Long Range Hydrogen Bond Mediated Effects in Peptides: ¹⁵N NMR Study of Gramicidin S in Water and Organic Solvents

The chemical shifts of the ¹⁵N's of the cyclic peptide gramicidin S in dilute aqueous solution were measured and assigned with use of polarization transfer via scalar coupling (INEPT). Long-range perturbations were detected in the ¹⁵N spectrum from comparison of these results and those in organic solvents. The effects are transmitted from one peptide linkage to another via an intramolecular hydrogen bond across a total of six bonds. The variation with temperature of the ¹⁵N shifts in these solvents further corroborates the roles of the intramolecular hydrogen bond in the propagation of shift effects. From the long-range effects it is possible to examine the relationship between solvent-peptide interactions and the properties of internal hydrogen bonds.