Molecular Endofullerenes: Nanoscale dipoles, rotors and oscillators

富勒烯是由碳原子组成的足球形状的笼子，英国科学家哈里·克罗托（Harry Kroto）因发现富勒烯而获得1996年诺贝尔奖。笼子里是一片空白。化学家和物理学家已经找到了许多巧妙的方法，将原子或分子困在微小的富勒烯笼子里。这些被包裹的化合物被称为内富勒烯。日本科学家小松（Komatsu）和村田（Murata）开创了一种非凡的方法，其中一人是当前提案的项目合作伙伴。他们进行了“分子手术”。首先，通过一系列的化学反应在富勒烯笼上开一个洞。然后通过高温高压将水（H2O）等小分子插入每个富勒烯笼中。最后，进一步的一系列化学反应被用来“缝合”这些洞。结果是一种非凡的化合物，称为水-内富勒烯，标记为H2O@C60。我们的团队已经成功地开发了一种新的合成路线，它需要更温和的条件，并提高了H2O@C60的产量。此外，我们将在富勒烯笼中封装其他小分子，包括氨（NH3）和甲烷（CH4）。普通的水分子有两种形式，称为正水和对水，它们的区别在于氢原子的磁性原子核指向的方式：对对水来说是相反的，对对水来说是相同的。在一般情况下，这两种形式相互转换迅速，不能被隔离。然而，通过将水分子困在富勒烯笼中，这两种形式被隔离开来，可以分别研究。我们最近观察到这两种形式的水具有不同的电学性质。在低温下，这两种形式在几十小时内相互转化。我们将研究两种形式的水的相互转化，并发展一种理论，为什么这种转化改变了电学性质。为了理解这些分子的行为，我们将使用几种技术。这些方法包括核磁共振（涉及强磁铁和无线电波）、中子散射（材料受到核反应堆中子的轰击）和红外光谱（涉及吸收低能光波）。通过结合这些不同技术的信息，我们将建立一个完整的被困分子量子力学行为的图像。由于邻位和对位水具有不同的电学性质，我们期望通过测量单分子的电响应来区分处于邻位和对位状态的单个H2O@C60分子。这将完成扫描表面上的负载富勒烯，使用非常锋利的尖端。通过这种方式，我们希望观察到单分子的邻位到对位跃迁-这是以前从未做过的事情。虽然这个项目大部分涉及基础科学，但这个项目可能会导致未来的技术甚至医学进步。例如，单个H2O@C60分子的正交和对位态可以允许在单个分子中存储一位信息，而不会以任何方式损坏它。这可能会导致一种新的非常密集的数据存储形式。由于一克H2O@C60含有大约10^19个分子，这一克原则上可以存储100万兆字节的信息，足以存储地球上每个人的DNA序列（尽管存储和检索这些信息将非常困难）。此外，包封分子的量子行为预计会大大增强磁共振信号，从而有可能大大增强MRI图像，具有相当大的医疗效益。

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.