Improvement of Photodynamic Activity by a Stable System Consisting of a C60 Derivative and Photoantenna in Liposomes.

A dyad system comprising a lipid membrane-incorporated fullerene derivative with an N,N-dimethylpyrrodinium group (C60-1) and a photoantenna molecule (DiD) did not exhibit the high photodynamic activity expected based on its singlet oxygen generation ability. Comparison with a fullerene derivative with an amide substituent (C60-2) suggested the cause to be that some of the fullerene derivative had been released from the liposomes, partly disrupting the dyad system. The dyad system of C60-2 and DiD exhibited about twice the photodynamic activity toward HeLa cells as that of C60-1 and DiD, due to the suppression of the release of the fullerene derivative from the liposomes. The hydrophobicity/hydrophilicity balance of the substituent in fullerene derivatives was shown to be very important to obtain a dyad system in liposomes characterized by high photodynamic activity.

Cyclodextrin complexed [60]fullerene derivatives with high levels of photodynamic activity by long wavelength excitation.

We have evaluated the photodynamic activities of C60 derivative·Î³-cyclodextrin (γ-CDx) complexes and demonstrated that they were significantly higher than those of the pristine C60 and C70·Î³-CDx complexes under photoirradiation at long wavelengths (610-720 nm), which represent the optimal wavelengths for photodynamic therapy (PDT). In particular, the cationic C60 derivative·Î³-CDx complex had the highest photodynamic ability because the complex possessed the ability to generate high levels of (1)O2 and provided a higher level of intracellular uptake. The photodynamic activity of this complex was greater than that of photofrin, which is the most widely used of the known clinical photosensitizers. These findings therefore provide a significant level of information toward the optimization of molecular design strategies for the synthesis of fullerene derivatives for PDT.

Preparation of highly photosensitizing liposomes with fullerene-doped lipid bilayer using dispersion-controllable molecular exchange reactions.

Fullerene-containing liposomes with high photosensitization ability were prepared. Disaggregated fullerenes were efficiently injected into the bilayer of liposomes by a phototriggered molecular exchange reaction. These liposomes showed far higher photoreactivity than liposomes thermally produced by heating and microwave irradiation. This result indicates that control of self-aggregation of fullerene leads to a high quantum yield for the photoreaction because of the suppression of self-quenching of photoexcited fullerenes.

Control of self-aggregation of fullerenes by connection with calix[4]arene: solvent- and guest-effects to particle size.

A new molecular design of fullerene derivatives exhibiting trigger-responsive self-aggregation in organic solvents has been established. Calix[4]arene was covalently connected with fullerene in order to apply host-guest interaction to the aggregation control. The self-assembly behaviour was studied in organic solvents by UV-vis absorption spectroscopy, dynamic light scattering and transmission electron microscopy. Results show that the bisfullerene formed self-aggregations with a low polydispersity index due to the fullerenes' tendency to aggregate in polar organic solvents. Furthermore, the aggregate sizes can be changed readily by solvent composition and the addition of guest cations. Especially, disaggregation of the bisfullerene was induced by addition of LiClO4 or NaClO4.