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.     

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.     

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.     

Catalytic hydrolysis of phosphate diester （BNPP） and plasmid DNA by mononuclear macrocyclic polyamine metal complexes

The activities of the catalytic hydrolysis of phosphate diester(BNPP)[bis(p-nitrophenyl)phosphate diester]and plasmid DNA (pUC18)by mononuclear macrocyclic polyamine metal complexes have been investigated in this paper.The results showed that the highest activity in hydrolysis of BNPP was obtained with 1e-Zn(Ⅱ)complex(composed of lipophilic group)as catalyst.The hydrolysis rate enhancement is up to 3.64×10~4 fold.These metal complexes could effectively promote the cleavage of plasmid DNA(pUC18)at physiol...     

Accelerated Hydrolysis of p-Nitrophenyl Picolinate Catalyzed by Metallomicelle Made from a Novel Macrocyclic Polyamine Copper（Ⅱ） Complex

A copper（Ⅱ） complex 1 of a novel macrocyclic polyamine ligand with hydroxylethyl pendant groups, 4,11-bis（hydroxylethyl）-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane （L） has been synthesized and characterized. Rate enhancement for hydrolysis of p-nitrophenyl picolinate （PNPP） catalyzed by 1 was studied kinetically under Brij35 micellar condition. For comparision, the catalytic activity of corresponding copper（Ⅱ） complex 2 of non-substituted macrocyclic polyamine ligand, 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraaza-cyclotetradecane （L＇） toward the hydrolysis of PNPP was also investigated. The results indicate that the macrocyclic polyamine copper（Ⅱ） complex 1 effectively catalyzed the hydrolysis of PNPP, and the pendant ligand hydroxyl group or deprotonated pendant ligand hydroxyl group can act as catalytically active species in the reaction. A ternary Complex kinetic model involving metal ion, ligand and substrate has been proposed, and the results confirmed the reasonability of such kinetic model.     

PREPARATION AND CATALYTIC BEHAVIOUR OF POLYMER-BOUND METALLOPORPHYRIN IN HYDROGENATION OF OLEFIN

The meso- tetraarylporphyrin has been anchored to styrene- divinylbenzenecopolymers by reaction of meso- tetra (4-hydroxylphenyl ) porphyrin with chloromethylatedresin under mild condition. A number of polymer transition metal complexes have beenprepared with the polymer ligand and metal salts. The polymeric ligand and its complexeshave been characterized by electronic spectra, and vibrational spectra. Cyclohexene can behydrogenated with the polymeric porphyrin palladium complex(P-THPPPd) as catalyst,and its catalytic activity was influenced by the polarity of solvents, the contents of water inethanol or reaction temperature. However, its catalytic activity was lower for nitro groups,carbonyl groups and olefins with steric hindrance substituents, and showed no activity foraromatic rings under these conditions.     

Molecular Recognition of Bases and Nucleosides by Mono－substituted Mononuclear Complexes of 1,4,7,10－Tetraaza－cyclododecane

The mononuclear macrocyclic polyamine metal complexes 5a-5e have been shown to form stable 1 : 1 complexes with bases and nucleosides. Their binding constants (K) were determined by UV-visible spectrometric titration. The results show that recognition ability of the complexes 5a--5e for uracil, U (Uridine), dT (Thymidine) is higher than that for the other bases or nucleosides (such as Cytidine, Guanosine, Adenosine). The metal ion also plays an important role for the recognition ability of complexes.     

STUDIES ON ORGANO-MOLYBDENUM AND TUNGSTEN COMPOUNDS(Ⅲ)——CATALYTIC POLYMERIZATION OF ACETYLENE BY M-O-C BOND-CONTAINING COMPLEXES OF Mo AND W

Catalytic polymerization of acetylene in the presence of n5-C5H5-M-(CO)3 R (M=Mo,W;R=CH3-,C2H5-) has been studied.The results show that these complexes possess catalytic activities for the polymerization and copolymerization of monosubstituted acetylene.The catalytic mechanism has been preliminarily discussed.It is suggested that the active species be metal-car-bene.In our previous publications we reported the synthesis of some new Fischer's molybdenum and tungsten-carbene complexes and catalytic activity for alkyne polymerization.The results show that the activity of Fischer's molybdenum-carbene is higher than that of tungsten.The catalytic polymerization of alkyne by M-σ-c bond-containing complexes of molybdenum and tungsten has not been reported yet in literature.Therefore,four M-σ-C bondontaining complexes of molybdenum and tungsten were synthesized by using the method reported in the literature,and catalyst polymerization of alkyne by these complexes was examined.     

