Angewandte Chemie International Edition

Increasing the strain in a series of macrocyclic disulfides was used to show that the kinetics of thiol/disulfide exchange is independent of force. The seemingly counterintuitive finding that pulling on a molecule does not accelerate its fragmentation is presented by R. Boulatov and co-workers on page 7040 ff. These results are consistent with the S_N2 mechanism of thiol/disulfide exchange and the simplest model of chemomechanical kinetics.

Light-sensitive inks for self-erasing images are formed from metal nanoparticles (NPs) covered with photoswitchable ligands dispersed in a polymer film, as described by B. A. Grzybowski and co-workers on page 7035 ff. Upon exposure to UV light, the NPs form metastable aggregates; the apparent color corresponds to the degree of aggregation. In the absence of light, the aggregates fall apart and the images gradually self-erase. Multicolor images can be also be created with a single NP ink.

“The most significant scientific advances of the last 100 years have been the discovery of penicillin and the development of vaccines for various infections. If I could be anyone for a day, I would be a novelist. …” This and more about Masakatsu Shibasaki can be found on page 6944.

John Wiley & Sons, Hoboken 2009. 608 pp., hardcover € 119.00.—ISBN 978-0470033944

Take this ring … Hybrid organic–inorganic rotaxanes can be prepared using a thread incorporating an alkyl ammonium functionality to template the self-assembly of an inorganic wheel cluster. This approach was used to assemble a range of examples, including a system combining two rings and two threads (see picture; C gray, H white, O red, Cu orange, Cr blue-gray, N blue, F light blue).

Juggling rings: A novel two-step procedure achieves the formal (4+1) annulation of a conjugated diene with a β-keto ester to form a functionalized cyclopentene in good yield under mild conditions. The transformation involves a palladium-catalyzed intramolecular oxidative cyclopropanation of an ε-dienyl β-keto ester followed by magnesium iodide mediated rearrangement of the resulting vinyl cyclopropane.

Back to the future: Major achievements have been made in copper-catalyzed Ullmann reactions since its renaissance in the early 2000s. This Minireview highlights developments since 2004 in the corresponding intermolecular arylations and vinylations of N, O, and C nucleophiles by aromatic and vinyl halides under homogeneous and heterogeneous conditions (see scheme; EWG=electron-withdrawing group, EDG=electron-donating group).

Being specific: A combination of selective chemical transformations and methods to modify biological species has yielded new insights into cellular processes. Key to these new techniques are bioorthogonal chemical reactions, whose components must react rapidly and selectively with each other under physiological conditions in the presence of the plethora of functionality found within living systems.

Through the looking glass: Holographic lithography through a microprism array enables the production of microstructured arrays with 3D internal nanoscale features (see picture). In a single-step exposure of 0.1 s, thousands of features are generated in a spot size of about 1 cm². They exhibit 14-times enhanced fluorescence compared with conventional microarrays.

Fitting in: Hexagram-shaped amphiphiles self-assemble in the presence of a spherical, hydrophobic guest molecule to form a tetrahedron-shaped tetrameric organic capsule in an aqueous methanol solution (see picture). In the presence of adamantane, an aqueous solution of a box-shaped hexameric capsule composed of hexagram-shaped amphiphiles was converted into a novel 1.7 nm sized tetrameric capsule that has an encapsulated adamantane template molecule.

Anchors away! Four banana-shaped ligands and two Pd^II ions assemble quantitatively to form a ball-shaped object with four large portals (see picture). The two Pd^II ions form stable, square-planar complexes with the pyridyl donors of the ligands, but can undergo further interactions with anions. Their positioning in a confined distance by the rigid ligands make them act as electrostatic anchors for dianionic guests of a certain size.

A label for six, please! A fluorescent tetrazine derivative was used to image trans-cyclooctene-modified affinity ligands on live cancer cells through a bioorthogonal cycloaddition with a reaction rate of approximately 6000±200 M⁻¹ s⁻¹ in serum at 37 °C (see scheme). To maximize the fluorescence signal, up to six trans-cyclooctene moieties were attached to the antibody used to pretarget cells for labeling.

The controlled oxygenation of ethylzinc complexed with a tridentate pyrroloimine leads to an unprecedented transformation of the resulting ethylperoxide into an acetate. The zinc acetate appears to form without involvement of redox-active metal centers by a combination of OO bond activation and multiple rearrangements of ZnO^. and ^.OEt radical species.

Binding with distinction: Photo-cross-linking followed by the complementary use of ESI and MALDI mass spectrometric techniques yielded the interaction sites of three prototypical amphipathic transcriptional activators (represented by different-colored helices in the picture) with the coactivator Med15. Investigation of the functional relevance of these sites in yeast revealed overlapping yet distinct binding patterns for the activators investigated.

Four steps in one: The direct prenylation of indoles at N-1 can be achieved by CH functionalization in the presence of a Pd^II source. This reaction proceeds by direct intermolecular olefin amination, tolerates a broad range of functional groups, and can be carried out on a gram scale, as demonstrated by the formal syntheses of a number of natural products and the synthesis of an antifungal natural product (see scheme).

An on/off relationship: A supramolecular binary “OR” logic gate that generates highly enhanced fluorescence emission as the output signal is demonstrated (see picture). The system comprises a mixture of organogelator and photochromic compound and is able to process dual inputs of UV irradiation and thermal heating.

