Metallomicellar Catalysis Hydrolysis of p-Nitrophenyl Picolinate Catalyzed by Copper(II), Nickel(II), and Zinc(II) Complexes of Long Alkyl Pyridine Ligands in Micellar Solution

The ternary complex kinetic model for metallomicellar catalysis has been proposed in this paper. The catalytic effects of bivalent metal ion (Cu(2+), Zn(2+), and Ni(2+)) complexes of long alkyl pyridine ligands upon the hydrolysis of p-nitrophenyl picolinate (PNPP) have been studied kinetically in aqueous buffer of pH ranging from 5.0 to 8.5 at 30 degrees C. The effect of pH on the reactivity is discussed. The results indicate that the metallomicelles formed by pyridine ligands promote the hydrolysis of PNPP, and the order is Cu(II) system>Ni(II) system>Zn(II) system. A stereochemical modification of the complex in the CTAB micelle is suggested as a likely explanation for the observed phenomena. Copyright 2000 Academic Press.     

HYDROLYSIS OF P-NITROPHENYL PICOLINATE CATALYZED BY COPPER(II ) COMPLEXES OF LONG ALKYL-PYRIDINES WITH HYDROXYL GROUPS IN MICELLAR SOLUTION

ABSTRACT

A ternary complex kinetic model for metallomicellar catalysis has been proposed in this paper. Hydrolysis of PNPP influenced by Co-micelles of long alkyl-pHridines with hydroxyl groups and CTAB was investigated in aqueous buffers of pH ranging from 5. 0 to 7. 0 at 30°C at present of Cu²⁺. The kinetic and the thermodynamic parameters (K_n', K_m', K_T) were obtained by the kinetic analyses,moreover,the rate constant K_n in metallomi-cellar phase was obtained. The pK_? s of the hydroxyl groups of these complexes were determined to be 5. 62,5. 53,5. 34,5. 32,respectively by analyses of pH-rate profiles. The results indicate that pyridine ligands exhibit a great catalysis on the hydrolysis of PNPP,which increases with increasing the hydrocarbon chain length.     

Catalytic cleavage of p-nitrophenyl picolinate by metallomicelles made up of copper(II) complexes of small molecular ligands bearing hydroxyl or carboxyl groups

The esterolytic activities of Cu²⁺ complexes (Cu²⁺L1, Cu²⁺L2 and Cu²⁺L3) of three small molecular ligands: N-(2-hydroxyethyl)ethylenediamine (L1), 2,2-iminodiethanol (L2) and iminodiacetic acid (L3), in the presence of the nonionic micelle (Brij35) towards the substrate p-nitrophenyl picolinate (PNPP) have been investigated. The catalytic reactivity order is: Cu²⁺L1 > Cu²⁺L2 > Cu²⁺L3, which can be attributed to the similarity of and the difference between their catalytic mechanisms, most likely resulting from the analogy and the discrepancy of the structure of the three complexes. The critical feature of the catalytic process is, quite likely, the formation of a ternary complex involving a binary metal ion complex and the substrate, followed by pseudo-intramolecular nucleophilic attack of the alcoholic hydroxyl (for Cu²⁺L1 and Cu²⁺L2) or metal ion bound hydroxide ion (for Cu²⁺L3), at carbonyl of the substrate. Detailed kinetic analyses are given for the hydrolysis of PNPP catalyzed by the three complexes.     

Metallomicellar Catalysis. Catalytic Hydrolysis of p-Nitrophenyl Picolinate by bis-{N-(2-Deoxy-β-D-glucopyranosyl-2-[3-carboxyl-salicylaldimino])} M2 (II) (M = Cu,Zn, Co) in CTAB Micellar Solution

The hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by the binuclear complexes bis-{N-(2-deoxy-β-D-glucopyranosyl-2-[3-carboxyl-salicylaldimino])} M₂ (II) (M = Cu, Zn, Co) was investigated kinetically by observing the rates of the release of p-nitrophenol in the presence of surfactant (hexadecyltrimethylammonium bromide CTAB at different pHs and 25°C. The scheme for binuclear complex metallomicelle catalyzed reaction acting mode involving a ternary complex composed of ligand, metal ion and substrate in micelle was established and the relative kinetic and thermodynamic parameters (k_N, K_s, pK_a) were obtained. The reaction is discussed in terms of a bifunctional catalytic mechanism.     

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.     

