Photodynamic Therapy Mediated by Fullerenes and their Derivatives
2 Synthesis of fullerene derivatives
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Cationic functional groups are generally considered as the addend of choice for attachment on the fullerene cage due to their potential surface binding contact with anionic residues of the bacteria cell wall via static charge interactions. A systematic trend to increase the number of positive charges per fullerene cage was observed in the recent report  to maximize such interactions and use them as the approach for targeting bacteria having a significant density of anionic residues at the cell wall surface. A number of chemical functionalization methods of fullerenes have been reviewed [59–62]. Among them, common convenient methods for the preparation of cationic fullerene derivatives include cyclopropanation  and pyrro-lidination  reactions due to their high consistency allowing product reproducibility. Examples of the latter were given in the preparation of quaternized dimethylpyrrolidinium fullerenyl monoadduct (BF4) and trisadduct (BF6) [65, 66]. In a typical reaction condition, C60 was treated with 1.0 or 3.0 equivalent of N-methylglycine (sarcosine) and paraformalaldehyde in toluene at the reflexing temperature to afford either mono-N-methylpyrrolidino fullerene or a large number of regioisomers of tris(N-methylpyrrolidino) fullerene derivatives, as shown in Figure 2-1. Upon quaternization of these intermediates using methyl iodide as the methylation agent, corresponding monocationic and tricationic products as BF4 and BF6 were obtained, respectively.