Investigation into the role of the hydrogen bonding network in cyclodextrin-based self-assembling mesophases

Abstract

The ability to form self-organized thermotropic mesophases of amphiphilic cyclodextrins correlates well with their ability to establish an intermolecular H-bond network.

A Family of Amphiphilic Cyclodextrin Liquid Crystals Governed by Dipole–Dipole Interactions

“…Amphiphilic cyclodextrin (CD) derivatives have the ability to self‐assemble to form ordered superstructures in solution because of the nanosegregation of their polar and apolar groups. In the absence of solvents, amphiphilic CD derivatives can also self‐organize through molecular reorganization; new materials such as thermotropic liquid crystals (LCs) can be obtained upon changing temperatures. CD‐based materials are of particular interest for LC research, because of their relatively rigid, truncated‐cone‐shaped geometry, making them a unique class of scaffolds.…”

“…The first class of amphiphilic CD derivatives known to form LC mesophases had all primary hydroxyl groups of β‐CD replaced with a n ‐octadecylthio group ( 1 , Figure ), which permits the remaining secondary hydroxyl groups to interact in the solid phase, forming a complex network of inter‐/intramolecular H‐bonds . This H‐bond network was believed to be crucial for driving the amphiphilic CDs to self‐assemble into thermotropic LCs; it is also the primary intermolecular force evoked in the literature in the design of amphiphilic CD‐based LC mesophases so far …”

“…Through a systematic study, previously, we synthesized a series of per‐6‐ n ‐octadecylthio‐β‐CD derivatives (Figure ) that are substituted either at all O2 positions with a small alkyl group (such as methyl ( 2 ), ethyl ( 3 )) and other larger groups such as allyl and benzyl groups (not shown); it was found only amphiphilic derivatives with smaller alkyl groups ( 2 , 3 ) formed LC mesophases while the other derivatives with larger substituents did not. We rationalized that the alkyl groups at the O2 positions served as delimitating groups that control the distance between the secondary face of CD molecules in the bilayers of the solid state; thus they effectively modulate the H‐bond strength.…”

“…Only amphiphilic CD derivatives with smaller groups could form LC mesophases because the molecules of the adjacent layers could get closer and thus interact with each other via a network of intermolecular H‐bonds of sufficient strength. On the other hand, when all the secondary hydroxyl groups were substituted with alkyl groups such as methyl ( 4 ) or benzyl ( 5 ) groups, they all lost their ability to form H‐bond networks and thus were unable to form LC mesophases . In theory, compound 5 could engage a network of π–π interactions between adjacent layers, but clearly, this type of intermolecular force is too weak to induce molecular self‐assembly in solid state.…”

Amphiphilic Cyclodextrin-Based Liquid Crystals for Proton Conduction

“…Over the past few years, we have been developing a group of supramolecular liquid crystals based on biodegradable cyclodextrins (CDs), a family of macrocyclic carbohydrates based on nontoxic glucose. − CDs were found to be excellent scaffolds to design liquid crystalline materials, due to their polyfunctionalities and the presence of a unique face-to-face pseudosymmetry that originates from the placement of all primary hydroxyl groups at one end of the macrocycle (primary face) and all secondary hydroxyl groups at the opposite end (secondary face). These features allow for efficient regioselective derivatization through which multiple copies of incompatible functionalities such as hydrophobic/hydrophilic groups can be grafted to each face of the macrocycle.…”