(606b) Thermodynamic Peptosome-Based Supramolecular Structures

There have been significant advances in the last ten years in the synthesis of ?hybrid? block copolymers wherein one block is a poly-á-amino acid and the other a ?conventional? polymer (e.g. polystyrene, polybutadiene, PEG) as well as block copolypeptides. These materials have been shown to self assemble into structures including vesicles, micelles, and hydrogels. While these materials are of great interest, they tend to form highly irreversible, i.e. kinetically trapped, structures. Here we report on the self-organization of poly(L-lysine)-b-polyglycine diblock and triblock copolypeptides in aqueous solution. Polyglycine was chosen as the hydrophobic block in the current work in lieu of other hydrophobic amino acids as polyglycine will not form secondary structures such as helices and sheets and has a higher solubility than most other hydrophobic amino acids. These polymers form vesicular structures on the 100-300 nm size scale in solution that appear thermodynamic in nature. A battery of methods including light scattering, conductivity, and microscopy are used to characterize the solution behavior. The key finding is that while a variety of vesicle sizes ranging from 200 ? 5000 nm in diameter can be formed based on initial processing conditions (including simple dissolution in buffer, extrusion/dialysis from organic solvents, and forming vesicles from polymer films deposited on surfaces) manipulation of the lysine block's secondary structure can be used to reversibly generate vesicles of well-defined size implying that the vesicles reported here are thermodynamic in nature. Moreover, the vesicles thus obtained can be reversibly formed after dilution and subsequent concentration of the solution, and even after precipitation/aggregation of the polypeptides by raising the pH to induce the coil-helix transition. The results of this work show that these previously unreported materials have unique properties of relevance to numerous applications including drug delivery, controlled released, encapsulation, and biomineralization/biomimetic syntheses of hard matter.