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L’arrêt N.D. c. Suisse N.D. c. Suisse de la Cour européenne des droits de l’homme:quelles obligations positives des États dans la prévention des féminicides ?
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Upgrading of glycerol to solketal over mesoporous gallosilicates with tuned hydrophobicity
No full textNovel mesoporous gallosilicates with tuned hydrophobicity were synthesized through methylation of extra small XS-SiO2 silica particle via condensation with trimethoxymethylsilane CH3Si(OCH3)3 followed by impregnation with gallium (III) precursors. The structural and textural properties of the solids obtained were extensively characterized by different techniques. The synthesized catalysts displayed excellent catalytic activity in the acetalization of acetone with glycerol to produce solketal. Among all the studied catalysts, the most active catalyst, XS-10 %Me-GaLac, displayed high turnover number and significantly improved glycerol conversion which is attributed to the relatively hydrophobic surface and high amount of accessible active acid sites. The high acidity and enhanced hydrophobicity of this catalyst was generated by the incorporation of the methyl groups which allowed a homogeneous dispersion of highly active gallium species on the silica matrix before calcination. The effect of reaction time, temperature, catalyst loading and acetone to glycerol molar ratio was investigated. Furthermore, the mesoporous gallosilicate materials were truly heterogeneous without leaching gallium active sites and can be efficiently reused in successive catalytic cycles.</p
Enhanced catalytic conversion of cellobiose/cellulose to 5-hydroxymethylfurfural using dual catalysts:Sulfonated activated carbon and Lewis acid catalyst
No full textAn activated carbon (SX+) was functionalized with sulfonic groups via the diazonium coupling method to impart Brӧnsted (B) acidity to catalyze cellobiose and cellulose upgrading into 5-HMF. X-ray photoelectron spectroscopy (XPS) confirmed SO3H groups grafting, which significantly enhanced the total acidity to 1.33 mmol/g cat., as confirmed by Boehm titration. The B nature of acidity was verified by 31P ssNMR. The catalytic activity of SO3H/SX+ alone and with AlCl3 as Lewis (L) acid was evaluated by optimizing reaction conditions such as temperature, solvent, and B/L ratio. A ∼47 % 5-HMF yield was obtained with 100 % cellobiose conversion at 150 °C, 4 h with SO3H/Al ratio of 1:10 in Milli-Q water (MQ)/tetrahydrofuran (THF) solvent. When AlCl3 was replaced with heterogeneous Lewis acidic catalysts (γ-Al2O3, AlOOH, and TiO2), TiO2 combined with SO3H/SX+ showed similar catalytic activity, achieving ∼50 % yield of 5-HMF with 100 % cellobiose conversion, attributed to its high total acidity (2.4 × 10−2 mol/g cat.). 5-HMF was isolated from the reaction mixture using liquid-liquid extraction, resulting in ∼98 % pure 5-HMF. Moreover, SO3H/SX+ efficiently cleaved the glycosidic bonds of microcrystalline cellulose by giving a ∼24 % 5-HMF yield when combined with Lewis acid TiO2. This study presents a novel dual catalytic system, utilizing an optimized B/L acidity ratio to achieve efficient cellulose conversion into 5-HMF.</p
Testing equivalent formulations of linear and nonlinear frequency-dependent electric-dipole polarizabilities
No full textIn response theory, the hypervirial relations provide alternative formulations for the dynamic (frequency-dependent) molecular response properties. In this contribution, though the length formulation is the most commonly used in the calculations, we derive the full velocity formulations of the dynamic electric-dipole polarizability, ααβ(-ω;ω), and the dynamic electric-dipole second-harmonic generation first hyperpolarizability, βαβγ(-2ω;ω,ω). Both formulations provide identical responses for exact wavefunctions and for variationally optimized wavefunctions in the limit of a complete basis set. To assess how the exact relations between the length and velocity formulations are satisfied for approximate wavefunctions, we performed TD-DFT and TD-HF calculations of the frequency-dependent polarizability and first hyperpolarizability of R-methyloxirane molecule, using increasingly large basis sets. For ααβ(-ω;ω), the results reproduce the expected qualitative and quantitative trends, with convergence toward the same values when the basis-set size increases. However, for βαβγ(-2ω;ω,ω), the results are more contrasted. Though the convergence with the basis-set size is evident, the first hyperpolarizability difference between the two formulations is frequency dependent, whereas it is not when the relations are satisfied. Moreover, for βαβγ(-2ω;ω,ω), we analyzed some of the hyper-Rayleigh scattering main observables and it is clear that the full velocity formulation converges slowly compared with the length formulation.</p
Assessing the influence of nanoscale morphology on the mechanical properties of semiconducting polymers
No full textThe ease of processability of conjugated organic polymers, alongside their capability of transporting charges, makes them excellent candidates for applications in flexible and biocompatible electronic devices. In such applications, retaining the electronic properties upon repeated cycles of mechanical strain is key to avoid losing device performance over time. To achieve an accurate mechanical characterization at the nanoscale of these partially crystalline systems, it is critical to have access to reference values of polymer elastic constants and to be able to relate them to the local morphology. With this objective, in the following, we set up a computational protocol for the calculation of elastic constants through molecular dynamics (MD) simulations in the linear deformation regime. We apply such a scheme to the prediction of the elastic behavior of two well-known semiconducting polymers (C16-IDTBT and C14-PBTTT) in crystalline and amorphous phases, showing that the local fluctuations of the Young's modulus can span two orders of magnitude owing to its strong dependence on morphology, anisotropy, and strain direction. The comparison with experimental measurements of the Young's modulus on the nanoscale suggests good agreement in calculated trends.</p
Robust binding energy distribution sampling on amorphous solid water models:Method testing and validation with NH<sub>3</sub>, CO, and CH<sub>4</sub>
