Association mechanism of S-dinitrophenyl glutathione with two glutathione peroxidase mimics: 2, 2 cent-ditelluro- and 2, 2 cent-diseleno-bridged b-cyclodextrins.

Complex formation of the glutathione peroxidase mimics 2,2 cent-ditelluro-bridged b-cyclodextrin (1) and 2,2 cent-diseleno-bridged b-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 b-cyclodextrin (b-CD) or 1, but it is located between the two secondary rims of 2. The complexes' stability constants (K(s)) from 19 to 37 degrees C, Gibbs free energy changes (DG degrees ), DH degrees and TDS degrees for 1:1 complexes of b-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>b-CD. The binding ability of 3 by b-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>2indicated that the length of linkage between two cyclodextrin units plays a crucial role in the interaction with 3.