20350-26-9

A series of dinuclear metal(ii)-acetato complexes: [Ni2(μ-LClO)(μ2-OAc)2](PF6)·3H2O (1), [Ni2(μ-LClO)(μ2-OAc)2](ClO4)·CH3COCH3 (2), [Cu2(μ-LClO)(μ2-OAc)(ClO4)](ClO4) (3), [Cu2(μ-LClO)(OAc)2](PF6)·H2O (4), [Zn2(μ-LClO)(μ2-OAc)2](PF6) (5) and [Mn2(LCl-O)(μ2-OAc)2](ClO4)·H2O (6), where LClO- = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-chlorophenolate, were synthesized. The complexes were structurally characterized by spectroscopic techniques and single crystal X-ray crystallography. Six-coordinate geometries with doubly bridged acetato ligands were found in Ni(ii), Zn(ii) and Mn(ii) complexes 1, 2, 5 and 6, whereas with Cu(ii) complexes a five-coordinate species was obtained with 4, and mixed five- and six-coordinate geometries with a doubly bridged dimetal core were observed in 3. The magnetic properties of complexes 1-4 and 6 were studied at variable temperatures and revealed weak to very weak antiferromagnetic interactions in 1, 2, 4 and 6 (J = -0.55 to -9.4 cm-1) and ferromagnetic coupling in 3 (J = 15.4 cm-1). These results are consistent with DFT calculations performed at the B3LYP/def2-TZVP(-f) level of theory. Under physiological conditions, the interaction of the dinculear complexes 1-5 with supercoiled plasmid ds-DNA did not show any pronounced nuclease activity, but Ni(ii) complexes 1 and 2 revealed a strong ability to unwind the supercoiled conformation of ds-DNA. The mechanistic studies performed on the interaction of the Ni(ii) complexes with DNA demonstrated the important impact of the nickel(ii) ion in the unwinding process. In combination with the DNA study, the phosphatase activity of complexes 1, 3, and 5 was examined by the phosphodiester hydrolysis of bis(2,4-dinitrophenol)phosphate (BDNPP) in the pH range of 5.5-10.5 at 25 °C. The Michaelis-Menten kinetics performed at pH 7 and 10.7 showed that catalytic efficiencies kcat/KM (kcat = catalytic rate constant, KM = substrate binding constant) decrease in the order: Ni(ii), 1 > Zn(ii), 5 > Cu(ii), 3. A similar trend was also observed with the turnover numbers at pH = 7. The results are discussed in relation to the coordination geometry and nature of the metal center as well as the steric environment imposed by the compartmental phenoxido ligand.

The development of artificial nucleases has been stimulated by the realization that hydrolytically active metal complexes may potentially find utility as robust versatile replacements for restriction enzymes in molecular biology research and as nucleic ac

The [2]pseudorotaxanes of cucurbit[6]uril with guest molecule 1,6-bis(imidazol-1-yl)hexane (BIMH) were synthesized and characterized by ESI-MS spectrometry, 1H NMR spectra, and X-ray diffraction crystallography. The influence of different anion

Preparation of chemically tunable magnetic nanoparticles (MNPs) is of great interest in many technological fields. Although numerous methods have been developed to prepare MNPs coated with functional organic moieties, most of them are complex, multistep, and involve the preparation of a specific ligand to be inserted on the particle surface. Herein, we describe the preparation of MNPs covered with reactive polymer poly(4-nitrophenyl methacrylate). The composite was prepared by the dispersion polymerization of 4-nitrophenyl methacrylate in the presence of magnetite nanoparticles stabilized by oleic acid. The novel material can be easily modified with amines to give chemically stable amide bonds without installation of pH-dependent features in the link. The extent of particle modification is readily monitored by the release of 4-nitrophenol from the polymer using UV-vis spectrophotometry. Good agreement between the degree of functionalization assessed by colorimetry and elemental analysis was obtained, and functionalization up to 3 mmol g-1 is easily attained. To illustrate the applicability of the method for catalyst development, we prepared imidazole-covered MNPs that accelerate the hydrolysis of a model organophosphate, with rate constants approximately 105-fold higher than the spontaneous hydrolysis. The catalyst can be recovered by a magnet and recycled without appreciable loss of catalytic activity.

Derivatives of the known dinucleating ligands HL1 (2,6-bis{[bis(pyridin-2-ylmethyl)amino]methyl}-4-methylphenol) and H2L2 (2-{[bis(pyridin-2-ylmethyl)amino]methyl}-6-{[(2-hydroxybenzyl)(pyridine-2-ylmethyl)amino]methyl}-4-methylphenol) with two pivaloylamido hydrogen bond donor substituents, H3L3 and H3L5, have been prepared. The mono-, homo- and heterodinuclear ZnII and GaIII complexes of these ligands have been prepared and characterized. The solution equilibria are discussed on the basis of extensive NMR spectroscopic, mass spectrometric and pH-dependent UV–vis spectroscopic titrations. The phosphoester hydrolysis activity of the complexes has been studied as a function of pH and substrate concentration and analyzed using Michaelis–Menten kinetics. It emerges that the mixed metal (mixed valent) complex of the ligand with an asymmetric disposition of the hydrogen bonding substituents (H3L3) is a functional model for the mixed valent, dinuclear metallohydrolase purple acid phosphatase. This complex combines the essential structural features of the active site of PAP and is the first heterodinuclear model complex mimicking the essential function of PAPs, i.e. the hydrolysis of phosphomonoesters.

