【作者】 王思怿；

【导师】 郭旭虹；

【作者基本信息】 华东理工大学 ， 化学工艺， 2013， 博士

【摘要】 聚电解质与生物大分子的相互作用研究能为其在蛋白质分离纯化、药物控释、创口修复、生物传感等领域的应用提供理论基础,因而成为当今最热门的科研方向之一。聚合物修饰的纳米粒子可以选择性地吸附蛋白质、酶、核酸、多糖和脂类等,也能注入人体血液中,并到达人脑和细胞。纳米球形聚电解质刷兼具聚电解质和纳米粒子的特性,既能选择性吸附蛋白质,也能通过改变环境条件可控地释放,因而能作为蛋白质固载、纯化、分离的载体,应用于靶向给药、疾病诊断和纳米生物反应器等领域。本文采用光乳液聚合方法,在粒径约为100nm的聚苯乙烯核表面上制备了厚度在30至150nm之间的阴离子型(聚丙烯酸)刷、阳离子型(聚2-氨基乙基酯盐酸盐)刷及核内包覆有四氧化三铁纳米粒子的磁性聚丙烯酸刷,研究了聚电解质刷可控吸附及脱附蛋白质的机理和影响因素,比较了阴离子刷与阳离子刷吸附蛋白质的行为差异,并将固载酶的球形聚丙烯酸刷和磁性聚丙烯酸刷作为纳米反应器进行酶促反应,观察了被聚合物刷固载前后酶的催化活性变化。主要的研究内容及结论如下：1.以牛血清蛋白(BSA)作为模型蛋白质,研究了其与聚丙烯酸刷(PAA-SPB)的相互作用。结合浊度滴定、动态光散射(DLS)和zeta电位的研究方法,从相态、尺寸和电荷的角度定性地观察了BSA与PAA-SPB相互作用随pH的变化。随着体系pH的降低,蛋白质与刷子呈现出吸附、团聚和脱附三种状态。等温滴定量热法(ITC)则从热力学和动力学角度提供了相互作用的定量信息,包括吸附过程中的热力学参数、结合强度及吸附量。小角X光光散射(SAXS)则观察到刷子吸附蛋白质前后结构上的细微差异,证实了蛋白质吸附于刷子层中。研究表明,蛋白质与聚电解质刷的相互作用主要是静电相互作用。体系的pH和离子强度共同决定了相互作用的强弱及蛋白质吸附量的大小。2.研究了阳离子型聚(2-氨基乙基酯盐酸盐)刷(PAEMH-SPB)与蛋白质BSA的相互作用。采用与1.中相同的研究手段,发现随着pH值的增加,阳离子刷与BSA也包含吸附、团聚和脱附三个阶段。但是,阳离子刷与BSA相互作用的pH窗口比阴离子刷更宽。除了pH和离子强度外,蛋白质与刷子的化学计量比和刷子的链长也能影响相互作用的pH窗口大小及吸附量。因此,通过调节体系的pH、离子强度、化学计量比和刷子的链长,阳离子刷能可控地吸附和脱附BSA。3.通过比较不同蛋白质与阴/阳离子刷的相互作用,发现阴离子刷与BSA/BLG(β-乳球蛋白)的相互作用行为较为相似,而阳离子刷吸附及脱附BSA/BLG的pH窗口却差别很大。因此,阴离子刷无法将BSA和BLG这两种等电点相近的蛋白质分开,而阳离子刷则能实现BSA和BLG的分离。这是由蛋白质表面电势的差异所致。通过DelPhi软件模拟,发现BLG的负电荷簇尺寸较大且分布很集中,而且具有类似偶极性的正负电荷簇。而BSA的“负电荷补丁”则由几个离散的负电荷簇组成。本文还研究了碱性木瓜蛋白酶与阳离子刷的相互作用。证实与酸性蛋白质相比,碱性蛋白质与阳离子刷的相互作用pH区间更窄并向高pH值迁移,结合较弱,吸附量较小。通过调节体系的pH、离子强度、化学计量比和刷子的链长,阳离子刷能有效地分离BSA、BLG(?)木瓜蛋白酶,而阴离子刷能吸附并固载多种酸性蛋白质。4.采用纳米球形聚丙烯酸刷和磁性聚丙烯酸刷吸附和固载葡萄糖糖化酶,并用于催化淀粉水解反应,利用浊度滴定、等温滴定量热法(ITC)和吸附实验分别从定性和定量的角度研究了纳米球形聚丙烯酸刷和磁性聚丙烯酸刷与葡萄糖糖化酶的相互作用随pH和离子强度的变化。将固载葡萄糖糖化酶的聚丙烯酸刷进行酶促淀粉水解反应,发现固定于聚丙烯酸刷和磁性刷中的葡萄糖糖化酶活性并没有降低,反而还略有增加,这可能是因为聚丙烯酸刷与葡萄糖糖化酶间的静电相互作用和氢键缔合使酶能稳定地固定在聚电解质刷的内部,并随聚电解质刷均匀地分散在水溶液中,而刷子内部稳定的pH值和盐浓度环境为酶活性的发挥提供了良好的空间。更多还原

