Metallomicellar catalysis: hydrolysis of phosphate monoester and phosphodiester by Cu(II), Zn(II) complexes of pyridyl ligands in CTAB micellar solution

The catalytic hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) and p-nitrophenyl phosphate (NPP) by metallomicelles composed of Cu(II) or Zn(II) complexes of bispyridine-containing alkanol ligands in CTAB micellar solution was investigated at 30 degrees C. The experimental results indicate that the complexes with a 1:1 ratio of ligands to metal ions for ligands 1 (1,7-bis(6-hydroxymethyl-2-pyridyl)-2,6-dioxaheptane) and 3 (1,4-bis[(6-hydroxymethyl-2-pyridyl)-2-oxapropyl]benzene) and a 1:2 ratio of ligands to metal ions for ligand 2 (1,14-bis(6-hydroxymethyl-2-pyridyl)-2,13-dioxatetradecane) in CATB micellar solution are the active species for the catalytic hydrolysis of BNPP and NPP, respectively. The ternary complex kinetic model for metallomicellar catalysis was employed to obtain the relative kinetic and thermodynamic parameters, which demonstrated the catalytic mechanism for the hydrolysis of BNPP and NPP by metallomicelles.     

Metallomicellar Catalysis: Hydrolysis of Phosphodiester with Cu(II) and Zn(II) Complexes in Micellar Solution

Abstract

The effects of two metal complexes of 2,2′‐dipyridylamine (bpya) ligand, [(bpya)Cu]Cl₂ and [(bpya)Zn]Cl₂, in promoting the hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP) have been kinetically investigated in Brij35 micellar solution and at 298 K, pH ranging from 6.41 to 8.6. In neutral micellar solution at 298 K, pH 7.02, the rate constants for the catalytic hydrolysis of BNPP by [(bpya)Cu]Cl₂ and [(bpya)Zn]Cl₂ are 1.2 × 10⁶ times and 1.5 × 10⁵ times higher than those for the spontaneous hydrolysis, respectively. Kinetic studies show that the active species in the catalytic hydrolysis of BNPP is the aquo‐hydroxy form, and the relative kinetic and thermodynamic parameters indicate that the mechanism of the reaction involves intramolecular nucleophilic attack on the metal center‐bound diester.     

Studies on BNPP Cleavage by Schiff Base Complexes Containing Benzoaza‐15‐Crown‐5 in DHAB Micellar Solution

Two novel benzoaza‐crown Schiff base cobalt (II) and manganese (III) complexes were synthesized and characterized. The hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP) catalyzed by the two complexes was studied in buffer solution containing dihexadecyldimethylammonium bromide (DHAB) at 25°±0.1°C and different pH values. The kinetic mathematical model of BNPP hydrolysis was proposed, and the effects of different reaction conditions on BNPP hydrolysis were discussed. The results indicate that the two complexes (MnLCl and CoL) can efficiently accelerate the catalytic cleavage of BNPP in DHAB micellar solution. The pseudo‐first‐order rate constants (k _obsd) of BNPP hydrolysis catalyzed by the metallomicelles of MnLCl/DHAB and CoL/DHAB are 2.32×10⁷ times and 1.45×10⁷ times higher than that of the BNPP spontaneous hydrolysis, respectively. Possible reasons for the huge rate accelerations include the lower critical micelle concentration (cmc) of DHAB and formation of metallomicelles made of complexes and DHAB. Furthermore, the BNPP cleavage catalyzed only by the two complexes was investigated in buffer solution. It was found that the hydrolytic rates of BNPP catalyzed only by the two complexes were about 1% of those catalyzed by MnLCl/DHAB and CoL/DHAB systems at 25°C, pH=7.00, and [BNPP]=2.0×10^?4 mol · dm^?3.     

