• Issue

    Chemistry – A European Journal: Volume 19, Issue 38

    12565-12905
    September 16, 2013

Cover Pictures

Free Access

Cover Picture: Re-examination of the C6Li6 Structure: To Be, or not To Be Symmetric (Chem. Eur. J. 38/2013)

  • Pages: 12565
  • First Published: 12 September 2013
Description unavailable

The potential energy surface and fluxionality of C6Li6 is discussed by G. Moreno et al. in their Full Paper on page 12668 ff., providing a new structure of C6Li6, which can be described as three C22− fragments, strongly aggregated through lithium bridges. At high temperatures fluxionality is perceived instead of dissociation. At 600 and 900 K, Born–Oppenheimer molecular dynamics simulations show that the lithium mobility is high, indicating that the cluster behaves like a liquid.

Free Access

Inside Cover: Unusual Inherent Electrochemistry of Graphene Oxides Prepared Using Permanganate Oxidants (Chem. Eur. J. 38/2013)

  • Pages: 12566
  • First Published: 12 September 2013
Description unavailable

On first sight it is plain graphene oxide. On the second look it is full of interesting and unusual features—like an empty shell which is, actually, not empty at all. For more details see the Full Paper by M. Pumera et al. on page 12673 ff.

Free Access

Back Cover: Synthesis of PAF, an Antifungal Protein from P. chrysogenum, by Native Chemical Ligation: Native Disulfide Pattern and Fold Obtained upon Oxidative Refolding (Chem. Eur. J. 38/2013)

  • Pages: 12908
  • First Published: 12 September 2013
Description unavailable

PAF, an antifungal protein found in P. chrysogenum, is stabilized with three disulfide bonds that are essential for bioactivity. G. Váradi, G. K. Tóth and co-workers in their Full Paper on page 12684 ff. show that the protein with its native fold and disulfide pattern can be prepared in good yield by using a combination of solid-phase synthesis and native chemical ligation followed by oxidative refolding.

Graphical Abstract

Graphical Abstract: Chem. Eur. J. 38/2013

  • Pages: 12569-12579
  • First Published: 12 September 2013

News

Concept

Drug Delivery

Polymeric Micelles for Multidrug Delivery and Combination Therapy

  • Pages: 12586-12601
  • First Published: 13 August 2013
Description unavailable

Right on target! This concept article presents current research and developments on the application of polymeric micelles as nanocarriers for multidrug delivery and combination therapy. The advances of this concept focus on the targeted drug delivery for cancer, gene, and RNA therapies using systemic administration. Finally, the application of multidrug micelles combined with drug-releasing implants for local delivery based on titania nanotubes is summarized.

Communications

Radiopharmaceuticals

Convenient Synthesis of 68Ga-Labeled Gadolinium(III) Complexes: Towards Bimodal Responsive Probes for Functional Imaging with PET/MRI

  • Pages: 12602-12606
  • First Published: 28 August 2013
Description unavailable

A killer application? Recently, fully integrated full-body positron-emission tomography (PET) and magnetic-resonance imaging (MRI) scanners were brought to market, allowing simultaneous recording of complementary 3D data sets. By using bimodal PET/MRI probes (see figure), in vivo 3D mapping of various parameters with medical relevance could become feasible.

Functionalized Polyoxometalates

Versatile Post-functionalization of Polyoxometalate Platforms By Using An Unprecedented Range of Palladium-Catalyzed Coupling Reactions

  • Pages: 12607-12612
  • First Published: 28 August 2013
Description unavailable

Handy POMs: Several palladium-catalyzed coupling reactions have been applied to polyoxometalate post-functionalization. The feasibility of each reaction with one model substrate was investigated and each set of synthetic conditions was optimized to obtain full conversions and high purity hybrid compounds (see scheme).

Organic–Inorganic Hybrids

Porphyrin-POSS Molecular Hybrids

  • Pages: 12613-12618
  • First Published: 26 August 2013
Description unavailable

Porphyrin-POSS hybrid: Porphyrin-POSS molecular hybrid composites (see scheme; POSS = polyhedral oligomeric silsesquioxanes) were synthesized and structurally characterized, allowing the realization of truly homogenous dispersion of basic functional building blocks between organic and inorganic components at the molecular level. These materials allow the optimization of aggregation/association behavior and thus the functional optical properties of the porphyrinato zinc compounds.

