Encapsulation of alkyldiammonium ions within two different cavities of twisted cucurbit[14]uril

Abstract

Binding interactions between twisted cucurbit[14]uril (tQ[14]) and a series of alkyldiammonium ions both in aqueous solution and DMSO media were investigated by NMR spectroscopy and ITC. Experimental data indicate that tQ[14] possesses two kinds of cavities with different space environments, which can encapsulate two or even three guest molecules with suitable shape and size.

Inclusion Complexes of Hymexazol with Three Different Cucurbit[n]uril: Preparation, and Physicochemical and Antifungal Characterization

“…The high enthalpy value could result from the stronger hydrophobic contacts between the guest and the inner wall of the host, with a moderate association constant [Ka = (1.06 AE 0.04) 3 10 3 L/mol], 2) The interaction of Q [7] with HMI is both enthalpy-and entropy-driven with an association constant of Ka = (1.90 AE 0.07) 3 10 2 L/mol, 3) For the case of interaction of tQ [14] with guest HMI, the data points (Figure 5c) are indicative of double binding. [20] From the data obtained, we surmise that both binding sequences are entropically favorable processes with j DH j < j TDS j . For both binding sequences, the positive entropy values may be attributed to the expulsion of the high-energy water molecules from the cavity of tQ [14].…”

“…The resonance of proton Ha displayed an upfield shift of ca. Generally, interaction of a Q[n] with a guest in different solvents, such as D 2 O and [D 6 ]DMSO is likely to result in different NMR spectra in terms of chemical shift, [20] even different interaction modes. The above results revealed that the opportunity of inclusion of a HMI guest is larger than that of exclusion of a HMI guest in the cavity of HHMeQ [6].…”

“…[4] Cucurbit[n]uril (Q[n]) [5][6][7] are a class of macrocyclic compounds synthesized by condensing glycoluril and formaldehyde in an acidic medium and are characterized by a rigid hydrophobic cavity and two identical carbonyl-fringed portals. [19,20] Moreover, tQ [14] is not only well soluble in water, but also dissolves in DMSO. Among them, cucurbit [7]uril (Q [7]) is employed as a host molecule due to its good solubility in water and relative large cavity and portals (Figure 1), it can accommodate guest molecules such as drugs, pesticides, dyes, and amino acids.…”

Supramolecular Recognition of Amino Acids by Twisted Cucurbit[14]uril

“…This feature is rarely observed in conventional supramolecular hosts. [22] In the presentw ork, we have investigated the bindingi nteractions between tQ [14] and the 20 standard AAs in aqueous HCl solution by isothermal titration calorimetry( ITC) and in DCl/D 2 Oa nd [D6]DMSO by 1 HNMR spectroscopy. [23] The results show that tQ [14] displays stronger binding affinity towards AAs with ap ositively charged side chain or ones incorporatinga na romatic ring, and weaker binding affinity towards AAs with an uncharged or negatively chargeds ide chain.…”

“…In ar ecent study concerned with the binding interactions between tQ [14] and as eries of alkyldiammonium ions in both aqueous solution and [D6]DMSO, we observed as imilars ituation with the binding of HCl salts of butanediamine or hexanediamine;o nly the titration 1 HNMR spectra in [D6]DMSO could be used to distinguish two different host-guest interaction modes. [22] Thus,f or comparison, the titration 1 HNMR spectra of tQ [14] with Lysi n[ D6]DMSO were acquired (Figure 2). The results showedd ifferent binding behavior for tQ [14] in [D6]DMSO as the number of equivalents of Lysw ere increased (Figure 2b to 2f): only one set of amino protons ignals (A ' ,B ' ) and the side-chain proton signals of Lys( b ' , g ' , d ' )w ereo bserved upon the addition of as malla mount of Lys( Figure2b and 2c), suggesting that the tQ [14] host shields both the amino groupsa nd side chain of Lysi n[ D6]DMSO.…”