Intramolecular Stacking in Ternary Complexes Containing Uridine 5′-Triphosphate, 2,2′-Bipyridyl,and a Divalent Metal Ion

The stability constants of the ternary complexes containing UTP, 2,2′-bipyridyl (bipy), and Co²⁺, Ni²⁺, Cu²⁺, or Zn²⁺ (M²⁺) have been determined by potentiometric titrations (Table 1). Changes in stability are quantified by Δlog K_M = log K–log K. For the Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ systems Δlog K_M is 0.10, ?0.13, 0.36, and 0.15, respectively. All these ternary complexes are considerably more stable than would be expected on statistical grounds; indeed, for Co²⁺, Cu²⁺, and Zn²⁺, UTP^4? binds more tightly to M (bipy)²⁺ than to M²⁺. An UV. difference spectroscopic study suggests that stacked adducts between bipyridyl and the pyrimidine moiety of uridine are formed. ¹H-NMR. studies of the bipy/uridine, bipy/UTP, and bipy/UTP/Zn²⁺ systems (Figs. 1 and 2) confirm the presence of stacking in the binary adducts and in the ternary complex. There is also evidence for the existence of the stacked protonated complex, Zn(bipy) (HUTP)^?, with the proton at the γ-phosphate group. The acidity constant of this ternary complex has been measured (Fig. 3). The observed stability enhancement of stacked adducts by the formation of a metal ion bridge is discussed (Fig. 4) and biological implications are indicated.     

Hydrolysis of p-nitrophenyl picolinate catalyzed by metal complexes of N-alkyl-3,5-bis(hydroxymethyl)-1,2,4-triazole in CTAB micelles

Two lipophilic ligands containing triazole and hydroxyl groups, N-alkyl(C(n)H(2n+1))-3,5-bis(hydroxymethyl)-1,2,4-triazole (n=10 and 12), were synthesized. Effects of their Cu(II) and Ni(II) complexes on the hydrolysis of p-nitrophenyl picolinate (PNPP) in cetyltrimethylammonium bromide (CTAB) micelles have been investigated kinetically, and some kinetic parameters of the reactions were obtained by employing the ternary complex kinetic model for metallomicellar catalysis. It was found that Cu(II) complexes of these triazole-based ligands showed more effective catalytic activity on the hydrolysis of PNPP than Ni(II) complexes. Also, the apparent first-order rate constants for product formation in the metallomicellar phase (k(N)(')), the association constants between the substrate and the binary complex (K(T)), and the association constants between the metal ion and the ligand (K(M)) increased with an increase in pH value, which may be attributed to an increase in the nucleophilicity of the hydroxyl groups in the ligand or the electrophilicity of the substrate at higher pH. In addition, at constant pH, k(N)(') and K(T) increased with an increase in the hydrocarbon chain length of the ligand, while K(M) decreased.     

1:1 Metal Complexes of Bivalent Cobalt,Nickel, Copper,Zink, and Cadmium with the Tripodal Ligand tris[2-(dimethylamino)ethyl]amine: Their stabilities and the X-ray crystal structure of its copper(II) complex sulfate

The complex formation by Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺ with tris[2-(dimethylamino)ethyl]amine (N(CH₂CH₂NMe₂)₃, Me₆tren) was investigated at 25° and at an ionic strength of 1, using VIS spectroscopy and potentiometric measurements. The stability constants of these complexes are compared with those of tris(2-aminoethyl)amine (N(CH₂CH₂NH₂)₃, tren), obtained under the same conditions. The values of the constants for Me₆tren are much lower than those for tren, due to the bulky Me substituents. The values of the constants can be correlated with the ability of the individual metal ions to adopt coordination number 5. This appears to be easier for Cu²⁺ and Co²⁺ than for Cd²⁺ and Zn²⁺ and is very difficult for Ni²⁺. The 1:1 complexes [ML(H₂O)]²⁺ are monoprotonic acids whose pK_s values are similar or lower than those of the corresponding aquametal ions. The X-ray crystal structure of the copper(II) complex [Cu(SO₄)(Me₆tren)] · 8H₂O reveals pentacoordination at the central ion. The UV/VIS spectra of the aqueous solutions of the Co²⁺, Ni²⁺, and Cu²⁺ 1:1 complexes confirm that the same coordination number is present also in these complexes.     