Herein, we describe the synthesis and X-ray structure of a new heteropentanuclear complex (2) containing a [Fe2 IIIZn3 II(μ-OH)3] structural unit and the unsymmetrical ligand H2L2/sup

Herein we describe the synthesis of a new heterodinuclear Fe IIICuII model complex for the active site of purple acid phosphatases and its binding to a polyamine chain, a model for the amino acid residues around the active site. The properties of these systems and their catalytic activity in the hydrolysis of bis(2,4-dinitrophenyl)phosphate are compared, and conclusions regarding the effects of the second coordination sphere are drawn. The positive effect of the polymeric chain on DNA hydrolysis is also described and discussed.

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Formation of dinitrophenoxide ion from 2,4- and 2,6-dinitrochlorobenzene (2,4- and 2,6-DNCB) and OH- (OD-) in 70:30 and 80:20 (v/v) DMSO-H2O (D2O) is accompanied by extensive 1H NMR line broadening of unreacted substrate and exchange of arene hydrogen with D2O, which is quantitative at the 3-position of 2,4-DNCB. Unproductive Meisenheimer complexes are detected spectrophotometrically in the course of reaction. For reaction of 2,4-DNCB, the Meisenheimer 3-complex is formed first and then the more stable 5-complex can be detected and characterized by NMR spectrometry. There is no hydrogen exchange of Meisenheimer complexes or dinitrophenoxide ions and their 1H NMR signals are not broadened. These results do not fit the classical mechanism of single-step nucleophilic addition, but they, and the kinetic results, are fitted by a reaction scheme involving single-electron transfer from OH- to give a charge-transfer complex of OH? and a radical anion which collapses to give Meisenheimer complexes and aryl oxide ion. This scheme is consistent with MO calculations by the AM1 method.

The rate coefficients for the alkaline hydrolysis of 2,4-dinitroanisole and 2-methoxy-5-nitropyridine have been measured in a series of aqueous dipolar aprotic solvents.These rates have been correlated with the acidity function H- for aqueous dimethyl sulphoxide, dimethylformamide, sulpholane, and pyridine, which were available, as well as for aqueous acetonitrile, tetramethylurea, and hexamethylphosphoramide, whose acidity function has been constructed.For aqueous dioxane, a satisfactory acidity function could not be constructed.The order of the solvents in increasing the basicity is: hexamethylphosphoramide >> dimethylsulphoxide > tetramethylurea > dimethylformamide >pyridine > sulpholane >> acetonitrile > dioxane.The latter order appears to be related directly to the hydrogen-bonding capacity of the solvent.Except for pyridine, the slopes of the rate-acidity function correlation have been found to be solely a function of the substrate and independent of the dipolar aprotic solvent used.Pyridine catalyses the substitution reactions by direct nucleophilic catalysis.

From the kinetics of the title reaction in 44 wtpercent aqueous ethanol at 25 deg C, ionic strength 0,2 M (KCl), a curved Broensted-type plot is obtained.The curve is interpreted in terms of a zwitterionic tetrahedral intermediate in the reaction path and a change in the rate-determining step from breakdown to products of this intermediate to its formation as the pyridine becomes more basic.A semiempirical equation based on this hypothesis accounts for the experimental results.The center of the Broensted-type curvature (pKa0) is located at pKa = 9.5, lower than the value found in the pyridinolysis of 2,4-dinitrophenyl p-nitrobenzoate in the same solvent, showing that electron withdrawal from the acyl group of the substrate favors amine expulsion relative to phenoxide from the tetrahedral intermediate.It is claimed that the influence of the acyl group of the substrate on the value of pKa0 cannot be quantified when comparing similar reactions in water and aqueous ethanol since the pKa0 value for a given reaction should be larger in the latter solvent.The activation parameters obtained support the hypothesis that for the title reactions, pKa0 > 9.

Plant based materials are considered to have broad applications in the remediation of toxic materials. In this report, we present an environmental friendly and economic Cicer arietinum, named as (CP) supported for the synthesis of Ni nanoparticles (NPs) designated as Ni@CP. The in situ Ni@CP NPs were obtained using aqueous medium in the presence of sodium borohydride (NaBH4) as a reducing agent. The prepared catalysts were applied for the hydrogenation/degradation of p-nitrophenol (PNP), o-nitrophenol (ONP), and 2,4-dinitrophenol (DNP), as well as congo red (CR), methyl orange (MO), methylene blue (MB) and rhodamine B (RB) dyes. The amount of total metal ions adsorbed onto the CP was evaluated by flame atomic absorption spectroscopy. The Ni@CP catalyst was characterized through PXRD, FTIR, FESEM and EDX analyses.

