Siderophore-Manganese(III) Interactions. I. Air-Oxidation of Manganese(II) Promoted by Desferrioxamine B
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- 作者：Owen W. Duckworth and Garrison Sposito
- 刊名：Environmental Science & Technology
- 出版年：2005
- 出版时间：August 15, 2005
- 年：2005
- 卷：39
- 期：16
- 页码：6037 - 6044
- 全文大小：229K
- 年卷期：v.39,no.16(August 15, 2005)
- ISSN：1520-5851
文摘
Recent studies suggest that aqueous Mn(III) complexes,particularly those with non-carboxylated ligands such asmicrobial siderophores, may be stable in soil and aquaticenvironments. In this paper, we determine the stabilityconstants for Mn(II) and Mn(III) complexes with the commontrihydroxamate siderophore, desferrioxamine B (DFOB).Base and redox titrations were conducted to determineDFOB conditional protonation constants and conditionalstability constants for 1:1 DFOB complexes with Mn(II) andMn(III). The conditional protonation constants agree wellwith literature values. We determined stability constants forthree Mn(II)-DFOB species and one Mn(III)-DFOBspecies at 25 
C in 0.1 M NaCl. The Mn(III) HDFOB+ complexcan be formed readily by air-oxidation of Mn(II)-DFOB.This reaction exhibits pseudo first-order kinetics with a ratecoefficient that can be characterized as the product ofoxygen concentration with a linear combination ofthe concentrations of the three Mn(II)-DFOB complexes.The second-order rate coefficients appearing in thislinear combination are 1 to 2 orders of magnitude smallerthan that associated with oxidation of the hydrolyticspecies Mn(OH)02. The Mn(III)HDFOB+ complex is stablefor pH in the range of 7.0-11.3; but, at pH < 7.0 it decomposesby internal electron transfer, yielding oxidized DFOBproducts and Mn(II). For p[H+] > 11.3, the complex degradesby disproportionation, yielding Mn(II) and solid MnO2.This range of pH stability supports the hypothesis thataqueous Mn(III) may play a vital role in the biogeochemicalcycling of not only manganese, but also other elements,such as carbon, sulfur, nitrogen, oxygen, and redox-activemetals.
C in 0.1 M NaCl. The Mn(III) HDFOB+ complexcan be formed readily by air-oxidation of Mn(II)-DFOB.This reaction exhibits pseudo first-order kinetics with a ratecoefficient that can be characterized as the product ofoxygen concentration with a linear combination ofthe concentrations of the three Mn(II)-DFOB complexes.The second-order rate coefficients appearing in thislinear combination are 1 to 2 orders of magnitude smallerthan that associated with oxidation of the hydrolyticspecies Mn(OH)02. The Mn(III)HDFOB+ complex is stablefor pH in the range of 7.0-11.3; but, at pH < 7.0 it decomposesby internal electron transfer, yielding oxidized DFOBproducts and Mn(II). For p[H+] > 11.3, the complex degradesby disproportionation, yielding Mn(II) and solid MnO2.This range of pH stability supports the hypothesis thataqueous Mn(III) may play a vital role in the biogeochemicalcycling of not only manganese, but also other elements,such as carbon, sulfur, nitrogen, oxygen, and redox-activemetals.