ACCELERATED CLEAVAGE OF P-NITROPHENYL PICOLINATE CATALYZED BY COPPER(II) AND ZINC(II) COMPLEXES OF D-GLUCOSAMINE SCHIFF BASE IN MICELLAE SOLUTION

Abstract

The hydrolysis of p-nirrophenyl picolinate (PNPP) catalyzed by the Cu(II) and Zn(H) complexes of d-glucosamine schiff base was investigated kinetically by observing the rates of the release of p-nitrophenol in the buffered micellor solution at different pit and 25°C. The scheme for reaction acting mode involving a ternary complex contain ligand, metal ion and substrate in micelle was establish and the reaction mechanisms were discussed The experimental results indicated that the complexes catalyzed efficiently the hydrolysis of PNPP, especially Zn(II) complex. The rate constant k_N, which shows the catalytic reactivity of complexes, WBI determined to be 0.4251 s^?1 far Cu(II) complex at pH 7 60 in micellar solution. The catalytic reactivity of Zn(II) complex were much larger than Cu(II) complex, the k_N was determined to be 3.1914 s^?1 at same pH value.     

N-Phthaloylglycinate ternary complexes with cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) metal ions and aromatic mono,bi and tridentate amines

Complexes of N-phthaloylglycinate (N-phthgly) and Co^II, Ni^II, Cu^II, Zn^II and Cd^II containing imidazole (imi), N-methylimidazole (mimi), 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen), and tridentate amines such as 2,2,2-terpyridine (terpy) and 2,4,6-(2-pyridyl)s-triazine (tptz), were prepared and characterized by conventional methods, i.r. spectra and by thermogravimetric analysis. For imi and mimi ternary complexes, the general formula [M(imi/mimi)₂(N-phthgly)₂]·nH₂O, where M = Co^II, Ni^II, Cu^II and Zn^II applies. For Cd^II ternary complexes with imi, [Cd(imi)₃(N-phthgly)₂]·2H₂O applies. For the bi and tridentate ligands, ternary complexes of the formula [M(L)(N-phthgly)₂]·nH₂O were obtained, where M = Co^II, Ni^II, Cu^II and Zn^II; L = bipy, phen, tptz and terpy. In all complexes, N-phthgly acts as a monodentate ligand, coordinating metal ions through the carboxylate oxygen, except for the ternary complexes of Co^II, Ni^II and Cu^II with mimi and Cu^II and Zn^II with imi, where the N-phthgly acts as a bidentate ligand, coordinating the metal ions through both carboxylate oxygen atoms.     

Rational Construction of Polymeric Cadmium(II) Benzimidazole for Transition Metal Ion Exchange

A 1D double‐helical coordination polymer {[Cd(pbbm)₂]₂(ClO₄)₄(H₂O)₂}_n ( 1 ) was successfully constructed by the reaction of Cd(ClO₄)₂ · 6H₂O with 1,1′‐(1,5‐pentanediyl)bis‐1H‐benzimidazole (pbbm). Interestingly, polymer 1 exhibits highly selective capacity for the ionic exchange of Zn²⁺ and Cu²⁺ over Co²⁺ and Ni²⁺ ions in the crystalline solid state when the crystals of 1 are immersed in the aqueous solutions of the perchlorate salts of Cu²⁺, Zn²⁺, Co²⁺, and Ni²⁺ ions, respectively, which indicates that central Cd^II ion exchange might be considered as being dominated by the coordination ability of metal ions to free functional groups, ionic radii of exchanged metal ions, and the solution concentration of adsorbed metal salts. The parent material‐ and ion‐exchange‐induced products are identified by FT‐IR spectroscopy, PXRD patterns as well as SEM and EDS measurements. In addition, the thermal stability of 1 was also investigated.     

Complexation of metal ion with poly(1-vinylimidazole) resin prepared by radiation-induced polymerization with template metal ion

Poly(1-vinylimidazole) (PVI) resin was prepared with Ni²⁺, Co²⁺, or Zn²⁺ as a template to study the adsorption of metal ions. The metal-1-vinylimidazole complex was copolymerized and crosslinked with 1-vinyl-2-pyrrolidone by γ-ray irradiation and the template metal ion was removed by treating the polymer complex with an acid. These PVI resins adsorbed metal ions more effectively than the PVI resin prepared without the template. The number of adsorption sites (As) and the stability constant (K) of Ni²⁺ complex were larger for the PVI resin prepared with the Ni ion template, caused by the smaller dissociation rate constant of Ni ion from the resin. The composition of the Ni²⁺ complex in the resin remained constant. This suggests that the complexation proceeded via a one-step mechanism.     

