Synthesis of Two Schiff Base Transition Metal Complexes Bearing Morpholine Side Chains and Kinetics of PNPP Catalytic Hydrolysis in Brij35 Micelle

Two Schiff base transitional metal complexes bearing morpholine side chains were synthesized and characterized, and were used as a simulative hydrolase in the catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) in this article. A mechanism of PNPP catalytic hydrolysis in the Brij35 micellar solution was proposed and supported by the results of the spectral analysis and the kinetic calculation. The kinetic model of PNPP catalytic hydrolysis was studied. The some kinetic and the thermodynamic constants on the catalytic reaction were calculated. The results of the study show that the metallomicelle made up of the Schiff base transitional metal complexes and Brij35 micelle revealed a good catalytic activity in PNPP catalytic hydrolysis; the rate of the PNPP catalytic hydrolysis is increased following the increase of the pH values in the buffer solution and affected by the polarization action of metal ion of complex.     

Studies on PNPP Hydrolysis Catalyzed by Divalent Metal Ion Macrocyclic Schiff Base Complexes in Micellar Solution

Two transitional metal ion macrocyclic Schiff base complexes, NiL and CuL were synthesized and characterized, and the metallomicelles made up of the nickel(II) and copper(II) complexes and surfactants(LSS, Brij35, CTAB), as mimic hydrolytic metalloenzyme, were used in catalytic hydrolysis of carboxylic ester (PNPP). The analysis of specific absorption spectrums of the hydrolytic reaction systems indicates that key intermediates, made up of PNPP and Ni(II) or Cu(II) complexes, have formed in the reaction processes of the PNPP catalytic hydrolysis. In this, based on the analytic result of specific absorption spectrum, the mechanism of PNPP catalytic hydrolysis has been proposed; a kinetic mathematical model, applied to the calculation of the kinetic parameter of PNPP catalytic hydrolysis has been established on the foundation of the mechanism proposed; the acid effect of reaction system, structure effect of the complexes, effect of temperature and effects of micelle on the rate of PNPP hydrolysis catalyzed by the complexes also have been discussed.     

聚醚桥连二异羟肟酸单核和双核过渡金属配合物催化PNPP水解

Two polyether bridged dihydroxamic acids and their mono-and binuclear manganese(Ⅱ), zinc(Ⅱ) complexes have been synthesized and employed as models to mimic hydrolase in catalytic hydrolysis of p-nitrophenyl picolinate (PNPP). The reaction kinetics and the mechanism of hydrolysis of PNPP have been investigated. The kinetic mathematical model for PNPP cleaved by the complexes has been proposed. The effects of the different central metal ion, mono-and binuclear metal, the pseudo-macrocyclic polyether constructed by polyethoxy group of the complexes, and reactive temperature on the rate for catalytic hydrolysis of PNPP have been examined. The results showed that the transition metal dthydroxamates exhibited high catalytic activity to the hydrolysis of PNPP, the catalytic activity of binuclear complexes was higher than that of mononuclear ones, and the pseudo-macrocyclic polyether might synergetically activate H20 coordinated to metal ion with central metal ion together and promote the catalytic hydrolysis of PNPP.     

Studies on PNPP Hydrolysis Catalyzed by Schiff Base Cobalt（Ⅱ） Complexes

Two cobalt（Ⅱ） complexes of the Schiff base with morpholino or aza-crown ether pendants, CoL^1 and CoL^2, as mimic hydrolytic metalloenzyme, were used in catalytic hydrolysis of carboxylic ester （PNPP）. The analysis of specific absorption spectra of the hydrolytic reaction systems indicates that key intermediates, made up of PNPP and Co（Ⅱ） complexes, have been formed in reaction processes of the PNPP catalytic hydrolysis. The mechanism of PNPP catalytic hydrolysis has been proposed based on the analytic result of specific absorption spectrum. A kinetic mathematical model, applied to the calculation of the kinetic parameter of PNPP catalytic hydrolysis, has been established based on the mechanism proposed. The acid effect of buffer solution, structural effect of the complexes, and effect of temperature on the rate of PNPP hydrolysis catalyzed by the complexes have been also discussed.     

