Chemistry - A European Journal

A new type of battery made of a lithium anode and a porous cathode has attracted attention in recent years because of the large impact this technology may have on several fields, including electric mobility. In this context, the electrolyte role in non-aqueous lithium/air batteries emerged as a fundamental issue, the choice of the solvent being a key factor to achieve the highest possible energy density, while allowing the rechargeability of the cell. In the Full Paper on page 3510 ff., T. Laino and A. Curioni describe, with first principle methods, the chemical degradation of the propylene carbonate exposed to a layer of lithium oxide (in the picture, on top of an additional layer of porous material).

The combination of macrocycles with fluorescent dyes affords supramolecular reporter pairs, which can be employed for the monitoring of catalytic, particularly biocatalytic, reactions. The resulting assays are unselective time-resolved variants of indicator displacement and uptake sensing systems. They are applicable to a large range of analytes and allow direct real-time monitoring in homogeneous solution, with the possibility of performing inhibitor and catalyst screening.

Charge-by-charge assembly: On the basis of a planar receptor–anion complex, bulky tetraalkylammonium cations were found to construct charge-by-charge assemblies comprising alternately stacked positively and negatively charged species. The number and length of long alkyl chains in the cations determine the states of assembled structures, resulting in the formation of a library of charge-based materials (see scheme).

Artificial allosterism: A ditopic ligand, which contains both bipyridine and tetra-aza-crown binding sites, coordinates one Cu^II through all four N-donors of the tetradentate aza-crown unit. Reaction at the bipyridine site with another Cu^II allosterically changes the aza-crown from being a tetradentate to a tridentate N-donor unit, a change in coordination mode that causes the successive binding of two Cu^II ions to proceed with severe negative cooperativity (see scheme).

Merging is the game! The coupling of a domino reaction and an internal neutral redox reaction constitutes an excellent manifold for the stereoselective synthesis of di- and trisubstituted olefins featuring a malonate unit, an ester, or a free carboxylic acid as substituents at the allylic position (see scheme; MW=microwave). The reaction utilizes simple starting materials (propargyl vinyl ethers), methanol or water as solvents, and a very simple and bench-friendly protocol.

An efficient and practical synthesis of optically pure β-pyrazole-substituted alcohols was achieved by an asymmetric ring-opening reaction of meso-epoxides with pyrazole derivatives as the nucleophile. In the presence of 1 mol % of an N,N′-dioxide–Sc(OTf)₃ complex, excellent enantioselectivity and yields were obtained from meso-epoxides. The process could also be used for a mixture of cis- and trans-stilbene oxides. A proposed transition-state model is provided.

Let there be light: A heterogeneous photocatalytic system based on easily recyclable TiO₂ or ZnO allows cross dehydrogenative coupling reactions of tertiary amines. The newly developed protocols have successfully been applied to various CC and CP bond-forming reactions to provide nitro amines as well as amino ketones, nitriles and phosphonates.

An etheric Negishi coupling: The first cross-coupling reaction between aryl alkyl ethers and dianion-type zincate reagents to afford biaryl compounds through selective cleavage of the etheric C(sp²)O bond was developed. Dianion-type zincates showed excellent reactivity toward the aromatic ethers under mild conditions, with good functional group compatibility (see scheme).

Get in the ring! The first examples of transition-metal-catalysed CC bond activation of 3-azetidinones and 3-oxetanones are reported. In the presence of a nickel catalyst and alkynes, a regioselective and high-yielding [4+2] cycloaddition occurs, leading to the formation of pyridinones, pyranones and eventually 4,5-disubstituted 3-hydroxypyridines (see scheme).

DADB synthesis: The diammoniate of diborane (DADB) was synthesized in a new metathesis reaction between the diammoniate of monochloroborane and potassium borohydride in liquid ammonia (see scheme). ¹H and ¹¹B NMR spectra of DADB are reported. The stability in THF was examined by variable-temperature ¹¹B NMR spectroscopy.

A novel {V₄Nb₆O₃₀} addenda: Through the successful introduction of a vanadium atom into the polyoxoniobate system, three novel compounds containing the same unprecedented mixed addenda vanadoniobate cluster {V₄Nb₆O₃₀} were obtained. The incorporation of suitable atoms like V is an intriguing subject providing vast possibilities to enrich polyoxoniobate chemistry.

TAPPing the potential: Perfluoroalkylation and core chlorination gives rise to tetraazaperopyrenes (TAPPs) with high-performance in n-channel transistors (see figure; field-effect mobility of up to 0.14 cm² V⁻¹ s⁻¹, on/off current ratio of >10⁶ and stabilities of up to 3–4 months under ambient conditions).

The main culprit for the degradation of propylene carbonate (PC) in batteries has been identified as Li₂O₂. The reactivity of lithium peroxide versus propylene carbonate has been investigated (see figure) and it was found that Li₂O₂ irreversibly decomposes the carbonate solvent, leading to alkyl carbonates; compared with a single Li₂O₂ unit in PC, a crystalline surface of Li₂O₂ exhibits an enhanced reactivity.

