Multiple lithium exchange under lithium cationization of cyclodextrins.

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Carbohydrate Chemistry

Background:

• Cyclodextrins are cyclic oligosaccharides with unique cavity structures.
• Electrospray ionization (ESI) is a common technique for analyzing biomolecules.
• Lithium ions can be incorporated into molecular ions during ESI.

Purpose of the Study:

• To investigate the extent and mechanism of lithium exchange in alpha-, beta-, and gamma-cyclodextrins during ESI.
• To characterize the fragmentation patterns of lithiated cyclodextrin ions.
• To compare lithium exchange in cyclodextrins versus linear oligosaccharides.

Main Methods:

• Electrospray ionization mass spectrometry (ESI-MS) of cyclodextrins in aqueous methanolic solution with LiOH.
• Tandem mass spectrometry (MS/MS) to analyze fragmentation pathways.
• Comparison of lithiation in cyclodextrins and maltoheptaose.

Main Results:

• Multiple lithium exchanges were observed in alpha-, beta-, and gamma-cyclodextrins, with up to 6, 7, and 8 lithium ions incorporated, respectively.
• Abundant multiply lithiated doubly charged ions ([M + nLi - (n - 2)H](2+)) were detected.
• Lithium exchange was less prevalent in the linear maltoheptaose.
• Fragmentation patterns differed based on ion charge state and lithium content, involving glycosidic and cross-ring cleavages.
• A maximum of two lithium exchanges per sugar unit was inferred.

Conclusions:

• The cavity structure of cyclodextrins facilitates extensive lithium exchange during ESI.
• LiOH trapped within the cyclodextrin cavity likely plays a role in multiply lithiated ion formation.
• Fragmentation analysis provides insights into the structure and stability of lithiated cyclodextrin ions.