STUDY OF SELF-AGGREGATION AND INSERTION INTO VESICULAR SYSTEMS OF AMPHIPHILIC C60 FULLERENE DERIVATIVES

Hydrophilic monoadducts of C60 fullerene, DF, have been the object of interest for their practical applications in the biological field (e.g. photodynamic terapy and inhibition of HIV enzymes1,2,3). Though the attachment of (only) a single hydrophylic addend promotes water solubility, these derivatives tend to form clusters4 in aqueous solutions rather than to dissolve as monomers. Synthesis of amphiphilic fullerene monoadducts can therefore be designed to obtain a new class of supramolecular synthetic systems characterized by different properties and functions. This communication presents a comparative study on the experimental conditions used for the formation of aggregates in aqueous solutions and in organic/aqueous mixtures of the following monoderivatives of fullero(C60)pyrrolidine: The aggregation properties depend on the Hildebrand’s5 polarity, but only to a limited extent on the nature of the solvent. The increase of polarity, produced by the addition of water to the organic solution of the monomers, leads to the formation of aggregates. Each derivative suddenly forms aggregates above a characteristic polarity value of the solvent. Aqueous solutions of aggregates can be prepared by following a suitably designed experimental protocol. A direct formation of aggregates in water by simple sonication was achievable only for DF2. Partition experiments between n-octanol and water and RP-HPLC have been used to evaluate the hydrophobicity of the DFs. Different techniques have been used to estimate the dimensions of the supramolecular aggregates formed by DF1 in aqueous solution: by static laser light scattering the mean diameter turned out to be 120 nm and, the molecular weight above 1000000 daltons by HPLC-GPC experiments. The insertion of DF and the fullerene C60 into the bilayer of vesicles from cationic double-chained surfactants has been observed by UV-Vis spectrophotometry. The rates of breakdown of the above vesicles in the presence and in the absence6 of DFs, induced by addition of single chained surfactants, have been compared. The rates have been measured by “stopped-flow” kinetics observing the decrease in turbidity caused by the breakdown of the vesicles.