Phosphate Diester Cleavage Promoted by the Metallomicelles of Ce(III) Complexes of Aza-Crown Ether with Different Numbers of Nitrogen Atoms

The design of artificial hydrolase has attracted extensive attention due to their scientific significance and potential application in the field of gene medicine and molecular biology. This work reports the catalytic activation of two aza-crown ether Ce(III) complexes and their metallomicelles as artificial hydrolase in bis(4-nitrophenyl) phosphate ester (BNPP) hydrolysis. The chemical composition of two complexes was determined by the fluorescence spectra and the mole ratio method for electronic absorption spectra. The bonding effect of BNPP and solubilizing effect of the complexes were proved by a method of fluorescence spectroscopy. The catalytic activity of different catalytic systems in BNPP hydrolysis was measured with UV-vis spectrophotometric method. These catalytic systems showed high catalytic activity for promoting BNPP hydrolysis at the almost physiological conditions. BNPP hydrolysis rate in these catalytic system is about 10⁷- to 10⁹-fold faster than that of the BNPP spontaneous hydrolysis in aqueous solution at the same conditions. The metallomicelle systems exhibited higher catalytic activity compared with the complex solution systems in BNPP hydrolysis, and hexadecyltrimethyl ammonium bromide micelle provides a useful catalytic environment for reaction. The acid effect of the catalytic system is ascribed to the formation of metal-bound hydroxide serving as a better kind of nucleophile.     

Studies on the reaction kinetics and the mechanism of hydrolysis of bis(4-nitrophenyl) phosphate (BNPP) catalyzed by oxamido-bridged dinuclear copper(II) complexes in micellar solution

Oxamido-bridged dinuclear copper(II) complexes, used as symmetric two-center catalysts for the cleavage of BNPP, were synthesized and characterized. The reaction kinetics and the mechanism of hydrolysis of BNPP catalyzed by metallomicelles, made from complex (A) or (B) and a surfactant (LSS or CTAB), were investigated. A kinetic mathematical model for BNPP cleavage was also proposed. The results showed that the reaction rate for the catalytic hydrolysis of BNPP, compared with spontaneous hydrolysis of BNPP, increased by a factor of ca. 1 × 10⁶ due to the synergistic effect of two copper ions in the complex and the local concentration effect of the micelle. The study indicates that the metallomicelle-containing oxamido-bridged dinuclear copper(II) complex may be a potential catalyst for the hydrolysis of BNPP.     

一种活性磷酸酯的分子内亲核取代反应动力学研究

合成和表征了大环过渡金属配合物NiL(L:高氯酸-5,7,7,12,14,14-六甲基-1,4,8,11-四氮杂环十四烷)。配合物NiL与表面活性剂组成的金属胶束作为模拟水解金属酶用于催化BNPP水解。提出了BNPP催化水解的机理;建立了用于计算动力学常数的动力学模型;计算了相关的动力学和热力学常数。结果表明,这种金属胶束表现出较高的催化活性;BNPP催化水解反应是分子内亲核取代反应;所提出的机理和建立的动力学模型是合理的。     

A green route to enantioenriched (S)-arylalkyl carbinols by deracemization via combined lipase alkaline-hydrolysis/Mitsunobu esterification

Herein we report results of the chemoenzymatic deracemization of a range of secondary benzylic acetates 1a–9a via a sequence of hydrolysis with CAL-B lipase in non-conventional media, combined with esterification of the recovered alcohol according to the Mitsunobu protocol following an enzymatic kinetic resolution (KR). The KR of racemic acetates 1a–9a via an enzymatic hydrolysis, with CAL-B lipase and Na₂CO₃, in non-aqueous media was optimized and gave high selectivities (E ? 200) at good conversions (C >49%) for all of the substrates studied. This method competes well with the traditional one performed in a phosphate buffer solution. The deracemization using Mitsunobu inversion gave the (S)-acetates in moderate to excellent enantiomeric excess 75% < ee < 99%, in acceptable isolated yields 70% < yield < 89%, and with some variations according to the acetate structure.     

