Hydrolysis Of P-nitrophenyl Picolinate Research Articles

Remarkable reactivity of alkoxide/acetato-bridged binuclear copper(II) complex as artificial carboxylesterase.

Bromo-containing binuclear Schiff base copper(II) complex, Cu2L(OAc), with an alkoxo/acetato-bridged moiety was employed as a model of carboxylesterases to promote the hydrolytic cleavage of p-nitrophenyl picolinate (PNPP). Furthermore, the reactivity of a mononuclear complex (CuHL) was evaluated for comparing it with that of binuclear one. The results reveal that the as-prepared binuclear Cu2L(OAc) efficiently accelerated the hydrolysis of PNPP, giving rise to excess four orders of magnitude rate enhancement in contrast to the un-catalyzed reaction. Cu2L(OAc) represented an enzyme-like bell-shaped pH-responsive kinetic behavior. Moreover, the binuclear one is more reactive than its mononuclear analogue (CuHL) by two orders of magnitude. The total efficiency of Cu2L(OAc) is about 61-fold than that of its mononuclear analogue, CuHL. In addition, a contrast experiment reveals that binuclear Cu2L(OAc) displayed good activity in the hydrolysis of PNPP as well another active ester, i.e., S-2-benzothiazolyl 2-amino-alpha-(methoxyimino)-4-thiazolethiolacetate (AE-active ester). Noteworthyly, it was found that mononuclear one inspired more obvious rate enhancement in the hydrolysis of AE-active ester relative to PNPP hydrolysis. The estimated pK a1 of bound water on the binuclear Cu2L(OAc) using second derivative method (SDM) is relatively smaller than that for CuHL by a gap of about 0.8 pK unit, which facilitates the hydrolysis of PNPP. Four orders of magnitude rate enhancement was observed for the catalytic hydrolysis of p-nitrophenyl picolinate (PNPP) by one μ-alkoxide/acetato-bridged binuclear copper(II) complex under physiological conditions. Substrate specificity of the resulting binuclear complexes was observed for the hydrolysis of PNPP and AE-active ester.

Distinguishable effects of varied micelles on the hydrolysis of PNPP by dinuclear copper(II) complexes containing oxo-bridged unit

Two alkoxo/hydroxide-bridged dinuclear copper(II) complexes (Cu2L1 and Cu2L2) were prepared for evaluating their activity towards the hydrolysis of p-nitrophenyl picolinate (PNPP). Importantly, this work investigated the effects of varied micelles of four surfactants, e.g., cationic gemini 16-2-16 and 16-6-16, single-chain CTAB (hexadecyltrimethylammonium bromide), and LSS (n-lauroylsarcosine sodium), on the PNPP hydrolysis by the as-prepared copper(II) complexes. The experimental results indicate that at neutral pH both of complexes exhibited much better activity by excess four-order of magnitude rate enhancement. For instant, rate constants of PNPP hydrolysis by Cu2L1 and bromo-containing Cu2L2 are approximate 49,569.6- and 31,123.5-fold than that of PNPP spontaneous hydrolysis. In addition, the hydrolytic reactivity of the bromo-containing Cu2L2 is subordinate to that one without bromine, Cu2L1. Moreover, it is found that the micellar solution of gemini 16-6-16 is proved to be the best medium, and whereas LSS micellar solution is the worst one. Particularly, the pK a values of the Cu(II)-bound H2O are determined by a new methodology which is correlative to second derivatives.

