Editors' Choice

Science  27 Oct 2006:
Vol. 314, Issue 5799, pp. 566

    Tuning Toroids

    1. Phil D. Szuromi

    Amphiphilic molecules with rigid-rod cores can form structures such as tubules, ribbons, and vesicles in aqueous solution. These processes are driven largely by the burial of hydrophobic groups, but the final structures often depend on a balance of energetic and entropic effects.

    Kim et al. have explored structures formed by dumbbell-shaped molecules with an aromatic core and distinct dendrimeric capping groups: on one end a hydrophilic oligoether and on the other a hydrophobic cluster of three alkyl chains, all either 6, 10, or 14 carbons in length. Transmission electron microscopy images show that these molecular building blocks form micelles. In particular, the hexyl-capped dumbbells form spheres and short cylinders, whereas those bearing decyl chains initially form curved cylinders that close to form toroids, a morphology that further isolates the hydrophobic cores. The compound capped by longer tetradecyl chains forms wider and more extended cylinders, a result that the authors attribute to a decrease in interfacial curvature relative to the decyl-capped species. — PDS

    J. Am. Chem. Soc. 128, 10.1021/ja065487b (2006).


    Visualizing the Casimir Force

    1. Ian S. Osborne

    When two perfectly conducting plates are brought close together, fluctuations in the vacuum field give rise to a difference in electromagnetic modes within the gap (which are limited to integral wavelength multiples equal to the gap width) and those outside the plates (which span an essentially infinite range). The resulting pressure difference thereby forces the two plates together. This quantum mechanical effect, termed the Casimir force, is of fundamental interest in its own right, but it is also becoming an important concern in micro- and nanoelectromechanical devices as a limiting factor in their operation.

    Experiments to gauge this effect have generally been limited to fairly simple geometries and materials. Petrov et al. present an optical technique based on dynamic holographic interferometry. Deformation of a reflective pellicle due to Casimir force variations, induced by the back-and-forth motion of an opposing aluminum-coated lens, is detected as a shift in the phase and diffraction pattern of an output hologram. The setup relies on two-wave mixing of interfering light beams in a photorefractive cobalt-doped barium titanate crystal. Because this technique is sensitive and quite general, it should be useful for studying realistic device considerations, as well as exploring the effects of dielectric properties and conductivity. — ISO

    Opt. Lett. 31, 3167 (2006).


    Pushing Polymers Around

    1. Marc S. Lavine

    Block copolymers self-assemble into intricately patterned structures because of the tendency for the chemically distinct blocks to segregate. Patterns can be tuned by changing the lengths and interactive properties of the two polymer segments or by adding another component to the mix.

    Laiho et al. explore the effects of adding fullerene (C60) molecules to a diblock copolymer of polystyrene (PS) and poly(4-vinylpyridine) (P4VP) dissolved in xylene. At the chosen block lengths, the polymer alone formed a PS matrix containing hexagonally ordered P4VP cylinders. Initially, added C60 was sequestered in the PS domain, as observed in solution by optical spectroscopy. This localization was mirrored in the morphology of cast films as a reduced abundance of cylinders, indicating that the PS had been swollen by dissolution of C60. However, when the solutions were aged, they underwent the same purple-to-brown color change observed in aging pyridine solutions of C60, consistent with the formation of charge transfer complexes between C60 and the electron-donating pyridyl fragments of the P4VP domains. In films cast from these solutions, the P4VP morphology shifted from cylindrical to spherical. The authors suggest that charge transfer complexation is thus a potentially useful tool in designing self-assembled morphologies. — MSL

    Macromolecules 39, 10.1021/ma061165g (2006).


    Vector Protector

    1. Stephen J. Simpson

    As with other vector-borne parasitic diseases, there are two sites at which an immune response might disrupt the lifestyle of the protozoan parasite Plasmodium falciparum: in the final host or in its arthropod vector. Indeed, the mosquito is fully capable of generating a robust antiparasitic response against the motile Plasmodium ookinete, which invades the insect's midgut to establish itself as an oocyst.

