Angewandte Chemie International Edition

Cover image for Vol. 45 Issue 18

April 28, 2006

Volume 45, Issue 18

Pages 2815–2983

    1. Cover Picture: Changing the Activity of Electrocatalysts for Oxygen Reduction by Tuning the Surface Electronic Structure (Angew. Chem. Int. Ed. 18/2006) (page 2815)

      Vojislav Stamenkovic, Bongjin Simon Mun, Karl J. J. Mayrhofer, Philip N. Ross, Nenad M. Markovic, Jan Rossmeisl, Jeff Greeley and Jens K. Nørskov

      Version of Record online: 21 APR 2006 | DOI: 10.1002/anie.200690063

      Alloying platinum surfaces … … with 3d transition metals makes better cathodes for fuel cells. In their Communication on page 2897 ff., J. K. Nørskov and co-workers show that this process results in a tuning of the electronic structure of the surface and increases its catalytic activity for the oxygen reduction reaction. The cover picture shows how a wave function involving oxygen p and surface platinum d states in Pt3Co is influenced by cobalt atoms in the second layer.

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      A Highly Enantio- and Diastereoselective Cu-Catalyzed 1,3-Dipolar Cycloaddition of Azomethine Ylides with Nitroalkenes (page 2828)

      Xiao-Xia Yan, Qian Peng, Yan Zhang, Kai Zhang, Wei Hong, Xue-Long Hou and Yun-Dong Wu

      Version of Record online: 21 APR 2006 | DOI: 10.1002/anie.200690065

      This article corrects:
    3. From Subphthalocyanines to Subporphyrins (pages 2834–2837)

      Tomás Torres

      Version of Record online: 21 APR 2006 | DOI: 10.1002/anie.200504265

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      Contracting porphyrins: An important step on the way to the as-yet unrealized contracted porphyrin, the so-called subporphyrin, is a tribenzosubporphyrin (see structure). The new system, which is closely related to boronsubphthalocyanines, comprises a 14-π-electron aromatic core and adopts a nonplanar bowl-shaped conformation.

    4. Palladium-Catalyzed Coupling Reactions for the Stereoselective Synthesis of Tri- and Tetrasubstituted Alkenes (pages 2838–2840)

      Oliver Reiser

      Version of Record online: 3 APR 2006 | DOI: 10.1002/anie.200600025

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      Making advances: Efficient strategies relying on palladium-catalyzed cross-coupling reactions are now available for the assembly of tri- and tetrasubstituted alkenes with excellent stereocontrol (see scheme; Y=Hal, X=ZnHal or MgHal; other variants: Y=BR2, X=I).

    5. Reactions at Very Low Temperatures: Gas Kinetics at a New Frontier (pages 2842–2861)

      Ian W. M. Smith

      Version of Record online: 21 APR 2006 | DOI: 10.1002/anie.200502747

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      It's amongst the stars: Over the past two decades, it has become possible to measure rate constants for elementary gas-phase reactions at temperatures as low as 10 K, largely by using the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) technique (experimental setup shown). The factors that determine the reaction rates and the implications in the chemistry of interstellar clouds are reviewed.

    6. Using Nonnatural Amino Acids to Control Metal-Coordination Number in Three-Stranded Coiled Coils (pages 2864–2868)

      Kyung-Hoon Lee, Chris Cabello, Lars Hemmingsen, E. Neil G. Marsh and Vincent L. Pecoraro

      Version of Record online: 5 APR 2006 | DOI: 10.1002/anie.200504548

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      It isn't natural: TRI peptides can selectively control the coordination number of a metal center by changing only one of the amino acids in the primary sequence. Replacement of the cysteine residue with penicillamine leads to a three-coordinate complex CdIIS3, whereas substitution of alanine for leucine gives four-coordinate CdS3O (see scheme).