Reactivity of Dinuclear Copper(II) Complexes with N‐Salicylidene Glycine Schiff Bases as Carboxylesterase Models

ABSTRACTTwo phenoxo‐bridged dinuclear copper(II) complexes (Cu2L12, Cu2L22) with N‐salicylidene glycine Schiff bases were prepared and evaluated their performance for catalyzing the hydrolysis of p‐nitrophenyl picolinate (PNPP). The observations reveal that the as‐prepared dinuclear copper(II) complexes exhibited better activity by two to three orders of magnitude rate enhancement in comparison with the autohydrolysis rate of PNPP. Chloro‐containing Cu2L22 aroused approximately three times kinetic advantage over chloro‐free Cu2L12 at pH 7.0, which is probably contributed to the electron‐withdrawing inductive effect of the 5′‐chloride group. Moreover, it was found that the pH‐responded kinetic behavior displayed an enzyme‐like property for the PNPP hydrolysis by the two complexes.

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.

Catalytic Reactivity of Phenoxo-Bridged Homobinuclear Copper(II) Complexes With L-Threonine Schiff Bases As a Carboxylesterase Model

Two novel phenoxo-bridged homobinuclear copper(II) complexes with L-threonine Schiff bases as artificial hydrolases were prepared and screened for catalytic activity in the hydrolysis of p-nitrophenyl picolinate (PNPP), a classic model of carboxylic acid esters. Kinetic analysis testified that the two complexes exhibited good activity with rate acceleration of two orders of magnitude in aqueous solution. In addition, the one copper(II) complex containing 5’-bromo substituent was much more efficient than its bromo-free analogue, showing approximately 1.1∼5.3 times kinetic advantage over a pH range of 7.00–8.20.[Supplementary materials are available for this article. Go to the publisher's online edition of Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry for Figures 1S–3S.]

Unprecedented reactivity of alkoxo/hydroxide-bridged dinuclear copper(II) complexes as artificial carboxylesterase: Effects of Gemini 16-6-16 micelles and bimetallic synergistic effect

One μ-alkoxo/hydroxide-bridged dinuclear copper(II) complex (Cu2L) and a mononuclear analogue (CuL) with symmetric Schiff base compound were employed as carboxylesterase models to promote the hydrolysis of a carboxylic acid ester, p-nitrophenyl picolinate (PNPP). Also the introducing of a Gemini surfactant, bis(hexadecyldimethylammonium)hexane bromide (16-6-16, 2Br−), gave interested observations relative to those controlled trials preformed in buffer and a micellar solution of traditional single-chain surfactant, CTAB (cetyltrimethylammonium bromide). The results indicated that the dinuclear Cu2L efficiently accelerated PNPP hydrolysis with 18,096- and 49,569.6-fold rate enhancement under moderate conditions (pH 7.00, 25°C) in buffer and 16-6-16 micellar solution, respectively. Much greater rate enhancement was observed in 16-6-16 micelles in contrast with CTAB micelles, launching 1.6–2.6 folds difference in hydrolysis rate of PNPP at pH 7.00. Additionally, the Cu2L-induced PNPP hydrolysis showed a bell-shaped rate-pH profile, which is an enzyme-like behaviour. Interestingly, rate–pH curves could provide the direct evidence for the interfacial effects of Gemini 16-6-16 micelles on the deprotonation of coordinated water, indicating about 0.2 unit pKa1 difference of the Cu2L-bound H2O between in micellar phase and bulk phase. Cu2L was found to be approximately 199.3- and 288.7-fold reactive than CuL in buffer and 16-6-16 micellar solution, respectively. Significant activity difference between both complexes probably results from the bimetallic coorperation of the two catalytic copper sites and more open binding site of Cu2L.

Hydrolytic cleavage of p-nitrophenyl picolinate by mononuclear Zn(II) and Co(II) complexes with imidazole derivative in CTAB micellar solution

One new hydroxyl-functionalized imidazole derivative (L) was synthesized and characterized. Further, the related mononuclear zinc(II) and cobalt(II) complexes were prepared and used as mimic hydrolases to catalyze the hydrolytic cleavage of p-nitrophenyl picolinate (PNPP) in buffered aqueous solution and a micellar solution of cetyltrimethylammonium bromide (CTAB). Observations show that for all of catalytic systems, the hydrolysis of PNPP was pH-dependent in the pH range of 7.00–8.20. Besides, hydrolysis rates of PNPP displayed a constant increase with the increasing concentration of substrate. In the case of CoL-containing system, moreover, much greater acceleration for PNPP hydrolysis was observed in comparison with the ZnL-containing system. However, micellar effect of CTAB micelle aggregates on the PNPP hydrolysis was not obvious only showing 1.0 ∼ 1.3 folds rate difference in contrast to buffered aqueous solution.

