Construction And Kinetic Studies Of Hydrolase Mimic Based On Cyclodextrin

Enzymes are proteins with high substrate specificities and large rate accelerations, as evolved natural products by several billion years. Enzymes catalyze almost all chemical reactions with stereoselectivities and specificities under mild conditions. The study of natural enzyme aroused the concern of both chemists and biologists, because of its high selectivity, catalytic activity and mild reactive condition in chemical reaction. Various simple or complicated chemical systems have been widely used as mimic models for natural enzyme. Through the investigation of enzyme mimic, the mechanism of the enzymatic catalytic reaction and correlation between the structure, character and function of the enzyme were explored which should lay a theoretic foundation for designing and synthesizing the catalysts with simple structure, high selectivity, high catalytic activity in mild reactive condition.The idea of the stabilization of the transition state inspires thinking about enzymatic catalysis for decades, and now it still serves as a conceptual guide for understanding enzymatic catalysis. In catalysis, the procedure that enzymatic catalytic sites delicately match with the structure of transition state, decreases the activated energy of high-energy transition state efficiently, and thus facilitates the catalyzed reactions by overcoming the energy barrier.Hydrolytic metalloenzyme is one kind of natural metalloenzymes in biology. These hydrolytic metalloenzyme can catalyze hydrolysis of the substrate. Hydrolase is not only in biology, but also participates in many physiological procrsses. Therefore, the design and synthesis of rational hydrolytic metalloenzyme mimics using chemical theory and experimental methods not only redound to understand the catalytic mechanism of natural enzymes, but also an important significance for the design of artifical hydrolytic metalloenzyme and engineering and functional materials. Fabrication of hydrlase models offers an ideal alternative for elucidating the origin of substrate binding and catalysis of enzyme.Mimicking the natures of molecular recognition and catalysis of enzymes by artificial enzymes is very essential for exploring the evolved biological process of enzymes as well as their properties of structures and functions. On the basis of structural understanding of hydrolase, we selected supramolecular host molecules—cyclodextrins as the scaffolds of enzyme models, and obtained a series of cyclodextrin-based hydrolase models and the detailed kinetics was also carried out.1. Construction and Kinetic Studies of Metallocyclodextrins with Both Substrate Recognition and Transition-State Binding SiteIncreasing the transition-state binding, as well as correctly incorporating and positioning the functional groups is essential for the construction of an effective enzyme model. Inspired by the transition-state binding and substrate binding, we designed and synthesized a series of copper complex of guanidinium-containing polyamine cyclodextrins, and characterized these hydrolase mimics by means of IR, 1H NMR, and MALDI-TOF MS. The guanidinium group acts as an effective binding site for the stabilization of the transition state of the hydrolysis reaction and metal ion acts as a catalytic center. A detailed kinetic study reveals that the catalytic hydrolysis efficiency by guanidinium-containing complexes is higher than those by polyamine complexes without guanidinium group. At the same time, non-covalent binding of substrate and cyclodextrin was studied by 1H NMR, the study provided an important communication for design of hydrolase mimics with high efficiency.2. Construction and Kinetic Studies of An Allosteric Supramolecular Hydrolase ModelThe natural enzymes have an appropriate rigidity and flexible. An allosteric regulation controlled the structure and increased catalytic efficiency of many enzymes in their catalysis processes. Inspired by the concept of allosteric regulation in synthetic catalysts, we constructed an artificial allosteric hydrolase model with cooperativity between the metal center and allosteric site through supramolecular assembly of an adamantanyl guanidinium and a copper (II) complex of tris(2-aminoethyl)amine modified cyclodextrin (tren-CD). In our system, guanidinium group can bind the oxyanion of tetrahedral transition state of DNDPC hydrolysis, and it acts as a regulatory site. The structure of the supramolecular inclusion has been determined by 1H NMR and selective NOESY measurement. Furthermore, the allosteric role of the guanidinium group was unambiguously demonstrated by the catalytic behaviors of the allosteric model, the kinetics studies in presence of the allosteric model revealed that allosteric guanidinium group strongly influences catalytic behaviors of the supramolecular catalyst. The study provided an important communication for design of artifical enzymes.3. Construction and Kinetic Studies of An Artificial Supramolecular Nanozyme Based onβ-Cyclodextrin-modified Gold NanoparticlesFor mimicking catalytic action of natural hydrolytic metalloenzymes containg two or more metal center in their active sites, the synergistic effect of two metal ions and the microenvironment of enzyme catalysis, an artificial nanozyme model was developed by the supramolecular complexation of aβ-cyclodextrin-modified gold nanoparticle and metal catalytic centers. The cyclodextrin-based monolayer was constructed on the surface of gold nanoparticle by using thiol modified cyclodextrin. The cyclodextrin-modified gold nanoparticle was utilized as a backbone to construct a supramolecular artificial enzyme. The catalytic behaviors of theβ-cyclodextrin-modified gold nanoparticles with adjacent multi-metal catalytic centers were investigated as an esterase mimic.