A study on the hydrolysis of bis(nitrophenyl)phosphate catalyzed by N‐methyldiethanolamine‐Ce(III) complex

The hydrolysis of bis(p‐nitrophenyl)phosphate (BNPP) catalyzed by N‐methyldiethanolamine‐Ce(III) complex in the presence and absence of cetyltrimethylammonium bromide (CTAB) and Brij35 surfactants at pH 7.20 and 303 K has been studied. The experimental results indicate that N‐methyldiethanolamine‐Ce(III) complex remarkably accelerates the hydrolysis of BNPP. The observed first‐order rate constant of the hydrolysis of BNPP catalyzed by N‐methyldiethanolamine‐Ce(III) complex at pH 7.20 and 303 K is 1.22 × 10^?2 s^?1, which is 1.09 × 10⁹ times of that of spontaneous hydrolysis of BNPP at pH 7. It is close to the activity of natural enzyme. A general quantitative treatment of the catalytic reaction involved a ternary complex as M_mL_lS has also been proposed in this paper. Applying this method to the catalytic hydrolysis of BNPP, we have obtained its thermodynamic and kinetic parameters. CTAB and Brij35 surfactant micelles obviously influence the rate constants of the catalytic hydrolysis of BNPP. Brij35 micelles promote the catalytic hydrolysis of BNPP, while CTAB micelles inhibit it. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 687–692, 2004     

Catalytic enantioselective oxidation of aromatic hydrocarbons with D4-symmetric chiral ruthenium porphyrin catalysts

The [Ru^II(D₄-Por¹)(CO)(MeOH)] (D₄-H₂Por¹ = tetrakis[(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracen-9-yl]porphyrin) complex 1 is an effective catalyst for asymmetric hydroxylation of aromatic hydrocarbons with 2,6-dichloropyridine N-oxide (Cl₂pyNO) as terminal oxidant. Up to 76% ee was achieved for the catalytic hydroxylation of 4-ethyltoluene, 1,1-diethylindan and benzylcyclopropane. Both electron-donating and -withdrawing substituents were found to accelerate the catalytic oxidation reaction, and a large primary H/D kinetic isotope effect (k_H/k_D = 11 at 298 K) was observed for the catalytic ethylbenzene-d₁₀ oxidation. A mechanism involving rate-limiting hydrogen atom abstraction by reactive oxoruthenium species is postulated.     

Construction and Activity of a New Catalytic System in the Hydrolysis of Bis(4‐nitrophenyl) Phosphate Ester

A new catalytic system containing an unsaturated heterocyclic nitrogen ligand and lanthanum(III) was constructed and used as a catalyst in the hydrolysis of bis(4‐nitrophenyl) phosphate ester (BNPP) in this work. The results indicated that this catalytic system showed greater catalytic activity in the hydrolysis of BNPP and better reproducibility and stability than other similar lanthanum(III) systems. The catalytic rate of the BNPP hydrolysis was about 10⁷‐fold faster than that of its spontaneous hydrolysis at the same conditions. Compared with the previous Cu(II) or Ni(II) complex containing the same ligand in the water, the activity of the macrocyclic La(III) complex increases ca. 10³‐fold for BNPP catalytic hydrolysis. The experimental data showed that the monohydroxy complex made of the heterocyclic nitrogen ligand and lanthanum(III) is the real active species as a catalyst in BNPP catalytic hydrolysis.     

Study of the Intramolecular Reaction of an Activated Phosphate Ester in the Micelle System Containing Macrocyclic Complex

The intramolecular nucleophilic substitution of an activated phosphate diester, bis(p-nitrophenyl) phosphate (BNPP) as the nucleic acids substitute, was investigated. A macro-cyclic ligand and the corresponding Cu (II) and Ni (II) complexes were synthesized and characterized. The metallomicelles made up of macrocyclic divalent metal complex and micelle, as mimic hydrolytic metalloenzyme, was used in BNPP catalytic hydrolysis. The metallomicelles displayed higher catalytic activity although they do not attain the catalytic efficiency of enzymes. The analysis of specific absorption spectra showed that the course of the BNPP catalytic reaction was different from that of the BNPP spontaneous hydrolysis, and was an intramolecular nucleophilic substitution reaction. Based on the analytic result of the specific absorption spectrum, an intramolecular nucleophilic substitution mechanism of BNPP catalytic hydrolysis was proposed and a correlative kinetic mathematical model was established, and the corresponding thermodynamic and kinetic constant was calculated. The result of this study proved validity of the mechanism and mathematical model proposed in the article.     

