International Journal of Mass Spectrometry 301 (2011) 174–183 Contents lists available at ScienceDirect International Journal of Mass Spectrometry journal homepage: www.elsevier.com/locate/ijms The formation and fragmentation of flavonoid radical anions  Linda Feketeová a,b,c , Christopher K. Barlow a,b,c , Timothy M. Benton a,b,c , Simone J. Rochfort d , Richard A.J. O’Hair a,b,c,∗ a School of Chemistry, The University of Melbourne, Australia b Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Victoria 3010, Australia c ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, Australia d Discovery Technologies, Biosciences Research, Department of Primary Industries, Primary Industries Research Victoria - Werribee Centre, Australia article info Article history: Received 21 April 2010 Received in revised form 17 August 2010 Accepted 18 August 2010 Available online 26 August 2010 Dedicated to Professor Michael Gross, on the occasion of his 70th birthday and in recognition of his important contributions to organic, organometallic and biological mass spectrometry and his service to the mass spectrometry community. Keywords: Metal complex Collision-induced dissociation Electrospray ionization Flavonoid Radical anion abstract Negative electrospray ionization of iron(III) salen complex of flavonoids, M, was used in conjunc- tion with collision-induced dissociation (CID) to examine the formation and subsequent fragmentation reactions of their radical anions [M−2H] •− . Sixteen different flavonoids were investigated from three different sub-groups (flavanone, flavone and flavanol). All formed the desired iron salen complex, [Fe III (salen)(M−2H)] − , and all but one of these complexes produced the radical anion upon CID. The CID fragmentation reactions of these radical anions, [M−2H] •− , were compared to their even electron counterparts [M−H] − . Generally the former provided more structural information, with novel cross-ring cleavages of sugar(s) often being observed. Isomeric flavonoids can often be distinguished based on the differences in the fragmentation pathways of their radical anions. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. 1. Introduction Since the first mass spectrometry based study on peptides using electron ionization (EI) appeared over 50 years ago [1], the diverse nature of biomolecules has offered interesting challenges and opportunities for the mass spectrometry community. Over the intervening period, two major breakthroughs have occurred: (i) the invention of a series of new ionization methods; (ii) the devel- opment of tandem mass spectrometry techniques. Professor Mike Gross has been at the forefront of applying these new technolo- gies to address fundamental and applied problems for different classes of biomolecules. Some of the highlights of his pioneering work include: (i) development and application of the powerful combination of fast atom bombardment (FAB) and tandem mass spectrometry on multisector instruments [2] for the analysis of a range of biomolecules including cyclopeptides [3], lipids [4] and  Part 72 of the series “Gas-Phase Ion Chemistry of Biomolecules”. ∗ Corresponding author at: School of Chemistry, The University of Melbourne, Parkville, Vic. 3010, Australia. Tel.: +61 3 8344 2452; fax: +61 3 9347 5180. E-mail address: rohair@unimelb.edu.au (R.A.J. O’Hair). nucleic acids [5]; (ii) the discovery [6] and coining of the term “charge remote fragmentation” [7,8]; (iii) some of the first studies on the gas phase chemistry of metal–peptide interactions [9]. Although radical cleavage reactions of biomolecules have been known from early EI/MS studies [10] and from high energy CID of FAB generated [M+H] + [11], these have largely remained a curios- ity due to challenges with volatility or ready access to appropriate instrumentation. Thus a major contemporary research theme in bioanalytical mass spectrometry has been the development of new methods that utilize radical cleavage reactions to gain novel structural information. While most efforts have been devoted to methods with potential applications in the analysis of peptides and proteins [12,13], reports have also appeared on other classes of biomolecules, including oliogonucleotides [14–21], oligosac- charides [22–24] and lipids [25,26]. The new types of radical fragmentation methods developed fall into four broad areas: (i) Ion–electron interactions, which can be further classified according to the nature of the ion (e.g., multiply charged versus singly charged, cation versus anion), the energy of the electron and the nature of the radical chemistry (for reviews see [27,28]). 1387-3806/$ – see front matter Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.ijms.2010.08.017