    7. Polyionic Gels: Efficient Heterogeneous Media for Metal Scavenging and Catalysis (pages 2868–2871)

      Carine Thiot, Marc Schmutz, Alain Wagner and Charles Mioskowski

      Version of Record online: 28 MAR 2006 | DOI: 10.1002/anie.200504580

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      A highly polar micro-environment, which is suitable for efficient metal scavenging and heterogeneous catalyst preparation, is provided by polyionic gel beads 1 (see scheme). These heterogeneous media enable easy product isolation and catalyst recycling. As an example, a Pd-soaked ionic gel 2 is shown to transform into a highly efficient and recyclable catalyst 3 in the Suzuki cross-coupling reaction.

    8. Efficient Route to Tetramethylalumoxane and Carboxylate Alumoxanes through the Alkylation of Phthalic Acid (pages 2872–2875)

      Janusz Lewiński, Wojciech Bury, Iwona Justyniak and Janusz Lipkowski

      Version of Record online: 21 APR 2006 | DOI: 10.1002/anie.200504414

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      Spaced out: The macrocyclic carboxylate-substituted alumoxane 1 and coordination polymer 2 were obtained by stepwise treatment of phthalic acid with AlMe3 and 1,2-bis(4-pyridyl)ethane. In this non-hydrolytic route to alumoxane derivatives, the selective formation of 1 or 2 is determined by the stoichiometric amount of AlMe3 employed.

    9. Self-Organization of Oriented Calcium Carbonate/Polymer Composites: Effects of a Matrix Peptide Isolated from the Exoskeleton of a Crayfish (pages 2876–2879)

      Ayae Sugawara, Tatsuya Nishimura, Yuya Yamamoto, Hirotaka Inoue, Hiromichi Nagasawa and Takashi Kato

      Version of Record online: 21 MAR 2006 | DOI: 10.1002/anie.200503800

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      Gone fishing: Unidirectionally oriented CaCO3 crystalline films have been prepared on chitin matrices in the presence of calcification-associated peptide (CAP-1), which was isolated from the exoskeleton of the red swamp crayfish. The interactions of CAP-1 with the matrix and the acidic nature of the peptide lead to a filmlike assembly of CaCO3 nanocrystals through transformation of amorphous calcium carbonate (see picture).

    10. Visible Sensing of Nucleic Acid Sequences with a Genetically Encodable Unmodified RNA Probe (pages 2879–2883)

      Atsushi Narita, Kazumasa Ogawa, Shinsuke Sando and Yasuhiro Aoyama

      Version of Record online: 21 MAR 2006 | DOI: 10.1002/anie.200503836

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      Sensing DNA with RNA: Simple and sensitive DNA sensing was achieved by using an RNA probe which is composed of a molecular-beacon-like cis-repressing sequence and a gene for the reporter protein. The RNase H activity coupled molecular-beacon–mRNA system enabled visible sensing of the target nucleotide sequence in a cell-free translation solution (see picture).

    11. Biomolecular Modification of Hierarchical Cellulose Fibers through Titania Nanocoating (pages 2883–2886)

      Jianguo Huang, Izumi Ichinose and Toyoki Kunitake

      Version of Record online: 23 MAR 2006 | DOI: 10.1002/anie.200503867

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      Natural cellulose sheets can be used as substrates for protein immobilization. Individual cellulose nanofibers are first coated with ultrathin titania layers to enable the chemisorption of biotin, and then streptavidin is anchored. The sheets have a high binding capacity for biomolecules (see the fluorescence micrographs) without deterioration of their mechanical and water-absorbing properties.

    12. Pd Nanoclusters in C[BOND]C Coupling Reactions: Proof of Leaching (pages 2886–2890)

      Mehul B. Thathagar, Johan E. ten Elshof and Gadi Rothenberg

      Version of Record online: 23 MAR 2006 | DOI: 10.1002/anie.200504321

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      A simple experiment based on exclusion of Pd nanoclusters was used to identify the true catalytic species in cluster-catalyzed Heck cross-couplings. A special reactor was used in which two compartments are separated by a nanoporous membrane that allows the passage of Pd atoms and ions but not of Pd nanoclusters (see picture). The results show that the real catalysts in the Heck coupling of n-butyl acrylate with iodobenzene are species leached from the Pd nanoclusters.

