Archive for November, 2012

Top ten most accessed articles in August

August saw the following articles from Chemical Communications in its top ten most accessed list:-

Interview with Gautam Desiraju
Chem. Commun.
, 2012, 48, 8997-8998, DOI: 10.1039/c2cc90268k

Porous salts based on the pamoate ion
Helene Wahl, Delia A. Haynes and Tanya le Roex
Chem. Commun., 2012, 48, 1775-1777, DOI: 10.1039/c2cc14753j

Pd-catalyzed double C–H bond activation of diaryl ketones for the synthesis of fluorenones
Parthasarathy Gandeepan, Chen-Hsun Hung and Chien-Hong Cheng
Chem. Commun., 2012, 48, 9379-9381, DOI: 10.1039/c2cc34344d

Carbon dioxide as a carbon source in organic transformation: carbon–carbon bond forming reactions by transition-metal catalysts
Yasushi Tsuji and Tetsuaki Fujihara
Chem. Commun., 2012, 48, 9956-9964, DOI: 10.1039/c2cc33848c

Regioselective palladium-catalyzed direct cross-coupling of coumarins with simple arenes
Minsik Min and Sungwoo Hong
Chem. Commun., 2012, 48, 9613-9615, DOI: 10.1039/c2cc34551j

Multifunctional catalysis by Pd-polyoxometalate: one-step conversion of acetone to methyl isobutyl ketone
Robert D. Hetterley, Elena F. Kozhevnikova and Ivan V. Kozhevnikov
Chem. Commun., 2006, 782-784, DOI: 10.1039/b515325e

Functional group effects on metal–organic framework topology
Phuong V. Dau, Kristine K. Tanabe and Seth M. Cohen
Chem. Commun., 2012, 48, 9370-9372, DOI: 10.1039/c2cc34938h

Copper-catalyzed conversion of aryl and heteroaryl bromides into the corresponding chlorides
Xiujuan Feng, Yiping Qu, Yanlei Han, Xiaoqiang Yu, Ming Bao and Yoshinori Yamamoto
Chem. Commun., 2012, 48, 9468-9470, DOI: 10.1039/c2cc34944b

Chiral assembly of dodecahedral cavities into porous metal–organic frameworks
Hui Yang, Fei Wang, Yao Kang, Tie-Hu Li and Jian Zhang
Chem. Commun., 2012, 48, 9424-9426, DOI: 10.1039/c2cc35024f

Metal catalyzed C(sp3)–H bond amination of 2-alkyl azaarenes with diethyl azodicarboxylate
Jin-Ying Liu, Hong-Ying Niu, Shan Wu, Gui-Rong Qu and Hai-Ming Guo
Chem. Commun., 2012, 48, 9723-9725, DOI: 10.1039/c2cc35309a 

Take a look at the articles then blog your thoughts and comments below.

Fancy submitting an article to Chemical Communications? Then why not have a look at the Chemical Comunications author guidelines and submit to us today, or alternatively, email us with your suggestions.

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Unusual Staudinger Reaction Enabled by Frustrated Lewis Pairs

Researchers at the University of Münster have developed an unusual variant of the Staudinger reaction which takes advantage of frustrated Lewis pair (FLP) frameworks to provide internal stabilisation.

The Staudinger reaction represents an important tool for the generation of iminophosphoranes, which can be subsequently utilized in the synthesis of a wide range of functional motifs, including amines, imines, and amides. Additionally, with the variation of the phosphorus compound, the Staudinger reaction can be employed in bio-ligation processes under mild conditions.

 the Staudinger reaction and the anomalous Staudinger reaction

Traditionally, the iminophosphorane product (3) is generated from the reaction of an organic azide (1) with a trivalent phosphorus compound. This is thought to proceed via transition state 2, from which elimination of dinitrogen yields the iminophosphorane (3). In the variation developed by the Erker group, such elimination of dinitrogen is avoided, generating products such as 4.

This unusual reactivity was cleverly obtained through the incorporation of the phosphorus moiety in an FLP; specifically, vicinal phosphane–borane FLPs (5). Upon reaction with mesityl azide, these FLPs led to the formation of 5-membered heterocycles (6). Following thermolysis or photolysis, phosphinimines (7) were obtained which benefit from internal stabilisation from borane. The by-product of this formation is indazole 8. While the mechanism of this unusual variation has yet to be confirmed, the authors propose a pathway proceeding via the ion pair 9.

The reaction scheme for the formation of 9 from 5

This work contributes to the broadening utility of the Staudinger reaction, and illustrates the potential of FLP chemistry in the development of new reactivity.

Read the ‘HOT’ Chem Comm article today (Free to access until the 7th of December):

Anomalous Staudinger reaction at intramolecular frustrated P–B Lewis pair frameworks

Annika Stute , Lukas Heletta , Roland Fröhlich, Constantin G. Daniliuc, Gerald Kehr and Gerhard Erker
Chem. Commun., 2012, 48, 11739-11741
DOI: 10.1039/C2CC36782C

Published on behalf of Ruth Gilligan, Chemical Communications web science writer.

