Probing secondary structures of end-capped tripeptide, BOC-Phe-Aib-Leu-OMe by combined study of infrared spectroscopy and quantum chemistry calculation

► Probed secondary structures of BOC-Phe-Aib-Leu-OMe in CCl4 solution and solid state. ► FTIR spectroscopy and quantum chemistry computations are used in the study. ► Study reveals largely different secondary structures in solid and solution phases. ► A β-turn structure in solid crystal, whereas the solution contains γ-turns.