    Frolet et al. reveal two pathways that contribute to the regulation of this response, presenting evidence that antiparasitic immunity is divided between two phases of parasite invasion. The pre-invasion stage is characterized by basal expression of two effectors: the complement-like thioester-containing protein 1 (TEP1) and leucine-rich repeat immune protein 1 (LRIM1), which increases in the ookinete invasion stage. The expression of both effectors could be inhibited by silencing the nuclear factor κB (NF-κB) family proteins Rel1 and Rel2, leading to an increase in parasite growth. Conversely, mosquito resistance increased upon inhibition of the IκB-related negative regulator Cactus, leading to high levels of parasite killing. This potent antiparasitic response within the mosquito vector—regulated by the balance between the negative effects of IκB/Cactus and the activation of two NF-κB/Rel transcription factors—could represent a target in the battle against malaria. — SJS

    Immunity 25, 10.1016/j.immuni.2006.08.019 (2006).


    Gilding Glucose

    1. Jake Yeston

    The relative inertness of gold has been long been valued for the manufacture of jewelry and other prized items that must resist oxidative tarnishing. Recently, however, homogeneous as well as nanometer-scale colloidal gold has proven increasingly useful in chemical catalysis. Comotti et al. explore the potential of gold particles supported on carbon to catalyze the aerobic oxidation of glucose to gluconic acid. Given the relative fragility of this highly functionalized substrate, industrial production of gluconic acid has relied on mild enzymatic methods. A comparison of two aqueous glucose oxidations—one catalyzed by a commercial enzyme preparation and the other by suspended Au/C—shows that under optimized conditions, the gold exhibits comparable activity to the enzymes, requiring only mild heating and vigorous stirring of a basic solution. — JSY

    J. Catal. 244, 122 (2006).


    Starved for Infection

    1. Paula A. Kiberstis

    About 600,000 people die each year from hepatitis B virus (HBV)-related liver disease or hepatocellular carcinoma. Recent vaccination programs have been highly effective in preventing new HBV infections, but millions of chronically infected individuals require treatment. Successful therapy development depends in part on identifying host factors in the liver essential for the HBV life cycle.

    Working with an HBV-luciferase construct in mice to track viral gene expression in real time, Shlomai et al. found that HBV transcription is tightly coupled to the nutritional state of the animals. Short-term starvation of the mice caused a robust induction of HBV expression that was completely reversible by re-feeding. This effect was dependent on peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a transcriptional regulatory protein that activates host metabolic genes expressed in response to starvation, including those involved in liver gluconeogenesis. The shared regulation of HBV genes and host metabolic genes suggests that the fluctuating nature of HBV infection may be due not only to mutational changes in the virus but also to changes in the host's nutritional state, a hypothesis offering new possibilities for therapy. — PAK

    Proc. Natl. Acad. Sci. U.S.A. 103, 16003 (2006)

  7. STKE

    Why a Diet Rich in Seafood is Healthy

    1. Nancy Gough

    Omega-3 fatty acids, which are found in marine organisms, have been associated with beneficial health effects. One mechanism for their anti-inflammatory effect is via competitive inhibition of the enzymatic activity of cyclooxygenase (COX), which is the rate-limiting step in the biosynthesis of prostaglandins. Massaro et al. report that exposure of vascular endothelial cells to the omega-3 fatty acid docosahexaenoate (DHA) for periods long enough for it to be incorporated into cellular membranes inhibits the activation of nuclear factor κB (NF-κB) and, subsequently, the expression of COX-2 and prostaglandin production in response to the proinflammatory signal interleukin-1α (IL-1α). Treatment of endothelial cells with DHA altered their responses to IL-1α by (i) decreasing the activation of extracellular-stimulated kinases 1 and 2, without changing the activation of p38 mitogen-activated protein kinase; (ii) decreasing reactive oxygen species production through inhibiting the membrane association of the p47phox subunit of NADPH oxidase, and (iii) decreasing the membrane association of protein kinase Cϵ (PKCϵ), but not PKCα or PKCζ. Thus, it appears that the benefits of omega-3 fatty acids may be due in part to their effects on membrane lipid composition, which reduces signaling in response to inflammatory stimuli. — NRG

    Proc. Natl. Acad. Sci. U.S.A. 103, 15184 (2006).