Chemistry - A European Journal

Fluorescent labeling of biomacromolecules with molecules that produce strong fluorescence allows the structures and functions of healthy as well as tumor cells to be investigated. In their Full Paper on page 8116 ff., W. Mier et al. describe the synthesis and characterization of dye oligomers with multiple fluorescent moieties attached to polyamidoamine (PAMAM) dendrimers. These dye oligomers can then be attached to biomacromolecules, such as antibodies, and retain their fluorescent activity.

How to isolate 1 out of 4 diastereomers with 100 % yield! Dynamic systems have readily been applied to obtain pure enantiomers starting from racemic mixtures. Herein we compare these classical methods such as dynamic kinetic resolution (DKR) with novel concepts of dynamic kinetic asymmetric transformation (DYKAT) involving diastereomers (see graphic).

A new perylene bisimide dye has been synthesized that forms highly fluorescent J-aggregates in various organic solvents and its gelation in polar solvents like acetone and dioxane is observed (see figure), whilst anisotropic highly viscous lyotropic mesophases are created in apolar solvents such as n-hexane or methylcyclohexane.

Unconvoluted synthesis: An enantioselective aldol reaction of acetone with various isatin derivatives, catalyzed by a novel organocatalyst, afforded convolutamydine A derivatives with high enantioselectivity (see scheme, TFA= trifluoroacetic acid). The catalyst loading can be reduced to 0.5 mol % without the loss of enantioselectivity, even though direct aldol reactions between ketones and organocatalysts generally need high catalyst loading.

Resolved dynamically: A new, expedient protocol has been developed for the asymmetric synthesis of β³- and β^2, 3-amino acid derivatives from enamine precursors (see scheme). The method relies on a fast equilibrium between the enamine and imine forms. Reduction of the imine with Cl₃SiH, catalyzed by the L-valine-derived formamide L* (5 mol %), afforded the corresponding amino esters in good yields, good enantioselectivities (≤90 % ee) and high diastereoselectivities (≤99 % de).

Mycotoxin synthesis: A versatile and modular synthesis of differently substituted tetrahydroxanthones is presented (see scheme). The core skeleton is obtained via a domino oxa-Michael–aldol condensation reaction and allows access to these privileged structures in larger quantities. The synthetic approach has led to the total synthesis of blennolide C as well as to several advanced synthetic intermediates for the preparation of secalonic acids.

Cooperation effects: A novel strategy to obtain heterogeneous catalysts for gas-phase hydrogenation has been developed, based on metallic nanoparticles stabilized by methylated cyclodextrins (CDs) and adsorbed onto charcoal. The CDs appear as multifunctional molecular receptors capable of stabilizing and dispersing the metallic particles on the support and modifying the stereoselectivity through host–guest interactions.

NH group makes all the difference: The highly stereoselective nitro-Mannich reaction of α-substituted nitroacetates and N-Boc aldimines was investigated catalyzed by novel chiral bifunctional thiourea/secondary-amine systems (an example is shown here). The presence of a basic NH group is crucial for the stereocontrol. The products with adjacent quaternary and tertiary chiral centers were directed isolated in moderate to good yields for an array of substrates (91–96 % ee).

Throw out the anchor! A new approach for the preparation of heterogeneous catalysts based on a covalent anchoring of an innovative multifunctional titanosisesquioxane on the inner surface silanols of mesoporous silicas (SBA-15 and non-ordered silica) is proposed (see figure).

New P,S-hybrids: The design, preparation (see scheme), and characterization of three types of bithiophene-fused benzo[c]phospholes are described. The structural, optical, and electrochemical properties of these compounds vary considerably depending on the π-conjugation modes at the bithiophene subunits and the substituents of the heterole components.

Team players win the game! The study of a large number of common dyes has shown that fluorescence resonance energy transfer (FRET) effects eliminated the fluorescence signals of dye multimers. In contrast, dansyl dyes multimerised on PAMAM dendrimers with up to 128 dye units acquired strong cooperative fluorescent signals (see figure).

Straight and bent: Bent hydrazinediides of the Group 4 metals Zr and Hf are thought to play a role in their reactions with nucleophiles and electrophiles. Such bent species were structurally characterised as Lewis acid adducts in this work, which also includes a detailed analysis of their bonding (see scheme; TBS: tBuMe₂Si).

