Magnetic Resonance of Dihydrogen Endofullerenes

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. One of the most remarkable methods was pioneered by the Japanese scientists Komatsu and Murata, who are project partners in 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 dihydrogen (H2) 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 dihydrogen endofullerene. A new notation even had to be invented to write the formula down. The result of encapsulating H2 in a C60 fullerene molecule is denoted H2@C60. In this project we will perform magnetic resonance experiments on derivatives of H2@C60. Magnetic resonance is a method in which a sample is placed in a strong magnetic field and illuminated with radiowaves. The nuclei of the hydrogen atoms produce a radiowave response that may be analyzed to obtain detailed information about the molecules in the sample, where they are located, and how they are moving. The most familiar form of magnetic resonance is magnetic resonance imaging (MRI) which is used in hospitals to obtain anatomical pictures and diagnose medical conditions.In this project we will perform magnetic resonance on H2@C60 compounds and their highly-symmetric substituted derivatives, which have a number of useful properties such as water solubility. We will study the motion of the H2 molecules inside the nanoscale cages.In one of the subprojects we will synthesize and crystallize H2@C60 molecules in such a way that they are held in a highly symmetrical crystal. According to certain theories, the hydrogen molecules will behave in an unusual way under these conditions. The molecules themselves will emit magnetic resonance signals, not just the nuclei. We will try to observe this phenomenon for the first time on solid materials.The second subproject concerns a phenomenon called ortho/para conversion. Werner Heisenberg received the Nobel Prize in 1932 for predicting that ordinary hydrogen has two distinct forms, called ortho and parahydrogen. This was proved to be correct. The H2@C60 forms therefore come in two different types, some containing ortho hydrogen, and some containing parahydrogen. We will study in situ how these two forms interconvert with each other, and in particular, whether the ortho/para conversion may be induced by light.If the effects are observed as expected, some important consequences may follow. In particular, it should become possible to enhance the strength of certain NMR signals by a large factor (up to of almost 1 million) by irradiating the sample with a suitable laser beam. If this works it will have implications for a wide range of sciences, possibly including medical MRI. One of the aims of this project is to perform the preliminary work which will determine the feasibility of this novel NMR enhancement scheme.

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? In addition the proposal is highly interdisciplinary involving also highly novel compounds in organic chemistry. The simplest molecule (dihydrogen) is married to the simplest and most symmetrical cage (fullerene) and then functionalized with external groups in order to generate desired physical quantum properties. 1.2 Worldwide scientific advancement The proposal is part of an ongoing global collaboration with project partners from USA, 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 and quantum physics. 1.4 Delivering and training researchers. Two researchers will be directly involved in this project. One graduate student will be trained in endofullerene chemistry. He/she will also be trained in modern solid-state NMR techniques and participate in the cryogenic NMR experiments in the last half of the project. The named postgraduate researcher will advance his training in quantum dynamical techniques and solid-state NMR. 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 This research will also contribute to the development of new efficient materials for, for example, photoelectric energy generation and hydrogen storage. 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. Follow-up projects to this project have the potential for commercial exploitation, for example NMR hyperpolarization by solid-state optical pumping. 2.4 National security and social welfare. Improvements to medical treatment improve social welfare. Improvements to energy generation and storage improve the long-term prospects of our environment and reduce our dependence on external energy sources. The pursuit of cross-continental scientific cooperation is beneficial for national security (as opposed to misguided foreign invasions).