Studies on p-nitrophenyl picolinate cleavage by mono-Schiff base complexes with aza-crown ether or morpholino pendants

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.

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.

Synthesis and Kinetic Studies of Mono-Schiff Base Manganese(Iii) and Cobalt(Ii) Complexes with Aza-Crown Ether or Morpholino Pendants as Synthetic Hydrolases for P-Nitrophenyl Picolinate

Two mono-Schiff base manganese(III) and cobalt(II) complexes with benzo-10-aza-crown ether pendants (MnL12Cl, CoL12), and the analogues with morpholino pendants (MnL22Cl, CoL22) have been synthesised and employed as models for hydrolase enzymes to promote the hydrolysis of p-nitrophenyl picolinate (PNPP) in buffer solution. A kinetic model of PNPP cleavage catalysed by these complexes is proposed. The effects of the structures of the complexes and reaction temperature on the rate of PNPP hydrolysis have been examined. All four complexes exhibit high catalytic activity and the rate increases with pH. In comparison with the crown-free analogues MnL22Cl and CoL22, the crowned Schiff base complexes MnL12Cl and CoL12 exhibit higher catalytic activity for promoting PNPP hydrolysis.

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.

Studies on P-Nitrophenyl Picolinate Cleavage by Unsymmetrical Bis-Schiff Base Complexes with Aza-Crown Ether or Morpholino Pendants

The unsymmetrical bis-Schiff base manganese(III) and cobalt(II) complexes with either benzo-10-aza-crown ether pendants (MnL1Cl, CoL1, CoL2) or a morpholino pendant (MnL3Cl) have been demonstrated as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP). A kinetic model of PNPP cleavage catalysed by these complexes is proposed. The effects of complex structures and reaction temperature on the rate of PNPP hydrolysis have been examined. All four complexes exhibit high catalytic activity and the rate increases with pH. The complexes of ligands containing a crown ether group exhibit higher catalytic activities than the non-crown analogue; the catalytic activity of the complexes follows the order Mn(III) > Co(II) (MnL1Cl > CoL1) with the same ligands.

Kinetic Study on P-Nitrophenyl Picolinate Hydrolysis Promoted by the Complex Bis(O,O'-Di(2-Benzyl)Dithiophosphato)Nickel(Ii)

The complex Ni[S2P(OCH2Ph)2]2 (MR) was synthesised and characterised by elemental analysis, IR spectroscopy and 1H NMR spectroscopy. The hydrolysis of p-nitrophenyl picolinate (PNPP) as promoted by this complex was investigated by the UV-vis method, the results showing that MR acts as a very efficient catalyst. The specific absorption spectra of the hydrolytic reaction systems indicated that the key intermediate, made up of PNPP and MR was formed during reaction. Based on these spectra, a mechanism for the catalytic hydrolysis of PNPP has been proposed and a kinetic mathematical model established.