Angewandte Chemie International Edition

The photoactivatable fluorescent dye … … rhodamine NN, whose structure is shown in the cover picture, was combined with two further caged fluorophores with similar spectroscopic properties in a microscopy scheme for imaging cellular structures such as peroxysomes, actin, and microtubuli. The scheme, which uses only one emission and one detection channel, enables the stepwise activation and detection of the dyes. The synthesis and properties of rhodamine NN are described in the Communication by V. N. Belov et al. on page 3520 ff. (Picture: H. Sebesse, MPI für biophysikalische Chemie, Göttingen).

Au/Ag alloyed nanostructures exhibit a bright three-photon luminescence upon excitation by a femtosecond laser, and have an intensity level one order of magnitude higher than pure Au or Ag nanoparticles. As Y. Xia, J.-X. Cheng, and co-workers describe in their Communication on page 3485 ff., the excitation is outside the range of plasmon resonance, thus enabling bioimaging with negligible photothermal toxicity.

“My most exciting discovery to date has been the functionalization of endohedral metallofullerenes. My biggest motivation is to realize that where there is a will, there is a way …” This and more about Takeshi Akasaka can be found on page 3408.

Wiley-VCH, Weinheim 2009. 262 pp., softcover € 39.00.—ISBN 978-3527325979

John Wiley & Sons, Hoboken 2009. 432 pp., hardcover € 125.00.—ISBN 978-0470699706

B and F become BFFs: The last of the neutral first-row main group diatomics, BF, has conspicuously eluded synthetic chemists and their attempts to stabilize it by transition metals. After decades of near misses, two contrasting families of fluoroborylene transition metal complexes have been definitively synthesized by the research groups of Aldridge and Andrews.

Branching out: Thiol–yne chemistry is emerging as new tool for polymer chemists, as it represents a unique and efficient coupling procedure to create highly branched structures (see scheme). This method can be used to prepare highly functional dendrimers and hyperbranched polymers.

The freaky molecule: From Odysseus' encounter with the cyclops and the appearance of cyclops-like sheep in Idaho more than 3000 years later, to the discovery of cyclopamine and the hedgehog signaling pathway as well as a highly selective anticancer therapy—this sometimes creepy but always interesting story is told in this Minireview.

An attractive concept: Quasihomogeneous magnetic nanoparticles and magnetic nanocomposites have found increasing application in organic synthesis; for example, they are ideal supports for the heterogenization of homogeneous catalysts (the picture shows a catalyst that can be removed with a simple magnet). This Review summarizes recent developments in the synthesis, characterization, and applications of these materials.

All present and accounted for? Cell mass spectrometry was used to determine the quantity of both gold and polystyrene nano-/microparticles taken up into cells (see picture). The uptake amounts measured for gold nanoparticles were similar to those determined by inductively coupled plasma mass spectrometry, a technique which can not be used to measure the cellular uptake of nonmetal particles.

In a crystal at last: CO₂ binds reversibly to the guanidine molecule TBD. The zwitterionic structure of the adduct is demonstrated by X-ray diffraction analysis and computational methods (see picture; left: C blue, H white, N pink, O red), while its fluxionality in solution is revealed by NMR spectroscopy.

Shape shifting linked to disease: A single-molecule fluorescence technique was used to probe structures of an intrinsically disordered brain protein. A mutation was found to tilt the coupled binding–folding energy landscape of the protein and inhibited switching between induced ordered structures (see picture). The observations provide fundamental insight into the molecular basis of Parkinson's disease.

Reloaded matrix: Facile optical encoding of polyethylene glycol (PEG) based resins provides a direct identification of compounds in combinatorial libraries, and the structures may be correlated with bioactivity. The new technique, microparticle matrix (MPM) encoding (see picture), circumvents some problems often encountered in solid-phase combinatorial chemistry and is extremely simple to implement.

Screening with codes: A versatile methodology for the development of small-molecule affinity chromatography ligands for protein targets is presented. The combination of computational enrichment with automated screening and affinity mapping of an optically encoded combinatorial library allows identification of a novel set of ligands for the single-step purification of human growth hormone (see picture).

Finger on the pulse: Selective experiments can be simultaneously run on different parts of the sample when NMR sequences based on a spatial encoding are used. This approach was applied to a gradient-encoded selective refocusing sequence. The resulting data provide a collection of all the couplings that involve a given proton spin, which can be conveniently assigned and measured from only one spectrum.

