Tuning the Reactivity of a Heterogeneous Catalyst using N-Heterocyclic Carbene Ligands for C−H Activation Reactions

We report the dramatic impact of the addition of N-heterocyclic carbenes (NHCs) on the reactivity and selectivity of heterogeneous Ru catalysts in the context of C−H activation reactions. Using a simple and robust method, we prepared a series of new air-stable catalysts starting from commercially available Ru on carbon (Ru/C) and differently substituted NHCs. Associated with C−H deuteration processes, depending on Ru/C-NHC ratios, the chemical outcome can be controlled to a large extent. Indeed, tuning the reactivity of the Ru catalyst with NHC enabled: 1) increased chemoselectivity and the regioselectivity for the deuteration of alcohols in organic media; 2) the synthesis of fragile pharmaceutically relevant deuterated heterocycles (azine, purine) that are otherwise completely reduced using unmodified commercial catalysts; 3) the discovery of a novel reactivity for such heterogeneous Ru catalysts, namely the selective C-1 deuteration of aldehydes.     

Electro-optical microscopy: mapping nonlinear polymer films with micrometric resolution

The first demonstration, to the best of our knowledge, of electro-optical microscopy is presented and applied to a polymer-based optical device. A confocal transmission microscope with interferometric homodyne detection is implemented to measure Pockels phase shifts with micrometric spatial resolution and an accuracy level down to 4 x 10(-7) rad. This technique is applied to poled polymer films in which noncentrosymmetric molecular orientation is preliminarily achieved in the sample plane between transverse planar electrodes. The electro-optic mapping of this structure exhibits nonuniform and asymmetric patterns of the nonlinear response that are characteristic of the poling spatial inhomogeneity as confirmed by second-harmonic generation microscopy.     

Investigating the Influence of Column Depth on the Treatment of Textile Wastewater Using Natural Zeolite

Textile industry production processes generate one of the most highly polluted wastewaters in the world. Unfortunately, the field is also challenged by the availability of relatively cheap and highly effective technologies for wastewater purification. The application of natural zeolite as a depth filter offers an alternative and potential approach for textile wastewater treatment. The performance of a depth filter treatment system can be deeply affected by the column depth and the characteristics of the wastewater to be treated. Regrettably, the information on the potential of these filter materials for the purification of textile wastewater is still scarce. Therefore, this study investigated the potential applicability of natural zeolite in terms of column depth for the treatment of textile wastewater. From the analysis results, it was observed that the filtration efficiencies were relatively low (6.1 to 13.7%) for some parameters such as total dissolved solids, electrical conductivity, chemical oxygen demand, and sodium chloride when the wastewater samples were subjected to the 0.5 m column depth. Relatively high efficiency of 82 and 93.8% was observed from color and total suspended solids, respectively, when the wastewater samples were subjected to the 0.5 m column depth. Generally, the 0.75 m column depth achieved removal efficiencies ranging from 52.3% to 97.5%, whereas the 1 m column depth achieved removal efficiencies ranging from 86.9% to 99.4%. The highest removal efficiency was achieved with a combination of total suspended solids and 1 m column depth (99.4%). In summary, the treatment approach was observed to be highly effective for the removal of total suspended solids, with a 93.8% removal efficiency when the wastewater was subjected to the 0.5 m column depth, 97.5% for 0.75 m column depth, and 99.4% for 1 m column depth. Moreover, up to 218.233 mg of color per g of the filter material was captured. The results derived in this study provide useful information towards the potential applicability of natural zeolite in the textile wastewater treatment field.     

Mass flow rate measurements in gas micro flows

The main objective of this experimental investigation on the gas flow slip regime is to measure the mass flow rate in isothermal steady flows through cylindrical micro tubes. Two technical procedures devoted to mass flow rate measurements are compared, and the measured values are also compared with the results yielded by different approximated analytical solutions of the gas dynamics continuum equations. Satisfactory results are obtained and the way is clearly opened to measuring mass flow rates for higher Knudsen numbers, over all the micro flow transitional regime.     