Mission Impossible: Metal nanoparticles (NPs) coated with photoresponsive ligands are used as “inks” for self-erasing “paper” whereby light-induced self-assembly of the NPs is transduced into local color changes (see picture). Depending on the degree of self-assembly, multicolor images can be written using only one type of NP ink. Duration of image erasure is regulated by the surface concentration of photoactive groups and can range from seconds to days.

S-S-Stretch! A series of increasingly strained macrocyclic disulfides investigated experimentally and by high-level DFT calculations reveals that the kinetics of thiol/disulfide exchange are independent of the restoring force in the disulfide moiety. This finding is consistent with the S_N2 mechanism of thiol/disulfide exchange and lends insight into the acceleration of disulfide reduction upon stretching of certain proteins.

Off means off: An in-stem molecular beacon in which D-threoninol units tether perylene and anthraquinone in the stem region effectively detected target sequences and was able to discriminate a one-base-deletion mutant from the wild-type (full-match) sequence without background emission (see picture).

A hole in one: Hollow nanoporous structures are prepared by controlled decomposition–dissolution. The partial thermal decomposition of transition-metal salts forms a metal oxide shell on the surface of the metal salt particles. Acid washing removes the metal salt cores, resulting in hollow nanoporous metal oxide shells (see picture). This new strategy provides a template-free single-source route to hollow structures.

Not SiSi, rather SiOSi: Dimethylformamide (DMF) acts as an oxygen source in the efficient transformation of tertiary silanes (R₃SiH; R₃=Ph₂Me, PhMe₂, Et₃) into disiloxanes R₃SiOSiR₃ in the presence of the catalyst [(η⁵-C₅H₅)Fe(CO)₂CH₃] (1; see scheme). This result contradicts a recently published related study, in which the formation of disilanes is reported.

A select club: The polyoxometalate [(γ-SiW₁₀O₃₂)₂(μ-O)₄]⁸⁻ (1⁸⁻) has a cavity that can size-selectively encapsulate the ions Pb²⁺, Sr²⁺, Na⁺, Ag⁺, K⁺, and Rb⁺ (see picture, light blue; Si hidden, W gray, O red). Larger Ba²⁺ and Cs⁺ ions (pink) are not encapsulated by 1. The molecular structures of [Mⁿ⁺⊂1]⁽⁸⁻ⁿ⁾⁻ (Mⁿ⁺=Pb²⁺, Sr²⁺, Ag⁺, Ba²⁺) were characterized by X-ray crystallography.

Crowning glory: The assembly of Cu^II or Cu^II and Ni^II and a new 1,4-aryl-linked bis(triketonato) ligand designed to adopt a ‘bent’ configuration leads to unusual Cu_6−nNi_nL₃ (n=0, 3) metallacycles that feature unique hexanuclear metallacoronand structural motifs. In the case of the hexanuclear Cu^II species, strong antiferromagnetic interactions exist between proximate pairs of metal ions in each structure.

The simultaneous construction of a CS and a CC bond under catalytic conditions forms the basis of an efficient route to diversely functionalized benzothiophenes from gem-dihalovinyl thiophenols. The CC bond can be formed in this tandem catalytic process with an organoboron reagent as shown in the scheme (R¹=H, Me, F, Cl, Br, OCH₂O; R²=H, Me; R³=aryl, heteroaryl, alkenyl, alkyl), or by Heck or Sonogashira coupling with an alkene or alkyne.

More than a protecting group: The trityl group senses the chirality of an alkyl substituent in chiral trityl ethers. The CD spectra of trityl-protected alcohols are highly sensitive to the chirality of the alcohol. The use of a trityl CD sensor provides new insight into the structure and mode of action of chiral molecular bevel gears and shows the relation between the absolute configurations of molecules and their Cotton effect patterns.

The layer-by-layer deposition of poly(diallyldimethylammonium chloride) and poly(acrylic acid) incorporating inorganic sheets of sodium montmorillonite clay leads to a stratified structure throughout the film interior, with micrometer-thick polymer complex layers and thin clay strata (see picture; right: cross-section).

Evenly spaced arrays: The unique molecular architecture of a self-assembled polypeptide template allows the electrostatic deposition of nanoparticles with uniform interparticle spacing. The hierarchical self-assembly mode of the polypeptide results in the display of charged patches at periodic distances along the length of the fibril architecture (see picture).

A refreshing cascade: General fluorocyclization reactions will breathe new life into the use of fluorinated hetero- and carbocycles as pharmaceuticals and agrochemicals. Allyl silanes have now been shown to undergo fluorination–cyclization with NF reagents to give cis- and trans-substituted fluorinated heterocycles selectively (see scheme). The correct choice of silyl group was critical to prevent competitive fluorodesilylation.

The big squeeze: On applying pressure to ZIF-8 (0.18 GPa), solvent can be squeezed into the porous cavities, initially increasing the pore size and unit-cell volume. On increasing pressure further to 1.47 GPa, a phase transition takes place (see picture). This transition allows more solvent to enter the original nanopores and enlarges the narrow channels connecting these pores, resulting in higher porous volume and solvent content.

Lovely lactams: Synthetically useful γ-lactam derivatives have been prepared through the unique title transformation. By utilizing the characteristic property of the molybdenum complex, two kinds of products (both of which have rarely been obtained by reactions catalyzed by late transition metals) were obtained selectively by adjusting the reaction conditions (see scheme).

Three CH bonds are cleaved in the direct transformation of methyl arenes to aryl nitriles under mild and neutral conditions (see scheme). This new synthetic tool may not only be used to construct synthetically and medicinally important aryl nitriles, it also achieves CH functionalization under mild conditions. PIDA=phenyliodonium diacetate.