Angewandte Chemie International Edition

A chemically mediated microfluidic approach to the generation of particle-coated bubbles is reported by E. Kumacheva and co-workers in their Communication on page 5300 ff. The approach employs rapid, controllable dissolution of CO₂ bubbles in a dispersion of carboxylated particles. Local increases in the acidity of the medium in the neighborhood of the bubbles lead to a change in the surface energy of the particles and their deposition on the gas–liquid interface.

A highly efficient protein delivery into cytoplasm is described by K. Kataoka, and co-workers on page 5309 ff. The charge-density increase of a protein cargo by reversible modification, which was based on the charge-conversional moieties citaconic amide and cis-aconitic amide, helped the stability of protein/block copolymer polyionic complex (PIC) micelles. The rapid protein charge conversion in endosomes induced the dissociation of the PIC micelles and efficient endosomal escape.

“My favorite subject at school was chemistry! The most significant scientific advance of the last 100 years has been the discovery of how DNA works. …” This and more about Uwe T. Bornscheuer can be found on page 5236.

Oxford University Press, Oxford 2009. 320 pp., hardcover, $ 130.00.—ISBN 978-0199213207

Elsevier Science, 2008. 320 pp., hardcover $ 185.00.—ISBN 978-0444530332

Repetition does not hurt! New strategies for the modulation of the reactivity of difunctional building blocks are discussed, allowing the palladium-catalyzed controlled iterative cross-coupling and, thus, the efficient formation of complex molecules of defined size and structure (see scheme). As in peptide synthesis, this development will enable the automation of these reactions. M^PG=protected metal, M^act=metal.

Bubbling to the surface: Microscale gas bubbles can be generated in a microfluidic device by simultaneously injecting CO₂ and a dispersion of particles whose hydrophobicity increases as the pH value decreases. The CO₂ dissolves rapidly out of the bubbles, which shrink, and render the dispersion increasingly acidic. This drives the particles to the bubble surface where they form a type of “armor” against further dissolution (see picture).

The structural features of polycyclic polyether natural products can, in some cases, be traced to their biosynthetic origin. However in case that are less well understood, only biosynthetic pathways that feature dramatic, yet speculative, epoxide-opening cascades are proposed. We summarize how such epoxide-opening cascade reactions have been used in the synthesis of polycyclic polyethers (see scheme) and related natural products.

The right fit: Plasmid DNA molecules show chirality-dependent interaction with gold surfaces modified by L and DN-isobutyrylcysteine. Relaxed DNA molecules have a stronger interaction and adsorption on the L surface, while their counterparts on the D surface maintain a supercoiled conformation, indicating a weak interaction (see picture).

Making connections: A hydroxy-centered trinuclear nickel cluster has been employed to construct a highly connected, highly symmetric framework with a uninodal nine-connected topology. An array of triakis tetrahedra leads to a biporous intersecting-channel system (see picture).

Top down goes bottom up: A family of microporous interpenetrating diamond frameworks can be constructed from a pentanuclear tetrahedral complex with nitrate groups at the apical positions as an inorganic precursor. A “bottom-up” methodology was used for substitution of the nitrate groups by linear ditopic carboxylate ligands (see picture). The Langmuir surface area of the resulting frameworks is higher than that of classical zeolites.

Bright lights: Fullerene–silica hybrid nanoparticles have bright photoluminescence, high photostability, and low cytotoxicity, which are assets for bioimaging agents. The origin of the photoluminescence of the nanoparticle is the C–O–Si bond (see picture).

Bubbling up: Dissolution of CO₂ bubbles in a suspension of colloidal particles chemically induces the assembly of particles on the surface of shrunken bubbles, and thus yields rapid continuous formation of a colloidal armor. This approach maintains the high colloidal stability of particles in bulk, has increased productivity, and allows the formation of bubbles with precisely controlled dimensions.

In phase: The title compounds lie in a new region of phase space for such a structure, and have stoichiometries in accord with a classical Zintl phase formulation. The small semiconductor gaps indicated by DFT calculations are also supported by their diamagnetic susceptibilities.

Special delivery! Polyionic complex (PIC) micelles that contain the charge-conversional moieties citaconic amide or cis-aconitic amide were developed for cytoplasmic protein delivery. The increase of the charge density on the protein cargo helped the stability of the PIC micelles without cross-linking, and the charge-conversion in endosomes induced the dissociation of the PIC micelles to result in efficient endosomal release (see picture).

Living on the edge: Three-dimensional reconstructions from electron tomography data recorded from Au/Ce_0.50Tb_0.12Zr_0.38O_2−x catalysts show that gold nanoparticles (see picture; yellow) are preferentially located on stepped facets and nanocrystal boundaries. An epitaxial relationship between the metal and support plays a key role in the structural stabilization of the gold nanoparticles.