Hydrolytic activity of μ-alkoxide/acetato-bridged binuclear Cu(II) complexes towards carboxylic acid ester

Two μ-alkoxide/acetate-bridged small molecule binuclear copper(II) complexes were synthesized, and used to promote the hydrolysis of a classic carboxylic acid ester, p-nitrophenyl picolinate (PNPP). Both binuclear complexes exhibited good hydrolytic reactivity, giving rise to ca. 15547- and 17462-fold acceleration over background value for PNPP hydrolysis at neutral conditions, respectively. For comparing, activities of the other two mononuclear analogues were evaluated, revealing that binuclear complexes show approximately 150- and 171-fold kinetic advantage over their mononuclear analogues. This study reports the hydrolysis of p-nitrophenyl picolinate (PNPP) with increase of rate acceleration up to four orders of magnitude by two μ-alkoxide/acetato-bridged binuclear copper(II) complexes when compared to uncatalysed reaction. Furthermore, the two binuclear complexes were more active than their mononuclear analogues in the catalytic hydrolysis of PNPP.

Studies on Hydrolysis of P-Nitrophenyl Picolinate by Unsymmetrical Bis-Schiff Base Manganese Complexes with Aza-Crown Ether or Morpholino Pendants

The unsymmetrical bis-Schiff base manganese complexes with either benzo-10-aza-crown ether pendants ( MnL1Cl, MnL2Cl) or morpholino pendant (MnL3Cl,MnL4Cl) have been employed as models for hydrolase by studying the hydrolysis reactions of p-nitrophenyl picolinate (PNPP). The effects of complex structures, reaction pH and reaction temperature on the rate of PNPP hydrolysis have been investigted. All four complexes exhibit high catalytic activity and the rate increases with pH increasing at 25 oC. The complexes of ligands containing a crown ether group exhibit higher catalytic activities than the non-crown analogues.

Kinetic studies of manganese(III) and cobalt(II) Schiff base complexes as synthetic hydrolases for p-nitrophenyl picolinate in CTAB surfactant micellar solution

Four symmetrical bis-Schiff bases with either benzo-10-aza-crown ether or morpholino pendants and their Mn(III) and Co(II) complexes have been employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP) in buffered CTAB micellar solution. A kinetic model of PNPP cleavage catalysed 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 buffer at 25 °C. The complexes containing two crown ether group exhibit higher catalytic activities than their crown-free analogues, and the catalytic activity of the phenyl-bridged Schiff base complex is larger than that of the ethyl-bridged Schiff base complex for the same substituents and metal. The catalytic activity of the manganese(III) complex exceeds that of the cobalt(II) complex in catalysing hydrolysis of PNPP under the same ligand.

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.

Mono-Schiff base complexes with aza-crown ether or morpholino pendants as synthetic hydrolases for p-nitrophenyl picolinate cleavage

