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Angewandte Chemie International Edition
Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Editor: Peter Gölitz, Deputy Editors: Neville Compton, Haymo Ross
Online ISSN: 1521-3773
Associated Title(s): Angewandte Chemie, Chemistry - A European Journal, Chemistry – An Asian Journal, Zeitschrift für Chemie
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| May 23, 2013 VIP: Structure of the Parallel Duplex of Poly(A) RNA: Evaluation of a 50-Year Old PredictionNozhat Safaee,* Anne M. Noronha, Dmitry Rodionov, Guennadi Kozlov, Christopher J. Wilds, George M. Sheldrick, and Kalle Gehring* Although the molecular structure of the double-stranded poly(rA) was predicted by Rich et al. in 1961, it has taken more than 50 years to confirm this prediction. The crystal structure of the parallel duplex of (rA)11 obtained at physiological pH, solved using ab initio direct methods, and refined to 1.0 Å resolution is reported. The geometry of purine rings suggests that the adenines are not protonated. Instead, supported by our thermal denaturation studies, bound ammonium ions are complexed by the adenines, stabilizing the duplex. The self-assembly of poly(rA) is a novel feature of an abundant nucleic acid motif. May 23, 2013 Hot Paper: BODIPY–Tetrazine Derivatives as Superbright Bioorthogonal Turn-on Probes
Jonathan C. T. Carlson, Labros G. Meimetis, Scott A. Hilderbrand, Ralph Weissleder* The fastest and the brightest: A new design that intimately connects tetrazine to a BODIPY fluorophore enables exceptionally efficient energy transfer and quenching. Upon reaction of the tetrazine, the brightness of the fluorophore increases more than a thousand-fold, which is a fluorogenic activation up to two orders of magnitude greater than previously described. Coming soon. May 22, 2013 Hot Paper: A Reactive Oxygen Species (ROS)-Responsive Polymer for Safe, Efficient, and Targeted Gene Delivery in Cancer Cells
Min Suk Shim, Younan Xia* Stimuli-responsive release: The high levels of reactive oxygen species (ROS) in prostate cancer cells can be exploited to trigger cancer-targeted gene delivery. A ROS-responsive thioketal-based cationic polymer was synthesized and functionalization with a cancer-targeting peptide led to selective and enhanced gene transfection in prostate cancer cells (see scheme). Coming soon. May 22, 2013 VIP: Combining NHC–Cu and Brønsted Base Catalysis: Enantioselective Allylic Substitution/Conjugate Addition with Alkynyl Aluminum Reagents and Their Stereospecific Isomerization to Trisubstituted AllenesJennifer A. Dabrowski, Fredrik Haeffner, and Amir H. Hoveyda* Catalytic enantioselective allylic substitution reactions that involve alkynyl nucleophiles and generate tertiary carbon stereogenic centers are presented for the first time. Transformations are promoted by a chiral N-heterocyclic carbine–Cu complex and require alkynyl aluminum reagents simply prepared in situ from an alkyne and di(iso)-butylaluminum hydride; products are obtained in up to >98 % yield, >98 % SN2′ selectivity and 98.5:1.5 enantiomeric ratio. The enantiomerically enriched skipped enynes are then converted to trisubstituted allenes with 15–100 mol % of a common amine base (dbu) typically with complete enantiospecificity. Mechanistic experiments and DFT calculations shed light on the mechanism of stereoselective alkyne-to-allene isomerization. Coming soon. May 21, 2013 VIP: Evidence for Low-Temperature Melting of Mercury Due To RelativityFlorent Calvo,* Elke Pahl, Michael Wormit, and Peter Schwerdtfeger* Among the many peculiarities of elemental metallic mercury, its liquid form at room temperature, and low melting temperature at -38.83 °C, has eluded fundamental understanding so far. Special relativity has been speculated as a possible cause for this unique state, but never was proven. Using Monte Carlo simulations, together with a diatomic-in-molecule method to simulate the many-body interactions in bulk mercury, was the key to solve this challenging problem. Relativistic and nonrelativistic calculations show that the melting temperature in bulk mercury is lowered by 105 °C due to relativistic effects. Thus, hypothetical nonrelativistic mercury remains solid under normal conditions. Coming soon. May 21, 2013 VIP: Graphene Oxide Nanoribbons from the Oxidative Opening of Carbon Nanotubes Retain Electrochemically Active Metallic ImpuritiesColin Hong An Wong, Chun Kiang Chua, Bahareh Khezri, Richard D. Webster, and Martin Pumera* Graphene nanoribbons are commonly synthesized using carbon nanotubes (CNTs) as a precursor through the oxidative opening of the nanotubes into elongated ribbons. However, CNTs contain significant amounts of metallic impurities even after purification. Herein, we show that these impurities persist at parts-per-billion levels after oxidative opening of CNTs to graphene oxide nanoribbons and heavily influence the electrochemical behavior of the resulting material. This may have negative impacts on the range and effectiveness of potential applications suitable for graphene