One Dimensional ¹³C-¹H Nuclear Overhauser Effect Experiments in Elucidating Solute-Solvent Interactions of CIS/Trans Isomers of β-Turn Model Peptides

Abstract

β-Turns are frequent conformational units in proteins and peptides and their role in structure-activity relationships is emphasized throughout the literature (Deslaurier and Smith, 1980; Rose et al., 1985). Turns are in general stabilized by an intramolecular hydrogen bond between the C=O of residue i and the NH, of residue i+3, particularly in cases involving heterochiral sequences (II or II′ β-turns). NMR spectroscopy is probably the most widely used method for determining the presence of β-turns in peptides in solution, although NMR data must be interpreted with great caution (Rose et al., 1985). Indeed the factors that contribute to the stability of turns in small peptides in water are not obvious. We report here the application of one-dimensional ¹³C, ¹H Overhauser effect spectroscopy (Kover and Batta, 1987; Gerothanassis et al., 1996) of [¹³C]Ac-L- Pro-D-Ala-NHMe in H₂O at 273 K which provides valuable information of solute-solvent interactions of the cis/rans carbonyl carbon atom, 98% ¹³C enriched.