Study of inclusion compound in solution involving tetracycline and β-cyclodextrin by FTIR-ATR

The objective of this article was to investigate the changes on the vibrations modes of the supramolecular system constituted between β-cyclodextrin (host) and the tetracycline (guest) by Fourier transform infrared attenuate total reflectance (FTIR-ATR) in aqueous solution as a new alternative probe for the host:guest complexes. To confirm the non-covalent interactions of this system, nuclear magnetic resonance spectroscopy techniques (1H NMR and NOESY), were also used. In addition the complex stoichiometry was determined using the FTIR-ATR results.Comparison between the tetracycline FTIR-ATR spectra of free to the inclusion compound, it was clear that the ν(CO), ν(CC), δ(OH), δ(CC), ν(CC), δ(NH) and ν(CN) signals of tetracycline in the inclusion compound were disturbed by the presence of β-cyclodextrin. In addition, the intensity of β-cyclodextrin vibration mode at 1031–1082 cm−1, corresponding to ν(COC), was strongly reduced when the concentration of tetracycline was increased. These results suggest the interaction between the molecules in aqueous solution.The 1H nuclear magnetic resonance experiment demonstrated a similar result to that obtained by FTIR-ATR concerning the changes which occurred in the chemical shits of the pure tetracycline as compared to that obtained upon forming the inclusion complex. In addition, the 2D NOESY experiment also confirmed the Tetracycline interaction not only with the cavity but also with the external protons of the cyclodextrin by cross peaks correlations present in the contour map.