Studies On Oxygenase-mimic And Hydrolase-mimic Of Crowned Schiff Bases And Crowned Hydroxamic Acids

The investigation of mimic enzyme not only can reveal the correlation between the structure and function of the natural enzyme and probe the mechanism of enzyme catalytic reaction, but also develop the useful green catalyst of high selectivity and high catalytic activity. Crown ethers, as the first generation organism of mimetic enzyme base compounds, endow special performance and characteristics due to the hydrophobicity of outer ethylene groups and orderly arrangement of inner oxygen atoms, and can effectively control the microenvironment around the enzyme model reactive site. For the purpose to employ the cooperativity of the azacrown ethers in mimetic enzyme aspect, we design and synthesis benzo-10-aza-15-crown-5 or aza-15-crown-5 substituted salicylaldimine Schiff bases and their transition-metal complexes as oxygenase and hydrolase models. Their thermodynamics of oxygenation reaction and the kinetics of catalytic hydrolysis have been also investigated. We have systematically studied the influences of azacrown ether substituentes and their bonding sites, as well as the alkali metal ions complexed by the crown ethers on biomimetic performance of these complexes. A series of useful and creative results have been obtained, which will supply much valuable information for the design and synthesis of new mimetic enzyme models. Three series of aza crown ethers or morpholino substituted mono-or bis-Schiff bases and their cobalt (II), manganese (III) complexes have been designed and successfully synthesized. They all have been characterized by IR,1H NMR,MS and elemental analyses. The azacrown substituted Schiff base cobalt (II) complexes have been employed as synthetic oxygen carriers. Their equilibrium constants Ko2 and thermodynamic parameters ? Ho and ?So for oxygenation in the presence of diethyleneglycol dimethy ether as solvent and pyridine as axial lingand over a range of –5oC to 25 oC have been determined and calculated. The results indicate that: 1.The dioxygen affinities of all the crown ether-Schiff base cobalt (II) complexes are superior to their crown-free analogues due to macrocyclic effect of crown ethers. Among of them, the azacrown ether symmetric substituted bis-Schiff base cobalt (II) complexes are best. 2. The bonding sites of the crown ether ring in the complexes visibly influence the dioxygen affinities of the complexes and the dioxygen affinities of 3-substituted in the ligands cobalt (II) complexes are higher than that of 5-substituted ones, respectively. 3. The dioxygen affinities of benzoazacrown ether substituted Schiff base cobalt (II) are superior to that of azacrown ether substituted analogues. The result showed that the former may possess stronger rigidity and hydrophobicity. 4. The addition of the alkali metal salt to oxygenation system can much enhance the dioxygen affinities of crowned Schiff base cobalt (II).Complexed alkalic ion by aza crown ether can conduce to the formation and stability of active species Co-O2-. The Schiff base manganese (III) complexes have been employed as cytochrome P-450 monooxygenase artificial models to catalyze epoxidation of styrene under ambient temperature and pressure using PhIO as oxygen source and as catalyst in the oxidation of p-xylene to p-toluic acid with air as oxidant. The influence of the structure of complexes on the selectivity and catalytic activity of oxidation reaction was examined. The result indicated: 1.The catalytic activity of complexes binding crown ring can be improved and the induce period of the oxidation for p-xylene to p-toluic acid was shortened. 2. The catalytic activity and selectivity of the crown ring symmetric substituted bis-Schiff base complexes for the oxidation of p-xylene are higher than that of asymmetric substituted bi-Schiff base and single substituted mono-Schiff base complexes. 3. The position of the bonded crown ring has distinct influence on the catalytic activity of complexes and azacrown ethers 3-substituted manganese (III) complexes are higher than that of 5-substituted ones. 4. The crownring complexed alkalic cation can enhance the catalytic activity of complexes. 5. There are some similar rule and certain relation between the catalytic oxidation of Mn (III) complexes and the dioxygen affinities of Co (II) complexes. Generally, the higher oxygenation constant Ko2 is, the shorter the produce period is. 6. The addition of N-hydroxyphthalimide(NHPI) as associate catalysts to oxidation system can obviously enhance the catalytic activity. For the first time, the crown ether substituted Schiff base and crowned hydroxamic acid transition-metal complexes as hydrolase models for the catalytic hydrolysis of PNPP and BNPP have been conducted. The kinetics of PNPP and BNPP hydrolysis in buffer solution catalyzed by above complexes has been investigated. The kinetics mathematical model of the reaction has been built. The proposed reaction mechanism has also been discussed. The results indicate that: 1. The hydrated complex may be real the active species in the PNPP and BNPP catalytic hydrolysis reaction. 2. The catalytic activities of crown ether substituted complexes are much higher than that of crown-free analogues in the hydrolysis. This indicates that the crown ethers can conduce to the molecule of hydrophobic PNPP comes easily to the active center of complexes and may synergize the central metal ion to activate the coordinated water molecule by the hydrogen bond formation. 3. In hydrolysis reaction the complex containing three crown ether rings is highest due to the influence of crown ring on microenvironment and hydrophobicity of active center. 4. The catalytic activities of the complex are correlated to Lewis acidity of central metal ions, the stronger the Lewis acidity of central metal ion is, the higher the catalytic activities of the complex is, so the catalytic activity of different metal ion in complex deceased in the order of Cu(II) >Co(II) >Zn(II)>Mn(II). 5. The catalytic activity of hydrolysis increases along with the increase of substrate concentration and the pH value of buffer solution, as well as the reactive temperature.