TY - JOUR
T1 - Hydroxamate siderophore-promoted reactions between iron(II) and nitroaromatic groundwater contaminants
AU - Kim, Dongwook
AU - Duckworth, Owen W.
AU - Strathmann, Timothy J.
N1 - Funding Information:
The American Chemical Society’s Petroleum Research Fund is acknowledged for support of this research. Dongwook Kim was partially supported by a fellowship from the Korean Army. We thank Prof. G. Sposito (UC Berkeley) for supply of DFOB used in early test experiments, and Prof. Benito Mariñas and Martin Page (Univ. Illinois) for assistance with stop-flow spectrometry experiments. The manuscript also benefitted from insightful comments provided by four anonymous reviewers. Appendix A
PY - 2009/3/1
Y1 - 2009/3/1
N2 - Recent studies show that ferrous iron (FeII), which is often abundant in anaerobic soil and groundwater, is capable of abiotically reducing many subsurface contaminants. However, studies also demonstrate that FeII redox reactivity in geochemical systems is heavily dependent upon metal speciation. This contribution examines the influence of hydroxamate ligands, including the trihydroxamate siderophore desferrioxamine B (DFOB), on FeII reactions with nitroaromatic groundwater contaminants (NACs). Experimental results demonstrate that ring-substituted NACs are reduced to the corresponding aniline products in aqueous solutions containing FeII complexes with DFOB and two monohydroxamate ligands (acetohydroxamic acid and salicylhydroxamic acid). Reaction rates are heavily dependent upon solution conditions and the identities of both the FeII-complexing hydroxamate ligand and the target NAC. Trends in the observed pseudo-first-order rate constants for reduction of 4-chloronitrobenzene (kobs, s-1) are quantitatively linked to the formation of FeII species with standard one-electron reduction potentials, EH0 (FeIII/FeII), below -0.3 V. Linear free energy relationships correlate reaction rates with the EH0 (FeIII/FeII) values of different electron-donating FeII complexes and with the apparent one-electron reduction potentials of different electron-accepting NACs, EH1′(ArNO2). Experiments describing a redox auto-decomposition mechanism for FeII-DFOB complexes that occurs at neutral pH and has implications for the stability of hydroxamate siderophores in anaerobic environments are also presented. Results from this study indicate that hydroxamates and other FeIII-stabilizing organic ligands can form highly redox-active FeII complexes that may contribute to the natural attenuation and remediation of subsurface contaminants.
AB - Recent studies show that ferrous iron (FeII), which is often abundant in anaerobic soil and groundwater, is capable of abiotically reducing many subsurface contaminants. However, studies also demonstrate that FeII redox reactivity in geochemical systems is heavily dependent upon metal speciation. This contribution examines the influence of hydroxamate ligands, including the trihydroxamate siderophore desferrioxamine B (DFOB), on FeII reactions with nitroaromatic groundwater contaminants (NACs). Experimental results demonstrate that ring-substituted NACs are reduced to the corresponding aniline products in aqueous solutions containing FeII complexes with DFOB and two monohydroxamate ligands (acetohydroxamic acid and salicylhydroxamic acid). Reaction rates are heavily dependent upon solution conditions and the identities of both the FeII-complexing hydroxamate ligand and the target NAC. Trends in the observed pseudo-first-order rate constants for reduction of 4-chloronitrobenzene (kobs, s-1) are quantitatively linked to the formation of FeII species with standard one-electron reduction potentials, EH0 (FeIII/FeII), below -0.3 V. Linear free energy relationships correlate reaction rates with the EH0 (FeIII/FeII) values of different electron-donating FeII complexes and with the apparent one-electron reduction potentials of different electron-accepting NACs, EH1′(ArNO2). Experiments describing a redox auto-decomposition mechanism for FeII-DFOB complexes that occurs at neutral pH and has implications for the stability of hydroxamate siderophores in anaerobic environments are also presented. Results from this study indicate that hydroxamates and other FeIII-stabilizing organic ligands can form highly redox-active FeII complexes that may contribute to the natural attenuation and remediation of subsurface contaminants.
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U2 - 10.1016/j.gca.2008.11.039
DO - 10.1016/j.gca.2008.11.039
M3 - Article
AN - SCOPUS:59649115651
SN - 0016-7037
VL - 73
SP - 1297
EP - 1311
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
IS - 5
ER -