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

Sirkku Hanski, Susanna Junnila, László Almásy, Janne Ruokolainen, Olli Ikkala

Research output: Article

10 Citations (Scopus)

Abstract

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 a-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 residue. Such a PLL(DBSA)1.0 is an infusible solid material at all temperatures until degradation. Introduction of additional DBSA, i.e., x = 1.5 or 2.0, plasticizes the material to be shear-deformable and birefringent. In organic solution, as witnessed by small-angle neutron scattering (SANS), the PLL(DBS A)x complexes form bottle-brush-like cylinders, which upon evaporation of the solvent self-assemble into hexagonal cylindrical morphology with α-helical PLL secondary structure. Heating of PLL(DB SA)x with x = 1.0-2.0 up to the range 120-160 °C leads to the formation of lamellar self-assembled domains with β-sheet conformation of PLL, which coexist with the hexagonal self-assembled structures with a-helical conformation, as shown by Fourier transform infrared spectroscopy (FTIR) and small-angle X-ray scattering (SAXS). Higher complexation ratio, i.e., x = 3.0, results in soft and shear-deformable hexagonally packed cylinders at room temperature, but heating irreversibly converts the PLL to a random coil conformation, which leads to a disordered structure. The present model studies show that in polypeptide-surfactant self-assemblies it is possible to change the properties of the material by thermal treatment due to irreversible structural and conformational transformations.

Original languageEnglish
Pages (from-to)865-872
Number of pages8
JournalMacromolecules
Volume41
Issue number3
DOIs
Publication statusPublished - febr. 12 2008

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ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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