Mesoporous Microspheres

Mesoporous Ta3N5 Microspheres Prepared from a High-Surface-Area, Microporous, Amorphous Precursor and Their Visible-Light-Driven Photocatalytic Activity

  • Pages: 12619-12623
  • First Published: 23 August 2013
Description unavailable

A light Ta3N5: Mesoporous Ta3N5 microspheres were synthesized by thermally nitriding a high-surface-area, microporous, amorphous Ta2O5 precursor at 750 °C, which is lower than the 900 °C needed for the complete nitridation of micrometer-sized Ta2O5 powder. The mesoporous Ta3N5 microspheres show significantly enhanced visible-light photoactivity in the degradation of methylene blue (MB) compared with similar photocatalysts reported under similar conditions.

Palladium Catalysis

Palladium-Catalysed Carbonylative α-Arylation of Acetone and Acetophenones to 1,3-Diketones

  • Pages: 12624-12628
  • First Published: 23 August 2013
Description unavailable

Three COmponent α-arylation: A carbonylative ketone α-arylation process employing acetone for the first time, as well as acetophenones, is described (see scheme). The reaction tolerates a range of (hetero)aryl iodides and several functionalised aryl ketone coupling partners. Only low pressures of molecular CO are applied and no additional solvent is necessary.

Supramolecular Flow Chemistry

Supramolecular Polymerization in Microfluidic Channels: Spatial Control Over Multiple Intermolecular Interactions

  • Pages: 12629-12634
  • First Published: 19 August 2013
Description unavailable

A novel supramolecular assembly has been developed in conjugation with microfluidics. Self-assembly of the programmed molecules was controlled precisely, in space and time, in a microflow channel as a result of a homogeneous solvent mixing process (see figure). Furthermore, through continuous organization of component molecules followed by orientation along microflow, the self-assembling event containing different molecules was spatially controlled from nano to micrometer scale in a single stream (GMP=guanosine 5′-monophosphate).

Carbonylation Cascade

Palladium-Catalyzed Carbonylative Synthesis of Quinazolinones from 2-Aminobenzamide and Aryl Bromides

  • Pages: 12635-12638
  • First Published: 23 August 2013
Description unavailable

C from CO! A straightforward procedure for the carbonylative synthesis of quinazolinones from readily available 2-aminobenzamide and aryl bromides has been developed. In the presence of a palladium catalyst, various quinazolinones were produced in moderate to excellent yields. Remarkably, no chromatography was needed for purification (see scheme).

Photochemistry

Enantioselective Access to Bicyclo[4.2.0]octanes by a Sequence of [2+2] Photocycloaddition/Reduction/Fragmentation

  • Pages: 12639-12643
  • First Published: 23 August 2013
Description unavailable

Tricks of the trade: Because intramolecular Cu-catalyzed access to bicyclo[4.2.0]octanes is not feasible, an oxygen bridge was introduced to facilitate the [2+2] photocycloaddition. Starting from compounds similar to 1, products such as 2 could be obtained enantioselectiviely in three steps after ring-opening metathesis (see scheme).

Natural Products

Open Access

Structure Reassignment of Laurefurenynes A and B by Computation and Total Synthesis

  • Pages: 12644-12648
  • First Published: 21 August 2013
Description unavailable

The originally assigned stereostructures of laurefurenynes A and B have been reassigned on the basis of DFT calculations of NMR chemical shifts, synthesis of model compounds and total synthesis of laurefurenyne B, demonstrating the power of this combined approach for stereostructure elucidation/confirmation (see scheme).

Total Synthesis

Total Synthesis and Structural Revision of Laurefurenynes A and B

  • Pages: 12649-12652
  • First Published: 19 August 2013
Description unavailable

Structural reassignment: A total synthesis of the proposed structure of (−)-laurefurenyne A has been accomplished that relies on organocatalytic aldehyde α-chlorination and a flexible chlorohydrin-based strategy for stereocontrolled access to the bis-tetrahydrofuran core of the natural product. Analysis of incongruities between the 1H NMR spectra of synthetic and natural material led to a configurational reassignment for the natural product, which was also confirmed by total synthesis.

