Abstract: We investigated the chiral transition mechanism of the ibuprofen molecules confined in the helically chiral SWCNT by using the ONIOM methods of combination of quantum mechanics and molecular mechanics. The results show that the deformation of ibuprofen molecules in the confinement region is more and more obvious with the decrease of chirality SWCNT diameter. There is only one reaction channel for the optical isomerism of ibuprofen molecules in SWCNT(6,4) and SWCNT(7,4), and there are two reaction channels for the optical isomerism in SWCNT(8,5). When the ibuprofen molecules are confined in SWCNT(6,4), SWCNT(7,4) and SWCNT(8,5), the energy barriers of ratedetermining step for the optical isomerism reaction are 24795,27383,29224 kJ/mol, respectively, while the total energy barrier are 278.96,291.91,325.88 kJ/mol. The optical isomerism of S-Ibu molecule is easy to be achieved in the smaller pore size of the helically chiral SWCNT, and SWCNT(6,4) can be used as a nanoreactor for optical isomerism of ibuprofen molecules.

Key words: ONIOM method, Gibbs free energy, perturbation theory, transition state, helical chirality, ibuprofen, density functional theory