Electric dipole moments and conformations of isolated peptides

The electric dipole moments of the isolated amino acid tryptophan and small glycine-based peptides (WG(n), n = 1-5, W = tryptophan, G = glycine) have been measured by deflection of a molecular beam in an inhomogeneous electric field.. The measurements are compared to the results of ab initio calculations and Monte-Carlo simulations. The conformation and the flexibility of the peptides, at different temperatures, are discussed. The WG(n) peptides are much more floppy than an isolated tryptophan, even a single glycine is enough to make the peptide floppy on the timescale of the electric deflection measurements.