DFT investigation of host–guest interactions between α-Terpineol and β-cyclodextrin

Two models A and B of inclusion complex of α-Terpineol (α-Terp) into β-cyclodextrin (β-CD) were investigated by M06-2X/6-311G(d,p) and ωB97X-D/6-311G(d,p) levels of theory in vacuum and in water. EDA, TD-DFT, NBO, AIM and NCI analyses were also done to give more information about the nature of interaction between α-Terp and β-CD. The calculated complexation energy gives that A model with partial encapsulation of α-Terp in β-CD is more favored than B one where guest molecule is totally embedded into β-CD cavity. EDA calculation shows that dispersion and electrostatic energies contribute greatly on total bonding energy of α-Terp @ β-CD inclusion complexes. Also, electronic transitions obtained by TD-DFT method suggest the charge transfer between α-Terp and β-CD. Finally, NBO and AIM analyses demonstrate the establishment of conventional H-bond interaction and NCI analysis illustrate H-bonds, van der Waals and steric repulsion during inclusion complex formation.