title: Zwitterion formation in gas-phase cyclodextrin complexes.
abstract: Protonated complexes of amino acids and underivatized beta-cyclodextrin, produced by electrospray ionization and trapped in the Fourier transform mass spectrometer, undergo formation of ternary complexes when reacted with alkyl amine. Based on the reactivities of the protonated amino acid complexes with alkylamines, the reactivities of the corresponding amino acid esters, and partially derivatized beta-cyclodextrin hosts, we conclude that the ternary complexes are salt-bridge zwitterionic species composed of amino acid zwitterions and protonated alkylamine all interacting with the hydroxyl groups on the narrow rim of the cyclodextrin. Molecular modeling calculations and experimental results suggest that the interactions of the amino acids with the rims contribute greatly to the formation of the zwitterionic species.
authors.affiliation: Department of Chemistry, School of Medicine, University of California at Davis, Davis, California 95616, USA.
authors.forename: Seonghee
authors.initials: S
authors.lastname: Ahn
authors.forename: Xin
authors.initials: X
authors.lastname: Cong
authors.forename: Carlito B
authors.initials: CB
authors.lastname: Lebrilla
authors.forename: Scott
authors.initials: S
authors.lastname: Gronert
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D005740:Gases / Q000737:chemistry*; D007700:Kinetics; D046911:Macromolecular Substances / Q000737:chemistry; D013058:Mass Spectrometry; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D020836:Protein Structure, Quaternary; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism; D047392:beta-Cyclodextrins / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D005740:Gases; D046911:Macromolecular Substances; D047392:beta-Cyclodextrins; C031215:betadex