Angewandte Chemie International Edition

Self-assembled two- and three-dimensional highly ordered aggregates of standing gold nanorods were obtained over unprecedentedly large superlattice domains. In their Communication on page 9484 ff., A. Guerrero-Martínez, L. M. Liz-Marzán, and co-workers report how the use of gemini surfactants was crucial for the growth of monodisperse nanorods and induction of the self-assembled structures into extended superlattices, which also display anisotropic optical response.

Bioengineering of proteins using mammalian cells has facilitated the development of potential pharmaceutical erythropoietins (EPOs) that bear N-linked oligosaccharides. In their Communication on page 9557 ff., Y. Kajihara and co-workers report the chemical synthesis of a homogeneous bioactive EPO analogue, which was prepared by native chemical ligation between a synthetic glycopeptide-α-thioester with two complex-type sialyloligosaccharides and a large polypeptide chain, obtained by expression in E. coli.

“If I could be anyone for a day, I would be the conductor of a symphonic orchestra. When I was eighteen I wanted to be a teacher. …” This and more about Gérard Férey can be found on page 9398.

Cambridge University Press 2009. 578 pp., hardcover £ 45.00.—ISBN 978-0521898638

DNA folding as an extended art form: Long strands of DNA can be folded in a controlled manner to yield 3D shapes. Moreover, twisted and curved shapes can be created with excellent control (see schematic representation). The key to these developments is the use of Holliday junctions, which connect different parts of the array and also create tension in the honeycomb system so that the DNA structure is forced to fold into the desired shape.

The unexpected stability of the exotic N₂^.3− species has been observed in its complexes with Dy³⁺ and Y³⁺. The three-electron reduction product of N₂ is isoelectronic with superoxide O₂^.− (see scheme) and is a possible bound intermediate in the conversion of N₂ into NH₃.

The higher, the better! The emergence in recent years of catalysis with high-oxidation-state palladium complexes has enabled the functionalization of alkyl and aryl compounds in a series of new reactions (see general scheme). Reaction processes and mechanistic aspects of these catalytic transformations are discussed in this Minireview.

Flower power: The structures, biological activities, and biosynthesis of α-methylene-γ-butyrolactone and α-alkylidene-γ-butyrolactone natural products—which are found, for example, in arnica, feverfew, and, peony—are reviewed, as are recent synthetic approaches.

Rigid bridges: NMR studies of the unfolded state (U) of the human prion protein (PrP) show that in the oxidized form the native disulfide bridge between two cysteine residues rigidifies the surrounding amino acids. This area is a hotspot region of the protein in terms of disease-related mutations that promote aggregation and formation of the abnormal “scrapie” form (PrP^Sc).

Diamonds are forever: A diamond-like framework in which the C–C bonds are replaced with rigid phenyl rings (see picture) is not only structurally stable but also has a large internal surface area. This porous aromatic framework (PAF-1) demonstrates high uptake capacities of hydrogen and carbon dioxide as well as benzene and toluene vapors, and has an unprecedented surface area of 7100 m² g⁻¹.

Dragon's lair: A large, single-walled metal–organic nanotube (MONT) with an exterior diameter of up to 3.2 nm and an internal channel diameter of 1.4 nm is presented. The tube can be depicted as hexastranded helices consisting of three right-handed and three left-handed helical chains, and resembles a rolled-up dragon column (see picture). The MONTs are held together by alkaline ions to form unique nanotubular arrays.

Dying on the inside: Functional dye molecules can be adaptively encapsulated in coordination nanoparticles (CNPs) of nucleotides and lanthanide ions in the course of their formation in water (see picture). Dyes confined in CNPs are conformationally restricted and surprisingly stable against molecular oxygen. These properties should be favorable for the development of light-harvesting CNPs.

