Surprise Route To Peptoid Nanosheets

Nanosheets composed of amphiphilic peptoids (peptide analogs) assemble by an unexpected mechanism that may be applicable to other types of nanosheets. Peptoid nanosheets were first reported last year (C&EN, April 19, 2010, page 7). Their potential applications include sensing, templating, filtering, molecular recognition, and catalysis. Ronald N. Zuckermann and coworkers at Lawrence Berkeley National Laboratory’s Molecular Foundry, who developed the nanosheets, initially believed they form by a nucleation and growth mechanism in which small peptoid oligomers act as “seeds” for nanosheet assembly. They now find instead that amphiphilic peptoids align at the air-water interface to create monolayers, and that surface compression, which occurs when the vial is shaken, causes the monolayers to collapse into nanosheets (J. Am. Chem. Soc., DOI: 10.1021/ja206199d). In the nanosheet bilayer, hydrophilic groups are on the outer surface and hydrophobic groups are inside. Nanosheet formation is irreversible, so more than 95% of peptoids in solution can be converted. This preparative route may also be useful in making nanosheets from other building blocks, Zuckermann says.