Angewandte Chemie International Edition

One, but not the same describes the painting “Double Me” (Michael Kvium) depicted on the cover which shows two men who appear at first to be competing. However, on closer inspection it appears that their shoes are joined together: Are they in fact cooperating? An analogy is drawn to two organocatalytic enantioselective arylation reactions presented in the Communications by K. A. Jørgensen and co-workers on pages 5515 and 5520 ff. Both reactions feature quinone but follow noncovalent (left) and covalent (right) organocatalytic pathways. (Thanks to M. Kvium for permission to use the painting.)

Chiral crystallization additives can determine the phase selection of calcium carbonate. W. Tremel and co-workers show this phenomenon in their Communication on page 5618 ff. for D and L amino acids, which adsorb chiroselectively on the surface of terraced calcite surfaces. Conversely, calcite may serve as a template during the formation of homochiral amino acids from racemic precursors.

It's logical! Molecular logic gates and circuits process chemical or physical inputs according to programmed Boolean logic functions. The integration of functions within individual molecules allows complex operations, as demonstrated by a recently reported molecular keypad access device (see picture).

Sound bubbles: Their collapse induces mechanical stress that can be transmitted to a target single bond by means of mechanosensitive polymers attached to the two sides of a benzocyclobutene. As surprising as it may be, ultrasound guides molecules into forbidden pathways by promoting the formation of only one isomer regardless of the starting benzocyclobutene.

“Very minute in their dimensions” is how Faraday described the metal particles present in a fine dispersion of colloidal gold upon observing its interaction with red light 150 years ago (see picture for a laser-light version of his experiment). This observation would come to serve as the basis for the modern nanoscience and nanotechnology of gold, including the use of gold nanoparticles in catalytic processes and the formation of self-assembled monolayers.

Filling the void: Efficient and flexible syntheses of many complex cyclotryptamine alkaloids are now possible because of the development of a set of stereocontrolled methods for accessing their multiple quaternary carbon stereocenters. The key steps include a cascade of Heck reactions or asymmetric dialkylation followed by an asymmetric Heck reaction (see scheme).

Bundle up: The introduction of streptavidin (as a linker) between two Fe^II(terpyridine–bis-biotin) connectors affords a one-dimensional metal–organic protein framework (MOPF). In the presence of calcium ions and CO₂ vapors, these MOPF aggregates form protein bundles that template the biomineralization of calcite.

Quintessential quinones: The reaction of β-ketoesters with quinones provides a strategy to perform α-arylations, particularly when the α-aryl ring contains electron-donating groups. The reaction can be carried out enantioselectively by using cinchona alkaloids as organocatalysts and allows the synthesis of complicated polycyclic and spiro chiral compounds.

Quinone pro quo: The organocatalytic enantioselective α-arylation of aldehydes using quinones as the aromatic partner was carried out. The reaction proceeds well using H₂O or EtOH/H₂O mixtures as solvent. The corresponding optically active α-arylated aldehydes are obtained in high yields and with excellent enantioselectivities (see scheme; TMS: trimethylsilyl).

The heteroatom-stabilized annularly fused hexapyrrolohexaazacoronene shown (N blue, F green) was synthesized and isolated as a representation of a new class of nitrogen-containing molecules with extended π systems. The reversible redox behavior, a consequence of the interior N atoms, hints at potential applications in organic electronics.

It's hip to be square: Squaraine rotaxanes have very similar photophysical properties to the commonly used Cy-5 fluorophore, but are substantially more photostable and resist self-quenching upon aggregation. Molecular probes containing squaraine rotaxanes (see structure) are shown to be versatile, high-performance NIR fluorescence stains for in vitro fluorescence imaging of cells (middle) and in vivo whole-body imaging of living mice (right).

Reduced and reoxidized: Thin films (100 nm) of tetrakis(thiadiazole)porphyrazine (see picture) are highly ordered in an unusual orientation of the molecular planes owing to the strong self-assembling ability of these crystals. Electrochemical reduction of the thin films induces reversible electrochromism and n-type carrier doping.