Aldehyde is critical: Atheronal-B, a cholesterol secosterol aldehyde (see structure), completely inhibits the misfolding of a prion protein fragment from its α to β form through a mechanism that involves adduction to the protein. This result offers a fresh view of lipid aldehyde-induced protein misfolding and provides a promising molecular scaffold on which to develop potential prion disease therapeutics.

All-in-one assemblies containing single-site water oxidation catalysts (red and blue) and redox mediators (green and blue) act as stable, robust catalysts toward water oxidation, both in solution and anchored to metal oxide surfaces by phosphonate linkers on the mediator. More than 28 000 turnovers have been achieved with >95 % Faradaic efficiency for oxygen production without reduced catalytic activity.

The chemical concepts of bond strength and steric hindrance are extended to the nanoscale to control “reactions” of composite nanoparticles into primitive “nanomolecules” of well-defined shapes and sizes. The progress of these nanoscale transformations is controlled by an interplay between the strength of bonding between particles' reactive domains and the entropic effects because of the bulkiness of the unreactive parts.

Catch and release: A hairpin-shaped sense strand (red)/antisense strand (blue) siRNA probe was designed to be activated by a trigger RNA molecule. In the presence of the trigger RNA, clear OFF-to-ON switching of RNAi activity was observed with high sequence dependency (see schematic illustration).

A super lattice: The title system allows the spontaneous formation of self-assembled 2D and 3D highly ordered aggregates of standing nanorods on large superlattice domains (see picture). The hexagonal close packing of nanorods perpendicular to the substrate resembles smectic-B liquid-crystalline phases. Optical characterization of the aggregates demonstrates their anisotropic optical response.

Magnetic measurements on a {Dy₄} single-molecule magnet (SMM) with a defect-dicubane central core, synthesized using 1,2-bis(2-hydroxy-3-methoxybenzylidene) hydrazone and 3-methoxysalicylaldehyde hydrazone as chelating agents (see structure; yellow Dy, red O, blue N, green Cl), confirm SMM behavior and reveal hysteresis loops at 7 K. The anisotropic energy barrier of U_eff=170 K is the highest reported to date.

Delivery by Trojan horse: A water-soluble derivative of the chemotherapeutic agent taxol was synthesized with bioconjugation functionality and attached to capsids of the bacteriophage MS2 (see picture). The modified capsids retained their form and released taxol when incubated with MCF-7 cells. The resulting cell-viability levels were similar to those observed upon treatment with free taxol in solution.

Harnessing energy from within: Energy transfer from the inside to the outside of MS2 capsids modified by positioning fluorescent dyes and a photocatalytic zinc porphyrin on their surfaces (see picture) enabled sensitization of the porphyrin at multiple wavelengths and thus broad-spectrum catalytic activity.

Tagging along: A DNA detection method has been developed that relies on the interfacial assembly of gold nanoparticles. The fluorous-tag-driven formation of nanoparticle networks (see scheme) at the gas/liquid, liquid/liquid, or solid/liquid interface is such that a single type of assembly architecture is suitable for an array of detection formats.

While the iron is hot: The first general and efficient iron-catalyzed reduction of secondary and tertiary amides into amines using polymethylhydrosiloxane (PMHS) has been developed (see scheme).

Fox in the carboxamide: Reduction of tertiary carboxamides to their corresponding amines is catalyzed by [Fe(CO)₅] or [Fe₃(CO)₁₂], using 1,1,3,3-tetramethyldisiloxane (TMDS) as the reducing agent. The reaction proceeds under either thermal or photochemical conditions. Unlike the hydrosilane reduction of amides using platinum or ruthenium catalysts, TMDS preferentially reduces a nitro group, even in the presence of competing amides.

The rate of H₂–D₂exchange increases in proportion to the inverse square of the mean diameter of gold particles supported on TiO₂ (see picture), which indicates that hydrogen dissociation takes place on the perimeter interfaces between the gold and TiO₂ and that the catalytic activity for H₂ dissociation is correlated neither to a change in the fraction of edge or corner sites nor to a change in the electronic nature induced by the quantum size effect.