An energy-transfer cascade is generated from a cationic conjugated polymer (PFP) and negatively charged, Y-shaped DNA labeled with three dyes at its termini (fluorescein (Fl), Tex Red, and Cy5). Multistep fluorescence resonance energy transfer regulates the fluorescence intensities of PFP and the dyes. Different types of logic gates can be operated by observing the emission wavelengths of different dyes with multiplex nucleases as inputs.

High pressure under the spotlight: A new milliliter-scale reactor is developed for using supercritical CO₂ to perform continuous photo-oxidation reactions. Changing from a traditional microliter-scale batch reaction to 8 hours of reaction using the new reactor gives a 3000-fold scale-up of the oxidation of α-terpinene (see picture).

Feature film: Thin films made by exponential layer-by-layer growth display high diffusivity and can be readily infiltrated with inorganic nanoparticles. They can sequestrate molecular systems from solution as a function of the composition of their layers, while providing intense surface-enhanced Raman scattering (SERS) signals (see picture).

Extremely fast fluorescence labeling (<1 min) of a recombinant alkene-encoded protein in living Escherichia coli cells was observed with tetrazole 1. The electron-donating methoxy substituent raises the energy of the highest occupied molecular orbital of the nitrile–imine intermediate derived from 1. This strategy greatly accelerates the functionalization of alkenes by 1,3-dipolar cycloaddition in living systems.

A stereoselective synthesis of cyathin A₃ and cyathin B₂ has been achieved by a Prins-type reaction of a cycloalkenyl cyclopropanol. Particularly noteworthy is the use of a spirocyclobutanone moiety as a convenient scaffold for an efficient ring-closing metathesis to stereoselectively construct a suitably functionalized seven-membered ring (see scheme).

In quarantine: Nitroxide spin probes are encapsulated by hexameric resorcinarene molecular capsules in dichloromethane solutions (see picture). A substantial reduction in the tumbling rates occurs upon encapsulation of two cationic probes and one neutral probe. As the molecular volume of the probe increases, the tumbling rate of the probe reflects the overall tumbling rate of the entire supramolecular assembly.

Involuntary association: Anionic β-galactosidase enzymes associate with positively charged Au nanoparticles to produce reduced-charge conjugates, which assemble at oil–water interfaces to result in stable microcapsules (see picture). The microcapsules were formed quickly and showed high enzymatic activity, which makes them promising materials for biotechnology applications.

From imines to amines through catalysis by Ir^I complexes of a new type of P,N ligand (see scheme): This reaction affords the corresponding optically active amines with up to 98 % ee and has also been used with perfect stereoselectivity in the asymmetric synthesis of sertraline (1), an important antidepressant chiral drug.

A simple but effective copper-catalyzed borylation of aryl halides, including electron-rich and sterically hindered aryl bromides, with alkoxy diboron reagents occurs under mild conditions (see scheme). Preliminary DFT studies of the mechanism suggest that σ-bond metathesis between a copper–boryl intermediate and the aryl halide generates the aryl boronate product.

It does get in! A fluoride-assisted direct cross-coupling of cyclic enamides with trialkoxy aryl silanes by a palladium-catalyzed CH activation leads to a wide range of enamides in yields of up to 95 %.

Fluoro power: In agreement with theoretical studies on α-fluorocarbanions an X-ray crystal structure shows the α-fluorobis(phenylsulfonyl)methide anion adopts a pyramidal configuration (see picture). High-level calculations and NMR spectroscopy studies demonstrate that electron-withdrawing substituents play a crucial role in modulating the properties of bis(phenylsulfonyl)methide anions.

Peanut clusters: Anion templates are used in a facile approach for the synthesis of high-nuclearity silver clusters. The cluster nuclearity can be controlled by adjusting the size of the templating anions and by using different alkynyl ligands. The largest silver alkynyl cluster, which consists of 35 silver(I) centers in the shape of a peanut, has been prepared by using chromate anions as templates (see picture).

Ringing the changes: The total synthesis of the title compound centers around a novel strategy that employs a nickel(0)–phosphine complex and triethyl borane in an efficient closure of a 14-membered ring through CC bond formation (see scheme; cod=cyclooctadiene). The synthesis was accomplished in 10 steps and in approximately 9 % overall yield.

Standing room only: Dense polymer brushes can be prepared by adsorbing a diblock copolymer comprising a neutral block and a polyelectrolyte block to an oppositely charged polyelectrolyte brush (see picture). The density of the resulting neutral brush is determined by charge compensation, leading to brush densities well over 1 nm⁻². The diblock copolymer can be desorbed by changing the solution conditions.

Quick access: A concise and efficient formal synthesis of platencin has been accomplished in nine steps from a commercially available starting material. The synthesis utilized only one protecting group. The base-catalyzed Michael cyclization of precursor 1 afforded the key diketone 2, which was converted into the desired core structure 4 via the radical intermediate 3.