    13. Precedent and Theory Unite in the Hypothesis of a Highly Selective Fluoride Receptor (pages 2890–2893)

      Mark Mascal

      Version of Record online: 21 MAR 2006 | DOI: 10.1002/anie.200504417

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      Room for a small one: A series of [1,3,5]cyclophane-based receptors incorporating triazine, cyanuric acid, or boroxine rings are predicted to strongly complex fluoride ions by a combination of anion–π interactions and ion-pair reinforced hydrogen bonding, while size-excluding the larger chloride anion. The top view of a calculated structure of the triazine cage with an included fluoride ion is shown.

    14. Formamide Hydrolysis in Alkaline Aqueous Solution: Insight from Ab Initio Metadynamics Calculations (pages 2893–2897)

      Jochen Blumberger, Bernd Ensing and Michael L. Klein

      Version of Record online: 28 MAR 2006 | DOI: 10.1002/anie.200600283

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      What is the active nucleophile in the alkaline hydrolysis of formamide: the hydroxide ion or a water molecule in its first solvation shell? To allow the two mechanisms in question to be distinguished, a 2D free-energy surface was computed (see picture) using Car–Parrinello metadynamics simulation. The results show that direct nucleophilic attack by a hydroxide ion is the preferred mechanism.

    15. Changing the Activity of Electrocatalysts for Oxygen Reduction by Tuning the Surface Electronic Structure (pages 2897–2901)

      Vojislav Stamenkovic, Bongjin Simon Mun, Karl J. J. Mayrhofer, Philip N. Ross, Nenad M. Markovic, Jan Rossmeisl, Jeff Greeley and Jens K. Nørskov

      Version of Record online: 5 APR 2006 | DOI: 10.1002/anie.200504386

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      Going platinum: The theoretical description of electrocatalytic phenomena is extremely challenging. A simple, density functional theory based model has been developed that is able to give a semiquantitative description of the reaction kinetics for the electrocatalytic oxygen reduction on several platinum binary alloys, Pt3M (see graph).

    16. Synthesis of (−)-Cubebol by Face-Selective Platinum-, Gold-, or Copper-Catalyzed Cycloisomerization: Evidence for Chirality Transfer (pages 2901–2904)

      Charles Fehr and José Galindo

      Version of Record online: 23 MAR 2006 | DOI: 10.1002/anie.200504543

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      Facing facts: Control of the configuration of the propargylic center in 1 is essential for the facial selectivity observed in the Pt-, Au-, or Cu-catalyzed enyne cycloisomerization. This route has been used for the stereoselective synthesis of the naturally occurring sesquiterpene (−)-cubebol (2).

    17. Reaction of Molecular Oxygen with a PdII– Hydride To Produce a PdII–Hydroperoxide: Acid Catalysis and Implications for Pd-Catalyzed Aerobic Oxidation Reactions (pages 2904–2907)

      Michael M. Konnick, Bhavesh A. Gandhi, Ilia A. Guzei and Shannon S. Stahl

      Version of Record online: 28 MAR 2006 | DOI: 10.1002/anie.200600532

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      A critical step: The reaction of molecular oxygen with a reduced palladium species represents the key step in Pd-catalyzed aerobic oxidation reactions. New PdII–hydride complexes 1 have been prepared which react with molecular oxygen to produce PdII–hydroperoxide adducts 2. Carboxylic acid catalysis of this reaction has important implications for Pd-catalyzed aerobic oxidation reactions.

    18. Design, Synthesis, and Membrane-Translocation Studies of Inositol-Based Transporters (pages 2907–2912)

      Kaustabh K. Maiti, Ock-Youm Jeon, Woo Sirl Lee, Dong-Chan Kim, Kyong-Tai Kim, Toshihide Takeuchi, Shiroh Futaki and Sung-Kee Chung

      Version of Record online: 23 MAR 2006 | DOI: 10.1002/anie.200600312

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      Delivery vehicles: Novel guanidine-containing “transporters” constructed on a dimeric inositol scaffold show significant translocation across the cell membrane and the blood–brain barrier, as well as unique in vitro and in vivo distributions. Doxorubicin was efficiently delivered to mouse-brain tissue by conjugating the compound with such a transporter (see the fluorescence microscopy image).