PNPP catalytic hydrolysis by mono- and binuclear transition-metal complexes with polyether-bridged dihydroxamic acids

Polyether-bridged dihydroxamic acids and their mono- and binuclear copper(II), and cobalt(II) complexes have been synthesized and employed as models to mimic hydrolase in the catalytic hydrolysis of p-nitrophenyl picolinate (PNPP). The kinetics and the mechanism of PNPP hydrolysis have been investigated. The kinetic mathematical model of PNPP cleavage by the complexes has been proposed. The effects of the different central metal ion, mono- and binuclear metal, the pseudo-macrocyclic polyether constructed by the polyethoxy group in complexes, and reactive temperature on the rate of PNPP catalytic hydrolysis have been examined. The results show that the transition-metal dihydroxamates exhibit high catalytic activity in the PNPP hydrolysis; the rate of the PNPP hydrolysis increases with the increase in pH of the buffer solution; the catalytic activity of binuclear complexes is higher than that of mononuclear complexes; the catalytic activity of copper(II) complex is about four times that of the cobalt(II) complex; the pseudo-macrocyclic polyether can synergetically activate H₂O coordinated to the metal ion with the central metal ion together and promote the PNPP catalytic hydrolysis.     

氮杂冠醚化双Schiff碱配合物催化羧酸酯水解的研究

将4种氮杂冠醚取代的双Schiff碱钴(H)、锰(m)配合物作为仿水解酶模型催化羧酸酯(PNPP)水解.考察了Schiff碱配合物中氮杂冠醚取代的位置、氮杂冠醚的数目对其仿水解酶性能的影响;探讨了Schiff配合物催化PNPP水解的动力学和机理;提出了配合物催化PNPP水解的动力学模型.结果表明,在25℃条件下随着缓冲溶液pH值的增大,配合物催化PNPP水解速率提高;四种氮杂冠醚取代的双Schiff碱配合物在催化PNPP水解反应中表现出良好的催化活性;氮杂冠醚3-取代的Schiff碱配合物CoL2的催化活性高于5-取代的Schiff碱配合物CoL1,含有2个氮杂冠醚的配合物CoL3的催化活性高于含有1个氮杂冠醚的配合物CoL2.     

Studies on PNPP Hydrolysis Catalyzed by Schiff Base Cobalt（Ⅱ） Complexes Containing Benzoaza-15-crown-5

Three novel Schiff base cobalt（Ⅱ） complexes containing benzoaza-15-crown-5, CoL^1, CoL^2 and CoL^3 were synthesized and characterized, and these complexes were used in catalytic hydrolysis of carboxylic ester （PNPP, p-nitrophenyl picolinate） as mimic hydrolytic metalloenzyme. The analysis of specific absorption spectra of the hydrolytic reaction systems indicated that the catalytic hydrolysis involved the key intermediates formed by PNPP with cobalt（Ⅱ） complexes. The CoL^3 bearing the electron withdrawing group shows better catalytic activity due to its stabilization effect on active species MLS^-. The catalytic mechanism of PNPP hydrolysis was also proposed. The kinetic parameter of PNPP catalytic hydrolysis has been calculated and the activation energy for the catalytic hydrolysis is 43.69, 39.76 and 35.44 kJ·mol^-1, respectively.     

Synthesis and studies of Schiff base complexes with aza-crown ether or morpholino pendants as synthetic hydrolases for <Emphasis Type="Italic">p</Emphasis>-nitrophenyl picolinate

Three symmetrical bis-Schiff bases with either benzo-10-aza-crown ether or morpholino pendants and their Mn(III) and Co(II) complexes have been synthesized and employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP). A kinetic model of PNPP cleavage catalyzed 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 analogs, and the catalytic activity of the phenyl-bridged Schiff base complex is larger than that of ethyl-bridged analogue for the same substituents and metal.     

Studies on Schiff Base Complexes with Aza-Crown Ether Pendants as Synthetic Hydrolases for p-Nitrophenyl Picolinate in Brij35 Surfactant Micellar Solution

Schiff base complexes with aza-crown ether pendants have been synthesized and employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP) in Brij35 surfactant micellar solution. A kinetic model of PNPP cleavage catalyzed by these complexes is proposed. The effects of complex structures and reaction temperature on the rate of catalytic PNPP hydrolysis have also been examined. The rate increases with pH of the buffered Brij35 micellar solution under 25°C; all four complexes exhibited high activity in the catalytic PNPP hydrolysis. The catalytic activity of the phenyl-bridged Schiff base complex is larger than that of ethyl-bridged Schiff base complex for the same substituent and metal. The catalytic activity of manganese(III) complex is superior over cobalt(II) complex in catalyzing hydrolysis of PNPP under the same ligand. The pseudo-first-order rate for PNPP hydrolysis catalyzed by CoL¹ containing aza-crown ether is 2.96 × 10⁴ times that of spontaneous hydrolysis of PNPP in Brij35 surfactant micellar solution at pH = 7.60, [S] = 2.0 × 10^?4 mol dm^?3.     

