Angewandte Chemie International Edition

Quality through diversity has been a hallmark of Angewandte Chemie from the beginning, and this is no doubt also the case in the 125th year. This jubilee will be celebrated by a symposium on March 12, 2013 in Berlin, and the program is part of the current issue. The diversity of topics that appear in Angewandte Chemie is illustrated by the tag cloud in the cover picture. The diversity of countries from which manuscripts come is shown by the top-ten list of countries of the Communications accepted in 2012, which is represented by the size of the spheres in the cover picture. The various sections are also diverse: Reviews and Communications, Highlights and Essays, Author Profiles and News, Obituaries and occasionally Correspondences. The history of Angewandte Chemie is presented in this Issue by the Chairman of the Editorial Board, François Diederich, in a major Review (pp. 2714 ff.), which brings to life the development of the journal and indeed of chemistry since 1888.

Carbon nanofiber aerogels can be fabricated on a large scale by using a low-cost biomass, bacterial cellulose, as a precursor, which can be produced industrially in a microbial fermentation process (see picture). As described by S. H. Yu and co-workers in their Communication on page 2925 ff., the aerogels are ultralight (a small piece can sit on a clover leaf), flexible, fire-resistant, and have a superior absorption capacity for organic solvents. Picture design: M.-R. Gao.

Let's have a party! The 125th-anniversary symposium of Angewandte Chemie offers eleven first-class speakers, among them three Nobel laureates. On March 12, in Berlin, or on the internet through ChemistryViews.

“If I won the lottery, I would buy a Steinway for me and a house for my Steinway. My favorite place on earth is Paris …” This and more about Paul Knochel can be found on page 2646.

Wiley-VCH, Weinheim, 2012. 642 pp., hardcover, € 69.00.—ISBN 978-3527323494

Spot on! Cell-free protein expression on surfaces can be implemented in biosensors and in microfluidic devices like that shown in the picture. Proteins are generated and immobilized successively on separated spots in a microfluidic reactor. This approach opens up novel opportunities for basic and applied biomedical research.

Fundamental aspects of chemically activated reactive intermediates can possibly be learned from the novel generation of arynes. The intramolecular [4+2] cycloaddition between a diyne and an (electronically activated) alkyne also provides a new route to generate arynes (see scheme).

Additive or non-additive, that is the question: The increasing awareness of non-additive cooperative mutational effects in protein engineering is currently providing new theoretical and practical insights. In particular, the directed evolution of stereoselective enzymes as catalysts in organic chemistry and biotechnology profits from this intriguing development.

The human population, doubling every 50 years, creates global problems, including limitations on energy, raw materials, food, water, health, and air. However, the future of humankind seems bright thanks to the even faster growth of human knowledge, doubling every 18 months, and the unpredictability of science. Our global challenges are likely to be met by yet unknown technologies, mostly invented by chemists.

Soot toxification: The increasing chemical activity of the emitted soot particulate produced by modern diesel engines is an unwanted side effect of modification of the motors. This makes Euro IV and VI soots chemically and biologically highly active and hazardous. Taking these factors into consideration, the question arises whether the reduced net mass of diesel soot particulate emitted overcompensates for the induced micro- and nanostructure.

Size matters: Chemistry has contributed strongly to the rapid development of nanoscience resulting in an ever-growing amount of nanosized systems and materials. The properties of these systems do not only arise from their size, but also surface modifications and structures. Nanomaterials thus have unique properties and can contribute to the development of chemistry, including nanocatalysts and nanomedicine.

Sharers are winners: The concept of “Collaborative Innovation” has the potential to overcome the significant challenges the pharmaceutical industry faces in its effort to improve the lives of patients by fighting increasingly complex diseases. In order to succeed, it is crucial to join forces on a global level and to combine different approaches in a flexible way, requiring the right mindset of all involved parties, a combination of internal excellence and external openness, and the right organizational setup.

Pores and protons: Development of new types of proton-conducting materials is important in fuel-cell technology. Newly developed proton-conducting materials formed from modularly built porous solids, including coordination polymers (CPs) or metal–organic frameworks (MOFs) are discussed (see scheme).