A kinetic study on nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted-cinnamates (1a-1f) and Y-substituted-phenyl cinnamates (2a-2g) with a series of alicyclic secondary amines in MeCN at 25.0 ± 0.1 °C is reported. The Br?nsted-type pl

Heterodinuclear mixed valence [Zn(II)?Fe(III)] and the homodinuclear [Zn(II)?Zn(II)] and [Ni(II)?Ni(II)] complexes of a bicompartmental ligand containing a bridging phenoxy as a O?donor and four pyridyl moieties and two amine moieties as the N?donors exhi

Herein, we report the synthesis and characterization of two dinuclear FeIIIZnII complexes [FeIIIZnIILP1] (1) and [FeIIIZnIILP2] (2), in which LP1 and LP2 are conjugated systems containing one and two pyrene groups, respectively, connected via the diamine -HN(CH2)4NH- spacer to the well-known N5O2-donor H2L ligand (H2L = 2-bis{[(2-pyridylmethyl)aminomethyl]-6-[(2-hydroxybenzyl)(2-pyridylmethyl)]aminomethyl}-4-methylphenol). The complex [FeIIIZnIIL1] (3), in which H2L was modified to H2L1, with a carbonyl group attached to the terminal phenol group, was included in this study for comparison purposes.1 Both complexes 1 and 2 were satisfactorily characterized in the solid state and in solution. Extended X-ray absorption fine structure data for 1 and 3 in an acetonitrile solution show that the multiply bridged structure seen in the solid state of 3 is retained in solution. Potentiometric and UV-vis titration of 1 and 2 show that electrostatic interaction between the protonated amino groups and coordinated water molecules significantly decreases the pKa of the iron(III)-bound water compared to those of 3. On the other hand, catalytic activity studies using 1 and 2 in the hydrolysis of the activated substrate bis(2,4-dinitrophenyl)phosphate (BDNPP) resulted in a significant increase in the association of the substrate (Kass ? 1/KM) compared to that of 3 because of electrostatic and hydrophobic interactions between BDNPP and the side-chain diaminopyrene of the ligands H2LP1 and H2LP2. In addition, the introduction of the pyrene motifs in 1 and 2 enhanced their activity toward DNA and as effective antitumor drugs, although the biochemical mechanism of the latter effect is currently under investigation. These complexes represent interesting examples of how to promote an increase in the activity of traditional artificial metal nucleases by introducing second-coordination-sphere effects.

Second-order rate constants (kN) for nucleophilic substitution reactions of O-phenyl O-Y-substituted-phenyl thionocarbonates (4a–4k) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in MeCN at 25.0 ± 0.1°C are reported. The reactivity of 4a–4k decreases as basicity of the leaving group increases except O-2,4-dinitrophenyl O-phenyl thionocarbonate (4a), which is less reactive than O-3,4-dinitrophenyl O-phenyl thionocarbonate (4b) although the former possesses 2 pKa units less basic nucleofuge than the latter. The Br?nsted-type plot for the reactions of 4b–4k is linear with βlg = ?0.50, a typical βlg value for reactions reported to proceed through a concerted mechanism. The Hammett plot correlated with σY? constants for the reactions of 4b–4k results in a better linear correlation than that correlated with σYo constants. Besides, the Yukawa-Tsuno plot exhibits an excellent linear correlation with ρY = 2.12, r = 0.68 and R2 = 0.990, indicating that a negative charge develops partially on the O atom of the leaving group in the rate-determining step (RDS). Thus, the reactions have been concluded to proceed through a forced concerted mechanism. Effects of steric hindrance on reactivity and reaction mechanism are also discussed in detail.

Ketene-forming elimination from C4H3(O)CH2C(O)OC6H3-2-X-4-NO2 (1) promoted by R2NH in MeCN has been studied. The reactions produced elimination products and exhibited second-orde

The patellamides (cyclic pseudo-octapeptides) are produced by Prochloron, a symbiont of the ascidians, marine invertebrate filter feeders. These pseudo-octapeptides are present in the cytoplasm and a possible natural function of putative metal complexes of these compounds is hydrolase activity, however the true biological role is still unknown. The dinuclear CuII complexes of synthetic patellamide derivatives have been shown in in vitro experiments to be efficient hydrolase model catalysts. Many hydrolase enzymes, specifically phosphatases and carboanhydrases, are ZnII-based enzymes and therefore, we have studied the ZnII and mixed ZnII/CuII solution chemistry of a series of synthetic patellamide derivatives, including solution structural and computational work, with the special focus on model phosphatase chemistry with bis-(2,4-dinitrophenyl)phosphate (BDNPP) as the substrate. The ZnII complexes of a series of ligands are shown to form complexes of similar structure and stability compared to the well-studied CuII analogues and the phosphatase reactivities are also similar. Since the complex stabilities and phosphatase activities are generally a little lower compared to those of CuII and since the concentration of ZnII in Prochloron cells is slightly smaller, we conclude that the CuII complexes of the patellamides are more likely to be of biological importance.

A kinetic study on dinitrophenylphosphate monoester hydrolysis in the presence of a cationic pillararene, P5A, has been carried out. Formation of the supramolecular complex between phosphate ester and P5A has been studied by NMR showing complexation-induced upfield proton shifts indicative of aromatic ring inclusion in the pillararene cavity. Molecular dynamic calculations allow structure characterization for the 1 : 1 and 1 : 2 complexes. As a result of the supramolecular interaction both the acidity of DNPP and its hydrolysis rate constants are increased. Catalysis results from combination of both electrostatic stabilization reducing the negative electron density on the PO3= oxygens and monoester dianion destabilization by the steric effects of close NMe3+ groups hindering the hydrogen-bonding with water and destabilising the monoester dianion.

