Ion Channels and Anisotropic Ion Mobility in a Liquid-Crystalline Columnar Phase As Observed by Multinuclear NMR Diffusometry

Abstract

The anisotropic diffusion of anions and cations in the columnar and isotropic phases of a fan-shaped imidazolium hexafluorophosphate salt is measured by (1)H and (19)F diffusion NMR experiments. The macroscopic orientation of the columnar phase is investigated by (2)H NMR spectroscopy. We find that the anions, confined by the cations, diffuse faster than the cations along the columns but slowly across them, which exemplifies the ion channel model of these materials. The cations and anions are dissociated in the columnar phase but are paired or clustered in the isotropic phase.

Molecular and Segmental Orientational Order in a Smectic Mesophase of a Thermotropic Ionic Liquid Crystal

“…A rotation/flip of the imidazolium core around N-C bond can also be accompanied by the chain re-alignment. The correlation of motion by ion-pairing, as has been observed in isotropic phase of ionic liquids, may impose additional restriction on the core dynamics [26][27][28][29]. On the other hand, diffusion and conductivity studies have indicated (partial) dissociation of cations and anions in mesophases [28][29][30].…”

“…The correlation of motion by ion-pairing, as has been observed in isotropic phase of ionic liquids, may impose additional restriction on the core dynamics [26][27][28][29]. On the other hand, diffusion and conductivity studies have indicated (partial) dissociation of cations and anions in mesophases [28][29][30]. With reservations for the complexity of the processes controlling the core alignment and dynamics, it is still possible make rough estimates of the order parameters using DFT structure analysis as presented in [19].…”

Ion conformation and orientational order in a dicationic ionic liquid crystal studied by solid-state nuclear magnetic resonance spectroscopy

“…The translational dynamics of ions is related to conductivity and as such is of high interest in the context of electrochemical applications. In mesophases, the self-diffusion and ion transport are strongly anisotropic which opens the possibility to design low-dimensional electrolytes 48,49 . High translational anisotropy is also indicative of phase stability.…”

Reversible Channel–Layer Structural Transformation of a Hydrogen-Bonded Bis-Urea Macrocycle

“…One-dimensional (1D) tubular channels have been utilized for ion and molecular transport, where coupled Na + -K + ionic transport has been observed in biological molecular assemblies. − Because the 1D transport system has both directionality and anisotropy, artificial ionic channels have attracted much attention for the fabrication of passive and gated ionic transport systems. − A large number of synthetic approaches have been reported for the fabrication of artificial 1D channels based on amphiphilic, polymeric, and macrocyclic molecules with hydrogen bonding and van der Waals interactions. − Simple and well-known low-molecular-weight van der Waals crystals of tris­( o -phenylenedioxy)­cyclotriphosphazene (TPP) derivatives have been reported to form 1D channels, where weak van der Waals interactions form 1D channels in the close-packing crystal structure. − Because the energies of van der Waals interactions are quite low, around 1–2 kJ mol –1 , van der Waals molecular assemblies are easily dissociated by external stimuli such as heat and ultrasonic energy . In contrast, hydrogen bonds have energies ranging from 5 to 20 kJ mol –1 , allowing controlled association–dissociation processes of molecular assemblies using external stimuli. − For example, hydrogen bonds in complementary base pairs in DNA and the secondary structures of proteins play an important role in the fabrication of biological molecular assemblies, and controllable hydrogen-bonding interactions have been utilized for repair and reconstruction of molecular assembly structures. − …”