liquid water properties generated from CPMD simulations run with the BLYP and HCTH∕120 XC functionals and two different values of μ (representative of "small" and "large" limits) by analyzing the effective pairwise atom-atom interactions. The force-matching (FM) algorithm is used to map CPMD interactions into non-polarizable, empirical potentials defined by bonded interactions, pairwise short-ranged interactions in numerical form, and Coulombic interactions via atomic partial charges. The effective interaction models are derived for the BLYP XC functional with μ=340 a.u. and μ=1100 a.u. (BLYP-340 and BLYP-1100 simulations) and the HCTH∕120 XC functional with μ=340 a.u. (HCTH-340 simulation). The BLYP-340 simulation results in overstructured water with slow dynamics. In contrast, the BLYP-1100 and HCTH-340 simulations both produce radial distribution functions (indicative of structure) that are in reasonably good agreement with experiment. It is shown that the main difference between the BLYP-340 and HCTH-340 effective potentials arises in the short-ranged nonbonded interactions (in hydrogen bonding regions), while the difference between the BLYP-340 and BLYP-1100 interactions is mainly in the long-ranged electrostatic components. Collectively, these results demonstrate how the FM method can be used to further characterize various simulation ensembles (e.g., density-functional theory via CPMD). An analytical representation of each effective interaction water model, which is easy to implement, is presented.     

Obionin B: An o-pyranonaphthoquinone decaketide from an unidentified fungus (MSX 63619) from the Order Pleosporales

A fungal extract (MSX 63619), from the Mycosynthetix library of over 50,000 fungi, displayed promising cytotoxicity against a human tumor cell panel. Bioactivity-directed fractionation led to the isolation of an o-pyranonaphthoquinone decaketide, which we termed obionin B (1). The structure of 1 was deduced via spectroscopic and spectrometric techniques. The IC₅₀ value of 1 was moderate, ranging from 3 to 13 μM, depending on the cell line tested.     

Issues and Opportunities in Exotic Hadrons

The last few years have been witness to a proliferation of new results concerning heavy exotic hadrons.Experimentally, many new signals have been discovered that could be pointing towards the existence of tetraquarks,pentaquarks, and other exotic configurations of quarks and gluons. Theoretically, advances in lattice field theory techniques place us at the cusp of understanding complex coupled-channel phenomena, modelling grows more sophisticated, and effective field theories are being applied to an ever greater range of situations. It is thus an opportune time to evaluate the status of the field. In the following, a series of high priority experimental and theoretical issues concerning heavy exotic hadrons is presented.     

Topology and predictability of El Niño and La Niña networks

We construct the networks of the surface temperature field for El Ni?o and for La Ni?a years and investigate their structure. We find that the El Ni?o network possesses significantly fewer links and lower clustering coefficient and characteristic path length than the La Ni?a network, which indicates that the former network is less communicative and less stable than the latter. We conjecture that because of this, predictability of temperature should decrease during El Ni?o years. Here we verify that indeed during El Ni?o years predictability is lower compared to La Ni?a years.