Smart microgel catalyst with modulatory glutathione peroxidase activity

Abstract

Glutathione peroxidase (GPx) is a key antioxidant enzyme involved in scavenging of reactive oxygen species and protects cells from oxidative damage. Consequently many efforts have been devoted to develop artificial catalysts with GPx functions. For constructing a smart GPx model, GPx active sites were introduced into temperature responsive poly(N-isopropylacrylamide) (polyNIPAM) scaffolds. By combining the binding ability endowed from micro-pores of functional microgels and the catalytic moiety tellurium, this new microgel catalyst exhibits high GPx-like catalytic activity with typical saturation kinetics behavior as a real catalyst. Compared with diphenyl diselenide (PhSeSePh), a well-studied GPx mimic, it is about 339 000-fold more efficient than that of PhSeSePh for catalyzing the reduction of cumene hydroperoxide (CUOOH) by 3-carboxyl-4-nitrobenzenethiol (TNB). More importantly, the catalytic efficiency of this microgel enzyme model displays an obvious temperature responsive characteristic. The catalytic activity of the microgel can be turned on and off reversibly by changing the temperature. At 32 °C it demonstrates the highest GPx-like activity, as the temperature increses up to above 50 °C, the GPx-like activity of the microgel is almost lost. Through detailed studies of catalytic behavior for structurally different substrates, the fluorescence spectra with a pyrene probe combined with the size determined by Zetasizer nano instrument demonstrate that the dramatic efficiency alteration of the microgel catalyst is mainly due to the change of the pore structure in the microgel.