Equilibrium Exchange Processes of the Aqueous Tryptophan Dipeptide

The tryptophan dipeptide (NATMA) in D2O shows two conformers having distinctive acetyl end amide-I' transition frequencies. In two dimensional echo spectroscopy cross peaks between these conformer transitions are used to show they are undergoing exchange on the 1.5 ps time scale. Simulations suggest that the accessibility of the amide group to water is restricted in one of the conformations.