Picosecond conformational transition of a cyclic peptide observed by infrared spectroscopy

By visible-pump/infrared-probe spectroscopy, a cyclic octapeptide with a photoswitchable azobenzene based pseudo amino acid (AMPB) embedded in its backbone is investigated. The linear corresponding molecule is used as a reference. The AMPB molecule can be switched by light between a cis and trans conformation. NMR investigations on bcAMPB show an ensemble of a few structures for the cis state and a well defined one for the trans state. A visible pump pulse is used to start the conformational change by switching the AMPB from cis to trans. The probe pulse covers a range of 1600 cm/sup -1/ to 1750 cm/sup -1/ with a time resolution of 0.7 ps.