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

As one of the many sweet-tasting molecules of various sizes and chemical/physical properties, interaction of saccharin with water molecules, and alpha-, beta-, and gamma-cyclodextrin in aqueous solution, is examined using NMR properties of both exchangeable and non-exchangeable protons. A thorough assignment of C-13 and H-1 signals of saccharin is achieved and corresponding precise chemical shifts were reported. Direct complexation interaction with alpha-cyclodextrin is absent, whereas partial interaction with beta-cyclodextrin and full immersion/complexation with gamma-cyclodextrin take place with reference to the NMR parameters including complexation induced chemical shift (CIS) changes, temperature coefficients, and exchange rates. The interaction with beta-cyclodextrin seems to be taking place on the surface without full insertion into cavity, resulting in only slight chemical shift changes of maximum vertical bar.017 vertical bar 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 beta-cyclodextrin hydroxy protons with a maximum of vertical bar 0.091 vertical bar ppm. For gamma-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 gamma-cyclodextrin. (C) 2019 Elsevier B.V. All rights reserved.