The methylation of peptides by histone lysine methyltransferases, the enzymes responsible for epigenetic regulation, can be continuously monitored in homogeneous solution by using a label-free supramolecular tandem assay strategy. The high affinity of the trimethylated enzymatic product towards p-sulfonatocalix[4]arene, used in combination with the displacement of lucigenin as a dye, allows for a time-resolved switch-ON fluorescence response as a fingerprint of the catalytic activity (see figure).

High density: Asymmetric syntheses of densely functionalized 7–11-membered carbocycles, fused 6/9- and 6/11-membered bicyclic carbocycles, and 9–11-membered lactones are described (see scheme). The key steps are modular syntheses of sulfoximine-substituted C- and O-tethered trienes and dienynes and their Ru-catalyzed ring-closing diene and enyne methasis (RCOEM and RCEYM), respectively. RCEYM of a sulfoximine-substituted 1,7-dien-10-yne with first- and second-generation Ru catalysts showed an unprecedented dichotomy and gave a 9-membered 1,3-dienyl carbocycle and a 9-membered 1,3-dienyl carbocycle truncated by one CH₂ unit.

Highly logical, captain: Logic gates were constructed from a gelator, which was responsive to protons and anions, in its solution, gel, and film states. The output of the logic gates were recorded by the naked eye and UV/Vis and fluorescence spectroscopy (see figure).

Landscape gardening: The energy landscape of the cesium chloride/lithium chloride system was explored by combining theoretical and experimental methods. Owing to the synergetic and complementary nature of these approaches, substantially improved efficiency of the exploration was achieved. Several new phases were found in this system and their thermodynamic ranking was clarified, thereby leading to the derivation of an improved CsCl/LiCl phase diagram.

Sweet 16: Copper(II) and zinc(II) benzofused porphyrin complexes with 16π-electron cores were prepared through two-electron oxidation of tetraphenyltetrabenzoporphyrin complexes with AgSbF₆ (see scheme). Structural characterization and a variety of spectroscopic studies were carried out to analyze the electronic structure and study key trends in the antiaromatic properties of these novel 16π-electron porphyrin species.

Soluble bacterial P450: The mutant Asp251Gly/Gln307His of the bacterial cytochrome P450 BM3 shows new catalytic activity towards diclofenac, ibuprofen and tolbutamide. It can be used to synthesise the metabolites of these drugs normally produced by the 2C subfamily of human cytochromes P450 (see scheme).

Get into the (major) groove! Dimeric calix[4]arenes with cationic groups at their upper rims and flexible alkyl bridges have been synthesized in relatively short synthetic sequences (3–5 steps). The compounds attach themselves to the major groove of double-stranded nucleic acids in a noncovalent fashion (see figure; red), with micro- to nanomolar affinities.

Tying the knot: A convergent synthesis of bafilomycin A₁ is presented. The synthesis relies on the zinc triflate mediated diastereoselective addition of a complex enyne to a sensitive aldehyde as the key fragment coupling. A ruthenium-catalyzed trans-reduction of the resulting propargylic enyne efficiently installs the required C10–C13 trans,trans-diene subunit.

Off the subs bench: 2,11-Dithia[3,3]-metaparacyclophanes were designed and synthesized to study the effect of substituents on the intramolecular aromatic–aromatic interactions between benzene rings. The energy barriers to topomerization were determined by variable-temperature NMR spectroscopy. The variation of the barriers as a function of the substitution on the interacting ring was not related to their effect on the polarity of the π-systems.

Bases coming on strong: A series of stable organosuperbases, N-alkyl- and N-aryl-1,3-dialkyl-4,5-dimethylimidazol-2-ylidene amines, were efficiently synthesized and their basicities were measured in acetonitrile, some of which are stronger bases than the phosphazene base (shown right) and tetramethylguanidine (shown left) in acetonitrile. The basicity depends on, among other factors, the size of the substituent at the imino group, which influences the degree of aromatization of the imidazole ring.

Together forever: A method for the synthesis of isolable chiral aggregates of achiral building blocks was developed and used for the isolation of the chiral homoaggregates of neutral achiral π-conjugated carboxylic acids in pure aqueous solutions.

Triangulation: Experimental and DFT calculations reveal the magnetic response of triangular Ni^II–oximato systems (see figure). The magnetic properties of several Ni₃, Ni₄ and Ni₅ complexes with topologies based on isolated, edge- or vertex-sharing triangular μ₃-OR nickel–oximate units have been elucidated and compared with analogous copper or manganese systems.

