Multiple lithium exchange under lithium cationization of cyclodextrins.
Multiple lithium exchange is observed during electrospray ionization of alpha-, beta- and gamma-cyclodextrins from aqueous methanolic solution containing LiOH. Apart from [M + Li](+) and [M + nLi - (n - 1)H](+) ions, abundant multiply lithiated doubly charged ions corresponding to [M + nLi - (n - 2)H](2+) ions were observed. At least six lithium exchanges in alpha-cyclodextrin, seven in beta-cyclodextrin and eight in gamma-cyclodextrin were noted. The propensity of multiply lithiated doubly charged ions is much less in the open-ended maltoheptaose. It appears that during droplet or cluster formation and subsequent desolvation, LiOH trapped in the cavity of cyclodextrin reacts to form multiply lithiated ions. The singly charged [M + Li](+) and doubly charged [M + 2Li](2+) ions fragment by glycosidic cleavages, giving B series of ions, whereas the multiply lithiated ions fragment by cross ring cleavages ((2, 4)A or (O, 2)X) followed by glycosidic cleavage. From the tandem mass spectra, it appears that a maximum of two lithium exchanges occur in one sugar unit in these cyclodextrins.
Madhusudanan
K P
KP
Regional Sophisticated Instrumentation Centre, Central Drug Research Institute, Lucknow-226 001, India. kpmadhusudanan@hotmail.com
D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002412:Cations / Q000737:chemistry; D003505:Cyclodextrins / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry*; D013058:Mass Spectrometry; D015394:Molecular Structure; D021241:Spectrometry, Mass, Electrospray Ionization
D002412:Cations; D003505:Cyclodextrins; D008094:Lithium