Hydrolysis Of Bis P-nitrophenyl Phosphate Research Articles

Tetranuclear iron(III) complexes with a carboxylate-rich ligand as synthetic mimics of phosphoesterases in aqueous media

The characterization and catalytic activities of two tetranuclear Fe(III) complexes of a carboxylate-rich ligand, N,N’-Bis[2-carboxybenzomethyl]-N,N’ -Bis[carboxymethyl]-1,3-diaminopropan-2-ol (H5ccdp) ligand towards the hydrolysis of p-nitrophenyl phosphate (PNPP) and bis(p-nitrophenyl) phosphate (BNPP) substrates in aqueous systems are described. Kinetic investigations were carried out using UV–vis spectrophotometric techniques at 25 °C and 37 °C and varied pH conditions (7 – 9.5). The kinetic studies showed that the turnover rate (kcat) values for the hydrolysis of PNPP by [Fe4(ccdp)2(μ-O)(μ-OH)(d-GluA)2]3- were marginally higher than [Fe4(ccdp)2(OH)2(o-phth)2]4- at 9.24 × 10-6 s−1 (pH 8 and 37 °C) and 4.27 × 10-7 s−1 (pH 8 and 25 °C), respectively. However, similar comparisons among the BNPP hydrolysis showed the turnover rate values for [Fe4(ccdp)2(OH)2(o-phth)2]4- was marginally better than [Fe4(ccdp)2(μ -O)(μ –OH)(d-GluA)2]3- with values of 1.85 × 10-6 s−1 (pH 8 and 37 °C) and 6.23 × 10-7 (pH 8 and 37 °C). ESI-MS techniques detected catalyst-substrate adduct species for both metal complexes with PNPP. Additionally, both complexes also showed evidence for complex-substrate-nucleophile adduct formation with both BNPP and PNPP substrates via ESI-MS. Based on the kinetic activity and structural information obtained in this study, a reaction mechanism for the hydrolysis of phosphorester has been proposed.

Homodinuclear copper(II) and zinc(II) complexes of a carboxylate-rich ligand as synthetic mimics of phosphoester hydrolase in aqueous solutions

The synthesis, characterization and catalytic activities of two homodinuclear Cu(II) and Zn(II) complexes of a carboxylate-rich ligand, N,N′-Bis[2-carboxybenzomethyl]-N,N′ -Bis[carboxymethyl]-1,3-diaminopropan-2-ol (H5ccdp) ligand towards the hydrolysis of (p-nitrophenyl phosphate) (PNPP) and bis(p-nitrophenyl) phosphate (BNPP) substrates in aqueous systems are described. Kinetic investigations were carried out using UV–Vis spectrophotometric techniques at 25 °C and 37 °C and different pH (7–10) conditions. The kinetic studies revealed that the turnover rate (kcat) values among the PNPP hydrolysis systems, the highest and the lowest kcat values were displayed by [Cu2(ccdp)(μ-OAc)]2− at 2.34 × 10−6 s−1 (pH 8 and 37 °C) and 2.13 × 10−8 s−1 (pH 8 and 25 °C), respectively. However, similar comparisons among the BNPP hydrolysis revealed that highest and the lowest kcat values were displayed by [Zn2(ccdp)(μ-OAc)]2− at 4.64 × 10−8 s−1 (pH 9 and 37 °C) and 2.38 × 10−9 (pH 9 and 25 °C). Significantly enough, the catalyst−substrate adduct species containing a metal bound PNPP and BNPP have been detected by ESI-MS techniques. Additionally, a PNPP-bound copper complex has been isolated and crystalized using single crystal X-ray diffraction technique. Based on the structural and activity information obtained in this study, reaction mechanisms for the hydrolysis of PNPP have been proposed.

Synthesis, characterization and biological properties of mixed ligand complexes of cobalt(II/III) valproate with 2,9‐dimethyl‐1,10‐phenanthroline and 1,10‐phenanthroline

