title: Studies on transition metal-quercetin complexes using electrospray ionization tandem mass spectrometry.
abstract: To systematically study the effects of the number of d electrons of the first transition metal ions (Fe, Co, Ni, Cu and Zn) on the formation and stability of metal flavonoid complexes, we took the quercetin/M2+ complex as a model system to investigate the structures and properties of these complexes. Based on considerable structural information obtained through ESI-MSn, all of the first transition metal ions (Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) were found to form different complexes with quercetin, while with the number of chelating flavonoids decreasing along with the reduction of the metal ionic radius. Quercetin forms different complexes with the above metal divalent ions through its 5-OH and 4-carbonyl groups; the complex stability is highly dependent on both the metallic ion and the flavonoid chelator itself. As for the central ion (M2+), when chelated with quercetin to form the complex, the stability of the complex decreased in the following order: Cu2+ > Ni2+ > Co2+ > Fe2+ > Zn2+. With flavonoid: metal stoichiometries at 2:1, the complexes formed between quercetin and metal ions (Fe2+, Ni2+, Co2+ and Zn2+) have the similar fragmentation mechanism, while Cu2+ displayed different fragmentation mechanism due to the concurrent oxidation.
authors.affiliation: Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture, Wuhan Botanical Garden of Chinese Academy of Sciences, Wuhan 430074, China. lyz19851001@wbgcas.cn.
authors.forename: Yuanzhen
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture, Wuhan Botanical Garden of Chinese Academy of Sciences, Wuhan 430074, China. guomq@wbgcas.cn.|The Keck School of Medicine, University of Southern California, Los Angeles, CA 90089, USA. guomq@wbgcas.cn.
authors.forename: Mingquan
authors.initials: M
authors.lastname: Guo
mesh_terms: D002614:Chelating Agents / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry; D004583:Electrons; D005419:Flavonoids / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D009532:Nickel / Q000737:chemistry; D011794:Quercetin / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D028561:Transition Elements / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry
chemical_list: D002614:Chelating Agents; D056831:Coordination Complexes; D005419:Flavonoids; D028561:Transition Elements; D003035:Cobalt; D003300:Copper; D009532:Nickel; D011794:Quercetin; D007501:Iron; D015032:Zinc
keywords: CID; ESI-MSn; flavonoid; fragmentation mechanism; metal complexes