Self-Assemblies Based on the “Outer-Surface Interactions” of Cucurbit[n]urils: New Opportunities for Supramolecular Architectures and Materials

Abstract

Supramolecular architectures and materials have attracted immense attention during the last decades because they not only open the possibility of obtaining a large variety of aesthetically interesting structures but also have applications in gas storage, sensors, separation, catalysis, and so on. On the other hand, cucurbit[n]urils (Q[n]s), a relatively new class of macrocyclic hosts with a rigid hydrophobic cavity and two identical carbonyl fringed portals, have attracted much attention in supramolecular chemistry. Because of the strong charge-dipole and hydrogen bonding interactions, as well as hydrophobic and hydrophilic effect derived from the negative portals and rigid cavities of Q[n]s, nearly all research in Q[n]s has been focused on utilizing the portals and cavities to construct supramolecular assemblies similar to other macrocyclic receptors such as cyclodextrin and calixarenes. Interestingly, a recent study revealed that other weak noncovalent interactions such as hydrogen bonding and π···π stacking, as well as C-H···π and ion-dipole interactions, could also be defined as "outer-surface interactions", which are derived from the electrostatically positive outer surface of Q[n]s. These interactions could be the driving forces in the formation of various novel Q[n]-based supramolecular architectures and functional materials. In this Account, we provide a comprehensive overview of supramolecular self-assemblies based on the outer-surface interactions of Q[n]s. These outer-surface interactions include those between Q[n]s, Q[n]s and aromatic molecules, Q[n]s and calixarenes, Q[n]s and inorganic complex ions, and Q[n]s and polyoxometalates. Pioneering work has shown that such weak noncovalent interactions play very important roles in the formation of various Q[n]-based functional materials and supramolecular architectures. For example, hydrogen bonds in outer-surface interactions between Q[n] molecules not only function as the sole driving force in the formation of one-dimensional Q[n] porous channels but also assist the bonding forces of the channels in capturing and accommodating acetylene molecules and carbon dioxide in the channel cavities. Moreover, upon introduction of a third species such as an aromatic molecule or inorganic anion into the Q[n]/metal system, "outer-surface interactions" could lead to Q[n]/metal-based self-assemblies from simple finite supramolecular coordination complexes to infinite polydimensional supramolecular architectures and other structures. Overall, this Account focuses on the novel self-assembly driving force derived from Q[n]s including (i) concepts of the outer-surface interactions of Q[n]s, (ii) providing plausible explanations of the mechanisms of the outer-surface interactions of Q[n]s, and (iii) introduction of an overview of the developments and practical applications of outer-surface interactions of Q[n]s in supramolecular chemistry. It is hoped that this study based on the outer-surface interactions of Q[n]s can enrich the field of molecular engineering of functional...

Surface modification induced enhanced CO2 sorption in cucurbit[6]uril, an organic porous material

“…38 It can therefore be anticipated that the modification of CB [6], either by chemical or physical means, provides an alternate option for the enhancement of the adsorption ability. 39,40 The high quadrupolar moment of CO 2 can be efficiently used for sequestration by logically employing a polar functional group with a high affinity towards CO 2 for modifying the pores of CB [6]. Such modifications will enhance the adsorption capacity as well as the selectivity for CO 2 .…”

Advances in the Development of Supramolecular Polymeric Biomaterials

“…101 In this way, CBs have been explored in a multitude of applications, ranging from drug delivery, molecular recognition, and self-assembly and have also been explored as multivalent scaffold. [102][103][104] Recent studies propose that the electrostatic positive outer surface of CB[n]s provides a balance in the various supramolecular driving forces for CB[n] assembly, including other CB[n]s, aromatic moieties, inorganic molecules based on hydrogen bonding between methine or methylene groups on the outer surface of CB[n]s. 101 Due to the larger cavity volume, CB [8] is able to host two guests in its cavity to form a 1:1:1 ternary complex affording high selectivity and molecular recognition. The guest pairs are composed of an electron-deficient guest, that is, viologen derivatives, and an electron-rich guest, that is, naphtol.…”

Assemblies of Alkaline‐Earth‐Metal Ions with o‐Tetramethyl‐Substituted Cucurbituril in the Presence of the Cadmium Tetrachloride Anion

“…[5,6] More recent works confirmed that the presence of polychloridometallate ions, in particular [M d-block Cl x ] nanions (M d-block = Cd, Zn, Cu, Co, Ni, and so on), which are structure inducers, could lead to the formation of novel Q[n]-based polydimensional coordination polymers. [2,7] For example, the formation of coordination complexes of lanthanide cations and cucurbit [7]uril (Ln 3+ /Q [7]) is generally very difficult, whereas one-dimensional coordination polymers easily form in the presence of [M d-block n-anions. [2,7,8] Driving forces, which are defined as the outer-surface interaction of cucurbit[n]uril, are the unusual hydrogen bonding of the "waist region" methine (ϵCH) or bridge methylene (=CH 2 ) groups on the back of Q[n] molecules with oxygen and chloride from the polychloridometallates.…”

“…[2,7] For example, the formation of coordination complexes of lanthanide cations and cucurbit [7]uril (Ln 3+ /Q [7]) is generally very difficult, whereas one-dimensional coordination polymers easily form in the presence of [M d-block n-anions. [2,7,8] Driving forces, which are defined as the outer-surface interaction of cucurbit[n]uril, are the unusual hydrogen bonding of the "waist region" methine (ϵCH) or bridge methylene (=CH 2 ) groups on the back of Q[n] molecules with oxygen and chloride from the polychloridometallates. These forces also include interactions of electron-deficient carbonyl carbon sites of Q[n] molecules with chloride of polychloridometallates and with portal carbonyl oxygen atoms of adjacent Q[n] molecules (Scheme 1).…”

“…These forces also include interactions of electron-deficient carbonyl carbon sites of Q[n] molecules with chloride of polychloridometallates and with portal carbonyl oxygen atoms of adjacent Q[n] molecules (Scheme 1). [7] Scheme 1. Outer-surface interactions of Q[n]s with polychloride M d-block anions.…”