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CARBON MONOXIDE BOOSTS GOLD CATALYSIS Carbon monoxide adsorbed on gold enhances the precious metal’s ability to catalyze oxidation of alcohols in an electrochemical cell, according to researchers at Leiden University, in the Netherlands (Nat. Chem., DOI: 10.1038/nchem.1221). CO is a classic example of a poison to many transition-metal catalysts because it typically binds strongly to metal active sites, denying access to reactant molecules. Not only does the study add to the growing list of catalytic transformations mediated by gold, long considered an inert material, but it also suggests “an unexpected and counterintuitive role for CO in electro-oxidation reactions, namely that of catalyst promoter,” says Marc T. M. Koper, who led the study. Paramaconi Rodriguez, Youngkook Kwon, and Koper found that for a gold electrode immersed in an aqueous alkaline solution, the minimum applied potential required to oxidize methanol (mainly to formaldehyde and formic acid) is significantly lower when CO is adsorbed on the gold than when it is absent. The team studied reactions of various alcohols and proposes that CO’s presence promotes binding of OH species, which catalyze a key hydrogen elimination step in alcohol oxidation.—MJ
The first-ever actinide nitrosyl complex has been synthesized, combining uranium, a bulky cyclopentadienyl ligand, and nitric oxide (J. Am. Chem. Soc., DOI: 10.1021/ja2096128). Lanthanide and actinide complexes are known to bind small molecules that are electronically similar to NO•, but previous attempts to form nitrosyl complexes with lanthanides and actinides produced bimetallic oxide compounds. A group led by William J. Evans and Filipp Furche of the University of California, Irvine, and Jeffrey R. Long of UC Berkeley used a uranium compound with three polyalkylcyclo[C5(CH3)4H]3UNO, pentadienyl ligands that they thought would sterishown with carbon in gray, uranium in cally block formation of bimetallic species. Reacting pink, nitrogen in blue, [C5(CH3)4H]3U with NO•, they succeeded in forming and oxygen in red. [C5(CH3)4H]3UNO. They analyzed the product using spectroscopy, magnetic susceptibility, X-ray crystallography, and density functional calculations and found that, electronically, the complex contains U4+ bound to NO– as –U–N=O in a linear geometry. That combination of electronic structure and geometry is unusual, because other linear nitrosyl complexes are formally NO+. The complex demonstrates that actinides can bind and activate small molecules in ways that aren’t observed for transition metals, Evans says.—JK
the catalyst performs three essential roles: substrate binding; nucleophilic delivery of methoxide to form a stabilized version of a tetrahedral intermediate, which would CATALYST PROMOTES otherwise be an unobservable high-energy intermediate; and palladium assistance (via ACYL TRANSFER transient association with nitrogen) for THREE WAYS departure of an amide leaving group, usually the most difficult step in amide or thioamide Computation and experiment have been hydrolysis reactions. “The demonstration of used to design a catalytic process with a this multifaceted catalytic role suggests how three-part mechanism that makes a metalbiological catalysts might operate in promotpromoted acyl transfer reaction occur 108 ing these sorts of difficult reactions,” Brown times faster than the uncatalyzed reaction. says. Brown, Mosey, and coworkNicholas J. Mosey, R. Stan Brown, ers are currently studying the paland coworkers at Queen’s UniPalladacycle catalyst accelerates ladacycle-catalyzed reactions of versity, in Kingston, Ontario, methanolysis by different thioamides, evaluating developed the unusual catalyst, binding substrate, solvent effects and performing a palladacycle, to promote the delivering methanolysis of a thioamide (J. methoxide to it, and theoretical simulations to better Am. Chem. Soc., DOI: 10.1021/ aiding departure of understand the reaction’s large rate acceleration.—SB ja209605r). They report that a leaving group. S
H3C H3C
N
Pd
CH3O
OCH3 H
Ph NRR´ Thioamide CH3OH
H3C H3C
N
Pd
CH3O
S Ph
NRR´
Ph = phenyl, R and R´ = functional groups
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ENGINEERED LIPASE CUTS OUT TRANS FATS
Biochemists led by Uwe T. Bornscheuer of Germany’s University of Greifswald have engineered the first enzyme capable of selectively hydrolyzing unhealthy fatty acids from triglycerides in partially hydrogenated vegetable oils. The development could lead to a new industrial food process. In 1901, German chemist Wilhelm Normann invented the catalytic process for hydrogenating double bonds in the fatty acid chains of vegetable oils. Modifying the oils helps prevent them from turning rancid and raises their melting points so they can be handled as solids. But there was an unforeseen catch: Trans fatty acids, a by-product of the hydrogenation process, are now known to be a risk factor for heart disease, obesity, and other health problems. Food processors have responded by chemically rePalladacycle, formulating their HNRR´, and products to reduce S CH OH H3C 3 trans fat content. In N Pd S H3C Ph OCH3 a different approach, R´RN CH3 Bornscheuer’s team Ph created a variant
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URANIUM NITROSYL COMPLEX REVEALED
