Synthesis, Separation And Supramolecular Self-assembly Of Rare Melon Rings

Using one pot synthesis strategy,that is,glycoluril reacts with paraformaldehyde with a ratio of 1:2 in aqueous HCl solution to yield a cucurbit[n]uril mixture containg Q[5],Q[6],Q[7],Q[8] as more than 90% main products,and the separation of these Q[n]s is relevant easier by the difference of solubility in water.The physical and chemical properties and potential applications of these cucurbit[n]urils have been extensively investigated.However,cucurbit[n]urils with special structure features or properties are only a handful so far,low yield and difficuty of separation are the main reasons.On the basis of the literature reports,a more convenient and efficient method was established,that is,using dowex-hydrogen cation exchange resin column chromatography,wich successfully separated the inverted cucurbit[6]uril(iQ[6])and inverted cucurbit[7]uril(iQ[7]).Moreover,another two twisted cucurbit[n]uril,the homologues of the twisted cucurbit[14]uril,named twisted cucurbit[13]uril and twisted cucurbit[15]uril were found in the separation progress for the twisted cucurbit[14]uril by TLC.The supramolecular self-assembly of the inverted cucurbit[6]uril with aliphatic diamine molecules induced by tetrachlorozincate ion([ZnCl4]2-)was studied.The 1H NMR and single crystal structure showed that the shortest chain of ethylenediamine interacts through portal by ion-dipole and hydrogen bonds.NMR showed no obvious interaction between 1,4-butanediamine with inverted cucurbit[6]uril,when the ZnCl2 solution was ade to the 1,4-butanediamine-inverted cucurbit[6]uril,1,4-butanediamine and part of the Zn2+ coordinate to the cucurbituril portal at synergistic effect,which was proved by the single crystal structure.1,5-pentamethylene,1,6-hexamethylenediamine and hexamethylenediamine interacted strongly with the inverted cucurbit[6]uril by encapsulating into the cavity.Coordination in supramolecular assemblies was also investigated by reacting alkali cation and the inverted cucurbit[6]uril.Single-crystal X-ray diffraction analysis revealed that the inverted cucurbit[6]uril-alkali-ZnCl42-interaction systems consisted of a supramolecular assembly into a honeycomb-like framework via outer surface interaction.The inverted cucurbit[7] can coordinate to K+ in the presence of the structure-directing agent [ZnCl4]2-,which can be used as gas absorption material.Futher absorption experiments was performed for some common volatile materials with different polarities(methanol,ethanol,carbon tetrachloride,acetone,acetonitrile),the inverted cucurbit[7]uril-based porous material show high affinity with alcohols.In order to obtain crystal structures of this twisted cucurbit[14]urils,we utilized an approach involving [CdCl4]2– anion-induced lanthanide coordination of metal ions to form twisted cucurbit[14]urils-based supramolecular assemblies,whereas lanthanide cations appeared to function as an adductor muscle of the shell by linking the two open side cavities of twisted cucurbit[14]urils.In the presence of [Cd6Cl19]7– cluster anions,we obtain a complex containing a metal-free cucurbit[14]urils molecule.Structural comparison revealed no significant differences between metal-free and metal-bound cucurbit[14]urils systems,and rigid enantiomeric structures were observed in both cases,which suggests racemization is an intrinsic property of the twisted cucurbit[14]urils system.More interesting,In the twisted cucurbit[14]urils–K+-HCl system,We yield a single chiral structure of cucurbit[14]urils coordinate with K~+.