Imidazole (IMZ) rings catalyze many biological dephosphorylation processes. The methyl positioning effect on IMZs reactivity has long intrigued scientists and its full understanding comprises a promising tool for designing highly efficient IMZ-based catalysts. We evaluated all monosubstituted methylimidazoles (xMEI) in the reaction with diethyl 2,4-dinitrophenyl phosphate by kinetics studies, NMR analysis and DFT calculations. All xMEI showed remarkable rate enhancements, up to 1.9×105fold, compared with spontaneous hydrolysis. Unexpectedly, the electron-donating methyl group acts to decrease the reactivity of the xMEI compared to IMZ, except for 4(5)methylimidazole, (4(5)MEI). This behavior was attributed to both electronic and steric effects. Moreover, reaction intermediates were monitored by NMR and surprisingly, the reactivity of the two different 4(5)MEI tautomers was distinguished.

Second-order rate constants (kOH-) for alkaline hydrolysis of 2,4-dinitrophenyl X-substituted benzenesulfonates (1a-1f) and Y-substituted phenyl 4-nitrobezenesulfonates (2a-2g) have been measured spectrophotometrically. Comparison of kOH/

It is becoming increasingly apparent that the secondary coordination sphere can have a crucial role in determining the functional properties of biomimetic metal complexes. We have therefore designed and prepared a variety of ligands as metallo-hydrolase mimics, where hydrogen bonding in the second coordination sphere is able to influence the structure of the primary coordination sphere and the substrate binding. The assessment of a structure-function relationship is based on derivates of 2,6-bis{[bis(pyridin-2-ylmethyl)amino]methyl}-4- methylphenol (HBPMP = HL1) and 2-{[bis(pyridin-2-ylmethyl)amino] methyl}-6-{[(2-hydroxybenzyl)(pyridin-2-ylmethyl)amino]methyl}-4-methylphenol (H2BPBPMP = H2L5), well-known phenolate-based ligands for metallo-hydrolase mimics. The model systems provide similar primary coordination spheres but site-specific modifications in the secondary coordination sphere. Pivaloylamide and amine moieties were chosen to mimic the secondary coordination sphere of the phosphatase models, and the four new ligands H3L2, H3L3, HL4, and H4L6 vary in the type and geometric position of the H-bond donors and acceptors, responsible for the positioning of the substrate and release of the product molecules. Five dinuclear ZnII complexes were prepared and structurally characterized in the solid, and four also in solution. The investigation of the phosphatase activity of four model complexes illustrates the impact of the H-bonding network: the Michaelis-Menten constants (catalyst-substrate binding) for all complexes that support hydrogen bonding are smaller than for the reference complex, and this generally leads to higher catalytic efficiency and higher turnover numbers.

The nucleophilic reactivities of hydroxamate (HA-) ions of the structure RCONHO- [R = CH3 (acetohydroxamate, AHA -), C6H5 (benzohydroxamate, BHA-), 2-OHC6H4

A series of dinuclear cobalt(II) complexes has been prepared and characterized to generate functional and spectroscopic models for cobalt(II) substituted phosphoesterase enzymes such as the potential bioremediator GpdQ. Reaction of ligands based on 2,2'-(((2-hydroxy-5-methyl-1,3-phenylene) bis(methylene))bis((pyridin-2-ylmethyl)azanediyl)))diethanol (L1) and 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)-4-methylphenol (L2) with cobalt(II) salts afforded [Co2(CO2EtH 2L1)(CH3COO)2](PF6), [Co 2(CO2EtL2)(CH3COO)2](PF 6), [Co2(CH3L2)(CH3COO) 2](PF6), [Co2(BrL2)(CH3COO) 2](PF6), and [Co2(NO2L2)(CH 3COO)2](PF6). Complexes of the L2 ligands contain a coordinated methyl-ether, whereas the L1 ligand contains a coordinated alcohol. The complexes were characterized using mass spectrometry, microanalysis, X-ray crystallography, UV-vis-NIR diffuse reflectance spectroscopy, IR absorption spectroscopy, solid state magnetic susceptibility measurements, and variable-temperature variable-field magnetic circular dichroism (VTVH MCD) spectroscopy. Susceptibility studies show that [Co 2(CO2EtH2L1)(CH3COO) 2](PF6), [Co2(CO2EtL2)(CH 3COO)2](PF6), and [Co2(CH 3L2)(CH3COO)2](PF6) are weakly antiferromagnetically coupled, whereas [Co2(BrL2)(CH 3COO)2](PF6) and [Co2(NO 2L2)(CH3COO)2](PF6) are weakly ferromagnetically coupled. The susceptibility results are confirmed by the VTVH MCD studies. Density functional theory calculations revealed that magnetic exchange coupling occurs mainly through the phenolic oxygen bridge. Implications of geometry and ligand design on the magnetic exchange coupling will be discussed. Functional studies of the complexes with the substrate bis(2,4-dinitrophenyl) phosphate showed them to be active towards hydrolysis of phosphoester substrates.