Multitasking: A multicatalytic system, consisting of tetrapropylammonium perruthenate/N-methylmorpholine N-oxide (TPAP/NMO) as oxidant and diarylprolinol TMS-ether as chiral amine catalyst, has been developed and applied in the efficient construction of valuable chiral molecules, such as formylcyclopropanes, β-substituted aldehydes, and chromenone derivatives.

An efficient route for the synthesis of 5,6-dihydropyridazin-4-one derivatives through a silver-catalyzed intramolecular tandem reaction of N-sulfonylhydrazone-propargylic esters has been disclosed. The reaction proceeds through a tandem 1,3-acyloxy migration/Mannich-type addition/elimination of a sulfonyl group sequence (see scheme).

Two trumps one! A synergistic antimicrobial effect between gold and silver is found in novel polynuclear {Au₂Ag}_n heterometallic compounds. The luminescence of these and related tri- Au₂Cu and dinuclear Au₂ organometallic derivatives has been studied and correlated with crystallographic data and metallophilic interactions. Most complexes display antibacterial activity, with Au₂Ag being highly active against Gram-positive and Gram-negative bacteria (see scheme).

Whither the water? The Gd^III MRI contrast agent shown has a pH-dependent relaxivity due to a change in inner-sphere hydration (q=2 to q=0) upon sulfonamide coordination. The biphenyl moiety imparts strong affinity for serum albumin, and protein binding was expected to increase pH-dependent relaxivity further. However, the inner-sphere waters are displaced when the complex binds albumin at low pH, and the pH-dependent relaxivity effect is muted.

Smart catalysis! A temperature-sensitive polymer/carbon nanotube composite film with high conductivity and electrocatalytic activity was fabricated on a gold surface (see figure). The modulation of bioelectrocatalysis and electron transfer of biomolecules were achieved on the film.

A new approach for the fabrication of mesoporous metal chalcogenide silica thin films and their conversion into mesoporous metal chalcogenides has been demonstrated. The metal precursors have been incorporated into the pore walls through a salt-assisted self-assembly process that produces homogenous metal oxide coatings over the pore walls of the mesoporous silica thin films (see figure).

Dual photoinduced action: The introduction of a rigid triptycenyl-like spacer between a photochromic azo unit and a fluorescent unit allow both moieties to keep their photophysical integrity ruled by picosecond dynamics in the excited state (see figure). This leads to fluorescent patterns in thin films that are subjected to interferential illumination.

The golden touch: Higher enantioselectivities were observed upon increasing the catalyst nuclearity, by combining symmetry-equivalent sites for a series of chiral gold(I) catalysts. The C₃-symmetric trinuclear catalyst surpassed its mono- and dinuclear congeners both in terms of activity and enantioselectivity.

Bacterial inspection: In this paper, the complete saccharidic structure of the lipopolysaccharide (LPS) that belongs to the human pathogen Halomonas stevensii bacterium is reported. The tridecasaccharide that contained the core region plus one O-chain repeating unit was obtained and characterized (see scheme).

Photoprotection in plants: The acylation of anthocyanins provides UV protection against photochemical damage by fast energy transfer (ET) from the excited co-pigment (Coum) to the anthocyanin (Cy) followed by ultrafast adiabatic proton transfer (PT) to water or internal conversion (IC) of the complex (see figure).

In their shells: Uniform core–shell and yolk–shell architectures (see figure), which combine the functions of a superparamagnetic iron oxide (SPIO) core and a europium-doped yttrium oxide (Y₂O₃:Eu) shell in a single material with tunable fluorescence and magnetic properties, are prepared. The shell thickness and interior cavity of SPIO@Y₂O₃:Eu nanostructures can also be tuned. Yolk–shell nanocapsules modified with amino groups serve as cancer-cell fluorescence imaging agents.

Making it sweet: A series of 2,2,6-trisubstituted piperidines containing a trifluoromethyl or alkyl group at the α position are prepared from a chiral imino lactone by employing two different synthetic strategies. The final products constitute quaternary derivatives of pipecolic acid, and fluorinated analogues of iminosugars can also be conveniently accessed (see scheme; TASF=tris(dimethylamino)sulfonium difluorotrimethylsilicate, TMSCF₃=(trifluoromethyl)trimethylsilane).

A propeller-shaped hetero-oligophenylene derivative, which exhibits aggregation-induced emission enhancement in H₂O/THF (80:20) was synthesized. The aggregates serve as a biological probe for three different proteins (bovine serum albumin (BSA), cytochrome c, and lysozyme), DNA, and two metal ions (Pb²⁺ and Pd²⁺) in contrasting modes. The fluorescence behavior between BSA and cytochrome c and between Pb²⁺ and Pd²⁺ ions mimics the performance of combinatorial logic circuits.

Grinding on one side! Ball milling under solvent-free conditions is presented herein for the synthesis of glycine Schiff bases and their subsequent asymmetric alkylation to prepare chiral natural and unnatural amino acids (see scheme). The use of a cinchona-derived catalyst provided good enantiomeric excesses up to 75 %.