Tandem Nazarov cyclization-michael addition sequence catalyzed by an Ir(III) complex

The first examples of a tandem Nazarov cyclization/Michael addition process are described. The sequence is efficiently catalyzed by Ir[Me(CO)(dppe)(DIB)]2+ and occurs with high diastereoselectivity, creating three contiguous stereocenters. The mechanistic factors controlling the reactivity and diastereoselectivity are discussed.     

Inverse problems related to ion channels

Ion channels are proteins with a hole down theirmiddle that allow ions to move across otherwise impermeable cellmembranes, thereby controlling many important physiological functions. The transport process of the ions can be described using the Poisson-Nernst-Plank equations, a system of coupled nonlinear partial differential equations. Based on this model we derive a simplified surrogate model that captures the main features of the associated current-voltage curves of the ion channel. This surrogate model is then used to identify individual channel parameters based on current data. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Back-reaction in the presence of thermalizing collisions

Preequilibrium parton production following an ultrarelativistic nucleus-nucleus collision is studied in terms of the decay of a strong chromoelectric field which generates pairs through the Schwinger mechanism. Back-reaction of the partons with the field is included and a model transport equation containing a collision term is solved for the central rapidity region based on an approximation in which the partons relax to a thermal distribution.     

The bulk viscoelastic properties of poly(styrene-co-sodium styrene-p-carboxylate)

The effect of up to 7.82 mol % ionic groups on the stress relaxation and dynamic mechanical (torsion pendulum) properties of poly(styrene-co-sodium styrene-p-carboxylate) was studied. The results obtained were compared with those reported elsewhere for polymers containing the same ionic groups at a different position on the polystyrene backbone (styrene-sodium methacrylate copolymers) and with polymers containing different ionic groups at the same position (styrene-sodium styrene-p-sulfonate copolymers). The results of these comparisons showed that positioning of ionic groups affects the size of ionic aggregates formed, while their type dictates the strength of the forces within the aggegrates.     

Miscibility of poly(vinyl chloride) with ethyl acrylate 4-vinyl pyridine copolymers

Blends (50:50, w:w) of poly(vinyl chloride) (PVC) and poly(ethyl acrylate-co-4-vinyl pyridine) (PEA–4-VP) of different 4-VP contents (2–14 mol %) were prepared. These were found to be partially miscible as evidenced by the presence of a single, through broad, tangent δ peak obtained from torsion pendulum experiments. Several possible types of interactions which might exist between PVC and PEA-4-VP, such as ion-dipole, crosslinking, charge transfer, hydrogen bonding, and dipole–dipole interactions, were explored. From ultraviolet, conductance, infrared, and solubility studies, it was shown that hydrogen bonding or dipole–dipole (or possibly a combination of the two) interactions were the most likely in this system. These interactions have been suggested previously for other systems by various investigators.     

Dynamic melt rheology of poly(styrene-co-vinylpyridine) and their methyl iodide salts

The dynamic melt rheology of random copolymers of polystyrene with 2–9 mol% 4-vinylpyridine was examined in their quaternized and nonquaternized forms. Time–temperature reducibility applies in all cases. Relative to the glass transition, the master curves of the nonquaternized materials are identical. Melt flow in the quaternized materials is mildly retarded, the extent increasing with ion content. At the highest ion contents, the relaxation processes appear to be of Arrhenius type. As in the glass transition region, the ionic interactions in the plateau and terminal zones are thermally labile.     

Dynamic mechanical properties of plasticized polystyrene-based ionomers. I. Glassy to rubbery zones

The plasticizing effect of a nonpolar and a polar diluent in ionomers was studied by dynamic mechanical methods in the glassy to rubbery regions. Specifically, a carboxylate and a sulfonate polystyrene-based ionomer were investigated with variation of diethylbenzene content and of glycerol content. It was found that the nonpolar diluent plasticizes the transition by formation of ionic aggregates as well as lowering the glass transition temperature. However, the ionic regions of the carboxylate ionomer are plasticized more than those of the sulfonate ionomer. This corroborates the results of other studies which had found that the sulfonate groups in ionomers interact more strongly than the carboxylate groups. The polar diluent causes the ionic transition to disappear; this is probably due to solvation of the ions by the diluent.