Tubular Network Formation by Mixing Amphiphilic Polypeptides with Differing Hydrophilic Blocks

Artificial tubular networks are promising structures for biomaterial applications because of their large surface areas. A tubular network was formed by co-assembling two different amphiphilic polypeptides, poly(ethylene glycol)-b-(l-Leu-Aib)₆ (PL12) and polysarcosine-b-(l-Leu-Aib)₆ (SL12). They both have the same hydrophobic 12-mer helical block (l-Leu-Aib)₆ but different hydrophilic chains, poly(ethylene glycol) and polysarcosine. In water, both polypeptides self-assembled into a tubular structure having a uniform 80 nm diameter that was formed by packing among the hydrophobic L12 blocks. The SL12 nanotubes were short (200 nm), straight, and robust. PL12 formed long (>1 μm), bendable, and fusogenic nanotubes. The amphiphiles were then co-assembled with various mixing ratios to form tubular networks. Higher concentrations of PL12 made the nanotubes more bendable and fusogenic between open tube ends, which produced branching junctions under heat treatment.

Sterical Recognition at Helix-Helix Interface of Leu-Aib-Based Polypeptides with and without a GxxxG-Motif

An amphiphilic polypeptide, poly(sarcosine)- b-(l-Leu-Aib)₈ (SL16), was reported to self-assemble into vesicles. A GxxxG motif, which is known to induce helix dimerization, is incorporated into the hydrophobic helical block of SL16 to synthesize poly(sarcosine)- b-(l-Leu-Aib)₂-(Gly-Aib-l-Leu-Aib-Gly-Aib)-(l-Leu-Aib)₃ (SG16). SG16 shows helix association in ethanol at a high concentration and low temperatures, which is not observed with SL16. SG16 self-assembles into vesicles, but are found to be more susceptible to rupture by the addition of Triton X-100 than SL16 vesicles. A mixture of SL16 and SG16 self-assembles into small sheets and micelles likely because of mismatch of the modes of helix association arising from sterical accommodation of iso-butyl groups at the helix-helix interface.

Compartmentalized host spaces accommodating guest aromatic molecules in a chiral way in a helix-peptide-aromatic framework

A novel host molecular assembly of a free-standing flat nanosheet with compartmentalized spaces was prepared using a bolaamphiphilic peptide composed of two amphiphilic helical peptides and an oligo(naphthaleneethynylene) (ONE) unit at the center of the molecule. The nanosheet possesses void host spaces that can accommodate two mol-equivalent ONE groups to form columns of ONE groups in a right-handed helical way and ONE channels over a long distance. The present molecular system therefore can provide a chiral pore channel for relatively large molecules.

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.