Immobilization of Fe chelators on Sepharose gel and its effect on their chemical properties

Iron chelates are usually costly and easily leached beyond the root zone. This creates a need to frequently replenish the rhizosphere with chelated Fe and might contaminate groundwater with organic compounds and metals. The development of a slow-release Fe fertilizer that will efficiently supply Fe to plants while exhibiting high resistance toward leaching and/or degradation in the rhizosphere has been the focus of this study. Desferrioxamine B (DFOB) and ethylenediaminebis(o-hydroxyphenylacetic acid) (EDDHA) were immobilized on Sepharose. ¹³C NMR and FTIR measurements confirmed that coupling of DFOB to the gel did not appear to influence its ability to chelate Fe ³⁺ or its binding nature. Isotherms for the immobilized ligands were determined in the presence of 1 mM HEDTA, at 25 °C and at an ionic strength of 0.1 M. The isotherms showed a high affinity of Fe³⁺ to the ligands and binding up to saturation level throughout the pH range examined (4.0-9.0). The K_app values for the immobilized Fe chelates were determined using a modified Scatchard model and found to be lower than the soluble ones. This decrease in K_app might facilitate Fe uptake from these chelates by plants.