Chemical Science Blog

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.

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.

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.

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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.

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.

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