Organotellurium-bridged cyclodextrin dimers as artificial glutathione peroxidase models

Abstract

To elucidate the importance of the goodness of fit in complexes between substrates and glutathione peroxidise (GPX) mimics, we examined the decomposition of a variety of structurally distinct hydroperoxides at the expense of glutathione (GSH) catalyzed by 2,2′-ditellurobis(2-deoxy-γ-cyclodextrin) (2-Te-γ-CD), and by the corresponding derivatives of β-cyclodextrin (β-CD) and α-cyclodextrin. The good fit of the cumene group into the γ-CD binding cavity reflected the result of well-defined reaction geometry, leading to the most excellent peroxidase activity with high substrate specificity. Furthermore, the catalytic constant and the combination with the best binding also exhibited the highest regioselectivity in the substrate decomposition. Saturation kinetics were observed and the catalytic reaction agreed with a ping-pong mechanism, in analogy with natural GPX, and might exert its thiol peroxidase activity via tellurol, tellurenic acid, and tellurosulfide. The stoichiometry of the inclusion complex was determined to be of 2:1 host-to-guest. The value of stability constant K c for (2-Te-γ-CD)2/GSH at room temperature was calculated to be 3.815 × 104 M−2, which suggested that 2-Te-γ-CD had a moderate ability to bind GSH. Importantly, the proposed mode of the (2-TeCD)2/GSH complex was the possible important noncovalent interactions between enzymes and substrates in influencing catalysis and binding.