Investigation Of The Hydrolytic Cleavage Of Esters Promoted By Mimic Hydrolytic Enzymes Using Metal Complexes And Metallomicelle

Metal complexes, especially metallomicelles formed by metal complex and micelles are widely employed as artificial hydrolases to catalyze the hydrolytic cleavage of carboxylic acid esters and phosphate esters. The cleavage of p-nitrophenyl picolinate (PNPP) and bis(p-nitrophenyl) phosphate (BNPP) catalyzed by metalomicelles, which is formed by crowned Schiff base metal complexes and Gemini (or double long-chain) surfactant micelles, has been studied systematically in this dissertation. Moreover, the effects of structure of complex on the hydrolytic rate of carboxylic acid esters and phosphate esters have been studied. Especially, micelle-catalyzed hydrolysis of HPNP (a RNA model) has firstly been investigated and some interesting information has been gained.A series of symmetrical (or unsymmetrical) single (or double) Schiff base metal complexes have been synthesized. And, their catalytic activities for the hydrolysis of PNPP and BNPP in Gemini surfactant micelles and conventional CTAB micelles have been investigated, respectively. The results show that the hydrolytic rates of PNPP and BNPP in Gemini micelles are greater than that in CTAB micelles, which may be due to the unique structure of Gemini surfactant. In addition, a seven-orders of magnitude rate acceleration has been observed in the hydrolysis of BNPP catalyzed by the two metallomicelles formed by the double long-chain surfactant DHAB and the unsymmetrical Salen-Mn(III) (or Salen-Co(II)). Observations imply that both Gemini and double long-chain surfactant micelle are the ideal reaction media, which provides useful information for the design of effective artificial hydrolases.The relationship between the catalytic activity and structure of complexes has been deeply discussed in the dissertation. The experimental results reveal that the key effect of the substitutes of ligand on the Lewis acidity of central metal is not only depend on the intrinsic electron-withdrawing (or -donating) property of substitute but also on the linked site of substitutes, which is accordance with the classic inductive effect theory. In addition, the catalytic activity of catalyst is also correlative to the coordinating sphere of the active site. Interestingly, the effects of the same pendant group inside different complexes with different backbones on the catalytic activity of catalysts may be apparently different, so far as to involve the transformation of the major and minor influencing-factors. Moreover, the effect of the center metal on the reactivity of catalyst has been evaluated, and it is found that the ratio of charge and radius of the metal is one of the important factors.The micellar system has firstly been introduced to the hydrolytic cleavage of HPNP as a RNA model substrate. Initially, the hydrolytic cleavage of HPNP induced by an imidazole derivative Zn(II) complex has been investigated in Gemini 16-2-16 micellar solution and traditional CTAB micelles, respectively. The results obtained show that the rate of HPNP catalytic cleavage in Gemini 16-2-16 micelles exhibited about 2.5-fold kinetic advantage compared to that in CTAB system. Furthermore, it is found that the addition of cationic surfactants in the homogenous system containing catalyst and HPNP with good water-solubility dramatically accelerated the hydrolytic cleavage of HPNP. A "sandwich absorptive mode (micelle-HPNP-catalyst)" is proposed to explain the interesting results. In general, to accelerate the mass transfer process in a heterogeneous reaction, surfactants are added to the catalytic system, in which the substrate and catalyst distributed in different pseudo-phases. Thus, our study extends the usage of cationic surfactants.