Adsorption of hydroxamate siderophores and EDTA on goethite in the presence of the surfactant sodium dodecyl sulfate

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

THE NATURE OF SIMPLE MONO-VALENT CATION SILICA INTERACTION AS REFLECTED IN THE SPIN-LATTICE RELAXATION-TIME OF NA-23

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ON THE NATURE OF ALKYLSULFONATE ADSORPTION AT THE RUTILE WATER INTERFACE

The adsorption density of dodecylsulfonate ions at the rutile/water interface was determined at different pH values, together with the surface charge density. The adsorption isotherms consist of four distinct regions. Region 1 (at low concentrations) is characterized by ion exchange of dodecylsulfonate ions with chloride ions in the electrical double layer. In region 2 the adsorbed surfactant ions associate through interaction of their hydrocarbon chains, forming hemimicelles. After reversal of the electrokinetic potential, there is a decrease in the slope of the isotherm in regions 3 and 4. This results from continuous increase in the electrostatic repulsion as the zeta potential becomes negative and the solution concentration approaches the critical micelle concentration. Adsorption phenomena are interpreted in terms of the Stern-Grahame model of the electrical double layer.X1128sciescopu