Second-order rate constants have been measured spectrophotometrically for the reactions of phenyl Ysubstituted- phenyl carbonates 7a-g with butane-2,3-dione monoximate (Ox-) in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The α-nucleophile Ox- is 53-95 times more reactive than the corresponding normalnucleophile 4-ClPhO- toward 7a-g, indicating that the α-effect is operative. The magnitude of the α-effect (e.g., the kOx/k4-ClPhO ratio) is independent of the electronic nature of the substituent Y. The cause of the α- effect for the reactions of 7a-g has been suggested to be ground-state (GS) effect rather than transition-state (TS) stabilization through a six-membered cyclic TS, in which Ox- behaves a general acid/base catalyst. This idea is further supported by the result that OH- exhibits negative deviation from the linear Bronsted-type plot composed of a series of aryloxides, while Ox- deviates positively from the linearity. Differential solvation of the GS of Ox- and 4-ClPhO- has been suggested to be responsible for the α-effect exerted by Ox-.

Two new dinucleating ligands (H3L2 and HL 3), derivatives of a well-known dinucleating ligand (HL1) with two bis-picolylamine sites connected to a bridging phenolate, with hydrogen-bonding donor groups at two of the pyridine moieties were designed and synthesized. Design of these ligands suggests that they will lead to dinuclear complexes with potential to stabilize phosphoester substrates as monodentate rather than bridging ligands. We report the diferric complexes [Fe III2(H2L2)(OH)]4+ and [FeIII2(L3)(OH)(OH2) 2]4+, which have been characterized by spectrophotometric titrations, UV-vis, IR, NMR, EPR, and Moessbauer spectroscopy. The phosphatase activity of the diferric systems, in addition to the partially reduced heterovalent [FeIIIFeII(L3)(OH)(OH 2)2]3+ complex, has been investigated, and the complexes are shown to catalytically hydrolyze the activated phosphodiester substrate BDNPP (bis-dinitrophenylphosphate) as well as the corresponding phosphomonoester substrate DNPP (dinitrophenylphosphate). The results indicate that indeed the secondary interactions lead to an increase of the phosphatase activity and to active phosphomonoesterase catalysts. Interestingly, the heterovalent form of the HL3-based complex is more efficient than the diferric complex, and this is also discussed.

Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and magnetochemistry, of two dinuclear copper(II) complexes, using the

The reactions of a series of anilines with phenyl 2,4-dinitrophenyl (1), 4-nitrophenyl 2,4-dinitrophenyl (2), and bis(2,4-dinitrophenyl) (3) carbonates are subjected to a kinetic investigation in 44 wt% ethanol-water, at 25.0 ± 0.1°C and an ionic strength of 0.2 M. Under amine excess pseudo-first-order rate coefficients (kobs) are obtained. Plots of kobs against free amine concentration at constant pH are linear, with slopes kN. The BrAnsted plots (log kN vs. anilinium pKa) for the anilinolysis of 1-3 are linear, with slope (β) values of 0.52, 0.61, and 0.63, respectively. The values of these slopes and other considerations suggest that these reactions are ruled by a concerted mechanism. For these reactions, the kN values follow the reactivity sequence: 3 > 2 > 1. Namely, the reactivity increases as the number of nitro groups attached to the nonleaving group increases. Comparison of the reactions of this work with the stepwise pyridinolysis of carbonates 1-3 indicates that the zwitterionic tetrahedral intermediate (T±) formed in the pyridinolysis reactions is destabilized by the change of its pyridino moiety by an isobasic anilino group. This is attributed to the superior leaving ability from the T± intermediate of anilines, relative to isobasic pyridines, which destabilize kinetically this intermediate. The kN values for the anilinolysis of carbonates 1-3 are similar to those found in the reactions of these carbonates with secondary alicyclic amines. With the kinetic data for the anilinolysis of the title substrates and 4-methylphenyl and 4-chlorophenyl 2,4-dinitrophenyl carbonates, a multiparametric equation is derived for log kN as a function of the pKa of the conjugate acids of anilines and nonleaving groups.

PhnP is a phosphodiesterase that plays an important role within the bacterial carbon-phosphorus lyase (CP-lyase) pathway by recycling a "dead-end" intermediate, 5-phospho-α-d-ribosyl 1,2-cyclic phosphate, that is formed during organophosphonate catabolism

The new trinuclear gadolinium complex [Gd3L2(NOa) 2(H2O)4]NO3-SH2O (1) with the unsymmetrical ligand 2-[A/-bis-(2-pyridylmethyl)aminomethyl]-4-methyl-6-[A/ -bis(2-hydroxy-2-oxoethyl)aminomethyl] phenol (H3L) was synthesized and characterized. The new ligand H3L was obtained in good yield. Complex 1 crystallizes in an orthorhombic cell, space group Pcab. Kinetic studies show that complex 1 is highly active in the hydrolysis of the substrate 2,4-bis(dinitrophenyl)phosphate (Km = 4.09 mM, Vmax = 2.68 x 10 -2 mM s-1 and kcat = Vmax/[1] = 0.67 s-1). Through a Potentiometrie study and determination of the kinetic behavior of 1 in acetonitrile/water solution, the species present in solution could be identified, and a trinuclear monohydroxo species appears to be the most prominent catalyst under mild conditions. Complex 1 displays high efficiency in DNA hydrolytic cleavage, and complete kinetic studies were carried out (Km = 4.57 x 10-4M, k'Cat=3.42h -1, and k'Cat/Km= 7.48 x 103M -1 h-1). Studies with a radical scavenger (dimethyl sulfoxide, DMSO) showed that it did not inhibit the activity, indicating the hydrolytic action of 1 in the cleavage of DNA, and studies on the incubation of distamycin with plasmid DNA suggest that 1 is regio-specific, interacting with the minor groove of DNA.

