Xie Jia-qing

Catalytic Hydrolyses of Carboxylic Acid Esters in the Presence of Gemini Surfactant

Hydrolyses of p‐nitrophenyl picolinate (PNPP) and p‐nitrophenyl acetate (PNPA) mediated by the micellar catalytic systems of two types of cationic surfactants [cetyltrimethylammonium bromide (CTAB), Gemini dimethylene‐1,2‐bis(cetyltrimethylammonium bromide) (16‐2‐16, 2Br−)] were investigated spectrophotometrically in the pH range of 7.0–9.0 and 25°C. Also, the effects of several kinds of additives, such as ethanol, cyclodextrins (CDs), on the hydrolytic reactions of PNPP and PNPA were studied systematically. It is noteworthy that: (1) double chain Gemini surfactant micellar system enhanced the hydrolyses of carboxylic acid esters notably compared with single chain surfactant (CTAB) micellar solutions under the same reaction conditions; (2) the apparent rate constants (k obsd) of PNPP and PNPA hydrolyses increased with the increasing in pH values of reaction media; (3) as additives, ethanol has effect on both PNPP and PNPA hydrolyses, and moreover, the k obsd for hydrolyses decreased with the increasing contents of ethanol (≤5%) at 25°C and pH 9.00; (4) the presence of CDs [α‐cyclodextrin (α‐CD), β‐cyclodextrin (β‐CD), γ‐cyclodextrin (γ‐CD)], as additives, showed different effects on PNPP and PNPA hydrolyses in different reaction systems.

Hydrolysis of Bis(4‐Nitrophenyl) Phosphate Catalyzed by Metallomicelle Made Up of the Crowned Schiff Base Complex as Synthetic Hydrolase

A crowned Schiff base ligand and its cobalt(II) and manganese(III) complexes were synthesized and characterized, and the metallomicelles made from the complexes and micelles (Brij35, LSS, CTAB) were investigated to catalyze the hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP). A kinetic mathematical model for simulating enzyme catalyzing reaction was proposed and employed to analyze the mechanism of BNPP catalytic hydrolysis. Michanelis constant and the apparent active energy for the catalytic reaction were calculated. The kinetic studies showed that the metallomicelle made from the micelle and crowned Schiff base transitional metal complexes is an effective mimetic hydrolytic enzyme for BNPP catalytic hydrolysis.

Catalytic hydrolysis of bis(p-nitrophenyl) phosphate by lipophilic diaquo(tetraamine) cobalt(III) in micellar solution

The catalytic hydrolysis of bis(p-nitrophenyl) phosphate by lipophilic diaquo-(tetraamine)Co(III) complex in Brij35 micellar solution was investigated at 25°C and at pH ranging from 4.1 to 9.0. The results indicated that the Co(III) complex in micellar solution exhibited a great rate enhancement effect on the hydrolysis of bis(p-nitrophenyl) phosphate compared with the Co(III) complex in aqueous solution. This may be explained by the decrease in pK for the dissociation of water molecule of the Co(III) complexes in micellar solution. A kinetic scheme is suggested for elucidating the mechanism.

ACCELERATED CLEAVAGE OF P-NITROPHENYL PICOLINATE CATALYZED BY COPPER(II) AND ZINC(II) COMPLEXES OF D-GLUCOSAMINE SCHIFF BASE IN MICELLAE SOLUTION

Abstract The hydrolysis of p-nirrophenyl picolinate (PNPP) catalyzed by the Cu(II) and Zn(H) complexes of d-glucosamine schiff base was investigated kinetically by observing the rates of the release of p-nitrophenol in the buffered micellor solution at different pit and 25°C. The scheme for reaction acting mode involving a ternary complex contain ligand, metal ion and substrate in micelle was establish and the reaction mechanisms were discussed The experimental results indicated that the complexes catalyzed efficiently the hydrolysis of PNPP, especially Zn(II) complex. The rate constant kN, which shows the catalytic reactivity of complexes, WBI determined to be 0.4251 s−1 far Cu(II) complex at pH 7 60 in micellar solution. The catalytic reactivity of Zn(II) complex were much larger than Cu(II) complex, the kN was determined to be 3.1914 s−1 at same pH value.

