Angewandte Chemie International Edition

Photodetachment of the oxyallyl radical anion leads to formation of the oxyallyl diradical, an elusive transient molecule involved in many organic reactions. As described by W. C. Lineberger et al. in their Communication on page 8509 ff., the photoelectron spectrum reveals that the oxyallyl ground state is singlet and the lowest triplet state is only 55 meV higher in energy. The spectral profile indicates that the planar singlet state is the transition state for ring-opening of cyclopropanone, whilst the CCC bending motion is activated upon photodetachment to the triplet state.

Oligomeric cation–cation complexes of actinyls are highly relevant for nuclear waste reprocessing and the migration of actinides in the environment. In their Communication on page 8477 ff., M. Mazzanti et al. show that the N,N′-bis(salicylidene)ethylenediamine (salen) ligand can stabilize uranium in the pentavalent state. A tetrametallic cation–cation complex shows stability towards disproportionation and hydrolysis, and an unambiguous antiferromagnetic coupling between the four oxo-bridged uranium centers.

“The biggest challenge facing scientists is the capture and utilization of solar energy. The secret of being a successful scientist is loving to solve problems and to share new findings with others …” This and more about Lawrence T. Scott can be found on page 8402.

Wiley-Blackwell, Chichester 2009. 640 pp., hardcover € 155.00.—ISBN 978-1405167208

Royal Society of Chemistry, Cambridge 2009. 192 pp., hardcover £ 70.00.—ISBN 978-1847558985

Flexible linkers: Surface chemists have long strived to prepare surfaces with properties that can be adjusted by a external stimulus. In a new platform method a substrate-bound triacatriangulinium spacer provides the attached azobenzene molecule enough room so that it can change configurations upon irradiation (see picture).

Selenium goes green! Recent advances in organoselenium chemistry clearly demonstrate that selenium-based catalysts can be used conveniently in a series of functional group transformations. Organoselenium compounds are promising “green catalysts” as they can transfer oxygen from environmentally friendly oxidants such as H₂O₂.

One particle, two faces: The synthesis of Janus particles is an emerging area of research. Such particles resemble the two-faced Roman god Janus who, according to mythology, had a face on either side of his head (see picture). Polymeric asymmetric particles in particular have recently received significant attention. Synthetic strategies and potential applications of such Janus particles are described.

The friendly approach: The use of hazardous molecular halogens can be avoided by applying an oxidative halogenation strategy. Hydrogen peroxide and oxygen are suitable oxidants to promote the oxidation of a halide, either in the presence of a catalyst or uncatalyzed, into an active halogenating species (see scheme). The uncatalyzed transformation occurs with 100 % halogen atom economy and can be improved further by using alternative reaction media.

Two distinct strategies uncovered potent inhibitors of the title enzyme. X-ray crystallography and isothermal titration calorimetry guided the systematic elaboration of fragments identified from biophysical screens. The excellent inhibitor shown in the enzyme active site on the right was formed by connection of the lead fragments (left) with an acyl sulfonamide linker and resembles the best inhibitor discovered by the fragment-growing strategy.

Take the rough without the smooth: The electrodeposition of patterned metal microelectrodes on a chip-based platform led to biosensors with varying sensitivity according to the degree of surface nanostructuring, which could be controlled systematically (see picture). The sensitivity of microelectrodes with highly nanostructured surfaces was superior to that of smooth microelectrodes.

In the time it takes for lunch: An electronic chip featuring nanostructured microelectrodes (NMEs) enables the analysis of microRNA expression profiles in just 30 min in small RNA samples without enzymatic amplification or sequence labeling. The multiplexed chip detects the hybridization of microRNA targets to NME surfaces and provides large electrocatalytic gain through the use of an ultrasensitive redox reporter system (see picture).

Don't be square: The title cages were synthesized by cooperative assembly of four-connected units and mixtures of two bridging dicarboxylate ligands (see picture). This work may open a new synthetic path towards complex coordination polyhedra that are inaccessible through reported synthetic procedures.

Same but different: L-Cysteine (L-cys) and L-penicillamine (L-pen) ligands are incorporated in similar pentanuclear Au^I₃M₂ (M=Ni^II, Co^III) structures with, however, opposite stereochemical configurations. This phenomenon is explained in terms of intramolecular hydrogen bonding and steric interactions, which may provide insight into why D-penicillamine behaves like L-cysteine in nature.

Close encounters: Bending a flat molecule to make better contact with the surface of a curved molecule introduces strain. If the curved molecule can flatten somewhat (see picture), the overall energy cost of maximizing the surface contact is shared by both partners. X-ray crystal structures illustrate this geometrical mutual adaptation phenomenon.

