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

Abstract

The 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.

Physicochemical Properties of Monolayers of a Gemini Surfactant with a Minimal-Length Spacer

“…We have also attempted to characterize the nanometer-scale morphology of deposited (Langmuir–Blodgett, LB) C 18 -0-C 18 monolayers. Previous attempts at the LB monolayer deposition of Ace(12)-2-Ace(12) and its longer-chain analogue onto various solid substrates have generally resulted in either poor transfer (at low surface pressures) or in the deposition of multilayer aggregates, typically with transfer ratios that were much larger than one (unpublished data; similar observations have been published for Fe 3+ -enriched subphases), likely because of the fluid nature of the films. Intriguingly, C 18 -0-C 18 films could be deposited onto glass substrates over a range of surface pressures with transfer ratios of ∼1, indicating efficient monolayer transfer.…”

Pattern Formation in Phase-Separated Langmuir and Langmuir Monolayer Films

“…We have also investigated the ion binding effects between the gemini surfactant and a number of cations at the air–water interface. , In general, results revealed a markedly weaker binding between the surfactant headgroup with divalent (Ca 2+ ) and trivalent (Fe 3+ ) ions as compared with EDTA-metal complex in the bulk, despite their similarity in molecular structures. Under AFM and BAM, clusters have been found at the surfactant monolayer in micrometer and sub-submicrometer scale, and with X-ray fluorescence technique, results suggested that the cluster found in Ace(18)-2-Ace(18)/Fe3+ systems can be attributed to complex with general formula Fe x (OH) y (3 x – y ) .…”

Atomic spectrometry update: review of advances in X-ray fluorescence spectrometry and its special applications

“…The binding of Fe ions by a monolayer film of gemini surfactant at the water air interface was studied 50 by angle-dependent TXRF spectrometry at the liquid-surface-scattering spectrometer (NSF's ChemMatCARS) at the APS. The angle scans showed that Fe was being accumulated in a thin surface layer on top of a Fe 3+ aqueous solution.…”