Angewandte Chemie International Edition

Light was used to create a wavelength-dependent interfacial tension gradient at a liquid/liquid interface to induce an interfacial flow; thereby generating droplet motion in the direction opposing the gradient. This “the chromocapillary effect” is described by D. Baigl et al. in their Communication on page 9281 ff. The liquid droplets can be controlled using light along the trajectories of any shape (e.g., a heart) with good precision.

Protein engineering holds the key to control, predict, and manipulate bio-inspired scaffolds on specific surfaces. In their Communication on page 9290 ff., D. Porath, O. Shoseyov, and co-workers describe selective, controlled, and tunable attachment of proteins to metal or insulating surfaces. SP1, a recently discovered ring-shaped protein, was genetically engineered to expose multiple binding sites simply by changing solvent conditions. Protein monolayers are created with no need for surface modifications.

“The secret of being a successful scientist is a good mixture of imagination and hard work. My biggest inspiration is looking at art or doing nothing …” This and more about Jörg Rademann can be found on page 9218.

Wiley-VCH, Weinheim 2009. 452 pp., hardcover € 149.00.—ISBN 978-3527320950

John Wiley & Sons, Hoboken 2009. 336 pp., hardcover € 119.00.—ISBN 978-0470518007

Reverse gear: Additions of primary radicals to sterically non-congested vinyl bonds may indeed not be as irreversible as commonly assumed. A ¹H-CIDNP NMR spectroscopic investigation on photoinitiated polymerization systems provides evidence that the addition of photolytically generated mesitoyl and phosphinoyl radicals to (meth)acrylate monomers at ambient temperatures may be reversible (see scheme; I=initiator).

Lost in translation: Ribosomes have developed sophisticated mechanisms to ensure a precise translation of the genetic information into functional proteins. The Nobel Prize in Chemistry for 2009 goes to three researchers who provide us with valuable insights into the structure of ribosome using X-ray diffraction, thus improving our understanding of the translation process at the molecular level.

Carnot versus electrochemistry: This essay critically compares the advantages and disadvantages of Carnot-cycle-based and electrochemical methods for the generation and storage of energy (see picture; left: PEM fuel cell; right: Au(111) model surface covered with 0.025 monolayers of Pt). The views of Wilhelm Ostwald (1853–1932) and today's understanding of energy conversion are contrasted.

Hitting the sweet spot: The combination of organotrifluoroborates and monocoordinated palladium complexes as catalysts in the Suzuki–Miyaura coupling reaction provides a powerful method for the creation of carbon–carbon bonds. The advantages of organotrifluoroborates include the numerous functional groups that are tolerated in the substrate, the mild reaction conditions, and the possibility to use different types of reagents.

Modeling job: Protonation of a closed seven-coordinate side-on heme peroxide can switch its spin state from high- to low-spin and convert the η² binding fashion into a monodentate configuration to afford the corresponding hydroperoxide (see scheme). The end-on low-spin ferric hydroperoxo–heme species bear a covalently appended axial imidazole ligand and are easily prepared.

Zipped together: The title system was synthesized by using a quaternary ammonium silane as a DNA-condensing agent and a co-condenser with the silica source. The small interaxial separation in electrostatic DNA–DNA “zippers” and silica walls formed between diagonally positioned DNA strands are optimal for formation of the p4mm structure.

Ligand sphere revealed: Cu ions were proposed to be linked to the aggregation of the amyloid-β peptide in Alzheimer's disease. However, unambiguous identification of the Cu ligands has remained difficult. The use of various EPR spectroscopies with specific isotopic labeling now allowed the assignment of the Cu^II ligands for both complexes present at physiological pH value (see 3D plots and structures). The results indicate that the peptide's first two amino acids are important for coordination and probably aggregation.

