Adsorption Properties of Cryptand 222 at the Charged Mercury−Solution Interface

Abstract

The adsorption of the macrocyclic ligand kryptofix 222 at the mercury−water interface has been studied as a function of the polarization potential and the ligand concentration. An automated apparatus has been used to measure interfacial tension by the drop−shape technique. The relative surface excess and the surface charge density have been obtained, and from these parameters, the molecular packing at the interface and the free energy of adsorption have been calculated. The results show that the macrocyclic ligand strongly adsorbs at the interface in the presence of an intermolecular repulsive electrostatic contribution due to Na+ cations trapped inside the macrocyclic cage. Moreover the adsorption driving force is similar to that reported for the adsorption of aliphatic compounds, i.e., the hydrophobic repulsion of the exposed molecular surfaces.

Interfacial Activity of the Diprotonated 222 Cryptand at the Water/"Oil" Interface Revealed by Molecular Dynamics Simulations

“…Crown ethers like 18-crown-6 and dicyclohexano-18-crown-6 which lack an amphiphilic topology are surface active and saturate the air/water interface at concentrations (loge) of -1.1 and -4.0, respectively [39]. The more "spherical" unsubstituted cryptates adsorb at the water side of the mercury /water interface, which bears some analogies with the interface studied here [40]. Agitated cryptands or cryptates solutions also form foams, as do neutral surfactants [41].…”

Interfacial Behavior of Ionophoric Systems: Molecular Dynamics Studies on 18-Crown-6 and Its Complexes at the Water-Chloroform Interface

“…59 Despite their positive charge and repulsive interactions, the 222 Na + cryptates adsorb at the water/mercury interface. 60 Our MD calculations on cation complexes of calixarenes, cryptands, CMPO, diamides or TBP also revealed similar behavior.…”

The Role of Reactant Adsorption in the Electrode Reactions of Tl(2,2,2)+ Cryptate Complexes at Mercury Electrodes

“…In aqueous solutions the Tl(2,2,2) was found to be reversibly reduced on the mercury electrode and its adsorption on the electrode was not reported [6,7]. However rather strong adsorption of cryptand (2,2,2) on the mercury electrode from aqueous solutions was found [9] in the presence of Na cations. It is well known that adsorption of ligands can induce the coadsorption of metal ions which form a complex with those ligands (see for instance [10 ± 12]).…”