Angewandte Chemie International Edition

Nanoscale molecular capsules are assembled by means of noncovalent interactions and enclose over 1300 ų of molecular space. The supramolecular interactions between two independent nanocapsules lead to changes in the dynamic structure of the capsule walls. This dramatically alters the packing and fluidity of the guest matrix within the host. In their Communication on page 5263 ff., J. L. Atwood and co-workers provide valuable insight into the interactions and fluidity of the so-called “new phase of matter”.

Molecular structure–property relationships for molecular electronics are beginning to emerge. Recent experiments lend credibility to the single-molecule nature of transport measurements and illustrate the molecular features that give rise to various interesting conductance behaviors (see picture).

Molecular mitosis: Figure-eight octaphyrins form binuclear metal complexes that can split into two covalently spiro-linked corrolates. In a unique case binuclear Cu^II [36]octaphyrin divides thermally into two Cu^II [18]porphyrins presumably with participation of a transient spirocyclobutane species (see schematic representation).

Species of curiosity for a long time and more recently ligands for metals, nucleophilic heterocyclic carbenes deserve renewed attention as reagents and catalysts in organic synthesis. Their known chemistry (see scheme) foretells an impressive future.

Metal-free synthesis: An increasing number of asymmetric organic reactions can be catalyzed by a chiral organic molecule. Although substrate dependency remains an important issue in many cases, a large number of organocatalytic transformations are as efficient as current standards in asymmetric synthesis demand (see example).

Fruits of the laboratory: Dendrimers containing up to six different functional groups can be prepared in multistep one-pot reactions by using a selective manipulation and deprotection strategy (see example). The authors call these multifunctional dendrimers molecular fruit-salad trees; they could function as useful building blocks for drug-delivery systems and novel materials.

Not only skin deep: A fluorescein–amphotericin B conjugate with a new piperazine linker (see structure) was prepared and used as a probe of the biomembrane and the mechanism of action of amphotericin B both in vivo and in liposomal experiments. The amphotericin B analogue localizes at the membrane of yeast cells but is internalized by mammalian cells.

Hair raising! Poly(methyl methacrylate) chains grown on a dendronized polymer (denpol) having repeat units with terminal 2-bromoisobutyramide groups produce a hairy surface. When adsorbed on mica, MoS₂, and highly oriented pyrolytic graphite, the hairy denpol molecules have a quasi two dimensional backbone conformation. The 50-nm-long hairs bend back on the MoS₂ (see image) and graphite substrates.

A protein rheostat: A strategy for controlling enzyme activity by cleavage of a low-affinity “pseudosubstrate” inhibitor from an autoregulated version of the enzyme (see figure) is described. Peptide-bond cleavage was mediated by conditional protein splicing. The small molecule rapamycin was used to induce intein trans-splicing of the catalytic subunit of cAMP-dependent protein kinase A (PKA).

A new, general and objective approach to locating critical points of fluid mixtures is described (see picture). It is new because it exploits the fact that the liquid phase forms preferentially on the surface of the sensor. It is general because it can be used with any type of surface-sensitive sensor, and it is objective because it is based on the numerical output of a sensor rather than the visual image normally used for phase equilibrium studies.

Understanding frustration: The control of structure through the choice of the template has allowed the synthesis of nona-nuclear metal wheels that contain {Cr₈Ni} or {Cr₇(VO)₂} cores. Magnetic studies (see picture) of one of these wheels shows that it behaves as a magnetic Möbius strip. These are the first detailed magnetic studies of an odd-numbered ring larger than trinuclear and should help in the understanding of spin-frustrated systems.

Molecular gymnastics: Ethylene molecules (C atoms in green) rotating along the principal axes impinge perpendicularly on an Ag (001) metal surface precovered with O₂ (O atoms in red) and may stick in some favorable cases. The sticking probability S depends on the approach of the CC bond to the surface: “helicopters” (d) stick better than “cartwheels” (b and c) or “cigars” (a).

A nucleophilic substitution–elimination reaction strategy in which difluoromethyl phenyl sulfone is used as a selective difluoromethylidene equivalent allows the facile synthesis of 1,1-difluoro-1-alkenes from primary alkyl halides (see scheme).

Gutsy chemistry: A solvothermal process has been developed for the controlled creation of interior space in TiO₂ intestines (either hollow (see TEM image) or partially filled) or spheres in the anatase polymorph. A morphological transformation from intestine to sphere is observed when the water content of the water/2-propanol mixture is decreased.

Dry films: An electrospinning process was used to form films with high water contact angles (166.7°) and low sliding-angles (4.3°). The electrospun films exhibit excellent superhydrophobic Cassie-regime stability: The figure shows a nonwetting water droplet, even after 400 Pa of uniaxial loading.