    19. Total Synthesis of (−)-Sarain A (pages 2912–2915)

      Neil K. Garg, Sheldon Hiebert and Larry E. Overman

      Version of Record online: 27 MAR 2006 | DOI: 10.1002/anie.200600417

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      The final synthetic challenges associated with sarain A have been overcome, thus leading to its first total synthesis. Critical to success was a late-stage intramolecular Stille coupling to construct the unsaturated macrocyclic ring and introduce the skipped triene functionality of the natural product.

    20. Stereoselective Synthesis of the Side Chains of Mycolactones A and B Featuring Stepwise Double Substitutions of 1,1-Dibromo-1-alkenes (pages 2916–2920)

      Ning Yin, Guangwei Wang, Mingxing Qian and Eiichi Negishi

      Version of Record online: 24 MAR 2006 | DOI: 10.1002/anie.200600012

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      Piecing them together: The side chains of mycolactones A and B are synthesized with a high degree of stereoselectivity. The components of the side chains are prepared separately, then combined through Pd-catalyzed cross-coupling (see scheme; Z1=tert-butyldimethylsilyl, Z2=methoxymethyl, TBAF=tetra-n-butylammonium fluoride).

    21. Synthesis and Characterization of Stable Ruthenabenzenes (pages 2920–2923)

      Hong Zhang, Haiping Xia, Guomei He, Ting Bin Wen, Lei Gong and Guochen Jia

      Version of Record online: 27 MAR 2006 | DOI: 10.1002/anie.200600055

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      A rare breed: Although many stable metallabenzene derivatives with a metal atom from the third transition series are known, those with a metal atom from the first and the second transition series are rare. Air-stable ruthenabenzenes (e.g. 1 and 2) have now been isolated and characterized.

    22. Preparation of Helicenes through Olefin Metathesis (pages 2923–2926)

      Shawn K. Collins, Alain Grandbois, Martin P. Vachon and Julie Côté

      Version of Record online: 28 MAR 2006 | DOI: 10.1002/anie.200504150

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      Metathesis with a twist! A ring-closing-metathesis strategy has been developed for the preparation of various substituted [5]helicene motifs and [6]- and [7]helicenes. The two optimized protocols include one method that utilizes the Grubbs second-generation catalyst under microwave-irradiation conditions and another that employs a modified Grubbs–Hoveyda catalyst at 40 °C in a sealed reaction vessel. (Mes=mesityl)

    23. Catalytic Antimony–Antimony Bond Formation through Stibinidene Elimination from Zirconocene and Hafnocene Complexes (pages 2926–2929)

      Rory Waterman and T. Don Tilley

      Version of Record online: 23 MAR 2006 | DOI: 10.1002/anie.200600318

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      Bringing together: Zirconium and hafnium d0 metallocene complexes catalyze the dehydrocoupling of the stibines MesSbH2 (Mes=mesityl) and dmpSbH2 (dmp=2,6-dimesitylphenyl) to Sb4Mes4 and (dmp)Sb[DOUBLE BOND]Sb(dmp), respectively, with liberation of H2. Kinetic analysis shows that thermal decomposition of hafnium stibide complexes proceeds through α-hydrogen migration and stibinidene elimination.

    24. o-Iodoxybenzoic Acid (IBX): pKa and Proton-Affinity Analysis (pages 2929–2934)

      Michael J. Gallen, Régis Goumont, Timothy Clark, François Terrier and Craig M. Williams

      Version of Record online: 27 MAR 2006 | DOI: 10.1002/anie.200504156

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      Not just a pretty oxidant! IBX (1-Hydroxy-1,2-benziodoxol-3(1H)-on-1-oxide), an important oxidant in organic synthesis, is shown to be relatively acidic on the organic scale. The pKa value and proton affinity of IBX were determined both in silico and in vitro. This acidity could explain the non-oxidation processes mediated by IBX.