Metallomicellar Catalysis Cleavage of p-Nitrophenyl Picolinate Catalyzed by Binuclear Metal Complexes Coordinating Tripeptide in CTAB Micellar Solution

The catalytic hydrolysis of p-nitrophenyl picolinate (PNPP) by Cu(II) and Zn(II) complexes coordinating tripeptide were studied kinetically by observing the rates of release of p-nitrophenol in the buffered micellar solution at 25 degrees C and different pH values. The experimental results indicate that 1 : 2 ligand : metal ion complexes in CTAB micellar solution are the active species in the reaction, and the complexes, especially that with Cu(II), efficiently catalyze the hydrolysis of PNPP. As a result, a kinetic model of binuclear metal complex catalysis involving a ternary complex in CTAB micellar solution is proposed to analyze the kinetic behavior of catalysis, and thus, relative kinetic and thermodynamic parameters are obtained. The results predict that the catalytic reaction by metallomicelle with binuclear complex involves a bifunctional mechanism. Copyright 2001 Academic Press.     

Cobalt(II) Schiff Base Complexes Bearing Aza Crown Ether Pendants as Synthetic Hydrolase Catalyzing PNPP Hydrolysis

Two Co^II complexes with aza crown ether substituted salicylaldimine Schiff base, CoL¹ ₂ and CoL² ₂, have been synthesized and employed as models to mimic hydrolase in catalytic hydrolysis of a carboxylic ester. The specific change of u.v.–vis. absorption spectra of the hydrolytic reactive systems has been observed, which indicates that key intermediates are formed by PNPP and Co^II complexes. The kinetics and the mechanism of PNPP hydrolysis have been investigated. The kinetic mathematical model for PNPP cleavage catalyzed by the Co^II complexes has been proposed. The results show that, compared with the crown-free analogous CoL³ ₂, the bis(aza crown ether)s Co^II complexes CoL¹ ₂ and CoL² ₂ exhibit high activity in the PNPP catalytic hydrolysis; the rate of the PNPP hydrolysis catalyzed by the complexes increases with the increase of pH of the buffer solution; the pseudo-first-order rate constants (k _ob) of PNPP hydrolysis catalyzed by the complexes is 1000 times more than that of spontaneous hydrolysis of PNPP.     

聚醚桥连二异羟肟酸配合物催化羧酸酯水解的动力学研究

研究羧酸酯和磷酸酯的水解在环境和生物应用等方面具有越来越重要的意义。为实现对环境友好、高经济效益的生产过程,许多研究者致力于研发反应条件温和、催化效率高和高度专一性的催化剂。因而,仿酶研究倍受人们的关注,其中,水解金属酶是被研究得较为广泛的一类。我们曾报道过异羟肟酸过渡金属配合物仿生催化氧化性能和二氧亲合性能。本文我们将4种聚醚桥连二异羟肟酸过渡金属铜（Ⅱ）、锌（Ⅱ）、钴（Ⅱ）和锰（Ⅱ）配合物（见图1）作为仿水解酶模型,在底物浓度高于催化剂浓度10倍以上的条件下,研究了配合物在缓冲溶液中催化α-吡啶甲酸对硝基苯酯（PNPP）的水解反应的机理,并建立了相应的动力学数学模型;考查了配合物中心金属离子、溶液酸度和反应温度等对催化PNPP水解反应性能的影响。     

Studies on the Kinetics and Mechanism of Hydrolysis of p-nitrophenyl Picolinate (PNPP) by Unsymmetrical bis-Schiff Base Complexes with Aza-crown Ether or Morpholino Pendants