Metal complexes of macrocyclic ligands. Part XXXIII. Effect of the side-chain length on the on/off equilibrium in the Ni2+ and Cu2+ complexes of 11-(2-aminoethyl)- and 11-(3-aminopropyl)-1,4,7,11-tetraazacyclotetradecane

Alkylation of 1,4,7-tritosyl-1,4,7,11-tetraazacyclotetradecane with CH₂O/KCN or acrylonitrile gave the corresponding cyanomethyl or 2-cyanoethyl derivatives, which, by treatment with Na in BuOH, were detosylated and reduced to the macrocyclic pentaamines 1 and 2 . The Ni²⁺ and Cu²⁺ complexes with 1 and 2 show a reversible pH-dependent change in geometry, in which the side-chain amino group is either coordinated to the metal ion (basic form) or protonated and, thus, non-coordinated (acidic form). The length of the side chain determines the log K_a values of these protonation/deprotonation equilibria: 1.89 and ～ 2.0 for the Cu²⁺ and Ni²⁺ complexes of ligand 1 with the 2-aminoethyl side chain, and 6.17 and 7.43 for the Cu²⁺ and Ni²⁺ complexes of ligand 2 with the 3-aminopropyl side chain.     

Mixed metal complexes in solution. Thermodynamic and spectrophotometric study of copper(II)-citrate heterobinuclear complexes with nickel(II), zinc(II) or cadmium(II) in aqueous solution

Summary A thermodynamic study of Cu^II–M^II-citrate (M^II=Ni^II, Zn^II or Cd^II) ternary systems has been performed by means of potentiometric measurements of hydrogen ion concentration at different temperatures (10, 25, 35 and 45°C) and at I=0.1 mol dm^–3 (KNO₃).The different binary and ternary systems involved have been further characterized by visible spectra and by calculating the spectra ( versus ) of all the Cu^II complexes.The thermodynamic data suggest strong entropic stabilization for the species under discussion. As regards the visible spectral characteristics of Cu^II(d-d transitions), the substitution of one Cu^II ion in the dimer [Cu₂(cit)₂H_–2]^4– by Ni^II or Zn^II to form heterobinuclear [CuM(cit)₂H_–2]^4– complexes, gives rise to a change in the visible spectrum.     

Comparative studies on hydrolysis of bis(p-nitrophenyl) phosphate catalyzed by short- and long-alkyl-multiamine metallomicelles

Four short- and long-alkyl-multiamine ligands L¹–L⁴ have been synthesized and characterized. The catalytic efficiency of complex CuL¹ and functional metallomicelles CuL²–CuL⁴ were comparatively investigated for the hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) in buffered solution at 30 °C. The ternary kinetic model for metallomicellar catalysis was suggested to analyze the experimental data. The kinetic and thermodynamic parameters k^′_N, K_T and pK_a were obtained. The results indicated that the complexes with 1:1 ratio of ligands L²–L⁴ to copper(II) ion were the kinetic active catalysts, and the deprotonized Cu(II) complex formed by activated water molecule was the real active species for BNPP catalytic hydrolysis. The real rate constant of the reaction catalyzed by CuL¹–CuL⁴ was 4.00 × 10⁻⁶, 7.44 × 10⁻⁵, 1.42 × 10⁻⁴ and 4.10 × 10⁻⁴ s⁻¹, respectively. The effects of ligand and microenvironment on the hydrolytic reaction of BNPP have been discussed in detail.     

Spectroscopic Characterization of <Emphasis Type="Italic">N,N-bis</Emphasis>(2-{[(2,2-Dimethyl-1,3-Dioxolan-4-yl)Methyl]Amino}Ethyl) N′,N′-Dihydroxyethanediimidamide and Its Complexes

A new dioxime ligand, N,N-bis(2-{[(2,2-dimethyl-1,3-dioxolan-4-yl)methyl]amino} ethyl)N′,N′-dihydroxyethanediimidamide (H₂L), and its mononuclear complexes with Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Cd²⁺ are synthesized. H₂L forms transition metal complexes [Co(LH)₂(H₂O)₂] and [M(LH)₂] (M = Ni²⁺, Cu²⁺) with a metal : ligand ratio of 1 : 2. Complexes [M(H₂L)(Cl)₂] (Zn²⁺, Cd²⁺) have a metal : ligand ratio of 1 : 1. The mononuclear Co²⁺, Ni²⁺, and Cu²⁺ complexes indicate that the metal ions coordinate ligand through its two N atoms, as the most of dioximes. In the Co²⁺ complex, two water molecules and in the Zn²⁺ and Cd²⁺ complexes two chloride ions are also coordinated to the metal ion. The structures of these compounds are identified by elemental analyses, IR, ¹H and ¹³C NMR, electronic spectra, magnetic susceptibility measurements, conductivity, and thermogravimetric analysis.__________From Koordinatsionnaya Khimiya, Vol. 31, No. 7, 2005, pp. 540–544.Original English Text Copyright © 2005 by Canpolat, Kaya.The text was submitted by the authors in English.     

