Solution and solid-state models of peptide CH...O hydrogen bonds.

Fumaramide derivatives were analyzed in solution by 1H NMR spectroscopy and in the solid state by X-ray crystallography in order to characterize the formation of CH···O interactions under each condition and to thereby serve as models for these interactions in peptide and protein structure. Solutions of fumaramides at 10 mM in CDCl3 were titrated with DMSO-d6, resulting in chemical shifts that moved downfield for the CH groups thought to participate in CH···OS(CD3)2 hydrogen bonds concurrent with NH···OS(CD3)2 hydrogen bonding. In this model, nonparticipating CH groups under the same conditions showed no significant change in chemical shifts between 0.0 and 1.0 M DMSO-d6 and then moved upfield at higher DMSO-d6 concentrations. At concentrations above 1.0 M DMSO-d6, the directed CH···OS(CD3)2 hydrogen bonds provide protection from random DMSO-d6 contact and prevent the chemical shifts for participating CH groups from moving upfield beyond the original value observed in CDCl3. X-ray crystal structures identi...