Evaluation of noncovalent interactions between peptides and polyether compounds via energy-variable collisionally activated dissociation.

Energy-variable collisionally activated dissociation (CAD) was used to analyze noncovalent interactions of protonated peptide/polyether complexes in a quadrupole ion trap complexes were formed with a series of four polyether host molecules and thirteen peptide molecules. Comparison of dissociation thresholds revealed correlations between the gas-phase basicities of the peptides and polyether molecules and the onset of dissociation. The dissociation thresholds of complexes containing the tripeptides or pentapeptides were inversely proportional to the gas-phase basicities of the sites of protonation of the peptides. Intramolecular hydrogen bonding of the pentapeptides affected the observed dissociation thresholds as well. The dissociation thresholds also scaled proportionally to the gas-phase basicities of the polyethers in the complexes, and the importance of the conformational flexibility of the polyether ligand was confirmed for one of the histidine-containing tripeptide complexes.