Characterization of a novel self-association of an alternating copolymer into nanotubes in solution

Abstract

The characterization of the association of an alternating copolymer was performed using theoretical methods (quantum mechanics and molecular mechanics) and experimental methods (cryo-Transmission Electron Microscopy (cryo-TEM), neutron reflectivity and neutron scattering). The most stable conformation obtained for the self-association at pH 7 using theoretical methods is a tubular structure in which eight SMA molecules make one twist of a helix. The tubes can grow in length by continued regular stacking of benzene rings. The nanotubes have inner and outer diameters of about 28 and 41 Å, respectively. The hydrophobic groups are mainly located inside the tube and the hydrophilic groups are mainly on the exterior surface of the tube. They can also associate with themselves creating planes of aligned tubes, which can stack upon each other. The association of alternating copolymers into nanotubes is a novel self-association process.

The association of SMA octamers into a tubular structure at pH7 was confirmed experimentally by cryo-TEM and the nanotubes observed were several micrometers long. The shape as well as the inner and outer diameter of the nanotubes were also characterized by neutron scattering and the conformation at the air–water interface by neutron reflectivity.

Keywords:

• Alternating copolymer
• Self-assembly
• Quantum mechanics
• cryo-TEM
• Neutron scattering

Acknowledgements

This work was supported by NSERC and by the “Wood Pulp” Network of Centers of Excellence (Canada). NIST and NCNR (Washington, USA) are thanked for support and neutron reflectometer facilities; ILL (Grenoble, France) is thanked for support and neutron scattering facilities. The authors gratefully acknowledge Dr T. Cosgrove and Dr R. Richardson (University of Bristol, UK) for help with the neutron reflectivity and scattering experiments and Dr H. Vali and Dr S.K. Sears (McGill University, Canada) for the cryo-TEM experiments. Paprican and NSERC are acknowledged for funding of an IRC.

Notes

HyperChem release 5.11 (1999) Hypercube Inc.