Various amphiphilic block polypeptides having aromatic groups at the C terminal of a Leu-based hydrophobic helical block, poly(sarcosine)-b-(l-Leu-Aib)6-ethylcarbazole, poly(sarcosine)-b-(d-Leu-Aib)6-naphthalimide, and poly(sarcosine)-b-(d-Leu-Aib)6-porphyrin, were synthesized and self-assembled in water. Molecular assemblies of distorted sheet, saddle-like sheet, and micelle were identified, which were different from the curved sheet of poly(sarcosine)-b-(l-Leu-Aib)6 without any aromatic groups, indicating that the attachment of the aromatic groups to the C terminal significantly influenced the morphology. Upon heating at 90 °C, vesicles were generated with the three amphiphilic polypeptides with aromatic groups as opposed to the nanotubes of poly(sarcosine)-b-(l-Leu-Aib)6. The precise observations of these vesicles by AFM revealed formation of monolayer for poly(sarcosine)-b-(l-Leu-Aib)6-ethylcarbazole and bilayers for poly(sarcosine)-b-(d-Leu-Aib)6-naphthalimide and poly(sarcosine)-b-(d-Leu-Aib)6-porphyrin. Attachment of aromatic groups at the C terminal therefore influences morphology and monolayer/bilayer alteration in accordance with the type of aromatic groups.
Amphiphilic block polypeptides of poly(sarcosine)- b -( l - or d -Leu-Aib) 6 (SL12OMe or SD12OMe) and poly(sarcosine)- b -( l -Leu-Aib) 7 (SL14OMe) were reported to self-assemble into a nanotube morphology. Herein, we tried to construct a phase-separated nanotube by sticking two different kinds of nanotubes. SD12OMe nanotubes were found to stick to SL14OMe nanotubes with a heat treatment at 50 °C, but the sticking yield was limited. The amphiphilic polypeptides were functionalized by replacement of methyl ester with aromatic groups of N -ethylcarbazole (SL12Ecz) and naphthalimide (SD12NpiTEG), but they lost the ability to form homogeneous nanotubes. A fraction of the functionalized amphiphilic polypeptides mixing in the nanotube-forming amphiphilic polypeptides, a mixture of SL12OMe and SL12Ecz (9:1) as well as a mixture of SD12OMe and SD12NpiTEG (9:1), allowed nanotube formation. These two kinds of nanotubes partly stuck together with a heat treatment at 15 °C to maintain a segregated state of two kinds of aromatic groups along the nanotube, resulting in the formation of a phase-separated nanotube.
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