【Abstract】 In recent years, interaction between polyelectrolyte (PE) and biomacromolecules has attracted many interests in biotechnology, which lead to multiple applications in protein separation, drug delivery, wound healing, and biosensing. PE modified nanoparticles (NPs) can be ideal candidate for selective adsorption of protein, enzyme, nucleic acid, polysaccharide, and lipid. Since NPs are small enough to interact with cellular machinery and potentially to reach previously inaccessible targets, such as the brain and blood. Spherical polyelectrolyte brushes (SPBs) as colloidal NPs can be used as carriers for protein immobilization and separation. Through adjusting surrounding conditions, SPBs can adsorb and desorb proteins tunably. Therefore, SPB should be ideal candidate for protein immobilization, purification, separation, and applied to targeting drug delivery, high-performance diagnostic assays, and nano-bioreactor.SPBs were synthesized by photo-emulsion polymerization, consisting of a polystyrene core with a diameter around100nm and a polyelectrolyte shell with a thickness from30to150nm densely grafted on the core surface. The polyelectrolyte shell consists of either weak anionic poly(acrylic acid)(PAA) or weak cationic poly(2-aminoethyl methacrylate hydrochloride)(PAEMH). Magnetic SPBs consist of magnetic nanoparticles in the polystyrene core and PAA chains. In this paper, the interactions between proteins and anionic SPBs as a function of pH and ionic strength have been systematically compared with that for cationic SPB in both qualitative and quantitative ways. Such studies provide valuable insight into the interaction mechanism between proteins and SPBs and effects on interaction. SPB and magnetic SPB were used as carrier for enzyme immobilization and as nano-sized bioreactor for catalytic reaction, and test enzymatic activity before and after the immobilization in SPB. Main work and conclusions as follow:1. Bovine serum albumin (BSA) is employed as model protein to investigate their interaction with PAA-SPBs. The pH dependence of phase state, architecture, interaction behavior between proteins and PAA-SPBs were examined by turbidimetric titration, dynamic light scattering (DLS), and zeta potential measurement. Results reveal the existence of three pH regions, corresponding to adsorption, aggregation, and desorption of BSA from SPB upon decreasing pH. Isothermal titration calorimetry (ITC) was applied to determine the amount of adsorption, binding affinity, and thermodynamics of BSA adsorption onto SPBs in quantitative way. Small angle X-ray scattering was employed to investigate the subtle change of shell structure of PAA-SPBs before and after adsorption of BSA, which demonstrated that BSA molecules were distributed inside the shell of SPBs. The interaction between proteins and SPBs is caused mainly by electrostatic interaction. Both pH and ionic strength of system influence the adsorption amount of BSA in PAA-SPBs simultaneously.2. Cationic spherical polyelectrolyte brushes were employed as carrier for BSA immobilization. In this section, we continue to investigate the interaction in both qualitative and quantitative ways, following the characterization methods as above. We also found that adsorption, aggregation, and desorption of BSA by cationic SPBs could be tuned by increasing pH. However, the extent of pH range for BSA and cationic SPBs was wider than anionic SPBs. In addition to pH and ionic strength, protein and SPBs stoichiometry, and SPB thickness can influence pH region for adsorption and adsorbed amount as well. Therefore, through modulating pH, ionic strength, bulk stoichiometry of system, and SPB thickness, cationic SPBs can adsorb and desorb BSA effectively under optimized conditions.3. Turbidimetric titration, DLS, zeta potential measurement, ITC, and adsorption measurement were used to investigate the interaction between various proteins and anionic/cationic SPBs. Results reveal that interaction behavior between anionic SPBs and BSA is very similar to BLG, while pH window for BSA adsorption by cationic SPBs is significantly different from that of BLG. Therefore, we find that it is difficult to use PAA-SPBs to discriminate these two proteins with similar pls. However, selective adsorption between BSA and BLG can be achieved with cationic SPBs by proper selection of pH, ionic strength, bulk stoichiometry, and SPB thickness. This may arise from the different electrostatic interaction behaviors between SPB and protein "charge patches" or "charge regulation". The larger negative charge patch of BLG distributes centrally. Furthermore, positive and negative charge patches of BLG display dipolar distribution. While, smaller negative charge patches of BSA distribute discretely. We also study the interaction between basic papain and cationic SPBs. Compared to acidic proteins, basic protein adsorption by cationic SPB is in a narrow pH region and shifts to higher pH value. Cationic SPBs adsorb basic protein much weaker than acidic proteins. The sequence of binding affinity and stoichiometry of proteins onto cationic SPBs was observed by ITC as BLG>BSA>papain, which resulted from the size, isoelectric point, and charge anisotropy of proteins. Therefore, through adjusting pH, ionic strength, bulk stoichiometry, and SPB thickness, cationic SPBs have potential applications in separation and selective binding of BSA, BLG, and papain under optimized conditions. While, anionic SPBs provide mild conditions for BSA and BLG co-immobilization. 4. Spherical poly(acrylic acid) brushes (PAA-SPBs) and magnetic PAA-SPBs were employed as carriers for glucoamylase (GA) to catalyze amylolysis. Firstly, turbidimetric titration, ITC, and adsorption experiment were used to investigate the pH and ionic strength dependent interaction between GA and PAA-SPBs/magnetic PAA-SPBs in both qualitative and quantitative ways. Then, GA immobilization in PAA-SPBs and magnetic PAA-SPBs carried out under optimal conditions. We study the dynamics of amyloysis and activity of GA before and after immobilized in PAA-SPBs and magnetic PAA-SPBs. Experimental results demonstrate that immobilization of GA in PAA-SPBs and magnetic PAA-SPBs does not lead to the loss of activity of GA. The electrostatic attraction and hydrogen bonding between GA and PAA chains grafted on SPBs enhances the enzymatic activity, and SPBs provide stable surrounding such as pH and ionic strength for GA immobilization, so the GA immobilized in PAA-SPBs and magnetic PAA-SPBs displays higher catalytic activity than free GA.更多还原