Chemical Science Blog

Scientists in Germany have shed new light on the addition of small molecules to the ubiquitous N-heterocyclic carbenes (NHCs), previously thought to be impossible for NHCs.

Ulrich Siemeling and colleagues have shown that stable NHCs can show strongly enhanced reactivities towards fundamentally important small molecules such as ammonia and carbon monoxide, which is unprecedented for diaminocarbene compounds. The scientists were able to add carbon monoxide to a number of carbene systems, including the simplest stable diaminocarbene, Alder’s C(NiPr₂)₂ ­ to which they added carbon monoxide. This provided a new entry to the important β-lactam ring systems commonly found in antibiotics.

Workhorses taking off: Ferrocene-based N-heterocyclic carbenes undergo reactions with fundamentally important small molecules

This newly discovered reactivity opens the door to an exciting area of synthetically useful carbene chemistry.

Read the Chemical Science Edge article for free online. Have you conquered the impossible? Tell the world by submitting to Chemical Science today.

Metal nanoparticles that can catalyse organic reactions in water can be made using polyelectrolyte nanoreactors, claim scientists. 

Thanks to their ionisable functional groups, polyelectrolytes can change their conformation in water. When there are few other ions in the solution, the chains stretch out because the charged groups on the chains repel each other.

But when Vy Dong, at the University of Toronto, Canada, and colleagues added an acidic palladium (II) chloride solution, the repulsive interactions were screened and the polyelectrolyte chains collapsed into globules around the chloride ions. Subsequent reduction of the palladium (II) ions in this collapsed-globule nanoreactor using sodium borohydride generated polyelectrolyte stabilised palladium nanoparticles that were bench stable for over a year.

The team used the nanoparticles as catalysts in aqueous Suzuki coupling reactions and achieved high yields at loadings as low as 0.01 mol % palladium. They now plan to transfer the counterion-induced collapse strategy to the synthesis of other polyelectrolyte–metal systems.

Read more about this work in Professor Dong’s Chemical Science Edge article.

US chemists have made a metal-organic framework (MOF) that changes from microporous to mesoporous when heated up. This makes it better at accommodating large guest molecules, potentially improving its ability to store and separate gases.

Hong-Cai Zhou, at Texas A&M University, and colleagues propose that the change in porosity is due to partial decarboxylation of the MOF’s ligands.

For more details, read their Chemical Science Edge article. 

You can find out more about MOFs in Metal Organic Frameworks, a Chem Soc Rev themed issue, or see Seth Cohen’s Chemical Science Mini review, Modifying MOFS: new chemistry, new materials.

And if you have some ‘hot’ science to report, submit your research to Chemical Science.

Optical antennas made of gold nanoparticles can enhance the sensitivity of photoluminescence and vibrational spectroscopy, according to research recently published in Chemical Science.

In traditional microscopy and spectroscopy, components such as lenses, mirrors and diffractive elements are used to control and focus the optical radiation. This relies on the wave nature of the radiation and means the smallest volume to which the radiation can be localised, and so the technique’s sensitivity, is limited by diffraction.

Now Lukas Novotny and colleagues at the University of Rochester, USA, have taken inspiration from radio wave manipulation and designed an optical antenna that can boost the interaction between light and the particle being studied. The fluorescence of a single molecule can be enhanced by more than a factor of 10 using this technique. The optical antenna, which consists of a single colloidal gold nanoparticle on the end of a pointed dielectric fibre, replaces a conventional focusing lens or objective, so the incoming light can be focused to dimensions smaller than the diffraction limit.

As well as improving chemical and biological sensing, the technique holds promise for resolving open questions in surface enhanced Raman scattering and fluorescence, says Novotny.

Read the Edge article to find out more. And to put the focus on your own exciting research, submit today to Chemical Science.

UK chemists have moved a step closer to conquering a significant synthetic challenge by developing a C–H bond functionalisation reaction that can generate a diversity of molecular frameworks at room temperature.

A broad range of C–H transformations can be catalysed by a variety of transition metals at high temperatures. But Matthew Gaunt’s group at the University of Cambridge aims to develop a synthetic toolbox comprising mild metal-catalysed C–H functionalisation reactions to make it easier to make complex molecules.

They investigated the reactions of β-arylethylamine, a motif commonly found in medicines and natural products. Attempts to catalytically transform the phenylalanine ethyl ester had previously failed but when the group introduced an aryl group onto the amine system, they were able to carbonylate, arylate and aminate the C–H bond. The reaction works on a variety of substrates and is tolerant of stereogenic centres and complex functionality.

Find out more in Dr Gaunt’s Edge article, now online and free to access.

A new family of cobalt-gadolinium cage compounds are highly efficient for low temperature cooling, say European scientists.

Liquid helium is currently used to achieve very low temperatures in a large amount of technology, such as super-conducting magnets that are needed for magnetic resonance imaging scanners. But the world supply of helium is falling, making it more expensive. An alternative method for low temperature cooling is to use demagnetisation of magnetic materials.

Now Richard Winpenny at the University of Manchester and colleagues have synthesised a new family of cobalt-gadolinium cage compounds, creating heterometallic molecular squares that show potential for the creation of magnetic coolants. Winpenny explains that magnetic coolants work because demagnetisation increases the entropy of the material, and this increase in entropy comes from taking heat out of the surroundings.

Juergen Schnack at the University of Bielefeld, Germany, an expert in the area of magnetic molecules, comments: ‘most interesting for me is the ability to synthesise such structures in such a great variety as demonstrated by the different grids of this work. This justifies our hopes that compounds with desired properties, for instance a large magnetocaloric effect – where compounds show a large change in temperature with a change in the magnetic field – are achievable.’

The highly anisotropic cobalt(II) ions in these compounds would be expected to have an adverse effect on the magnetocaloric effect, according to the scientists, but anti-ferromagnetic exchange between the octahedral cobalt ions appears to cancel out their contribution.

‘We have a fairly precise understanding of what is needed for a good magnetic coolant,’ says Winpenny. ‘What is surprising is that cobalt(II) complexes shouldn’t meet those requirements, and yet the complexes we’ve studied look interesting. Therefore I think we are going to find a few more surprises along the way and maybe we will need better theory as we proceed.’

Rachel Cooper

To find out more about this ‘cool’ research, download the Chemical Science Edge article for FREE.

US chemists have made a new type of molecular bowl that binds strongly to C₇₀ fullerenes.

hexabenzocoronene

Colin Nuckolls, at Columbia University, New York, and colleagues joined together the proximal carbons of contorted hexabenzocoronenes using solution-based, palladium-catalysed chemistry. The resulting shallow bowl-shaped molecules bind C₇₀ very strongly and are also better than their hexabenzocoronene precursors at stabilising negative charge.

The unique optical, electronic and structural properties of these new bowl-shaped polycyclic aromatic hydrocarbons provide opportunities to create new organic materials, novel host-guest complexes and improved photovoltaics, says Nuckolls.

Bowled over by this research? Read the Edge article and tell us what you think below.

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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. 

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.

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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.

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.