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Low energy induced homolytic fragmentation of flavonol 3‐ O ‐glycosides by negative electrospray ionization tandem mass spectrometry
Author(s) -
Yang WenZhi,
Qiao Xue,
Bo Tao,
Wang Qing,
Guo DeAn,
Ye Min
Publication year - 2014
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6794
Subject(s) - chemistry , homolysis , fragmentation (computing) , tandem mass spectrometry , collision induced dissociation , glycosidic bond , electrospray ionization , aglycone , mass spectrometry , photochemistry , bond cleavage , stereochemistry , quadrupole ion trap , glycoside , ion trap , organic chemistry , radical , chromatography , computer science , enzyme , operating system , catalysis
RATIONALE Negative ESI‐QIT‐MS of several subtypes of flavonoid O ‐glycosides is known to produce deprotonated molecular ions which undergo homolytic fragmentation at the glycosidic bond upon collision‐induced dissociation (CID). However, these subtypes have never been simultaneously compared under unified MS conditions. METHODS The (−)‐ESI‐MS n fragmentations of 69 flavonoid O ‐glycosides, involving eight subtypes, were analyzed using a quadrupole ion‐trap mass spectrometer with collision energies varying from 18–44%. Factors influencing the homolytic glycosidic bond fragmentation, such as collision energy, hydroxylation of aglycone, and glycosylation pattern, were comprehensively studied. RESULTS Under the unified CID‐QIT‐MS 2 conditions, the precursor deprotonated molecular ions [M–H] – for 3‐ O ‐glycosyl, 3,7‐di‐ O ‐glycosyl and 3,6,7‐tri‐ O ‐glycosyl flavonols experienced homolytic fragmentation at the glycosidic bond and generated the radical aglycone ion [Y 0 –H] –• . This gas‐phase CID fragmentation behavior was not observed for the other subtypes. A general trend was found that hydroxyl substitution at C‐6, glycosylation at C‐6/C‐7, and acetylation of the saccharide moiety remarkably suppressed this fragmentation. In addition, flavonol 3‐ O ‐diglycosides (disaccharides) possessing a 1 → 2 glycosidic bond generated more abundant [Y 0 –H] –• product ions than those with a 1 → 3 or 1 → 6 bond. The terminal sugar triggered the homolytic fragmentation in the order Rha > Xyl > Glc. Moreover, new counterexamples were found for previously reported fragmentation rules. CONCLUSIONS The low‐energy CID homolytic fragmentation was diagnostic for structural identification of flavonol 3‐ O ‐glycosides. We have summarized key factors affecting this fragmentation. The results could be useful for rapid characterization of flavonoid O ‐glycosides in complicated herbal extracts. Copyright © 2014 John Wiley & Sons, Ltd.