Mechanism of Intramolecular Nucleophilic Substitution in the Catalytic Hydrolysis of Bis(4-Nitrophenyl) Phosphate Ester in a Metallomicelle

An Anionic Surfactant Metallomicelle: Catalytic Activity and Mechanism for the Catalytic Hydrolysis of a Phosphate Ester

An aza-crown ether ligand was synthesised and characterised. The chemical composition of the binary complex containing cerium(III) and the ligand was determined by fluorescence spectroscopy. A new metallomicellar system comprising the cerium(III) complex of the ligand and an anionic micelle (n-lauroylsarcosine) was used as catalyst in the hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP). The catalytic rate of BNPP hydrolysis and the local concentration effect of the micelle were measured kinetically using UV-Vis spectrophotometry. The results indicated, that compared with a cationic metallomicelle system made from the aza-crown ether, lanthanum(III) ion and CTAB cationic surfactant in our previous report, the anionic metallomicelle exhibited a six-fold higher catalytic activity in BNPP hydrolysis at neutral pH and the same other conditions, thus the micelle based on LSS provides a more effective catalytic environment for reaction. A reaction mechanism has been proposed.

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.

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.

Kinetic and Mechanistic Investigations of Cleavage of P-Nitrophenyl Picolinate Catalysed by Ethylenediamine Cobalt(Ii) Complexes

Two novel ethylenediamine cobalt(II) complexes, CoL1 and CoL2, were synthesized and characterized, and were used as mimic hydrolases in the catalytic hydrolysis of a carboxylic ester p-nitrophenyl picolinate, (PNPP). Analysis of the specific absorption spectra of the hydrolytic reaction systems indicated that the catalytic hydrolysis involved key intermediates formed by PNPP with the cobalt(II) complexes. A mechanism for the PNPP hydrolysis has been proposed and the associated kinetic parameters have been calculated. The effects of acidity of the buffer solution, of the structure of the complexes, and of temperature on the rate of the catalysed hydrolysis have also been discussed.

Kinetic Studies of the Hydrolysis of Carboxylic Esters Catalysed by Ethylenediamine Nickel(Ii) Complexes

Three novel ethylenediamine nickel(II) complexes, NiL1, NiL2 and NiL3, were synthesized and characterized, and used as mimic hydrolases in the catalytic hydrolysis of a carboxylic ester (PNPP, p-nitrophenyl picolinate). Analysis of the specific absorption spectra of the hydrolytic reaction systems indicated that the catalytic hydrolysis involved the key intermediates formed by PNPP with the nickel(II) complexes. The catalytic mechanism of PNPP hydrolysis was also proposed. The kinetic parameters of the catalytic hydrolysis were calculated, thus the activation energies (∓ 5%) for the catalytic hydrolyses are 15.1, 12.4 and 11.2 kJ mol −1, respectively.

Metallomicellar Catalysis: Hydrolysis of Pnpp by Crowned Schiff Base Cobalt(Ii) Complexes in Micellar Solution

It has been reported that three aza crowned Schiff cobalt(II) complexes have been synthesised and characterised, and that the metallomicelles, made up of the three cobalt(II) complexes and surfactants(LSS, Brij35, CTAB) as mimic hydrolytic metalloenzyme, were used in the catalytic hydrolysis of carboxylic ester (PNPP) over a pH range of 7.0 - 8.2. The results revealed that the metallomicelles made up of the three cobalt(II) complexes and the surfactants are both efficient for catalysing PNPP hydrolysis with about three orders of magnitude in rate acceleration compared with the background rate of PNPP spontaneous hydrolysis. The effect of different surfactant micelles on the catalytic hydrolysis of PNPP in the metallomicelles follows the order: LSS > Brij35 > CTAB. The results showed that using the aza crowned Schiff base cobalt(II) complexes and their metallomicelles as the hydrolase mimics exhibit good catalytic activity and similar catalytic character to natural enzyme.

Aqueous solutions of transition metal containing micelles

Incorporation of d- or f-block metals into ligand systems that renders a metal complex surface-active or drives its partitioning into surfactant phases enables the localisation of chemical functionality at interfaces. This article discusses a number of fundamental aspects of these interesting materials and examines potential applications.

Kinetics of Hydrolysis of an Activated Phosphate Ester in Brij35 Micelle Containing a Macrocyclic Complex of Cu(II) OR Ni(II)

A macrocyclic ligand and its corresponding Cu(II) and Ni(II) complexes were synthesized and characterized. The kinetics of hydrolysis of bis( p-nitrophenyl) phosphate (BNPP, an activated phosphate diester) in Brij35 micelle containing each macrocyclic complex was investigated. The metallomicelles made up of the macrocyclic metal complex and micelle, as a mimic hydrolytic metalloenzyme, display higher catalytic activity although they do not attain the catalytic efficiency of enzymes. The analysis of specific absorption spectra show that the course of the catalytic BNPP reaction is different from that of the spontaneous hydrolysis of BNPP, and is an intramolecular nucleophilic substitution reaction. 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. The validity of the mechanism and the proposed mathematical model is confirmed by the results of this study.