【作者】 张志明；

【导师】 刘俊秋；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2009， 博士

【摘要】 酶是自然界进化的产物,是有着高底物特异性和强大催化能力的蛋白质,它能在温和条件下高效立体专一性地催化某些化学反应。化学和生物学家特别关注用人工方法来模拟酶的高选择性和高活性。各种简单或复杂的化学模型被广泛地应用于天然酶的模拟。通过仿酶研究大大促进了对天然酶的结构、性质和功能之间的关系的了解,为探索酶催化反应机理,设计并合成结构简单、高效、稳定的理想催化剂奠定了基础。在生物体众多的天然金属酶中,金属水解酶是一大类。它们能催化底物的加水分解。因此,借助化学的理论和实验手段,设计合成高效的水解金属酶模型,不仅有助于深化对天然酶作用机制的认识,而且,对人工酶、功能材料与器件的设计合成等都具有十分重要的意义。我们基于对天然水解酶结构与功能和酶底物识别的理解,从小分子模型化合物出发,通过修饰构建了一系列金属水解酶模型体系。在此基础上,利用超分子化学的方法和原理构建了基于金纳米胶束的超分子人工水解酶（纳米酶）,并分别对上述体系的催化能力和动力学进行了详细的研究。1.具有底物识别的三角配体金属水解酶的构建及动力学研究基于底物识别与催化基团的协同性,设计合成了以Ce³⁺为催化中心的水解酶模型,Ce³⁺与四种三角架配体形成复合物。分别研究了这些复合物催化RNA替代物2-羟基丙基硝基苯基磷酸酯（HPNP）和二（对硝基苯基）磷酸酯（BNPP）的水解动力学。其中Ce³⁺-L4复合物在25°C pH值为7.0缓冲溶液中对HPNP的水解催化能力比其自发裂解反应提高了10⁵倍以上（kcat/kuncat = 4.1×10⁵）。实验结果表明,这些单核Ce³⁺复合物对磷酸二酯键表现出不同程度的识别能力和选择性。通过引入不同位置的辅助羟基（邻、间、对位）获得了这些三角架配体与底物（HPNP或BNPP）可能的催化模式。催化机理分析为更好地理解“识别是酶反应中进行假分子内反应的必要条件”提供了基础。2.具有可翻转两亲性空腔的金属水解酶模型的构建及动力学研究基于胆酸分子简单的两亲结构和作为构筑基元对溶剂的良好响应,设计合成了具有可翻转两亲性空腔金属水解酶模型。利用季戊四醇胆酸三聚体（含三唑）三取代衍生物作为主体,通过Zn²⁺离子与三唑配位的方式在胆酸衍生物分子上引入金属离子催化位点。研究发现此模型能够在水/二甲基亚砜混合溶液中包合疏水底物分子对硝基苯酚乙酸酯（PNPA）并催化其裂解。在25°C对PNPA水解催化能力比其自发裂解反应提高了超过了103倍（kcat/kuncat）。改变水和DMSO的体积比获得不同的PNPA水解速率常数kobs,该研究清楚地表明该分子两亲性空腔只有在一定溶剂比例时才能结合疏水中性底物PNPA,并表现出催化活性。改变Zn²⁺与胆酸衍生物比例对PNPA水解所得表观速率常数kobs表明该金属复合物中金属与配体配位比例是1:1。该研究是利用Zn²⁺离子与三唑配位形成复合物,并根据胆酸分子的两亲性来调节酶模型对底物结合能力的重要尝试。3.金纳米晶胶束超分子人工纳米水解酶的构建及其动力学研究为了研究酶催化微环境对底物结合催化的影响以及模拟天然金属酶的催化作用,我们利用十二烷基修饰的金纳米晶为骨架,将金属(Cu2+、Zn²⁺)催化中心通过自组装法安装到金纳米晶表面,构建了金纳米晶胶束水解酶模型。水溶性的金纳米晶胶束水解酶模型表现出高效的类核酸酶活性,对于RNA的模拟物HPNP具有较好的催化活性,其催化水解速率是在相同条件下HPNP的自发水解速率的10⁵倍,从而发展了一种新的制备高效磷酸酯水解酶的方法。纳米酶对磷酸酯动力学实验证明金纳米胶束形成的微环境以及催化中心的协同作用是其水解能力增加的主要原因。更多还原