Asymmetric Synthesis

α-Isocupreine, an Enantiocomplementary Catalyst of β-Isocupreidine

  • Pages: 12653-12656
  • First Published: 26 August 2013
Description unavailable

Complementary chemistry! α-Isocupreine (α-ICPN) was synthesized for the first time in one step from quinine by treatment with CF3SO3H (see scheme). This compound serves as an enantiocomplementary catalyst to β-isocupreidine (β-ICD) in the Morita–Baylis–Hillman reaction.

Full Papers

Imaging Agents

Highly Water-Dispersible Surface-Modified Gd2O3 Nanoparticles for Potential Dual-Modal Bioimaging

  • Pages: 12658-12667
  • First Published: 28 August 2013
Description unavailable

Luminescent and water-dispersible ultrasmall gadolinium oxide nanoparticles were designed and synthesized for potential dual-modal biological imaging. They were obtained by capping gadolinium oxide (GO) nanoparticles with a fluorescent glycol-based conjugated carboxylate that can also sensitize the luminescence of an EuIII dopant through an antenna effect. They are suitable for both magnetic resonance imaging (MRI) and photoluminescent (PL) imaging (see figure).

Structure Elucidation

Re-examination of the C6Li6 Structure: To Be, or not To Be Symmetric

  • Pages: 12668-12672
  • First Published: 19 July 2013
Description unavailable

Global minimum: The potential energy surface of C6Li6 (see figure) was re-examined and a new non-symmetric global minimum was found. The new structure can be described as three C22− fragments strongly aggregated through lithium bridges. At high temperatures, fluxionality is perceived instead of dissociation.

Graphene Materials

Unusual Inherent Electrochemistry of Graphene Oxides Prepared Using Permanganate Oxidants

  • Pages: 12673-12683
  • First Published: 09 August 2013
Description unavailable

Electrochemical devices: Graphene oxides prepared with different oxidants show distinct electrochemistry; those prepared using chlorate exhibit chemically irreversible reductions, whereas graphene oxides prepared through permanganate-based methods exhibit very unusual inherent chemically reversible electrochemistry of their oxygen-containing groups (see figure). These findings have strong implications for energy-storage and sensing devices.

Protein Synthesis

Synthesis of PAF, an Antifungal Protein from P. chrysogenum, by Native Chemical Ligation: Native Disulfide Pattern and Fold Obtained upon Oxidative Refolding

  • Pages: 12684-12692
  • First Published: 23 August 2013
Description unavailable

Thiol soul mates: PAF, an antifungal protein from P. chrysogenum, can be prepared synthetically by using a combination of solid-phase peptide synthesis (SPPS) and native chemical ligation followed by oxidative folding (see scheme; Boc=tert-butoxycarbonyl, Fmoc=9-fluorenylmethoxycarbonyl, MBHA=methylbenzhydrylamine). Using this method, PAF is prepared with the correct disulfide-bond connectivity and fold.

Donor–Acceptor Chromophores

Donor–Acceptor (D–A)-Substituted Polyyne Chromophores: Modulation of Their Optoelectronic Properties by Varying the Length of the Acetylene Spacer

  • Pages: 12693-12704
  • First Published: 06 August 2013
Description unavailable

Spacer length matters: The influence of the length of polyyne spacers on the optoelectronic properties of push–pull chromophores was comprehensively investigated in a combined experimental and theoretical study. The high solubility of chromophores allowed for INADEQUATE NMR measurements without 13C labeling, thus providing unique insight into the π-electron delocalization along the polyyne chain. Very high, off-resonant specific third-order optical nonlinearities were measured at a spacer length of two and three triple bonds.

Spectroscopy

19F NMR Spectroscopy as a Probe of Cytoplasmic Viscosity and Weak Protein Interactions in Living Cells

  • Pages: 12705-12710
  • First Published: 06 August 2013
Description unavailable

The soft cell: Cytosolic viscosity and weak protein–protein interactions in cells affect mobility, but examining these effects is challenging. A 19F NMR method to quantify these effects in living Escherichia coli cells has been developed and the origins of resonance broadening in E. coli cells have been investigated (see figure).

