Constructing Endohedral Fullerenes Using Open-Cage Fullerenes and Heterofullerenes

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Professors Alan L. Balch and Marilyn M. Olmstead of the University of California-Davis are supported by the Macromolecular, Supramolecular and Nanochemistry Program of the Division of Chemistry to develop new methods for the preparation of endohedral fullerenes (nano-sized soccer ball-like carbon cages encapsulating metal ions). The synthetic methods are designed to carefully, and selectively, control the insertion of metal atoms into fullerenes, where the atom will be stabilized. Endohedral fullerenes have only been prepared in minute quantities in a gas phase process. They have already shown promise in medical imaging technology as magnetic resonance imaging (MRI) contrast agents (using paramagnetic gadolinium) and X-ray contrast agents (using the strong X-ray absorber lutetium). The project is focused on the development of new methods for the preparation of endohedral fullerenes in large quantities to facilitate their practical use for such diagnostic medical imaging and other possible technological applications. Students at college and high school levels are involved in the project and trained in state of the art synthetic and structure characterization techniques. Several outreach activities, including a chemistry peer mentoring program, and seminar courses, such as " Symmetry in Art and Science" and "Chemicals and their Effect on California History" are being developed. In this project, known chemical procedures are used to fashion holes in the fabric of the fullerene cages of C60 and C70 to form open-cage fullerenes. These open cage structures frequently have Lewis base sites suitable for metal ion bonding near the orifice. Subsequently, metal ions are attached to these open cage fullerenes and eventually inserted into their interior. Reduction of the cage is used to attract the metal ion through the opening and into the interior. These reactions are monitored by spectroscopic means and the products, including metal ion complexes of the open cage fullerenes with metal ions on the outside and on the inside, are isolated and structurally characterized, particularly by single crystal X-ray diffraction. Once the metal center enters the cage, chemical reactions are used to begin to close the hole in the fullerene network. Physical properties, such as ability to function as MRI contrast agents and X-ray contrast agents, of the new endohedral species will be examined. The project is also designed to examine two new synthetic routes to make macroscopic amounts of metallo-heterofullerenes, carbon cages with some of the carbon atoms replaced with metal atoms. Such metallo-heterofullerenes have never previously been obtained as solids that can be characterized through spectroscopic and X-ray crystallographic means.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.