The conformation of the polysaccharide hyaluronan (HA) has been investigated by tapping mode atomic force microscopy in air. HA deposited on a prehydrated mica surface favored an extended conformation, attributed to molecular combing and inhibition of subsequent chain recoil by adhesion to the structured water layer covering the surface. HA deposited on freshly cleaved mica served as a defect in a partially structured water layer, and favored relaxed, weakly helical, coiled conformations. Intramolecularly condensed forms of HA were also observed, ranging from pearl necklace forms to thick rods. The condensation is attributed to weak adhesion to the mica surface, counterion-mediated attractive electrostatic interactions between polyelectrolytes, and hydration effects. Intermolecular association of both extended and condensed forms of HA was observed to result in the formation of networks and twisted fibers, in which the chain direction is not necessarily parallel to the fiber direction. Whereas the relaxed coil and partially condensed conformations of HA are relevant to the native structure of liquid connective tissues, fully condensed rods may be more relevant for HA tethered to a cell surface or intracellular HA, and fibrous forms may be relevant for HA subjected to shear flow in tight intercellular spaces or in protein-HA complexes.

The poly(N-isopropylacrylamide-co-1-vinylimidazole) hydrogel nanoparticles (nanogels; 30−300 nm in diameter) with hydrophobic N-octadecylacrylamide chains exposed on their surfaces have been prepared by UV-induced polymerization. The internal reservoir of liposomes was used as a container for the water-soluble components of a gel-forming medium while the interlayer space of the liposomal lipid membrane was used as a container for the water-insoluble components. The abrupt collapsing of the nanogels was accompanied with their aggregation above the volume phase transition temperature, as was observed by dynamic light scattering (DLS). The combined DLS and atomic force microscopy (AFM) study shows that the obtained hydrogel nanoparticles were highly compatible with the lipid bilayer. This compatibility led to a self-initiated coating of the hydrogel particles by a lipid layer upon mixing of liposomes and nanogels. Swollen and collapsed states of the nanogels at different pH values were visualized by AFM. The flattening of the liposomes and nanogels was compared upon their deposition onto a mica surface in air. The quantitative characteristics of the nanogels in swollen and collapsed states were revealed by cross sectioning of AFM images. The findings indicate great potential for using the spherical nanoparticles (liposomes and nanogels) as starting materials for the fabrication of planar and hemispherical biophysical nanodevices.

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Organic salts consisting of an organic cation, composed of an alkylated pyridinium ion linked to a dimethylamino group by a π-system, and an inorganic anion were incorporated in polymeric networks formed by photopolymerization of dimethacrylates of different size and polarity. The response of the probe's emission to changes in its environment during photopolymerization was determined and compared with the response of 4-(dimethylamino)-4‘-nitrostilbene, a typical charge transfer probe. Emissions in solvents of low viscosity but with different polarities are also reported. A mechanism to explain the probe's response is presented.

Alkaline sucrose solution was demonstrated to be a good solvent for the solubilization of water-insoluble drugs. At high concentration and alkaline pH, sucrose solubilizes water-insoluble molecules through intramolecular conformations. Tetracyline and chloramphenicol, when dissolved in alkaline sucrose solution, retained their bactericidal activity. Gel permeation-chromatography analysis and atomic-force-microscopy studies confirmed the formation of sucrose-antibiotics complex.