Effect of Recognized and Unrecognized Salt on the Self-Assembly of New Thermosensitive Metal-Chelating Surfactants

Abstract

New functional thermoreversible metal complexing surfactants consisting of a chelating amino acid residue grafted to the tip of a nonionic surfactant [alkyl poly(oxyethylene) CiEj] or in a branched position are studied. Nonionic surfactants are thermoreversible and exhibit a clouding phenomenon associated with phase separation of micelles. The functional molecules retain both the surface-active properties and the characteristic thermoreversible behavior. Because of the hydrophilic contribution of the chelating group (acetyl lysine), the cloud point and the area at the air-water interface are higher for functional surfactants than for nonionic precursors. These new surfactants have efficient complexing properties toward metal ions and are more efficient than the mixture of the corresponding nonionic surfactant and the acetyl lysine ligand solubilized in micelles. This reveals the synergistic effect obtained by the covalent link between the two functions. Addition of a bulky group on classical amphiphilic structures modifies markedly the packing constraints at the origin ofmicellar structures. Small-angle X-ray or neutron scattering results, modeled jointly on the absolute scale, demonstrate the influence of unrecognized lithium nitrate (LiNO3) as well as specifically recognized uranyl nitrate [UO2(NO3)2] salts on micellar structure and phase boundaries. The determination of the micellar shape variations induced by a recognized salt, that is, a decrease of the polar headgroup, allows the rationalization of uncommon synergistic effects on the cloud point variation: increase with lithium nitrate, no decrease in the presence of uranyl nitrate, and a very large decrease when these two salts are present together.

Clouding behaviour in surfactant systems

“…Colombian et al [89] recently investigated the clouding phenomena of new functional thermoreversible metal complexing surfactants consisting of a chelating amino acid residue (acetyl lysine) grafted to the tip of a nonionic surfactant [alkyl poly(oxyethylene) C i E j ] or in a branched position to examine the role of surfactant structure on CP with the comparison of CP data of the synthesized surfactant to their precursors. CP was raised from 6°C (C 12 E 4 at 1%, w/w) to 57°C (C 12 LE 4 :1 at 20%, w/w; minimum of the clouding curve) when the lysine block was grafted as a pendant group.…”

XAS Study of a Metal-Induced Phase Transition by a Microbial Surfactant

“…1,2 Assemblies of metal-chelating surfactants have been utilized in a variety of fields such as catalysis, 3,4 environmental remediation of toxic metals, 5,6 and magnetic resonance imaging contrast agents. 7 Some metal chelating surfactants undergo a change in aggregate morphology upon metal coordination.…”

Lanthanum(III) and gadolinium(III) separation by cloud point extraction

“…The pressure to decrease organic solvent use in industries has encouraged the requirement for solvent-free procedures for which supramolecular assemblies are excellent candidates. Supramolecular assemblies result from the spontaneous association of a large number of components into a specific phase (i.e., micelles, vesicles) and new separation methods based on innovative concepts are currently being developed [3][4][5][6] as an interesting alternative to traditional liquid-liquid solvent extraction.…”