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Origami, without the papercut, visualised

Researchers in China have been able to visualize the intracellular location of DNA origami with a label-free fluorescent probe.

But let’s unfold a few things first and figure out what that means. DNA origami is the folding of a strand of DNA to make arbitrary 2 or 3 dimensional shapes; this serves as a ‘scaffold’ for shorter DNA strands that help hold the structure in its folded shape. These structures may be used for drug delivery, biosensors and more. I once made an origami frog; I wonder if there are any similarities…

Direct visualisation of the distribution and stability of DNA origami in live, cellular systems has not been achieved. Fluorescent labels can be attached to DNA strands but these have their drawbacks, such as weak emission intensity, photobleaching and expensive. Ding and co-workers looked at alternatives to visualize DNA origami in live cells.

The group were inspired by research on a series of carbazole-based cyanine fluorescence probes, which have a weak emission when they are monomolecularly dissolved but switch to a strong luminescent state upon binding to DNA or protein molecules.  The significant enhancement is attributed to restricted intramolecular rotational (RIR) motions by anchoring the DNA molecules, which causes the large reduction in the non-radiative decay of fluorescence molecules.

DNA-origami visualised in cells

Follow the instructions (a) and you too won’t make DNA-origami visualised in cells (b)

Ding and co-workers then took some tubular DNA origami, the cyanine fluorophore and found that the carbazole-based cyanine molecules could be used as a sensitive optical switch, turned on when DNA origami is detected and turned off when the nanostructure degrades. After incorporating the cyanine probe molecules, the DNA origami-probe complex was administered to live cells. Excitingly, the green-yellow frog… erm, I mean, fluorescence was visible inside the cells treated with the probe. The group went further to try and understand the internalization mechanism of the DNA origami and found the probe localized in lysosomes. Finally, degradation studies showed that most DNA origami were dissociated after 60 hours, also a bit like my origami frog.

Unlike my attempts at origami, Ding and co-workers have demonstrated an exciting step in scaffolded DNA origami and its future applications in nanomedicine.

Read this HOT Chem Comm article today (free to access until the  5th of December 2012):

Visualization of the intracellular location and stability of DNA origami with a label-free fluorescent probe
Xibo Shen, Qiao Jiang, Jinye Wang, Luru Dai, Guozhang Zou, Zhen-Gang Wang, Wei-Qiang Chen, Wei Jiang and Baoquan Ding
Chem. Commun., 2012, 48, 11301-11303

Published on behalf of Sarah Brown, Chemical Communications web science writer.

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Flexible post-synthetic approach to functionalised MOFs

Metal-organic frameworks (MOFs), formed from the assembly of metal ions and organic bridging ligands, often have large pores and high surface areas.  Such properties are attractive for various potential applications from gas storage to catalysis.  The diverse structures and properties of MOFs can be extended by incorportaing functional groups onto the organic linker after MOF formation through post-synthetic modification.

MIL-101(Cr), a MOF first reported by Ferey et al. in 2005, exhibits mesoporous cages with accessible metal sites as well as high chemical and hydrothermal stability.  Amine functionalisation of the framework’s benzene dicarboxylate ligands has been reported for analagous iron and aluminium frameworks, but has so far proven elusive for MIL-101(Cr).

Burrows et al. from the University of Bath have synthesised MIL-101(Cr)-NH2 using a hydrothermal method, and found that the resultant framework is stable up to 250 °C and, most interestingly, is stable to acids.  This unusual stability has allowed them to post-synthetically transform the amine group into an arenediazonium salt which they used in situ to generate a variety of functional groups.  MIL-101(Cr)-azo, in particular, showed excellent CO2 selectivity at low pressure.

This new approach to post-synthetic modification has provided a flexible route to functionalised MIL-101 materials, with further studies concentrating on selected frameworks already underway.

Read this HOT Chem Comm article today (free to access until the  7th of December 2012):

Synthesis and post-synthetic modification of MIL-101(Cr-NH2) via a tandem diazotisation process

Dongmei Jiang, Luke L. Keenan, Andrew D. Burrows and Karen J. Edler
Chem. Commun., 2012, Advance Article
DOI: 10.1039/c2cc36344e

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3D donor for organic photovoltaics with improved power efficiency

Scientists in China have developed a 3D donor for organic photovoltaics based on a spiro-fluorene molecule, which exhibited a power conversion efficiency of 4.82%.

Traditional 1D small molecule donors had only reached an efficiency of 1.69%. Small molecule donors have many advantages over conjugated polymer donors: high solubility allowing for high purification, good reproducibly and high charge-carrier mobility (because of its ordered, crystalline nature).

Donors with a 3D structure, including small molecular and dendritic macromolecular structures, have been expected to start a completely new self-assembly approach and more stable morphologies by increasing the dimension of the donor molecules.

