Computational study of inclusion complex of l-Glutamine/beta-Cycldextrin: Electronic and intermolecular interactions investigations

Abstract Density functional theory (DFT) calculations at the B97-D3/6-31G (d)level are performed to investigate the inclusion complex of l -Glutamine/β–Cyclodextrin. The results indicate, the orientation in which the guest molecule points toward the primary hydroxyls of the hydrophobic cavity of β–Cyclodextrin is energetically preferred and in consistency with experimental observation. Energy decomposition analysis, thermodynamic parameters, the electronic properties, such as the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies and the global indices of reactivity such as, electronegativity (χ), electronic potential (μ), hardness (η) global electrophilicity index (ω) and molecular electrostatic potential surface (MESP) mapping have been dealt and interpreted at same level of theory. Natural atomic charge and non-covalent interactions-reduced density gradient analysis properties of the two complexes were also calculated and interpreted. Natural bond orbital (NBO) analysis is carried out to analyze mutual interactions between donor and acceptor orbital of l -Glutamine and β-CD play an important role to the stabilization of such complex. Finally, the quantum theory of atoms in molecules (QAIM) theory has been also used to examine the properties of the bond critical points: their electron densities and Laplacians.