Exohedral Functionalization and Applications of the Trimetallic Nitride Endohedral Metallofullerenes
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This dissertation addresses the exohedral cage functionalization and potential applications of the Sc3N@C80 and Sc3N@C78 trimetallic nitride endohedral metallofullerenes. In addition, this dissertation discusses miscellaneous research that is relevant to the aformentioned metallofullerenes and their applications, such as the discovery of a new cage isomer (D5h) of Sc3N@C80, the synthesis of Lu3N@C80 as a novel X-ray contrasting agent, and the synthesis of Sc315N@C80 with 15N2 gas.
The first derivative of Sc3N@C80 was synthesized by functionalizing the exterior of the cage via a [4 + 2] cycloaddition reaction with a 13C-labeled intermediate. Addition occurred across the [5,6] ring-juncture of the cage to form a mono-adduct, which has a mirror plane of symmetry as observed from the time-averaged 13C NMR spectrum. The structure of the mono-adduct was confirmed by X-ray crystallography. Diethyl and dibenzyl malonate adducts of Sc3N@C80 were synthesized, in addition to a 15N-labeled terminal amine derivative. Water-soluble metallofullerenols, Sc3N@C80(OH)~10(O)~10, were synthesized from polyanionic intermediates.
The Sc3N@C78 metallofullerene was derivatized with a 13C-labeled reagent to afford mono-, di- and tri-adducts. A single structural isomer of the mono-adduct was found, while several isomers of the di- and tri-adducts were observed by HPLC. 13C and 1H NMR data of the mono-adduct support a structure that results from addend addition to an asymmetric site on the C78 carbon cage.
The HPLC isolation and characterization of Lu3N@C80 is discussed. When irradiated with X-rays, Lu3N@C80 provided a small level of contrast that can only be attributed to the large atomic number (Z) of the lutetium atoms. Mixed-metal species that contains gadolinium and lutetium or holmium and lutetium could be employed as multifunctional contrasting agents for X-ray, MRI and radiopharmaceuticals, thereby eliminating the need for three separate agents.
A new cage isomer of the Sc3N@C80metallofullerene was synthesized and partially isolated by HPLC. This carbon cage possesses D5h symmetry, as indicated by the time-averaged six line 13C NMR spectrum with a 1:2:2:1:1:1 ratio.
The internal metal-nitride cluster of Sc3N@C80 was synthesized with a 15N-label for studying the motion(s) of the cluster (within the carbon cage) at various temperatures using 15N NMR spectroscopy.
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