Editors' Choice

Science  16 Dec 2005:
Vol. 310, Issue 5755, pp. 1743

    Nanotube Firefighters

    1. Marc S. Lavine

    When polymers are heated and reach the temperature at which they begin to decompose, bubbles often form beneath the surface because the boiling points of the degradation products are usually lower than the decomposition temperature of the parent polymer. The evolution of these bubbles prevents the formation of a solid layer of char, which would insulate the rest of the polymer from further heating. With the advent of restrictions on halogenated flame-retardant additives, nanoscale reinforcing materials, such as clay particles, have been investigated as alternatives.

    Kashiwagi et al. have found that carbon nanotubes and nanoparticles can also act both as reinforcing materials and as flame retardants, and in some cases can surpass the performance of nanoclay materials. Coaxing the asymmetric fibers into a continuous network structure is the key to reducing bubbling. At fixed loads under radiant heat, the best results were obtained using single-walled carbon nanotubes (SWNTs), which left a residue with an undulating surface but no deep cracks. In contrast, multiwalled carbon nanotubes (MWNTs) yielded only islands of protection, and neither carbon nanofibers (CNF) nor carbon black particles helped very much. Flame retardancy was found to correlate with rheology, because the best materials showed a gel-like response, which matches their ability to form networks. — MSL

    Nat. Mater. 4, 928 (2005).


    Building a Better Wacker

    1. Jake S. Yeston

    The Wacker oxidation is a well-established method for the conversion of olefins to aldehydes and ketones. The reaction involves activation of the olefin toward water addition by a palladium catalyst, followed by regeneration of the catalyst by oxygen. In general, however, the regeneration step cannot be accomplished directly, but instead requires a copper or quinone derivative to shuttle electrons between Pd and O2.

    Mitsudome et al. show that a judicious choice of solvent eliminates the need for the co-catalyst. Using PdCl2 in dimethylacetamide (DMA) solvent, they achieve efficient conversion of long-chain (up to C20) terminal olefins to the corresponding 2-ketones on treatment with water under O2 pressure. The catalyst tolerates hydroxyl and cyano groups and can be recycled several times after heptane extraction. Electrochemical studies suggest that DMA lowers the oxidation potential of the catalyst in its Pd(0) state, thereby promoting direct oxidation by O2. — JSY

    Angew. Chem. Int. Ed. 10.1002/anie.200502886 (2005).


    Frozen in Time

    1. Gilbert J. Chin

    Humans may be unique in being aware of their own mortality. In any case, being reminded that we are, in fact, mortal is apt to evoke feelings of anxiety and to call forth mechanisms for alleviating or managing our reactions to lives being extinguished. One such strategy is to seek reinforcement of one's worldview, which has the consequence of skewing our opinions of others (and others' actions) toward the extremes of good (in accord with one's views) and bad. Furthermore, these valuations may very well become fixed at their best or worst if the other person has died.

    Eylon and Allison provide evidence for the immutability of judgments in the form of two experiments in which subjects were assessed for the change in their valuations when a good person (fictitious in the first case, real in the second) was described as having behaved immorally and, conversely, when a bad person was reported as having acted meritoriously. They found that the decrement in positive ratings and the increase in negative ratings were both smaller when the persons in question were dead versus still alive, suggesting that our impressions of people, favorable or not, become resistant to change when they die. — GJC

    Pers. Soc. Psychol. Bull. 12, 1708 (2005).