Differential growth: The growth of crystals of α-resorcinol (see picture; C gray, H white, O red) from the vapor phase is asymmetric along the polar axis. By means of molecular-dynamics simulations, the slower growth at the (011) polar surface is traced back to conformational change of the molecule and to surface reconstruction, which may be a general phenomenon in polar crystals.

Luminous nanorods: The self-assembly of core-twisted perylene bisimide fluorophores (see structures) in nonpolar organic solvents is directed by hydrogen-bonding interactions. This supermolecular concept resulted in one-dimensional J-aggregates with a fluorescence quantum yield of near unity.

The awesome power of metathesis is reflected in the synthesis of the proposed structure of the cytotoxic natural product amphidinolide V, as well as of all other stereomers containing a trans-epoxide unit. It can be concluded from the comprehensive data set obtained that the 8S,9R,10R,13S-configured compound 1 most likely represents amphidinolide V, even though a single resonance in the ¹H NMR spectrum deviates from the reported value.

Puzzlingly logical: The characteristic fluorescence of Hg²⁺-selective OFF-ON and Cu²⁺-selective ON-OFF operations can be monitored and controlled reversibly by the sequence and ratio of Hg²⁺ and Cu²⁺ inputs. These inputs have been used to construct a molecular keyboard that is capable of crossword puzzles and logic memory (see picture).

A seamless join: An efficient method to construct a C(sp²)C(sp²) bond has been developed by using a Suzuki–Miyaura-type coupling of N-alkyl acetanilides with boronic acids. The reaction was catalyzed by a Pd^II species and the CH bond activation was directed by the acetamino group (see scheme). This reaction offers a halogen-free method to construct complicated structures.

It all adds up: Straightforward access to 2-alkyl-substituted 1,3-diketones is provided by a regioselective addition of aldehydes to enones catalyzed by the ruthenium hydride catalyst [RuHCl(CO)(PPh₃)₃] (see scheme). The reaction involves a hydrometalation of the enone to form a metal enolate, a cross-aldol reaction to form an alkoxymetal species, and a subsequent β-metal hydride elimination.

It's what's on the inside that counts: The structure of Sc₂C₂@C₈₂(III), as suggested by ¹³C NMR spectroscopy and density functional calculations (see picture, left; C red and gray, Sc blue), contains two Sc and two C atoms inside the C₈₂ cage. This mode of encapsulation is verified by X-ray single-crystal analysis of the cycloadduct of Sc₂C₂@C₈₂(III) and adamantylidene carbene (see picture, right).

Sexpress: Quaternary carbon atoms are constructed in excellent yields with high enantioselectivities by a highly efficient chiral Brønsted acid catalyzed Friedel–Crafts reaction of indoles and α-aryl enamides (see scheme). The presence of H atoms on the N atoms of both the indole and enamide moieties is essential for the reaction to occur. The indole molecule attacks from the Re face to give S-configured products.

All in the family: Organophosphonate complexes of high-valent vanadium are common, but their V^III analogues are few and far between. Reaction of VCl₃ precursors and phosphonates under solvothermal conditions leads to a family of corresponding vanadium(III)-based phosphonates, including the layered {V^III₁₂(V^IVO)} cluster shown in the picture (V green, P purple, O red, C black). Preliminary magnetic studies are also reported.

Completing the quattuorvirate: Amino acids that contain primary amines directly catalyze syn-selective asymmetric aldol reactions between unprotected dihydroxyacetone and a variety of aromatic and aliphatic aldehydes (see scheme). This new strategy provides the organocatalytic mimics of the L-rhamnulose 1-phosphate and D-fructose 1,6-diphosphate aldolases.

Marginally stable natural products: The asymmetric total synthesis of the hydrolytically and thermally labile natural product (+)-isomigrastatin was demonstrated. The thermodynamic instability of a 2E-configured double bond in the context of this 12-membered macrolide was further demonstrated by phosphine-catalyzed isomerization to the 2Z configuration.