Au/Ag alloyed nanostructures exhibit a bright three-photon luminescence (3PL; see picture, left) upon excitation by a femtosecond laser at 1290 nm, with an intensity level one order of magnitude higher than pure Au or Ag nanoparticles. As the excitation is outside the range of plasmon resonance, 3PL enables bioimaging (right) with negligible photothermal toxicity.

Transfer ticket: A group transfer polymerization (GTP) reaction mechanism operates in the living polymerization of diethyl vinylphosphonate, in which high-molecular-weight homo- and copolymers are produced using simple rare-earth-metal complexes (see scheme). The mechanism is consistent with the well-known and established mechanism for polar monomers such as acrylates, and opens up a new approach toward phosphorus-containing polymeric materials.

Line them up: Uniform CeVO₄ nanorod arrays (see picture) were synthesized in a self-assembly approach assisted by ethylenediaminetetraacetic acid (EDTA) molecules in aqueous media. EDTA is important not only in controlling anisotropic growth by restricting the active points of certain faces, but also in mediating the assembly by forming intermolecular hydrogen bonds.

Iridium pyridyl species are key intermediates in the title reactions. Thermal elimination of benzene from complexes 1 (R=Me, Ph) creates a vacant coordination site accessible to unsaturated hydrocarbons. Subsequent intramolecular nucleophilic attack by the pyridyl nitrogen atom to the alkene or vinylidene leads to iridacyclic pyridylidene structures (see scheme).

Shell shock: The one-pot synthesis of shell cross-linked (SCL) micelles was achieved using an ABC triblock copolymer in a 9:1 alcohol/water mixture. These SCL micelles were dialyzed against water, leading to solvation of the core-forming PMPC chains. If the cross-linking is not too high, these chains migrate through the inner shell to join the coronal PEO chains, hence forming nanocages.

The Dark Crystal: A hybrid material is reported that is comprised of 1–2 nm sized gold nanoparticles, accessible only through zeolite micropores in a silicalite-1 crystal, as shown by three-dimensional TEM tomography (see picture). Calcination experiments indicate that the embedded nanoparticles are highly stable towards sintering.

Tunneling through: The sequencing of electron-donating and electron-accepting components that are separated by a σ-electron bridge has resulted in the highest rectification ratio to date from a molecular diode.

The golden touch: Total synthesis of natural (−)-englerin A from (R)-citronellal has been achieved using a gold-catalyzed cyclization as the key step (see scheme). No protecting-group manipulations were required in the synthetic sequence.

All that glitters is gold: The total synthesis of the natural enantiomers of englerins A and B has been completed using a gold-catalyzed stereoselective domino alkyne/alkene/carbonyl cyclization of an enyne with an unprotected alcohol group at a stereogenic allylic position (see scheme; TES=triethylsilyl).

A bright future: The reaction of diazomethane with acid chlorides obtained from N,N,N′,N′-tetraalkylrhodamines affords 2-diazo-2,3-dihydro-1H-indenespiro[1,9′]-9H-xanthen-3-ones—a novel class of caged rhodamines. These dyes allow new imaging procedures based on the step-wise activation and detection of several fluorescent markers (see picture).

Make it spiro! Readily synthesized heteroatom-substituted spiro[3.3]heptanes generally show higher aqueous solubility than their cyclohexane analogues, and show a trend towards higher metabolic stability. The novel framework can be mounted onto scaffolds of druglike structures, such as fluoroquinolones, to afford active compounds with similar or even improved metabolic stability.

The adventures of titin: in vertebrates, titin filaments control the extendibility of the muscle sarcomere. The titin immunoglobulin 27 unfolds through an intermediate (see structure; arrow: hydrogen bonds ruptured to reach intermediate) that it is highly independent of the force load applied. It is shown that this intermediate acts as a “force buffer” that protects immunoglobulin from unfolding at physiologically applied forces.

A new spin on C₆₀: Axially chiral, push–pull buta-1,3-diene chromophores conjugated to vicinally methylated fullerenes (see picture) have high barriers of rotation about their chiral axes. These high barriers allowed their optical resolution and the determination of the absolute configuration by comparison of experimental and calculated circular dichroism spectra. The methyl group is rigidly fixed upon the surface of the carbon sphere and is responsible for the high rotational barriers.

Give Me strength: Methylation of the easily accessible weakly coordinating dianion [B₁₂Cl₁₂]²⁻ affords Me₂B₁₂Cl₁₂ (see picture). This neutral compound is a stronger methylating agent than commonly used methyl triflate, and it even methylates benzene. The synthesis, crystal structure, and reactivity of Me₂B₁₂Cl₁₂ in solution and the gas phase are discussed.