Useful connection: The self-assembly of four salen complexes of pentavalent uranyl ions by mutual coordination affords a tetrametallic complex that is highly stable toward disproportionation and hydrolysis, and shows an unambiguous antiferromagnetic coupling between the four oxo-bridged uranium centers (see picture; O red, U green). The first mixed-valent U^V₃/U^VI compound has been selectively synthesized from this complex.

An open superstructure: A Pd/CeO₂ catalyst prepared by solution combustion synthesis is three to five times more active for CH₄ combustion than the best conventional palladium-based systems. The catalyst contains an ordered, stable Pd-O-Ce surface superstructure (see picture; cyan arrow is a square-planar Pd site, red arrow is an undercoordinated O atom) and is an example of ultra-highly dispersed, stable PdO within an oxide carrier.

Stand and deliver: Degradable polyelectrolyte microcapsules (PMs; see picture) as antigen delivery vehicles are taken up by dendritic cells (DCs) by macropinocytosis. Following uptake, the shell of the microcapsules ruptures, resulting in the invasion of the capsules by the cellular cytoplasm, thus allowing DCs to efficiently process encapsulated antigen.

Smart microgels: High internal phase emulsions (HIPEs) with a volume fraction up to 0.9 are prepared using soft microgel particles as stabilizer. Adsorption of microgels at the interface can effectively hinder droplet coalescence, and the excess particles form a gel in the continuous phase to inhibit creaming and phase inversion. Drying such HIPEs in air leads to porous materials.

DNA origami: A DNA nanotube containing gold-binding peptides can nucleate nanoparticles of a discrete size from soluble chemical precursors. The peptide–DNA nanostructure was used to direct the assembly of an inorganic nanostructure, with gold nanoparticles distributed along the surface of the DNA nanotube (see picture). The resulting nanostructure is an important step forward in the synthesis of programmable inorganic materials by self-assembly.

It happens at the Met: The DNA platination rate is substantially enhanced by methionine binding to trans-coordinated platinum antitumor drugs (see scheme). Platinum–methionine intermediates were also formed in a cell system and could play a major role in the mechanism of action of trans compounds.

An unforgettable monolayer: Dialkylthiolate-tethered metal complex self-assembled monolayers (see picture; thickness 3 nm) provide stable and reproducible molecular monolayer nonvolatile memory (MMNVM) characterized by its hysteretic current–voltage (I–V) properties and retention time for write–multiple read–erase–multiple read pulse cycles. This is the first known voltage-driven MMNVM using only a molecular monolayer.

Polymorph hunting: The crystal structure of a third polymorph (form III; see picture: N blue, S yellow, O red) of 6-amino-2-phenylsulfonylimino-1,2-dihydropyridine, a crystal-structure-prediction blind-test molecule, was obtained using polymer-induced heteronucleation. Experimental stability determination finds that the in silico predicted thermodynamically stable form (form II) is actually least stable among the three polymorphs.

Small S–T splitting: The photoelectron spectrum of the oxyallyl radical anion (see picture) reveals that the electronic ground state of oxyallyl is singlet, and the lowest triplet state is separated from the singlet state by only (55±2) meV in adiabatic energy.

Palladium-ringed gold: The acid-pretreated Au–Pd catalysts supported on TiO₂ have a well-defined gold-rich core (blue) and palladium-rich shell (green). This type of core and shell enhances the catalytic activity of the catalyst for the direct synthesis of H₂O₂ from H₂ and O₂.

Totally logical: The well-known complex [Ru(bpy)₃]²⁺ (bpy=2,2′-bipyridine) can perform as both a 4-to-2 encoder and a 2-to-4 decoder (see picture; gray C, blue N, red Ru) by a combination of electronic and photonic inputs and outputs. The system can be reset in situ without the addition of chemical reagents. This approach is considered as an alternative route to solid-state molecular electronics and the design and construction of chemical computers.

The affinity of methylmercury towards capping leuko-squaraine groups (see picture, white) induces the opening of the pores of a capped mesoporous hybrid material and the release of entrapped safranine dyes (orange), thus allowing the selective optical detection of methylmercury in complex biological samples.

A flashy protein: The flash-induced transient protonation of pyranine has been studied in the presence of the cross-linked double mutant E166C/A228C (red trace), a reduced mutant (blue trace), and wild-type bacteriorhodopsin (gray traces). If helices F and G are cross-linked, there is a delay in both proton release (extracellular side) and proton uptake (cytoplasmic side). Together with flash photolysis and FTIR studies, these data support a rigid-body mechanism of bacteriorhodopsin proton transport.

