Chemistry - A European Journal

Promotion of liquid-crystalline behavior in oligothiophenes was achieved by M. Melucci and co-workers (see p. 10046 ff.) by applying a new design-strategy based on the insertion of a rigid inner core, such as dithienothiophene, benzothiadiazole, or carbazole, and hexyl chains as ends. Oligomers of different size and shape were synthesized by a highly efficient microwave-assisted protocol. Most of the newly synthesized materials showed ordered smectic mesophases and maintained the smectic order by slow cooling to room temperature. Semiconducting behavior in field-effect transistors from cast and vacuum-evaporated films was demonstrated.

A mechanism and a chemical reaction: Solid–solid phase transitions unfold a rich set of physical and chemical effects upon atomistic simulations (see graphic).

Clusters within clusters: A combination of lacunary polyoxometalate (POM) precursors (trivacant Keggin B-α-XW₉ fragments) and transition-metal clusters (TMCs) induced by the structure-directing role of the lacunary sites of POMs under hydrothermal conditions results in the formation of a series of novel TM-substituted POMs from double-cluster, dimeric/tetrameric poly(POM) species to three-dimensional frameworks (an example of which is shown here).

Solution-processable, liquid-crystalline oligothiophene semiconductors of different size and shape are described. Their thermal behaviour in relation to their molecular structure has been investigated by means of polarised optical microscopy (see picture), differential scanning calorimetry and X-ray diffraction. The electrical properties of vacuum-sublimed, cast and melted films of the newly synthesised compounds have also been investigated.

See the light! A series of new dispirofluorene–indenofluorenes (DSF-IFs) has been synthesised. These new building blocks for blue-light-emitting devices and electroactive polymers combine indenofluorene (IF) and spirobifluorene (SBF) properties. The thermal, structural, photophysical and electrochemical properties of these molecules are discussed (see graphic).

Elementary aluminum nanorods: Zeolite ZSM-22 crystals are formed by sideways aggregation of nanorods. These grow along the direction of the micropores until the silicon source is used up. Aluminum preferably resides in the outer sides of the rods. Only after the nanorods aggregate (see figure) are the catalytically active sites formed in abundance. This is one example where nanosize is not superior for a catalytic application.

The bonding properties in the tris(ethylene) complexes of Ni, Pd, and Pt have been studied by charge density analysis and vibrational spectroscopy of the matrix-isolated [Pd(C₂H₄)₃] complex (see picture).

Wheel change! The compounds [Ru₂X₂(DPhF)₃] (X=Cl, Br, I, and NO₃⁻; DPhF=diphenylformamidinate) reported here constitute a new class of complexes in diruthenium chemistry that have open-paddlewheel structures (see picture). None of the formamidinatodiruthenium complexes described display the classical magnetic behaviour found in almost all Ru₂⁵⁺ complexes known to date.

Alkylation versus electron transfer: Polyaromatic hydrocarbon dianions (PAHs⁻²) react with fluoroalkanes in a nucleophilic fashion in spite of being generally regarded as powerful electron-transfer reagents (see graphic). The regiochemistry of the reductive alkylations can be easily predicted by simple MO calculations.

Protons control anticancer drug energetics: Theoretical calculations on carboplatin are used to obtain energy profiles and optimised structures for the rate-limiting process in the neutral hydrolysis of carboplatin (see scheme). The results indicate that if carboplatin undergoes a hydration process, it should be doubly hydrated prior to reaction with DNA.

Methanol under a new light: The presence of the thiazoline moiety strongly influences the chemical and luminescence properties of phosphino-amino-thiazoline bischelated complexes of Pt^II. Reaction with Au^I salts affords dimetallic complexes, while hydrogen bonding to MeOH exerts a rigidochromic effect (see figure) resulting in the “switching on” of the luminescence. A combined photophysical and crystallographic study is described.

Size does not matter, it is the link that counts: In niobium/tantalum calixarene α-olefin polymerisation catalysis, there is no increase in activity on increasing the size of the methylene-bridged calix[n]arene (n=4, 6 or 8), whereas incorporation of dimethyleneoxa bridges (see picture) is beneficial to catalytic activity. However, the effect is less dramatic than that observed for vanadium.

Peptide templates: Racemic parallel β-sheet architectures, operating as efficient templates in enantioselective chain elongation at the polymer/crystal interface, are self-assembled in the course of polymerisation in racemic crystals (see scheme; NCA: N-carboxyanhydride). The composition of the diastereoisomeric libraries of oligopeptides was determined by MALDI-TOF and MALDI-TOF-TOF MS analysis of the products obtained from monomers enantiolabelled with deuterium.

Carbon substitutes oxygen: Starting from easily available glycals and malonates more than 40 carbohydrate 2-C-analogues were synthesized in only a few steps by radical addition and various further transformations (see scheme). The reactions are characterized by good yields and stereoselectivities and afford interesting precursors for C-disaccharides.

Enzyme powered! Integrated, electrically contacted NAD(P)⁺-dependent enzyme–carbon nanotube electrodes act as amperometric biosensors for glucose and alcohol, and upon coupling to bilirubin oxidase functionalized carbon nanotube electrodes yield biofuel cell elements (see figure).

