Molecular Endofullerenes: Nanoscale dipoles, rotors and oscillators

Fullerenes are football-shaped cages of carbon atoms, for the discovery of which the British scientist Harry Kroto won the Nobel prize in 1996. Inside the cage is an empty space. Chemists and physicists have found many ingenious ways of trapping atoms or molecules inside the tiny fullerene cages. These encapsulated compounds are called endofullerenes.

A remarkable method was pioneered by the Japanese scientists Komatsu and Murata, one of whom is a project partner on the current proposal. They performed "molecular surgery". First, a series of chemical reactions was used to open a hole in the fullerene cages. A small molecule such as water (H2O) was then inserted into each fullerene cage by using high temperature and pressure. Finally, a further series of chemical reactions was used to "sew" the holes back up again. The result was the remarkable chemical compound called water-endofullerene, denoted H2O@C60.

Our team has succeeded in developing a new synthetic route which requires milder conditions and has improved yield for the production of H2O@C60. In addition we will encapsulate other small molecules in the fullerene cage, including ammonia (NH3) and methane (CH4).

Molecules of ordinary water have two forms, which are called ortho and para-water, which are distinguished by the way the magnetic hydrogen nuclei point: in opposite sense for para-water, and in the same sense for ortho-water. In ordinary conditions, these two forms interconvert rapidly, and cannot be isolated. However, by trapping water molecules inside fullerene cages, the two forms are isolated and may be studied separately.

We recently observed that these two forms of water have different electrical properties. At low temperatures, the two forms interconvert over a period of tens of hours. We will study the interconversion of the two forms of water, and develop a theory of why this conversion changes the electrical properties.

In order to understand how these molecules behave, we will use several techniques. These methods include nuclear magnetic resonance (which involves a strong magnet and radiowaves), neutron scattering (in which the material is bombarded with neutrons from a nuclear reactor) and infrared spectroscopy (which involves the absorption of low-energy light waves). By combining the information from these different techniques, we will build up a complete picture of the quantum-mechanical behaviour of the trapped molecules.

Since ortho and para-water have different electrical properties, we expect to distinguish between single H2O@C60 molecules in the ortho and para states, by measuring the electrical response of single molecules. This will be done scanning over a surface loaded with the fullerenes, using a very sharp tip. In this way, we hope to observe the ortho to para transition of single molecules - something that has never been done before.

Although most of this project concerns basic science, this project could lead to technological and even medical advances in the future. For example, the ortho and para states of the individual H2O@C60 molecules could allow the storage of one bit of information inside a single molecule, without damaging it in any way. This might lead to a new form of very dense data storage. Since a single gram of H2O@C60 contains about 10^19 molecules, this single gram could in principle store 1 million terabytes of information, sufficient to store the DNA sequences of everyone on the planet (although it will be very difficult to store and retrieve this information). In addition, the quantum behaviour of the encapsulated molecules is expected to give rise to greatly enhanced magnetic resonance signals, leading to the possibility of greatly enhanced MRI images, with considerable medical benefits.

1. Academic impact

1.1 New knowledge and scientific advancement.
The research in this proposal is basic in nature since it is directed to very basic questions at the heart of quantum physics: how do nuclear angular momenta interact with molecular angular momenta? Can molecular angular momentum be converted into nuclear polarization, giving rise to enormously enhanced NMR signals in the solid state? Can nuclear spin isomers be detected electrically? Can nuclear spin isomers be detected and manipulated on a single-molecule level?

In addition the proposal is highly interdisciplinary involving also highly novel compounds in organic chemistry. Simple and familiar molecules such as water, ammonia, and methane are married to the simplest and most symmetrical cage (C60-fullerene) and in order to generate unusual and fundamentally interesting quantum properties.

1.2 Worldwide scientific advancement
The proposal is part of an ongoing global collaboration with project partners from Japan and Estonia.

1.3 Development of new methodologies, equipment, techniques, cross-disciplinary approaches.
The project fits perfectly into all of these categories. It uses new methodologies, equipment and techniques, in particular the low-temperature magnetic resonance equipment newly installed in Southampton and which is in many aspects world-unique. The project is highly cross-disciplinary, involving organic chemistry, quantum physics, surface science, neutron scattering, magnetic resonance, scanning microscopy and electromagnetic spectroscopies.

1.4 Health of academic disciplines
It is essential for the health of academic disciplines that they are not locked into "silos". This project will establish close contact between many different academic disciplines such as synthetic chemistry, quantum molecular physics, microscopy, and magnetic resonance, to great benefit of all.

1.5 Delivering and training researchers.
All researchers involved in this project will be exposed to multiple disciplines and will acquire an excellent oversight of spectroscopic and physical techniques applied to molecular quantum systems. These are skills of great general applicability to a very wide range of scientific problems. Unfortunately, under the new EPSRC rules, we are unable to apply for, and offer, studentships under this project which would offer excellent interdisciplinary training opportunities for young UK students during their PhD. We will endeavour to fund such PhD studentships through other sources.

2. Economic and Societal Impact
2.1 Cultural. Science is a cultural activity - especially basic science. Basic research of this nature is therefore culturally enriching.

2.2 Societal benefits. In the long term the research described here is directed towards the development of more readily available methods for enhanced NMR spectroscopy, which would have considerable benefits in the medical, chemical and engineering areas. NMR is an extraordinarily broad field of science so fundamental advances in NMR have the potential for broad societal impact, as evidenced by the adoption of MRI technology worldwide.

2.3 Effects such as the electrical response of spin-isomer conversion may also contribute to the development of new information storage modalities on the single molecule level, with potential industrial benefits.

2.4 Economic benefits. Magnet technology is a strength of UK engineering so enhancements in NMR and MRI are of long-term economic benefit to the UK. This has been recognized by the recent strong investment in "quantum technology".

2.5 National security and social welfare. Improvements to medical treatment improve social welfare. Improvements to information processing and storage may improve social welfare if handled wisely. Cross-continental scientific cooperation is beneficial for national security.