Investigation of Interactions of Methyl-β-cyclodextrin with Salicylic Acid and Benzene by Nuclear Magnetic Resonance Techniques

A nuclear magnetic resonance (NMR)-based methodological investigation supported by a theoretical calculation has been carried out to understand both qualitatively and quantitatively, the molecular interactions between salicylic acid and benzene in methyl-β-cyclodextrin (M-β-CD) solution. Two-dimensional diffusion ordered NMR spectroscopy (DOSY) and nuclear Overhauser effect (NOE) were used to detect the presence of the inclusion complex of salicylic acid and M-β-CD. The quantitative 1H-NMR, in comparison with the conventional UV method, was used satisfactorily for quantification of salicylic acid in M-β-CD solution. The competition between salicylic acid and benzene in M-β-CD solution for the formation of inclusion complex was monitored both qualitatively and quantitatively and was further interpreted by a theoretical calculation of coordination energy. The described NMR-based method can serve as a simple and useful tool for the qualification and quantification of molecular interactions, especially those between drugs and large molecules.