Dinuclear [(V(V)O(putrebactin))2(μ-OCH3)2] formed in solution as established from LC-MS measurements using 50V-enriched V2O5.
Analysis of 1:1 solutions of V(V) and the macrocyclic dihydroxamic acid siderophore putrebactin (pbH2) in 1:1 H2O/CH3OH using triple quadrupole liquid chromatography-mass spectrometry (LC-MS-QQQ) (pH ≈ 4) showed two well-resolved peaks (tR(1) 10.85 min; tR(2) 14.27 min) using simultaneous detection modes (absorbance, 450 nm; selective ion monitoring, m/z 437) characteristic of the previously identified oxidoV(V) complex [V(V)O(pb)](+) ([M](+), m/zcalc 437.1). Peak 1 gave mass spectrometry (MS) signals consistent with [V(V)O(pb)](+), together with [V(V)O(pb)(OH)] and the dinuclear complexes [(V(V)O(pb))2(μ-OH)](+) and [(V(V)O(pb))2(μ-OH)2]. Peak 2 gave MS signals consistent with [V(V)O(pb)](+), together with [V(V)O(pb)(OCH3)] and the dinuclear complexes [(V(V)O(pb))2(μ-OCH3)](+) and [(V(V)O(pb))2(μ-OCH3)2]. This analysis showed that two groups of V(V)/pbH2 complexes with water- or methanol-derived ancillary ligands were resolved by liquid chromatography (LC). The detection of [V(V)O(pb)](+) in both peaks could be accounted for by its production from dissociation (peak 1: [(V(V)O(pb))2(μ-OH)](+) → [V(V)O(pb)](+) + [V(V)O(pb)(OH)]; peak 2: [(V(V)O(pb))2(μ-OCH3)](+) → [V(V)O(pb)](+) + [V(V)O(pb)(OCH3)]). The assignment of the signal at m/zobs 959.2 (100%) as the dinuclear complex [(V(V)O(pb))2(μ-OCH3)2] ([M + Na(+)](+), m/zcalc 959.3) and not an ion cluster of mononuclear [V(V)O(pb)(OCH3)] ({2[M] + Na(+)}(+), m/zcalc 959.3) was made unequivocal by the use of (50)V-enriched V2O5, which gave a signal with an isotope pattern comprising the sum of the patterns of the three constituent (51)V-(51)V, (51)V-(50)V, and (50)V-(50)V species. Coordination of methoxide was confirmed upon the replacement of CH3OH with CD3OD, which generated [(V(V)O(pb))2(μ-OCD3)2] ([M + Na(+)](+), m/zcalc 965.3, m/zobs 965.3). Analysis of 1:1 solutions of Mo(VI) and pbH2 showed a single peak in the LC (tR 16.04 min), which gave MS signals that were characterized as mononuclear [Mo(VI)(O)2(pb)] ([M + Na(+)](+), m/zcalc 523.1, m/zobs 523.1) and dinuclear [(Mo(VI)O(pb))2(μ-O)2] ([M + Na(+)](+), m/zcalc 1019.1, m/zobs 1019.2). The steric and electronic effects of the cis-dioxido group(s) in [Mo(VI)(O)2(pb)] mitigated coordination of solvent-derived ancillary ligands. The work highlights the value of using isotopically enriched metal ion sources and deuterated solvents to deconvolute metal/siderophore solution speciation. The results have relevance for an improved understanding of the coordination chemistry of pbH2 and other marine siderophores in V(V)- and Mo(VI)-rich surface ocean waters.
School of Medical Sciences (Pharmacology) and Bosch Institute and ‡School of Chemistry, The University of Sydney , Sydney, New South Wales 2006, Australia.
Cho Zin
CZ
Soe
Amalie A H
AA
Pakchung
Rachel
R
Codd
D002853:Chromatography, Liquid / Q000379:methods*; D013058:Mass Spectrometry / Q000379:methods*; D015394:Molecular Structure; D017968:Vanadium Compounds / Q000737:chemistry*
D017968:Vanadium Compounds