Solvent-induced and temperature-induced ' 0 chemical shifts of , LeuSI-enkephalin and solvent-induced spectral modifications of the amide-I' stretching vibrations of [1-13C-Gly2, Leu51-enkephalin and [1-13C-Gly2, Leu51-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 170-NMR and Fourier transform infrared is a unique methodology for studying the hydration state of specific peptide oxygens in peptide hormones.Peptides and proteins in biological systems are usually surrounded by a predominantly aqueous solvent. Their small size, large dipole moment and high capacity for forming hydrogen bonds means that the water molecules have unique effects on peptide and protein conformations [l -31. Hydrogen-bonding interactions between the oxygen atom of the peptide groups and the molecules of water undoubtedly contribute to the overall conformational stability of peptides and proteins in aqueous medium. The knowledge of these solvent interactions is of importance for any conformational study since it is known that biomolecules often change their conformation as the solvent is varied.As a first step towards the solution of hydration of peptides and proteins, numerous experimental and theoretical investigations on the most probable sites for binding of the water molecules have been undertaken on amides [4-lo]. These molecules are considered as the simplest representatives of the peptide bond; therefore, the determination of the possible monohydrated and multihydrated species has been considered as crucial in gauging the magnitude of specific hydration of more complex peptides and proteins. Furthermore, several theoretical calculations of model peptides [11 -201 and numerous X-ray structural investigations of several peptide hydrates and proteins [21-281 revealed thermodynamical and geometrical aspects of peptide-backbone hydration.

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Chemical shifts of the amide resonances in model dipeptides at dilute concentrations are shown to be strongly dependent on the formation of (3-turns. P-Turns are frequent conformational units in proteins and peptides and their role in structure-activity relationships is emphasized throughout the literature. 132 Turns are in general stabilized by an intramolecular hydrogen bond between the