Chromatography and purification of endohedral metallofullerenes

Abstract

At the conception of this research, a separation methodology for obtaining purified mctallofullerene [A_m@C_2n, m = # of metal atoms, A, and C_2n = # of carbons in the surrounding cage] samples was not yet developed. Isolation of these metal-encapsulated fullerenes was strongly desired for characterization of their physical and chemical properties. Predicted applications for these novel species include their use as possible superconductors, catalysts, and non-linear optical devices. However, initial purification efforts have been hindered by several difficulties. These factors include a low abundance (< 1%) in the raw extract, uncertain stability in aerobic environments, co-elution of A_m@C_2n with empty-cage fullerenes, and the need for selective chromatographic detection.

In this research, these difficulties have been overcome with the development of a continuous-flow, on-line HPLC-EPR apparatus. Advantages include a selective, non-invasive detector with chromatographic separations being performed in a controlled anaerobic environment. This on-line approach permits the selective detection of only those metallofullerenes with an odd-number of encapsulated atoms. The ability to continually monitor separations of these paramagnetic species ultimately permits the optimization of chromatographic parameters. The methodology developed from this on-line HPLC-EPR approach has ultimately resulted in purified empty-cage (C₆₀, C₇₀...C₉₆) and metallofullerene samples (Sc₂@C₇₄, Sc₂@C₇₆, Sc₂@C₇₈, Sc₂@C₈₀, Sc₂@C₈₂, Sc₂@C₈₄ - two isomers, Sc₂@C₈₆, Sc₂@C₈₈, Sc₂@C₉₀, Sc₃@C₈₂, Sc₄@C₈₂, La₂@C₇₂, Er@C₈₂, Er₂@C₈₂ - two isomers, and Er₂@C₉₂).