Association Mechanism of S-Dinitrophenyl Glutathione with Two Glutathione Peroxidase Mimics: 2, 2′-Ditelluro- and 2, 2′-Diseleno-bridged β-cyclodextrins

Complex formation of the glutathione peroxidase mimics 2,2′-ditelluro-bridged β-cyclodextrin (1) and 2,2′-diseleno-bridged β-cyclodextrin (2), with S-substituted dinitrophenyl glutathione (3) were determined by ultraviolet-visible (UV-Vis) absorption spectroscopy in phosphate buffer (pH 7.4) and (1)H-NMR spectroscopy. Molecular mechanics (MM2) modeling calculations were used to deduce a three-dimensional model for each complex. The dinitrophenyl (DNP) group of 3 appears to penetrate the cavity of β-cyclodextrin (β-CD) or 1, but it is located between the two secondary rims of 2. The complexes’ stability constants (K(s)) from 19 to 37 °C, Gibbs free energy changes (ΔG°), ΔH° and TΔS° for 1:1 complexes of β-CD, 1 and 2 with ligand 3 as obtained from UV-Vis spectra were compared. The binding of 3 by the three cyclodextrin hosts generally decreased in the order of 1>2>β-CD. The binding ability of 3 by β-CD, 1 and 2 was discussed with regard to the size/shape-fit concept, the induced-fit interaction, and the cooperative interaction of the dual hydrophobic cavities. The binding ability of 1>2 indicated that the length of linkage between two cyclodextrin units plays a crucial role in the interaction with 3.