Molecular “Fosbury flop”: Correlated rotations were evidenced experimentally and theoretically in sterically hindered ruthenium(II) complexes. The rotation of the upper cyclopentadienyl ligand (rotation 1, see graphic) results in the p-bromophenyl paddles tipping over (rotation 2).

Bright zeolites: The novel framework of AV-21, a microporous lanthanide silicate prepared under hydrothermal conditions, has been investigated by synchrotron and conventional single-crystal X-ray analyses, as well as NMR and photoluminescent spectroscopy.

Fullerene-appended organogelator C60TT self-assembles into nanowire structures on application of the Langmuir–Blodgett (LB) method. The surface morphology of the C60TT LB film depends on the holding time at a surface pressure of π=5 mN m⁻¹ before deposition and changes from a homogeneous monolayer to a bilayer fibrous structure via a fibrous monolayer structure, as revealed inter alia by plotting the normalized area per molecule A* against time (see picture).

Melting into shape: Crystalline graphitic carbon nitride (see graphic for structure) has been prepared by temperature-induced condensation in a salt melt of lithium chloride and potassium chloride. The structure was studied by powder X-ray diffraction and high-resolution transmission electron spectroscopy.

The power of weak interactions: The new Rh^I complex trans-[Rh(CO)₂(monophosphine)₂]BF₄ has a nonlinear OCRhCO fragment and weak intramolecular CH⋅⋅⋅Rh interactions (see figure). Both experimental and theoretical evidence indicate that these structural attributes are strongly interdependent. Moreover, the weak CH⋅⋅⋅Rh interactions have been found to exert a significant effect on the reactivity of the metal center.

Being included is just as good: Cyclodextrins can be used to overcome the water insolubility and increase the bioavailability of ferrocifen complexes (see scheme), without changing either their reactivity or their antiproliferative activity against hormone-independent breast-cancer cell lines.

Platinum lockbox: Pt@MOF-177, platinum nanoparticles embedded in MOF-177, was synthesised by means of deposition of a sublimeable organoplatinum compound followed by reduction with H₂ and characterisation by transmission electron microscopy and powder X-ray diffraction. Alcohol oxidation catalysis using air as an oxidant and hydrogen-storage capacity of the hybrid material was investigated (see figure).

Size matters! The La₃N cluster is the largest metallic nitride encapsulated in fullerene cages with a preference for the C₉₆ cage. The redox properties of La₃N@C₈₈ are very different from those observed for other metallic nitride endohedral fullerenes with the same carbon cage (see figure).

Clarification of indefinable configurations: Any compound that interrupts type III secretion systems (TTSS) of bacteria is a potentially ideal anti-infectious drug. The reliable asymmetric synthesis of guadinomines (see scheme), which express a selective inhibition of TTSS, has revealed their absolute configurations, which could not have been defined without the synthetic approach chosen.

Successful strategy: A Pd-catalyzed Stille allylation/Nozaki–Hiyama–Kishi coupling sequence has been successfully employed for the preparation of two new neodolabellane-type diterpenoids 1 and 2.

Benzene! New synthetic approaches to substituted aromatic compounds are reported. Ring-closing olefin metathesis (RCM)/dehydration and RCM/ tautomerization are the key processes in the synthesis of substituted benzenes and phenols, respectively.

TEMPO was immobilized on carbon-coated cobalt nanoparticles via click chemistry resulting in a remarkably stable and recyclable organocatalyst (see graphic) which maintains its high reactivity throughout several iterative oxidation reactions. The quantitative recovery of the catalyst succeeds plainly by applying an external magnet followed by decantation of the reaction mixture.

A dual-function material has been designed for the simultaneous chromofluorogenic detection and removal of Hg²⁺ in aqueous environment. A mesoporous silica decorated with SH groups is treated with a blue squaraine dye, which is transformed into an anchored colourless leuko form. In the presence of mercury(II) ions, the intensely coloured dye is released into solution and Hg²⁺ is adsorbed in the solid, as depicted schematically.