Mono-Schiff base complexes of Co(II) and Mn(III) with either benzo-10-aza-crown ether pendants (MnL 2 1 Cl, MnL 2 2 Cl) or morpholino pendants (MnL 2 3 Cl, CoL 2 3 ) have been 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 catalytic PNPP hydrolysis have also been examined. The rate increases with pH of the buffer solution; all four complexes exhibited high activity in the catalytic PNPP hydrolysis. Compared with the crown-free analogs MnL 2 3 Cl and CoL 2 3 , the crowned Schiff base complexes (MnL 2 1 Cl, MnL 2 2 Cl) exhibited higher catalytic activity. The pseudo-first-order rate constant for the PNPP hydrolysis catalyzed by the complex MnL 2 1 Cl, containing a benzo-10-aza-crown ether pendant, is 1.84 × 103-fold higher than that of spontaneous hydrolysis of PNPP at pH 7.60, 25 °C, [S] = 2.0 × 10−4 mol dm−3. Four mono-Schiff base complexes of Mn(III) and Co(II) with either benzo-10-aza-crown ether pendants (MnL 2 1 Cl, MnL 2 2 Cl) or morpholino pendants (MnL 2 3 Cl, CoL 2 3 ) have been employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP). The effects of ligand structure and reaction temperature on PNPP catalytic hydrolysis have been also discussed. All four complexes exhibited high activity in the catalytic PNPP hydrolysis. Compared with the crown-free analogy MnL 2 3 Cl and CoL 2 3 , the crowned Schiff base complexes MnL 2 1 Cl and MnL 2 2 Cl exhibit higher catalytic activity, the catalytic activity of the complexes follows the order Mn(III) > Co(II) under the same ligand.

Comparative Study of p-nitrophenyl picolinate Hydrolysis Catalyzed by Bis(O,O’-di(2-phenylalkyl)dithiophosphate) nickel(II)

The hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by two nickel (II) complexes (bis(O,O’-di(2-phenylmethyl) dithiophosphate) nickel(II) (NiR1) and bis(O,O’-di(2-phenylethyl) dithiophosphate) nickel(II) (NiR2)) was investigated kinetically in this work. The results indicate that both metal complexes accelerate the hydrolysis of PNPP dramatically and the NiR1 exhibits higher catalytic function on PNPP hydrolysis in the buffered solution with relatively low pH values, while NiR2 shows slightly more efficacy on hydrolysis of PNPP in relatively high pH buffered solutions. This variance is ascribed to the synergism effect of space hindrance of the complexes and the nucleophilic attack of metal-hydroxy species generated by the complexes.

Use of bacteria for rapid, pH-neutral, hydrolysis of the model hydrophobic carboxylic acid ester p-nitrophenyl picolinate

Caulobacter crescentus, Escherichia coli and Bacillus subtilis cultures promote the hydrolysis of the model ester p-nitrophenyl picolinate (PNPP) at neutral pH with high efficiency. Hydrolysis is related to cell concentration, while the interaction of PNPP with both bacterial cells and their extracellular molecules is required for a maximum rate of PNPP hydrolysis in C. crescentus cultures. Furthermore, C. crescentus cultures hydrolyse PNPP at concentrations useful in synthetic chemistry.

Metallovesicular catalytic hydrolysis of p-nitrophenyl picolinate catalyzed by zinc(II) complexes of pyridyl ligands in vesicular solution

The hydrolysis of p-nitrophenyl picolinate (PNPP) catalyzed by the Zn(II) complexes of 6-(n-butyloxymethyl)-2-(hydroxymethyl)pyridine and 6-(n-dodecyloxymethyl)-2-(hydroxymethyl)pyridine was kinetically investigated by observation of the rates of release of p-nitrophenol in a vesicular solution at different pH values and temperatures. A 1:1 ligand:Zn 2+ stoichiometry was found to produce the most active species based on a kinetic version of the Job plot analysis. Experimental results also showed that the complex formed from ligand 2 and Zn 2+ exhibited a more remarkable rate acceleration effect on the hydrolysis of PNPP in vesicular solution than that formed from ligand 1 and Zn 2+.