Read the ChemComm ‘HOT’ article:

Spiro-fluorene based 3D donor towards efficient organic photovoltaics
Shuying Ma , Yingying Fu , Debin Ni , Jian Mao , Zhiyuan Xie and Guoli Tu
Chem. Commun., 2012, DOI: 10.1039/C2CC36301A

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Site-Selective Protein Modification via Bioorthogonal Wittig Reaction

Synthetic organic chemists have long regarded the Wittig reaction as one of the most significant methods for the creation of new C–C bonds. Now, researchers at Peking University have reported that this time-honoured reaction can be used for the modification of proteins in a bioorthogonal process.

Bioorthogonal processes represent a growing area of interest, encompassing reactions which can take place under physiological conditions. That is, the reaction must proceed at neutral pH in an aqueous solvent at ambient temperature and low concentrations, with high selectivity. Given these challenging parameters, the range of bioorthogonal processes remains limited.

The Ye group, based at the Key State Laboratory of Natural and Biomimetic Drugs, have contributed to the expansion of this fascinating area of chemistry by successfully applying the Wittig reaction to their one-pot site-selective protein modification. The first step involves the incorporation of an aldehyde at the N-terminus of a peptide chain (1). This could be achieved by the periodate oxidation of N-terminal serine or threonine residues, or by PLP (pyridoxal-5-phosphate) oxidation of N-terminal glycines. The resulting aldehyde (2), without the need for isolation or purification, could be reacted with an ylide (3) to form a wide variety of functionalised peptide products (4). Di-, penta- and hexa-peptide substrates could be functionalised in this manner, using water and t-butanol as co-solvents at room temperature.

The strength of this site-selective reaction was further demonstrated by modifying myoglobin. Crucially, this was achieved with no damage to the protein’s secondary or tertiary structure and, furthermore, Prof. Ye’s group established that myoglobin’s oxygen storage and release function was unaffected.

The functionality introduced offers the potential for further structural modification, or for use in medical imaging. With protein-based pharmaceuticals becoming widely used, greater insight into protein function and behaviour is of paramount importance. This methodology has the potential to be a valuable tool in that understanding. 

Read the ‘HOT’ Chem Comm article today:

Enabling Wittig reaction on site-specific protein modification

Ming-Jie Han, De-Cai Xiong and Xin-Shan Ye
Chem. Commun., 2012, 48, 11079-11081
DOI: 10.1039/C2CC35738K

Published on behalf of Ruth Gilligan, Chemical Communications web science writer.

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Ligand-enhanced lanthanide luminescence for anion sensing

Lanthanide luminescenceLuminescence from lanthanide-based compounds is currently exploited in electroluminescent devices ranging from glucose monitoring sensors to thin-film displays. Triarylboron groups are known to greatly enhance the fluorescence or phosphorescence of transition metal complexes, but such compounds are very sensitive to oxygen quenching and are unsuitable for use as sensors under ambient conditions.  The combination of these groups with lanthanides may offer enhanced luminescence in more ambient-friendly lanthanide-based materials.

The Wang group from Queen’s University, Canada have synthesised the first examples of triarylboron functionalized Tb(III) and Eu(III) compounds, and have shown that the BMes2 group is extremely effective at activating lanthanide emissions.  The new compounds have been tested as sensors, showing that such triarylboron functionalized lanthanides may be promising new CN and F anion sensors.

To find out more, download this HOT article now (free to access until the 5th of December 2012).

Selective activation of lanthanide luminescence with triarylboron-functionalized ligands and visual fluoride indicators

Maria Varlan, Barry A. Blight and Suning Wang

Chem. Commun., 2012, Advance Article
DOI: 10.1039/C2CC36172H

Posted on behalf of Katie Renouf, Chemical Communications web science writer.

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Prescription nanoreactors

Scientists in Switzerland have developed a nanoreactor that can synthesise and release the antibiotic cephalexin, which is used to treat bacterial infections.

Lowering the drug dose required to effectively treat a patient would save money and reduce side effects. To achieve this, one area of research is focusing on using a ‘prodrug’ approach in which less toxic substrates, or prodrugs, are given to a patient and are converted to the active drug form by an enzyme only at a specific site.

To maintain its catalytic activity, the enzyme needs to be protected from the surrounding environment, but also be accessible to the prodrug and able to release the final active drug.

Wolfgang Meier and colleagues at the University of Basel have designed a biocompatible nanoreactor that can effectively protect an enzyme. The nanoreactor comprises a copolymer, an outer membrane protein from bacteria cells (OmpF) and the catalyst penicillin acylase. When mixed together, the copolymer self assembles into vesicles forming, along with the membrane protein, a membrane around the catalyst that allows passage of molecules such as a drug and substrates.

Read the whole Chemistry World story or download the full ChemComm article:

Communication Polymer nanoreactors shown to produce and release antibiotics locally
Karolina Langowska , Cornelia G. Palivan and Wolfgang Meier
Chem. Commun., 2012, DOI: 10.1039/C2CC36345C

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