Structural and conformational transformations in self-assembled polypeptide - Surfactant complexes

Self-assembled polypeptide−surfactant complexes are usually infusible solids in the absence of solvent and do not allow fluidlike liquid crystallinity even when heated, which seriously limits their polymer-like applications in the solid state due to processing problems. This work is partly inspired by nature's liquid crystalline processing of silk and subsequent structural interlocking due to β-sheet formation. We demonstrate here polypeptide−surfactant complexes that are fluidlike liquid crystalline at room temperature with hexagonal cylindrical self-assembly. The hexagonal structure with α-helical polypeptide chains is then partially converted to lamellar self-assembly with β-sheet conformation through thermal treatment. We use poly(l-lysine)−dodecylbenzenesulfonic acid complexes, PLL(DBSA)x (x = 1.0−3.0), where the branched dodecyl tails suppress the side-chain crystallization. In the stoichiometric composition, x = 1.0, there is one anionic DBSA molecule ionically complexed to each cationic lysine res...