title: Intrinsic properties of α-cyclodextrin complexes with benzoate derivatives in the gas phase: an experimental and theoretical study.
abstract: The noncovalent interactions in host-guest complexes of α-cyclodextrin (α-CD) with a series of benzoic acid derivatives (RBA) were investigated by electrospray ionization tandem mass spectrometry and density functional theory (DFT) calculations. The 1:1 stoichiometry of the anionic host-guest complexes was unequivocally confirmed by their mass-to-charge ratios (m/z) and isotope patterns. Collision-induced dissociation experiments revealed exclusive fragmentation into [α-CD](-) and neutral RBA and afforded the gas-phase kinetic stability trend [α-CD·3,5-diMeBA](-) < [α-CD·3-MeBA](-) < [α-CD·BA](-) < [α-CD·3-OHBA](-) < [α-CD·3,5-diOHBA](-). This trend follows that of the gas-phase basicities of the guest anions used, indicating that host-guest pairs with more comparable basicities form more stable complexes. DFT calculations at the M06-L/6-31+G(d,p) level of theory provided detailed structural assignments and further elucidated the experimental observations, suggesting that the anionic [α-CD·RBA](-) inclusion complexes are favored over the nonspecific complexes in the gas phase and that hydrogen bonding constitutes the primary host-guest interaction. Additionally, the results provide an estimated gas-phase basicity ΔG(0) = 325-327 kcal mol(-1) for [α-CD](-).
authors.affiliation: Laboratorium für Organische Chemie, ETH Zürich, Wolfgang-Pauli-Strasse 10, CH-8093, Switzerland.
authors.forename: Zhongshu
authors.initials: Z
authors.lastname: Li
authors.forename: Erik P A
authors.initials: EP
authors.lastname: Couzijn
authors.forename: Xiangyang
authors.initials: X
authors.lastname: Zhang
mesh_terms: D001565:Benzoates / Q000737:chemistry*; D005740:Gases; D006860:Hydrogen Bonding; D008962:Models, Theoretical; D015394:Molecular Structure; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D047391:alpha-Cyclodextrins / Q000737:chemistry*
chemical_list: D001565:Benzoates; D005740:Gases; D047391:alpha-Cyclodextrins