Lipase-catalyzed kinetic and dynamic kinetic resolution of 1,2,3,4-tetrahydroisoquinoline-1-carboxylic acid

A dynamic kinetic resolution method for the preparation of enantiopure 1,2,3,4-tetrahydroisoquinoline-1-carboxylic acid (R)-2 was developed involving the CAL-B-catalyzed enantioselective hydrolysis of the corresponding ethyl ester (±)-1 in toluene/acetonitrile (4:1) containing 1 equiv of added water and 0.25 equiv of dipropylamine. This method allowed the preparation of (R)-2 (ee = 96%) with 80% isolated yield. The kinetic resolution of (±)-1 in diisopropyl ether at 3 °C afforded both enantiomers with ee ⩾92%.     

Terahertz absorption spectroscopy of protein-containing reverse micellar solution

Terahertz time-domain spectroscopy has been carried out for AOT/isooctane reverse micellar solution with myoglobin at the water-to-surfactant molar ratios (w₀) of 0.2 and 4.4. The amplitude of the absorption spectrum increases with increasing the protein concentration at w₀ = 0.2, whereas it decreases at w₀ = 4.4. The molar extinction coefficients of the protein-filled reverse micelle, and the constituents, i.e., myoglobin, water, and AOT, have been derived by use of the structural parameters of the micellar solution. The experimental results are interpreted in terms of hydration onto the protein and surfactant in the reverse micelle.     

A convenient method for the kinetic resolution of racemic 2-hydroxyalkanoates using diphenylacetic anhydride (DPHAA) and a chiral acyl-transfer catalyst

Diphenylacetic anhydride (DPHAA) was found to be a useful reagent for the kinetic resolution of racemic 2-hydroxyalkanoates in the presence of a catalytic amount of (R)-benzotetramisole ((R)-BTM). The combined use of DPHAA and (R)-BTM effectively produced a variety of the optically active 2-hydroxyalkanoates and the corresponding 2-acyloxyalkanoates from racemic 2-hydroxyalkanoates (s-values = 42–177). A fairly broad substrate scope was demonstrated by this novel chiral induction system. We also revealed that the use of only 0.3 equiv of DPHAA is enough to provide the optically active 2-acyloxyalkanoates in good yields and with excellent ee’s by the added use of 0.3 equiv of pivalic anhydride for the kinetic resolution of the racemic 2-hydroxyalkanoates.     

Catalytic effect of CTAB on the interaction of dipeptide glycyl-tyrosine (Gly-Tyr) with ninhydrin

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of dipeptide glycyl-tyrosine (Gly-Tyr) with ninhydrin under varying conditions has been studied spectrophotometrically at 70 °C and pH 5.0. The reaction followed first- and fractional-order kinetics with respect to [Gly-Tyr] and [ninhydrin], respectively. Increase in total concentration of CTAB from 0 to 70 × 10⁻³ mol dm⁻³ resulted in an increase in the pseudo-first-order rate constant (k_ψ) by a factor of ca. 3. Quantitative kinetic analysis of k_ψ − [CTAB] data was performed on the basis of pseudo-phase model of the micelles (proposed by Menger and Portnoy and developed by Bunton) and Piszkiewicz model. A possible mechanism has been proposed and the kinetic data have been used to evaluate the micellar binding constants K_S (268 mol⁻¹ dm³ for Gly-Tyr) and K_N (64 mol⁻¹ dm³ for ninhydrin).     

Metallomicellar catalysis: accelerated hydrolysis of BNPP by copper(II), zinc(II), and nickel(II) complexes of long alkanol-imidazole in CTAB micellar solution

Two alkanol-imidazole ligands have been synthesized. Metal (Cu(II), Zn(II), Ni(II)) complexes of these ligands have been investigated as catalysts for the hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) in the buffered CTAB co-micellar solution at 30 degrees C and various pH values, respectively. The ternary complex kinetic model for metallomicellar catalysis was employed to analyze the results, to obtain the kinetic and thermodynamic parameters. The effect of the structure of the ligands and the microenvironment of the reaction on the hydrolytic reaction of BNPP has been discussed in detail. The results indicate that the hydrophobic interaction between the substrate and the metallomicellar catalyst and the micellar microenvironment are important factors.     