Running relay: Incorporating an energy-relay dye (ERD) into the hole transporter of a dye-sensitized solar cell increased power-conversion efficiency by 29 % by extending light harvesting into the blue region. In the operating mechanism (see picture), absorption of red photons by the sensitizer transfers an electron into TiO₂ and a hole into the electrolyte. Blue photons absorbed by the ERD are transferred by FRET to the sensitizer.

Ace of hearts: Liquid droplets can be manipulated in a controlled fashion along trajectories of any desired shape (such as a heart, see picture) by using light to create a wavelength-dependent interfacial tension gradient at a liquid/liquid interface. In this new phenomenon, the “chromocapillary effect”, an interfacial flow generates droplet motion in the direction opposite to the gradient.

Its a small world: Nanoscale reactivity maps of working heterogeneous catalysts are recorded under in situ conditions by localizing single fluorescent reaction products (see picture). This approach allows quantification of the reactivity of catalytic nanodomains.

Ringing the changes: A selective, controlled, and tunable attachment of proteins to a metal or to insulating surfaces is presented. A ring-shaped protein encapsulating SiO₂-binding peptides (see picture: yellow) was engineered to expose multiple binding sites simply by changing solvent conditions, thereby creating a single monolayer without the need for surface modification.

Two in one: A novel strategy for efficiently coencapsulating both arsenic- and platinum-based drugs into 100 nm-scale liposomes (NBs) relies on the formation of Pt^II–As^III adducts. This co-loaded system presents a robust platform for further modification with targeting ligands and affords a method of improving the therapeutic efficacy of anticancer agents.

Properly shielded: The fluorene groups used as capping agents for new diphenylanthracene (DPA), pyrene, and anthracene derivatives impart steric hindrance which prevents interchromophore interactions, giving these molecules high photoluminescence quantum yields. Fluorene-based DPA (1) is characterized by a highly efficient and stable blue electrogenerated chemiluminescence (ECL).

Four crystal phases are accessible by thermally and light-induced spin crossover associated with symmetry breaking for [Fe^IIH₂L^2MeH₂L^2Me](PF₆)₂ (H₂L^2Me is an acyclic hexadentate N₆ Schiff base). In this novel molecular material, the arrays of Fe^II complex cations (high-spin: red triangles; low-spin: blue triangles) are separated by layers of counteranions (green zigzag lines).

A trick of light: An optically active preferred-handed helical polymer synthesized by asymmetric anionic polymerization underwent stereomutation upon photoirradiation, whereas the helix remained stable upon heating (see picture). This photoinduced racemization of a synthetic helical polymer occurred without any changes in chemical bonding, such as bond formation, bond cleavage, or the isomerization of a double bond.

Se-ing is believing: Many proteins are cross-braced by disulfide bonds that frequently play key roles in protein structure, folding, and function. Unfortunately, the methods available for assignment of disulfide-bond connectivities in proteins are technically difficult and prone to misinterpretation. Now disulfide bond connectivities in native proteins can be visualized directly using ⁷⁷Se NMR spectroscopy.

Waiting in line: Aldehyde groups take turns reacting in a SmI₂-mediated cyclization cascade to form the skeleton 2 of the antibacterial natural product pleuromutilin. Two rings and four contiguous stereocenters are constructed during the cascade with complete diastereocontrol.

A crush on sweetness! The coupling of a urethane-protected N-carboxyanhydride of an amino acid with another amino acid derivative under ball-milling conditions gives a protected dipeptide in very high yield (see scheme; PG: protecting group). The reaction takes place in the solid state. The synthesis was applied to the preparation of a tripeptide and the sweetener aspartame, without any organic solvent or purification.

Hydrogen bonds are ubiquitous interactions in proteins, and are important for their folding and functionality. Scalar coupling constants across hydrogen bonds in the protein backbone, some as small as 0.5 Hz, can be directly measured in the solid state by NMR spectroscopy (see figure). The nuclei on both sides of the hydrogen bond can be identified and the size of the coupling constant can be measured accurately.

