Editors' Choice

Science  03 Jun 2005:
Vol. 308, Issue 5727, pp. 1379

    Urban Air Quality

    1. H. Jesse Smith

    The oxidation of volatile organic compounds (VOCs) is an important step in the formation of photochemical smog in urban areas, but the rate at which VOCs are oxidized has been difficult to quantify. A reliable way to measure this rate would lead to improved prediction of smoke/fog events.

    Volkamer et al. used differential optical absorption spectroscopy (DOAS) to make direct measurements of atmospheric glyoxal concentrations over Mexico City in the spring of 2003. They show that VOC oxidation, of which glyoxal is a product, begins about an hour after sunrise and continues throughout the day. These observations allow a lower limit to be placed on the rate of VOC oxidation and reveal that VOC chemistry is active throughout sunlit hours. On the basis of these results, satellite measurements of glyoxal appear to be feasible, which would support the identification of photochemical hot spots in the atmosphere. — HJS

    Geophys. Res. Lett. 32, 10.1029/2005GL022616 (2005).


    Weeding Out Osteoclasts

    1. Paula A. Kiberstis

    More than half of individuals age 50 and older are at risk for osteoporosis, a disorder characterized by low bone mass. One of the principal cell types regulating skeletal growth and integrity is the osteoclast, which functions to resorb bone. Several drugs currently in clinical use for osteoporosis, such as the bisphosphonates, act by inhibiting osteoclast activity.

    A surprising new molecular player in bone growth and remodeling is identified by Idris et al., who find that mutant mice deficient in cannabinoid type 1 (CB1) receptors have increased bone mass that appears to be caused by aberrant apoptosis (cell death) of osteoclasts. Moreover, mutant female mice were protected against bone loss induced by ovary removal, which is a model of postmenopausal bone loss in women, and this protective effect could be reproduced pharmacologically in wild-type mice by the administration of cannabinoid antagonists. Thus, osteoporosis joins a growing list of human disorders, including obesity and nicotine dependence, that may be treatable by drugs targeting the cannabinoid receptors, a class of proteins originally discovered as the binding sites for the major psychoactive ingredient of marijuana. — PAK

    Nat. Med. 10.1038/nm1255 (2005).


    Recovered on Tape

    1. Jake S. Yeston

    A central challenge in homogeneous catalysis is achieving facile separation and recovery of the catalyst once the reaction is over. An increasingly common solution is to append fluorocarbon chains to the catalyst. Because fluorocarbons are poorly miscible with most organic solvents, this modification makes it possible to remove the catalyst by extraction into a fluorous solvent or, in some cases, simply by cooling the reaction mixture to induce precipitation. However, both of these methods can be inefficient at low catalyst loadings.

    Dinh and Gladysz show that a rhodium catalyst for hydrosilylation of ketones can be recovered efficiently and easily using Teflon tape. The catalyst, bearing three fluoroalkylphosphine ligands, was dissolved with the reagents in dibutyl ether at 55°C, with a strip of tape added to the flask. Upon cooling, the orange catalyst stuck to the tape (and not to the stir bar!) and could be recycled two more times by heating in a fresh reaction mixture. — JSY

    Angew.Chem. Int. Ed. 10.1002/anie.200500237 (2005).


    Complex Cellularization

    1. Stella M. Hurtley

    Early insect development involves multiple nuclear divisions within a single cytoplasm to form syncytial embryos. The syncytium is divided into separate cells (each with a single nucleus) in a process termed cellularization, which involves the generation of membrane furrows between adjacent nuclei and produces a polarized cortical cell layer. The formation of the cleavage furrow requires concerted delivery (from the Golgi complex) of membrane components to the growing furrow. This delivery increases the cell surface area by 20-fold and is directed by the microtubule network. Papoulas et al. followed the apically directed movement of Golgi complexes toward the sites of furrow formation, which depended on the activity of the microtubule-based molecular motor dynein. The Golgi membranes themselves interacted with dynein and other motility factors via a peripheral Golgi membrane protein of the golgin family, Lava lamp. These interactions were disrupted and cellularization blocked when domains from the Lava lamp protein that bound to dynein or the motility factors were injected into living embryos. — SMH

    Nat. Cell Biol. 10.1038/ncb1264 (2005).