Poking crystals: The application of nanoindentation in crystal engineering provides an important breakthrough in establishing links between microscopic structures and macroscopic properties. This Minireview highlights some of the advantages of this technique for studying the mechanical behavior of organic crystals.

The development ofAngewandte Chemie and the changes in chemical research over the first 125 years of its existence are the topic of this Review. Even from the content of its first 50 years, the journal offers numerous milestones in chemical research, and today, with its attractive layout and successful mix of articles, it covers chemical research worldwide in its full breadth.

How to solve the riddle? When phenotypic screens are performed, mostly there are missing pieces (of information) that would explain the link between a biologically active compound and the appearance of a certain phenotype. The interplay of organic synthesis, cell biology, proteomics, genetics, molecular biology, biochemistry, informatics, and biophysics is required to find the missing pieces and to assemble the whole puzzle of a compound's cellular activity.

Making connections: The latest generation of alkyne metathesis catalysts holds considerable promise for synthesis, as they are exceptionally active, remarkably tolerant, and, in the form of their phenanthroline adducts, bench stable (see scheme). Numerous applications to material science and natural product synthesis illustrate the excellent performance and structural scope of this method.

Various levels of resolution, for example, electronic, atomic, supramolecular, are combined in one model in multi-resolution simulations. The basic choices when setting up a multi-resolution model are reviewed. As an illustration the differential catalytic properties of two enzymes with similar folds are explored using multi-resolution simulation at three different levels of resolution.

Chemistry is key for understanding the fundamental processes that underlie the evolution of matter towards states of increasing complexity through self-organization. It has developed from the molecular to the supramolecular level and has, through constitution dynamic systems, acquired the features of adaptive chemistry. Hence, chemistry opens the door towards complex matter.

New possibilities: There is a growing awareness that organometallic complexes based on ruthenium, iridium, palladium, and even iron as the central metal offer new opportunities for catalytic hydroformylations (see scheme; TM=transition metal). Research from the past few decades is critically summarized in this Review.

Layer by layer: Electron-transport layers (ETLs) of transferable graphene oxide (GO) inserted by using a stamping nanotechnology (see picture) result in bulk-heterojunction (BHJ) solar cells with enhanced power conversion efficiency because of enhanced electron-charge transport and reduced electronic charge barrier with low series resistance. The GO ETL also increases the stability of the device in air.

TNP can't hide from MOF: A three-dimensional fluorescent metal–organic framework (MOF), [Cd(NDC)_0.5(PCA)]⋅G_x, can be used for the detection of 2,4,6-trinitrophenol (TNP). The MOF exhibits high selectivity towards TNP, even in the presence of other nitro explosives in aqueous and organic solutions, owing to electron- and energy-transfer mechanisms and electrostatic interactions.

And then there was one: Anisotropic nanoparticle syntheses often contain impurity nanostructures. Functionalization of the products of such syntheses with DNA (see scheme (1)) allows the relative interaction strengths between particles to be tailored. The desired nanoparticle component can then be crystallized selectively (2) and separated to arrive at samples of significantly improved purity (3).

Combustion causes a soft robot to jump: Rapid actuation of a soft robot (composed of silicone elastomers) was achieved using high-temperature chemical reactions. Computer-controlled electrical sparks triggered the combustion of premixed CH₄ and O₂ gases inside the robot, which pressurized the pneumatic channels of the robot and caused it to jump (see figure). The heat from the explosions dissipated quickly and did not damage the robot even over many jumps.

On the surface: CdSe surfaces have been used as a prototype for the investigation of the spatiotemporal characteristics of solvation by environmental scanning ultrafast electron microscopy (see picture, GSED=gaseous secondary electron detector). This study has shown that the ultrafast relaxation dynamics of polar molecules, such as water, in the adsorbate layers exhibit a striking dependence on the CdSe surface structure.

The self-assembly of triangular, tetrahedral, and trigonal-prismatic molecular building blocks affords the first example of a trinodal family of metal–organic materials. Four examples of isoreticular expanded and functionalized frameworks are detailed. Gas adsorption experiments validated the permanent porosity of the parent structure.

