Archive for the ‘Subject Areas’ Category

Worm-like peptides form gels at physiological pH

Salt can induce gelation of functionalised dipeptides at high pH, say a team of scientists from the UK and France. The finding will significantly expand the utility of hydrogels, they claim. 

Hydrogels are formed when molecules assemble into nanofibres, which then entangle and form a gel matrix. They can be used for a variety of applications, including drug delivery and scaffolds for tissue engineering. Peptide-based gelators are of particular interest at present, in part because they are potentially biocompatible. 

Gelation is commonly triggered by pH, temperature or solvent composition. Dave Adams, at the University of Liverpool, and colleagues discovered that functionalised dipeptides that adopt a worm-like micelle structure at high pH form gels when salts are added to them. High pH is normally outside the window for gelation so the finding could be very useful for the field. Importantly, now that these gels can be made at physiological pH, they should find increased use in bioapplications.

Graphical abstract: Salt-induced hydrogelation of functionalised-dipeptides at high pH

Read more in Adams’ ChemComm communication, free to access for a limited period.

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Easy xenon capture and release using MOFs

Graphical abstract: Facile xenon capture and release at room temperature using a metal–organic framework: a comparison with activated charcoalXenon is naturally present in very small amounts in the atmosphere but radioactive forms are released following nuclear detonations, reprocessing and explosions, such as the recent catastrophe at Fukushima Daiichi Nuclear Power Plant in Japan. Xenon is also used in a variety of other applications, from lighting to medical imaging, so capturing and separating it (from its sister noble gas krypton) is important for both commercial uses and atmospheric monitoring.

Praveen Thallapally, at Pacific Northwest National Laboratory, Richland, US, and colleagues made two well-known metal–organic frameworks (MOFs) known as MOF-5 and NiDOBDC and compared their ability to capture and separate xenon with activated carbon. They found that NiDOBDC adsorbs significantly more xenon than MOF-5, and is more selective for xenon over krypton than activated carbon.

To find out more, download Dr Thallapally’s ChemComm communication.

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81 days until 100 issues…

….and did you know?….

There are 81 articles in ChemComm‘s supramolecular chemistry web themed issue. The issue, guest edited by Philip Gale, Jonathan Sessler and Jonathan Steed, was published to celebrate the International Year of Chemistry 2011.  

Jonathan Sessler and Jonathan Steed are ChemComm Associate Editors, handling supramolecular chemistry communications from North America and the rest of world respectively. Submit your next urgent communication to their editorial offices.

Also of interest
100 days to 100 issues
96 days until 100 issues…
93 days until 100 issues…

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Improved DNA chips to detect pathogens

A new probe selection method leads to better DNA chips with fewer false positives and paves the way to improved technology development.

DNA chips are now ubiquitous tools in both genomics and diagnostics, for example pathogen detection. But selecting the correct DNA molecules for immobilising onto the chips’ surface is necessary to improve the chips’ accuracy.

The improved method involves loading the DNA probes onto the surface according to length, melting temperature and specificity. The approach was used to correctly identify 19 different types of human papilloma virus and was used to analyse 1000 clinical samples, giving identical results to sequencing data obtained from the same samples.

Reference:
A generalized probe selection method for DNA chips
S B Nimse, K-S Song, J Kim, V-T Ta, V-T Nguyen and T Kim, Chem. Commun., 2011
DOI:
10.1039/c1cc15137a

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Synthetic DNA synthesises RNA by transcription: ‘click’ here for more

What’s better than a short synthetic DNA sequence? That’s right: a long synthetic DNA sequence, able to take part in biological processes.

DNA and RNA are routinely synthesised using solid phase synthesis, connecting the bases through phosphodiester linkages.  This method, however, imposes limitations on the length of the strand produced. Current methods employ enzymes to achieve larger oligonucleotides, which have disadvantages such as poor quality and stability and can be laborious.

Tom Brown and Afaf El-Sagheer at the University of Southampton, UK, have now demonstrated that these limitations can be overcome by the flick of a ‘click’ – they chemically ligated oligonucleotides functionalised with chemoselective azide and alkyne moieties using click chemistry to produce long nucleic acid sequences. After personally struggling to conjugate biological moieties using click chemistry for my Ph.D., I can assure you this is no mean feat!

Previous work by the group has shown that oligonucleotides with triazole-modified backbones do not inhibit replication and so they were interested to see if the same would be true for transcription – a fundamentally different process. The primary concern was how modification of the phosphodiester backbone would affect the template strand’s ability to participate in the transcription process.

By synthesising two triazole-modified DNA template strands, one with the triazole unit in the coding sequence and the other with the modification in the T7 RNA promoter region, El-Sagheer and Brown were able to evaluate the impact of changing the template strand backbone in comparison with the equivalent non-modified templates. Both modified strands successfully took part in transcription to produce RNA in good yield.  The result: fully-synthetic, biologically-active DNA templates successfully synthesising RNA. This is not only an elegant demonstration of the abilities of click chemistry but could also be fundamental in changing approaches to the synthesis of biological constructs.

