N-ethylformamide dimer. A β-turn model peptide in the gas phase

Reported here are CP-FTMW experiments on N-ethylformamide (NEF), previously studied by pure rotational spectroscopy in the gas phase by Hirota and co-workers (2005). Two conformers of the monomer (trans sc and cis ac), the trans-trans sc dimer, and several NEF-water complexes have been detected. (Only trans sc was observed in the earlier experiments.) Of these species, the trans-trans sc dimer is the most interesting since its three-dimensional structure bears a striking resemblance to β-turns in folded peptides. The well-known anti-parallel β-sheet structures would be expected to have near-zero dipole moments and are therefore discriminated against by the CP-FTMW method