CATALYTIC HYDROLYSIS OF P-NITROPHENYL PICOLNATE BY BIOXOCYLAM ZINC(II) COMPLEXES IN MICELLAR SOLUTION

The effects of dioxocyclam Zn³ ion complexes in micellar solution on ihe hydrolysis of PNPP have been investigated in this paper. Second order rate constants of Ihe hydrolysis of PNPP catalyzed by dio*ocyclam Zn²⁺ion complexes at various pH and the deprotonation constants of H₂ cooriinated to the dioxocyclam Zn²⁺ion complexes pKwere determined kinetically, and the catalytic mechanism was discussed. The results unexpectedly showed that the activation was much larger for Itpophilic ligand under miccllar condition than for bydrophilic ligands under non-miccllar conditions, indicating the dioxocyclam Zn²⁺ ion complex to be an excellent model of carbonic anhydnue.     

Metal Complexes with Macrocyclic Ligands. Part XXXVIII. Steric effects in the copper(II) and nickel(II) complexes with tetra-N-alkylated 1,4,8,11-tetraazacyclotetradecanes

A series of tetra-N-alkylated 1,4,8,11-tetraazacyclotetradecanes have been synthesized and their complexation potential towards Ni²⁺ and Cu²⁺ studied. In the case of sterically demanding alkyl substituents, such as i-Pr, PhCH₂, or 2-MeC₆H₄CH₂, no metal complexes are formed, whereas for substituents such as Me, Et, and Pr, the metal ion is incorporated into the macrocycle. The spectroscopic properties of the Ni²⁺ and Cu²⁺ complexes in aqueous solution indicate that, depending on the sterical hindrance of the N-substituents, the complexes are either square planar or pentacoordinated. All these Ni²⁺ and Cu²⁺ complexes react with N to give ternary species, the stability of which have been determined by spectrophotometric titrations. The tendency to bind N decreases with increasing steric hindrance of the alkyl substituents. The X-ray studies of the Ni²⁺ complex with the macrocycle 11 , substituted by two Me and two Pr groups, and that of the Cu²⁺ complex with the tetraethyl derivative 8 show that in the solid state, the metal ions exhibit square planar coordination with a small distortion towards tetrahedral geometry.     

Supramolecular Phosphatases Formed by the Self‐Assembly of the Bis(Zn2+–Cyclen) Complex,Copper(II), and Barbital Derivatives in Water

In our previous paper, we reported that a dimeric Zn²⁺ complex with a 2,2′‐bipyridyl linker (Zn₂L¹), cyanuric acid (CA), and a Cu²⁺ ion automatically assemble in aqueous solution to form 4:4:4 complex 3 , which selectively catalyzes the hydrolysis of mono(4‐nitrophenyl)phosphate (MNP) at neutral pH. Herein, we report that the use of barbital (Bar) instead of CA for the self‐assembly with Zn₂L¹ and Cu²⁺ induces 2:2:2 complexation of these components, and not the 4:4:4 complex, to form supramolecular complex 6 a , the structure and equilibrium characteristics of which were studied by analytical and physical measurements. The finding show that 6 a also accelerates the hydrolysis of MNP, similarly to 3 . Moreover, inspired by the crystal structure of 6 a , we prepared barbital units that contain functional groups on their side chains in an attempt to produce supramolecular phosphatases that possess functional groups near the Cu₂(μ‐OH)₂ catalytic core so as to mimic the catalytic center of alkaline phosphatase (AP).     

Out-cage metal ion coordination by novel benzoazacrown bisamides with carboxyl,pyridyl and picolinate pendant arms

A new series of macrocyclic diamides with carboxyl, pyridyl and picolinate pendant arms have been synthesized and the stability constants of their complexes with Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺ in water were determined. Complexes with a stoichiometry of 1 : 1 (M: L) were found for all ligands with the exception of 15-membered crown ethers with one pendant carboxyl or pyridine group. The ligand containing two picolinate backbone groups exhibits the highest values of the stability constants for all studied cations (logβ_ML?=?12.5–15.7). X-ray study of free ligands showed that the introduction of benzene and amide fragments into the macrocyclic moiety provides a flatten open structure of the ligand. The crystallographic analysis of Cu²⁺ and Zn²⁺ complexes revealed the external coordination of the metal atom by amine N atoms of the macrocycle and heteroatoms of the pendant groups.