Toward resolving the current controversy regarding the validity of the α-effect, we have examined the reactions of Y-substituted phenyl methanesulfonates 1a-1l with HOO-, OH-, and Z-substituted phenoxides in the gas phase versus solu

Caged versions of the most common mitochondrial uncouplers (proton translocators) have been prepared that sense the reactive oxygen species (ROS) hydrogen peroxide to release the uncouplers 2,4-dinitrophenol (DNP) and carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP) from caged states with second order rate constants of 10 (±0.8) M-1 s-1 and 64.8 (±0.6) M-1 s-1, respectively. The trigger mechanism involves conversion of an arylboronate into a phenol followed by fragmentation. Hydrogen peroxide-activated uncouplers may be useful for studying the biological process of ageing.

The reaction of hydroxylamine with 2,4-dinitrophenyl diethyl phosphate gives the O-phosphorylated product, which is rapidly converted to hydrazine and nitrogen gas in the presence of the excess of hydroxylamine. The Royal Society of Chemistry.

Elimination reactions of C6H5C(R)HCO 2C6H3-2-X-4-NO2 [R = H (1), Ph (2), X = H (a), Cl (b), NO2 (c)] promoted by R2NH in MeCN have been studied kinetically. The reactions are second-order and exhibit Broensted β = 0.46-0.89 and |β1g| = 0.37-0.76 and an E2 mechanism is evident. When the base-solvent was changed from R 2NH/R2NH2+-70 mol% MeCN(aq) to R2NH-MeCN, β and |β1g| values remained nearly the same within experimental error. For eliminations from 1 and 2, β and |β1g| values were nearly identical, although the rate was retarded by the β-Ph group. Noteworthy is the relative insensitivity of the ketene-forming transition state to the base-solvent and β-R group variation. Copyright

A series of methyl aryl phosphorothiolate esters (SP) were synthesized and their reactions with pyridine derivatives were compared to those for methyl aryl phosphate esters (OP). Results show that SP esters react with pyridine nucleophiles via a concerted SN2(P) mechanism. Bronsted analysis suggests that reactions of both SP and OP esters proceed via transition states with dissociative character. The overall similarity of the transition state structures supports the use of phosphorothiolates as substrate analogues to probe mechanisms of enzyme-catalyzed phosphoryl transfer reactions. This journal is The Royal Society of Chemistry.

(Chemical Equation Presented) Ketene-forming eliminations from ArCH 2CO2C6H3-2-X-4-NO2 (Ar = thienyl, 1) promoted by R2NH/ R2NH2+ in 70 mol % MeCN(aq) have

(Chemical Equation Presented) A kinetic study is reported for aminolysis of aryl diphenylphosphinothioates (2a-i). The phosphinothioates 2a-i are less reactive than aryl diphenylphosphinates (1a-i), the oxygen analogues of 2a-i, regardless of the basicity

The phenolysis and benzenethiolysis of S-methyl 4-nitrophenyl thiocarbonate (1) and S-methyl 2,4-dinitrophenyl thiocarbonate (2) in water are studied kinetically. The Brnsted plots (log kN versus nucleophile basicity) are linear for all reactions. The Bronsted slopes for 1 and 2 are, 0.51 and 0.66 (phenolysis) and 0.55 and 0.70 (benzenethiolysis), respectively. These values suggest a concerted mechanism for these reactions, as found in the corresponding carbonates. Namely, substitution of OMe by SMe in the nonleaving group does not change the mechanism. Copyright 2007 John Wiley & Sons, Ltd.

Second-order rate constants have been measured for the reactions of 2,4-dinitrophenyl X-substituted benzoates (1a-f) with a series of primary amines in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The Bronsted-type plot for the reactions of 1d with primary amines is biphasic with slopes β1 = 0.36 at the high pKa region and β2 = 0.78 at the low pKa region and the curvature center at pKa° = 9.2, indicating that the reaction proceeds through an addition intermediate with a change in the rate-determining step as the basicity of amines increases. The corresponding Bro nsted-type plot for the reactions with secondary amines is also biphasic with β1 = 0.34, β2 = 0.74, and pKa° = 9.1, indicating that the effect of amine nature on the reaction mechanism and pKa° is insignificant. However, primary amines have been found to be less reactive than isobasic secondary amines. The microscopic rate constants associated with the aminolysis have revealed that the smaller k 1 for the reactions with primary amines is fully responsible for their lower reactivity. The electron-donating substituent in the nonleaving group exhibits a negative deviation from the Hammett plots for the reactions of 1a-f with primary and secondary amines, while the corresponding Yukawa-Tsuno plots are linear. The negative deviation has been ascribed to stabilization of the ground state of the substrate through resonance interaction between the electron-donating substituent and the carbonyl functionality.