To read more about Brown’s research, download the ChemComm article today.

Posted on behalf of Sarah Brown, web science writer for ChemComm.

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Fullerene ‘hide and seek’ in lipid membranes

Japanese researchers have experimentally proven that fullerenes reside in the hydrophobic core of liposome membranes.

Liposomes are vesicular structures made up of a phospholipid bilayer. Due to their ability to encapsulate a range of different substances and target numerous cell types, they have great potential as drug delivery agents. Recently, liposomes have been modified with fullerene for a number of uses such as DNA photocleavage, anti-bacterial agents, and photodynamic therapy. Although theoretical simulations have been performed to characterise these fullerene–liposomes, up until now there has been no experimental proof of where the fullerene units end up in the lipid membranes.

Using differential scanning calorimetry and 13C NMR spectroscopy, Atsushi Ikeda and colleagues have determined that the fullerenes self-aggregate in the core of the bilayer, separating themselves from the alkyl chains. The fullerene units are expected to be located in a similar fashion in a cell membrane, say the team. This new insight means efforts can commence on bringing the fullerenes up to the surface of the lipid which may help improve the photoactivity of the fullerenes whilst reducing any deleterious effects they may have.

Download Ikeda’s ChemComm article to find out more…

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Ionic Liquids web theme issue – welcoming submissions

ChemComm is delighted to announce a high-profile web themed issue on Ionic Liquids.

Guest editors: Robin D. Rogers (University of Alabama), Doug MacFarlane (Monash University) and Suojiang Zhang (Institute of Process Engineering)

Picture courtesy of Photodisc

This issue will consist of a series of Communications and Feature Articles from prominent scientists working on all aspects of ionic liquid chemistry. The scope will range from new fundamental knowledge about ionic liquids to novel applications of ionic liquids which take advantage of their unique attributes.  Follow on studies or those of routine interest will not be considered. 

The level of quality of this issue will be extremely high, and all manuscripts will undergo strict peer review. You are therefore encouraged to report work that you consider to be very important and conceptually significant in accord with the ChemComm mandate. Please note that inclusion in the issue is subject to the discretion of the guest editors.

Publication of the peer-reviewed articles will occur without delay to ensure the timely dissemination of the work. The articles will then be assembled on the ChemComm website as a web-based thematic issue.

Submit your work before 29th February 2012. Please add “ionic liquids” in the comments to the editor section.

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Modelling reveals interconnect between SERS enhancement mechanisms

Surface enhanced Raman scattering (SERS) uses noble metal substrates to enhance the inherently weak Raman signal from analytes. In some cases, the enhancement stems from two different mechanisms: a physical enhancement that comes from excitation of the metal surface plasmons and a chemical enhancement arising from charge transfer between the metal surface and an adsorbed molecule.

Up until now, theoretical SERS models have tended to treat these mechanisms separately. However, Duan and colleagues point out that this simplification is not always valid since plasmonic properties can be significantly affected by adsorbed molecules. Using state-of-the-art density functional models, they have revealed the connection between the two mechanisms, allowing more accurate modelling of SERS spectra.

To learn more about how Duan’s team have implemented this model, download the ChemComm article.

Also of interest:

Visit the ChemComm Surface Enhanced Raman Spectroscopy web theme issue for more articles.

Posted on behalf of Iain A. Larmour, ChemComm web writer.

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Extension of Hirsch’s rule opens the door on spherical aromaticity

Miquel Solà and Jordi Poater working University of Girona in Spain have put forward an extension of Hirsch’s rule to open-shell spherical species. 

The famous Hückel rule allows one to estimate whether or not a planar ring molecule would have aromatic properties. When the molecule has 4N + 2 π-electrons then it follows Hückel’s rule. In 2000 Andreas Hirsch found a rule to predict the aromaticity of fullerenes, known as the 2(N +1)2 rule and now Solà has extended this rule to spherical systems with an open-shell.

They found that spherical compounds with a half filled last energy level, e.g. those with 2N2 + 2N + 1 electrons, are aromatic. This was backed up with computational evidence and showed that for example C6019+ and C601- both have strong aromatic character.

Solà speculates that this finding could be an important tool for those working in the in stable high spin molecules such as molecular magnets. 

Interested in finding out more? Then download the full ChemComm article for free today.

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New electrochemiluminescence possibilities

Electrogenerated chemiluminiscence (ECL) is a promising detection technique but its application to certain targets, such as small ions, is compromised due to the necessity to use high concentrations of reagents which can contaminate the sample.

Eric Bakker and co-workers have devised a system which separates the sample compartment, where the analyte is introduced alongside the ruthenium-based ECL reagent, from the compartment which contains the co-reactant necessary for the chemiluminescence to be generated. The technique relies on a liquid membrane to selectively transport the ECL ruthenium compound from the sample towards the detector.

This electro-separation technique opens the door to even more targets capable of being detected using ECL.

To learn more about how Bakker and his team have implemented this strategy, download the ChemComm article.

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