Framework and catalytic activity of a metallomicelle system made from an azacrown ether, lanthanum(III) ion and a cationic surfactant

A metallomicelle system comprising an azacrown ether, lanthanum(III) ion and a cationic surfactant was constructed and used as catalyst in the hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP). The interaction between La(III) and the azacrown ether, and the resulting complex and BNPP, were analysed by fluorescence spectroscopy. The catalytic rate of BNPP hydrolysis was measured kinetically by UV-Vis spectrophotometry. The results indicated that the metallomicelle system exhibited relatively high stability and excellent catalytic function in BNPP hydrolysis, the rate of which, compared with the spontaneous hydrolysis, increased by a factor of ca 2 × 107 due to the catalytic effect of the active species and the local concentration effect of the micelle in the metallomicellar system. The results also showed that the complex, comprising La(III) ion, and the azacrown ether, is the active catalytic species, while the micelles provide a useful catalytic environment for reaction. On the basis of these results, a reaction mechanism for the catalytic hydrolysis of BNPP is proposed.

Hydrolysis of p-Nitrophenyl Picolinate Catalyzed by Copper(II) and Zinc(II) Binuclear Complexes Coordinating Tripeptide in Micellar Solution

The kinetic model of binuclear metal complex catalysis involving a ternary complex in CTAB micellar solution is proposed in this paper. The catalyzed hydrolysis of p-nitrophenyl picolinate catalyzed by Cu(II) and Zn(II) coordinating tripeptide was studied kinetically by observing the rates of the release of p-nitrophenol in the buffered micellar solution at 25°C and different pH values. The proposed kinetic model is confirmed by experimental results which indicate that the 1 : 2 complexes of the ligand to metal ion are the active species in the reaction and the complexes catalyze efficiently the hydrolysis of PNPP, especially Cu(II) complex. The pKa of hydroxyl group of the ternary complex was determined to be 8.24, and the maximum rate constant which shows that the nucleophilic reactivity of complexes was determined to be 0.0262 s−1 for Cu(II) complex. The catalytic mechanism of reaction is discussed in bifunctional mechanism.

Synthesis, characterisation and molecular recognition of novel Zn(II) macrocyclic complexes with imidazole or benzimidazole pendants

Macrocyclic polyamine Zn(II) mononuclear and dinuclear complexes bearing imidazole or benzimidazole pendants have been synthesised and their binding constants determined by UV-Vis spectrometric titration. The binding ability of the complexes is stronger than that of the control materials with cytosine (Cyt). The recognition abilities of the dinuclear complexes for Cyt are much higher than that for the other bases or nucleosides (such as uracil, 5-hydroxymeyhyl uracil, adenosine, thymidine and uridine); the binding constants of the dinuclear complexes with m-xylyl or pyridyl as linkers are 25,360 and 22,550 dm3 mol−1 respectively.

Mechanism of DNA cleavage catalysed by the system comprising an unsaturated tetraaza macrocycle and La(III) and Ce(III) ions

In order to further the design of efficient artificial nuclease models for hydrolytic cleavage of DNA, the catalytic system made from an unsaturated tetraaza macrocycle and La(III) and Ce(III) ions was constructed and used as catalyst in the cleavage of plasmid PUC19 DNA. The interactions of these catalytic systems with plasmid PUC19 DNA has been investigated by UV-Vis absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry and gel electrophoresis. The results show that the combination of the catalytic system with DNA involves electrostatic binding through the phosphodiester linkages of DNA. The gel electrophoresis results also showed that supercoiled PUC19 plasmid DNA (cccDNA) was converted to the nicked form of DNA (ocDNA) under a nitrogen atmosphere. On the basis of these results, a mechanism for the catalytic cleavage of DNA is proposed.