Hierarchical Ionic Self-Assembly of Rod-Comb Block Copolypeptide Surfactant Complexes

摘要

Novel hierarchical nanostructures based on ionically self-assembled complexes of diblock copolypeptides and surfactants are presented.Rod-coil diblock copolypeptide poly(gamma-benzyl-L-glutamate)-block-poly(L-lysine),PBLG-b-PLL (M_n=25 000 and 8000 for PBLG and PLL,respectively,polydispersity index 1.08),was complexed with anionic surfactants dodecanesulfonic acid (DSA) or dodecyl benzenesulfonic acid (DBSA),denoted as PBLG-b-PLL(DSA)_(1.0) and PBLG-b-PLL(DBSA)_(1.0),respectively.The complexation leading to supramolecular rod-comb architectures was studied by transmission electron microscopy (TEM),small-angle X-ray scattering (SAXS),Fourier transform infrared spectroscopy (FTIR),and polarized optical microscopy (POM).PBLG-b-PLL,PBLG-b-PLL(DBSA)_(1.0),and PBLG-b-PLL(DSA)_(1.0) self-assemble with alternating PBLG lamellae and PLL-containing lamellae with a periodicity of 27-33 nm.Within the PBLG lamellae,the rod-like PBLG helices pack with a periodicity of ca.1.3 nm.The internal structure of the PLL-containing lamellae depends on the complexation.For pure PBLG-b-PLL,the PLL chains adopt a random coil conformation and the PLL domains are disordered.For PBLG-b-PLL(DSA)_(1.0),lamellar self-assembly of periodicity of 3.7 nm within the PLL(DSA)_(1.0) domains is observed due to crystalline packing of the linear n-dodecyl tails.For PBLG-b-PLL(DBSA)_(1.0) with branched dodecyl tails,a distinct SAXS reflection is observed,suggesting self-assembly within the PLL(DBSA)_(1.0) domains with a periodicity of 2.9 nm.However,due to the absence of higher order reflections,the internal structure cannot be conclusively assigned.The efficient plasticization which leads to fluid-like liquid crystallinity in PBLG-b-PLL-(DBSA)_(1.0) and an alpha-helical conformation according to FTIR allows us to suggest that the PLL(DBSA)_(1.0) domains have a hexagonal internal structure.The interplay of self-assembly at different length scales combined with rodlike liquid crystallinity can open new routes to design functional materials.