Immobilization of Retinoic Acid by Cationic Polyelectrolytes

Retinoic acid was immobilized by precipitating its complexes with cationic polyelectrolytes from aqueous solution. Polyelectrolytes with different architectures, such as poly(ionene-6,3 bromide), poly(dimethyldiallylammonium chloride), and poly( N -methyl-4-vinylpyridinium chloride), form self-assembling complexes containing retinoic acid (70% (w/w)). All these complexes are thermodynamically stable and can be processed into mesomorphously ordered films with interesting physical properties. In contrast to the brittle crystalline retinoic acid the complexes with polyelectrolytes are highly deformable viscoelastic materials. All materials show lamellar mesophase structures; their T g value strongly depends on the polyelectrolyte. It is suggested that these materials have great potential as pharmaceutical agents as well as models for the investigation and the mimicking of chromophores in visual pigments and photosynthetic bacteria. The properties of the complexes are examined by X-ray diffraction, differential scanning calorimetry, polarization optical microscopy, UV−vis spectroscopy, and stress−strain measurements.