The synthesis and electrochemistry of CpTiCl2(OR) (R = alkyl, aryl) complexes

The syntheses of several new CpTiCl₂(OR) (R = alkyl, aryl) complexes are described. It was possible to isolate pure product when the R group is substituted such as to cause steric crowding at the metal centre; for example, particularly good yields of the phenolate complexes were obtained when there were isopropyl substituents in the 2 and 6 positions of the phenolate. Electrochemical studies of the complexes in dry THF show that the Ti^III complexes are relatively stable, but only a diol complex could be reduced further to a Ti^II species. In general, the Ti^IV complexes undergo a reversible 1e⁻ reduction reaction. The chemistry is more complex if the electrolyte contains added water: both the Ti^IV and Ti^III complexes can react with water, the OR group being replaced by OH. The reaction is particularly rapid for the Ti^III alkoxide complexes.     

Silica particle-stabilized emulsions of silicone oil and water: aspects of emulsification

A study of the emulsification of silicone oil and water in the presence of partially hydrophobic, monodisperse silica nanoparticles is described. Emulsification involves the fragmentation of bulk liquids and the resulting large drops and the coalescence of some of those drops. The influence of particle concentration, oil/water ratio, and emulsification time on the relative extents of fragmentation and coalescence during the formation of emulsions, prepared using either batch or continuous methods, has been investigated. For batch emulsions, the average drop diameter decreases with increasing particle concentration as the extent of limited coalescence is reduced. Increasing the oil volume fraction in the emulsion at fixed aqueous particle concentration results in an increase in the average drop diameter together with a dramatic lowering of the uniformity of the drop size distribution as coalescence becomes increasingly significant until catastrophic phase inversion occurs. For low oil volume fractions (phi(o)), fragmentation dominates during emulsification since the mean drop size decreases with emulsification time. For higher phi(o) close to conditions of phase inversion, coalescence becomes more prevalent and the drop size increases with time with stable multiple emulsions forming as a result.     

Naturally occurring spore particles at planar fluid interfaces and in emulsions

We have investigated the potential of utilizing naturally occurring spore particles of Lycopodium clavatum as sole emulsifiers of oil and water mixtures. The preferred emulsions, prepared from either oil-borne or aqueous-borne dispersions of the monodispersed particles of diameter 30 microm, are oil-in-water. The particles act as efficient stabilizers for oils of different polarity. Droplets as large as several millimeters are stable to coalescence indefinitely, despite the low coverage of interfaces by particles observed microscopically. Consistent with the emulsion findings, we discover that particles spontaneously adsorb to bare oil-water interfaces of single drops from oil dispersions, whereas adsorption is less spontaneous and extensive from aqueous dispersions. Monolayers of the spore particles at both air-water and oil-water planar interfaces contain particles in an aggregated state forming clusters and chains. The influence of particle concentration, oil/water ratio, and additives in the aqueous phase is studied.     

NMR-assisted computational studies of peptidomimetic inhibitors bound in the hydrophobic pocket of HIV-1 glycoprotein 41

Due to the inherently flexible nature of a protein–protein interaction surface, it is difficult both to inhibit the association with a small molecule, and to predict how it might bind to the surface. In this study, we have examined small molecules that mediate the interaction between a WWI motif on the C-helix of HIV-1 glycoprotein-41 (gp41) and a deep hydrophobic pocket contained in the interior N-helical trimer. Association between these two components of gp41 leads to virus–cell and cell–cell fusion, which could be abrogated in the presence of an inhibitor that binds tightly in the pocket. We have studied a comprehensive combinatorial library of α-helical peptidomimetics, and found that compounds with strongly hydrophobic side chains had the highest affinity. Computational docking studies produced multiple possible binding modes due to the flexibility of both the binding site and the peptidomimetic compounds. We applied a transferred paramagnetic relaxation enhancement experiment to two selected members of the library, and showed that addition of a few experimental constraints enabled definitive identification of unique binding poses. Computational docking results were extremely sensitive to side chain conformations, and slight variations could preclude observation of the experimentally validated poses. Different receptor structures were required for docking simulations to sample the correct pose for the two compounds. The study demonstrated the sensitivity of predicted poses to receptor structure and indicated the importance of experimental verification when docking to a malleable protein–protein interaction surface.     

SNR phase order k-space encoding (SPOKE)

A method of determining the phase-encode order for MR Fourier-encoded imaging is described, which provides an additional option for optimizing images from samples with signals that change during data acquisition. Examples are in hyperpolarized helium gas imaging of the lungs where polarization is lost with each RF pulse or the signal changes observed in rapid dynamic studies with T₁ or T₂* contrast agents when mixing is taking place. The method uses a single frequency-encoded projection in the proposed phase-encoding direction. The projection is subsequently sorted into signal-to-noise ratio (SNR) order. The indices of the sorted array are then used to create the phase-encode table to be used for the scan. This phase table is sorted in descending SNR order for signals that decrease during data acquisition and in ascending order for signals that increase during data acquisition. Simulations suggest that this technique can produce higher resolution than centric-ordered phase encoding at the expense of increased modulation (ghosting) artifact for dynamically changing signals. Initial practical implementation of the technique has been carried out on a dedicated 0.2-T Niche MR system, and the test object results agree well with simulations. Hyperpolarized 3-He lung images have also been acquired and postprocessed using the SNR phase order k-space encoding (SPOKE) methodology and show potential for improved imaging with high flip angles where polarization is rapidly lost. Applications may also be found for 3D volumetric acquisitions where two dimensions can be SPOKE encoded.     

Sterine

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Messungen von Aerosolen,die durch phtochemische Oxydation von Schwefeldioxid in Luft erzeugt wurden

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