Reactivity of Schiff Base Manganese(III) Complexes with Different Pendants toward the Hydrolysis of p‐Nitrophenyl Picolinate

AbstractThis paper describes the catalytic performance of two manganese(III) complexes with mono‐Schiff base ligands as artificial hydrolases towards the hydrolysis of p‐nitrophenyl picolinate (PNPP). Observations reveal that the one complex (MnL22Cl) containing morpholine pendants exhibits 1.2–1.7 fold kinetic advantage over the other one (MnL21Cl) containing benzoaza‐15‐crown‐5 group. Especially, optimum molecule structures using a Gaussian 03 software confirm that MnL22Cl indeed possesses a relatively open linked site for the approaching of PNPP, resulting in higher efficiency due to a convenient association between substrate (PNPP) and MnL22Cl. In addition, the steric hindrance of two pendants, i.e., benzoaza‐15‐crown‐5 and morpholine, may be a main influencing factor for tuning catalytic activities of the synthesized Mn(III) catalysts. Both Mn(III) catalysts used here were found to have fine tolerance to the operated temperature and pH. Related kinetic and thermodynamic analyses were also given to demonstrate their structure‐activity relationships (SAR) of both catalysts used.

P‐Nitrophenyl Picolinate Cleavage by Unsymmetrical Bis‐Schiff Base Manganese(III) and Cobalt(II) Complexes with Aza‐Crown Ether or Morpholino Pendants

AbstractThe 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 P-Nitrophenyl Picolinate by Triethanolamine Co(II) Complex-Based Metallomicelle

The catalytic hydrolysis of p-nitrophenyl picolinate (PNPP) by triethanolamine Co(II) complex in the presence or in the absence of CTAB and Triton X-100 micelle was investigated. The results indicated that triethanolamine Co(II) complex promoted the hydrolysis of PNPP by the addition of the catalytic effect of triethanolamine and Co(II), however, in the presence of CTAB and Triton X-100 micelle, triethanolamine Co(II) complex exhibited a remarkably catalytic effect on the hydrolysis of PNPP, indicating the formation of the metallomicelle. According to the proposed ternary complex kinetic model for metallomicellar catalysis, the obtained thermodynamic and kinetic parameters explained well the mechanism of the catalytic hydrolysis of PNPP.

Catalytic Hydrolysis of p-Nitrophenyl Picolinate by Triethanolamine [Co(II)] Complex-Based Metallomicelle

The catalytic hydrolysis of p-nitrophenyl picolinate (PNPP) by triethanolamine Co(II) complex in the presence or in the absence of CTAB and Triton X-100 micelle was investigated. The results indicated that triethanolamine Co(II) complex promoted the hydrolysis of PNPP by the addition of the catalytic effect of triethanolamine and Co(II), however, in the presence of CTAB and Triton X-100 micelle, triethanolamine Co(II) complex exhibited markably catalytic effect on the hydrolysis of PNPP, indicating the formation of the metallomicelle. According to the proposed ternary complex kinetic model for metallomicellar catalysis, the obtained thermodynamic and kinetic parameters explained well the mechanism of the catalytic hydrolysis of PNPP.

Hydrolysis Kinetics of p-Nitrophenyl Picolinate Catalyzed by Mono-Schiff Base Complexes with Aza-Crown Ether or Morpholino Pendants in CTAB Surfactant Micellar Solution

Two mono-Schiff base manganese (III) and cobalt (II) complexes with benzo-10-aza-crown ether pendants (), and the analogy with morpholino pendants () have been synthesized and employed as models for hydrolase enzymes to promote the hydrolysis of p-nitrophenyl picolinate (PNPP) in the buffered CTAB micellar solution. The kinetic mathematical model and mechanism cleavage on PNPP hydrolysis catalyzed by these complexes was proposed. The effects of complexes structure and reactive temperature on the rate of catalytic PNPP hydrolysis have been also examined. The results showed that the reactive rate increases with pH of the buffered CTAB micellar solution; all four complexes exhibited high activity for the catalytic PNPP hydrolysis in the buffered CTAB micellar solution. In comparison with the crown-free analogy and , the crowned Schiff base complexes and exhibit higher catalytic activity for promoting PNPP hydrolysis.