The use of heated capillary dissociation and collision-induced dissociation to determine the strength of noncovalent bonding interactions in gas-phase peptide-cyclodextrin complexes

Complexes of four peptides and permethylated-beta-cyclodextrin are produced in the gas phase by using electrospray ionization. The four peptides-bradykinin (BK), des-Arg-1 bradykinin (dR(1)BK), des-Arg-9-bradykinin (dR(9)BK), and Gly-5-Gly-8-bradykinin (G(5)G(8)BK)-were chosen because the relative inclusion and protonation sites varied with each peptide. Collision-induced dissociation (CID) was performed to determine the dissociation threshold of the four complexes. Heated capillary dissociation (HCD) was used to determine the dissociation temperatures of the peptide complexes. CID and HCD indicate the same ordering of stability in the complexation of the peptides to the oligosaccharides. Increasing strength of interaction follows the order dR(9)BK < BK < dR(1)BK approximate to G(5)G(8)BK. The absence of Arg-9 destabilizes the complex, whereas the absence of Arg-1 stabilizes it relative to BK. Replacing both Phe residues with Gly similarly strengthens the interaction, suggesting that the Phe destabilizes the complex. CID and HCD are useful methods for obtaining relative strengths of interaction in noncovalent bound complexes. (C) 1997 American Society for Mass Spectrometry.