Shulan Cai

Kinetic Study of the Hydrolysis of BNPP by the Cerium(III) Complex

5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane (L) was synthesized and characterized. The kinetics of hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) in the catalytic system containing macrocyclic ligand and cerium(III) was investigated. This catalytic system show high catalytic activity and better reproducibility and stability than other similar systems in the range of pH of around 5.6–7.2. The stoichiometry and spectral analysis showed that the real active species is the macrocyclic complex of cerium(III). Based on the analytical results of the specific absorption spectra, an intramolecular nucleophilic substitution mechanism for the catalytic hydrolysis of BNPP is proposed, a correlative kinetic mathematical model is established, and the corresponding thermodynamic and kinetic constants are calculated.

Hydrolysis of BNPP Catalyzed by Metallomicelles Made of Pr(III) Complexes

A macrocyclic ligand was synthesized and characterized. The kinetics of hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) in the catalytic system containing macrocyclic ligand and praseodymium(III) was investigated. The analysis of specific absorption spectrums of the hydrolytic reaction systems indicated that key intermediates made up of BNPP and praseodymium(III) complexes are formed in the reaction process of BNPP catalytic hydrolysis. In this, the mechanism of BNPP catalytic hydrolysis proposed is based on the analytic result of specific absorption spectrum, and the corresponding kinetic constants are calculated. The results showed that the praseodymium(III) complexes as hydrolase mimics exhibit good catalytic activity and similar catalytic character to natural enzyme.

studies of DNA binding and DAN cutting mechanism of an azamacrocyclic cerium complex with carboxyl branch

An azamacrocyclic compound with a carboxyl branch, 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-tetradecane-N/-acetic acid (L), and its cerium complex were synthesised and characterised. The mode of combination of the cerium complex with DNA was investigated by fluorescence and UV-Vis absorption spectroscopy. The cutting function of the cerium complex towards supercoiled DNA was studied by the gel electrophoresis method. The results show that metal complex can bind to the phosphate group of DNA double helix and promote the hydrolysis of the phosphodiester bond of supercoiled DNA (Form I); under certain conditions, supercoiled form DNA (Form I) was transformed into the nicked form DNA (Form II) under the strong cutting effect of the macrocyclic cerium complex; the cutting is completed by a hydrolysis mechanism.

Catalytic mechanism and activity of a nitrogen heterocycle lanthanum(III) complex in the hydrolysis of bis(4-nitrophenyl) phosphate ester

The system made up of a nitrogen heterocycle ligand and lanthanum(III) ion was used in the catalytic hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP). This catalytic system showed higher catalytic activity in this hydrolysis and better reproducibility and stability than other similar lanthanum(III) ion systems. The rate of the catalytic hydrolysis was about 108-fold faster than that of its spontaneous hydrolysis under the same conditions. Compared with previous Cu(II) or Ni(II) complexes containing the same ligand in water, the activity of the macrocyclic La(III) complexe is increased ca 104-fold. The experimental evidence showed that the mon-hydroxy complex made of the nitrogen heterocycle ligand and lanthanum(III) ion is the active species as catalyst in the catalytic hydrolysis of BNPP.

Function of the Metallomicelle from an Aza-Crown Ether Complex with an Acetamide Branch as a Highly Potent Promoter of Phosphate Diester Hydrolytic Cleavage

This study reports the synthesis method of a new aza-crown ether with an acetamide branch ligand, 2-(1,10-dioxa-4,7,13,16-tetraaza-cyclooctadec-4-yl)-acetamide (L), and determines the chemical composition of the cerium complex containing the aza-crown ether ligand by a new fluorescence spectrophotometric method. In the report, the cerium complex and its metallomicellar systems were used as catalysts in the hydrolysis of bis(4-nitrophenyl)phosphate ester (BNPP), and their catalytic activity was studied by the comparative method. The interaction between the metallomicelle and BNPP was proved by the fluorescence spectrum. The catalytic rate of BNPP hydrolysis was measured kinetically using the UV-Vis spectrophotometric method. The results indicated that the metallomicellar system of the anionic surfactant exhibited excellent catalytic function and relatively higher catalytic activity than that of the complex solution, the metallomicelle of nonionic and cationic surfactants, and the micelle provided an effective catalytic environment for the catalytic reaction. The experimental results also showed that the best acidity for the metallomicelle catalysis is pH 8.0, and the mono-hydroxy complex may be the real active species uaed as a catalyst in BNPP catalytic hydrolysis. The reaction mechanism was proposed on the basis of the research results. GRAPHICAL ABSTRACT

Phosphate Diester Cleavage Promoted by the Metallomicelles of Ce(III) Complexes of Aza-Crown Ether with Different Numbers of Nitrogen Atoms

The design of artificial hydrolase has attracted extensive attention due to their scientific significance and potential application in the field of gene medicine and molecular biology. This work reports the catalytic activation of two aza-crown ether Ce(III) complexes and their metallomicelles as artificial hydrolase in bis(4-nitrophenyl) phosphate ester (BNPP) hydrolysis. The chemical composition of two complexes was determined by the fluorescence spectra and the mole ratio method for electronic absorption spectra. The bonding effect of BNPP and solubilizing effect of the complexes were proved by a method of fluorescence spectroscopy. The catalytic activity of different catalytic systems in BNPP hydrolysis was measured with UV-vis spectrophotometric method. These catalytic systems showed high catalytic activity for promoting BNPP hydrolysis at the almost physiological conditions. BNPP hydrolysis rate in these catalytic system is about 107- to 109-fold faster than that of the BNPP spontaneous hydrolysis in aqueous solution at the same conditions. The metallomicelle systems exhibited higher catalytic activity compared with the complex solution systems in BNPP hydrolysis, and hexadecyltrimethyl ammonium bromide micelle provides a useful catalytic environment for reaction. The acid effect of the catalytic system is ascribed to the formation of metal-bound hydroxide serving as a better kind of nucleophile. GRAPHICAL ABSTRACT

Kinetic and mechanistic investigations of the catalysed hydrolysis of bis( p -nitrophenyl) phosphate by a macrocyclic neodymium(III) complex

The macrocyclic ligand 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-tetradecane (L) was synthesised and characterised. The kinetics of hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) in a catalytic system comprising the macrocyclic ligand and neodymium(III) was investigated. The analysis of specific absorption spectra of the hydrolytic reaction system indicated that key intermediates containing BNPP and the Nd(III) complex are formed in the reaction. The mechanism proposed for the catalytic hydrolysis proposed is based on the analytical results of the specific absorption spectrum, and the corresponding kinetic constants are calculated. The results showed that the Nd(III) complex as a mimic hydrolase exhibits good catalytic activity, i.e. similar to that of the natural enzyme.

The catalytic oxidation of aqueous phenol by H 2 O 2 using a macrocyclic (N-donor) cobalt(II) complex

A new macrocyclic (N-donor) cobalt(II) complex, denoted CoR, was synthesized and characterized, and used as a mimetic peroxidase in the catalytic oxidation of phenol by H2O2. The catalytic system displayed high catalytic activity and the catalytic character of a metalloenzyme, although it did not attain the catalytic efficiency of enzymes. The final products were maleic and oxalic acids. Intermediate products, such as catechol and hydroquinone and p-benzoquinone, were detected by high-pressure liquid chromatography (HPLC) and UV-Vis spectrophotometry. The effects of temperature and the pH of the system on the rate of the catalytic oxidation were investigated. A reaction mechanism and kinetic model for the catalytic oxidation are proposed, which are supported by the results of the experimental and calculation data.