(621f) Solid and Liquid Core Polyelectrolyte Complex Micelles

Polyelectrolyte complexes form by mixing oppositely charged polymers in solution. The resultant complex phase separates from solution into either irregularly shaped solids (or rather glasses), called precipitates, or micron sized liquid droplets that can coalesce into a distinct phase, called a coacervate. Using oppositely charged polypeptides, one can tune between solid and liquid complexes by manipulating the chirality of the polyelectrolyte. Homochiral complexes form precipitates with hydrogen bonded b-strand structure. In contrast, if one or more polypeptide is composed of both L and D monomers, coacervates are formed with no secondary structure. This inability to form secondary structure is attributed to steric hindrance of the racemic polypeptide impeding hydrogen bond formation. Therefore, since both types of complexes are formed using weak polyelectrolytes, the ability of the homochiral molecules to hydrogen bond causes the difference in phase. Using oppositely charged block-copolyelectrolytes that contain neutral blocks covalently linked to charged blocks allows the phase separation to be stabilized on the nanoscale, creating self-assembled micellar structures in dilute solutions. These polyelectrolyte complexes micelles can be used as drug and gene delivery vehicles for charged therapeutics like nucleic acids and proteins. Using diblock copolypeptides of varying chirality the resulting micellar structure can have both solid and liquid polyelectrolyte cores. This presentation will focus on characterization of polypeptide based polyelectrolyte complex micelles using scattering techniques (light, x-rays, neutrons), circular dichroism, and electron microscopy to reveal structural differences of solid and liquid micellar cores. In addition, the exchange kinetics of solid and liquid core micelles will be investigated by mixing solid and liquid core micelles that contain FRET pairs. Insight will be provided as to how differences in solid and liquid cores influence the design of drug delivery vehicles. If time permits, investigations into related micelles with dynamic coronas will be discussed.