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Issue 19, 2010
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Side chain assisted nanotubular self-assembly of cyclic peptides at the air–water interface

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Abstract

Langmuir monolayers of two artificial cyclic peptides with an alternating sequence of L-glutamic acid and 3-aminobenzoic acid subunits, a cyclohexapeptide (C6G) and a cyclooctapeptide (C8G), were investigated using a variety of techniques, including πA isotherms, in situ surface sum-frequency generation (SFG) and Brewster angle microscopy. The monolayers were also transferred onto a solid substrate by the Langmuir–Blodgett technique and characterized by grazing incident X-ray diffraction (GIXD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The investigations indicated that C6G forms 2D crystallite structures at the air–water interface, whereas no such structures were observed for C8G. Being amphiphilic, both peptides attain a horizontal orientation on the water surface after spreading. Surface compression causes the molecules to flip to a perpendicular state, thus minimizing the molecular area. The measurements also indicate that, in the perpendicular state, self-assembly of C6G leads to a tubular arrangement of the peptide rings. According to GIXD and TEM data, pairs of tubes arrange in a well defined and oriented order producing 2D crystals. Surface vibrational spectroscopic methods (sum-frequency generation and polarization modulation IR reflection–absorption) combined with molecular modeling gave insight into the arrangement of individual C6G molecules in the tubes. Overall, our results indicated that the tubular assembly of C6G is most likely due to intermolecular H-bonding between the CO group in the glutamic acid side chains and peptide NH group of a neighboring peptide ring.

Graphical abstract: Side chain assisted nanotubular self-assembly of cyclic peptides at the air–water interface

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Publication details

The article was received on 23 Mar 2010, accepted on 21 May 2010 and first published on 17 Jun 2010


Article type: Paper
DOI: 10.1039/C0SM00143K
Citation: Soft Matter, 2010,6, 4701-4709

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    Side chain assisted nanotubular self-assembly of cyclic peptides at the air–water interface

    B. Kwak, K. Shin, S. Seok, D. Kim, F. Ahmad, K. E. Geckeler, O. H. Seeck, Y. Seo, S. K. Satija and S. Kubik, Soft Matter, 2010, 6, 4701
    DOI: 10.1039/C0SM00143K

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