Cluster Compounds

Unprecedented Electron-Poor Octahedral Ta6 Clusters in a Solid-State Compound: Synthesis, Characterisations and Theoretical Investigations of Cs2BaTa6Br15O3

  • Pages: 12711-12719
  • First Published: 05 August 2013
Description unavailable

Reshuffle the cards: Synchrotron X-ray powder diffraction and absorption combined with EPR measurements evidence unprecedented electron-poor metallic clusters with thirteen e per Ta6 in the solid-state compound Cs2BaTa6Br15O3 (see figure). DFT calculations reveal the electronic structure of this material and demonstrate a strong influence of the solid-state environment on the Ta6 octahedron geometry.

DNA Polymerase

Benzofurazane as a New Redox Label for Electrochemical Detection of DNA: Towards Multipotential Redox Coding of DNA Bases

  • Pages: 12720-12731
  • First Published: 09 August 2013
Description unavailable

DNA redox coding: The first orthogonal set of three redox tags for DNA nucleobase coding has been developed based on the combination of a benzofurazane label with the known nitrophenyl and aminophenyl tags (see scheme). This represents a significant step towards redox coding of DNA for electrochemical DNA diagnostics.

Nanostructures

Growth of Au@Ag Core–Shell Pentatwinned Nanorods: Tuning the End Facets

  • Pages: 12732-12738
  • First Published: 09 August 2013
Description unavailable

In tip-top shape: Au@Ag core–shell nanorods with tunable end facets are obtained by coating Au bipyramids (BPs) with Ag. The resultant nanorods exhibit a pentatwinned crystal structure with tips terminated with either {110} or {111} end facets. Control over the end facets is achieved by varying the capping agents and tuning the reduction rate of Ag (see figure).

G-Quadruplexes

Multitasking Water-Soluble Synthetic G-Quartets: From Preferential RNA–Quadruplex Interaction to Biocatalytic Activity

  • Pages: 12739-12747
  • First Published: 06 August 2013
Description unavailable

A molecular swiss knife: Water-soluble synthetic G-quartets are valuable molecular tools that demonstrate interesting properties in terms of DNA/RNA interactions and catalytic activities (performing peroxidase-like hemin-mediated oxidations either in an autonomous fashion or in conjunction with quadruplex DNA; see figure). These results provide a solid scientific basis for synthetic G-quartets to be used as tools for bionanotechnological applications.

Click Chemistry

Reversible Control over Molecular Recognition in Surface-Bound Photoswitchable Hydrogen-Bonding Receptors: Towards Read–Write–Erase Molecular Printboards

  • Pages: 12748-12758
  • First Published: 08 August 2013
Description unavailable

Sticky fingers: A photoactive barbiturate receptor is covalently bound to a surface to prepare molecular printboards in which hydrogen-bonding recognition can be written using light thanks to the intramolecular dimerization of appended anthracenes (see figure).

Porphyrins

Tunable Self-Assembly of Triazole-Linked Porphyrin–Polymer Conjugates

  • Pages: 12759-12770
  • First Published: 12 August 2013
Description unavailable

Tunable building blocks: Triazole-linked porphyrin–polymer conjugates (PPCs) were prepared in high yield using the copper(I)-catalysed azide–alkyne cycloaddition (CuAAC) “click” reaction. The triazole groups were introduced from CuAAC coupling to guide the self-assembly of the PPCs into short oligomers (2–6 units in length) via intermolecular porphyrinatozinc–triazole coordination. Association constants of the PPCs could be tuned by altering the polymer microenvironment around the porphyrin core, thus presenting a modular platform for designing self-assembled porphyrin–polymer materials.

Synthetic Methods

Copper-Catalyzed Oxidative Amination and Allylic Amination of Alkenes

  • Pages: 12771-12777
  • First Published: 22 July 2013
Description unavailable

A new protocol for the direct synthesis of enamides and allylic amines by oxidative NH/CH coupling of N-sulfonylanilines with vinylarenes is presented. The reaction works in both inter- and intramolecular modes and is catalyzed by copper salts by using MnO2 as the stoichiometric oxidant (see scheme). Nitrogen heterocycles including indoles, benzothiazine dioxides, and dibenzazepines can be formed.

Glycomimetics

Addition of Electrophilic Radicals to 2-Benzyloxyglycals: Synthesis and Functionalization of Fluorinated α-C-Glycosides and Derivatives

  • Pages: 12778-12787
  • First Published: 16 August 2013
Description unavailable

Go radical! The reactions between highly electrophilic radicals and a 2-benzyloxyglucal or galactal provide 2-keto-hexopyranosides. Reduction of these compounds affords substituted α-C-glycosides, featuring groups such as CF2CO2R or CF2Br, which allow further synthetic elaboration (see scheme).