Peptides see the light: The photoactivation of peptide precursor cations during electron transfer dissociation (ETD) led to the generation of isotopic cluster peaks that more closely resembled theoretically predicted product-ion distributions. This method should enable the application of ETD to low-charge-density peptide precursors, the gas-phase secondary structure of which prevents the direct formation of c- and z^.-type fragment ions.

Go for the burn! Sol–gel autocombustion is an energy-efficient approach to synthesizing metals, such as Co, Ni, Cu, Ag, Bi, and Co–Ni alloy. Based on differential thermal analysis (DTA) and mass spectrometry measurements (see picture for Ni gel), a reaction mechanism is proposed that leads to the formation of metals and metal alloys instead of metal oxides.

Fast and furious: The mobile ring of a copper-complexed [2]rotaxane incorporates an endocyclic but nonsterically hindering bidentate chelate. The rotaxane axis contains three different chelates (see picture), and both terminal coordination sites are separated by about 23 Å. The shuttling motion is triggered by oxidation or reduction of the copper center and is as fast as that in a related two-station rotaxane whose terminal stations are 10 Å apart.

Singles party: A compound with a Si^ISi^I bond was prepared by the reduction of amidinatotrichlorosilane with potassium graphite. There is no multiple-bond character in the SiSi bond, and the X-ray structural analysis (see picture) shows that this bis(silylene) possesses a gauche-bent geometry.

Keep your eye on the oxygen: In situ time-resolved neutron diffraction measurements can be used to study the structural changes occurring during oxygen exchange in a material (see graph of the increase in oxygen content when the gas flux is switched from Ar to O₂). The method is demonstrated for a layered cobaltite, which is a promising cathode material for intermediate-temperature fuel cells.

Oxatropanes from oxiranes: An expedient assembly of the compact platensimycin core is described. The synthetic approach relies on a Suzuki cross-coupling, a late-stage dearomatization reaction, and a copper-catalyzed vinyl oxirane ring expansion for accessing the oxatropane moiety of the natural product.

Let relief flow forth! A three-step, continuous-flow synthesis of ibuprofen was accomplished using a simplified microreactor. By designing a synthesis in which excess reagents and byproducts are compatible with downstream reactions, no intermediate purification or isolation steps are required.

Making introductions: The CF₃S unit can be added in an electrophilic fashion to alkenes and alkynes in reactions with trifluoromethanesulfanylamide reagents (see scheme; Ts=toluene-4-sulfonyl). The products obtained may be of interest, for example, in pharmaceutical chemistry and materials science.

On the flipside: A reversible photochromic mechanism for the complex [Ru(bpy)₂(pySO)]²⁺ (bpy=2,2′-bipyridine, pySO=2-(isopropylsulfinylmethyl)pyridine) is presented. Isomerization from the S-bonded (see picture; blue) to the O-bonded form (red) occurs upon excitation with UV light with a time constant τ of 1.5 ns (Φ=0.11), for the reverse process τ=6.3 ns (Φ=0.027).

Capable and efficient: Carbon-coated nanoparticles of LiMn_0.8Fe_0.2PO₄ (see TEM image) synthesized by a solid-state reaction were found to be an excellent cathode material for lithium-ion batteries: A stable reversible capacity of up to 165 mA h g⁻¹ was observed, along with excellent cycling, very fast rate capabilities, excellent thermal stability, and very low surface reactivity in lithium-battery electrolyte solutions.

The first members of a new class of depsipeptides with tartaric acid as the core unit, called Siamese depsipeptides, are described. These compounds were synthesized from a branched precursor in only one cyclization step. The structural manipulation of a natural bioactive depsipeptide (sansalvamide A) gives analogues with greater activity, and thereby provides additional information on structure–activity relationships (see structures).

Feeling the pinch: Remarkably facile SiC(sp³) and SiC(sp²) bond cleavage processes occur in [(CyPSiP)M(alkyl)] species (M=Ni, Pd; see picture); in the case of Ni, these SiC bond activation processes are reversible on the NMR timescale in solution. Such examples of metal-mediated cleavage of an unstrained SiC(sp³) bond are extremely rare and are unprecedented for Ni.

A new twist: The catalytic asymmetric semipinacol rearrangement reaction of 2-oxo allylic alcohols 1 in the presence of a catalytic amount of chiral phosphoric acid (R)-2 a or its silver salt (R)-2 b affords enantiomerically pure spiroethers 3.