Peroxo Complexes of Molybdenum(VI) Containing Mannich Base Ligands

The molybdenum(VI)-peroxo complexes containing Mannich base ligands having a formula as [MoO(O2)2(L-L)] [where L-L＝morpholinobenzyl benzamide (MBB), piperidinobenzyl benzamide (PBB), morpholinobenzyl urea (MBU), piperidinobenzyl urea (PBU), morpholinobenzyl thiourea (MBTU), piperdinobenzyl thiourea (PBTU)] have been synthesized and characterized by physico-chemical, electrochemical techniques and TGA/DTA studies. The complexes have been prepared by stirring ammonium molybdate and excess of 30% aqueous-H2O2 and then treatment with ethanolic solution of the ligand. Studies revealed that these complexes were non-electrolytes and diamagnetic in nature. The ligands are bound to metal in a bidentate mode through carbonyl oxygen/thiocarbonyl sulphur and the ring nitrogen. The cyclic voltammograms of the complexes show two quasi-reversible steps involving complexes. The complexes have also been tested for antibacterial activity against Salmonella and Kleibsella. The antibacterial study of the ligands and complexes indicate that the complexes exhibit higher activity than the free ligands.     

Density Functional Theory Study on the First Hyperpolarizabilities of Mono-and Bimetal Ir(Ⅰ)/Rh(Ⅰ) 2,2?-Bidipyrrins Complexes

Metal complexes with excellent nonlinear optical(NLO) properties have attracted considerable attention. The geometry structure, electronic spectra and NLO properties of 2,2?-bidipyrrins(L) and mono-and bimetal Ir(I)/Rh(I)–L complexes have been investigated by density functional theory method. Our calculations revealed that L with planar configuration shows the largest first hyperpolarizability value, which is 2.2 to 5.5 times larger than that of others. It is attributed to the single direction of intramolecular charge transfer. When metal ions were embedded in ligands, the first hyperpolarizability values of mono-and bimetal Ir/Rh(I)–L complexes were smaller than that of L, and that of bimetal Ir/Rh(I)–L complexes were smaller than the corresponding monometallic Ir/Rh(I)–L. This is caused by the intramolecular charge transfer from multiple directions as well as the amount of charge transfer. On the other hand, on increasing the number of metal ions, the charge transfer in the opposite direction cancels each other more obviously. Our work would provide some theoretical reference for the second-order NLO responses of mono-and bimetal complexes.     

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.     

氮杂冠醚或吗啉基取代的单Schiff碱配合物催化α-吡啶甲酸对硝基苯酯水解

两种含5-取代苯并-10-氮杂-15-冠-5的Schiff碱锰(III)、钴(II)配合物( , )及其吗啉基取代的类似物( , ) 用于催化α-吡啶甲酸对硝基苯酯(PNPP)水解。探讨了氮杂冠醚Schiff 碱配合物催化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;考察了配合物结构、反应温度、缓冲溶液pH值等对PNPP水解反应的影响。结果表明,在25℃条件下随着缓冲溶液pH值的增大,催化PNPP水解速率提高;含取代苯并-10-氮杂-15-冠-5的Schiff碱配合物表现出更高的催化活性。根据阿累尼乌斯公式和不同温度下的表观一级常数求出水解反应的表观活化能。     

Catalytic hydrolysis of p‐nitrophenyl picolinate by copper(II) and zinc(II) complexes of N‐(2‐deoxy‐β‐D‐glucopyranosyl‐2‐salicylaldimino)

D‐glucosamine Schiff base N‐(2‐deoxy‐β‐D‐glucopyranosyl‐2‐salicylaldimino) and its Cu(II) and Zn(II) complexes were synthesized and characterized. The hydrolysis of p‐nitrophenyl picolinate (PNPP) catalyzed by ligand and complexes was investigated kinetically by observing the rates of the release of p‐nitrophenol in the aqueous buffers at 25°C and different pHs. The scheme for reaction acting mode involving a ternary complex composed of ligand, metal ion, and substrate was established and the reaction mechanisms were discussed by metal–hydroxyl and Lewis acid mechanisms. The experimental results indicated that the complexes, especially the Cu(II) complex, efficiently catalyzed the hydrolysis of PNPP. The catalytic reactivity of the Zn(II) complex was much smaller than the Cu(II) complex. The rate constant k_N showing the catalytic reactivity of the Cu(II) complex was determined to be 0.299 s^?1 (at pH 8.02) in the buffer. The pK_a of hydroxyl group of the ternary complex was determined to be 7.86 for the Cu(II) complex. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 345–350, 2002     

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.     

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.     

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.     

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.     

The Assembly of Macrocyclic Bis‐ and Tetra‐β‐lactams with Embedded Platinum or Palladium Square‐Planar Centers

The synthesis, isolation, and full characterization of different types of stable, metal‐assembled macrocyclic β‐lactams are reported. By using adequately functionalized bis‐β‐lactams with defined stereochemistry as building blocks, a series of mono‐ and bimetallic Pd and Pt macrocycles has been prepared in good to quantitative yields. These novel structures combine the β‐lactam moiety with transition‐metal fragments with cis‐square‐planar geometry and constitute a new class of metal‐assembled cavities involving molecules with biological relevance as building blocks. By combining the adequate ligands, metallic fragments, and tuning the reaction conditions, different mono‐ and bimetallic macrocyclic β‐lactam cavities can be selectively obtained. Macrocycles with Pt–ethynyl groups are suitable to form host–silver triflate guest complexes in a tweezer fashion.     

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.