Stable! The first stable salts containing a simple, inorganic cation with an NCl bond are prepared (see picture). They are [NH₃Cl]⁺[BF₄]⁻, [NH₃Cl]⁺[AsF₆]⁻, and [NH₃Cl]⁺[SbF₆]⁻ and can be safely prepared from (Me₃Si)₂NCl in mixtures of HF and the corresponding Lewis acids and could be used as storable generators for monochloramine gas.

The bigger the better: Increasing metal size seems to be the determining factor in the formation of an unprecedented series of homoleptic linear pyrazolates of the heavy alkaline-earth metals (Ca, Sr, Ba, see picture, Ba=green, N=blue, C=black), with the formation of trinuclear calcium, tetranuclear strontium, and hexanuclear barium derivatives. The linear oligomers display a noteworthy array of metal–ligand bonds.

Straight to the point! Preactivation of a p-tolyl thioglycoside donor, followed by sequential addition of p-tolyl thioglycosyl acceptors in one reaction flask allowed rapid syntheses of oligosaccharides independent of anomeric reactivities of donors and acceptors (see scheme). This strategy greatly streamlines the assembly of oligosaccharides.

Reversed Berry pseudorotation (see picture) results in a severely distorted trigonal-bipyramidal geometry with C_2v symmetry in the paramagnetic (d¹) anion [Ti(C₆F₅)₅]²⁻, which was obtained by the low-temperature reaction of TiCl₄⋅x Et₂O and LiC₆F₅ and is the first homoleptic organometallic compound containing a [TiR₅]²⁻ unit.

Catalytic converter: A (salen)iron(III) complex (salen*=asymmetric bis(salicylidene)ethylenediamine ligand) can be used as a catalyst system for the asymmetric oxidation of aryl sulfides by iodosylbenzene (see scheme). An iodosylbenzene(salen)iron(III) species has been identified as the active intermediate by EPR and NMR spectroscopy. R=aryl, R′=alkyl.

A bicontinuous cubic structure was revealed by electron crystallography on a large-pore mesoporous silica with a cubic Iad symmetry synthesized by using a triblock copolymer as a structure-directing agent. Its reconstructed structure (picture, left) is composed of an enantiomeric pair of interwoven three-dimensional mesoporous networks. Ordered complementary pores form interconnections between the two main channel systems at a special flat point of the G-surface (right).

Top banana! Hydrogen-bonded bent complexes of benzoic acids (H donor) and nonmesomorphic V-shaped 4′-stilbazoles (H acceptor) give rise to polar smectic C (SmCP, see graphic) mesophases. The multifunctional character of these noncovalent materials is confirmed through their electrooptical, dielectric, and luminescent responses.

Solution-phase synthesis of single-crystal ZnO disks and rings was achieved in high yield at low temperature (70–90 °C) by using an anionic surfactant as a template. The reaction can be controlled by means of the growth temperature and the molar ratio of reagents to favor formation of disks or rings. A growth mechanism is proposed on the basis of structural information provided by SEM and TEM.

Genetic vaccination and gene therapy research could benefit from the application of carbon nanotubes. Functionalized, positively charged, water-soluble carbon nanotubes are able to penetrate into cells (see figure) and can transport plasmid DNA by formation of noncovalent DNA–nanotube complexes. Such nanotubes can be used as novel nonviral delivery systems for gene transfer.

One-dimensional supramolecular assembly of dendrimers (see picture) has been achieved by multiple weak interactions between highly branched molecules with irregular structures. This finding contradicts the widely accepted assumption that precise matching of directional interactions and steric constraints is required to facilitate long-range one-dimensional supramolecular assembly.

A new spin on things? Spin trapping of ¹³C-labeled bicyclic mimics of natural nine-membered enediynes provided persuasive evidence for the spontaneous thermal generation of biradicals 1 and the differential reactivity of the resulting C3 and C6 radical centers (see scheme; ST spin trap; TBS tert-butyldimethylsilyl).

Novel pyboxazines and the known pybox ligands are used in the ruthenium-catalyzed asymmetric epoxidation of olefins with H₂O₂ (see scheme). This new catalytic system is successful in the conversion of differently substituted aromatic olefins and gives ee values of up to 84 %.

T time: The new binary antimonide Hf₅Sb₉ forms a unique variant of a square-planar net, namely an unprecedented yet simple T-shaped net (see picture, green) formed by antimony atoms (red). The electronic structure and bonding in the solid state are analyzed by theoretical methods.

The facile self-assembly of six pyrogallol[4]arene molecules leads to a globular truncated octahedron, which encapsulates a guest cluster consisting of ethyl acetate and water molecules (see scheme). The interactions between host capsules can be controlled by derivatization of the exterior surface of the capsule.

All change: Three different output signals, chromic, nonlinear optical, and magnetic, can be altered simultaneously with the molecular switch based on radical 1. The electrochemical reduction and oxidation of 1 is completely reversible. These redox cycles can be repeated several times, and the corresponding changes in the optical properties can be monitored by visible spectroscopy.