Etch a sketch: Robust TiO₂ mesoporous layers can be fabricated on Ti surfaces by a combination of non-thickness-limited anodization and selective etching. Layers more than 50 μm thick with highly regular feature and pore sizes in the range 5–10 nm can be produced (see picture, FTO=fluorine doped tin oxide). The layers are highly flexible, well-adhered, and can be used directly after appropriate annealing in efficient dye-sensitized solar cells.

Colorful palette: A new class of highly selective Eu³⁺-based multi-frequency PARACEST agents is reported. The complexes can be tuned when administered simultaneously thereby allowing for the possibility of monitoring multiple biomarkers in parallel. PARACEST = paramagnetic chemical exchange saturation transfer.

“Clicked” into place: Densely grafted poly(γ-propargyl-L-glutamate)-g-poly(ethylene glycol) polypeptides have been synthesized by combining ring-opening polymerization of N-carboxyanhydrides with click chemistry. Various lengths of poly(ethylene glycol) (PEG) side chains (750 g mol⁻¹ to 5000 g mol⁻¹) were attached to a rigid α-helical poly(γ-propargyl-L-glutamate); extremely high grafting efficiencies of over 96 % were achieved.

A pinch of salt: The first catalytic addition of dialkylzinc reagents to N-acylpyridinium salts with good yields and excellent enantioselectivities uses a copper–(S)-L complex as the catalyst. The versatility of the method is illustrated in the formal synthesis of the alkaloid (R)-coniine. Bn=benzyl, Tf=trifluoromethanesulfonyl.

Nitro versus nitro: 4-Nitro-5-styrylisoxazoles were used as masked α,β-unsaturated carboxylic acids in the titled catalytic asymmetric transformation. The 4-nitroisoxazole core acts as an activator of the conjugated alkene and a latent carboxylate functionality. The reaction proceeded with 5 mol % of a readily prepared phase-transfer catalyst at room temperature with remarkable diastereo- and enantioselectivity (see scheme).

Easy does it: The unique properties of benziodoxolone alkynyl periodinane 1 and gold catalysts have allowed the development of a high yielding, operationally simple (room temperature, no dry solvents or inert conditions, commercially available catalyst) reaction for the introduction of silylacetylenes on a large range of indole and pyrrole heterocycles with a wide range of functional groups (see scheme).

For copper only: The decarboxylative cross-coupling of readily accessible and nonvolatile potassium polyfluorobenzoates with aryl iodides and bromides using a copper catalyst provides polyfluorobiaryls and polyfluorostilbenes in excellent yields (see scheme). Mechanistic analyses are reported for the title reaction.

Biocompatible: A modular chemoenzymatic synthesis (see scheme) based on asymmetric organo- and biocatalytic reaction sequences allows the sequential construction of both stereogenic centers of 1,3-diols and leads to all four possible stereoisomers in enantiomerically pure form. The biocompatibility of the organocatalytic aldol reaction allows its direct use in the subsequent enzymatic reduction without the need for a work-up step.

The first addition of photoinitiator radicals formed by the photolysis of a bisacylphosphine oxide photoinitiator to an acrylate double bond proceeds reversibly (see scheme; R¹=tBu, H; R²=MeOC(O), BuOC(O)). Moreover, hydrogen transfer between substituted benzoyl radicals and the growing radical chain explains the formation of aldehydes in such a transformation.

Fluorescence is ON and transcriptional control is OFF when the guanidinium-modified zinc phthalocyanine Zn-DIGP binds a G-quadruplex DNA from the c-Myc promoter. With an equilibrium dissociation constant K_d of less than 2 nM, this interaction is the strongest binding interaction between a G-quadruplex structure and a small molecule reported to date.

A record Co₃₆ cluster is prepared. This mixed-valent compound containing Co^II and Co^III centers is formed in the reaction of a dinuclear cobalt pivalate species with the polydentate 2,3-dicarboxypyrazine ligand. In terms of magnetic properties it behaves as a {Co₁₆–Co₁₆} supramolecular dimer in which the S=4 spin ground states of each monomer do not interact.