Iron Binding in an Ethylenediaminetetracetic Acid‐Based Gemini Surfactant Monolayer Film

Abstract

AbstractThe ability of Fe3+ to bind to Langmuir monolayers of an N, N, N′, N′‐dialkyl‐N, N′‐diacetate ethylenediamine gemini surfactant has been explored. Fe3+ in the subphase resulted in the formation of compacted, liquid‐phase monolayers with a mesh‐like morphology at the micron length scale in comparison with expanded, unstructured liquid‐phase monolayers in the absence of iron. The response of the monolayer to subphase Fe3+ was different from that reported for Na+ and Ca2+ for an affiliated, shorter‐tail gemini surfactant. Combined surface potential and X‐ray reflectivity measurements indicated that Fe3+ induced minor conformational changes in the monolayer, suggesting ionic association with the head group. Direct evidence for the binding of iron was provided by total reflection X‐ray fluorescence measurements, which revealed that multiple ions were associated with each head group as opposed to chelating with 1:1 stoichiometry as observed with bulk ethylenediaminetetracetic acid. Cumulative data suggest the adsorption of Fex(OH)y(3x−y)+ complexes with the monolayer surface as has been reported with other charged and uncharged monolayers.