Quantifying non‐covalent binding affinity using mass spectrometry: A systematic study on complexes of cyclodextrins with alkali metal cations. (6th April 2015)

• Record Type: Journal Article
• Authors: Wei, Wanghui; Chu, Yanqiu; Wang, Rizhi; He, Xiaodan; Ding, Chuanfan
• Is Part Of: Rapid communications in mass spectrometry. Volume 29:Number 10(2015)
• Page Start: 927
• Page End: 936
• Publication Date: 2015-04-06
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.7181
• Languages: English
• ISSNs: 0951-4198

Abstract

Abstract : Rationale: To date, the quantification of binding affinities for non‐covalent complexes between cyclodextrin (CD) and alkali cations including Li +, Na +, K +, Rb +, and Cs + has not been investigated in detail by electrospray ionization mass spectrometry (ESI‐MS) due to the unknown ionization efficiencies of the different species. In this study, the binding constants of CD‐Cs + complexes were determined by an improved mass spectrometric titration methodology, which was based only on the peak intensities of equilibrium CD. Hence, the discrepancy of ionization efficiencies of CD, alkaline cation and their complex would not affect the measurement. Then the obtained lg Ka values were provided as references for competitive ESI‐MS. The binding constants for complexes of α‐, β‐ or γ‐CD with Li +, Na +, K + and Rb + could be derived directly and quickly. Methods: The lg Ka values between α‐, β‐ or γ‐CD and Cs + data were processed by curve fitting. These lg Ka values were provided as references for competitive ESI‐MS. In addition, linear fit equations for complexes of α‐, β‐ or γ‐CD with Cs + were derived. Through the linear fit equations of competitive ESI‐MS, the binding constants for complexes of Li +, Na +, K + and Rb + with α‐, β‐ or γ‐CD were acquired. Results: Results showed that the binding constant (lg Ka ) values for the complexes of Cs + with α‐, β‐ and γ‐cyclodextrins were 3.94, 3.88 and 3.80, respectively, revealing that the binding strength decreased with the increase in diameter of cyclodextrins. The competitive ESI‐MS results showed a clear trend of decreasing affinity for complexes of cyclodextrins in the order of Li +, Na +, K +, Rb + . Conclusions: The binding constants of non‐covalent cyclodextrin‐alkali cation complexes have been systematically studied by an improved mass spectrometric titration and competitive ESI‐MS. Also, the structural features of the complexes were discussed. Our results are valuable for better understanding of mechanisms driving inclusion chemistry under well‐defined conditions. Copyright © 2015 John Wiley & Sons, Ltd.