Structural Aspects and Stability of Interactions between Phenyl-3,3'-Bis(Indolyl)Methanes and β-Cyclodextrin from Density Functional Theory

The theoretical investigation of five 3,3'-(phenylmethylene)bis(1H-indole) derivatives (BIM1, BIM2, BIM3, BIM4 and BIM5) with β-cyclodextrin (β-CD) were studied using density functional theory B3LYP 3-21G method as basis set. Substituents (–OCH2COOH and -OCH3) at the ortho-, para- and meta- positions in the phenyl ring of BIMs (BIM 1–5) has changed the stability of inclusion complexes BIMs:β-CD with forming 1:1 stoichiometric ratio. To access the chemistry behind this orientation and composition, we have studied the geometrical parameters, complexation energy, HOMO-LUMO energy gap, chemical reactivity, thermodynamic parameters, Mulliken charges and molecular electrostatic potential (MEP) map for all inclusion complexes (BIMs:β-CD) with stable orientation. Natural bond orbital (NBO), NCI-RDG and QTAIM analysis revealed the prospects of hydrogen bonds (=N–H–O and –O–H–O) between BIMs and β-CD.