【Abstract】 Construction and Kinetic Studies of Metallohydrolase MimicsEnzymes are the natural products by evolution, they have high substrate specificity and catalytic ability, under mild conditions in high-performance to stereospecific catalyze certain chemical reactions. Because of their high selectivity, high activity and the advantages under mild reaction conditions, a variety of simple or complex chemical systems are widely used in the simulation of natural enzymes, to understand the mechanism of the natural enzymes. It is essential for the design and synthesis of simple structure with high activity and high selectivity under mild reaction conditions to mimic the enzyme structure, and investigate the relationship between the structure and the function, and explore the mechanism of enzyme-catalyzed reaction.In vivo metal hydrolases are a large class. Therefore, using of theoretical and experimental chemical methods, design and synthesis of reasonable hydrolytic metalloenzyme models can not only help us to deepen the understanding of natural enzyme mechanism, but also play an very important role on design other artificial enzymes, functional materials and devices.Based on the understanding of the identification of the natural structure and function of enzymes, we constructed a series of metal-modified enzyme model system. And based on the experiment above-mentioned and in view of using supramolecular chemistry methods and principles, we designed a gold nanoparticle-based supramolecular micelles artificial hydrolase （nano-enzyme）, and a detailed study of the kinetics of the above system were carried out respectively.1. Construction and Kinetic Studies of Metallohydrolase Model Composed of Tripodal Mono-Binuclear Cerium （III） ComplexesIt is necessary for the construction of an effective enzyme model to correctly incorporate and position the functional groups. Inspired by substrate binding, four tripodal ligands, the Ce（III） complexes of N,N’,N”-tris[（2-benzylamino）ethyl]amine （L1）, N,N’,N”-tris[（2-hydroxybenzylamino）ethyl]amine （L2）, N,N’,N”-tris[（3-hydroxybenzylamino）ethyl]amine （L3）, N,N’,N”-tris[（4-hydroxybenzylamino）ethyl]amine （L4） were prepared. The hydrolytic kinetics of 2-hydroxy-propyl-p-nitrophenyl phosphate （HPNP） and bis（p-nitrophenyl）phosphate （BNPP） catalyzed by these complexes were studied in buffer solution respectively. Ce-L4 displays the excellent catalytic efficiency in the complexes for hydrolysis of HPNP with an increase of 4×10⁵ fold （kcat/kuncat） for the spontaneous cleavage of HPNP in the buffer at 25°C pH 7.0. The catalysis result suggests these mono nuclear cerium（III） complexes express different recognizability and selectivity to the P-O bond of different phosphate diester. The cerium ion complexes of L3 and L4 served as structural models for the binding mode of coordinated water as well as substrates in the active site of hydrolytic enzyme. By introducing different position of the additional hydroxy （L3 and L4）, the possibly catalytic mechanism of tripodal ligand and hydrophilic or hydrophobic substrates （HPNP or BNPP） were achieved.2. Construction and Kinetic Studies of Invertible Molecular Pockets for Metallohydrolase ModelBased on the amphiphilic structure of cholate acid molecules and taking advantage of its good response to the solvent, we design metal hydrolase model with reversible amphiphilic cavity. We use cholate acid trimer （including triazole） pentaerythritol derivatives as the host and introduce Zn²⁺ ions to the triazole ligand to act as catalytic center. We found that the compounds could recognize hydrophobic substrate molecules （PNPA） in the water/DMSO mixed solution, and catalyze its cleavage. At 25°C pH 7.0 the catalytic capacity of above complexes for PNPA is 103-fold （kcat/kuncat） larger than the background rate of PNPA spontaneous cleavage. By changing the ratio of the water and DMSO, the apparent rate constant kobs clearly showed that the amphiphilic molecules can regulate the polarity of the cavity. In addition, the experimental results revealed that the binding ratio of ligand and Zn²⁺ was 1:1 by regulating the concentration of Zn²⁺.3. Construction and Kinetic Studies of An Artificial Supramolecular Nanozyme Based on Au NC MicellesFor mimicking catalytic action of natural hydrolytic metalloenzymes containg two or more metal center in their active sites and the synergistic effect of two metal ions and the microenvironment of enzyme catalysis, water-soluble gold nanocrystal micelles （Au NC micelles） with inserted catalytic Cu （II） center that act as excellent nanoenzyme models for imitating ribonuclease were constructed by supramolecular self-assembly. The dodecane-1-thiol-based Au nanocrystal （NC） was first constructed, subsequently a cationic surfactant hexadecyltrimethylammonium bromide （CTAB） and a catalytic ligand （N1,N1-bis（2-aminoethyl）-N2-dodecylethane-1,2-diamine） Cu（II） （Cu（II）L） was installed on the surface of Au nanocrystal （NC） via hydrophobic interaction. The catalytic capability of designed Au NC micelles was estimated by the cleavage of typical RNA analogue, 2-hydroxypropyl p-nitrophenyl phosphate （HPNP）. The study of the catalytic behavior of Au NC micelle catalysis showed that the Au NC micelles exhibited dramatic ribonuclease-like activity, and a high rate acceleration of kcat/kuncat = 1.1×10⁵ for the cleavage of HPNP in comparison to the spontaneous cleavage of HPNP （kuncat） was observed. The catalytic capability for HPNP cleavage by these functionalized Au NC micelles can be considerable compared to that of covalent gold nanoparticles reported previously as nanozymes under comparable conditions. A detailed investigation of enzymatic kinetics was carried out and a possible mechanism was suggested.更多还原