Hot Articles – Page 31 – Chemical Science Blog

Archive for the ‘Hot Articles’ Category

Exploring magnetisation behaviour in frozen solutions

04 Oct 2010

If you thought squid only belonged in the depths of the ocean, think again. SQUID, or superconducting quantum interference device, has been used to study single-molecule magnets (SMMs) in solution, which could help us store more information on hard drives in future.

As the demand for increased information storage continues to rise, scientists have turned to the development of new nanostructured materials, incorporating SMMs. These tiny magnets can store information depending on the charge and spin properties of their electrons. But until now, there have been few studies to examine how much of these molecules’ magnetic properties come from their molecular properties and how much comes from the way they are packed together in the solid-state. Graphical abstract: Frozen-solution magnetisation dynamics of hexanuclear oxime-based MnIII Single-Molecule Magnets

Using SQUID, which is a very sensitive device for detecting weak magnetic fields, Euan Brechin and colleagues have studied the spin properties of frozen solutions of two different hexanuclear manganese (Mn₆) complexes. The two compounds display different spin-relaxation properties in the solid-state, but similar spin-dynamics once in solution. Brechin believes the study demonstrates that the SMM behaviour is intrinsically a molecular effect that can be modulated in the solid-state by crystal packing strain effects.

Read the full story in the Chemical Science Edge article, which, like all Chemical Science articles, is free to download until the end of 2011.

Be seen with the best – submit to Chemical Science today.

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Dissecting tunicamycin biosynthesis

01 Oct 2010

40 years after it was first isolated, UK scientists have identified the biosynthetic genes of an important antibiotic, offering insights into its poorly understood biosynthetic pathway.

Tunicamycin antibiotics have attracted much attention (over 8000 citations) due to their unusual structure and potent inhibition of bacterial cell wall biosynthesis. Although they have been chemically synthesised, the lack of a sequence for the tunicamycin gene cluster (or any part of it) has left scientists puzzled over its biosynthetic pathway.

Now Benjamin Davis, at the University of Oxford, and colleagues have identified the tunicamycin biosynthesis genes in Streptomyces chartreusis, a soil bacterium, using genome sequencing and mining. Using this genetic insight, they have proposed the detailed biosynthetic pathway to this family of antibiotics.

Graphical abstract: Dissecting tunicamycin biosynthesis by genome mining: cloning and heterologous expression of a minimal gene cluster

The studies unlock a comprehensive and unusual toolbox of biosynthetic machinery with which to create variants of this natural product, says Davis. He anticipates this will lead to future therapeutic antibiotics with improved antibacterial activity and reduced cytotoxicity.

Find out more in Davis’ Chemical Science Edge article, downloadable for free. Access our free content any time, any place by registering for an RSC Publishing personal account today.

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Hot article round-up – September

28 Sep 2010

Phew! Other than the weather it has been a hot month here at Chemical Science. Here’s the monthly round up of the articles our referees thought were particularly exciting:

A couple of catalysts for coupling
Stephen Buchwald and colleagues report their studies on the use of two catalyst systems that provide the widest scope for palladium-catalysed C–N cross-coupling reactions to date. What were these systems? Find out in their Edge Article.

Frustrated about global warming?
Nitrous oxide is three times more potent a greenhouse gas than carbon dioxide and can hang around for over 150 years in the stratosphere. So Douglas Stephan and colleagues have been investigating how frustrated Lewis pairs interact with nitrous oxide with a view to converting the gas into a less environmentally harmful species. Read what they discovered in their Edge Article.

Additions to the molecular toolbox
The interaction of a sulfamate ester-derived metallonitrene with an allene generates a versatile intermediate with 2-amidoallylcation-like reactivity. In their Edge Article, Armin Stoll and Simon Blakey outline reactivity patterns for this novel dipolar species, demonstrating both [3 + 2] reactions with benzaldehyde, and unusual [3 + 3] annulation reactions with a variety of nitrones.

Economical extensions
The hydroxymethylation reaction is one of the most powerful and atom-economical one-carbon extension methods. Now Xiaoming Feng and colleagues have managed to hydroxymethylate unprotected oxindoles, which they say could provide practical and broadly applicable access to chiral linchpins bearing oxindoles. Find out how they did it in their Edge Article.

Mechanistic insights
Intermediates in gold(I)-catalysed cyclizations of enynes are not simple carbocations, say Antonio Echavarren and colleagues. They’ve investigated the mechanism of the gold-catalysed cyclopropanation of alkenes with 1,6-enynes, showing that it is stereospecific and mechanistically related to the Simmons-Smith reaction. Read all their insights in their Edge Article.

