Structural and Conformational Transformations in Self-Assembled Polypeptide-Surfactant Complexes

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• 作者：Sirkku Hanski ; Susanna Junnila ; L&aacute ; szló ; Alm&aacute ; sy ; Janne Ruokolainen ; Olli Ikkala
• 刊名：Macromolecules
• 出版年：2008
• 出版时间：February 12, 2008
• 年：2008
• 卷：41
• 期：3
• 页码：866 - 872
• 全文大小：446K
• 年卷期：v.41,no.3(February 12, 2008)
• ISSN：1520-5835

文摘

Self-assembled polypeptide-surfactant complexes are usually infusible solids in the absence ofsolvent and do not allow fluidlike liquid crystallinity even when heated, which seriously limits their polymer-likeapplications in the solid state due to processing problems. This work is partly inspired by nature's liquid crystallineprocessing of silk and subsequent structural interlocking due to mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-sheet formation. We demonstrate herepolypeptide-surfactant complexes that are fluidlike liquid crystalline at room temperature with hexagonalcylindrical self-assembly. The hexagonal structure with mages/gifchars/alpha.gif" BORDER=0>-helical polypeptide chains is then partially convertedto lamellar self-assembly with mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-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 suppressthe side-chain crystallization. In the stoichiometric composition, x = 1.0, there is one anionic DBSA moleculeionically complexed to each cationic lysine residue. Such a PLL(DBSA)_1.0 is an infusible solid material at alltemperatures until degradation. Introduction of additional DBSA, i.e., x = 1.5 or 2.0, plasticizes the material tobe shear-deformable and birefringent. In organic solution, as witnessed by small-angle neutron scattering (SANS),the PLL(DBSA)_x complexes form bottle-brush-like cylinders, which upon evaporation of the solvent self-assembleinto hexagonal cylindrical morphology with mages/gifchars/alpha.gif" BORDER=0>-helical PLL secondary structure. Heating of PLL(DBSA)_x with x= 1.0-2.0 up to the range 120-160 mages/entities/deg.gif">C leads to the formation of lamellar self-assembled domains with mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-sheetconformation of PLL, which coexist with the hexagonal self-assembled structures with mages/gifchars/alpha.gif" BORDER=0>-helical conformation,as shown by Fourier transform infrared spectroscopy (FTIR) and small-angle X-ray scattering (SAXS). Highercomplexation ratio, i.e., x = 3.0, results in soft and shear-deformable hexagonally packed cylinders at roomtemperature, but heating irreversibly converts the PLL to a random coil conformation, which leads to a disorderedstructure. The present model studies show that in polypeptide-surfactant self-assemblies it is possible to changethe properties of the material by thermal treatment due to irreversible structural and conformational transformations.