Smart synthesis of silver nanoparticles supported in porous polybenzoxazine nanocomposites via a main-chain type benzoxazine resin

Novel silver nanoparticles immobilized on macroporous polybenzoxazine nanocomposites were prepared as catalysts for catalytic reduction reaction.     

Solution studies of tris(2-benzylaminoethyl)amine complexes of zinc(II) and copper(II): The catalytic hydrolysis of toxic organophosphate

Solution studies of the tetradentate ligand tris(2-benzylaminoethyl)amine, BzTren with both zinc(II) and copper(II) salts were investigated in aqueous methanol (33% v/v) by means of ¹H NMR, potentiometric, and UV-visible titrations as well as cyclic voltammetry. Subsequently, their zinc(II) and copper(II) complexes [BzTren-M(OH₂)]²⁺ 1 and 2 (M²⁺ = Zn²⁺ and Cu²⁺) were synthesized and fully characterized by using FT-IR spectroscopy, elemental analysis, and thermal analysis. Complexes 1 and 2 are investigated kinetically for the catalytic hydrolysis of the toxic organophosphate parathion at 50 °C in aqueous methanol (33%, v/v). The kinetic results indicate that copper(II) complex 2 is more active than zinc(II) complex 1, presumably a reflection of the effective electron-withdrawing as well as the greatest electrophilicity of copper(II) ion.     

Studies on the reaction kinetics and the mechanism of hydrolysis of bis(4-nitrophenyl)phosphate (BNPP) by hydroxamic acid complexes containing benzo-15-crown-5

A hydroxamic acid (HL) containing benzo-15-crown-5 and their copper(II), zinc(II), cobalt(II) and manganese(II) complexes have been synthesized and studied as catalysts for the cleavage of bis(4-nitrophenyl)phosphate (BNPP). The catalytic properties of these complexes and the kinetics and mechanism of BNPP hydrolysis have been investigated. The kinetic mathematical model of BNPP cleavage catalyzed by these complexes has been proposed. The effects of reaction temperature and metal ion in the complexes on the rate of BNPP catalytic hydrolysis have been discussed. The results show that the hydroxamic acid complexes containing benzo-15-crown-5 exhibit high activity in the BNPP catalyzed hydrolysis; the pseudo-first-order-rate constants of BNPP hydrolysis catalyzed by the complexes increase along with the increases of pH of the buffer solution from 7.50 to 9.50; the activity of different metal ions decreases in the order: Co²⁺ > Cu²⁺ > Zn²⁺ > Mn²⁺; the pseudo-first-order-rate constants of BNPP hydrolysis catalyzed by the complexes is 2.24 × 10⁵ ~ 3.24 × 10⁵ times as large as that of spontaneous hydrolysis of BNPP.     

Sucrose ester micellar-mediated synthesis of Ag nanoparticles and the antibacterial properties

Ag nanoparticles with diameter in the range of 10–25 nm had been synthesized using a simple sucrose ester micellar-mediated method. Ag nanoparticles were formed by adding AgNO₃ solution into the sucrose ester micellar solution containing sodium hydroxide at atmospheric condition after 24 h of aging time. Trace amount of dimethyl formamide (DMF) in the sucrose ester solution served as a reducing agent while NaOH acted as a catalyst. The produced Ag nanoparticles were highly stable in the sucrose ester micellar system as there was no precipitation after 6 months of storage. The as-synthesized Ag nanoparticles were characterized using transmission electron microscope (TEM), X-ray diffractometer (XRD), dynamic light scattering (DLS) and UV–vis spectroscopy (UV–vis). Formation mechanism of Ag nanoparticles in the micellar-mediated synthesis is postulated. The antibacterial properties of the Ag nanoparticles were tested against Methicillin-resistant Staphylococcus aureus (MRSA) (Gram-positive) and Aeromonas hydrophila (Gram-negative) bacteria. This work provides a simple and “green” method for the synthesis of highly stable Ag nanoparticles in aqueous solution with promising antibacterial property.