ELECTRON AND LIGHT-MICROSCOPIC INVESTIGATION OF DEFECT STRUCTURES IN MESOPHASES OF PHARMACEUTICAL SUBSTANCES

Transmission electron microscopy of freeze fractured and replicated sa mples (TEM) and polarizing light microscopy (PLM) are used to investig ate the defect structures of the thermotropic and lyotropic mesophases of the nonsteroidal antiinflammatory drug fenoprofen sodium and of th e thermotropic mesophase of the nonionic surfactant sucrose oleate (O1 570). All mesophases have a layered, smectic structure. The thermotrop ic liquid crystal of fenoprofen sodium is an interdigitated smectic A phase (smectic Ad) having the highest viscosity of the investigated sa mples. The thermotropic mesophase of the sugar ester is also of the ty pe smectic A, likely to be of subtype smectic A2 (bilayered smectic st ructure). The lyotropic mesophase is of lamellar liquid crystalline na ture and has a much lower viscosity than the thermotropic mesophases. In the PLM the lyotropic fenoprofen mesophase has a strong tendency to form a pseudoisotropic texture, indicating a strong tendency to form undisturbed layered structures. Other textures exhibited in the PLM ar e fan-shaped texture and maltese-cross texture. Confocal domains, cyli nders, pits and peaks as well as screw dislocations are found in great number in the TEM. However, no greater regions of undisturbed lamella r arrangement in the lyotropic mesophase could be detected. The only t exture of the thermotropic fenoprofen mesophase visible in the PLM is the fan-shaped texture, indicating confocal domains as predominant str uctural elements. However, no confocal domains (tori or Dupin cyclides ) are found in the TEM. In the PLM the sugar-ester mesophase exhibited a fan-shaped texture, maltese crosses and oily streaks as dominant te xtures. In the TEM only a few +pi and -pi disclinations and imperfect confocal domains could be detected. The discrepancies in the appearanc e of defect structures and textures between the mesophases as well as the discrepancies in the findings in the PLM and in the TEM investigat ions are caused by the different sample preparation and the different viscosities of the mesophases.