Nonionic hydrazine reacts with anionic bis(2,4-dinitrophenyl) phosphate (BDNPP), giving 2,4-dinitrophenyl hydrazine and dianionic 2,4-dinitrophenyl phosphate by an SN2(Ar) reaction, and at the phosphoryl center, giving 2,4-dinitrophenoxide ion and a transient phosphorylated hydrazine that rearranges intramolecularly to N-(2,4-dinitrophenyl)-N-phosphonohydrazine. Approximately 58% of the reaction at pD = 10 occurs by N-phosphorylation, as shown by 31P NMR spectroscopy. Reaction of HO2- is wholly at phosphorus, and the intermediate peroxophosphate reacts intramolecularly, displacing a second 2,4-dinitrophenoxide ion, or with H 2O2, giving 2,4-dinitrophenyl phosphate and O2. Rate constants of O- and N-phosphorylation in reactions at phosphorus of NH2-NH2, HO2-, and NH2OH and its methyl derivatives follow Broensted relationships with similar slopes, but plots differ for oxygen and nitrogen nucleophiles. The reaction with NH2NH2 has been probed by using both NMR spectroscopy and electrospray ionization mass and tandem mass spectrometry, with the novel interception of key reaction intermediates in the course of reaction.

The reactions of 4-nitrophenyl and 2,4-dinitrophenyl S-methyl thiocarbonates (1 and 2, respectively) with a series of 3- and/or 4-substituted pyridines in aqueous solution, at 25.0°C and an ionic strength of 0.2 M (KCl), are subjected to a kinetic investigation. The reactions are studied by following spectrophotometrically the release of 4-nitrophenoxide (400 nm) or 2,4-dinitrophenoxide (360 nm) anions. Under amine excess, pseudo-first-order rate coefficients (kobsd) are found. Plots of kobsd vs [pyridine] are linear and pH-independent, with slope kN. The Bronsted-type plot (log KN vs pKa of pyridinium ions) for the reactions of 1 is linear, with slope β = 1.1, in contrast to the plot for the reactions of 2, which is biphasic, with slopes β1 = 0.25 (high pKa) and aβ2 = 0.90 (low pKa) and the curvature center at pKa = pK a0 = 7.3. The latter Bronsted plot is consistent with a stepwise mechanism, through a zwitterionic tetrahedral intermediate (T±) on the reaction path, and a change of the rate-determining step, from breakdown to formation of T±, as pyridine basicity increases. For the reactions of 1 the β value indicates that the mechanism is also stepwise with expulsion of the nucleofuge from T ± as the rate-determining step. By comparison of the reactions under investigation among each other and with similar aminolyses, the following conclusions can be drawn. (i) Thiocarbonate 2 is more reactive than 1 toward pyridines. (ii) The pKa0 value for the pyridinolysis of 2,4-dinitrophenyl methyl carbonate (4) is larger than that for thiocarbonate 2. (iii) The k1 values (pyridine attack to form T±) are smaller for thiocarbonates 1 and 2 than the corresponding oxy carbonates 3 and 4, respectively. This is not in accordance with the electronic effects of MeS and MeO and could be attributed to steric hindrance of the MeS group toward pyridine attack. (iv) The kN values for the pyridinolysis of carbonates 3 and 4 are larger than those for thiocarbonates 1 and 2, respectively, when the k2 step is rate-limiting.

Second-order rate constants have been measured spectrophotometrically for the reactions of O-2,4-dinitrophenyl thionobenzoate (1) and 2,4-dinitrophenyl benzoate (2) with a series of substituted pyridines in 80 mol % H 2O/20 mol % DMSO at 25.0 ± 0.1 °C. The Bronsted-type plots obtained are nonlinear with β1 = 0.26, β2 = 1.07, and pKa° = 7.5 for the reactions of 1 and β2 = 0.40, β2 = 0.90, and pKa° = 9.5 for the reactions of 2, suggesting that the pyridinolyses of 1 and 2 proceed through a zwiterionic tetrahedral intermediate T± with a change in the rate-determining step at pKa° = 7.5 and 9.5, respectively. The thiono ester 1 is more reactive than its oxygen analogue 2 except for the reaction with the strongest basic pyridine studied (pK a = 11.30). The k1 value is larger for the reactions of 1 than for those of 2 in the low pKa region, but the difference in the k1 value becomes negligible with increasing the basicity of pyridines. On the other hand, 1 exhibits slightly larger k2/k -1 ratio than 2 in the low pKa region but the difference in the K2/k-1 ratio becomes more significant with increasing the basicity of pyridines. Pyridines are more reactive than alicyclic secondary amines of similar basicity toward 2 in the pKa above ca. 7.2 but less reactive in the pKa below ca. 7.2. The k1 value is slightly larger, but the k2/k-1 ratio is much smaller for the reactions of 2 with pyridines than with isobasic secondary amines in the low pKa region, which is responsible for the fact that the weakly basic pyridines are less reactive than isobasic secondary amines.

Mono- and dimethylation of hydroxylamine on nitrogen does not significantly affect rates of initial attack of NHMeOH and NMe2OH on bis(2,4-dinitrophenyl)phosphate (BDNPP), which is largely by oxygen phosphorylation. O-Methylation, however, blocks this reaction and NH 2OMe then slowly reacts with BDNPP via N-attack at phosphorus and at the aryl group. With NHMeOH, the initial product of O-attack at phosphorus reacts further, either by reaction with a second NHMeOH or by a spontaneous shift of NHMe to the aryl group via a transient cyclic intermediate. There is a minor N-attack of NHMeOH on BDNPP in an SN2(Ar) reaction. Reactions occurring via N-attack are blocked by N-dimethylation, and reaction of NMe 2OH with BDNPP occurs via O-attack, generating a long-lived product. Reaction mechanisms have been probed, and intermediates identified, by using both NMR and MS spectroscopy, with the novel interception of key reaction intermediates in the course of reaction by electrospray ionization mass and tandem mass spectrometry.

