Protein dielectrophoresis: Key dielectric parameters and evolving theory

Globular proteins exhibit dielectrophoresis (DEP) responses in experiments where the applied field gradient factor ∇E² appears far too small, according to standard DEP theory, to overcome dispersive forces associated with the thermal energy kT of disorder. To address this a DEP force equation is proposed that replaces a previous empirical relationship between the macroscopic and microscopic forms of the Clausius–Mossotti factor. This equation relates the DEP response of a protein directly to the dielectric increment δε⁺ and decrement δε⁻ that characterize its β-dispersion at radio frequencies, and also indirectly to its intrinsic dipole moment by way of providing a measure of the protein's effective volume. A parameter Γ_pw, taken as a measure of cross-correlated dipole interactions between the protein and its water molecules of hydration, is included in this equation. For 9 of the 12 proteins, for which an evaluation can presently be made, Γ_pw has a value of ≈4600 ± 120. These conclusions follow an analysis of the failure of macroscopic dielectric mixture (effective medium) theories to predict the dielectric properties of solvated proteins. The implication of a polarizability greatly exceeding the intrinsic value for a protein might reflect the formation of relaxor ferroelectric nanodomains in its hydration shell.     

A Photochemical Route to Dibenzobarrelenes

Dibenzobarrelenes have been prepared by the cycloaddition of benzyne to anthracenes. The first method gives complex mixtures from which only poor yields of 1, 4-adducts may be obtained,¹ exceot wgeb tetragakivebztbes are enokited,^2,3 Muller and Vergne have reported⁴ that dibenzobarrelene is formed by the reaction of acetylene with anthracene, but it may be significant that later workers have chosen to use either the above-mentioned benzyne route or a modification of the cycloaddition to anthracenne involving dichlorethylene followed by dechlorination to prepare the parent compound.⁵ Our approach to the synthesis of this ring system employs our previously described 1,2–photoaramatisation reactions.⁶ A significant feature of the present work is that it demonstrates that a photochemical reaction can be employed to generate compounds, in this case dibenzobarrelenes, known to be photolabile.⁷     

Rack-mounted chemistry IV: the thermal rearrangement of 7-oxabenzonorbornadienes into benzo[b]oxepines on and off the polycyclic rack

The thermal rearrangement of [3]polynorbornane bis-imide rack-mounted 7-oxabenzonorbornadienes has been conducted using flash vacuum pyrolysis (FVP) at 520 °C and is compared with the FVP of similar 7-oxabenzonorbornadienes off the rack. The isomerisation is considered to involve (a) C–O bond cleavage to a vinylogous 1,5-dipole, (b) formation of a benzene epoxide by nucleophilic ring-closure and (c) valence-isomerisation of the benzene epoxide to the oxepine. Competing fragmentation to the isobenzofuran by ejection of acetylene and other rearrangements become prominent pathways off the rack, whereas isomerisation to the oxepine is highly favored on the rack.     

The First Catalytic Synthesis of an Acrylate from CO2 and an Alkene—A Rational Approach

For more than three decades the catalytic synthesis of acrylates from the cheap and abundantly available C₁ building block carbon dioxide and alkenes has been an unsolved problem in catalysis research, both in academia and industry. Herein, we describe a homogeneous catalyst based on nickel that permits the catalytic synthesis of the industrially highly relevant acrylate sodium acrylate from CO₂, ethylene, and a base, as demonstrated, at this stage, by a turnover number of greater than 10 with respect to the metal.     

Study of internal ring rotation and molecular reorientation in the liquid crystal 5O.7 by deuterium N.M.R. spectroscopy

Abstract

The spectral densities of motion were determined by deuterium N.M.R. relaxation measurements in the nematic, smectic A and smectic C phases of 4-n-pentyloxybenzylidene-d ₁-4′-heptylaniline and 4-n-pentyloxybenzylidene-4′-heptylaniline-2,3,5,6-d ₄. By examining two atomic sites on a 5O.7 molecule, we were able to gain information on the reorientation motion and internal rotation of the aniline ring. It was also found that director fluctuations make some contribution to the spectral density J ₁ (ω). We use the superimposed rotations model to account for the internal ring motion and the small step rotational diffusion model for the molecular reorientation. The derived rotational diffusion constants for the spinning and tumbling motions appear to give physically plausible activation energies in the mesophases of 5O.7.     

Regioselectivity in the Acid Cleavage of Bicyclo[4.1.0]Heptan-3-Ones

Acid-promoted cyclopropane cleavage reactions have been employed with great success for the generation of angular methyl groups.² Sims has shown that the regioselectivity of such reactions may be influenced by acid strength.^2d We now report a case in which steric factors appear to direct the cleavage pathway.     

Synthetic Studies Towards Taxol Analogs: Chemoselective Cleavage of C-5 Cinnamoyl Group in Taxane Group of Diterpenoids with Hydroxylamine

Taxane group of diterpenoids 2 and 3 which possess cinnamoyl moiety at C-5 position underwent selective cleavage to C-5 hydroxy compounds 4 and 5 on treatment with hydroxylamine. The resulting compounds were characterised based on their spectral data.     

Ignition delay times of methane and hydrogen highly diluted in carbon dioxide at high pressures up to 300 atm

The need for more efficient power cycles has attracted interest in super-critical CO₂ (sCO₂) cycles. However, the effects of high CO₂ dilution on auto-ignition at extremely high pressures has not been studied in depth. As part of the effort to understand oxy-fuel combustion with massive CO₂ dilution, we have measured shock tube ignition delay times (IDT) for methane/O₂/CO₂ mixtures and hydrogen/O₂/CO₂ mixtures using sidewall pressure and OH* emission near 306?nm. Ignition delay time was measured in two different facilities behind reflected shock waves over a range of temperatures, 1045–1578?K, in different pressures and mixture regimes, i.e., CH₄/O₂/CO₂ mixtures at 27–286 atm and H₂/O₂/CO₂ mixtures at 37–311 atm. The measured data were compared with the predictions of two recent kinetics models. Fair agreement was found between model and experiment over most of the operating conditions studied. For those conditions where kinetic models fail, the current ignition delay time measurements provide useful target data for development and validation of the mechanisms.