Let us know what you think of these articles by commenting below. And if you have your own hot research, submit it to Chemical Science today.

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Water splitting over nanowires

23 Sep 2010

Nanowires that efficiently split water into oxygen and hydrogen could be an important step toward affordable chemical storage of solar power according to US scientists.

Water and sunlight are highly abundant and nature uses these to make energy through photosynthesis. Despite intensive studies on artificial photolysis, making it as efficient as nature is proving difficult. Titanium dioxide electrodes are one way to split water under ultraviolet light but the efficiency is low as they are only able to absorb ultraviolet light and the amout of light converted to energy is low.

Now, Hongkun Park and colleagues, at Harvard University, have synthesised TiO₂ nanowires with high surface areas, deposited them on an electrode and found that chemically crosslinking them increases their optical density – allowing more light to be absorbed. This allows the light to energy conversion to be doubled compared to previous TiO₂ electrodes, says Park.

Doping the nanowire network with gold or silver nanoparticles allows the water splitting reaction to take place under visible light, adds Park. This could lead to a ten fold improvement in the catalysts ability to split water, he says.

‘Our work shows that the performance of a material can be enhanced by putting it in a nanostructured network, and this design can potentially be extended to many other materials to achieve the goal of highly efficient solar water-splitting,’ says Park.

Steve Dunn, an expert in materials chemistry, at the Centre for Materials Research, Queen Mary University of London comments, ‘This work is very interesting with the most significant new finding being the morphological change from using more traditional titania powders to using nanorods. The advantages of using titania, over other more exotic systems, is that the chemistry is well known, it is highly photostable, it is cheap and is also non-toxic.’

The group now plan to study water photoelectrolysis with other metal oxides, such as iron oxide, that can absorb visible light and to study how their efficiency is enhanced in a similar nanowire networks.

Carl Saxton

Want to find out more? Read the Chemical Science Edge article.

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Perspective: A powerful method for C–X bond formation

17 Sep 2010

Metal catalysed asymmetric allylic alkylation (AAA) reactions have been an extensively studied and fruitful area of research in organic chemistry. The use of heteroatom-centered nucleophiles in this reaction is a powerful method for asymmetric C–X (X = heteroatom) bond formation.

In issue 4’s Perspective, Barry Trost and colleagues summarise developments and applications of metal catalysed AAA reactions employing heteroatom nucleophiles.

Graphical abstract: Catalytic asymmetric allylic alkylation employing heteroatom nucleophiles: a powerful method for C–X bond formation

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Mini review: Biocompatibility and drug delivery systems

16 Sep 2010

Drug delivery technology has emerged as an important focus of biotechnological research and commercial enterprise. While much attention is focused on the design and effectiveness of drug delivery devices, the nature of their interaction with surrounding tissues – their biocompatibility – is crucial.

Graphical abstract: Biocompatibility and drug delivery systems

In the latest Chemical Science Mini review Daniel Kohane and Robert Langer discuss biocompatibility, specifically as it relates to drug delivery systems, which differ from other biomaterial-based devices by possibly containing large quantities of drugs with their own effects on tissues. Let us know your thought on this topic by commenting below.

If you are interested in writing a review for Chemical Science, please contact the Editorial Office.

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Rapid cell extraction using droplets

01 Sep 2010

An aqueous two-phase microdroplet system that isolates and extracts cells could aid research into tissue engineering and regenerative medicine, say UK scientists.

Droplet-based microfluidic systems, using a fluorescence-based detection method have been used to locate, identify and discriminate cells within a specific droplets and more recently two-phase systems have been investigated for their ability to separate different biological materials. Target cells distribute between phases by their own thermal motion to reach equilibrium but so far this has proved a slow process.

Now, Andrew deMello and his team at Imperial College London have devised a novel method to separate cells using microfluidic droplets. The process could enable high throughput cell separation which would be ideal for clinical applications such as cell therapy and regeneration.

A PEG microdroplet completely encases the DEX droplet

In deMello’s device, human T lymphoma cells enter the microdroplet system within a dextran solution. At a T-junction in the device, the dextran meets a polyethylene glycol (Peg) inlet where a droplet of Peg completely encapsulates a dextran droplet. These droplets then follow a winding channel in the device that causes both phases to mix – forming an emulsion and allowing the cells to experience the environment of both phases. When the two phases separate back into a double droplet, the cells remain in the outer Peg phase.