Tandem Reactions

Tandem Synthesis of Benzo[b]carbazoles and Their Photoluminescent Properties

  • Pages: 12788-12793
  • First Published: 09 August 2013
Description unavailable

Lord of the rings: A series of benzo[b]carbazoles was synthesized through a tandem Wolff-rearrangement/aza-Wittig-reaction/biradical-ketenimine-cyclization/1,5-H-shift process. The products emitted intense light with high emission quantum yields (see scheme).

Supercritical Fluids

Influence of Perfluorinated End Groups on the SFRD of [Pt(cod)Me(CnF2n+1)] onto Porous Al2O3 in CO2 under Reductive Conditions

  • Pages: 12794-12799
  • First Published: 05 August 2013
Description unavailable

Cod and Al2O3 chips: A series of [Pt(cod)Me(CnF2n+1)] complexes with different perfluorinated end groups was prepared and their supercritical fluid reactive deposition (SFRD) onto porous Al2O3 in CO2 under reductive conditions was investigated (see scheme).

Trifluoromethylation

Copper-Mediated Deoxygenative Trifluoromethylation of Benzylic Xanthates: Generation of a CCF3 Bond from an O-Based Electrophile

  • Pages: 12800-12805
  • First Published: 06 August 2013
Description unavailable

Highly compatible and useful: The copper-mediated trifluoromethylation of benzylic xanthates using Umemoto's reagent as the source of CF3 to form CCF3 bonds is described (see scheme). The method is compatible with an array of benzylic xanthates bearing useful functional groups. A preliminary mechanistic investigation suggests that the CCF3 bond forms by reaction of the substrate with in situ generated CuCF3 and CuOTf.

Drug Delivery

A Designed 5-Fluorouracil-Based Bridged Silsesquioxane as an Autonomous Acid-Triggered Drug-Delivery System

  • Pages: 12806-12814
  • First Published: 08 August 2013
Description unavailable

My name is Bond, H-Bond: A new 5-fluorouracil (5-FU) prodrug, showing cytotoxicity against breast cancer cells, was successfully maintained through H-bonds to an organobridged silsesquioxane (BS). The resulting complex is not affected under physiological conditions but operates under lysosomal pH to deliver the prodrug (see figure). The designed 5-FU prodrug/BS is a promising autonomous pH-sensitive material carrier, which avoids the side effects of the anticancer drug due to a controlled and targeted release.

Rotaxanes

Use of Cleavable Coordinating Rings as Protective Groups in the Synthesis of a Rotaxane with an Axis that Incorporates More Chelating Groups Than Threaded Macrocycles

  • Pages: 12815-12823
  • First Published: 09 August 2013
Description unavailable

Securing rotaxanes: A new method of preparing a linear “unsaturated” [3]rotaxane consisting of an axis containing more coordination sites than threaded rings was developed (see figure). It was based on the preliminary synthesis of a “saturated” [5]rotaxane consisting of a four-chelating site axis threaded through four macrocyclic components, with two of them acting as protective groups. Subsequent removal of the protective macrocycles from the [5]rotaxane afforded the desired unsaturated [3]rotaxane in quantitative yield.

Lipids

General Synthesis and Physicochemical Characterisation of a Series of Peptide-Mimic Lysine-Based Amino-Functionalised Lipids

  • Pages: 12824-12838
  • First Published: 09 August 2013
Description unavailable

Copycats: Malonic acid diamides, a new class of amino-functionalised lipids, have been synthesised and characterised. These peptide-mimic lipids are suitable for polynucleotide transfer. Six head-group structures, which vary in size and number of amino groups, are used. The modularly composed synthesis of the backbone allows easy alkyl-chain variation (see figure). Phase transitions are discussed in terms of head-group and alkyl-chain variations.

Energetic Materials

High-Nitrogen-Based Pyrotechnics: Perchlorate-Free Red- and Green-Light Illuminants Based on 5-Aminotetrazole

  • Pages: 12839-12845
  • First Published: 16 August 2013
Description unavailable

Getting into the “green” scene! Perchlorate-free red-and green-light-emitting pyrotechnic illuminants (see figure) for military interests have been developed in a cost-effective manner. The optimal formulations have been successfully proven for a prototype and were found to be stable toward various ignition stimuli.