The synthesis of mononuclear cobalt(II/III) complexes with two different ligands (complex 2: [Co(valp)2(2,9‐dmp)] and complex 3: [Co(valp)2(H2O)(1,10‐phen)]) was investigated and the characterization of both complexes was achieved using IR, UV–Vis, and single crystal X‐ray diffraction. Using single crystal X‐ray diffraction, the crystal structure of each of the complexes was determined. Additionally, the biological activity of these complexes was studied in five gram‐positive and four gram‐negative bacterial strains. Whereas in all gram‐negative bacteria tested, cobalt valproate complexes did not show any anti‐bacterial activity, both complexes had effects on gram positive bacteria. Complex 2 demonstrated good anti‐bacterial activity against all gram‐positive bacteria with inhibition zone diameter (IZD) ranging between 15–28 mm. Complex 3 exhibited low inhibition activity against all gram‐positive bacteria except E. faecalis with IZD ranging between 11.3–13.7 mm. Moreover, as an indication of its uses as industrial catalyst, the rate of bis(p‐nitrophenyl) phosphate (BNPP) hydrolysis when catalyzed by these complexes was measured at different temperatures, concentrations and pH. Complex 2 proved to be a better catalyst to induce the hydrolysis of BNPP.

Synthesis and phosphate ester cleavage properties of copper(II) complexes of guanidinium-bridged bis(1,4,7-triazacyclononane) ligands

The synthesis and characterization of three new bis(1,4,7-triazacyclononane) ligands, L1, L2 and L3, featuring a bridging guanidinium group between two macrocyclic units, is reported. The corresponding binuclear copper(II) complexes have been studied as agents to accelerate the cleavage of P–O bonds within two model phosphodiesters, namely bis(p-nitrophenyl)phosphate (BNPP) and 2-hydroxypropyl-p-nitrophenylphosphate (HPNPP). The results of a comparative study of cleavage rates, using the mononuclear copper(II)–tacn complexes bearing single alkylguanidinium groups as a reference, revealed that the binuclear copper(II) complexes are generally less effective cleavage agents, which may be related to a tendency to form hydrolytically inactive hydroxo-bridged species at near-neutral pH and above. However, at pH 7, these complexes produced 4–18-fold increases in the rate of BNPP hydrolysis compared to the parent complex, [Cu(tacn)(OH2)2]2+. Likewise, at pH 6, the complexes cleaved HPNP 5–130-fold faster than [Cu(tacn)(OH2)2]2+, suggesting some degree of cooperative interplay between the two proximal copper(II) centers and the protonated guanidinium bridging group in promoting phosphodiester hydrolysis under these conditions.

Hydrolysis of BNPP Catalyzed by Metallomicelles Made of Pr(III) Complexes

A macrocyclic ligand was synthesized and characterized. The kinetics of hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) in the catalytic system containing macrocyclic ligand and praseodymium(III) was investigated. The analysis of specific absorption spectrums of the hydrolytic reaction systems indicated that key intermediates made up of BNPP and praseodymium(III) complexes are formed in the reaction process of BNPP catalytic hydrolysis. In this, the mechanism of BNPP catalytic hydrolysis proposed is based on the analytic result of specific absorption spectrum, and the corresponding kinetic constants are calculated. The results showed that the praseodymium(III) complexes as hydrolase mimics exhibit good catalytic activity and similar catalytic character to natural enzyme.

Hydrolysis of BNPP Catalyzed by the Dodecyliminodiacetate Nickel (II) Complexes

One novel dodecyliminodiacetate nickel (II) complex were synthesized and characterized, and these complexes were used as mimic hydrolytic in catalytic hydrolysis of bis (p-nitrophenyl) phosphate (BNPP). The analysis of specific absorption spectra of the hydrolytic reaction systems indicated that the catalytic hydrolysis involved the key intermediates formed by BNPP with nickel (II) complexes. The kinetic parameter of BNPP catalytic hydrolysis has been calculated and the activation energy for the catalytic hydrolysis is 95.26kJ·mol-1.

Hydrolysis of phosphodiester catalyzed by metallomicelles with histidine residue: Kinetics and mechanism

A new 2-amino-N-dodecyl-3-(1H-imidazole-4-yl)propanamide (L2) surfactant was synthesized and its metallomicelles made of La(III), Cu(II), Co(II) and Zn(II) complexes were used as hydrolytic metalloenzyme mimics to catalyze the hydrolysis of phosphodiester bis(p-nitrophenyl) phosphate (BNPP) in buffer solution at 35°C. The effects of long alkyl ligand, metal ions, temperature and pH on the catalytic hydrolysis of phosphodiester were investigated. The ternary complex kinetic model for metallomicellar catalysis was suggested to analyze the experimental data. The kinetic and thermodynamic parameters k′N, KM, KT, Km and pKa were obtained. The effect of pH was especially analyzed. The pH-independent rate constant of the reaction catalyzed by metallomicelles LaL2, CuL2, CoL2 and ZnL2 was evaluated as 7.03×10−4, 6.51×10−5, 4.28×10−5 and 1.78×10−5s−1, respectively. The different association manners between metallomicelles and substrate were proposed. A hydroxide ion OH− associated metallomicelle, which was detected by ESI-MS spectral analysis, was suggested as the real active species to catalyze the hydrolysis of phosphodiester. Imidazole group might accelerate the hydrolysis by activating H2O associated the metal into metal-OH−. Effect of microenvironment of micelle on the catalysis hydrolysis of BNPP was also discussed.

