Dielectrophoresis with 3D microelectrodes fabricated by surface tension assisted lithography

This paper demonstrates the utilization of 3D semispherical shaped microelectrodes for dielectrophoretic manipulation of yeast cells. The semispherical microelectrodes are capable of producing strong electric field gradients, and in turn dielectrophoretic forces across a large area of channel cross‐section. The semispherical shape of microelectrodes avoids the formation of undesired sharp electric fields along the structure and also minimizes the disturbance of the streamlines of nearby passing fluid. The advantage of semispherical microelectrodes over the planar microelectrodes is demonstrated in a series of numerical simulations and proof‐of‐concept experiments aimed toward immobilization of viable yeast cells.     

Observation of the internal network structure of a polymer-stabilized liquid crystal via transmission electron microscopy

The internal structure of the network component of a polymer-stabilized liquid crystal has been observed for the first time. These are systems in which a small amount of a monomer is dissolved within a LC host and then polymerized in situ to produce a network. Studies performed on a system prepared using the diacrylate monomer RM60 and the nematic mixture BL087 are presented. The concentration of the monomer was 1 wt %. After formation of the network through photopolymerization of the monomer between Melinex layers within a glass cell, the LC host was removed by dissolving it in heptane. Subsequent observation of the internal network structure by transmission electron microscopy was made possible by bromine staining of the network, followed by embedding and ultramicrotomy. A collection of solid, near-circular objects was observed, of mean diameter 0.13 μm. These objects were found to be highly permeable to bromine vapour, suggesting an open, but homogeneous structure.     

Pd‐PEPPSI‐IHeptCl: A General‐Purpose,Highly Reactive Catalyst for the Selective Coupling of Secondary Alkyl Organozincs

Dichloro[1,3‐bis(2,6‐di‐4‐heptylphenyl)imidazol‐2‐ylidene](3‐chloropyridyl)palladium(II) (Pd‐PEPPSI‐IHept^Cl), a new, very bulky yet flexible Pd–N‐heterocyclic carbene (NHC) complex has been evaluated in the cross‐coupling of secondary alkylzinc reactants with a wide variety of oxidative addition partners in high yields and excellent selectivity. The desired, direct reductive elimination branched products were obtained with no sign of migratory insertion across electron‐rich and electron‐poor aromatics and all forms of heteroaromatics (five and six membered). Impressively, there is no impact of substituents at the site of reductive elimination (i.e., ortho or even di‐ortho), which has not yet been demonstrated by another catalyst system to date.     

Study of polymerizing styrene through depolarized light scattering

The thermal polymerization of clean styrene has been studied through Rayleigh-Brillouin light scattering. The frequency shifts, Rayleigh to Brillouin intensity ratios, Rayleigh depolarization ratios, and depolarized intensities were measured as the polymerization proceeded to completion at 90°C. The depolarized intensities decreased and the frequency shifts increased smoothly from the monomer to the polymer values. The Vv intensities and Rayleigh to Brillouin intensity ratios increase dramatically during the first stages of polymerization then decrease systematically to their final values. There is a large increase in the Rayleigh to Brillouin intensity ratio from the monomer to the final polymer value. The vertical depolarization ratio pv and the horizontal depolarization ratio pV were found to be respectively 0.4 and 1 for the polymer. Our observations are explained in terms of light being scattered from concentration fluctuations in the early stages of polymerization and from spherically symmetric strain fields in the polymer. We believe that the background, which we observed to embrace a wide range of frequencies, was due to rotational Raman transitions.     

Solvent Effect and Reactivity Trend in the Aerobic Oxidation of 1,3‐Propanediols over Gold Supported on Titania: NMR Diffusion and Relaxation Studies

In recent work, it was reported that changes in solvent composition, precisely the addition of water, significantly inhibits the catalytic activity of Au/TiO₂ catalyst in the aerobic oxidation of 1,4‐butanediol in methanol due to changes in diffusion and adsorption properties of the reactant. In order to understand whether the inhibition mechanism of water on diol oxidation in methanol is generally valid, the solvent effect on the aerobic catalytic oxidation of 1,3‐propanediol and its two methyl‐substituted homologues, 2‐methyl‐1,3‐propanediol and 2,2‐dimethyl‐1,3‐propanediol, over a Au/TiO₂ catalyst has been studied here using conventional catalytic reaction monitoring in combination with pulsed‐field gradient nuclear magnetic resonance (PFG‐NMR) diffusion and NMR relaxation time measurements. Diol conversion is significantly lower when water is present in the initial diol/methanol mixture. A reactivity trend within the group of diols was also observed. Combined NMR diffusion and relaxation time measurements suggest that molecular diffusion and, in particular, the relative strength of diol adsorption, are important factors in determining the conversion. These results highlight NMR diffusion and relaxation techniques as novel, non‐invasive characterisation tools for catalytic materials, which complement conventional reaction data.     

Oxidative Addition of Haloheteroarenes to Palladium(0): Concerted versus SNAr‐Type Mechanism

The kinetics of the oxidative additions of haloheteroarenes HetX (X=I, Br, Cl) to [Pd⁰(PPh₃)₂] (generated from [Pd⁰(PPh₃)₄]) have been investigated in THF and DMF and the rate constants have been determined. In contrast to the generally accepted concerted mechanism, Hammett plots obtained for substituted 2‐halopyridines and solvent effects reveal a reaction mechanism dependent on the halide X of HetX: an unprecedented S_NAr‐type mechanism for X=Br or Cl and a classical concerted mechanism for X=I. These results are supported by DFT studies.     

Graph Duality in Surface Dynamics

Journal of Nonlinear Science - We compare one-dimensional representations for the isotopy stable dynamics of homeomorphisms in two dimensions. We consider the skeleton graph representative, which...