Angewandte Chemie International Edition

Programmable organic light-emitting diodes: UV irradiation converts an oxetane-functionalized dithienylethene derivative from its colorless open form into a dark blue closed form, while visible light reverses the reaction. In the Communication on page 4038 ff., K. Meerholz and co-workers describe a reversibly switchable organic light-emitting diode based on this principle.

Wrong handedness? No problem! K.-H. Ernst et al. describe in their Communication on page 4065 ff. how the chirality of single adsorbates can be switched into the opposite enantiomeric state. By using inelastically tunneling electrons from the tip of a scanning tunneling microscope in an ultra-high vacuum, certain molecular vibrations are excited that, in turn, cause different actions such as hopping, rotation, and chirality conversion at the surface.

„When I wake up I row. When I was eighteen I wanted to be Morrissey. …“ This and more about Benjamin G. Davis can be found on page 3900.

Wiley-VCH, Weinheim 2009. 306 pp., hardcover, 129.00 €.—ISBN 978-3527320370

Wiley-VCH, Weinheim 2008. 866 pp., hardcover € 279.00.—ISBN 978-3527318155

Seeing is believing: In light of recent advances, the pros and cons of using electrons and X-rays for in situ studies of catalysts are analyzed: by using X-rays the structure of bound reactants at steady state are obtained from extended X-ray adsorption fine structure spectroscopy (EXAFS) data (see graph), thereby affording mechanistic insights.

Turn the light on: The synthesis, folding and maturation kinetics of individual green fluorescent protein (GFP) molecules have been studied using a cell-free transcription–translation system and single-molecule fluorescence. Ribosomes, which were labeled with a red fluorophore and tethered to a glass surface, were used to synthesize GFP Emerald molecules that become fluorescent after maturation.

En route to molecular electronics: As extended, conjugated oligomers are desirable for molecular electronics, their electrical conductance should display a low attenuation factor. Zinc-complexed oligo(ethynyleneporphyrindiylethynylene)s have been prepared that are distinguished by ultralow attenuation factors in single-molecule conductance.

A black whole: The black insoluble biopolymer eumelanin is prepared through the oxidative polymerization of 5,6-dihydroxyindoles (see scheme). It has a largely unknown heterogeneous structure and unique optoelectronic properties. Current structural models are presented and possible applications are discussed.

Forces to reckon with: Supramolecular complexes, such as the one shown, are normally based on a combination of different interactions such as ion pairing, hydrogen bonds, and stacking interactions. The not always simple characterization of the nature and strength of intermolecular forces provides assistance to the understanding of biomimetic systems, as well as for the design of synthetic receptors, drugs, and intelligent materials.

Oil on troubled waters: Stimuli-sensitive emulsions have been used to prepare temperature- and pH-responsive microgels. The emulsion stability at oil–water interfaces is not governed by the particle packing density, and structural changes induced by the interface lead to connections between the individual microgels (see picture; scale bar 1 μm), which behave very differently compared to solid-particle-stabilized emulsions.

Let's drink to that! Two alcohols (one primary and one secondary) can be coupled in an atom-efficient process by a hydrogen-autotransfer catalytic system in the form of silver subnanoclusters supported on γ-Al₂O₃. The recyclable heterogeneous catalyst promoted the one-pot CC cross-coupling in the presence of a catalytic amount of the weak base Cs₂CO₃ (see reaction mechanism).

Oil and water: A new energy-efficient and atom-economical catalytic route for the production of alkanes and methanol by upgrading the phenolic fraction of bio-oil has been developed. The one-pot aqueous-phase hydrodeoxygenation process is based on two catalysts facilitating consecutive hydrogenation, hydrolysis, and dehydration reactions.

Turing lead into gold: Hollow hybrid PbS_x–Au nanostructures of about 10 nm in diameter were synthesized using a one-step reaction under mild experimental conditions. The redox reaction of gold precursors with PbS nanocrystals in the presence of dodecylamine leads to the hollow feature of hybrid nanostructures (see picture).

A real turn-on: The emission intensity of heterocycle 1 increases upon binding to Pb²⁺. Thus, 1 acts as a small-molecule “turn-on” fluorescent sensor for lead. The sensor is highly selective and is functional over a wide range of pH values.

Ring leader: PtCl₂ catalyzes intramolecular cyclization of o-isopropyl or o-benzyl aryl alkynes to give substituted indene derivatives with good yields and high selectivity. This reaction appears to proceed through an sp³ CH activation and 1,4-hydrogen migration pathway (see scheme).

Mind the (narrow) gap: α-Ethynylphospholes generated in situ from the corresponding silyl-capped precursors were converted into a series of α-(arylethynyl) phospholes bearing functional substituents as well as an α,α′-linked terphosphole (see scheme). The terphosphole has a narrow HOMO–LUMO gap owing to efficient π conjugation over the three phosphole rings.

Give me a tip: In situ production of diazonium salts from nitro compounds allows the use of diazonium chemistry for microelectrochemical patterning of surfaces by scanning electrochemical microscopy. The nitro precursor is reduced at the tip to the amine, which is diazotized in the interelectrode space as it diffuses (see picture). The tip acts as a source of diazonium salts, allowing sample derivatization just beneath the tip.