Hydrolysis of BNPP Catalyzed by the Dodecyliminodiacetate Nickel(II) and Copper(II) Complexes

Two novel dodecyliminodiacetate nickel (II) and copper (II) complexes were synthesized and characterized, and these complexes were used as mimic hydrolytic in catalytic hydrolysis of bis (p-nitrophenyl) phosphate (BNPP). The analysis of specific absorption spectra of the hydrolytic reaction systems indicated that the catalytic hydrolysis involved the key intermediates formed by BNPP with nickel (II) complexes. The kinetic parameter of BNPP catalytic hydrolysis has been calculated and the temperature effect of reaction system and structure effect of the complexes on the rate of BNPP hydrolysis catalyzed by the complexes have been discussed.

Kinetic Study of the Hydrolysis of BNPP by the Cerium(III) Complex

5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane (L) was synthesized and characterized. The kinetics of hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) in the catalytic system containing macrocyclic ligand and cerium(III) was investigated. This catalytic system show high catalytic activity and better reproducibility and stability than other similar systems in the range of pH of around 5.6–7.2. The stoichiometry and spectral analysis showed that the real active species is the macrocyclic complex of cerium(III). Based on the analytical results of the specific absorption spectra, an intramolecular nucleophilic substitution mechanism for the catalytic hydrolysis of BNPP is proposed, a correlative kinetic mathematical model is established, and the corresponding thermodynamic and kinetic constants are calculated.

Intramolecular Nucleophilic Substitution in the Hydrolysis of Bis(4-Nitrophenyl) Phosphate Ester Catalyzed by the Metallomicelle

A macro-cyclic Schiff base ligand and the corresponding Cu (II) and Ni (II) complexes were synthesized and characterized. And the catalytic efficiency of the metallomicelles made of these complexes and noninonic micelle Brij35, as mimetic hydrolytic metalloenzyme, was investigated in the catalytic hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) in this paper. The results show that the rate of the BNPP hydrolysis in the metallomicelles is about 106 -fold faster than that of the BNPP spontaneous hydrolysis in aqueous solution at the same conditions. The analysis of the characteristic absorption spectra of the hydrolytic reaction systems indicates that the key intermediate, composing of BNPP and Ni(II) or Cu(II) complexes, has been formed and the catalytic hydrolysis of BNPP is an intramolecular nucleophilic substitution reaction. Based on the results of characteristic absorption spectra, the mechanism of BNPP catalytic hydrolysis has been proposed and also the corresponding kinetic mathematical model has been established.

Metal Complexes of a Multidentate Cyclophosphazene with Imidazole‐Containing Side Chains for Hydrolyses of Phosphoesters – Bimolecular vs. Intramolecular Dinuclear Pathway

AbstractA multidentate imidazole‐containing cyclophosphazene (Im6Cpz) ligand was synthesized and its metal complexes (MxIm6Cpz; M = ZnII, CuII, CoII; x = 1, 2, 3) were prepared and used as phosphoesterase models towards hydrolysis of the model substrates p‐nitrophenylphosphate (NPP) and bis(p‐nitrophenyl)phosphate (BNPP) in 75 % DMSO buffer solution at pH = 7–11 at 37 °C. The hydrolysis of BNPP by Cu3Im6Cpz exhibits enzyme‐like saturation kinetics with kcat = 1.4 × 10–5 s–1 and kcat/Km = 0.0027 M–1 s–1. The CuII complex exhibits a tremendous selectivity toward NPP, showingnearly a stoichiometric binding with kcat = 6.8 × 10–4 s–1 under saturation conditions and a significant second‐order rate constant kcat/Kd = 136 M–1 s–1, which is 5.0 × 104 times higher than that for BNPP hydrolysis. An intramolecular dinuclear pathway was revealed for the complexes Cu2Im6Cpz andCu3Im6Cpz; whereas an intermolecular dinuclear pathway was observed for CuIm6Cpz. Cu3Im6Cpz shows an order of magnitude higher activity than the simple CuII complex of the untethered ligand N‐methylimidazole, Cu(MeIm)2, suggesting a possible contribution from the proximity effect in the Im6Cpz complexes. The high catalytic specificity of Cu3Im6Cpz towards the phosphomonoester NPP suggests that it can serve as a good model system and a blueprint for further exploration of catalytic activity and specificity in phosphoester hydrolysis.

