Cucurbit[6]uril: A Possible Host for Noble Gas Atoms

Abstract

Density functional and ab initio molecular dynamics studies are carried out to investigate the stability of noble gas encapsulated cucurbit[6]uril (CB[6]) systems. Interaction energy, dissociation energy and dissociation enthalpy are calculated to understand the efficacy of CB[6] in encapsulating noble gas atoms. CB[6] could encapsulate up to three Ne atoms having dissociation energy (zero-point energy corrected) in the range of 3.4-4.1 kcal/mol, whereas due to larger size, only one Ar or Kr atom encapsulated analogues would be viable. The dissociation energy value for the second Ar atom is only 1.0 kcal/mol. On the other hand, the same for the second Kr is -0.5 kcal/mol, implying the instability of the system. The noble gas dissociation processes are endothermic in nature, which increases gradually along Ne to Kr. Kr encapsulated analogue is found to be viable at room temperature. However, low temperature is needed for Ne and Ar encapsulated analogues. The temperature-pressure phase diagram highlights the region in which association and dissociation processes of Kr@CB[6] would be favorable. At ambient temperature and pressure, CB[6] may be used as an effective noble gas carrier. Wiberg bond indices, noncovalent interaction indices, electron density, and energy decomposition analyses are used to explore the nature of interaction between noble gas atoms and CB[6]. Dispersion interaction is found to be the most important term in the attraction energy. Ne and Ar atoms in one Ng entrapped analogue are found to stay inside the cavity of CB[6] throughout the simulation at 298 K. However, during simulation Ng2 units in Ng2@CB[6] flip toward the open faces of CB[6]. After 1 ps, one Ne atom of Ne3@CB[6] almost reaches the open face keeping other two Ne atoms inside. At lower temperature (77 K), all the Ng atoms in Ngn@CB[6] remain well inside the cavity of CB[6] throughout the simulation time (1 ps).

Recent Progress in Gas Phase Cucurbit[n]uril Chemistry

“…On the other hand, larger CB[n]s predominantly form 1 : 1 complexes with doubly protonated a,w-n-alkyldiamines. The optimal a,w-n-alkyldiamine lengths for binding large CB[n]s (n > 5) under gas phase conditions were determined, and found to be 3-4 methylene units for CB [6], 4-5 methylene units for CB [7], and 5-6 methylene units for CB [8]. These results are consistent with threaded, rotaxane structures in the gas phase.…”

“…Yang et al investigated gas-phase complexes of a,w-nalkyldiammonium ions with a series of CB[n]s, including cucurbit [5]uril (CB [5]), decamethylcucurbit [5]uril (mc5), penta(cyclohexano)cucurbit [5]uril (CB* [5]), hexa(cyclohexano) cucurbit [6]uril (CB* [6]), cucurbit [7]uril (CB [7]) and cucurbit [8]uril (CB [8]) using ESI-FTICR-MS and sustained offresonance irradiation collision-induced dissociation (SORI-CID) techniques. [5] The results show that CB [5], mc5, and CB* [5] form singly-charged 1 : 1 and doubly-charged 2 : 1 diamine:CB[n] complexes.…”

“…Kovalenko et al studied the association of CB [7] with a series of amino acids (AA) possessing different side chains (Asp, Asn, Gln, Ser, Ala, Val, and Ile), and compared the aromatic and basic amino acids using ESI-MS techniques. [6] Both 1 : 1 [CB [7] + AA + 2H] 2 + adducts and 1 : 2 [CB [7] + 2AA + 2H] 2 + dications were observed, depending on the molar ratio of CB [7] : AA in the electrospray solvent.…”

Encapsulation of small gas molecules and rare gas atoms inside the octa acid cavitand

“…The successful incorporation of Rg atoms within the fullerene cages [65] drew significant attention from both theoreticians and experimentalists for further exploration about the systems having endohedrally confined Rg atoms [66][67][68][69][70][71][72][73][74]. Smaller cages like dodecahedrane, adamantane, cubane, BN-cages, other hydrocarbon cages, cucurbit [6] uril, and carbon nanotube were also adopted to encapsulate Rg atoms [68,[70][71][72][73][74]. Though they were found to be thermochemically unstable, they are kinetically stable with respect to the dissociation into the individual cage and Rg atoms.…”

In silico studies on the origin of selective uptake of carbon dioxide with cucurbit[7]uril amorphous material

“…The similar trend of binding enthalpies are also observed for the four gas molecules inside the CB [7] cavity. 47 The NCI results reveal that the flue gas molecules have attractive Van der Waals interaction 14,47-49 among themselves and also with the host walls as represented in colour-coding scheme. M06-2X/6-311+G(d,p)//M06-2X/6-31G(d) calculated binding energy (∆E) results show the similar trend as obtained with M06-2X/6-31G(d) calculated binding enthalpies (∆H) ( Figure 5).…”