Synthesis, Characterization, and Neutron Activation of Holmium Metallofullerenes

• Published in: Journal of the American Chemical Society 1996-08, Vol.118 (34), p.8043-8047
• Main Authors: Cagle, Dawson W, Thrash, Thomas P, Alford, Michael, Chibante, L. P. Felipe, Ehrhardt, Gary J, Wilson, Lon J
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja960841z

Isolation of the first macroscopic quantities of endohedral holmium metallofullerenes (principally Ho@C82, Ho2@C82, and Ho3@C82 by LD-TOF mass spectrometry) has been accomplished by carbon-arc and preparative HPLC methodologies. The detailed procedure for production and isolation of the metallofullerenes includes a new technique whereby holmium-impregnated electrodes are prepared simply by soaking porous graphite rods in an ethanolic solution of Ho(NO3)3·xH2O. Monoisotopic 165Ho offers a unique combination of advantages for neutron-activation studies of metallofullerenes, and purified samples containing 165Ho@C82, 165Ho2@C82, and 165Ho3@C82 have been activated by high-flux neutron irradiation (Φ = 4 × 1013 n cm-2 s-1) to generate 166Ho metallofullerenes, which undergo β- decay to produce stable 166Er. Chemical workup of the irradiated samples, followed by re-irradiation, has been used to demonstrate that observed decomposition of holmium metallofullerenes is due mainly to “fast” neutron damage rather than to holmium atom nuclear recoil (E max = 200 eV). This implies that metallofullerene damage can be minimized by using neutron fluxes with the highest possible thermal component. A detailed analysis of the neutron-activation results is presented as a prelude to the possible use of neutron-activated metallofullerenes in nuclear medicine.