Self-assembled nanotubes are interesting and useful nanostructures, holding potential applications in biomedical engineering, catalysis, gas storage and separation. Here, we report a new type of amphiphilic diglycine peptide which self-assembles into hollow cylindrical tubes in water driven by β-sheets. We studied the hierarchical structures and the formation mechanism of the nanotubes. To understand better of the self-assembly process of our amphiphilic diglycine peptide, we co-annealed mixture of peptides and polyelectrolytes at different ratio. Intermediate self-assembly structures were obtained by supramolecular electrostatic interactions between polyelectrolytes and the peptides. We found that the self-assembly process of our amphiphilic diglycine peptides could be fixed at several different intermediate stages, i.e., nanofibers and chiral ribbons with decreased pitches, towards the final formation of closed tubular structures at different co-assembly ratios in a manner resembling to time-resolved process. Our peptide nanotubes form hierarchical microscale long-range ordered lamellar structures which could be observed from SEM images and SAXS. The formation and strength change of β-sheets could be observed from gradient variable-temperature experiments with 1HNMR, FT-IR, and WAXS, demonstrating that the nanotubes were formed through hydrophobic-hydrophilic effects and local β-sheets between the primary chemical structures simultaneously. The study of nanotubes was extended from hydrogels to porous aerogels formed by aggregated nanotube bundles. The nanotube aerogel composed of hierarchical pores with abundant surfaces rich of free amines were used as gas-absorbents for CO2 chemisorption and gas separation. CO2 isotherms at different temperatures revealed unusual adsorption behavior compared with non-porous standard material. The gas separation efficiency for mixture gases containing CO2 is seven times higher than un-modified carbon nanotubes with similar diameters.

Self-assembled dipeptide nanotubes for CO2 chemisorption and separation

ACS Spring 2022

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