阳离子淀粉与硒化淀粉混合对淀粉基仿生谷胱甘肽过氧化物酶催化活性的影响

为了提升淀粉基仿生谷胱甘肽过氧化物酶（GPx）的催化活力，采用木薯淀粉（CS）制备的硒化淀粉（SCS）和阳离子淀粉（CCS）进行混合，获得含催化中心和底物识别位点的目标淀粉（SCS/CCS）。首先，采用辛烯基琥珀酸酐、硒氢化钠和2,3-环氧丙基三甲基氯化铵分别对CS进行改性制备SCS和CCS；通过核磁共振波谱仪（1H NMR）、傅里叶变换红外光谱仪（FT-IR）、X射线衍射仪（XRD）、同步热分析仪（TG）和扫描电子显微镜（SEM）等手段对改性后的样品进行表征；最后以氮和硒物质的量比为变量，考察SCS与CCS的混合对GPx催化活力的影响。结果表明，与CS相比，硒含量为11.35 μg/g的SCS的1H NMR图谱在化学位移0.6~2.5之间出现了辛烯基琥珀酸酯分子链上质子的信号峰；SCS的FT-IR谱图与CS FT-IR谱图相似，但羟基（3300 cm?1）和结合水（1639 cm?1）特征峰的强度降低，表明SCS的合成过程消耗了CS骨架上的羟基，并提高了CS的疏水性；CCS的1H NMR图谱上3.22 ppm处出现季铵基的特征峰，同时，CCS的FT-IR谱图在1483 cm?1处出现了归因于季铵基C?N拉伸振动的特征峰，表明阳离子基团季铵基已成功修饰于CCS骨架上；与CS相比，SCS和CCS的颗粒形状无明显变化，但颗粒表面粗糙，表明改性反应主要发生在淀粉颗粒的表面；CS、SCS和CCS的XRD花样和失重曲线无明显差别，说明反应未显著影响淀粉的结晶结构和热稳定性。当SCS/CCS中氮和硒物质的量比为1200时，其在4-硝基苯硫酚+枯烯过氧化氢（NBT+CUOOH）、3-羧基-4硝基苯硫酚+氧化氢（TNB+H₂O₂）、NBT+CUOOH和NBT+H₂O₂反应体系中的GPx催化活力分别为13.94、11.25、12.91、10.87 μmol/min，比SCS分别提高了22.1%、25.8%、17.5%、19.6%。本研究为构建高催化活性的淀粉基仿生GPx提供了简单方法。

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.