Lyotropic liquid crystals from designed helical β-peptides

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.