title: Effect of double-tailed surfactant architecture on the conformation, self-assembly, and processing in polypeptide-surfactant complexes.
abstract: This work describes the solid-state conformational and structural properties of self-assembled polypeptide-surfactant complexes with double-tailed surfactants. Poly(L-lysine) was complexed with three dialkyl esters of phosphoric acid (i.e., phosphodiester surfactants), where the surfactant tail branching and length was varied to tune the supramolecular architecture in a facile way. After complexation with the branched surfactant bis(2-ethylhexyl) phosphate in an aqueous solution, the polypeptide chains adopted an alpha-helical conformation. These rod-like helices self-assembled into cylindrical phases with the amorphous alkyl tails pointing outward. In complexes with dioctyl phosphate and didodecyl phosphate, which have two linear n-octyl or n-dodecyl tails, respectively, the polypeptide formed antiparallel beta-sheets separated by alkyl layers, resulting in well-ordered lamellar self-assemblies. By heating, it was possible to trigger a partial opening of the beta-sheets and disruption of the lamellar phase. After repeated heating/cooling, all of these complexes also showed a glass transition between 37 and 50 degrees C. Organic solvent treatment and plasticization by overstoichiometric amount of surfactant led to structure modification in poly(L-lysine)-dioctyl phosphate complexes, PLL(diC8)(x) (x = 1.0-3.0). Here, the alpha-helical PLL is surrounded by the surfactants and these bottle-brush-like chains self-assemble in a hexagonal cylindrical morphology. As x is increased, the materials are clearly plasticized and the degree of ordering is improved: The stiff alpha-helical backbones in a softened surfactant matrix give rise to thermotropic liquid-crystalline phases. The complexes were examined by Fourier transform infrared spectroscopy, small- and wide-angle X-ray scattering, transmission electron microscopy, differential scanning calorimetry, polarized optical microscopy, and circular dichroism.
authors: Molecular Materials, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo, Finland.
authors: Susanna
authors: S
authors: Junnila
authors: Sirkku
authors: S
authors: Hanski
authors: Richard J
authors: RJ
authors: Oakley
authors: Sami
authors: S
authors: Nummelin
authors: Janne
authors: J
authors: Ruokolainen
authors: Charl F J
authors: CF
authors: Faul
authors: Olli
authors: O
authors: Ikkala
mesh_terms: D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D046529:Microscopy, Electron, Transmission; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D010455:Peptides; D013501:Surface-Active Agents