Two novel unsymmetrical bis-Schiff base manganese(III) and cobalt(II) complexes with benzo-10-aza-crown ether pendants (MnL¹Cl, CoL¹), and their analogoues with morpholino pendants (MnL²Cl, CoL²), have been synthesized and employed as models to mimic hydrolase in p-nitrophenyl picolinate (PNPP). The kinetics and the mechanism of PNPP hydrolysis catalyzed by these complexes were investigated. A kinetic mathematical model of PNPP cleavage catalyzed by these complexes was proposed. The effects of the complexes structure and reactive temperature on the rate of catalytic PNPP hydrolysis have been also examined. The results showed that the rate for the catalytic PNPP hydrolysis increased following the increase in pH of the buffer solution; four complexes exhibited high activity in the catalytic PNPP hydrolysis. Compared with the crown-free analogoues MnL²Cl and CoL², the crowned Schiff base complexes (MnL¹Cl, CoL¹) exhibit a higher catalytic activity; the pseudo-first-order-rate (k_obs) for the PNPP hydrolysis catalyzed by the complex MnL¹Cl containing benzo-10-aza-crown ether is 1.04 × 10³ that of spontaneous hydrolysis of PNPP at pH = 7.00, [S] = 2.0×10⁻⁴ mol dm⁻³.     

Hydrolysis of PNPP Catalyzed by Cu (II), Ni (II) Schiff Base Complexes in CTAB Micellar Solution

The kinetics of hydrolysis of p‐nitrophenyl picolinate(PNPP) catalyzed by metallomicelles formed from Cu (II), Ni (II) Schiff base complexes (CuL, NiL) and CTAB micelle were investigated in the pH range of 6.0–9.0 at 30°C. For the Cu (II) Schiff base complex CuL, the apparent rate constants (k _obsd) of PNPP hydrolysis initially increased with the increasing pH of reaction media, then fell off. For the Ni (II) Schiff base complex NiL, the k _obsd always increased with the increasing pH. The kinetic and thermodynamic parameters were calculated. The hydrolysis rate of PNPP catalyzed by Cu (II) complex was much larger than that by Ni (II) complex in CTAB micellar solution. The catalytic mechanism of the PNPP hydrolysis was discussed in detail, and the possibly active specie for the catalytic hydrolysis of PNPP was the monohydroxo metal complex.     

PNPP Cleavage Catalyzed by Schiff Base Mn(III) Complexes Containing Polyether Side Chains in CTAB Micellar Solutions

Two Schiff base Mn(III) complexes containing polyether side chain were synthesized and characterized. The catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) by the two complexes in the buffered CTAB micellar solution in the pH range of 6.60–8.20 was investigated kinetically in this study. The influences of acidity, temperature, and structure of complex on the catalytic cleavage of PNPP were also studied. The mechanism of PNPP hydrolysis catalyzed by Schiff base manganese(III) complexes in CTAB micellar solution was proposed. The relative kinetic and thermodynamic parameters were determined. Comparied with the pseudo‐first‐order rate constant (k ₀) of PNPP spontaneous hydrolysis in water, the pseudo‐first‐order rate constants (k _obsd) of PNPP catalytic hydrolysis are 1.93×10³ fold for MnL¹ ₂Cl and 1.06×10³ fold for MnL² ₂Cl in CTAB micellar solution at pH=7.00, T=25°C, and [S]=2.0×10^?4mol · dm^?3, respectively. Furthermore, comparing the k _obsd of PNPP catalytic hydrolysis by metallomicelles with that of PNPP hydrolysis catalyzed only by metal complexes or CTAB micelle at the above‐mentioned condition, metallomicelles of MnL₂(L=L¹, L²) Cl/CTAB exhibit notable catalytic activities for promoting PNPP hydrolysis, and MnL¹ ₂Cl/CTAB system is superior in promoting cleavage of PNPP relative to MnL² ₂Cl/CTAB system under the same experimental conditions. The results indicate that the rate of PNPP catalytic cleavage is influenced by the structures of the two complexes, the acidity of reaction systems, and the solubilization of PNPP in CTAB micelles.     

