Infrared photon echo signatures of hydrogen bond connectivity in the cyclic decapeptide antamanide

Distinct hydrogen bonding patterns are predicted in the amide I and amide A vibrational bands of four dominant conformations of antamanide using anharmonic vibrational Hamiltonians constructed at the DFT and AM1 levels. We show how these conformations may be distinguished using coherent three pulse infrared measurements with several pulse polarization configurations in the amide I region. The amide A hydrogen bonded N–H stretching modes are highly localized and have conformation-dependent frequencies, but their anharmonicities are insensitive to local structure at the hydrogen bond distances in antamanide.