Oxidation decomposition of unsaturated fatty acids with singlet oxygen generated from a photosensitizing agent was investigated in liposome bilayer membranes under a light irradiation condition. The liposome of which the bilayer membrane was composed of L-alpha-dipalmitoylphosphatidylcholine (DPPC), protoporphyrin IX (PpIX), and an unsaturated fatty acid (oleic acid, linoleic acid, alpha-linolenic acid, or arachidonic acid) were prepared with Bangham's method. In irradiating the liposome dispersion with light ranged from 550 to 750 nm, the unsaturated fatty acid was decomposed through an oxidation reaction with singlet oxygen. The decomposition rate constant was obeyed as the following order: arachidonic acid > oleic acid > alpha-linolenic acid > linoleic acid. This result indicates that oleic acid is readily degraded despite its lower unsaturated degree. In addition, micropolarity and microfluidity of the hydrocarbon region in the liposome bilayer membrane including the unsaturated fatty acid and PpIX decreased with an increase in light irradiation time. These findings suggest that interaction among the hydrocarbon chains of DPPC in the liposome bilayer membrane is promoted by migration of the oxidized unsaturated fatty acid from the hydrocarbon region, leading to form close-packed and well-ordered orientation of the hydrocarbon chains.

Three amphiphilic block polypeptides, (sarcosine) -b-(l- or d-Leu-Aib) (L16, D16, D14), having different helical chain lengths or helicity are synthesized. A mixture of L16, D16, and D14 generates vesicles of diameters more than ca. 130 nm by injecting the ethanol solution into water and heating at 90°C for 1 h. On the other hand, when nanotubes composed of L16 and D14 having ca. 50 nm diameter are mixed with nanosheets composed of D16, smaller and homogeneous vesicles of ca. 60 nm diameter are obtained with the heat treatment. The time lapse TEM image analysis of the mixtures revealed some transient structures of nanotubes sticking a nanosheet or a vesicle at the open end of nanotubes. The precise size control of vesicles is therefore attainable by using nanotubes as a structural template regulating the size of vesicles near to the nanotube diameter upon the membrane fission processes.

is one of the endogenously formed porphyrins and is synthesized in the heme biosynthetic pathway (1). PpIX is known to be a photosensitizing agent. It is excited by light and transfers the energy to molecular oxygen, resulting in formation of singlet oxygen. Singlet oxygen is a sort of active oxygen species and is highly reactive with various chemical compounds (2). PpIX is then expected to be usable as a herbicide, disinfectant, and so on. In the medical field, in particular, PpIX has also been used as a photosensitizer in photodynamic therapy (PDT) for tumor tissues (3-5). In PDT, photosensitizing agent located in tumor tissues are excited by light of a specific wavelength and generates cytotoxic singlet oxygen, leading to a sequence of photochemical and photobiological processes that cause irreversible photo-135

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