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.     

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.     

Catalytic Kinetics of the Schiff Base Metal Complexes Bearing Side Chain of Cyclic morpholine in Carboxylic Ester Hydrolysis

It has been reported that two Schiff base transition metal complexes bearing the side chain of the morpholine ring were synthesized and characterized, and two complexes with the same base agent but different metal ions were used as a simulant hydrolase in the catalytic hydrolysis of p-nitrophenyl picolinate in this paper. The mechanism of PNPP catalytic hydrolysis is proposed and supported by the results of the spectral analysis and the kinetic calculation. A kinetic mathematical model, applied to the calculation of the kinetic and thermodynamics parameters of PNPP catalytic hydrolysis, has been established on the foundation of the mechanism proposed. The result of the study shows that the two complexes have a good catalytic activity in PNPP catalytic hydrolysis, and the rate of the PNPP catalytic hydrolysis was increased with the increase of the pH values in the buffer solution and affected by the polarization effect of metal ion of the complexes.     

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.     

大环钴(Ⅱ)配合物模拟水解酶催化羧酸酯水解的比较研究

在Brij35胶束溶液中,比较研究了四氮大环席夫碱(5,7,7,12,14,14-六甲基-1,4,8,11-四氮杂十四环-二烯,L)的钴(Ⅱ)配合物1催化对硝基苯酚吡啶甲酸酯(PNPP)及对硝基苯酚乙酸酯(PNPA)水解的动力学.结果表明:配合物1对PNPP及PNPA的催化作用具有酸碱催化的特征,催化活性物种为与金属离子结合的氢氧根离子CoL-OH-;配合物1催化PNPP水解的速度远远大于其催化PNPA水解的速度,在pH 7.40、30℃时,表观二级速率常数kc分别为0.997mol-1@L@s-1和1.12×10-3mol-1@L@s-1,这种反应速率的差异可归因于反应机理的不同;Brij35胶束对PNPP及PNPA的水解均有抑制作用.     

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.     

Hydrolytic reactivities of p-nitrophenyl picolinate accelerated by Schiff base Co(II) complexes in micellar solutions

Two Schiff base Co(II) complexes were synthesized and used to catalyze the hydrolysis of p-nitrophenyl picolinate (PNPP) in Gemini 16-2-16 micellar solution. For comparison, hydrolytic kinetics of PNPP was respectively investigated in the micellar solutions of three kinds of conventional single-chain cationic, anionic, and nonionic surfactants, i.e., hexadecyltrimethylammonium bromide (CTAB), n-lauroylsarcosine sodium (LSS), and polyoxyethylene(23) lauryl ether (Brij35). Experimental results showed that the one complex with small Schiff base ligands exhibited better catalytic activity than the other one with bigger ligands towards the PNPP hydrolysis under comparable conditions, which testified that a relatively open catalytic site is essential for tuning the activities of the two mimic hydrolases. Moreover, compared effects of various micellar solutions demonstrated that Gemini 16-2-16 micellar solution is the best reaction medium relative to its single-chain analogs.     

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 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.     

Metallomicellar catalysis: effects of bridge-connecting ligands on the hydrolysis of PNPP catalyzed by Cu(II) complexes of ethoxyl-diamine ligands in micellar solution

The syntheses of three ligands are reported: N,N,N′,N′-tetra(2-hydroxyethyl)-1,3-propylene-diamine (1), N,N,N′,N′-tetra(2-hydroxyethyl)-1,10-decadiamine (2), N,N,N′,N′-tetra(2-hydroxyethyl)-1,4-xylyldiamine (3). The catalytic hydrolysis of p-nitrophenyl picolinate (PNPP) by the bivalent metal ion Cu(II) complexes of these ligands was studied kinetically in a buffered CTAB or Brij35 micellar solutions at 25 °C and different pH values. The results indicate that 1:2 and 2:1 complexes of these ligands and metal ion are the active species for the catalytic hydrolysis of PNPP in CATB and Brij35 micellar solutions. The ternary complex kinetic model for metallomicellar catalysis was employed to obtain the relative kinetic and thermodynamic parameters. The effects of the structure of the ligands and the microenvironment of reaction on the hydrolytic reaction of PNPP have been discussed in detail.     

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 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.     

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.     

Effect of manganese(III) Schiff base complexes on the hydrolysis of <Emphasis Type="Italic">p</Emphasis>-nitrophenyl picolinate

Two mono-Schiff base Mn(III) complexes were used to catalyze the hydrolysis of p-nitrophenyl picolinate (PNPP) in micellar solutions of n-lauroylsarcosine sodium (LSS) and polyoxyethylene(23) lauryl ether (Brij35). The results show that both catalysts enhance the hydrolysis of PNPP by over two orders of magnitude relative to the spontaneous rate at 25 °C. Moreover, Mn(III)-promoted hydrolysis of PNPP was faster in LSS micellar solution than in both Brij35 micellar solution and pure buffer. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

双Schiff碱过渡金属配合物在胶束溶液中催化BNPP水解的研究

双Schiff碱过渡金属配合物和胶束形成的金属胶束作为模拟磷酸二酯水解酶用于催化BNPP水解，探讨了催化作用机理；提出了一种金属胶束催化BNPP水解的动力学数学模型。研究表明，本文所用的金属胶束在适当酸度、温度、介质的条件下对催化BNPP水解具有较高的活性。     

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.     

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.     

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.     

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.     

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.