of a fat-cleaving lipase, originating from the yeast Candida antarctica, and expressed it in Escherichia coli using a new protein-engineering strategy combined with high-throughput enzyme screening (Angew. Chem. Int. Ed., DOI: 10.1002/ anie.201106126). The variant selectively hydrolyzes trans and fully saturated fatty acid chains; the cleaved unhealthy fatty acids can be separated from the remaining mono- and diglycerides in the vegetable oil.—SR
body (ACS Nano, DOI: 10.1021/ nn203430m). The new material, designed by Stanford University’s Richard N. Zare and colleagues, is based on conductive-polymer nanoparticles loaded with drugs. When exposed to a weak electric field, which can easily be generated by a AA battery, Immune cells can sneak between blood-vessel cells the charge on the polymer that have pulled apart from each other on stiff changes, causing the material tissue scaffolding. The enzyme ROCK regulates cell to release the drugs. Zare and contraction via proteins such as actin. his team hold the particles in TAGGING SULFENIC place by suspending them in a temperature-sensitive material that is liqsue by about 2 µm. Whether ROCK itself ACIDS uid at room temperature and turns into a is the best target for future therapeutics gel at body temperature. Preliminary tests rather than other molecules further By tweaking a chemical probe, chemists showed that they could control the dosage downstream in the ROCK signaling pathhave learned that a protein modification and timing of the drug release by varying way remains to be seen, comments biocalled sulfenylation influences signaling the strength and duration of the applied logical engineer Douglas A. Lauffenburger in the epidermal growth factor receptor field. They also injected nanoparticles of MIT, but the results of this study are (EGFR), a kinase enzyme implicated in loaded with a fluorescent dye under the “enticing.”—LKW multiple cancers (Nat. Chem. Biol., DOI: skin of mice and watched the dye spread 10.1038/nchembio.736). Sulfenylation, through the animals’ sides after a short or formation of sulfenic acid (–SOH) MAKING ZEOLITES electrical pulse. The Stanford group is groups, can occur if a cysteine amino acid now studying controlled drug dosages in is exposed to an oxidant such as hydrogen WITHOUT TEMPLATES animals with support from the drug comperoxide. Tracking occurrences of the repany Sanofi.—JNC A template-free synthesis procedure can be action and determining their implications used to prepare zeolites if the earliest stagin living cells remain challenging because es of the crystallization process are carefulestablished probes lack sensitivity or cell HARDENED ARTERIES ly controlled, according to work reported permeability. To make their latest probe, in Science (DOI: 10.1126/science.1214798). Kate S. Carroll of Scripps Florida and coHAVE LEAKY TISSUE Zeolites are a class of porous crystalline workers replaced the azide in a previous Closing the gaps between cells that line aluminosilicates that are widely used as version with an alkyne. The probe turned patients’ arteries could be a new strategy catalysts in oil refining and petrochemical out to be sensitive enough to detect differto treat atherosclerosis, a condition that synthesis. Expensive organic compounds, ences in sulfenylation rates among various often leads to heart attacks and strokes such as the ether 18-crown-6, often serve proteins in human cells. The team showed (Sci. Transl. Med., DOI: 10.1126/ the crucial role of structure-directing that sulfenylation of scitranslmed.3002761). Increased agents (templates) in zeolite preparation a specific active-site O O permeability between arterial cells methods. Efforts to omit these costly cysteine in EGFR, allows cholesterol and immune compounds have until now met with Cys797, enhanced its cells to accumulate in blood-vessel little success. Svetlana Mintova of Caen kinase activity. That Sulfenylation probe walls, leading to dangerous plaque University, in France, together with cocysteine is the target formation. Using fluorescent dyes, workers based in Malaysia and Germany, of several covalent engineered tissue, and aortas from mice, find that by fine-tuning the reactant radrugs under development, but the drugs Cynthia A. Reinhart-King and coworktios, nucleation temperatures and times, are designed to latch onto the cysteine in ers at Cornell University showed that and heating procedures (conventional its thiol form. This development raises hardened arteries—those with stiff tissue and microwave-driven), they can grow interesting questions about how to design scaffolding—cause cells embedded within crystals of a zeolite known as EMT from irreversible inhibitors that target amino them to increase their contractile forces a Na2O–Al2O3–SiO2–H2O precursor sysacids subject to redox modifications such and pull apart from one another. To pretem without using templates. The team as sulfenylation, Carroll says.—CD vent this cell contraction, the researchreports that their low-temperature proers focused on rho-associated kinase cedure (30 °C) yields ultrasmall and pure SMART DRUGS (ROCK), an enzyme that helps regulate EMT zeolite crystals with diameters in the cell forces and movement via struc6- to 15-nm range. And because the crysGET ZAPPED tural proteins such as actin. By inhibiting tals are made without templates, the highA gel that can be injected under the skin ROCK with the small molecule Y-27632, temperature treatment typically used to releases drugs when stimulated by a weak Reinhart-King’s group decreased the averremove the templates is unnecessary, they electric field applied from outside the age cell-cell gap in hardened synthetic tisnote.—MJ WWW.CEN-ONLINE.ORG
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