Hydration of the Gly2 and Gly3 peptide oxygens of [Leu5]-enkephalin in aqueous solution as revealed by the combined use of 17O-NMR and Fourier-transform infrared spectroscopy

Abstract

Solvent-induced and temperature-induced 17O chemical shifts of [17O-Gly2, Leu5]-enkephalin and [17O-Gly3, Leu5]-enkephalin and solvent-induced spectral modifications of the amide-I' stretching vibrations of [1-13C-Gly2, Leu5]-enkephalin and [1-13C-Gly2, Leu5]-enkephalin are reported and correlated with the spectroscopic characteristics of model amides. It is demonstrated that both Gly2 and Gly3 peptide oxygens are motionally equivalent and form solvation species which are essentially monohydrated in aqueous solution, contrary to several simple amides and model peptides in which water largely forms dihydrates. It is shown that the combined use of 17O-NMR and Fourier transform infrared is a unique methodology for studying the hydration state of specific peptide oxygens in peptide hormones.