Give 'em structure: The presence of structuring elements in polymers that were functionalized with catalytic units resulted in a new class of enzyme mimics, which are only active in the folded state (see picture). The conformationally adaptive hydrophobic environment that surrounds the catalytic site allows the very efficient catalysis of an aldol reaction in water with Michaelis–Menten kinetics.

Too OT to handle? In oxygen transfer (OT) reactions the inversion of the ρ value is not representative of a change in mechanism. Substituents bonded to aromatic sulfoxides have the opposite effect on the rates of oxidation depending on whether the reaction is dominated by electrostatic or orbital-overlap effects (see picture).

At the double: Cucurbit[8]uril-mediated protein dimerization enables reversible control over strong enzyme activation of caspases. Simple addition of a short N-terminal FGG motif allows for a supramolecular-mediated 50-fold enhancement of caspase-9 catalytic activity.

Filling a honeycomb: The thienothiophene-based covalent organic framework (COF) can be loaded with a complementary semiconductor, such as a fullerene derivative, and electronic interactions are observed (see figure). The novel periodic interpenetrated donor–acceptor system shows the spectroscopic signatures of efficient charge transfer on the nanoscale. Photovoltaic activity was demonstrated upon integrating the COF:fullerene film into a device.

Thirsty fibers: The aerogels described in the title can be fabricated in large scale by using a low-cost biomass, bacterial cellulose, as a precursor, which can be produced at industrial level in a microbial fermentation process. The carbon nanofiber aerogels (black pieces in picture) exhibit superior absorption capacity for organic solvents (red solution) and high potential for pressure sensing.

Illuminating results: Activation of non-emissive [Au^III(N N N)(NHC)]⁺ complexes (such as 1) through reduction by intracellular glutathione gives active Au^I–NHC complexes, which show promising anti-cancer properties, accompanied by release of the highly fluorescent ligand. The high fluorescence “switch-on” efficiency makes these Au^III complexes excellent probes for cellular thiol detection.

As easy as π: Fulvenes serve as 6π dipolarophiles in the title reaction in the presence of the chiral Cu^I/(S)-L complex. The present system provides a unique and straightforward access to enantioenriched, highly functionalized piperidine derivatives in good yields and excellent diastereoselectivities and enantioselectivities.

Beyond the Tolman electronic parameter: The ³¹P NMR chemical shifts of easily synthesized carbene–phenylphosphinidene adducts allow the determination of the relative π-acceptor properties of carbenes. In combination with the Tolman electronic parameter value, the relative pure σ-donation of carbenes can also be evaluated.

Make it simple! A convenient and general palladium-catalyzed oxidation of internal olefins to ketones is reported. The transformation occurs at room temperature and shows wide substrate scope. Applications to the oxidation of seed-oil derivatives and a bioactive natural product (see scheme) are described, as well as intriguing mechanistic features.

Exploring the alternatives: Ruthenium imidazoyl phosphine complexes catalyze the domino hydroformylation/reduction of alkenes to alcohols in good yields and with good selectivities (see scheme). Linear aliphatic alcohols are synthesized under reaction conditions typically used in industrial hydroformylations.

The activation of the inert CO bonds in mesylates through the use of a new class of imidazolyl phosphines allows the decarboxylative coupling of aryl mesylates as well as polysubstituted alkenyl mesylates. Variation of the ligands leads to two complementary methods providing the corresponding biaryls and polysubstituted olefins in good yields.

One in, one out: In the presence of a copper/silver bimetallic catalyst system, aromatic carboxylate salts undergo ortho CH alkoxylation with concomitant loss of the carboxylate directing group in a protodecarboxylation step (see scheme, FG=functional group). This process provides a convenient synthetic access to the important class of aromatic ethers from widely available carboxylic acids.

A trapped silicon atom: The compound (L:)₂Si with low-valent silicon was synthesized from its dichloride biradical precursor (L:)₂SiCl₂ by reduction with KC₈. Theoretical analysis suggest that there are two donor–acceptor σ bonds L:→Si←:L. There is one σ lone-pair orbital at Si and one π orbital which features significant π-back-donation L:←Si→:L giving short SiC bonds.

