Move like caged hydrogen: Buckyball traps

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  • Published: Sep 1, 2012
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Move like caged hydrogen: Buckyball traps

Fulfilling fullerenes

Move like caged hydrogen: Buckyball traps Credit: PNAS/Horsewill et al 

Cryogenic NMR spectroscopy and other techniques have been used to investigate how small molecules, including water, are trapped by the all-carbon cages known as fullerenes. The work might open up the possibility of using such caged systems as alternative contrast agents for magnetic resonance imaging or as innovative components of a molecular transistor.

An international team that includes scientists from The University of Nottingham, England, has investigated the space within [60]fullerene the Nobel-winning carbon allotrope informally known as the buckyball. The cavity is nanoscopic but big enough to enclose small molecules such as dihydrogen or water. The team has modelled the quantum mechanical behaviour of such entities trapped within a buckyball at a detailed level to see whether they can shed life on the notion of wave-like behaviour fundamental to all matter.

Quantum rattle

The team - which includes scientists from Estonia France, Japan, the US and the UK universities of Nottingham and Southampton - has revealed a movement referred to as a "quantum rattle" in within the buckyball cage. Nottingham's Tony Horsewill explains that, "For me a lot of the motivation for carrying out this investigation came from the sheer pleasure of studying such a unique and beautiful molecule and teasing out the fascinating insights it gave into the fundamentals of quantum molecular dynamics. Intellectually, it's been hugely enjoyable."

The discovery of [60]fullerene, buckminsterfullerene, and the fullerenes in general in the mid-1980s earned Harry Kroto, Robert Curl and the late Richard Smalley the Nobel Prize in Chemistry in 1996. Since the fullerenes were first posited, chemists have wondered about what might occur if smaller molecules were trapped inside. The Japanese contingent, based at Kyoto University have now used a technique akin to molecular surgery to open up the buckyball at high temperature and pressure and to push another molecule inside and to then seal the incision by cooling and so permanently transplant small molecules such as dihydrogen and water into the [60]fullerene.

The Nottingham team then used inelastic neutron scattering (INS) to investigate "rattling" within the buckyball; studies were also carried out with far-infrared spectroscopy. The study reveals the wavelike nature of the smaller molecules and their orbital and rotational motion as they move within the buckyball. Malcolm Levitt of the University of Southampton used NMR spectroscopy to study the properties of the caged molecules in detail. "Under these conditions, the confined molecules reveal a wave-like nature and behave according to the laws of quantum mechanics. Apart from their intrinsic interest, we expect that the special properties of these materials will lead to a variety of applications, such as new ways to brighten the images of MRI scans, and new types of computer memory," he says.

Water in a spin

Writing in the journal Proceedings of the National Academy of Sciences (USA), the team also highlights how their study has pinned down how two subtly different forms of water - the spin-isomers of ortho-water and para-water - might exist as distinct quantum species.

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Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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