Hydrolysis of Bis(p-nitrophenyl)phosphate by Tetravalent Metal Complexes with Kläui’s Oxygen Tripodal Ligand

The treatment of HfCl(4) with NaL(OEt) (L(OEt)(-) = [(eta(5)-C(5)H(5))Co{P(O)(OEt)(2)}(3)](-)) in nitric acid afforded L(OEt)Hf(NO(3))(3) (1). Hydrolysis of 1 in acetone/water (4:1, v/v) yielded the hydroxy-bridged dimer [(L(OEt))(2)Hf(2)(H(2)O)(4)(mu-OH)(2)][NO(3)](4) (2). The treatment of (NH(4))(2)[Ce(NO(3))(6)] with 2 equiv of NaL(OEt) in water afforded (L(OEt))(2)Ce(NO(3))(2) (3), whereas that with 1 equiv of NaL(OEt) in CH(2)Cl(2) gave L(OEt)Ce(NO(3))(3) (4). While 4 is stable in organic solvents such as acetone, it was converted completely to 3 in acetone/water. The treatment of 3 with bis(p-nitrophenyl)phosphate (BNPP) afforded (L(OEt))(2)Ce[eta(1)-OPO(OR)(2)](2) (5; R = p-NO(2)C(6)H(4)), whereas the reaction of 4 with NaPO(2)(OR)(2) yielded dinuclear [L(OEt)Ce(NO(3))(2){mu-O(2)P(OR)(2)}](2) [R = p-NO(2)C(6)H(4) (6), Ph (7)]. The addition of 3 in acetone to an aqueous solution of NaH(2)PO(4) yielded the cerium(IV) dihydrogen phosphate complex (L(OEt))(2)Ce(PO(4)H(2))(2) (8). Complexes 1-5 and 7 have been characterized by X-ray crystallography. The hydrolysis of BNPP with L(OEt)M(NO(3))(3) (M = Zr, Hf, Ce) in acetone/water has been studied by (1)H NMR spectroscopy. At 25 degrees C, with [Ce] = 20[BNPP], in an acetone-d(6)/N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid (4:1, v/v) buffer solution (50 mM) (4:1, v/v), the hydrolysis of BNPP with 4 was found to exhibit first-order kinetics with a rate constant of (1.1 +/- 0.1) x 10(-3) s(-1).

Mechanistic role of each metal ion in Streptomyces dinuclear aminopeptidase: Peptide hydrolysis and 7×1010-fold rate enhancement of phosphodiester hydrolysis

The dinuclear aminopeptidase from Streptomyces griseus (SgAP) and its metal derivatives catalyze the hydrolysis of the phosphoester bis(p-nitrophenyl) phosphate (BNPP) and the phosphonate ester p-nitrophenyl phenylphosphonate with extraordinary rate enhancements at pH 7.0 and 25 degrees C [A. Ercan, H. I. Park, L.-J. Ming, Biochemistry 45, (2006) 13779-13793.], reaching 6.7 billion-fold in terms of the first-order rate constant of the di-Co(II) derivative with respect to the autohydrolytic rates. Since phosphoesters are transition state-like inhibitors in peptide hydrolysis, their hydrolysis by SgAP is quite novel. Herein, we report the investigation of this proficient alternative catalysis of SgAP and the role of each metal ion in the dinuclear site toward peptide and BNPP hydrolysis. Mn(II) selectively binds to one of the dinuclear metal sites (M1), affording MnE-SgAP with an empty (E) second site for the binding of another metal (M2), including Mn(II), Co(II), Ni(II), Zn(II), and Cd(II). Peptide hydrolysis is controlled by M2, wherein the k(cat) values for the derivatives MnM2-SgAP are different yet similar between MnCo- and CoCo-SgAP and pairs of other metal derivatives. On the other hand, BNPP hydrolysis is affected by metals in both sites. Thus, the two hydrolytic catalyses must follow different mechanisms. Based on crystal structures, docking, and the results presented herein, the M1 site is close to the hydrophobic specific site and the M2 site is next to Tyr246 that is H-bonded to a coordinated nucleophilic water molecule in peptide hydrolysis; whereas a coordinated water molecule on M1 becomes available as the nucleophile in phosphodiester hydrolysis.