Hydrogen adsorption on microporous materials at ambient temperatures and pressures up to 50 MPa

High surface area microporous adsorbents are often proposed as potential hydrogen storage materials, although typically at 77?K and less than 5?MPa. In this study, we focus on conditions more suitable for automotive applications by investigating the storage capacities of microporous materials at 298?K and at pressures up to 50?MPa. In an effort to derive trends within and across material classes, we examined a wide range of materials with varying microstructures including the activated carbons AX-21, KUA-5, and MSC-30; a zeolite templated carbon; a hypercrosslinked polymer; and the Metal Organic Frameworks MOF-177, IRMOF-20, MIL-53, ZIF-8, and Cu₃(btc)₂. The peak excess adsorption of these materials ranged from 0.8–1.8?wt.%, although many did not reach their maximum capacity even at high pressures. However, the total volumetric storage gains over compressed hydrogen gas were quite low and, in many cases, negative. In addressing ambient temperature adsorption at significantly higher pressures than previously reported, our data confirms and extends the range of validity of several existing DFT calculations. Furthermore, our data suggest that, for both activated carbons and MOFs, factors other than specific surface area govern ambient temperature adsorption capacity. Contrary to some reports, the high fractions of sub-nanometer pores in some of the investigated MOFs did not appear to enhance the excess adsorption even at high pressures. For on-board applications with ambient temperature storage, significant enhancements to the attractive force at the materials’ surface are required, beyond merely increasing specific surface area, or for MOFs, tuning of pore sizes.     

Rhodium-Catalyzed Enantioselective Synthesis of Highly Fluorescent and CPL-Active Dispiroindeno[2,1-c]fluorenes

The enantioselective synthesis of chiral [7]-helical dispirodihydro[2,1-c]indenofluorenes (DSF-IFs) was achieved for the first time in good yields with high er values (er up to 99 : 1). The crucial step of the whole reaction sequence was the enantioselective intramolecular [2+2+2] cycloaddition of tethered triynediols to indenofluorenediols, which was catalyzed by a Rh/SEGPHOS® complex. Further transformations led to the corresponding DSF-IFs. The prepared helically chiral DSF-IFs combine circularly polarized luminescence (CPL) activity (g_lum=∼10⁻³) with exceptionally high fluorescence quantum yields (up to Φ_lum=0.97).     

Wringing out DNA

The chiral nature of DNA plays a crucial role in cellular processes. Here we use magnetic tweezers to explore one of the signatures of this chirality, the coupling between stretch and twist deformations. We show that the extension of a stretched DNA molecule increases linearly by 0.42 nm per excess turn applied to the double helix. This result contradicts the intuition that DNA should lengthen as it is unwound and get shorter with overwinding. We then present numerical results of energy minimizations of torsionally restrained DNA that display a behavior similar to the experimental data and shed light on the molecular details of this surprising effect.     

Aqueous Flow Reactor and Vapour-Assisted Synthesis of Aluminium Dicarboxylate Metal–Organic Frameworks with Tuneable Water Sorption Properties

Energy-efficient indoors temperature and humidity control can be realised by using the reversible adsorption and desorption of water in porous materials. Stable microporous aluminium-based metal–organic frameworks (MOFs) present promising water sorption properties for this goal. The development of synthesis routes that make use of available and affordable building blocks and avoid the use of organic solvents is crucial to advance this field. In this work, two scalable synthesis routes under mild reaction conditions were developed for aluminium-based MOFs: (1) in aqueous solutions using a continuous-flow reactor and (2) through the vapour-assisted conversion of solid precursors. Fumaric acid, its methylated analogue mesaconic acid, as well as mixtures of the two were used as linkers to obtain polymorph materials with tuneable water sorption properties. The synthesis conditions determine the crystal structure and either the MIL-53 or MIL-68 type structure with square-grid or kagome-grid topology, respectively, is formed. Fine-tuning resulted in new MOF materials thus far inaccessible through conventional synthesis routes. Furthermore, by varying the linker ratio, the water sorption properties can be continuously adjusted while retaining the sigmoidal isotherm shape advantageous for heat transformation and room climatisation applications.