Studies On The Hydrolysis Of Carboxylic Acid Ester (PNPP) Catalyzed By Micelle And Metallomicelle

The chemical functional mimicry of hydrolytic metalloenzyme is one of frontier research fields in chemistry and bionics. Recently, micelle, metal complex, especially metallomicelle made of metal complex and micelle as model systems for artificial hydrolytic enzyme are the very active research fields. This dissertation focuses on the following aspect: the hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by metal complex and metallomicelle. The results obtained may provide theoretical basis and significative information for finding out the hydrolytic mechanism of enzymes and for designing highly efficient artificial enzyme model systems. For the purpose of studying the influence of the geometry of metal ion coordination on the hydrolysis of the carboxylic ester, the hydrolysis of PNPP catalyzed by metallomicelles made of Ni(II) complexes of bis(dioxocyclam) and three kinds of surfactants(CTAB, Brij35 and LSS) have been investigated kinetically, respectively. The results suggested that the open ring Ni(II)complex exhibited a greater catalytic activity in LSS micellar solutions than that in CTAB and Brij35 micellar solutions, which may be due to the different coordinating ability of substrates to complexes and the electrostatic interaction between micelle and complexes or substrates. Moreover, it is worth noting that the catalytic activity in the Ni(II) complex on the hydrolysis of PNPP also depends on the space hindrance of complex. Small space hindrance of complex is favorable for the catalytic hydrolysis of the substrate . In order to elucidate the effects of different metal ions on hydrolysis of esters, two Schiff base Cu(II) and Ni(II) complexes were synthesized and characterized. The hydrolysis of PNPP catalyzed by these two complexes was investigated in CTAB micellar systems. The results obtained indicate that Cu(II) complex with open ring ligand exhibited highly catalytic activity on the hydrolysis of PNPP, which may be due to the different coordinating ability of the substrates to complexes and the electrostatic interaction between micelle and complexes or substrates. With the development of surfactant chemistry, researchers have paid much more attention to Gemini surfactant owing to its unique properties. The hydrolysis of PNPP mediated by dimethylene-1,2-bis(dodecyltrimethylammonium bromide)(12-2-12, 2Br-), compared with cationic Gemini dimethylene-1,2-bis(cetyltrimethylammonium bromide)(16-2-16, 2Br-) were investigated kinetically. It was noteworthy that long hydrophobic chain Gemini surfactant micellar system enhanced the hydrolysis of carboxylic acid esters more notably than the short one did, which provide useful information to understand the effect of microenvironment of mimicking esterase.