Synthesis of poly(vinyl acetate) block copolymers by successive RAFT and ATRP with a bromoxanthate iniferter

Poly(vinyl acetate)-b-polystyrene, poly(vinyl acetate)-b-poly(methyl acrylate) and poly(vinyl acetate)-b-poly(methyl methacrylate) block copolymers with low polydispersity (M(w)/M(n) < 1.25) were prepared by successive reversible addition-fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) employing a bromoxanthate iniferter (initiator-transfer agent-terminator).     

Iron salts catalyzed synthesis of β-N-substituted aminoacrylates

The direct condensation of amines with β-ketoesters to produce functional enamine derivatives has been investigated with iron Lewis acid catalysts. FeCl₃·6H₂O shows good catalytic activity and makes possible the chemo- and stereoselective formations of (Z)-enamine derivatives from aliphatic and aromatic primary amines under mild conditions.     

An efficient method to convert lactams and amides into 2,2-dialkylated amines

A practical method for the synthesis of gem-2,2-disubstituted tertiary amines from the corresponding lactams (or amides) is reported. It is based on the reaction of thioiminium ions, easily prepared from lactams and amides with organometallic reagents such allylmagnesium, benzylmagnesium, and primary alkylcerium reagents.     

Bi‐directional ACET micropump for on‐chip biological applications

The ability to control and pump high ionic strength fluids inside microchannels forms a major advantage for clinical diagnostics and drug screening processes, where high conductive biological and physiological buffers are used. Despite the known potential of AC electro‐thermal (ACET) effect in different biomedical applications, comparatively little is known about controlling the velocity and direction of fluid inside the chip. Here, we proposed to discretize the conventional electrodes to form various asymmetric electrode structures in order to control the fluid direction by simple switching the appropriate electric potential applied to the discretized electrodes. The ACET pumping effect was numerically studied by solving electrical, thermal and hydrodynamic multi‐physic coupled equations to optimize the geometrical dimensions of the discretized system. PBS solutions with different ionic strength were seeded with 1 μm sized fluorescent particles and electrothermally driven fluid motion was observed inside the channel for different electrode structures. Experimental analyses confirm that the proposed micropump is efficient for a conductivity range between 0.1 and 1 S/m and the efficiency improves by increasing the voltage amplitude. Behavior of the proposed electrode–electrolyte system is discussed by lumped circuit model. Frequency response of system illustrated that the optimal frequency range increases by increasing the conductivity of medium. For 0.18 S/m PBS solution, the constant pumping effect was observed at frequency range between 100 kHz and 1 MHz, while frequency range of 100 kHz to 5 MHZ was observed for 0.42 S/m. The characteristics of experimental results were in good agreement with the theoretical model.     

Preliminary assessment of the modification of polystyrene‐divinylbenzene resin with lipid‐tethered ligands for selective separations

Functionalized lipid tethered ligands use physical adsorption to anchor reactive head groups to hydrophobic supports. We previously demonstrated the use of these species adsorbed onto polypropylene capillary‐channeled polymer fibers. The general use of lipid tethered ligands on other hydrophobic chromatographic supports is demonstrated here for polystyrene‐divinylbenzene. Evaluation of ligand adsorption conditions was performed using a fluorescein isocyanate head group to quantify the extent of loading by UV‐Vis absorbance and by fluorescence microscopy. Selective protein capture was demonstrated by the detection of Texas Red labeled streptavidin (using fluorescence microscopy imaging, with quantification assessed through the depletion of solution‐phase protein using UV‐Vis absorbance. A second demonstration of the coupling involved an iminodiacetic acid head group lipid tethered ligand to capture the cationic dye, methylene blue. Two common means of alleviating nonspecific binding, adsorption in detergent media and use of a bovine serum albumin block, were evaluated. The first was found to cause release of the ligands, while the second was nominally effective. Indeed, the lipid tethered ligands itself may be most effective at impeding nonspecific binding. While further optimization and chromatographic evaluation is required, the general viability of this ligand immobilization method onto this common polymer support is demonstrated.     