Get PDFContext. The astrochemically efficient icy mantles surrounding dust grains in molecular clouds have been shown to be of an amorphous water-rich nature. This therefore implies a distribution of binding energies (BEs) per species instead of a single value. Methods proposed so far for inferring BEs and their distributions on amorphous ices rely on different approaches and approximations, leading to disparate results or BE dispersions with partially overlapping ranges. Aims. This work aims to develop a method based on a structurally reliable ice model and a statistically and physicochemically robust approach to BE distribution inference, with the aim of being applicable to various relevant interstellar species. Methods. A multiscale computational approach is presented, with a molecular dynamics heat and quench protocol for the amorphous water ice model, and an ONIOM(B3LYP-D3(BJ)/6-311+G(d,p):GFN2-xtb) scheme for the BE inference, with a prime emphasis onto the convergence of the computed BEs with the real system size. The sampling of the binding configurations is twofold, exploring both regularly spaced binding sites as well as various adsorbate-to-substrate orientations on each locally distinct site. This second source of BE diversity accounts for the local roughness of the potential energy landscape of the substrate. Three different adsorbate test cases are considered, NH3, CO, and CH4, owing to their significance in icy dust mantles, and their distinct binding behavior with water ices. Results. The BE distributions for NH3, CO, and CH4 have been inferred with converged statistics. The distribution for NH3 is better represented by a double Gaussian component profile. Three starting adsorbate orientations per site are required to reach convergence for both Gaussian components of NH3, while two orientations are sufficient for CO, and one unique one for CH4 (symmetric). Further geometrical and molecular surrounding insights have been provided. These results encompass previously reported results.</p
Increasing the Lewis Acidity of Pyramidal Boranes:Cationic 9-Bora-1-Azatriptycenes as Strong Boron Lewis Superacids
No full textBora-azatriptycenes have been synthesized and used as geminal pyridine–boranes pairs, which exhibit unusual binding modes with weakly coordinating anions, to unique aza-triptycene/bora-triptycene Lewis adducts, and to bis-triptycenes dimers with unprecedented architectural motifs. Embedding a boron atom at the edge of a triptycene scaffold, in a strongly pyramidalized and geometrically constrained environment, and protonation of the adjacent pyridine ring strongly enhances the Lewis acidity of the boron atom. High levels of Lewis acidity are reached at the boron atom of these cationic boron Lewis superacids. Experimental and quantum-chemistry screening of their Lewis acidity enables elucidation of the interplay between Lewis acidity, pyramidalization angle, reorganization energy, and charge position in the adjacent pyridinium ring, and identifies new dicationic Lewis superacids
Identification of Potential Inhibitors of Plasmodium Falciparum L-Lactate Dehydrogenase from Selected African Compound Libraries: Virtual Screening, Molecular Mechanics-Generalized Born Surface Area, and Molecular Dynamics Studies
No full textWe evaluated 4,512 natural products from natural product library from Central African medicinal plants for drug discovery and South African natural compounds database libraries for the identification of potential Plasmodium falciparum L-lactate dehydrogenase inhibitors considering the virtual screening process. Extra precision virtual screening enabled the ranking of the top hundred hit molecules based on their docking properties. The selected hits were further shortened based on docking and molecular mechanics-generalized born surface area parameters in comparison with the reference. As a result, four hits were chosen: Mol1, Mol2, Mol3, and Mol4, all of them from the chalcone and quinone families. These molecules showed good predicted absorption, distribution, metabolism, and excretion, and toxicity properties. Finally, the molecular dynamics simulation results showed that the three chalcones, Mol1-4, formed an H-bond, hydrophobic interaction with key amino acids in the active site. This in silico study suggests that the chalcone compounds could serve as a potential source for developing new effective antimalarial drugs to combat malaria. Further in vitro or in vivo studies might be conducted to determine their actual effectiveness.</p
Wide spectral response enables efficient photochemistry-assisted selective hydrogenation of butadiene over Pd/N-TiO<sub>2</sub>
No full textSelective hydrogenation driven by heat is a critical industrial process for purifying alkene feedstocks with serious problems of energy and H2 consumption. Photochemistry-assisted strategy offers a sustainable alternative owing to its superiority of H2-free reaction under ambient temperature, unfortunately, with a challenging demand on efficient catalysts. Herein, a wide-spectrum-responsive Pd/N-TiO2 photo-thermal catalyst was developed by a solvothermal method for photochemistry-assisted selective hydrogenation of butadiene in propene. It shows an excellent catalytic performance, with 100 % alkenes selectivity and 100 % butadiene conversion under irradiation of full-light (i.e., 320 nm∼780 nm). Notably, over 53 % butadiene conversion with 100 % alkenes selectivity was successfully retained on Pd/N-TiO2 after shortening the wavelength range to visible light, much superior to that on Pd-TiO2 (i.e., <1 % butadiene conversion). Further exploration reveals that the nitrogen doping extends the light-responsive wavelength of titanium oxide from ∼380 nm to above 500 nm owing to the formation of Ti3+ and oxygen vacancies, which later create a defect energy level (i.e., ∼-0.53 to -0.12 eV) between the valence-conduction band of TiO2. The wide spectral response of N-TiO2 enhances the water photolysis to produce intermediate hydrogen ([H]) that acts as the hydrogen source for the tandem butadiene hydrogenation over the Pd surface. The work indicates that developing a dual-functional catalyst with an expanded light-responsive wavelength is an efficient way to enhance the photochemistry-assisted selective hydrogenation.</p