Preview: Chem. Eur. J. 41/2011

Written by Chemistry - A European Journal on September 26, 2011 – 5:00 am -


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Spotlights on our sister journals: Chem. Eur. J. 40/2011

Written by Chemistry - A European Journal on September 26, 2011 – 5:00 am -


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Graphical Abstract: Chem. Eur. J. 40/2011

Written by Chemistry - A European Journal on September 26, 2011 – 5:00 am -


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Inside Cover: Surface-Modified Protein Microspheres Capture Amyloid-β and Inhibit its Aggregation and Toxicity (Chem. Eur. J. 40/2011)

Written by Michal Richman on September 26, 2011 – 5:00 am -

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Accumulation and aggregation of amyloid-β (Aβ) in the brain is the primary pathogenic event in Alzheimer's disease (AD). Thus reducing the level of Aβ in the brain is considered to be a promising strategy for AD therapy. In their Full Paper on page 11171 ff., S. Rahimipour et al. describe sonochemically prepared protein microspheres, the surfaces of which are modified with an Aβ recognition peptide. The microspheres can bind with high affinity and selectivity to Aβ, sequester it from the medium, inhibit its aggregation, and directly reduce its toxicity toward neuron-like cells.


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Cover Picture: Modifying Cage Structures in Metal–Organic Polyhedral Frameworks for H2 Storage (Chem. Eur. J. 40/2011)

Written by Yong Yan on September 26, 2011 – 5:00 am -

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The synthesis of metal–organic polyhedral framework materials, based upon trigonal hexacarboxylate isophthalate linkers, leads to a strategy that generates highly porous materials with relatively high stability and surface areas. These polyhedral MOFs (NOTT-113, NOTT-114 and NOTT-115) show high H2-adsorption capacities. For more details see the Full Paper on page 11162 ff. by M. Schröder, N. R. Champness et al.


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Modifying Cage Structures in Metal–Organic Polyhedral Frameworks for H2 Storage

Written by Yong Yan on September 26, 2011 – 5:00 am -

Abstract

Three isostructural metal–organic polyhedral cage based frameworks (denoted NOTT-113, NOTT-114 and NOTT-115) with (3,24)-connected topology have been synthesised by combining hexacarboxylate isophthalate linkers with {Cu2(RCOO)4} paddlewheels. All three frameworks have the same cuboctahedral cage structure constructed from 24 isophthalates from the ligands and 12 {Cu2(RCOO)4} paddlewheel moieties. The frameworks differ only in the functionality of the central core of the hexacarboxylate ligands with trimethylphenyl, phenylamine and triphenylamine moieties in NOTT-113, NOTT-114 and NOTT-115, respectively. Exchange of pore solvent with acetone followed by heating affords the corresponding desolvated framework materials, which show high BET surface areas of 2970, 3424 and 3394 m2 g−1 for NOTT-113, NOTT-114 and NOTT-115, respectively. Desolvated NOTT-113 and NOTT-114 show high total H2 adsorption capacities of 6.7 and 6.8 wt %, respectively, at 77 K and 60 bar. Desolvated NOTT-115 has a significantly higher total H2 uptake of 7.5 wt % under the same conditions. Analysis of the heats of adsorption (Qst) for H2 reveals that with a triphenylamine moiety in the cage wall, desolvated NOTT-115 shows the highest value of Qst for these three materials, indicating that functionalisation of the cage walls with more aromatic rings can enhance the H2/framework interactions. In contrast, measurement of Qst reveals that the amine-substituted trisalkynylbenzene core used in NOTT-114 gives a notably lower H2/framework binding energy.

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Linked in! Trimethylphenyl, phenylamine and triphenylamine linkers have been incorporated into isostructural (3,24)-connected polyhedral metal–organic frameworks (denoted NOTT-113, NOTT-114 and NOTT-115, shown here from left to right) by combining hexacarboxylate isophthalate linkers with {Cu2(RCOO)4} paddlewheels. The effects of these groups on N2 and H2 uptakes in the resultant porous materials are reported.


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The Catalytic Asymmetric Diels–Alder Reactions and Post-cycloaddition Reductive Transpositions of 1-Hydrazinodienes

Written by Hao Xie on September 26, 2011 – 5:00 am -

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Cycling through: Type I cyclohexenes are produced with high margins of stereoselectivity by chiral, catalyst-controlled, Diels–Alder reactions between 1-hydrazinodienes and N-acryloyl oxazolidinone dienophiles, and readily transformed to cyclohexenes III via a putative, transient allylic diazene II (see scheme). This chemistry gives access to functionalized cyclohexenes that can be difficult to construct by alternative methods.


