Adsorption of hydroxamate siderophores and EDTA on goethite in the presence of the surfactant sodium dodecyl sulfate |
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Authors: | Naraya Carrasco Ruben Kretzschmar Jide Xu Stephan M Kraemer |
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Institution: | (1) Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Sciences, ETH Zurich, CHN, CH-8092 Zurich, Switzerland;(2) Chemistry Department, University of California, Berkeley, California 94720-1460, USA;(3) Department of Environmental Geosciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria |
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Abstract: | Siderophore-promoted iron acquisition by microorganisms usually occurs in the presence of other organic molecules, including
biosurfactants. We have investigated the influence of the anionic surfactant sodium dodecyl sulfate (SDS) on the adsorption
of the siderophores DFOB (cationic) and DFOD (neutral) and the ligand EDTA (anionic) onto goethite (α-FeOOH) at pH 6. We also
studied the adsorption of the corresponding 1:1 Fe(III)-ligand complexes, which are products of the dissolution process. Adsorption
of the two free siderophores increased in a similar fashion with increasing SDS concentration, despite their difference in
molecule charge. In contrast, SDS had little effect on the adsorption of EDTA. Adsorption of the Fe-DFOB and Fe-DFOD complexes
also increased with increasing SDS concentrations, while adsorption of Fe-EDTA decreased. Our results suggest that hydrophobic
interactions between adsorbed surfactants and siderophores are more important than electrostatic interactions. However, for
strongly hydrophilic molecules, such as EDTA and its iron complex, the influence of SDS on their adsorption seems to depend
on their tendency to form inner-sphere or outer-sphere surface complexes. Our results demonstrate that surfactants have a
strong influence on the adsorption of siderophores to Fe oxides, which has important implications for siderophore-promoted
dissolution of iron oxides and biological iron acquisition. |
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