Abstract
We show double smectic-like self assemblies in the solid state involving alternating layers of different polypeptide alpha-helices. We employed rod-coil poly(gamma-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 alpha-helices of fixed diameter and PLL-surfactant complexes adopting either alpha-helices of tunable, diameters or beta-sheets For PBLG-b-PLL(diC4P), that is, using a surfactant with short n-butyl tails, both blocks were alpha-helical of roughly equal diameter and thus with minor Racking frustrations, leading to alternating PBLG and PLL(diC4P) smectic layers of approximately perpendicular alignment Of both types of alpha-helices. Surfactants With longer and branched alkyl tails lead to an increased diameter of the PLL-surfactant alpha-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 alpha-helices. In PBLG-b-PLL(diC8/12P), the PLL(diC8/12P) alpha-helices are even larger and the overall structure is poor. Using a surfactant with two linear n-dodecyl tails leads to well ordered. beta 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 alpha-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