No transition metals are necessary in the reaction of in situ generated arynes with nitrosoarenes to give substituted carbazoles. Depending on the fluoride source and the solvent, either N-arylated carbazoles or NH-carbazoles are obtained (see scheme; DME=dimethoxyethane, OTf=trifluoromethanesulfonate). In these cascades a CC and one or two CN bonds are formed. The reactions are easy to conduct and proceed under mild conditions.

Pentaphosphaferrocene redox chemistry: Unprecedented dianionic and PP coupled and monomeric products are obtained by the reduction of pentaphosphaferrocene with KH or K metal, whereas by oxidation a PP coupled P₁₀²⁺ ligand coordinated to two Cp*Fe units is obtained. The redox behavior clearly distinguishes pentaphosphaferrocene from its organometallic relative, ferrocene.

Take two: By employing two equivalents of an aldehyde in an asymmetric organocatalytic domino reaction, the nucleophilic enamine intermediate is also converted into the corresponding iminium species through oxidation with o-iodoxybenzoic acid. Thus, polyfunctionalized cyclohexene derivatives are formed from two simple starting materials in good yields and stereoselectivities (see scheme; Bn=benzyl, EWG=electron-withdrawing group).

Halide abstraction from cationic base-stabilized borylene complexes led to extremely electronically and coordinatively unsaturated platinum complexes. The formally 14-electron borylene complexes show no agostic interactions with the phosphine ligands, and only small Lewis donor ligands could be added to the Pt center.

Link! Two, three, four! A rapid and flexible synthesis of native (1→n)-linked C-disaccharides (n=2, 3, 4; left) is possible. The configuration of the pseudoanomeric carbon was readily established by an epoxidation/ring-opening sequence. The synthesis of (1→n)-linked 2-deoxy-C-disaccharides (right) with high diastereoselectivity follows an even shorter route.

The fab four: Far-infrared difference spectra and DFT-calculated properties for mixtures of protic ionic liquids (PILs) and water clearly indicate that a minimum of four water molecules are needed to transfer contact (CIPs) into solvent-separated (SIPs) ion pairs. SIPs are favored over CIPs owing to additional H-bonds and cooperative effects. This enthalpic advantage overcompensates for the entropic penalty of separation by water.

Compact and informative: Individual nucleosides are statistically mutated by replacement with a non-nucleosidic spacer unit Δ that encodes the “deletion” in a single DNA library. This efficient mutagenesis approach enables minimization of functional DNA, identifying essential nucleotides, as demonstrated for two nucleic-acid ligating deoxyribozymes.

Horseradish peroxidase (HRP) can be used for the enzymatic cross-linking of thiol-functionalized polymers under mild conditions to form hydrogels and nanogels without the need for added H₂O₂. Cells can be embedded in the hydrogels and proteins can be entrapped and released from the nanogels. These gels are fully degradable under mild and cytocompatible reductive conditions.

Making Ns meet: Triphenylphosphinazine N₂(PPh₃)₂ is a donor–acceptor complex between nitrogen in the highly excited ¹Γ_g state and two anti-periplanar coordinated phosphine ligands (see structure). Although the dissociation into N₂+2 PPh₃ is calculated to be exergonic by 75 kcal mol⁻¹, the compound is kinetically very stable as a result of the very large Lewis acidity of N₂ in the excited ¹Γ_g state.

Catch me if you can: The ClpP protease mediates protein homeostasis and can be efficiently inhibited by β-lactones. A combination of molecular docking, mutagenesis, activity-based protein profiling, and kinetics studies now reveals the mechanism of ClpP inhibition. A hydrophobic pocket next to the active site allows binding of long aliphatic and aromatic residues. The preferred stereoisomer binds into the oxyanion hole.

Unprecedented reactivity of a metastable cobalt trisulfide complex has been observed, and several direct CS bond formation reactions by CH functionalization were developed. These reactions produced a series of photofunctional motifs of sulfur-rich cobalt complexes (see picture). The measured photophysical properties of these complexes suggest promising molecular designs for photocurrent generating materials.

What could be simpler than C₂, a diatomic molecule that has the second strongest homonuclear bond? This molecule turns out to be a microcosm of the bonding issues that bother chemists, as is shown in this trialogue. Join the three authors in their lively debate, light a candle, as Faraday did, and see the excited states of C₂!