Structural analysis of saccharin in aqueous solution by NMR and supramolecular interactions with α-, β-, γ-cyclodextrins

Abstract

Abstract As one of the many sweet-tasting molecules of various sizes and chemical/physical properties, interaction of saccharin with water molecules, and α-, β-, and γ-cyclodextrin in aqueous solution, is examined using NMR properties of both exchangeable and non-exchangeable protons. A thorough assignment of 13C and 1H signals of saccharin is achieved and corresponding precise chemical shifts were reported. Direct complexation interaction with α-cyclodextrin is absent, whereas partial interaction with β-cyclodextrin and full immersion/complexation with γ-cyclodextrin take place with reference to the NMR parameters including complexation induced chemical shift (CIS) changes, temperature coefficients, and exchange rates. The interaction with β-cyclodextrin seems to be taking place on the surface without full insertion into cavity, resulting in only slight chemical shift changes of maximum |0.017| ppm on saccharin proton signals with the signal patterns almost identically similar to uncomplexed form. This superficial interaction does, nevertheless, have effect on CIS values of β-cyclodextrin hydroxy protons with a maximum of |0.091| ppm. For γ-cyclodextrin, the full complexation interaction is directly visible from the large CIS of C(5)H and C(8)H protons of saccharin, as well as those of O(2)H and O(6)H of γ-cyclodextrin.