The [Cp*CpZrNCMe₃(thf)] system provides the first direct measurement of kinetic selectivity in sp, sp², and sp³ CH bond activation with Group 4 imido complexes. This feature allows the design of selectivity and mechanistic experiments to probe the 1,2-RH-addition event. Substrates reacting with the highest relative rates generally form the most thermodynamically stable products. Cp*=η⁵-C₅Me₅, Cp=η⁵-C₅H₅.

Cheap but good: Readily available CuO nanoparticles are not only less expensive than other catalysts used for the CS cross-coupling of thiols with aryl halides, but they are also effective at a moderate temperature and low concentration. The title reaction proceeds with a variety of alkyl and aryl thiols to give the corresponding sulfides in high yields (see scheme).

Metal-free partner: No organometallic coupling partner is required for a Pd-catalyzed cross-coupling reaction that employs N-tosylhydrazones as the nucleophilic component (see scheme; Ts=4-toluenesulfonyl).

An uneven split: Cooperative Cu^II and B^III metalation of meso-heptakis(pentafluorophenyl)[32]heptaphyrin (1) triggers an extrusion reaction to produce B^III meso-tris(pentafluorophenyl)[14]subporphyrin (2) along with a Cu^II porphyrin (3-Cu). Subporphyrin 2 exhibits unique optical properties that reflect the rotational restriction of its electron-withdrawing substituents.

Discrimination with a difference: The N-hydroxysuccinimide ester of HCCA (α-cyano-4-hydroxycinnamic acid) was used as a labeling reagent to increase the MALDI MS signal of weakly concentrated peptides of interest in a proteolytic mixture derived from cytochrome c relative to the signals of other peptides. The desired effect was only observed with the neutral MALDI matrix HCCE (the methyl ester of HCCA; see mass spectra).

Gold rush: Gold catalysis remains a highly attractive field of research for the discovery of new reaction types. A novel intermolecular addition of aldehydes and ketones to enynes leads to the diastereoselective synthesis of 2-oxabicyclo[3.1.0]hexanes (see scheme).

Silver service: Addition of silver(I) to an oligonucleotide comprising 1-deazaadenine and thymine nucleobases leads to the formation of a Hoogsteen-type double helix with specific binding of one metal ion per base pair (see scheme). Each base pair is mediated by one hydrogen bond and by two coordination bonds.

The Matryoshka theory: This unique type of shell-in-shell microcapsule facilitates the stable spatial separation of biopolymers (enzymes) within distinct compartments of a single capsule entity. Architecture and wall properties of this system allow for the concerted action of enzymes from separate capsule compartments by metabolite diffusion across a semipermeable, intersecting polyelectrolyte membrane.

This is IT for chemical analysis: The use of structured sample injection sequences (bar codelets) in chromatography allows to increase the sample throughput by self-encoding of individual samples and mathematical deconvolution of the overlapping chromatograms (see picture). Analysis of up to 453 samples per hour could be achieved with a single separation column in gas chromatography.

Small electronic changes matter! All three Group 10 metal hydrides MH⁺ (M=Ni, Pd, Pt) bring about thermal CH bond activation of methane, but for each system the potential energy surfaces and thus the mechanisms of the ligand exchange MH⁺ + CH₄→M(CH₃)⁺ + H₂ differ.

On the phase of it: The phase selection of calcium carbonate (spheres: C gray, Ca green, O red) is determined by chiral amino acids (stick models) present during the crystallization. The interplay of composition and chirality of the crystal surfaces and additives leads to enantiospecific adsorption of the D and L amino acids on chiral surface steps. The resulting surface passivation creates a kinetic barrier, which controls the phase selection.

Greenhouse gas “al dente”: Exposure of the nonpolar ZnO(100) surface to CO₂ at 95 K leads to the formation of an unusual tridentate carbonate species (see picture; C green, O red, Zn gray). Use of several experimental techniques (for example, high-resolution electron energy loss spectroscopy (HREELS)) and theoretical calculations provides insight into the activation of CO₂ on the surface.