    Is That Your Final Answer?

    1. Gilbert J. Chin

    Taking a multiple-choice test or patronizing a crowded supermarket, we may find ourselves in a predicament, after having made a selection, in deciding whether to stick with it or to switch. The widespread belief is that it's better to stay put rather than moving to another, apparently faster-moving, checkout line. Similarly, on a test, college students believe that the first choice is more likely to be correct.

    Using more than 2000 exams from 2 years of an undergraduate psychology course, Kruger et al. show that switching (detected as erasures) from an incorrect to a correct answer occurred twice as often as the converse, which is consistent with decades of empirical studies. Why then do we prefer to stay with our first choices? A series of follow-up experiments revealed that students became more frustrated after learning that they'd switched to a wrong answer as opposed to alighting on it at the start and that, as a consequence, the former instances were more memorable than the latter even though the outcomes (an incorrect choice) were precisely the same. In other words, the negative emotion engendered by having given up on the right choice weights the encoding/retrieval of memories so as to convince us of what the authors term the first instinct fallacy. — GJC

    J. Pers. Soc. Psychol. 88, 725 (2005).


    Cleaning Up CO

    1. Phillip D. Szuromi

    For use in fuel cells, hydrogen (H2) can be produced by reacting alcohols or hydrocarbons with steam or oxygen, yielding byproducts that include CO and CO2. Although CO can be removed or converted through the water-gas-shift reaction to CO2 and additional H2, even small amounts of residual CO inhibit reactions at the Pt anode of polymer electrolyte fuel cells (PEFCs). Onboard H2 production would likely need to remove CO in the presence of its oxidation product, CO2, and to do so without oxidizing the H2 to water. Landon et al. report the selective oxidation of CO to CO2 in the presence of H2, water vapor, and CO2 at 80C, which is below the operating temperature of PEFCs, with a single-stage reactor. They report that a gold catalyst on an Fe2O3 support, prepared in a two-step heating process up to 550C, created a catalyst with high CO oxidation activity but no H2 oxidation activity under typical PEFC conditions. — PDS

    Chem. Commun. 10.1039/b505295p (2005).

  7. STKE

    Geometry of Calcium Signaling

    1. Elizabeth M. Adler

    Changes in intracellular calcium concentration ([Ca2+]i) that occur after Ca2+ influx through N-methyl-D-aspartate-type glutamate receptors (NMDARs) play a key role in long-term plastic changes in postsynaptic function that are thought to underlie learning and memory. For most excitatory synapses in the central nervous system, the postsynaptic partners are dendritic spines: small protrusions on the dendritic shaft that have the effect of localizing changes in [Ca2+]i to individual synapses (as opposed to the entire dendrite).

    Noguchi et al. used two-photon photolysis of caged glutamate and two-photon Ca2+ imaging to release transmitter onto single spines of rat hippocampal neurons and to assess quantitatively the influence of spine structure on [Ca2+]i. NMDAR-dependent current increased with spine head volume. On the other hand, NMDAR-mediated increases in the [Ca2+]i at the spine head were larger in small mushroom-shaped spines, whereas increases in dendritic shaft [Ca2+]i at the base of the spine were greater for large stubby spines. These differences were dictated by the geometry of the spine neck. The stubby spine morphology favored a rapid diffusion (an energetically downhill process) of Ca2+ from the spine head through the neck into the dendritic shaft, whereas in small spines, the lower conductance of the thin necks means that clearance of calcium from the head relies in part on the energetically uphill and slower process of calcium extrusion. The authors conclude that these differences in Ca2+ handling enable the preferential induction of long-term potentiation, which depends on changes in [Ca2+]i, in smaller spines. — EMA

    Neuron 46, 609 (2005).

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