Editors' Choice

Science  24 Oct 2003:
Vol. 302, Issue 5645, pp. 535

    Trapping Radicals

    A variety of oxy-and peroxy radicals (RO and ROO) are known, but among the trioxy radicals, only HOOO and FOOO have been characterized. Nevertheless, higher trioxy species have been suggested to be important participants in atmospheric chemistry. The CF3OOO radical in particular is thought to play a role in ozone depletion, and von Ahsen et al. have now formed and isolated this species. The products of the flash thermolysis of the peroxy species CF3OC(O)OOCF3 in excess oxygen were trapped in a cold matrix. Analysis of infrared and ultraviolet spectra differentiated the product from CF3O, which is produced in the absence of oxygen; upon intense irradiation, the formation of COF2 and FOO as products confirmed that a trioxy species had been generated initially. The formation of CF3OOO has implications for the reactions of CF3O radicals and may bolster claims for the involvement of ClOOO radicals in ozone loss chemistry. — PDS

    Angew. Chem. Int. Ed. 42, 4690 (2003).


    Well-Preserved Brines

    Sedimentary basins are geological depressions in which sediments have accumulated, and in which most of the world's petroleum reserves are found. The deepest parts of many Phanerozoic sedimentary basins, such as the Gulf of Mexico and the North Sea, are saturated with brines rich in Ca, poor in SO4, and of uncertain origin. One popular theory about how these brines formed is that ancient seawater, first concentrated by evaporation, reacted in a complicated fashion with the surrounding rocks, losing MgSO4 and gaining CaCl2 in the process. This scenario is based on the assumption that the chemical composition of Phanerozoic seawater was like that of modern seawater.

    Lowenstein et al. challenge this theory by suggesting that the chemistry of Phanerozoic brines reflects the composition of the seawater from which they formed, thereby eliminating the necessity of invoking a series of unlikely chemical transformations, as well as avoiding associated mass balance problems. They base this conclusion on data that show that the oceans have alternated between MgSO4-rich and CaCl2-rich compositions over the past 550 million years, and they discuss their proposal in the context of brines in the Illinois basin. — HJS

    Geology 31, 857 (2003).


    A Dead-End Shortcut

    Flagella and cilia project from the cell surface. They can provide a means of propulsion for single cells, and they are an integral component of the signaling apparatus in some sensory organs. The prototypical structure of the flagellum is conserved from unicellular organisms through to higher mammals.

    Kohl et al. have examined the contribution of the flagellum to cellular architecture in the protozoan parasite Trypanosoma brucei. Using RNA interference, they blocked the production of proteins required for intraflagellar transport—a critical step in flagellum assembly. During the early stages of gene silencing, before assembly had been completely abolished, they noticed that cells with short flagella were correspondingly shorter than their sisters who had full-length flagella. This unexpected observation suggests that the flagellum is involved in sensing the size of the cell and in promoting cytokinesis—the separation of daughter cells after mitosis. It appears that the tip of the flagellum, which sits on the cell surface, defines the site of cleavage during cytokinesis, probably by virtue of its connections to the cytoskeleton. Hence, cells completely devoid of flagella and the intracellular flagellum attachment zone (FAZ) cannot divide. — SMH

    EMBO J. 22, 5336 (2003).


    Graphite Yields to Force

    Crystalline graphite serves as a calibration standard for scanning tunneling microscopy (STM), but the images show only every other atom (the β atoms) in the graphite lattice. In contrast, atomic force microscopy (AFM) should, in principle, be able to image all atoms (α and β), yet AFM measurements of attractive forces yield the same incomplete images as STM. Efforts to measure repulsive forces have not been successful because the instrument sensitivity is too low.

    Hembacher et al. show that an AFM with enhanced sensitivity to short-range forces can image all of the carbon atoms on a graphite surface. Their instrument can measure tunneling current and force at the same time, and thus serves as both an STM and an AFM. Although the STM image shows only a trigonal lattice, the AFM image reveals the hexagonal carbon rings of the graphite lattice in their entirety. In the AFM images, the forces are different for atoms that lie directly above atoms in the layer underneath than for atoms that are above hollow sites; only the latter atoms are visible to the STM. This instrument may be useful in imaging other soft surfaces at atomic resolution. — JFU

    Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.2134173100 (2003).


    Washing with Detergents

    Reversible inhibition of enzymes is most often achieved via the design of small molecules that bind noncovalently and specifically as in the targeting of cyclooxygenase by nonsteroidal antiinflammatory drugs. Fischer et al. have pursued the use of nanoparticles consisting of a 2-nm gold core covered by anionic alkane chains attached by a sulfhydryl linkage. These particles inhibit chymotrypsin, apparently by glomming on to cationic residues around the active site, and are able to bind and perturb the native structures of several molecules of chymotrypsin with little effect on other enzymes such as elastase and β-galactosidase. The authors show that this inhibitory interaction can be readily reversed by adding cationic alkyl surfactants, which release the reactivated and refolded chymotrypsin into solution. — GJC

    Proc. Natl. Acad. Sci. U.S.A. 99, 5018 (2002); J. Am. Chem. Soc. 10.1021/ja0352505 (2003).


    Sinking Whales

    We tend to think that if only we stop human depredations on a wild animal population, it will then recover. A longer-term analysis by Springer et al. suggests the reverse.

    These authors have traced the knock-on effects of industrial whaling since the 1940s in the North Pacific Ocean. They suggest that with the demise of the great whales, killer whales shifted their attentions to smaller sea mammals. A similar phenomenon seems to have occurred in the Southern Ocean, which was once home to vast whale populations. This “top down” effect, rather than the “bottom up” effect of a decrease in prey for the smaller mammal species, may explain the sudden decline in Steller sea lion populations, as well as those of several other seals and of sea otters, in the North Pacific since the 1980s. An added complication is that as whale populations increase, they are checked as they again become vulnerable to the adaptable killer whales. It seems that even if human beings cease implementing techniques for industrial-scale slaughter in the oceans, the disturbances to long-established ecosystems may be irreversible. — CA

    Proc. Natl. Acad. Sci. U.S.A. 100, 12223 (2003).


    Taking a Quick Vote Under Pressure

    When making decisions, individual animals face a tradeoff between speed and accuracy (or between reaction time and error rate). When time is limited—for instance, when environmental conditions are adverse—the accuracy of decisions may be compromised.

    Franks et al. investigated whether such tradeoffs exist when decision-making involves many individuals. Their experimental subject is an ant species, Leptothorax albipennis, which uses “quorum sensing” when choosing a new nest site: Once a certain threshold number of individual ants gather at a potential new nest site, there is an acceleration in the recruitment of the remaining colony members. Under harsh conditions such as wind, the househunting ants choose a new site more rapidly, by lowering the quorum threshold needed for site selection. In these circumstances, where fewer individuals are effectively making the decision, the ants are more prone to choose inferior sites even when aware of the presence of better sites. Under benign conditions, the quorum threshold is raised, and the ants take their time. — AMS

    Proc R. Soc. London Ser. B 10.1098/rspb.2003.2527 (2003).