Stimuli-Responsive Vesicles, Micelles and Rods from Polypeptide-Based Amphiphilic Block Copolymers
D.A. Savin, K.E. Gebhardt, S. Ahn and G. Venkatachalam
University of Vermont, US
self-assembly, block copolymers, polypeptides, responsive materials
Amphiphilic block copolymers consisting of poly(butadiene) and poly(L-lysine) (PB-P(Lys)) were synthesized and their solution properties studied using dynamic light scattering and transmission electron microscopy. These materials exhibit a rich diversity of morphologies and were found to self-assemble in solution into spherical micelles and vesicles when the side chain amine groups on the lysine units are protected. Upon deprotection, the lysine units become sensitive to solution pH and temperature. At high pH, the P(Lys) chain assumes either an alpha-helical or a beta-sheet conformation depending on temperature, while at lower pH the side chains become protonated, resulting in an expanded coil configuration. We exploit these changes in polypeptide secondary structure to observe morphological changes in these assemblies as a function of solution conditions. In these studies, four molecular weights and compositions of PB-P(Lys) were studied. For short P(Lys) blocks, these block polymers assemble into vesicles that swell with decreasing pH. For longer P(Lys) blocks, cylindrical micelles are formed that undergo a morphological shift to spherical micelles with decreasing pH.
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Nanotech 2006 Conference Program Abstract