Comparison of a range of rhodium-based catalysts for the hydroformylation of selected alkenes

Four rhodium-based catalyst systems 1, 2, 3, and [Rh(OAc)₂]₂/PPh₃ have been used in the hydroformylation of 1-hexene, styrene and some phosphino-, amino- and amido-alkenes. In general the catalysts showed very similar reactivity and selectivity.     

Study of the sodium dodecyl sulphate–protein complexes: evidence of their wormlike conformation by treating them as random coil polymers

The Kuhn statistical segment length, A, was determined for the sodium dodecyl sulphate (SDS)–protein complexes in two binding levels of SDS adsorbed onto the protein. These complexes are treated as random coil polymers. For the SDS–protein complex of binding level 1.4 g SDS per gram of protein, the value of A was found equal to 76 and 37 Å in 0.01 and 0.1 M ionic strength, correspondingly. For the complex of binding level 0.4 g SDS per gram of protein, the value of A was found equal to 30 Å. The calculation was based mainly on two equations (Eqs. 4 and 5; Dondos and Benoît, Polymer 18:1161, 1977; Dondos and Staikos, Colloid Polym Sci 273:623, 1995, correspondingly). Our findings are supported by gel permeation chromatography results, drawn according to the “modified universal calibration” and suggest that these complexes should be considered as wormlike polymers presenting a considerable draining effect.     

Modification of the universal calibration of gel permeation chromatography to include macromolecules presenting a draining effect

A new universal calibration for gel permeation chromatography is proposed in which the hydrodynamic volume of the macromolecular chains is expressed by the quantity [η]M/Φ instead of the commonly used quantity [η]M (where [η] is the intrinsic viscosity, M is the molecular mass, and Φ is Flory's parameter). Introducing Φ into the hydrodynamic volume is necessary because its value changes from one polymer to another when the polymers present a certain draining effect. The proposed procedure also allows the determination of Φ of any wormlike polymer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 707–710, 2003     

A Theoretical Approach to Actin Filament Dynamics

Dynamic control of the actin network in eukaryotic cells plays an essential role in their movement, but to date our understanding of how the network properties are controlled in space and time is still rudimentary. For example, how the cell maintains the pools of monomeric actin needed for a rapid response to signals, how the filament length distribution is controlled, and how the actin network properties are modulated by various bundling and severing proteins to produce the mechanical response is not known. Here we address the simplest aspect of this, which is to understand the temporal evolution of the length distribution in vitro in order to understand what the relevant time scales are for establishment of a time-invariant distribution. Surprisingly, we find that there are very long-lived intermediate length distributions that are not exponential. The results shed light on the time scale needed to observe genuine steady-state distributions, and emphasize the necessity of control molecules for modulating the time scale. Research supported in part by NSF grants DMS 9805494 and DMS 0317372. Also in the Digital Technology Center, University of Minnesota. Research supported in part by NIH grant GM 29123, the Max Planck Institute for Mathematics in the Sciences and the Alexander von Humboldt Foundation     

On finitely generated projective modules

It is shown that the set End _A (M) is a Waelbroeck algebra, for every topological Waelbroeck algebraA and for every finitely generated projectiveA-moduleM. The research of Mart Abel was supported by Greek State Scholarship Foundation and Estonian Science Foundation grant 6205.     

Rapid transport of gases in carbon nanotubes

We report atomistic simulations for both self- and transport diffusivities of light gases in carbon nanotubes and in two zeolites with comparable pore sizes. We find that transport rates in nanotubes are orders of magnitude faster than in the zeolites we have studied or in any microporous material for which experimental data are available. The exceptionally high transport rates in nanotubes are shown to be a result of the inherent smoothness of the nanotubes. We predict that carbon nanotube membranes will have fluxes that are orders of magnitude greater than crystalline zeolite membranes.     

Voltammetric Determination of Trace Heavy Metals by Sequential-injection Analysis at Plastic Fluidic Chips with Integrated Carbon Fiber-based Electrodes

This work describes a sequential injection analysis (SIA) method for on-line strippping voltammetric determination of Pb(II), Cd(II) and Zn(II) using an injection-moulded electrochemical fluidic chip consisting of 3 conductive carbon fiber-loaded polymer electrodes embedded in a plastic fluidic holder. The sample containing the target metals and a solution containing Bi(III) were aspirated in the holding coil of the SIA manifold. Then, the flow was reversed and the two solutions were directed to the fluidic cell through a mixing coil which induced mixing of the two zones. Upon reaching the cell, simultaneous reduction of the target metals and Bi(III) occurred resulting in the formation of a metal-Bi alloy on the working electrode. Finally, the accumulated metals were stripped off the bismuth-film electrode via a positive potential scan and the oxidation current was recorded. The experimental variables (concentration of the bismuth plating solution, deposition potential, sample volume, stripping mode) were investigated and the potential interferences were assessed. The limits of quantification were 2.8 μg L⁻¹ for Pb(II), 3.6 μg L⁻¹ for Cd(II) and 4.2 μg L⁻¹ for Zn(II) and the the within-chip and between-chip % relative standard deviations were ≤6.3 % and ≤14 %, respectively. Finally, the sensor was applied to the determination of trace metals in a fish food sample.