Exploring halide anion affinities to native cyclodextrins by mass spectrometry and molecular modelling

• Published in: European journal of mass spectrometry (Chichester, England) Vol. 24; no. 3; p. 269
• Main Authors: Xu, Chongsheng, He, Nan, Li, Zhenhua, Chu, Yanqiu, Ding, Chuan-Fan
• Format: Journal Article
• Language: English
• Published: England 01.06.2018
• Subjects: density functional calculation; mass spectrometry; Cyclodextrins; halide anions; inclusion complexes
• ISSN: 1469-0667
• DOI: 10.1177/1469066717748658

The binding affinities of cyclodextrins complexation with chlorine (Cl ), bromine (Br ) and iodine (I ), were measured by mass spectrometric titrimetry, and the fitting of the binding constants was based on the concentration measurement of the cyclodextrin equilibrium. The binding constants (lg K ) for α-, β- or γ-cyclodextrin with Cl were 3.99, 4.03 and 4.11, respectively. The gas-phase binding affinity of halide anions for native cyclodextrins was probed by collision-induced dissociation. In collision-induced dissociation, the centre-of-mass frame energy results revealed that in the gas phase, for the same type of cyclodextrin, the stability of the complexes decreased in order: Cl > Br > I, and for the same halide anion, the binding stability of the complex with α-, β- or γ-cyclodextrin decreased in the order: γ-cyclodextrin >β-cyclodextrin > α-cyclodextrin. The density functional theory calculations showed that halide anion binding on the primary face had a lower energy than the secondary face and hydrogen bonding was the main driving force for complex formation. The higher stability of the γ-cyclodextrin complex with the Cl anion can be attributed to the higher charge density of the Cl anion and better flexibility of γ-cyclodextrin.