Gas sensing selectivity of hexagonal and monoclinic WO3 to H2S

Hexagonal and monoclinic tungsten oxide (h- and m-WO₃) samples were produced by annealing hexagonal ammonium tungsten bronze, (NH₄)_0.07(NH₃)_0.04(H₂O)_0.09WO_2.95 at 470 and at 600 °C, respectively. Their structure, composition and morphology were analyzed by XRD, Raman, XPS, ¹H-MAS NMR and SEM. In order to study the effect of crystal structure on the gas sensitivity of tungsten oxides, h- and m-WO₃ were tested as gas sensors to CH₄, CO, H₂, NO and H₂S (1000 and 10 ppm) at 200 °C. Monoclinic WO₃ responded to all gases, but its gas sensing signal was two magnitudes greater to 10 ppm H₂S than to other gases, and it also detected H₂S even at 25 °C. Hexagonal WO₃ responded only to 10 ppm H₂S. Its sensitivity was smaller compared to m-WO₃, however, the response time of h-WO₃ was significantly faster. The gas sensing tests showed that while m-WO₃ had relative selectivity to H₂S in the presence CH₄, CO, H₂, NO; h-WO₃ had absolute selectivity to H₂S in the presence these gases.     

Epi-cinchona based thiourea organocatalyst family as an efficient asymmetric Michael addition promoter: enantioselective conjugate addition of nitroalkanes to chalcones and alpha,beta-unsaturated N-acylpyrroles

A small set of easily available epi-cinchona based thiourea organocatalysts have been synthesized and tested in enantioselective Michael addition of nitroalkanes to chalcones. These bifunctional catalyst systems promoted the conjugate additions with high enantioselectivities and chemical yields. The extension of this methodology was further explored to encompass alpha,beta-unsaturated N-acylpyrroles, as a chalcone mimic. Functionally, the N-acylpyrrole moiety in the adduct acts as an ester surrogate; therefore, it can easily be transformed to various valuable and biologically relevant compounds. This approach allowed the concise stereoselective synthesis of (R)-rolipram.     

The Plancherel Theorem for Fourier–Laplace–Nahm Transform for Connections on the Projective Line

We prove that the Fourier–Laplace–Nahm transform for connections with finitely many logarithmic singularities and a double pole at infinity on the projective line, all with semi-simple singular parts, is a hyper-Kähler isometry.     

Redox‐ and pH‐Responsive Cysteamine‐Modified Poly(aspartic acid) Showing a Reversible Sol–Gel Transition

Synthesis and characterization of a pH‐ and redox‐sensitive hydrogel of poly(aspartic acid) are reported. Reversible gelation and dissolution are achieved both in dimethylformamide and in aqueous medium via a thiol‐disulphide interconversion in the side chain of the polymers. Structural changes are confirmed by Raman microscopy and rheological measurements. Injectable aqueous solutions of thiolated poly(aspartic acid) can be converted into mechanically stable gels by oxidation, which can be useful for drug encapsulation and targeted delivery. Reduction‐facilitated release of an entrapped drug from disulphide cross‐linked hydrogels is studied.

     

EDITORIAL 2021: Journal of Thermal Analysis and Calorimetry

Journal of Thermal Analysis and Calorimetry - In this article, the thermal analyses of heat pump systems using photovoltaic-thermal collectors are reviewed. Initially, the energy balance equations...     

Double diastereocontrol in bifunctional thiourea organocatalysis: iterative Michael-Michael-Henry sequence regulated by the configuration of chiral catalysts

The importance and reactivity consequences of the double diastereocontrol in noncovalent bifunctional organocatalysis were studied. The results suggest that the bifunctional thioureas can have synthetic limitations in multicomponent domino or autotandem catalysis. Nevertheless, we provided a means to exploit this behavior and used the configuration of the chiral catalyst as a control element in organo-sequential reactions.     

Structure Elucidation of Two Acetylated Derivatives of Oligomycin A

Partial acetylation of oligomycin A (1) resulted in the formation of 5,9, 33-tri-O-acetyl (2) and 5,9,13,33-tetraacetyl (3) derivatives whose structures have been established through complete assignments of their H and ¹³C NMR spectra. These derivatives were devoid of inhibitory activity when tested on Aspergillus niger spores.     

Structural and Optical Properties of Gold/Silica “Mushroom” Particles Prepared by Interfacial Templating

Complex shaped nanoparticles featuring structural or surface chemical patchiness are of special interest in both fundamental and applied research areas. This study reports the preparation and optical properties of gold/silica “mushroom” nanoparticles, where a gold particle is only partially covered by the silica cap. The synthetic approach allows precise control over the particle structure. The interfacial preparation method relies on partially embedding the gold particles in a polystyrene layer that masks the immersed part of the gold particle during silica shell growth from an aqueous solution. By adjusting sacrificial polystyrene film thickness and silica growth time, precise control over the coverage and cap thickness can be achieved. Correlative electron microscopy and single particle scattering spectroscopy measurements underline the high precision and reproducibility of the method. The good agreement between the measured and simulated single particle spectra supported by near‐field calculations indicates that the observed changes in the dipolar plasmon resonance are influenced by the extent of coverage of the gold core by the silica cap. The straightforward methods readily available for gold and silica surface modification using range of different (bio)molecules make these well‐defined nanoscale objects excellent candidates to study fundamental processes of programmed self‐assembly or application as theranostic agents.     

Uniqueness of Markov-Extremal Polynomials on Symmetric Convex Bodies

For a compact set K\subset R ^d with nonempty interior, the Markov constants M _n (K) can be defined as the maximal possible absolute value attained on K by the gradient vector of an n -degree polynomial p with maximum norm 1 on K . It is known that for convex, symmetric bodies M _n (K) = n ² /r(K) , where r(K) is the ``half-width' (i.e., the radius of the maximal inscribed ball) of the body K . We study extremal polynomials of this Markov inequality, and show that they are essentially unique if and only if K has a certain geometric property, called flatness. For example, for the unit ball B ^d (\smallbf 0, 1) we do not have uniqueness, while for the unit cube [-1,1] ^d the extremal polynomials are essentially unique. September 9, 1999. Date revised: September 28, 2000. Date accepted: November 14, 2000.