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Surface-Modified Protein Microspheres Capture Amyloid-β and Inhibit its Aggregation and Toxicity

Written by Michal Richman on September 26, 2011 – 5:00 am -

Abstract

The biocompatible and biodegradable properties of protein microspheres and the recent advances in their preparation have generated considerable interest of utilizing these core-shell structures for drug delivery and diagnostic applications. However, effective targeting of protein microspheres to desirable cells or loci still remains a challenge. Here, we describe for the first time a facile one-pot sonochemical approach for covalent modification of protein microspheres made from serum albumin; the surface of which is covalently decorated with a short recognition peptide to target amyloid-β (Aβ) as the main pathogenic protein in Alzheimer’s disease (AD). The microspheres were characterized for their morphology, size, and entrapment efficacy by electron microscopy, dynamic light scattering and confocal microscopy. Fluorescence-activated cell-sorting analysis and Thioflavin-T binding assay demonstrated that the conjugated microspheres bind with high affinity and selectivity to Aβ, sequester it from the medium and reduce its aggregation. Upon incubation with Aβ, the microspheres induced formation of amorphous aggregates on their surface with no apparent fibrillar structure. Moreover, the microspheres directly reduced the Aβ-induced toxicity toward neuron like PC12 cells. The conjugated microspheres are smaller than unmodified microspheres and remained stable throughout the incubation under physiological conditions.

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Undercover agent: An easy, one-pot, sonochemical approach for the synthesis of protein microspheres decorated with an amyloid-β (Aβ) recognition peptide is described (see scheme). The microspheres bind with high affinity and selectivity to Aβ, the main pathogenic protein in Alzheimer's disease, then sequester it from the medium and directly block its aggregation. Incubation of the cells with microspheres significantly reduced the Aβ-induced toxicity.


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Visible–Near-Infrared and Fluorescent Copper Sensors Based on Julolidine Conjugates: Selective Detection and Fluorescence Imaging in Living Cells

Written by Debabrata Maity on September 26, 2011 – 5:00 am -

Abstract

We present novel Schiff base ligands julolidine–carbonohydrazone 1 and julolidine–thiocarbonohydrazone 2 for selective detection of Cu2+ in aqueous medium. The planar julolidine-based ligands can sense Cu2+ colorimetrically with characteristic absorbance in the near-infrared (NIR, 700–1000 nm) region. Employing molecular probes 1 and 2 for detection of Cu2+ not only allowed detection by the naked eye, but also detection of varying micromolar concentrations of Cu2+ due to the appearance of distinct coloration. Moreover, Cu2+ selectively quenches the fluorescence of julolidine–thiocarbonohydrazone 2 among all other metal ions, which increases the sensitivity of the probe. Furthermore, quenched fluorescence of the ligand 2 in the presence of Cu2+ was restored by adjusting the complexation ability of the ligand. Hence, by treatment with ethylenediaminetetraacetic acid (EDTA), thus enabling reversibility and dual-check signaling, julolidine–thiocarbonohydrazone (2) can be used as a fluorescent molecular probe for the sensitive detection of Cu2+ in biological systems. The ligands 1 and 2 can be utilized to monitor Cu2+ in aqueous solution over a wide pH range. We have investigated the structural, electronic, and optical properties of the ligands using ab initio density functional theory (DFT) combined with time-dependent density functional theory (TDDFT) calculations. The observed absorption band in the NIR region is attributed to the formation of a charge-transfer complex between Cu2+ and the ligand. The fluorescence-quenching behavior can be accounted for primarily due to the excited-state ligand 2 to metal (Cu2+) charge-transfer (LMCT) processes. Thus, experimentally observed characteristic NIR and fluorescence optical responses of the ligands upon binding to Cu2+ are well supported by the theoretical calculations. Subsequently, we have employed julolidine–thiocarbonohydrazone 2 for reversible fluorescence sensing of intracellular Cu2+ in cultured HEK293T cells.

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Seeing is believing: The julolidine–carbonohydrazone and julolidine–thiocarbonohydrazone ligands detect Cu2+ colorimetrically with characteristic absorbance in the near-infrared (NIR, 700–1000 nm) region, which allows the detection of different concentrations of Cu2+ by the naked eye due to the appearance of distinct coloration. Fluorescent julolidine–thiocarbonohydrazone reversibly senses intracellular Cu2+ in cultured HEK293T cells (see figure).


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Enantioselective and Regioselective Friedel–Crafts Alkylation of Pyrroles with Nitroalkenes Catalyzed by a Tridentate Schiff Base–Copper Complex

Written by Fengfeng Guo on September 26, 2011 – 5:00 am -

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On a (pyr)role: A mild and highly efficient catalytic system has been developed for the asymmetric Friedel–Crafts alkylation of pyrroles with nitroalkenes (see scheme). High yields, and excellent enantioselectivities and regioselectivities were obtained for a broad range of substrates. The synthetic utility of this methodology and mechanistic studies involving a novel, negative, nonlinear effect are also presented.


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