Effect of the Mixture of Cationic Starch and Selenized Starch on the Catalytic Activity of Starch-based Biomimetic Glutathione Peroxidase

In order to promote the catalytic activity of starch-based biomimetic glutathione peroxidase (GPx), the selenized starch (SCS) and cationic starch (CCS) prepared from cassava starch (CS) were mixed, resulting in the targeted starch (SCS/CCS) with both the catalytic center and the recognition site of substrate. First, CS was modified with octenyl succinic anhydride and sodium selenide hydride, respectively, to prepare SCS. The CCS was synthesized by modifying CS with 3-chloro-2-hydroxypropyltrimethylammonium chloride. Some technologies including nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal analysis (TG) and scanning electron microscopy (SEM) were used to characterize the samples. Finally, the effect of the mixture of SCS and CCS on the catalytic activity of GPx was investigated by changing the molar ration of nitrogen and selenium. Results showed that the ¹H NMR spectrum of SCS with selenium content of 11.35 μg/g revealed some new peaks (0.6~2.5 ppm) attributed to protons of the octenyl succinate compared with CS. In comparison to the FT-IR spectrum of CS, SCS showed lower intensities in the characteristic peaks of hydroxyl (3300 cm⁻¹) and bound water (1639 cm⁻¹), indicating the consumption of hydroxyl groups of CS in the synthesis of SCS. This would increase the hydrophobicity of the resultant starch. The appearances of the proton signal quaternary ammonium group (3.22 ppm) in the ¹H NMR spectrum of CCS and the C−N stretching (1483 cm⁻¹) in the FT-IR spectrum indicated the introduction of the positively charged quaternary ammonium group on the CCS backbone. With a similar particle size to the CS, SCS and CCS revealed a rough surface, indicating that the modification reaction mainly occurred on the surface of starch granules. No significant change was observed in the XRD patterns and TG curves of CS, SCS and CCS, indicating that the modified reaction did not dramatically affect the crystalline structure and thermal stability of starch. When the molar ratio of nitrogen and selenium in SCS/CCS was 1200, the catalytic activities of the biomimetic GPx in the reaction systems of 4-nitrothiophenol+cumene hydroperoxide (NBT+CUOOH), 3-carboxy-4-nitrothiophenol+hydrogen oxide (TNB+H₂O₂), NBT+CUOOH and NBT+H₂O₂ were 13.94, 11.25, 12.91 and 10.87 µmol/min, respectively, which were 22.1%, 25.8%, 17.5%, 19.6% higher than that of SCS, respectively. This study provided a simple method for constructing starch-based biomimetic GPx with high catalytic activity.