Siderophore-manganese(lll) Interactions. II. Manganite dissolution promoted by desferrioxamine B.
Recent laboratory and field studies suggest that Mn(lll) forms persistent aqueous complexes with high-affinity ligands. Aqueous Mn(lll) species thus may play a significant but largely unexplored role in biogeochemical processes. One formation mechanism for these species is the dissolution of Mn(lll)-bearing minerals. To investigate this mechanism, we measured the steady-state dissolution rates of manganite (gamma-MnOOH) in the presence of desferrioxamine B (DFOB), a common trihydroxamate siderophore. We find that DFOB dissolves manganite by both reductive and nonreductive reaction pathways. For pH > 6.5, a nonreductive ligand-promoted reaction is the dominant dissolution pathway, with a steady-state dissolution rate proportional to the surface concentration of DFOB. In the absence of reductants, the aqueous Mn(lIl)HDFOB+ complex resulting from dissolution is stable for at least several weeks at circumneutral to alkaline pH and at 25 degrees C. For pH < 6.5, Mn2+ is the dominant aqueous species resulting from manganite dissolution, implicating a reductive dissolution pathway. These results have important implications for the biogeochemical cycling of both manganese and siderophores--as well as Fe(lll)--in natural waters and soils.
Duckworth
Owen W
OW
Division of Ecosystem Sciences, University of California, Berkeley, California 94720-3114, USA. owend@nature.berkeley.edu
Sposito
Garrison
G
D003676:Deferoxamine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D017895:Manganese Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen; D017262:Siderophores / Q000737:chemistry*; D012995:Solubility
D017895:Manganese Compounds; D017262:Siderophores; C494384:manganite; D003676:Deferoxamine; D010100:Oxygen