Spontaneous recovery of the pH of seawater from acidic to physiological ranges can take place through simultaneous CaCO₃ dissolution and proton consumption. The pH dependence of CaCO₃ dissolution in seawater can be described in terms of the pH dependence of a solubility product: [HCO₃⁻][Ca²⁺]. The oscillating stability of the pH of seawater inhabited by calcareous organisms can thus be achieved, in the absence of effects of anthropogenic CO₂ on oceanic pH. A scanning electron microscopy image of a CaCO₃ fragment is shown.

Super devices: Supramolecular structures of meso-tetraphenylporphyrin and fullerene composites on SnO₂ electrodes exhibit the largest incident photon-to-current efficiency (IPCE) value (ca. 60 %) reported among this type of photoelectrochemical device. More importantly, a simple methoxy-group substituent at the meta position of the meso-phenyl groups is responsible for both the highly ordered nanostructures of the electron and hole highways and the efficient photocurrent generation (see picture).

Spare the rod but don't spoil the triplet! Increasing the length of supposedly highly conjugated molecular rods does not necessarily lead to a lowering of their spectroscopic triplet energies. The synthesis and characterization of molecular rods, as depicted, is also described.

The conformational features and membrane activity of two newly synthesised peptides, hIAPP17–29 and rIAPP17–29 (see figure), encompassing the 17–29 sequences of human and rat IAPP, respectively (IAPP=islet amyloid polypeptide), were studied in water and in several membrane-mimicking environments. The results confirm that the 17–29 domain of IAPP is able to recapitulate many properties of the full-length protein.

Add a pinch of palladacycle! The loading of the optimum cobalt oxazoline palladacycle (COP) catalyst was minimised to 0.25 mol % for the highly enantioselective rearrangement of trichloroacetimidates into trichloroacetamides (see scheme; ee=enantiomeric excess). The factors responsible for the activity of COP catalysts for this reaction are discussed.

Linking together: The asymmetric synthesis of scyphostatin has been achieved by condensation of the cyclohexane unit and side chain (see scheme). The epoxy cyclohexenone unit was modified at a late stage of the total synthesis, and the primary alcohol was deprotected in the final step.

Two birds with one stone: The combination of a crown ether and a bicentric Lewis acidic organotin moiety gives a stable heteroditopic receptor 1 that simultaneously binds the cation and anion in sodium fluoride in organic solvents (see picture).

An effective organocatalyst based on a siloxyproline with a highly hydrophobic moiety catalyzes the aldol reaction in the presence of water with excellent diastereo- and enantioselectivities (see scheme). This approach represents a green method for the large-scale preparation of aldols with the minimal use of an organic solvent, even in the purification step.

Ruthenium-based wires: Di- and tetranuclear 4-vinylpyridine-bridged styryl- and divinylphenyleneruthenium complexes (see picture) were studied experimentally and by quantum chemistry as building blocks for conducting organometallic oligomers. These complexes undergo a series of ligand-based oxidations with smaller, yet still detectable, contributions from the metal.

Sweet radiators: Novel glycoconjugated 2,2′-bipyridines containing thioglycosidically linked monosaccharides bind to rhenium and 99m-technetium carbonyl cores to form luminescent complexes (see picture) that exhibit stability against histidine over a period of 4.5 h and an easily tuneable solubility in organic solvents or water.

Bright lights: Electroluminescent Eu^III complexes have been prepared based on functional single-coordinate phosphine oxide ligands (see picture). The singlet and triplet energy levels of the ligands are tuned to fit those of anionic ligands by direct introduction of hole-transport groups. The complexes exhibit low self-quenching and good double-carrier injection ability.

Fulfilled satisfactorily: As a reply to the statements of F. P. Rotzinger [Chem. Eur. J., 2007, 13, 800] we demonstrate that the MP2 method can be applied to uranyl(VI) complexes because dynamic electron correlation effects dominate and static electron correlation of the near-degeneracy type is absent.

Not fulfilled satisfactorily: As a reply to the preceding Comment of V. Vallet, U. Wahlgren, and I. Grenthe, I prove that the conditions which must be fulfilled for the application of the MP2 technique are not satisfied unequivocally for uranyl(VI) complexes—a plea for a careful selection of the computational methods.

Errors in the solubility behavior and in the number of components for the application of the rule of phases led D. G. Blackmond, in a previous Concept article in this journal, to non-valid conclusions and to a wrong thermodynamic interpretation of the Viedma experiment (transition towards homochirality by strong grinding of solid chiral phases of NaClO₃ in equilibrium with a saturated solution).

No errors: We address the preceding Correspondence by Ribó and co-workers, demonstrating that our previous Concept article did not include errors concerning solubility behavior and addressing the challenge of representing phase behavior for systems of racemizing enantiomers. In addition we re-emphasize the point that the homochiral state is not more stable than the heterochiral state and we show that the Ribó treatise for rationalizing Viedma's results misinterprets the Frank model for the evolution of homochirality. There is neither experimental evidence for such interactions nor a need to invoke them to produce a lucid explanation of Viedma's compelling results.