    25. Modulation of Viscoelastic Properties of Physical Gels by Nanoparticle Doping: Influence of the Nanoparticle Capping Agent (pages 2934–2937)

      Santanu Bhattacharya, Aasheesh Srivastava and Asish Pal

      Version of Record online: 21 MAR 2006 | DOI: 10.1002/anie.200504461

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      Cap in hand: The viscoelastic properties of low-molecular-mass organogelator–gold nanoparticle (LMOG–Au NP) composites can be modulated by the capping agent on the nanoparticle. The interactions between the LMOG and Au NP depend on the ability of ligands to interdigitate within the gel aggregates (see picture).

    26. A Simple and Efficient Iron-Catalyzed Intramolecular Hydroamination of Unactivated Olefins (pages 2938–2941)

      Kimihiro Komeyama, Takayuki Morimoto and Ken Takaki

      Version of Record online: 23 MAR 2006 | DOI: 10.1002/anie.200503789

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      A new catalytic activity of iron salts for intramolecular hydroamination is revealed. A number of aminoolefins underwent the reaction under mild conditions to form the corresponding pyrrolidine derivatives in good yield. The reaction displayed good functional-group compatibility and resistance to air and moisture. (Ts=e-toluenesulfonyl)

    27. Regiospecific C[BOND]H Bond Activation: Reversible H/D Exchange Promoted by CuI Complexes with Triazamacrocyclic Ligands (pages 2941–2944)

      Xavi Ribas, Raül Xifra, Teodor Parella, Albert Poater, Miquel Solà and Antoni Llobet

      Version of Record online: 28 MAR 2006 | DOI: 10.1002/anie.200504222

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      The first reversible and regiospecific H/D exchange promoted by CuI proceeds in weakly coordinating deuterated “acidic” solvents, such as [D6]acetone or [D4]methanol (see scheme). The kinetics of the reaction have been studied in both directions (H/D and D/H exchange) by 1H and 2H NMR spectroscopy, and a molecular mechanism is proposed that is in accordance with all experimental and theoretical data.

    28. A Left-Handed 9-Helix in γ-Peptides: Synthesis and Conformational Studies of Oligomers with Dipeptide Repeats of C-Linked Carbo-γ4-amino Acids and γ-Aminobutyric Acid (pages 2944–2947)

      Gangavaram V. M. Sharma, Pagadala Jayaprakash, Kongari Narsimulu, Ampapathi Ravi Sankar, Kondreddy Ravinder Reddy, Palakodety Radha Krishna and Ajit C. Kunwar

      Version of Record online: 23 MAR 2006 | DOI: 10.1002/anie.200504380

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      A rare twist: A new class of mixed γ-peptides, derived from dipeptide repeats with alternating C-linked carbo-γ4-amino acids and γ-aminobutyric acid have shown the presence of left-handed 9-helices in solution with CDCl3 (see superimposition of 15 minimum-energy structures of a hexapeptide).

    29. A Dynamic Random Access Memory Based on a Conjugated Copolymer Containing Electron-Donor and -Acceptor Moieties (pages 2947–2951)

      Qi-Dan Ling, Yan Song, Siew-Lay Lim, Eric Yeow-Hwee Teo, Yoke-Ping Tan, Chunxiang Zhu, Daniel Siu Hhung Chan, Dim-Lee Kwong, En-Tang Kang and Koon-Gee Neoh

      Version of Record online: 27 MAR 2006 | DOI: 10.1002/anie.200504365

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      Remember this: The conjugated copolymer PFOxPy, which contains both electron-donor and -acceptor groups, exhibits dynamic random access memory behavior in the sandwich structure ITO/PFOxPy/Al (see picture). The device is characterized by low read, write, and erase voltages, a high ON/OFF current ratio (up to 106), stable ON and OFF states under a constant stress of −1 V, and up to 108 read cycles at a read voltage of −1 V.

    30. A Catalytic, Me2Zn-Mediated, Enantioselective Reformatsky Reaction With Ketones (pages 2951–2954)

      Pier Giorgio Cozzi

      Version of Record online: 23 MAR 2006 | DOI: 10.1002/anie.200504239

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      Kill two birds with one … Salen! A catalytic and practical Me2Zn-mediated enantioselective Reformatsky reaction promoted by [ClMn(salen)] with a ketone as the electrophile is presented (see scheme). The broad scope and simple nature of this procedure, which allows the use of commercially available starting materials and leads to useful building blocks containing quaternary stereocenters, make it extremely attractive. (salen=N,N′-ethylenebis(salicylideneamine).)