    Awakening HIV

    1. Stephen J. Simpson

    One of the pressing issues in HIV research is understanding the mechanisms of viral latency, in which small numbers of memory CD4+ T cells harbor a transcriptionally silent form of the integrated provirus. Because this latent virus can be reactivated and because it exists in this dormant form within a long-lived population of lymphocytes, it represents a life-long reservoir. To overcome the in vivo paucity of latently infected memory cells, Williams et al. studied a human T cell line containing a single integrated provirus and found that RNA polymerase II did not bind to the proviral long terminal repeat (LTR) because of alterations in the chromatin structure that had been induced by the binding of the histone deacetylase enzyme HDAC1 to the LTR. Inhibition of HDAC1 or knockdown of NF-κB p50 (which recruits and complexes with HDAC1) were sufficient for the production of short nonproductive viral transcripts, and full viral transcription could be achieved by coexpressing the viral transactivating protein Tat. Establishing this mechanism in primary CD4+ T cells will be the next step in determining whether combinations of HDAC1 inhibition and Tat activation will prove viable as a means of overcoming latency in the clinic. — SJS

    EMBO J. 10.1038/sj.emboj.7600900 (2005).


    Pressure Under Pressure

    1. Paula A. Kiberstis

    Hypertension is an extremely common disorder that, left untreated, can lead to stroke, heart disease, and kidney failure. Individuals of African descent are at greater risk of developing high blood pressure than are those of European descent, and this may reflect adaptations to distinct environmental selection pressures experienced by ancestral populations. For example, ancient human populations living in hot humid climates where salt was scarce would likely have a physiology adapted to maximize salt retention (which would concomitantly increase blood vessel tone), but this selective pressure would be lost once populations moved to cooler regions.

    Young et al. present genetic data consistent with the hypothesis that differential susceptibility to hypertension among modern humans is due to climatic adaptation during the out-of-Africa expansion. Studying worldwide variation in five genes implicated in blood pressure regulation, they find that the prevalence of allelic variants that would increase heat adaptation (and hence hypertension susceptibility) is significantly greater in populations living at low latitudes or in hot wet climates than in those at high latitudes or cold dry climates. In addition, using data from an epidemiologic study of blood pressure in 52 different populations, they conclude that a major portion of the worldwide variation in blood pressure can be accounted for by latitude and a variant allele of GNB3, the beta-3 subunit of guanine nucleotide-binding protein. — PAK

    PLoS Genet. 10.1371/journal.pgen.0010082.eor (2005).


    Chiral Golden Rings

    1. Phil D. Szuromi

    The self-assembly of a large chiral aggregate with luminescent properties from achiral building blocks is reported by Yu et al., who have exploited aurophilic interactions between Au(I) atoms to drive assembly. Two equivalents of the Au(I) dimer, [Au2(dppm)Cl2] where dppm is the bridging bis(diphenylphosphino)methane ligand, bind to piperazine-1,4-dicarbodithiolate in anhydrous methanol; the thiol groups add a second bridging group to two gold dimers. This compound crystallizes as a tetramer in which the 16 gold atoms form a continuous loop: The two pairs of gold atoms from one monomer bind to the ends of a pair from an adjacent monomer, and two sets of bridging groups end up on each side of the loop. This interleaved cyclic assembly imparts chirality on the tetramer, which crystallizes with a 70% preference for one form in each sample prepared (but with essentially equal probability of either handedness for any given sample). The tetramer also displays intense green phosphorescence. — PDS

    J. Am. Chem. Soc. 10.1021/ja0565727.

  7. STKE

    Galanin Antagonists as Antidepressants

    1. L. Bryan Ray

    The neuropeptide galanin influences a broad range of processes in the central and peripheral nervous systems. Swanson et al. used two small molecules that selectively inhibit the Gal3 receptor subtype to help define the effects mediated through this receptor in behavioral studies of anxiety and depression in three rodent model systems. They compared the effects of the inhibitors to those of chlordiazepoxide (a benzodiazepine anxiolytic) and fluoxetine (an antidepressant). In several assays, including the social interaction test and the forced swim test, the Gal3 inhibitors showed acute and chronic antidepressant and anxiolytic effects equal to those of the control drugs, suggesting that Gal3-selective agonists may be useful therapeutics. — LBR

    Proc. Natl. Acad. Sci. U.S.A. 102, 17489 (2005).