Selective Cationic Binding at the Air−Water Interface by Thin Films of Rigid Amphiphiles Bearing Laterally Attached Crown Ether Moieties

Abstract

Three 4,4′′-didecyloxy-p-terphenyl derivatives with laterally attached crown ether units of different ring size [(1,4,7,10-tetraoxacyclododecyl)-, (1,4,7,10,13-pentaoxacyclopentadecyl)-, and (1,4,7,10,13,16-hexaoxacyclooctadecyl)-2-methyl 2,5-bis(4-decyloxyphenyl)benzoate] have been synthesized, and their Langmuir films were investigated by means of a film balance. They form well-ordered thin films when spread at the air-water interface which are characterized by two sharp breaks in their surface pressure-area isotherms separated by a large plateau. The lateral pressure in the plateau regionsin which the molecules undergo a first-order phase transition with formation of a defined triple layerssignificantly increases on enhancing the number of oxyethylene units in the crown ether units. Additionally, it depends on the type and concentration of alkali metal ions (Li + , Na + , K + , Rb + , Cs + ) in the subphase. Cations which fit the cavity of the appended crown ethers most significantly stabilize the films. It seems that the surface pressure in the plateau region is reminiscent of the binding constants of alkali metal ions to the crown ether units. This shows that facial amphiphiles could represent an interesting new platform for the investigation of guest-host interactions and molecular recognition processes at the air-water interface.

Liquid crystal engineering – new complex mesophase structures and their relations to polymer morphologies, nanoscale patterning and crystal engineering

“…[202][203][204][205] Beside the organization of the T-shaped amphiphiles in thermotropic and lyotropic liquid crystalline phases these molecules have also a strong tendency to form well organized structures at surfaces, as for example at the air water interface. [206][207][208] 6 Summary LC research is a rapidly developing field which is just at the beginning and has a significant and not yet fully realized potential with significant impact on other disciplines of science. A whole zoo of new and complex mesophase structures has become available by appropriate designed of relatively simple polyphilic molecules.…”

Reverse hydrotropy by complex formation

“…A ''chain-like'' assembly of stacking ACE molecules can be easily imagined based on their solid state behaviour. [20][21][22][23] A 1D-water channel reported by Fromm et al 22 in the solid state could even explain the low water-to-ACE molar ratio (r1, see Table 1). Nevertheless, the amount of water present in toluene solutions of ACE is probably only sufficient to solvate the ACE headgroups and thus is not available for the hydrophilic dyes solubilised in ACE solutions.…”

“…A ''chain-like'' assembly of stacking ACE molecules can be easily imagined based on their solid state behaviour. [20][21][22][23] Fig. 4 SANS profile of deuterated ACE-16 in protonated toluene.…”

Synthesis and Surface‐Active Properties of F‐Alkylated Polar Loops

“…They have enjoyed widespread use in various areas of science and technology [2][3][4][5][6] ever since the first preparation of the ligands by Pederson [1]. From a surfactant science viewpoint, crown ethers functionalized with pending alkyl groups are special ionophores allowing ion transport across lipophilic barriers [7,8]. The attachment of lipophilic long-chain alkyl groups allows crown ethers to acquire some amphiphilic properties [9,10].…”