Effect of nano‐modified SiO2/Al2O3 mixed‐matrix micro‐composite fillers on thermal,mechanical, and tribological properties of epoxy polymers

Thermo‐mechanically durable industrial polymer nanocomposites have great demand as structural components. In this work, highly competent filler design is processed via nano‐modified of micronic SiO₂/Al₂O₃ particulate ceramics and studied its influence on the rheology, glass transition temperature, composite microstructure, thermal conductivity, mechanical strength, micro hardness, and tribology properties. Composites were fabricated with different proportions of nano‐modified micro‐composite fillers in epoxy matrix at as much possible filler loadings. Results revealed that nano‐modified SiO₂/Al₂O₃ micro‐composite fillers enhanced inter‐particle network and offer benefits like homogeneous microstructures and increased thermal conductivity. Epoxy composites attained thermal conductivity of 0.8 W/mK at 46% filler loading. Mechanical strength and bulk hardness were reached to higher values on the incorporation of nano‐modified fillers. Tribology study revealed an increased specific wear rate and decreased friction coefficient in such fillers. The study is significant in a way that the design of nano‐modified mixed‐matrix micro‐composite fillers are effective where a high loading is much easier, which is critical for achieving desired thermal and mechanical properties for any engineering applications. Copyright © 2016 John Wiley & Sons, Ltd.     

Fluorescent perylene diimide rotaxanes: spectroscopic signatures of wheel-chromophore interactions

[2]- and [3]-rotaxanes with a tetraphenoxy perylene diimide core were synthesized. Hydrogen bonding between the wheel and the imide changes the optical properties of the perylene chromophore: the absorption and fluorescence spectra are red-shifted. The decay times of the rotaxanes are shorter in comparison with that of the axle. Single molecule fluorescence measurements reveal relatively narrow distributions of emission maxima and decay times. The averages are in agreement with ensemble measurements. The observed red shifts make the perylene diimide a suitable chromophore for sensing the position of the wheel on the axle.     

A virtual valve for smooth contamination-free flow switching

We present a channel geometry that allows for clean switching between different inlets of a microchip without any contamination of the inlets or the downstream flow. We drive this virtual valve with a pneumatic pressure setup that minimizes disturbance of the downstream flow during the switching procedure by simultaneous variation of the pressures applied to the different inlets. We assess the efficiency of the setup by spectroscopic measurement of downstream dye concentrations, and demonstrate its practical utility by sequentially constructing multiple layers of alginate hydrogel. The method is potentially useful for a whole series of further applications, such as changing perfusion liquids for cell culture and cell analysis, metering, chemical-reaction initiation and multi-sample chromatography, to name a few.     

Thiophenol-mediated 1,5-hydrogen transfer for the preparation of pyrrolizidines, indolizidines, and related compounds

The efficient preparation of 1-azabicyclic alkanes is described. Highly functionalized skeletons are prepared in a concise manner using a radical tin-free 1,5-hydrogen transfer-cyclization process. The precursors for the radical reactions are readily assembled either from pyrrolidine/piperidine/hexahydro-1H-azepine or via condensation of a properly designed N-alkylimine with an allenylzinc species.     

Aharonov-Bohm oscillations in the presence of strong spin-orbit interactions

We have measured highly visible Aharonov-Bohm (AB) oscillations in a ring structure defined by local anodic oxidation on a p-type GaAs heterostructure with strong spin-orbit interactions. Clear beating patterns observed in the raw data can be interpreted in terms of a spin geometric phase. Besides h/e oscillations, we resolve the contributions from the second harmonic of AB oscillations and also find a beating in these h/2e oscillations. A resistance minimum at B=0 T, present in all gate configurations, is the signature of destructive interference of the spins propagating along time-reversed paths.