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

•Encapsulation behavior of phenylalanine and 3,4-dihydroxyphenylalanine with β-CD.•UV–visible spectral data indicated the formation of 1:1 inclusion complexes.•FT-IR, PXRD and SEM results were confirmed the formation of inclusion complexes.•Binding energy and HOMO–LUMO orbital calculations confirm the better stability of the inclusion complexes.

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.

Graphical abstractThe optimized structure of the inclusion complexes PA:β-CD (B) and DPA:β-CD (A).Figure optionsDownload full-size imageDownload as PowerPoint slide