『Abstract
Siderophores are biogenic chelating agents exuded in terrestrial
and marine environments to increase the bioavailability of ferric
iron. Recent work suggests that both solid and aqueous manganese
may affect the aqueous speciation of siderophores and thus siderophore-mediated
iron transport. Although the interaction of the trihydeoxamate
siderophore desferrioxamine B (DFOB) with several lower-valence
manganese oxides has been studied, the effects of siderophores
on Mn(III,IV) oxide dissolution are unknown. To remedy this situation,
we measured the dissolution rates of two synthetic layer-type
Mn(IV) oxides and a biogenic oxide produced by a model organism,
Pseudomonas putida GB-1. For pH 5-7, we find that all minerals
studied dissolve by traditional reductive (R1) dissolution, yielding
Mn(II); for pH 7-9, dissolution yields Mn(III)-siderophore complexes,
either by selective ligand-promoted dissolution of structural
Mn(III) or by reduction of ＞Mn(IV) to ＞Mn(III) followed by complexation
and solubilization of Mn(III) by DFOB. Because reductive dissolution
results in siderophore oxidation, manganese oxide dissolution
at acidic pH may provide a significant abiotic sink for siderophores
in natural waters. At alkaline pH, Mn(III)-siderophore complexes
produced may profoundly affect the aqueous speciation of siderophores
as well as provide a source of reactive Mn(III) complexes.
Keywords: Manganese oxide; Biomineral; Desferrioxamine B; Siderophore;
Dissolution; Aqueous Mn(III)』
1. Introduction
2. Pathways of dissolution
2.1. Reactions with DFOB
2.2. Reactions with dissolution products
2.2.1. Conproportionation and disproportionation
2.2.2. Autocatalytic dissolution
2.2.3. Homogeneous oxidation of Mn(II)
2.2.4. Homogeneous reduction of Mn(III) complexes
2.2.5. Sorption of Mn(III)-DFOB complexes
3. Materials and methods
3.1. Materials
3.2. Characterization of Mn oxides
3.3. Steady-state dissolution rates
3.4. Initial dissolution rates
3.5. Characterization of Mn(III)-DFOB complexes
4. Results and discussion
4.1. Steady-state dissolution rates of synthetic Mn oxides
4.2. Initial dissolution rates of biogenic and synthetic Mn oxides
4.3. R1 reductive dissolution rates
4.4. Complex-forming dissolution rates
5. Biogeochemical implications
Acknowledgements
Appendix A. Supplementary data
References