Keeping it simple: A simple strategy for the total synthesis of three complex natural products has been developed, while also confirming the putative generation of 1 and 2 from 3. The benefits of a simple dissymmetric 2,5-cyclohexadienone are illustrated and provide the foundation for rapid diastereoselective functionalization leading to the first total synthesis of these compounds.

Premium bonds: The pH-dependent coordination of Cu^II to the Alzheimer′s disease amyloid-β peptide has been studied by NMR spectroscopy. Several equivalent ligands are in equilibrium for Cu^II binding near pH 6.6 and 8.7. Fewer conformers are detected at high pH, in line with a reshuffling of the Cu^II binding site induced by deprotonation of the Asp1Ala2 peptide bond (see picture).

The hole truth: A low-energy band in the absorption spectrum of the oxidized Watson–Crick complex of guanosine and cytidine derivatives (see scheme) is attributed to charge-transfer localizing the hole from one-electron oxidation on the cytidine moiety. The band provides an estimate of the energy of one of the low-lying electronic states of oxidized duplex DNA.

A sound reaction: The ultrasonically driven disproportionation of CO in water causes formation of hydrated polymer of carbon suboxide (C₃O₂)_n (see picture) enriched with a heavy ¹³C isotope. This finding indicates the presence of vibrationally excited CO molecules with a non-equilibrium Treanor distribution inside the cavitating bubble.

Breaking the taboo: The direct use of allylic alcohols in catalytic and enantioselective Friedel–Crafts alkylation is described for the first time in the presence of chiral gold complexes. This intramolecular Friedel–Crafts reaction was used to prepare a broad range of functionalized tetrahydrocarbazoles (see scheme; X=Me, F, Br, Cl, OMe; R=Me, Et, tBu; R′=H, Me).

Taking hydrogen from water: Gold catalysis enabled the selective reduction of nitro compounds under very mild conditions with a combination of H₂O and CO as the reductant (see scheme). This environmentally friendly reaction proceeded in high yield and with high chemoselectivity in the presence of a wide range of functional groups.

Under control: A formal [4+1]/[3+2] cycloaddition cascade of sulfur ylides and alkene-tethered nitroolefins has been developed, and provides an efficient synthesis of fused polycyclic heterocyclic compounds in good to excellent overall yields with excellent diastereocontrol (see scheme). A catalytic asymmetric variant of this reaction has also been disclosed.

A novel biocatalytic protocol for CC bond formation is described and is an equivalent to Friedel–Crafts alkylation. S-Adenosyl-L-methionine (SAM), the major methyl donor for biological methylation catalyzed by methyltransferases (Mtases), can perform alkylations (see scheme). These enzymes can accept non-natural cofactors and transfer functionalities other than methyl onto aromatic substrates.

Running rings around aluminum: An efficient procedure for radical cyclization of α-bromo esters is reported. Reduction of the esters by DIBAL-H at low temperature gives aluminum acetals, which are cyclized in the presence of nBu₃SnH and Et₃B (see scheme). These one-pot conditions lead to polysubstituted γ-lactols in high yields, and the mildness of the reaction conditions allows the preparation of acid-sensitive derivatives.

Copper-bottomed catalysis! The direct alkynylation of azoles through a copper-based CH bond activation, using alkynylbromides as the coupling partner, has been developed (see scheme). The method is very rapid, is functional-group tolerant, and provides a straightforward entry to diverse alkynyl heterocycles that is complementary to the Sonogashira reaction.

Highly expressive: Cell proliferation was observed with concentrations of an erythropoietin (EPO) analogue above 50 pg mL⁻¹. The EPO analogue has two human complex-type sialyloligosaccharides (see picture) and was formed by the combined use of chemical synthesis and protein expression in E. coli. Both the 24- and 30-positions are glycosylated, but the two sialyloligosaccharides do not interfere with binding of the EPO analogue to a receptor.