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United States Department of Agriculture

Agricultural Research Service

Title: Adsorption and Ligand-Assisted Feooh(goethite) Dissolution by Aminocarboxylate Chelating Agents

Authors
item Stone, Alan - JOHNS-HOPKINS UNIV
item Whitehead, Charles - JOHNS-HOPKINS UNIV
item Chaney, Rufus
item Kukier, Urszula - VPI, BLACKSBURG

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: November 14, 2001
Publication Date: November 11, 2002

Technical Abstract: In order for extracellular chelating agents to solubilize Fe(III) (hydr)oxides, the following criteria must be met: 1. The chelating agent must adsorb. Amine groups structurally close to a carboxylate group strongly diminish adsorption (via hydrogen-bonding), while distal amine groups slightly diminish adsorption (via electrostatics). 2. The chelating agent must detach iron atoms from the surface. Chelate ring formation is necessary, which (unlike adsorption) is favored by a short distance between amine and carboxylate groups within the molecule. 3. The log K for iron-chelating agent complex formation must be high enough to maintain appreciable concentrations of iron in solution. 4. The iron-chelating agent complex must not re-adsorb to any appreciable extent. A chelating agent denticity less than the coordination number for iron enables "metal-like" ternary surface complex formation; "ligand-like" surface complex formation is possible when the opposite is true. Experiments performed with the naturally-occurring ligands and the synthetic chelating agents NTA, HEDTA, EDTA, CDTA, TMDTA, and EDDS provide the basis for developing structure-reactivity relationships. We believe results are relevant to metal-induced Fe deficiency chlorosis of grasses which secrete chelating phytosiderophores to obtain soil Fe.

Last Modified: 9/21/2014