Phosphodiester hydrolysis and specific DNA binding and cleavage promoted by guanidinium-functionalized zinc complexes

Two new Zn(II) complexes containing guanidinium groups, [Zn(L(1))Cl(2)](ClO(4))(2).H(2)O.CH(3)OH (1) and [Zn(L(2))Cl(2)](ClO(4))(2).0.5H(2)O (2), were synthesized and characterized (L(1)=5,5'-di[1-(guanidyl)methyl]-2,2'-bipyridyl bication and L(2)=6,6'-di[1-(guanidyl)methyl]-2,2'-bipyridyl bication). Both complexes are able to catalyze bis(p-nitrophenyl) phosphate (BNPP) hydrolysis efficiently. Obtained kinetic data reveal that both 1 and 2 show nearly 300- and 600-fold rate enhancement of BNPP hydrolysis, respectively, compared to their simple analogue without the guanidinium groups [Zn(bpy)Cl(2)] (bpy=2,2'-bipyridy) (3). Enhanced acceleration for cleavage of BNPP could be attributed to cooperative interaction between the Zn(II) ion and the guanidinium groups by electrostatic interaction and H-bonding. Studies on inhibition of sequence-specific endonucleases (DraI and SmaI) by complexes show that 1 and 2 are able to recognize nucleotide sequence, -TTT;AAA-, and highly effectively cleave the plasmid DNA in the presence of hydrogen peroxide, while 3 has no specific binding to the DNA target sequences and only shows low DNA cleavage activity.

Iron(III) Complexes of Metal‐Binding Copolymers as Proficient Catalysts for Acid Hydrolysis of Phosphodiesters and Oxidative DNA Cleavage – Insight into the Rational Design of Functional Metallopolymers

AbstractFe3+ complexes of pyridine‐containing copolymers were found to be efficient and selective catalysts toward phosphodiester hydrolysis and show significant activity toward oxidative DNA cleavage. The catalysis toward bis(p‐nitrophenyl)phosphate (BNPP) hydrolysis exhibits enzyme‐like pre‐equilibrium kinetics with maximum activities in the range of ca. pH 6–8 and a first‐order catalytic proficiency (kcat/ko) of 4.2 × 107‐fold at the acidic pH value of 5.3 (i.e., pKa of the coordinated nucleophilic water) and 25 °C, entitling this Fe3+ copolymer an acid phosphodiester catalyst. This catalyst also shows significant selectivity toward BNPP hydrolysis relative to the hydrolyses of p‐nitrophenyl phenylphosphonate and p‐nitrophenylphosphate monoester, with a ratio of 4250:16:1 in terms of their first‐order catalytic proficiencies at pH 8.0 and 25 °C. Fe3+ complexes of a few pyridine‐containing copolymers show different hydrolytic activities, which points a direction for rational design of catalytic metallopolymers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Hydrolytic cleavage of bis(p-nitrophenyl) phosphate by Schiff base MnIII complexes containing morpholine pendants in Gemini 16-6-16 micelles

Catalytic efficiency of two Schiff base manganese(III) complexes toward the hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) was evaluated in a micellar media formed by bis(hexadecyl-dimethylammonium)hexane bromide (abbr. 16-6-16, 2Br−) at 25°C. Effects of various reaction conditions on the hydrolysis of BNPP were systematically investigated. The observations obtained indicate that the two Mn(III) catalysts can efficiently promote hydrolysis of BNPP with a six order of magnitude rate enhancement relative to the background rate constant (k 0). Different structures of the two complexes lend to their distinguishing activities each other. Furthermore, rates of BNPP hydrolysis in Gemini 16-6-16 micellar medium are much higher than that in hexadecyltrimethylammonium bromide (CTAB) and n-lauroylsarcosine sodium (LSS) micelles.

