Host–guest complex of cypermethrin with β-cyclodextrin: A spectroscopy and theoretical investigation

An inclusion complex of β-CD with cypermethrin was synthesized. To reveal the host–guest interaction, UV–vis and Raman spectroscopic analysis in combination with DFT calculations at B3LYP/6-31G(d) level were performed on cypermethrin and its β-CD inclusion complex. Upon examining the optimized geometry of inclusion complex, we find that the cypermethrin molecule inserts into the cavity of β-CD from the larger opening, and the phenyl moiety is staying inside the cavity. Partial density of states spectra (PDOS) and natural bond orbital (NBO) analysis reveals that intermolecular hydrogen bond is main driving force of formation of inclusion complex. DFT calculations reproduce well the experimental spectra and the deviation is within 20 cm−1. Comparing the same vibrational modes of inclusion complex with those of free cypermethrin and β-CD, we note that most of characteristic bands of free molecules present in the Raman spectrum of inclusion complex, but a small Raman shift of 2–13 cm−1 has been observed on the same mode. The presence of characteristic bands and the small Raman shifts affirm the weak interaction between cypermethrin and β-CD. Calculated thermodynamic analysis reveals that the formation of β-CD cypermethrin inclusion complex is a spontaneous and enthalpy-driven process.