materials. Coming soon. May 17, 2013 VIP: Organic Semiconductor Doping: Impact of Dopant Strength and Electronic CouplingHenry Méndez, Georg Heimel,* Andreas Opitz, Katrein Sauer, Patrick Barkowski, Martin Oehzelt, Junshi Soeda, Toshihiro Okamoto, Jun Takeya, Jean-Baptiste Arlin, Jean-Yves Balandier, Yves Geerts, Norbert Koch, and Ingo Salzmann* The standard model for molecular electrical p-doping of organic semiconductors (OSCs) assumes integer charge transfer between OSC and dopant. Here, it is contrasted to an alternative model based on intermolecular complex formation between OSC and dopant. Systematically varying the acceptor strength of prototypical dopants in a matrix of a solution processible OSC allowed discriminating the two models. Determining the actual structure of intermolecular complexes and correlating it with the optical and electronic properties of p-doped samples clearly favored the alternative model. Consequences for chemical design strategies of more efficient molecular dopants are deduced. Coming soon. May 17, 2013 Hot Paper: Single and Double N–H Bond Activation of Ammonia by [Al2O3]·+: Room Temperature Formation of the Aminyl Radical and Nitrene
Robert Kretschmer, Zhe-Chen Wang, Maria Schlangen, Drs. h. c. Helmut Schwarz* Crime scene: N–H bond activation. When ammonia gets in the crosshairs of [Al2O3]·+ the reaction is not limited to a single hydrogen-atom transfer, double hydrogen abstraction takes place as well and free nitrene is liberated at room temperature. These results are confirmed by mass spectrometric and theoretical investigations. Published online, DOI: 10.1002/anie.201302506 – Read now May 16, 2013 VIP: C–H Functionalization Logic Enables a Synthesis of (+)-Hongoquercin A and Related CompoundsBrandon R. Rosen, Leah R. Simke, Peter S. Thuy-Boun, Darryl D. Dixon, Jin-Quan Yu, and Phil S. Baran A synthesis of the sesquiterpenoid antibiotic (+)-hongoquercin A using sequential site-specific C–H methylation and oxidation reactions is described. A key advancement toward this goal was the development of a ligand-accelerated C–H methylation reaction. This unique strategic disconnection enables the generation of a library of eight structurally diverse analogs, highlighting the utility of these reactions in the synthesis and modification of structurally complex molecules. Coming soon. May 16, 2013 VIP: Enantioselective Isomerization of Primary Allylic Alcohols into Chiral Aldehydes with the Tol-Binap/Dbapen–Ruthenium(II) CatalystNoriyoshi Arai, Keisuke Sato, Keita Azuma, and Takeshi Ohkuma* Enantioselective isomerization of γ-substituted primary allylic alcohols into the β-substituted aldehydes is catalyzed by the [RuCl2{(S)-tol-binap}{(R)-dbapen}]–KOH system. The reaction is conducted with a substrate-to-catalyst molar ratio in the range of 100–2000 at 25°C for 0.5–1 h. A turnover number of about 1550 is achieved in the best case. A series of (E)- and (Z)-configurated aromatic and aliphatic allylic alcohols, including a simple primary alkyl-substituted compound (E)-3-methyl-2-hepten-1-ol, is transformed to the aldehydes in at least 99% ee. The plausible mechanism for this reaction, which is promoted by the hemilability of the dbapen–Ru chelate structure, is also discussed. Coming soon. May 16, 2013 Hot Paper: Oxidative Coupling Reactions of Grignard Reagents with Nitrous Oxide
Gregor Kiefer, Lo[iuml]c Jeanbourquin, Kay Severin* Catalysis with laughing gas: N2O in combination with transition-metal catalysts allow the oxidative homo- and cross-coupling of Grignard reagents. The reactions can be performed under mild conditions despite the inert character of N2O. Published online, DOI: 10.1002/anie.201302471 – Read now May 15, 2013 Hot Paper: The Fatty Acid Composition of Diacylglycerols Determines Local Signaling Patterns
André Nadler, Gregor Reither, Suihan Feng, Frank Stein, Sabine Reither, Rainer Müller, Carsten Schultz* Caged compounds are designed to release biologically active signaling molecules with temporal, spatial, and even subcellular resolution. But how localized does the signal stay? Using the example of diacylglycerol, some signal responses (PKC) are shown to remain spatially distinct while other signals ([Ca2+]i) spread across the entire cell. Surprisingly, this distribution patterns depend on the fatty acid composition of the lipid species. Coming soon. | May 23, 2013 May 23, 2013 May 21, 2013 May 17, 2013 May 16, 2013 May 16, 2013 May 15, 2013 May 14, 2013 May 14, 2013 May 14, 2013 May 13, 2013 May 08, 2013 May 08, 2013 May 06, 2013 May 06, 2013 May 05, 2013 May 01, 2013 April 30, 2013 April 30, 2013 April 25, 2013 April 24, 2013 April 24, 2013 April 24, 2013 April 23, 2013 April 23, 2013 April 22, 2013 April 22, 2013 April 16, 2013 April 14, 2013 April 13, 2013 April 12, 2013 April 11, 2013 April 11, 2013 April 10, 2013 April 08, 2013 April 05, 2013 March 25, 2013 March 25, 2013 March 13, 2013 March 13, 2013 March 11, 2013 March 08, 2013 March 07, 2013 February 28, 2013 February 26, 2013 February 21, 2013 January 31, 2013 |
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