Metal-promoted hydrolysis of bis(p-nitrophenyl)phosphate by trivalent manganese complexes with Schiff base ligands in Gemini micellar solution

Abstract Two crowned Schiff base manganese(III) complexes (MnL2Cl, L = L1, L2) were used to catalyze the hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) in Gemini surfactants [bis(hexadecyldimethylammonium)hexane bromide (abbreviation 16-6-16, 2Br−)] solution. In comparison with the rate of BNPP spontaneous hydrolysis, a six orders of magnitude in rate enhancement was observed in Mn L 2 1 Cl /16-6-16 and Mn L 2 2 Cl /16-6-16 systems. Owing to the different structure, Mn L 2 2 Cl shows better activity than Mn L 2 1 Cl . Especially, the effects of three different micelles, i.e., 16-6-16 micelles, CTAB (hexadecyltrimethylammonium bromide) micelles, LSS (n-lauroooylsarcosine sodium) micelles, on the hydrolysis of BNPP catalyzed by Mn L 2 2 Cl were evaluated at pH7.50. Experimental observations clearly demonstrate that Gemini 16-6-16 micelle is the best one for BNPP hydrolysis among three kinds of micellar media.

Solvent Effects and Alkali Metal Ion Catalysis in Phosphodiester Hydrolysis

The kinetics of the alkaline hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) have been studied in aqueous DMSO, dioxane, and MeCN. In all solvent mixtures the reaction rate steadily decreases to half of its value in pure water in the range of 0-70 vol % of organic cosolvent and sharply increases in mixtures with lower water content. Correlations based on different scales of solvent empirical parameters failed to describe the solvent effect in this system, but it can be satisfactorily treated in terms of a simplified stepwise solvent-exchange model. Alkali metal ions catalyze the BNPP hydrolysis but do not affect the rate of hydrolysis of neutral phosphotriester p-nitrophenyl diphenyl phosphate in DMSO-rich mixtures. The catalytic activity decreases in the order Li+ > Na+ > K+ > Rb+ > Cs+. For all cations except Na+, the reaction rate is first-order in metal ion. With Na+, both first- and second-order kinetics in metal ions are observed. Binding constants of cations to the dianionic transition state of BNPP alkaline hydrolysis are of the same order of magnitude and show a similar trend as their binding constants to p-nitrophenyl phosphate dianion employed as a transition-state model. The appearance of alkali metal ion catalysis in a medium, which solvates metal ions stronger than water, is attributed to the increased affinity of cations to dianions, which undergo a strong destabilization in the presence of an aprotic dipolar cosolvent.

Phosphate diester hydrolysis promoted by new Cu(II) alkoxide complexes

Three Cu(II) complexes of N3 donor pyridyl-amine ligands, bis-(2-pyridin-2-yl-ethyl)-amine (L1), which does not have an alcohol pendant, and 2-[bis-(2-pyridin-2-yl-ethyl)-amino]-ethanol (L2) and 3-[bis-(2-pyridin-2-yl-ethyl)-amino]-propan-1-ol (L3), both containing alcohol pendants, have been synthesized and structurally characterized. The reactivities of CuL1 (1), CuL2 (2), and CuL3 (3) for promoting the hydrolysis of bis(p-nitrophenyl)phosphate (BNPP) have been investigated, showing that 3 is much more active (observed second order rate constant k=6.1×10−1M−1s−1 at pH 8.4, 50°C) than 1 (k=9.4×10−3M−1s−1 at pH 8.4, 50°C) or 3 (observed second order rate constant k=5.2×10−3M−1s−1 at pH 8.4, 50°C) at promoting the hydrolysis of BNPP. The much higher reactivity of 3 compared to 2 and 1 may be explained by the higher flexibility of the alkoxide tether in 3, which may allow the nucleophilic alkoxide O-atom in 3 better access to attack a metal-bound BNPP substrate, whereas 2, which has a shorter alkoxide tether, may resort to hydrolyzing the BNPP substrate with a metal-bound hydroxide instead of utilizing its alkoxide moiety because of constraints in the ligand tether. The similar reactivities of 1 and 2 suggest that this is a possible scenario. Another possible explanation for the difference in reactivity between 3 and 2 may be attributed to the alcohol pendant in 3 being better oriented to serve as a proton acceptor from a Cu(II)-bound aqua ligand, which would facilitate its deprotonation and the subsequent nucleophilic attack of the Cu(II)-hydroxide moiety towards the substrate. The reactivities of 2 and 3 towards hydrolyzing BNPP are also compared with that of their Zn(II) analogues, showing that the Cu(II) complexes of the same ligand sets are more hydrolytically active than the corresponding Zn(II) complexes. Single crystal X-ray structures of 1, 2, and 3 are also reported, which show that complexes 2 and 3 form dimers with bridging alkoxide ligands in the solid state, while 1 forms a dimer with bridging chloride ligands in the solid state.

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 °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.