Hitoshi Kasai

Organic microcrystals ranging from several tens nm to µm in size of several chromophores were successfully prepared by simply dispersing ethanol solutions of compounds into stirred water, i.e. by a reprecipitation method. The size of microcrystals was found to depend on concentration of ethanol solutions, dispersing conditions, temperature and so on.

Perylene microcrystals with different sizes from about 50 nm to about 200 nm were prepared using the reprecipitation method. Their excitonic absorption peaks were found to shift to the high energy side with decreasing crystal size, that is to say, the shifts from that of the bulk crystal were about 500 cm -1 and 1420 cm -1 for 200 nm and 50 nm microcrystals, respectively. Moreover, strong fluorescence from the free-exciton energy level in the microcrystals was observed even at room temperature,

A method for preparing nanoparticles of a water-insoluble drug that are suitable for administration to the human body has been established. A reprecipitation method was used to fabricate 50 nm nanoparticles of dimerized SN-38, an anticancer camptothecin derivative, that form stable aqueous dispersions and can penetrate into cancer cells to inhibit cell proliferation more potently than irinotecan.

Abstract In this study, we found that, in perylene microcrystals, luminescence peak position from free-exciton state was gradually shifted to high energy side with reducing the crystal size, even if the microcrystals were fabricated by different kinds of preparation techniques. The life time of luminescence from self-trapped exciton state became shorter when the crystal size reduced. The main reason was estimated to be based on the change of lattice state.

Abstract The crystal growth of α-perylene microcrystals in the reprecipitation method was studied using of light-scattering technique and absorption spectroscopy. A certain model for microcrystallization has been established. The relationship between the reprecipitation conditions and the crystal size was clarified on the basis of this model. Especially, the water temperature was confirmed to be one of the most important parameters used to control the size of the microcrystals in the reprecipita

Abstract The optical properties of perylene microcrystals in wide range of crystal size from 50 ran to 1 μm were measured. The interesting behavior of exciton in microcrystals with less than 200nm was found. For example, with decreasing the crystal size, self-trapped exciton states in microcrystals shifted to the high energy side. Therefore, the strong luminescence from free-exciton was observed, and life time of self-trapped exciton became shorter .

The controlled release of an anticancer agent from drug nanoparticles could be achieved by varying the linker length of dimeric compounds as prodrug. Notably, the cytotoxicity of the cancer cells was closely related to the release rate of drug compounds. This strategy will lead to the establishment of the novel delivery system using drug nanoparticles.

Abstract Single molecular chains of π-conjugated polymers such as polythiophene and polydiacetylene were clearly observed by STM, and their molecular structures and/or conformation were discussed in relation to bonding characteristics. It should be noted that even molecular weight could be determined using well-resolved STM images.