title: Double smectic self-assembly in block copolypeptide complexes.
abstract: We show double smectic-like self-assemblies in the solid state involving alternating layers of different polypeptide α-helices. We employed rod-coil poly(γ-benzyl l-glutamate)-block-poly(l-lysine) (PBLG-b-PLL) as the polymeric scaffold, where the PLL amino residues were ionically complexed to di-n-butyl phosphate (diC4P), di(2-ethylhexyl) phosphate (diC2/6P), di(2-octyldodecyl) phosphate (diC8/12P), or di-n-dodecyl phosphate (diC12P), forming PBLG-b-PLL(diC4P), PBLG-b-PLL(diC2/6P), PBLG-b-PLL(diC8/12P), and PBLG-b-PLL(diC12P) complexes, respectively. The complexes contain PBLG α-helices of fixed diameter and PLL-surfactant complexes adopting either α-helices of tunable diameters or β-sheets. For PBLG-b-PLL(diC4P), that is, using a surfactant with short n-butyl tails, both blocks were α-helical, of roughly equal diameter and thus with minor packing frustrations, leading to alternating PBLG and PLL(diC4P) smectic layers of approximately perpendicular alignment of both types of α-helices. Surfactants with longer and branched alkyl tails lead to an increased diameter of the PLL-surfactant α-helices. Smectic alternating PBLG and PLL(diC2/6P) layers involve larger packing frustration, which leads to poor overall order and suggests an arrangement of tilted PBLG α-helices. In PBLG-b-PLL(diC8/12P), the PLL(diC8/12P) α-helices are even larger and the overall structure is poor. Using a surfactant with two linear n-dodecyl tails leads to well-ordered β-sheet domains of PLL(diC12P), consisting of alternating PLL and alkyl chain layers. This dominates the whole assembly, and at the block copolypeptide length scale, the PBLG α-helices do not show internal order and have poor organization. Packing frustration becomes an important aspect to design block copolypeptide assemblies, even if frustration could be relieved by conformational imperfections. The results suggest pathways to control hierarchical liquid-crystalline assemblies by competing interactions and by controlling molecular packing frustrations.
authors.affiliation: Molecular Materials, Department of Applied Physics, Aalto University School of Science (formerly Helsinki University of Technology), P.O. Box 15100, FI-02015 Espoo, Finland.
authors.forename: Johannes S
authors.initials: JS
authors.lastname: Haataja
authors.forename: Nikolay
authors.initials: N
authors.lastname: Houbenov
authors.forename: Hermis
authors.initials: H
authors.lastname: Iatrou
authors.forename: Nikos
authors.initials: N
authors.lastname: Hadjichristidis
authors.forename: Anastasis
authors.initials: A
authors.lastname: Karatzas
authors.forename: Charl F J
authors.initials: CF
authors.lastname: Faul
authors.forename: Patrice
authors.initials: P
authors.lastname: Rannou
authors.forename: Olli
authors.initials: O
authors.lastname: Ikkala
mesh_terms: D050866:Liquid Crystals / Q000737:chemistry; D010455:Peptides / Q000737:chemistry*; D011099:Polyglutamic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D011107:Polylysine / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013501:Surface-Active Agents / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D010455:Peptides; D011108:Polymers; D013501:Surface-Active Agents; D014867:Water; C003172:poly-gamma-benzyl-L-glutamate; D011107:Polylysine; D011099:Polyglutamic Acid