Characterization of Bromide Ions in Charge-Stacked Zwitterionic Micellar Systems

Abstract

A novel zwitterionic surfactant, N-dodecyl-N,N,N',N'-tetra-methyl-ethylene-di-ammonio-propane-sulfonate bromide (DEPB), has been synthesized, and Br(-) involved in the micellar system has been characterized by potentiometry, NMR, and X-ray absorption fine structure (XAFS). Although the dissociation degree of Br(-) from the micelle evaluated by potentiometry almost agrees with that determined by NMR, the former is significantly smaller than the latter over the entire range of concentrations of DEPB. This is explained by assuming that the bromide ions in the micellar system have several different peripheral structures. XAFS has given significant insight into the hydration structures of Br(-) involved in the system. Some of the bromide ions partitioned into the micelle are dehydrated and are directly bound by the ammonium groups in the DEP molecules. However, some of the bromide ions are still completely hydrated even when they are partitioned into the micelles. The average hydration number of the bromide ions directly bound by the ammonium groups was determined to be approximately 3.3. The partial dehydration of Br(-) is possibly facilitated by the characteristic hydration circumstances provided by the charge-stacked structure of the surfactant and by the resulting thick palisade layer of the DEP micelle.

Hydration of Ions in Confined Spaces and Ion Recognition Selectivity

“…Also, effects of the structures of anion-exchange groups can be seen; zwitterionic surfactant molecules appear to facilitate the dehydration of Br -in comparison with the trimethylammonium group. [63][64][65] This implies that Br -is more effectively shielded from a bulk solution by the propylene sulfonate groups. In particular, an NMR study has elucidated that Br -is delocalized on the inside ammonium group in the N-dodecyl-N,N¢-tetramethylethylendiammonium-N¢-propane sulfonate micelle.…”

“…In particular, an NMR study has elucidated that Br -is delocalized on the inside ammonium group in the N-dodecyl-N,N¢-tetramethylethylendiammonium-N¢-propane sulfonate micelle. 64 Thus, Br -is taken up into the interior of the monolayer or aggregates of the zwitterionic surfactants and is dehydrated to a greater extent possibly because of water-shortage circumstances.…”

Eutectic Transition of Local Structure for Bromide Ion in Bulk and on Surface of Doped Ice

“…Also, revealing the local structures of ions below and above t eu should allow the discussion of a phase transition on a molecular basis. We have studied the local structures of Br − by X-ray absorption fine structure (XAFS) in an anion-exchange resin, , on a cationic micellar surface, , on a cationic Langmuir monolayer, , and in concentrated aqueous polyethyleneglycol, , and have revealed that hydrated Br − can release some water molecules from its first hydration shell under some conditions. When the temperature of salt-doped ice is raised above the eutectic temperature ( t eu ) of the system, a liquid phase starts to emerge.…”

Retention characteristics of water‐soluble compounds on water‐holding adsorbents with immobilized zwitterionic copolymers having different ionicities

“…And it is estimated that the influence of the anion site on the retention properties is not strong. Okada and co‐workers reported that the partition of ions to zwitterionic surfaces depends on the nature of analyte anions, and is not strongly affected by analyte cations . Analyte anions having a lower hydration property tend to associate directly with the cation sites of the zwitterionic functional group.…”