Theoretical investigation on structure and stability of some inverted cucurbit[n]urils

What is it about?

In the wide area of supramolecular chemistry, cucurbit[n]urils present themselves as a young family of molecular containers, able to form stable complexes with various guests, including drug molecules, dyes, hydrocarbons, and even highmolecular. We have demonstrated the structure and stability of some inverted cucurbit[n]urils by using density functional theory. To obtain the initial geometric structure of the models for DFT calculations, PM6-D3H4 method, the semiempirical Hartree-Fock method implemented in MOPAC2016 software (Version: 16.146W), was used with L-BFGS routine. For the optimization of the geometric and electronic structure of the CB[n] models, DFT calculations were carried out with the B3LYP hybrid functional and the 6-311G(d,p) basis set in ORCA software(Version: 4.0).

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Why is it important?

A density functional theory was carried out using the basis set such as 6-311G(d,p). The 6-311G(d,p) is known as more reliable basis set than others. At the previous research by using DFT(B3LYP/6-31G(d)), it was found that i-CB[8] was more stable than the normal CB[8]. But our result by DFT(B3LYP/6-311G(d,p)) shows that all of the inverted CB[n]s including i-CB[8] were less stable than their normal ones. Finally, their relative stability is different as the normal CB[n]> mono-inverted CB[n] > doubly-inverted CB[n]. Dipole moments of the inverted CB[n]s are much larger than that of the normal ones and MEP values are exchanged between the inner and outer sides of the inverted part of the isomers as compared with the normal ones.

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