Lyotropic Liquid Crystals from Designed Helical β-Peptides

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Abstract
We demonstrate that 14-helical β-peptides can self-assemble to form lyotropic liquid crystalline (LC) phases in water. β-Peptides 1−4 were designed to form globally amphiphilic 14-helices of increasing length. Optical microscopy showed that several of these β-peptides formed LC phases in aqueous solutions at concentrations as low as 2.5 wt % (15 mM). Liquid crystallinity appears to require the adoption of a globally amphiphilic conformation because a scrambled sequence, 5, does not display LC behavior. Thermal stability and reversibility of LC phase formation were assessed by variable temperature 2H NMR spectroscopy and optical microscopy. The LC phase formed by β-peptide 3 at 10 wt % is disrupted above 40 °C in D2O and re-forms within minutes upon cooling. LC phase behavior for solutions of 3 is influenced by concentration and net charge. These studies demonstrate that highly folded 14-helical β-peptides can produce LC phases at shorter lengths than do α-helical α-peptide mesogens and can provide a basis for tailoring properties of LC phases for future applications.