110th Anniversary: Near-Total Epoxidation Selectivity and Hydrogen Peroxide Utilization with Nb-EISA Catalysts for Propylene Epoxidation

The Nb-EISA catalyst with relatively low Nb loadings (∼2 wt %) shows exceptional propylene epoxidation performance with H2O2 as oxidant at 30–40 °C, 5–9 bar propylene pressure with nearly total propylene oxide (PO) selectivity (>99%), H2O2 utilization (>99%) toward PO formation, high productivity (∼3200 mg/h/g), and mild Nb leaching (3–6%). The predominantly Lewis acidic nature of the Nb-EISA catalysts favors epoxidation while their relatively low Brønsted acidity inhibits H2O2 decomposition and Nb leaching. At higher Nb loadings (8–17 wt %), the catalytic performance deteriorates. However, significant performance improvements were achieved when the Nb-EISA materials are calcined in N2 (instead of air) during synthesis, depositing a carbon layer in the pores. The resulting pore hydrophobicity not only inhibits epoxide ring opening but also increases propylene concentration inside the pores resulting in higher EO productivity and lower H2O2 decomposition. The carbonized Nb-EISA materials also show improved stability to leaching

Towards highly selective ethylene epoxidation catalysts using hydrogen peroxide and tungsten- or niobium-incorporated mesoporous silicate (KIT-6)

This is the published version. Copyright 2014 Royal Society of ChemistrySignificant ethylene epoxidation activity was observed over Nb- and W-incorporated KIT-6 materials with aqueous hydrogen peroxide (H2O2) as the oxidant and methanol as solvent under mild operating conditions (35 °C and 50 bar) where CO2 formation is avoided. The Nb-KIT-6 materials generally show greater epoxidation activity compared to the W-KIT-6 materials. Further, the ethylene oxide (EO) productivity observed with these materials [30–800 mg EO h−1 (g metal)−1] is of the same order of magnitude as that of the conventional silver (Ag)-based gas phase ethylene epoxidation process. Our results reveal that the framework-incorporated metal species, rather than the extra-framework metal oxide species, are mainly responsible for the observed epoxidation activity. However, the tetrahedrally coordinated framework metal species also introduce Lewis acidity that promotes their solvolysis (which in turn results in their gradual leaching) as well as H2O2 decomposition. These results and mechanistic insights provide rational guidance for developing catalysts with improved leaching resistance and minimal H2O2 decomposition

Paper-based electroanalytical devices with an integrated, stable reference electrode

This paper describes the development of a referenced Electrochemical Paper-based Analytical Device (rEPAD) comprising a sample zone, a reference zone, and a connecting microfluidic channel that includes a central contact zone. We demonstrated that the rEPADs provide a simple system for direct and accurate voltammetric measurements that are referenced by an electrode with a constant, well-defined potential. The performance of the rEPADs is comparable to commercial electrochemical cells, and the layout can be easily integrated into systems that permit multiplexed analysis and pipette-free sampling. The cost of this portable device is sufficiently low that it could be for single-use, disposable applications, and its method of fabrication is compatible with that used for other paper-based systems.Chemistry and Chemical Biolog

Shifts in the Distribution of Mass Densities Is a Signature of Caloric Restriction in Caenorhabditis elegans

Although the starvation response of the model multicellular organism Caenorhabditis elegans is a subject of much research, there is no convenient phenotypic readout of caloric restriction that can be applicable to large numbers of worms. This paper describes the distribution of mass densities of populations of C. elegans, from larval stages up to day one of adulthood, using isopycnic centrifugation, and finds that density is a convenient, if complex, phenotypic readout in C. elegans. The density of worms in synchronized populations of wildtype N2 C. elegans grown under standard solid-phase culture conditions was normally distributed, with distributions peaked sharply at a mean of 1.091 g/cm3 for L1, L2 and L3 larvae, 1.087 g/cm3 for L4 larvae, 1.081 g/cm3 for newly molted adults, and 1.074 g/cm3 at 24 hours of adulthood. The density of adult worms under starvation stress fell well outside this range, falling to a mean value of 1.054 g/cm3 after eight hours of starvation. This decrease in density correlated with the consumption of stored glycogen in the food-deprived worms. The density of the worms increased when deprived of food for longer durations, corresponding to a shift in the response of the worms: worms sacrifice their bodies by retaining larvae, which consume the adults from within. Density-based screens with the drug Ivermectin on worms cultured on single plates resulted in a clear bimodal (double-peaked) distribution of densities corresponding to drug exposed and non-exposed worms. Thus, measurements of changes in density could be used to conduct screens on the effects of drugs on several populations of worms cultured on single plates

Polymer-based mesh as supports for multi-layered 3D cell culture and assays

Three-dimensional (3D) culture systems can mimic certain aspects of the cellular microenvironment found in vivo, but generation, analysis and imaging of current model systems for 3D cellular constructs and tissues remain challenging. This work demonstrates a 3D culture system–Cells-in-Gels-in-Mesh (CiGiM)–that uses stacked sheets of polymer-based mesh to support cells embedded in gels to form tissue-like constructs; the stacked sheets can be disassembled by peeling the sheets apart to analyze cultured cells—layer-by-layer—within the construct. The mesh sheets leave openings large enough for light to pass through with minimal scattering, and thus allowing multiple options for analysis—(i) using straightforward analysis by optical light microscopy, (ii) by high-resolution analysis with fluorescence microscopy, or (iii) with a fluorescence gel scanner. The sheets can be patterned into separate zones with paraffin film-based decals, in order to conduct multiple experiments in parallel; the paraffin-based decal films also block lateral diffusion of oxygen effectively. CiGiM simplifies the generation and analysis of 3D culture without compromising throughput, and quality of the data collected: it is especially useful in experiments that require control of oxygen levels, and isolation of adjacent wells in a multi-zone format.Chemistry and Chemical Biolog

Rapid fabrication of pressure-driven open-channel microfluidic devices in omniphobic RF paper

This paper describes the fabrication of pressure-driven, open-channel microfluidic systems with lateral dimensions of 45-300 microns carved in omniphobic paper using a craft-cutting tool. Vapor phase silanization with a fluorinated alkyltrichlorosilane renders paper omniphobic, but preserves its high gas permeability and mechanical properties. When sealed with tape, the carved channels form conduits capable of guiding liquid transport in the low-Reynolds number regime (i.e. laminar flow). These devices are compatible with complex fluids such as droplets of water in oil. The combination of omniphobic paper and a craft cutter enables the development of new types of valves and switches, such as “fold” valves and “porous switches,” which provide new methods to control fluid flow.Chemistry and Chemical Biolog