Metallomicellar Catalysis: Hydrolysis of PNPP Catalyzed by Copper(II), Zinc(II), Cerium(IV) Complexes with Long Alkyl Pyridine Ligands in CTAB Micellar Solution

A kind of new functional surfactant with substituted long alkyl pyridine was synthesized and its Ce(IV), Zn(II), and Cu(II) complexes were used as hydrolytic metalloenzyme models. The hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by the metallomicelles in CTAB micellar solution was investigated at different pH and 30°C. Kinetic parameters of catalytic hydrolysis were obtained by employing the ternary complex kinetic model for metallomicellar catalysis. Effects of the structure of ligands and microenvironment of reaction on the hydrolytic reaction of PNPP have been discussed in detail. From the apparent rate constants (k _obsd ) of the catalytic hydrolysis of PNPP, it can be seen that the catalytic effect of complexes of ligand L² with long hydrocarbon chain was stronger than that of ligand L¹, and complex CuL² showed higher catalytic efficacy on the hydrolytic reaction than those of ZnL² and CeL². However, experiment results in this article showed that ZnL² and CeL² are more susceptible to environment than CuL². The catalytic mechanism was proposed, and the possibly active species for the catalytic hydrolysis of PNPP was determined to be the hydroxylated metal complex.     

p‐Nitrophenyl Picolinate Cleavage by Unsymmetrical Bis‐Schiff Base Manganese(III) and Cobalt(II) 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, MnL²Cl) or morpholino pendant (MnL³Cl, CoL³) have been employed as models for hydrolase by studying the kinetics of their hydrolysis reactions with p‐nitrophenyl picolinate (PNPP). A kinetic model of PNPP cleavage catalyzed 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 under 25°C. The complexes of ligands containing a crown ether group exhibit higher catalytic activities than the non‐crown analogues. The catalytic activity of the complexes follows the order Mn(III)>Co(II) under the same ligands.     

Catalytic hydrolysis of carboxylic acid esters by Cu(II) and Zn(II) complexes containing a tetracoordinate macrocyclic Schiff base ligand in Brij35 micellar solution

The macrocyclic Schiff base complexes of Cu(II) and Zn(II) in Brij35 micellar solution are investigated kinetically for the catalytic hydrolysis of p-nitrophenyl acetate (PNPA) and p-nitrophenyl picolinate (PNPP) at 30 °C. The results indicate that different mechanisms are operative for the two complexes in the hydrolysis of PNPA and PNPP. The Cu(II) complex can only catalyze the hydrolysis of PNPP by the mechanism which involves the nucleophilic attack of external hydroxide ion on the carbonyl, while the Zn(II) complex can accelerate the hydrolysis of both PNPP and PNPA, by way of the intramolecular nucleophilic attack of zinc-bound hydroxide ion on carbonyl for PNPP and the less effective intermolecular nucleophilic attack of zinc-bound hydroxide ion on carbonyl for PNPA, respectively. The catalytic activity of Zn(II) complex is close to or even higher than that of Cu(II) complex. The reason is discussed in details.     

Hydrolysis of BNPP Catalyzed by the Crowned Schiff Base Co(II) Complex Containing Benzoaza‐15‐Crown‐5 in Micellar Solution

It has been reported that three aza crowned Schiff base cobalt (II) complexes were synthesized and characterized, and the metallomicelle made up of the cobalt (II) complexes and surfactants(Brij35, CTAB, LSS), as mimic hydrolytic metalloenzyme, was used in catalytic hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP). The analysis of specific absorption spectrums of the hydrolytic reaction systems indicated that key intermediates made up of BNPP and Co (II) complexes are formed in the reaction process of BNPP catalytic hydrolysis. The mechanism of BNPP catalytic hydrolysis proposed is based on the analytic result of specific absorption spectra. Based on the mechanism proposed, a kinetic mathematical model for the calculation of the kinetic parameter of BNPP catalytic hydrolysis has been established. The acid effect of reaction system, structure effect of the complexes, effect of temperature and effect of micelles on the rate of BNPP hydrolysis catalyzed by the complexes have been discussed.     

Studies on p-Nitrophenyl Picolinate Cleavage by Unsymmetrical Bis-Schiff Base Manganese(III) and Cobalt(II) Complexes in CTAB Surfactant Micellar Solution

The unsymmetrical bis-Schiff base manganese(III) and cobalt(II) complexes with either benzo-10-aza-crown ether pendants (MnL¹Cl, MnL²Cl) or morpholino pendant (MnL³Cl, CoL³) have been employed as models for hydrolase by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP) in the buffered CTAB micellar solution. A kinetic model of PNPP cleavage catalyzed 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 higher catalytic activity in the buffered CTAB micellar solution and the rate increases with pH of the buffered CTAB micellar solution under 25°C. The complexes containing a crown ether group exhibit higher catalytic activities than the free-crown analogues. The catalytic activity of manganese(III) complex is superiority over cobalt(II) complex in catalyzing hydrolysis of PNPP under the same ligand.