The synthesis and stability of endohedral actinium-225(²²⁵Ac@C₆₀)

Due to their chemical and thermodynamic stability, fullerenes could play an important role in encapsulation of radionuclides for applications in radio-immunotherapy. In this thesis, we report the first synthesis of actinium endohedral fullerenes. The alpha-emitter Actinium-225 (²²⁵Ac, t_1/2 =10 d) was trapped in fullerenes by the direct current (D.C) arc discharge-catcher method in a He atmosphere. Endohedral ²²⁵Ac and the bulk of fullerene C₆₀ was dissolved from the catcher electrode (a Pt disk covered with a thin layer of C₆₀) in toluene under N₂, and converted to the malonic ester derivative. Repeated washing of the organic phase with dilute HNO₃ demonstrated that a small fraction of ²²⁵Ac (1.0 %) could not be removed from the organic phase and presumably was inside the fullerenes. The Fr- 221 (the α-decay daughter of ²²⁵Ac), however, was observed to be leaking from the cage probably as a result of nuclear recoil. The cage stability was enhanced significantly by coupling the fullerene surface with organic adducts. After repetitive extractions, a 45% fraction of original activity was still retained in the cage. The radioactivity distribution coefficients {Kd = (²²⁵Ac radioactivity in aqueous- phase)/ (²²⁵Ac radioactivity in organic phase)} were investigated. We propose that, if Kd and back to back extractions, collectively are to be study in timely manner, the rate in which ²²⁵Ac@C₆₀ dissociate into individual components would be obtained.