title: MALDI-MS of flavonoids: a systematic investigation of ionization and in-source dissociation mechanisms.
abstract: Matrix assisted laser desorption ionization (MALDI) is a technique widely employed in the analysis of proteins and peptides, and nowadays it has also been applied to small molecules. There is little significant information regarding the in-source dissociation processes on MALDI for natural products. Twenty-six flavonoids (flavanones, flavones and flavonols) were analyzed by MALDI using different methods (with different matrices) and without matrix to comprehend the in-source reactions and establish good analysis methods for these compounds. Depending on the class, structure and the laser intensity applied, methoxylated flavonoid aglycones can eliminate methyl radicals (˙CH3) in the source, such as flavonols, but lithium 2,4-dihydroxybenzoate matrix suppresses the ˙CH3 eliminations and retro-Diels-Alder cleavages in the source. All of the flavonoid O-glycosides evaluated herein eliminated the sugar in source, even in the presence of the matrix, and its product radical ions ([M-H-sugar](-)˙) were observed in the negative mode. The flavone C-glycosides suffered intense dissociation, which was reduced by the addition of a matrix and the application of low laser intensity, mainly in the negative mode. Depending on the hydroxyl substituents, the [M-H-H](-)˙ ion was observed with variable relative intensity in the spectra.
authors.affiliation: Núcleo Pesquisas em Produtos Naturais e Sintéticos, Department of Physics and Chemistry, Faculty of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, 14040-903, Ribeirão Preto, SP, Brazil.
authors.forename: Denise B
authors.initials: DB
authors.lastname: Silva
authors.forename: Norberto P
authors.initials: NP
authors.lastname: Lopes
mesh_terms: D044950:Flavanones / Q000032:analysis / Q000737:chemistry; D047309:Flavones / Q000032:analysis / Q000737:chemistry; D005419:Flavonoids / Q000032:analysis* / Q000737:chemistry; D044948:Flavonols / Q000032:analysis / Q000737:chemistry; D006027:Glycosides / Q000737:chemistry; D062385:Hydroxybenzoates / Q000737:chemistry; D015394:Molecular Structure; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D044950:Flavanones; D047309:Flavones; D005419:Flavonoids; D044948:Flavonols; D006027:Glycosides; D062385:Hydroxybenzoates; C017704:beta-resorcylic acid
keywords: MALDI; dissociation; flavanones; flavone; flavonol