    31. Soluble Single-Molecule Nanogels of Controlled Structure as a Matrix for Efficient Artificial Enzymes (pages 2955–2958)

      Günter Wulff, Byong-Oh Chong and Ute Kolb

      Version of Record online: 28 MAR 2006 | DOI: 10.1002/anie.200503926

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      Copy cats! Soluble single-molecule nanogels (see STEM micrograph; scalebar=20 nm) with a densely packed structure are prepared by a new method, and for the first time efficient molecular imprinting is possible. These nanogels with defined molecular weights of, for example, 40 000 Da, low polydispersities, and on average one active site per particle proved to be catalytically active enzyme mimics.

    32. Mixed Mg/Li Amides of the Type R2NMgCl⋅LiCl as Highly Efficient Bases for the Regioselective Generation of Functionalized Aryl and Heteroaryl Magnesium Compounds (pages 2958–2961)

      Arkady Krasovskiy, Valeria Krasovskaya and Paul Knochel

      Version of Record online: 28 MAR 2006 | DOI: 10.1002/anie.200504024

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      Two are better than one: Mixed lithium-magnesium complexes of the type R2NMgCl⋅LiCl are kinetically highly active bases that convert a range of polyfunctional aromatic and heteroaromatic substrates into the corresponding magnesiated derivatives with high regioselectivity.

    33. Periodic Electron Circulation Induced by Circularly Polarized Laser Pulses: Quantum Model Simulations for Mg Porphyrin (pages 2962–2965)

      Ingo Barth and Jörn Manz

      Version of Record online: 23 MAR 2006 | DOI: 10.1002/anie.200504147

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      What goes round comes round! Quantum dynamical simulations predict that ultrashort circularly polarized laser pulses can selectively induce the circulation of electrons in a ring-shaped molecule—with near equal laser and electron periods below one femtosecond (see figure).

    34. On the Role of Oxygen Defects in the Catalytic Performance of Zinc Oxide (pages 2965–2969)

      Sebastian Polarz, Jennifer Strunk, Vladislav Ischenko, Maurits W. E. van den Berg, Olaf Hinrichsen, Martin Muhler and Matthias Driess

      Version of Record online: 28 MAR 2006 | DOI: 10.1002/anie.200503068

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      Systematic errors”, namely, oxygen vacancy sites in ZnO, are the active centers for the hydrogenation of CO to give methanol. Nanocrystalline ZnO with a high density of oxygen vacancies was prepared from special organometallic precursors, and its catalytic properties for methanol synthesis were studied.

    35. Hockey-Puck Micelles from Oligo(p-benzamide)-b-PEG Rod–Coil Block Copolymers (pages 2969–2975)

      Tobias W. Schleuss, Robert Abbel, Michael Gross, Dieter Schollmeyer, Holger Frey, Michael Maskos, Rüdiger Berger and Andreas F. M. Kilbinger

      Version of Record online: 28 MAR 2006 | DOI: 10.1002/anie.200503514

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      Hard-core visualization: Bilayer hockey-puck micelles are formed in nonpolar solvents from “sticky” rod–coil block copolymers based on oligo(p-benzamide)s. Images obtained by scanning force microscopy (SFM) give insight into the structure of the anisotropic micellar core. The picture shows a model (left) and an SFM image (right) of the micelle consisting of an aramide core and a poly(ethylene glycol) corona.

    36. Highly Efficient Photolabile Protecting Groups with Intramolecular Energy Transfer (pages 2975–2978)

      Dominik Wöll, Julia Smirnova, Wolfgang Pfleiderer and Ulrich E. Steiner

      Version of Record online: 23 MAR 2006 | DOI: 10.1002/anie.200504091

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      Brought to light: The light sensitivity of photolabile protecting groups of the nitrophenylpropoxycarbonyl (NPPOC) type was enhanced by up to a factor of 25. This was achieved by covalently linking the protecting group to a sensitizer with a much better absorptivity and the ability to transfer its electronic excitation to the protecting group (see scheme).

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