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Production and Characterization of Desmalonichrome Relative Binding Affinity for Uranyl Ions in Relation to Other Siderophores

Mo, Kai-For, Dai, Ziyu, Wunschel, David S.
Journal of natural products 2016 v.79 no.6 pp. 1492-1499
Fusarium oxysporum, acetates, binding capacity, chelating agents, chelation, deferoxamine, electrospray ionization mass spectrometry, fungi, ions, iron, iron chlorides, ligands, pH, secondary metabolites, siderophores
Siderophores are iron (Fe)-binding secondary metabolites that have been investigated for their uranium-binding properties. Previous work has focused on characterizing hydroxamate types of siderophores, such as desferrioxamine B, for their uranyl (UO₂)-binding affinity. Carboxylate forms of these metabolites hold potential to be more efficient chelators of UO₂, yet they have not been widely studied. Desmalonichrome is a carboxylate siderophore that is not commercially available and so was obtained from the fungus Fusarium oxysporum cultivated under Fe-depleted conditions. The relative affinity for UO₂ binding of desmalonichrome was investigated using a competitive analysis of binding affinities between UO₂ acetate and different concentrations of Fe(III) chloride using electrospray ionization mass spectrometry. In addition to desmalonichrome, three other siderophores, including two hydroxamates (desferrioxamine B and desferrichrome) and one carboxylate (desferrichrome A), were studied to understand their relative affinities for the UO₂²⁺ ion at two pH values. The binding affinities of hydroxamate siderophores to UO₂²⁺ ions were observed to decrease with increasing Fe(III)Cl₃ concentration at the lower pH. On the other hand, decreasing the pH has a smaller impact on the binding affinities between carboxylate siderophores and the UO₂²⁺ ion. Desmalonichrome in particular was shown to have the greatest relative affinity for UO₂ at all pH and Fe(III) concentrations examined. These results suggest that acidic functional groups in the ligands are important for strong chelation with UO₂ at lower pH.