Fused porphyrins: L- and T-shaped porphyrin tapes have been synthesized as extensible structural motifs of 2D extended-porphyrin tapes (see figure). Systematic measurement of the two-photon adsorption (TPA) properties of linear, L-, and T-shaped porphyrin tapes clearly indicate the importance of directionality in the π-conjugation pathway for the enhancement of the TPA properties.

Close encounter: The OO bond formation mechanism in photosystem II is investigated by density-functional calculations and comparison with the X-ray structures. In order to stay as closely as possible to the X-ray structures, the positions of the backbone atoms included in the model were held fixed at the positions suggested by the London structure (e.g., DFT-optimized structure depicted).

Heterolytic OO bond cleavage of a radical probe peroxide by a functional diiron monooxygenase model (see figure) results in the formation of intermediate species the UV/Vis spectra and kinetic behavior of which suggest parallel reactivity to that seen in reactions with oxygen-atom-donor molecules. Kinetic analysis of the reaction indicates that there is a preequilibrium binding step that manifests as saturation behavior in peroxide concentration.

Chiral nanosurfaces: Adsorption of model chiral molecules on a solid surface with a chiral nanoarray of active sites provides a new mechanism of chiral selection (see figure). Manipulating the footprint and binding energy of the molecules allows for fine tuning of the selectivity of the surface.

Mercury rising: Oxidation pathways of gaseous elementary mercury (GEM) in the polar regions are proposed (for example, see scheme) based on theoretical and experimental data.

DNA delivery: Tetra- and diether-type archaeal lipid analogues with a PEG chain and a folate moiety have been synthesised (see figure). These targeting co-lipids have afforded ligand–receptor internalisation of lipoplexes and efficient transfection of HeLa cells.

Luminescent metallopolyynes: Conjugated organometallic polymers containing the fluorene unit and the trans-bis(3-ethynylcarbazolyl)bis(tributylphosphine)platinum(II) chromophore along with the corresponding model compounds were prepared and characterized. Steady-state and time-resolved spectroscopy demonstrated intrachain photo-induced fast singlet electron and slower triplet energy transfer from the platinum–ethynylcarbazole donor to the fluorene acceptor unit.

Gold catalysis: Phosphine gold(I) complexes [(PR₃)AuCl], in conjunction with silver triflate (AgOTf), catalyze intermolecular hydroarylation of aryl and aliphatic alkenes and conjugated dienes with indoles under thermal and microwave-assisted conditions. This synthetic protocol provides convenient access to a variety of C3-alkylated indoles under mild reaction conditions (see scheme).

Molecular scaffolds and batteries: Dendrimers containing up to 21 viologen units have been investigated. They can host a number of eosin dianions (Ey²⁻) equal to the number of viologen units, quenching the fluorescence of Ey²⁻, and can store a number of electrons comparable to the number of viologen units in their outer shells (see schematic).

A nose for coke: A proof of principle of a reagentless aptameric sensor based on surface-enhanced Raman scattering (SERS) spectroscopy with a “signal-on” architecture using a model target of cocaine (see scheme) is reported.

A straightforward to assemble catalytic system for the intermolecular hydroacylation reaction of β-S-substituted aldehydes with activated and unactivated alkenes and alkynes is reported. The catalysts are based upon [Rh(cod)(DPEphos)][ClO₄] (cod= cyclooctadiene, DPEphos=bis(2-diphenylphosphinophenyl)ether, E=O; see scheme) and were designed to make use of the hemilabile capabilities of the DPEphos ligand to stabilise key acyl–hydrido intermediates against reductive decarbonylation.

Derivatives azulike: Tris[1,1,4,4,-tetracyano-2-(1-azulenyl)-3-butadienyl] chromophores have been synthesized in excellent yields through steps that include both the Pd-catalyzed alkynylation of ethynylated arenes under Sonogashira–Hagihara conditions and a [2+2] (see scheme) cycloaddition reaction.

Simple and speedy synthesis: Metal (hydr)oxide nanoparticle synthesis usually needs to be adapted for each system separately. Here we report on a general procedure for the fabrication of uniform metal (hydr)oxide particles with sizes down to a few nanometers, all with well-defined sizes and magnetic properties (see figure).