Phase-Separated Molecular Assembly of a Nanotube Composed of Amphiphilic Polypeptides Having a Helical Hydrophobic Block

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.