Binding the cells with an antibody-N-isopropylacrylamide (Ab-NIPAM) is crucial to the separations explains deMello as this makes them favour the Peg phase. Without the Ab-NIPAM, 98 per cent of the cells remain located within the dextran. But once bound this reverses to 93 per cent moving to the outer Peg droplet.

Shashi Murthy, an expert in microfluidic devices design at Northeastern University in Boston, comments that conventional approaches ‘are quite effective, but there’s a lot of interest in trying to make them more simple and as microfluidic systems are being proposed as disposable and cheap alternatives to more expensive instrumentation, this is of significant interest.’

The team believe that the technique will be able to separate heterogeneous cell populations in a high-throughput manner. Also, the use of Ab-NIPAM conjugates can be applied to a wide range of other cell systems simply by changing the antibody.

Rapid cell extraction in aqueous two-phase microdroplet systems
Kalpana Vijayakumar, Shelly Gulati, Andrew J. deMello and Joshua B. Edel, Chem. Sci., 2010
DOI: 10.1039/c0sc00229a

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Imaging ions

18 Aug 2010

Understanding the way ions behave in the gas phase is important for solving atmospheric, astrochemical and biological problems. In Chemical Science’s latest Mini review, Arthur Suits, at Wayne State University, Detroit, US, and colleagues illustrate how high-resolution ion and electron imaging techniques can be used to study photofragmentation and photoionisation dynamics in ions. Examples discussed include the use of cation photodissociation to explore the upper atmosphere of Titan, Saturn’s largest moon.

Interested? Find out more…

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Biogenetically inspired approach to alkaloid family

17 Aug 2010

US chemists have synthesised an entire family of marine alkaloids that show potent anticancer activity and potential for treating Alzheimer’s disease.

Mohammad Movassaghi and colleagues at Massachusetts Institute of Technology, Cambridge, were intrigued by the molecular architecture of agelastatin alkaloids, in particular the cyclopentane C-ring, which others had proposed is formed at an early stage in the alkaloid’s biosynthesis. Conversely, Movassaghi envisaged a biosynthetic sequence where the C-ring forms at an advanced stage of the synthesis and so he designed a total synthesis plan inspired by his biogenetic hypothesis.

This unique approach gave Movassaghi access to all known members of this alkaloid family. Although 10 different research groups had made agelastatin A before, Movassaghi’s route was the shortest, most efficient and largest scale synthesis to date, generating over 1.4 g of the highly potent antitumour agent.

To find out more about the new transformations developed, including an imidazolone-forming annulation reaction and a carbohydroxylative trapping of imidazolones, read the Chemical Science Edge Article.

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Visualising DNA sequences

16 Aug 2010

A new, fast way to analyse DNA has been developed by European scientists that could be used to sequence the genomes of viruses and in the future help tackle genetic disorders such as schizophrenia and congenital heart defects.

Current DNA sequencing methods are able to sequence short regions of the genome (30² to 1500² bases in length). Regions that are either duplicated or deleted relative to a reference genome are an important cause of structural variation in the human genome with links to a variety of genetic disorders. Using current sequencing methods, studying these repeats is time consuming and labour intensive.

Now, Robert Neely and colleagues, at Catholic University Leuven, Belgium, have used a DNA methyltransferase enzyme to label the 5′-GCGC-3′ DNA sequences with a fluorescent marker. Immobilising and stretching the DNA on a surface then produces a unique and reproducible pattern when combined with the fluorescent markers. The result is a ‘fluorocode’ – a simple description of the DNA sequence, which can be read and analyzed like a barcode.

Sequences of DNA are tagged with a fluorescent marker

DNA barcodes using fluorescent tagging can be read quickly as labelled samples pass a detector, but Neely’s fluorocode gives significantly enhanced resolution and uses a much smaller number of DNA molecules. ‘The method from unlabelled DNA to fluorocode can be achieved in less than 8 hours for a DNA molecule that is around 50000 bases in length,’ says Neely. Current single molecule mapping methods have a timeframe of around one week for analysing individual genomes.

Kalim Mir, an expert in DNA sequencing and genomics at the Wellcome Trust Centre for Human Genetics, University of Oxford, comments, ‘the advantage the system has over conventional optical mapping is that it can provide ultra-high density mapping of genomic DNA and could easily be extended to much longer fragments from larger genomes, from bacteria to humans. The most significant challenge the authors face is to scale the technique up to the human genome.’

The group now plan to scale the fluorocode up from viral genomes to bacterial and on to eukaryotic genomes with the immediate aim of producing multi-coloured fluorocodes with even more detail.

Carl Saxton

Find out more in the Chemical Science Edge article.

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