Encapsulation of phenylalanine and 3,4-dihydroxyphenylalanine into β-cyclodextrin: Spectral and molecular modeling studies

Encapsulation behavior of phenylalanine (PA) and 3,4-dihydroxyphenylalanine (DPA) with β-cyclodextrin (β-CD) were analyzed by UV–visible, Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and molecular modeling methods. The stoichiometric ratio of the inclusion complexes was found to be 1:1 and the binding constant was evaluated using the Benesi–Hildebrand equation. FT-IR, PXRD, and SEM results confirmed the formation of inclusion complexes. PM3 calculations suggest that orientation B is more favored for PA and orientation A is more favored for DPA. The hydrophobic and H-bond interaction between PA/DPA and β-CD plays an important role in the inclusion complexes. NBO analysis confirmed that mutual interactions formed between occupied and vacant orbitals of both host (β-CD) and guest (PA/DPA) molecules which is the driving force for the formation of inclusion complexes.