title: Aqueous solution speciation of Fe(III) complexes with dihydroxamate siderophores alcaligin and rhodotorulic acid and synthetic analogues using electrospray ionization mass spectrometry.
abstract: Aqueous solutions of Fe3+ complexes of cyclic (alcaligin) and linear (rhodotorulic acid) dihydroxamate siderophores and synthetic linear eight-carbon-chain and two-carbon-chain dihydroxamic acids ([CH3N(OH)C=O)]2(CH2)n; H2Ln; n = 2 and 8) were investigated by electrospray ionization mass spectrometry (ESI-MS). Information was obtained relevant to the structure and the speciation of various Fe(III)-dihydroxamate complexes present in aqueous solution by (1) comparing different ionization techniques (ESI and FAB), (2) altering the experimental parameters (Fe3+/ligand ratio, pH, cone voltage), (3) using high-stability hexacoordinated Fe(III) siderophore complex mixtures (ferrioxamine B/ferrioxamine E) as a calibrant to quantify intrinsically neutral (H+ clustered or protonated) and intrinsically charged complexes, and (4) using mixed-metal complexes containing Fe3+, Ga3+, and Al3+. These results illustrate that for all dihydroxamic acid ligands investigated multiple tris- and bis-chelated mono- and di-Fe(III) species are present in relative concentrations that depend on the pH and Fe/L ratio.
authors.affiliation: Department of Chemistry, Duke University, Box 90346, Durham, North Carolina 27708, USA.
authors.forename: I
authors.initials: I
authors.lastname: Spasojević
authors.forename: H
authors.initials: H
authors.lastname: Boukhalfa
authors.forename: R D
authors.initials: RD
authors.lastname: Stevens
authors.forename: A L
authors.initials: AL
authors.lastname: Crumbliss
mesh_terms: D002138:Calibration; D006877:Hydroxamic Acids; D007501:Iron; D008958:Models, Molecular; D008968:Molecular Conformation; D010879:Piperazines / Q000737:chemistry*; D017262:Siderophores / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013329:Structure-Activity Relationship
chemical_list: D006877:Hydroxamic Acids; D010879:Piperazines; D017262:Siderophores; C092056:alcaligin; C003305:rhodotorulic acid; D007501:Iron