title: Balance of xanthophylls molecular and protonated molecular ions in electrospray ionization.
abstract: This paper reports the chemical evidence of the balance between radical molecular ions and protonatedmolecules of xanthophylls (an oxygen-containing carotenoid) with a conjugated pi-system (polyene) and oxygen as a heteroatom in ESI and HRESI mass spectrometry. The ionization energy of neutral xanthophylls was calculated by semi-empirical methods. The results were compared with those previously published for carotenoids and retinoids, which have also been shown in ESI-MS to form M(+*) and [M + H](+), respectively. This study demonstrates, for the first time, the correlation of an extended conjugation and the presence of oxygen in the formation and balance of M(+*) or [M + H](+) for the carotenoids, neoxanthin, lutein, violaxanthin and zeaxanthin.
authors.affiliation: Universidade de São Paulo, Instituto de Química, Departamento de Bioquímica, Av Professor Lineu Prestes, 748 CP 20780, CEP 05508900, São Paulo-SP, Brazil.
authors.forename: Thais
authors.initials: T
authors.lastname: Guaratini
authors.forename: Ricardo
authors.initials: R
authors.lastname: Vessecchi
authors.forename: Ernani
authors.initials: E
authors.lastname: Pinto
authors.forename: Pio
authors.initials: P
authors.lastname: Colepicolo
authors.forename: Norberto P
authors.initials: NP
authors.lastname: Lopes
mesh_terms: D007477:Ions / Q000737:chemistry; D014975:Lutein / Q000737:chemistry; D015394:Molecular Structure; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization; D024341:Xanthophylls / Q000096:biosynthesis / Q000737:chemistry*; D065146:Zeaxanthins; D019207:beta Carotene / Q000031:analogs & derivatives / Q000737:chemistry
chemical_list: D007477:Ions; D011522:Protons; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene; C031140:antheraxanthin; C005613:violaxanthin; C011947:neoxanthin; D014975:Lutein