Phospholipid-coated colloidal magnetic nanoparticles with mean magnetite core size of 8 nm are shown to be effective ion exchange media for the recovery and separation of proteins from protein mixtures. These particles have high adsorptive capacities (up to 1200 mg protein/mL adsorbent, an order of magnitude larger than the best commercially available adsorbents) and exhibit none of the diffusional resistances offered by conventional porous ion exchange media. Protein-laden particles are readily recovered from the feed solution using high-gradient magnetic filtration.

Oxygen-transfer enhancement has been observed in the presence of colloidal dispersions of magnetite (Fe3O4) nanoparticles coated with oleic acid and a polymerizable surfactant. These fluids improve gas−liquid oxygen mass transfer up to 6-fold (600%) at nanoparticle volume fractions below 1% in an agitated, sparged reactor and show remarkable stability in high-ionic strength media over a wide pH range. Through a combination of experiments using physical and chemical methods to characterize mass transfer, it is shown that (i) both the mass transfer coefficient (k L) and the gas−liquid interfacial area (a) are enhanced in the presence of nanoparticles, the latter accounting for a large fraction of the total enhancement (80% or more), (ii) the enhancement in k L measured by physical and chemical methods is similar and ranges from 20 to 60% approximately, (iii) the enhancement in k L levels off at a nanoparticle volume fraction of approximately 1% v/v, and (iv) the enhancement in k L a shows a strong temperature dependence. These results are relevant to a wide range of processes limited by the mass transfer of a solute between a gas phase and a liquid phase, such as fermentation, waste treatment, and hydrogenation reactions.

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The structure of single wall peptide nanotubes is presented for the model surfactant-like peptide A(6)K. Capillary flow alignment of a sample in the nematic phase at high concentration in water leads to oriented X-ray diffraction patterns. Analysis of these, accompanied by molecular dynamics simulations, suggests the favourable self-assembly of antiparallel peptide dimers into beta-sheet ribbons that wrap helically to form the nanotube wall.

The self-assembly of the trifluoroacetate salt of the short peptide (ala)6-lys (A6K) in water has been investigated by cryo-transmission electron microscopy and small-angle X-ray scattering. For concentrations below ca. 12%, the peptide does not self-assemble but forms a molecularly dispersed solution. Above this critical concentration, however, A6K self-assembles into several-micrometer-long hollow nanotubes with a monodisperse cross-sectional radius of 26 nm. Because the peptides carry a positive charge, the nanotubes are charge-stabilized. Because of the very large aspect ratio, the tubes form an ordered phase that presumably is nematic.