Outer Surface Interactions Research Articles

Coordination of alkaline earth metal ions in the inverted cucurbit[7]uril supramolecular assemblies formed in the presence of [ZnCl4]2- and [CdCl4]2-.

A convenient method to isolate inverted cucurbit[7]uril (iQ[7]) from a mixture of water-soluble Q[n]s was established by eluting the soluble mixture of Q[n]s on a Dowex (H(+) form) column so that iQ[7] could be selected as a ligand for coordination and supramolecular assembly with alkaline earth cations (AE(2+)) in aqueous HCl solutions in the presence of [ZnCl(4)](2-) and [CdCl(4)](2-) anions as structure-directing agents. Single-crystal X-ray diffraction analysis revealed that both iQ[7]-AE(2+) -[ZnCl(4)](2-) -HCl and iQ[7]-AE(2+) -[CdCl(4)](2-) -HCl interaction systems yielded supramolecular assemblies, in which the [ZnCl(4)](2-) and [CdCl(4)](2-) anions presented a honeycomb effect, and this resulted in the formation of linear iQ[7]/AE(2+) coordination polymers through outer-surface interactions of Q[n]s.

Cucurbit[6]uril-based supramolecular assemblies: possible application in radioactive cesium cation capture.

Multidimensional supramolecular assemblies based on cucurbit[n]uril (n = 6 or 7) were constructed via the outer-surface interactions of cucurbit[n]urils with the polyaromatic compound 4,4',4″-benzene-1,3,5-triyl-tribenzoate as a structure-directing agent. Most impressively, the cucurbit[6]uril-based assembly exhibits high selectivity for capture of cesium cations among the common alkali metal ions in a basic medium and releases the cesium cations under acidic conditions. This reversible process enables possible applications in cesium cation capture.

Theoretical Investigation of Inner and Outer Surface Interaction of H2 and Cl2 Adsorption with C20 (cage) Fullerene

In this research, the structure of C20 cage fullerene which has carbon-bound to H2 atoms is designed and quantum computations is conducted through using density function theory (DFT) at the level of B3LYP and basis set of 6-31G. By modeling the structure of H2@ C20, H2 adsorption on the H2@C20 surface at angles of 90 and 180 degrees is the appropriate optimized location for adsorption. To study the type of gas interaction with surface, and changes of electronic properties of fullerenes, the AIM calculations are performed. Therefore, the results show that the binding power of exterior hydrogen (H23-H24) is stronger than interior hydrogen (H21-H22) in H2@C20, H2@C20-H2-90o, H2@C20 -H2-180o molecules. Also, the results are obtained from the chlorine adsorption in the surface structure of H2@C20-90o and 180o and compared with H2. The results about chlorine show that the joint power of exterior chlorine is stronger than interior hydrogen in the H2@C20-H2-90o and H2@C20-H2-180o molecules. Also, the comparison of the joint power of exterior chlorine for these molecules shows that the binding power of H2@C20-Cl2-180o is stronger than H2@C20-Cl2-90o.

Coordination and supramolecular assemblies of meta-hexamethyl-substituted cucurbit[6]uril with alkali metal ions

Coordination assemblies have been investigated by reactions between alkali metal salts and a meta-hexanomethyl-substituted cucurbit[6]uril (m-HMeQ[6]) in aqueous solutions. X-ray diffraction analysis revealed that each m-HMeQ[6] coordinates with three alkali metal ions, K+, Rb+ or Cs+ and forms a 1:2, m-HMeQ[6]:Malkali+ complex. This complex forms a one-dimensional supramolecular chain through hydrogen bonding. The m-HMeQ[6]/Malkali+ complex-based chains often form honeycomb-like frameworks in which each channel is filled with counter anions and water molecules. The driving forces resulting in the formation of such supramolecular assemblies could be attributed to the outer-surface interaction of Q[n]s.

Synthesis of supramolecular polyrotaxanes assemblies incorporating symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril moieties using polychloride zinc(II) and cadium(II) anions

Three methyl-substituted cucurbituril-based supramolecular assemblies, {Cd2Cl6(C4N3)@TMeQ[6]} 6H2O (1), {Cd(H2O)Cl3(C6N3)@TMeQ[6]}Cl·16H2O (2) and {Zn2Cl6(C4N3)@TMeQ[6]}·10H2O (3), were prepared with N,N′-bis(3-pyridylmethyl)-1,4-butanediamine dichloride (C4N3) and N,N′-bis(3-pyridylmethyl)-1,6-hexanediamine dichloride (C6N3), incorporating a symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril (TMeQ[6]) using polychloride zinc(II) and cadium(II) anions as structure-directing agents. X-ray diffraction analyses confirmed that all three compounds included three different interactions: cucurbit[n]uril (Q[n])-based host–guest interaction, coordination of metal ion to the active sites of the guest and the outer-surface interaction of Q[n]s.

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

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 supramolecular systems and provide new opportunities for the construction of functional materials and architectures.