SCIENCE & TECHNOLOGY
CONCENTRATES Express spacecraft, which orbits the planet [Science, 307, 566 (2005)}. On the day side of Mars, extreme ultraviolet light from the sun breaks down N 2 , The high-resolution crystal structure (shown) of human cytidine deaminase (CDA) with a bound potent inhibitor (gold) has 0 2 , andC0 2 into N and O. The been determined for the first time by Gregory L. Verdine and atoms then migrate to the night coworkers at Harvard University $ Med. Q side of the planet, I where they combine Chem., 48,658 (2005)}. CDA plays an | toformNQTheNO essential catalytic role in a key cytidine | glow is particularly and deoxycytidine breakdown pathway £ bright in the winter It also breaks down nucleoside-type an| night at Mars's south ticancer and antiviral agents (such as | pole, where the atgemcitabine and cytarabine), shortening £ mosphere is transthe drugs' duration ofaction and somela ported downward; as times inducing unpleasant side effects. i much as 30% of the Researchers have thus been trying to ° atmosphere freezes design inhibitors of CDA as therapeuat the surface. tic additives, but theyVe been hampered by insufficient structural data on the enzyme. Now,\erdine's structure reveals that several moderate inhibitors bind CDA by coordinating to its zinc ion but that a strong inhibitor binds differendy The strong inhibitor doesn't bind zinc and makes up for this lack of metal coordination by participating in a jtAt edge-to-face interaction instead. The findings could aid in the design of CDA inU 3 hibitors that enhance the efficacy of CDA-sensitive drugs. The first peek at the structure of a membrane-spanning lar ethylene oxide chain sub- metalloenzyme capable ofconstituents mixed in 2-propanol. verting methane into methanol These molecules align parallel to has beenprovided by crystallogone another to form spherical raphers at Northwestern Uniaggregates. The researchers use versity Amy C. Rosenzweig and electron microscopy to observe Raquel L. Lieberman have Three decades ago, it was predicted that magnetic fields the nanocapsules slowly flatten solved a 2.8-A-resolution struccould be used to deform spher- as the molecules realign in a ture of particulate methane ical phospholipid bilayer vesi- magneticfieldofup to 20 teslas. monooxygenase (pMMO), the cles into elongated shapes, but Magnetic manipulation of the dominant methane-oxidation this anticipated deformation nanocapsules might be used to enzyme in methane-consumhasn't been experimentally ob- encapsulate or release guest ing bacteria [Nature, published online Jan. 26, http://dx.doi. served until now. Peter C. M. species for many applications. org/10.1038/nature03311].They Christianen of Radboud Unishow that the enzyme is made versity Nijmegen and Albertus up ofthree monomers that clusP. H. J. Schenning of Eindhoter to form a membrane-spanven University of Technology, ningbarrel. Each monomer conboth in the Netherlands, and colleagues report that thio- An international team of sci- tains two metal centers in its phene-based nanocapsules can entists has detected a night- soluble region (one, a single copbe deformed into flattened glowing blanket of nitric oxide per ion and the other, a pair of spheres in a magneticfieldand surrounding Mars that could copper ions) and a third (a sinthat the flattened shape can be be used to track circulation in gle metal ion of yet-to-be-conretained when the nanocap- the martian atmosphere. Jean- firmed identity in vivo) within sules are removed from the Loup Bertaux at the Service its membrane-spanning region. magneticfieldif they are fixed d'Aeronomie du Centre Na- They are now trying to figure in an organogel matrix [J. Am. tional de la Recherche Scienti- out which ofthese centers is catChem. Soc, 127,1112 (2005)}. fique, in France, and coworkers alytic and where the electrons The team makes the nanocap- recorded the ultraviolet glow needed to oxidize CH 4 come sules from a nonpolar sexithio- with a spectrometer aboard the from. This information may phene oligomer containing po- European Space Agency's Mars facilitate the development of
Structure of drug-breakdown enzyme is determined
A peek at how nature turns CY\ into CH 0H
Magnet deforms self-assembled nanocapsules
Martian NO glows at night
HTTP://WWW.CEN-ONLINE.ORG
synthetic catalysts capable of converting CH 4 into CH3OH, Rosenzweig says. Such catalysts might make natural gas a realistic alternative to petroleum for the synthesis ofuseful fuels and chemicals, she suggests.
Bowl-shaped aromatic anion A convex, nitrogen-containing aromatic polycycle has been prepared and characterized by chemists Mark Mascal andjordi Ceron Bertran at the University of California, Davis [J.Am. Chem. Soc, 121,\2>S2 (2005)}. This new aromatic heterocycle, called the azaacepentalenide anion (shown, N is blue), is derived from oxidation of 10-azatriquinacene, a hemispherical N-containing tricycle. "The synthesis of [the new} molecule opens up lots of questions about TT system reactivity and metal binding," among others, comments Jay S. Siegel of the University of
Zurich. Other scientists have predicted the aromaticity ofthe azaacepentalenide anion from theoretical calculations. The UC Davis work comes in the wake of another group's earlier synthesis of the acepentalene dianion, which is an aromatic bowl-shaped fragment of C20 fullerene and is the hydrocarbon analog of the new anion. Spectroscopic and other measurements indicate that the aromaticity of the anion forces the fused framework to become much less bowl-shaped than fused triquinacenes prefer to be. C&EN
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