Spectroscopic and theoretical study on inclusion complexation of beta-cyclodextrin with permethrin

Due to the poor water solubility of permethrin (PERM), an inclusion technique has been developed to modify its physical and chemical properties so as to improve its function finishing properties. In this paper, the inclusion complex of permethrin (PERM) and β-CD was synthesized and characterized. To reveal the inclusion mechanism, FT-IR and Raman spectrum analyses in conjugation with DFT calculations were performed on PERM, β-CD and β-CD·PERM inclusion complex. The ground-state geometries, vibrational wavenumbers, IR and Raman intensities were calculated by DFT at B3LYP/6-31G (d) level. The calculated mean bond lengths of glucose units for β-CD and β-CD·PERM inclusion complex are longer by 0.005–0.029 Å and 0.002–0.025 Å than those of the XRD structure of β-CD·11H2O inclusion complex, respectively. Upon examining the optimized geometry of inclusion complex, we notice that a PERM molecule is inserted into the toroid of β-CD from the larger opening. Calculated vibrational wavenumbers are calibrated and compared with experimental fundamentals and the errors are within 20 cm−1. The significant changes on Raman spectrum of PERM, when it is encapsulated by β-CD, in combination with normal mode analysis reveal that the ring A of PERM penetrates through the toriod of β-CD and is exposed to the outside of the cavity, but the ring B is inside the cavity. The good agreements between predicted spectra and experimental ones prove that the theoretical predicted geometries are correct and accord with the real structures.