2009: A boraanthracene odyssey: General routes to boraanthracene derivatives—long proposed, but never observed—are disclosed, along with the structural and photophysical properties of these compounds and their remarkable reactivity towards oxygen.

High-de-hydride! A straightforward reaction between a magnesium silylamido/N-heterocyclic carbene adduct and phenylsilane provides a {Mg₄H₆} cluster molecule that may be regarded as a combination of two magnesium dihydride and two magnesium monohydride moieties.

Multistep in flow: The Seyferth–Gilbert reagent 1 has been applied in a flow system to rapidly synthesize terminal alkynes. The system has been further applied to synthesize triazole 3 from alcohol 2 in a three-step oxidation/homologation/copper(I)-catalyzed azide–alkyne cycloaddition sequence without isolation of intermediates (see scheme).

Fully interactive: Overlap between extended unoccupied molecular orbitals leads to the high photoconductivity of interactive radical dimers. Sandwich-type cells (see picture; ITO=indium tin oxide) comprising highly oriented thin films of a disjoint diradical, 4,4′-bis(1,2,3,5-dithiadiazolyl) (BDTDA) exhibit a photocurrent with a high on/off ratio at reverse bias voltages and photovoltaic behavior at zero bias voltage.

Custom built: A promising new approach towards more efficient self-assembled cage receptors through computer-aided design is demonstrated. The resulting M₄L₆ tetrahedral cage, internally functionalized with accurately positioned urea hydrogen-bonding groups (see structure; yellow: predicted, blue: experimental, space-filling: SO₄²⁻), proved to be a remarkably strong sulfate receptor in water.

Sialome sweet sialome: As sialic acids are involved in many host–pathogen recognition events and are markers of embryonic and malignant tissues, there is great interest in methods for the enrichment and identification of sialylated glycoproteins from complex tissues. Now N-(4-pentynoyl)mannosamine can be used to metabolically label sialylated glycoproteins in living animals, enabling future identification of new biomarkers.

Fast detection of cellular thiols in aqueous medium was achieved using a newly developed fluorescence probe (see picture). Based on this probe, a high-throughput fluorescence assay for glutathione reductase was developed.

Enlightening the memory: The integration of a crosslinkable photochromic dithienylperfluorocyclopentene (DTE) into organic light-emitting diodes (OLED) allows for the individualization of the emissive area of the OLED device, for example, for signage applications. The operation principle is based on switching the injection barrier for holes (positive charge carriers). Very large ON/OFF ratios of up to 3000 for current as well as electroluminescence have been achieved.

Light aqueduct: Periodic mesoporous organosilica exhibits strong light absorption due to densely packed organic chromophores within the pore walls. Light energy absorbed by 125 biphenyl groups in the pore walls is funneled into a single coumarin 1 molecule in the mesochannels with almost 100 % quantum efficiency, and results in significant enhancement of emission from the coumarin 1 dye.

Now you bind it—now you don't! Chemical degradation of a dendritic scaffold allows multivalent interactions with DNA to be “switched off” as the multivalent array of ligands breaks down into smaller fragments, offering an approach by which a molecule can be temporarily endowed with high affinity for a biological target—an important concept in the development of new synthetic systems to intervene in biological pathways.

A shuttle system has been developed to genetically encode unnatural amino acids in mammalian cells using aminoacyl-tRNA synthetases (aaRSs) evolved in E. coli. A pyrrolysyl-tRNA synthetase (PylRS) mutant was evolved in E. coli that selectively aminoacylates a cognate nonsense suppressor tRNA with a photocaged lysine derivative. Transfer of this orthogonal tRNA–aaRS pair into mammalian cells made possible the selective incorporation of this unnatural amino acid into proteins.

Translation of specific small peptides on the ribosome can confer resistance to macrolide antibiotics. To reveal the molecular details of this and related phenomena, stable RNA–peptide conjugates that mimic peptidyl-tRNA would be desirable, especially for ribosome structural biology. A flexible solid-phase synthesis strategy now allows efficient access to these highly requested derivatives without restriction on the RNA and peptide sequences.

Chirality chameleon: Inelastic electron tunneling manipulation can be used to change a single chloronitrobenzene (ClNB) molecule, randomly adsorbed on Au(111), into its desired enantiomeric form (r or l, see STM images and ball-and-stick representation) and to vary its rotational orientation. The different threshold voltages for chirality change (260 mV) and rotation (380 mV) allow these processes to be induced separately.

Pumped up: Propene molecules form chiral complexes when adsorbed on a copper surface. Inelastically scattered tunneling electrons from the tip of a scanning tunneling microscope induce rotation or diffusion of the adsorbate on the surface. Higher tunneling currents can lead to conversion of the adsorbate into the opposite enantiomer.

SiSe matters: Diselenadisiletane 2, formed from direct reaction of a racemic silylene 1 with elemental selenium, gives the first bis(silaselenone) upon hydrolysis with water (3; see picture, C gray, H white, N blue, O red, Se purple, Si green; d(SiSe)=215 pm). The reaction is stereoconvergent: only racemic forms of 3 are obtained from a mixture of racemic and meso forms of 2.