Biosensors

Polymer-Templated Perylene-Probe Noncovalent Self-Assembly: A New Strategy for Label-Free Ultrasensitive Fluorescence Turn-On Biosensing

  • Pages: 12846-12852
  • First Published: 31 July 2013
Description unavailable

Signaling a change: A cationic polymer induces aggregation of a negatively charged perylene probe. Competitive binding of the negatively charged nucleic acid (a polyanion) to the cationic polymer resulted in the release of a monomer (compound 1 in figure). A turn-on fluorescence signal was detected. Based on these observations, a new strategy for the highly sensitive detection of alkaline phosphatase (ALP) activity has been demonstrated.

Photochemistry

Squarylium-Triazine Dyad as a Highly Sensitive Photoradical Generator for Red Light

  • Pages: 12853-12858
  • First Published: 05 August 2013
Description unavailable

Put on the red light: Diads based on a squarylium dye and triazine derivatives absorb light in the red region strongly, giving rise to an intramolecular photodissociative electron-transfer reaction that releases radicals (see figure).

Metallocene Synthesis

Alkaline Earth Metallocenes Coordinated with Ester Pendants: Synthesis, Structural Characterization, and Application in Metathesis Reactions

  • Pages: 12859-12866
  • First Published: 09 August 2013
Description unavailable

Alkaline earth metallocenes: Heavier alkaline earth (Ca, Sr, Ba) metallocenes containing two intramolecularly coordinated ester pendants and bearing multiply substituted cyclopentadienyl ligands (see scheme) can be prepared efficiently. These metallocenes can undergo metathesis reactions to form the transition-metal metallocenes.

Molecular Crystals

Identification of Molecular Crystals Capable of Undergoing an Acyl-Transfer Reaction Based on Intermolecular Interactions in the Crystal Lattice

  • Pages: 12867-12874
  • First Published: 09 August 2013
Description unavailable

Reactive crystal gazing? Characterization of functional groups in small organic molecules allows the prediction of their reactivity in solution, and often the structure of the resulting products with fairly good accuracy. This, however, is not true for reactions in the solid state. It was demonstrated that an understanding of the non-covalent interactions in molecular crystals can aid in identifying crystal structures that support chemical reactions (see figure).

Enzyme imaging

Specific Detection and Imaging of Enzyme Activity by Signal-Amplifiable Self-Assembling 19F MRI Probes

  • Pages: 12875-12883
  • First Published: 16 August 2013
Description unavailable

MR imaging probes: New signal-amplifiable self-assembling 19F NMR/MRI probes for turn-on detection and imaging of specific enzymatic activity are reported. The probes are “silent” when aggregated, but exhibit a disassembly-driven turn-on signal change upon cleavage of their substrate part by nanomolar concentrations of the enzyme. These turn-on probes can be used to visualize the activity of endogenously secreted matrix metalloproteinases from tumor cells (see graphic).

Organic Functionalization

Tuning the Dispersibility of Carbon Nanostructures from Organophilic to Hydrophilic: Towards the Preparation of New Multipurpose Carbon-Based Hybrids

  • Pages: 12884-12891
  • First Published: 09 August 2013
Description unavailable

Moving carbon nanostructures: Functionalised graphene and carbon nanotubes are easily transferred from chloroform to the aqueous phase and vice versa (see figure). They can also deliver hydrophobic molecules, such as pyrene chromophores or drugs, into the aqueous phase and can disperse homogenously in polymers.

N-Heterocyclic Carbenes

Electronic Structure Trends in N-Heterocyclic Carbenes (NHCs) with Varying Number of Nitrogen Atoms and NHCTransition-Metal Bond Properties

  • Pages: 12892-12905
  • First Published: 16 August 2013
Description unavailable

Trends explained: The electronic structures of fourteen five-membered N-heterocyclic carbenes with two, three or four nitrogen atoms in the heterocycle are studied by means of DFT calculations (see figure). Trends and similarities in the electronic parameters are identified and discussed. It is proposed how these parameters can be used to describe the bonding interaction between these NHCs and gold as well as titanium fragments.