The IR spectra of LVS, HPβ-CD, the physical mixture, and complexes prepared by the coevaporation and the kneading methods
are presented in Figure 3. The spectrum of pure LVS presented characteristic peaks at 3510 cm–1 (alcohol O–H stretching vibration); 3016 cm–1 (olefinic C–H stretching vibration); 2970, 2930, and 2876 cm–1 (methyl and methylene C–H stretching vibration); 1725, 1713, and 1690 cm–1 (lactone and ester carbonyl stretch [hydrogen bonded for 1711 and 1700 cm–1 ]); 1430, 1378, and 1350 cm–1 (methyl and methylene bending vibration); 1275, 1228, 1080, and 1050 cm–1 (lactone and ester C–O–C bending vibration); 972 cm–1 (alcohol C–OH stretch); and 873 cm–1 (trisubstituted olefinic C–H wag).
Figure 3: Fourier transform infrared spectrograms of (a) lovastatin, (B) hydroxypropyl-β-cyclodextrin, (c) the physical mixture,
and complexes prepared by (d) the coevaporation method and (e) the kneading method.
The IR spectrum of the HPβ-CD is characterized by intense bands at 3300–3500 cm–1 because of O–H stretching vibrations. The vibration of the –CH and CH2 groups appears in the 280–3000-cm–1 region. The spectrum patterns of the physical mixture correspond with the superposition of the IR spectra of the two components.
The absence of characteristic peaks of LVS and the presence of characteristic peaks caused by HPβ-CD in the IR spectra of
complexes prepared by the coevaporation and the kneading methods indicate that LVS is inside the cavity of HPβ-CD. The IR
spectra of the physical mixture and complexes prepared by the coevaporation method and the kneading methods showed most of
the characteristic peaks were similar to that of HPβ-CD, except one peak at 1700 cm–1 for lactone and ester carbonyl stretching vibration (hydrogen bonded for 1711 and 1700 cm–1 ), which is characteristic of LVS. This effect indicates that the pyrol part of LVS remains outside the HPβ-CD, whereas the
remaining part fits inside the HPβ-CD cavity.