In this paper we discuss the preparation of complexes formed by polyethylenimine (PEI) and retinoic acid. The molecular weights of the PEIs were 600, 2000, 25 000, and 750 000 g/mol. All complexes form smectic A-like structures whose orders decrease with increasing molecular weight. The complexes in the bulk material obey Porod's law. Macroscopically oriented multilayer films of the complexes were prepared in a single-step procedure by spin coating and were characterized by X-ray reflectivity. The release of retinoic acid from the films was investigated by FTIR and surface tension measurements. It was found that the release from the complexes with the high molecular weight PEIs is faster than that from the complexes with low molecular weight. Steric stabilized nanoparticles of the complexes were prepared with sizes ranging from 170 to 580 nm by using Poloxamer 188 as the dispersing agent in aqueous media. Their characterization was carried out using dynamic light scattering and atomic force microscopy. It was found that the particle sizes decreased with the increasing molecular weight of the PEIs. Further, the particle structure became more compact with the increasing molecular weight of the PEIs. The particles of the complexes with the lowest molecular weight were assumed to be doughnutshaped (toroids).

We discuss the preparation, the X-ray spectra and their theory, and electron microscopy of nanoparticles showing a lamellar internal structure. Retinoic acid was immobilized by complexation with poly(L-arginine), poly(L-histidine), and poly(L-lysine). The resulting solid-state complexes were prepared as nanoparticles with diameters of 320-380 nm, and with internal structures, which are smectic A-like. By small-angle X-ray scattering the unit cell was determined to be in the range of 3.10-3.62 nm, thus depending linearly on the monomer mass. The X-ray scattering of finite lamellar structures of "onion"-and "tart"-type spherical nanoparticles were determined theoretically. The uniform boundary of the onion-type particles results in secondary maxima near the Bragg reflections. Further, the highest degree of polydispersity to find these secondary maxima in scattering experiments was determined to be about 1% if the particle size is 300 nm. When electron microscopy was used, it was shown that the particles consist of a complex-containing core surrounded by a dispersing agent-containing shell. The core was revealed to be more of the tart-than the onion-type. When circular dichroism was used, the conformation of poly(L-arginine) and poly(L-lysine) within the complexes was determined to be an R-helix, whereas that of poly(L-histidine) was predominantly of the coil-type.

Properties of the complexes formed by poly(ethylene oxide)-b-poly(L-lysine)s (PEO-PLL) and all-trans-retinoic acid were investigated by differential scanning calorimetry, wide-and small-angle X-ray scattering, circular dichroism, dynamic light scattering, and atomic force microscopy. It was determined that for micellar solutions of complexed PEO-PLL the poly(L-lysine) blocks form an R-helix structure at pH values higher than 9 and that the coil-helix transition spans from pH 3.7 to 9.0. The high stability of the R-helix was attributed to a protective effect of the retinoate moieties and the PEO surrounding. Micelle structures were found to be of core-shell type. Each micelle has a compact core, which is formed by a smectic A-like poly(L-lysine) retinoate complex. The shell is formed by the PEO. When the pH value is lowered, the micelle sizes increases. The conformation of the noncomplexed PEO-PLL in the solid state was found to be a mixture of R-helix and β-sheet structures while that of the complexed polymers is a pure R-helix. The PEO blocks crystallize in the solid state of the pristine and the complexed polymers, but the degree of crystallinity is considerably lower in the complexed state. Such block copolymer complexes are considered to be useful for the development of new drug delivery formulations.

The influence of different amounts of anionic copolymers of N-Methyl N-vinyl acetamide (NMVA) and acrylic acid with various charge densities on the formation of the lamellar liquid crystal formed by sodium dodecyl sulfate ( SDS )/decanoVwater was investigated by means of polarization microscopy, small angle x-ray scattering (SAXS), transmission electron microscopy and rheology. On the contrary to the incorporation of poly(acrylic acid) a one phase lamellar liquid cristalline region was obtained in all investigated formulations with the different copolymers. Although a shrinking of the liquid cristalline region for all systems that contain copolymers could be generally proved by SAXS-measurements, no change of the phase boundaries due to the different amounts or charge densities could be shown over a wide range.However, for the investigated weight ratios water / ( SOS + decanol ) the interlayer spacings of the lamellar mesophases decreased with increasing copolymer amount whereas the value for the extrapolated interlayer spacing (do) remained constant.Transmission electron microscopy proves the formation of spherical suprarnolecular structures in good agreement with the rheological behaviour of the systems.