The reactions of anilines with 4-methylphenyl and 4-chlorophenyl 2,4-dinitrophenyl carbonates (MPDNPC and ClPDNPC, respectively) and the latter substrate with secondary alicyclic (SA) amines are subjected to a kinetic study in 44 wt % ethanol-water solution, at 25.0 °C, and an ionic strength of 0.2 M (KCl). The reactions are studied by following spectrophotometrically (360 nm) the release of 2,4-dinitrophenoxide anion. Under amine excess, pseudo-first-order rate coefficients (kobsd) are found. Plots of kobsd vs [amine] are linear and pH-independent, with slope kN. The Bronsted-type plots (log kN vs pKa of aminium ions) are linear, with slopes β = 0.68 and 0.66 for the reactions of anilines with MPDNPC and ClPDNPC, respectively, and β = 0.44 for the reactions of SA amines with ClPDNPC. The magnitude of the slope for the latter reaction indicates that its mechanism is concerted. The slope values for the reactions of anilines are in the borderline between stepwise and concerted mechanisms. The sensitivity of logkN to the basicity of the nonleaving group (βnlg) is ca. -0.7 for the reactions of anilines, in agreement with that found for the SA reactions (βnlg ca. -0.6). These results suggest that the reactions of anilines are concerted, although it is also possible that both mechanisms (stepwise and concerted) operate simultaneously. By comparison of the reactions under investigation between them and with similar aminolyses, the following conclusions can be drawn: (i) ClPDNPC is more reactive than MPDNPC toward the two amine series. (ii) The change of water to aqueous ethanol destabilizes a zwitterionic tetrahedral intermediate. (iii) The change of the nonleaving group from MeO to 4-methylphenoxy or 4-chlorophenoxy also destabilizes this intermediate.

Second-order rate constants have been measured for the reaction of 2,4-dinitrophenyl X-substituted benzenesulfonates with a series of primary amines. The nucleophilic substitution reaction proceeds through competitive S-O and C-O bond fission pathways. The S-O bond fission occurs dominantly for reactions with highly basic amines or with substrates having a strong electron-withdrawing group in the sulfonyl moiety. On the other hand, the C-O bond fission occurs considerably for the reactions with low basic amines or with substrates having a strong electron-donating group in the sulfonyl moiety, emphasizing that the regioselectivity is governed by both the amine basicity and the electronic effect of the sulfonyl substituent X. The apparent second-order rate constants for the S-O bond fission have resulted in a nonlinear Bronsted-type plot for the reaction of 2,4-dinitrophenyl benzenesulfonate with 10 different primary amines, suggesting that a change in the rate-determining step occurs upon changing the amine basicity. The microscopic rate constants (k1 and k2/k-1 ratio) associated with the S-O bond fission pathway support the proposed mechanism. The second-order rate constants for the S-O bond fission result in good linear Yukawa-Tsuno plots for the aminolyses of 2,4-dinitrophenyl X-substituted benzenesulfonates. However, the second-order rate constants for the C-O bond fission show no correlation with the electronic nature of the sulfonyl substituent X, indicating that the C-O bond fission proceeds through an SNAR mechanism in which the leaving group departure occurs rapidly after the rate-determining step.

The reactions of 2,4-dinitrophenyl and 2,4,6-trinitrophenyl methyl carbonates (DNPC and TNPC, respectively) and S-(2,4-dinitrophenyl) and S-(2,4,6-trinitrophenyl) ethyl thiolcarbonates (DNPTC and TNPTC, respectively) with a series of benzenethiolate anions were subjected to a kinetic investigation in water, at 25.0 °C, and an ionic strength of 0.2 M (KCl). These reactions obey pseudo-first-order kinetics, under excess of benzenethiolate, and are first order in the latter reactant. However, comparable reactant concentrations were used in the reactions of 4-nitrobenzenethiolate anion with TNPC and TNPTC, which showed second-order kinetics. The nucleophilic rate constants are pH independent, except those for the reactions of TNPC with 4-methoxy- and pentafluorobenzenethiolates, and TNPTC with benzenethiolate and 4-chloro- and 3-chlorobenzenethiolates, which show acid dependence. The Bronsted-type plots for the nucleophilic rate constants are linear with slopes β = 0.9, 1.0, 0.9, and 0.9 for the reactions of DNPC, TNPC, DNPTC, and TNPTC, respectively. No break in the Bronsted plot was found for the reactions of DNPC and DNPTC at pKa ca. 4.1 and 3.4, respectively, consistent with concerted mechanisms. TNPC is more reactive toward benzenethiolate anions than DNPC, and TNPTC more than DNPTC due to the better leaving groups involved. Comparison of the kinetic results obtained in this work with those for the concerted phenolysis of the same substrates shows that benzenethiolate anions are better nucleophiles toward carbonates than isobasic phenoxide anions. This is explained by Pearson's hard and soft acids and bases principle.

For dephosphorylation of bis(2,4-dinitrophenyl) phosphate (BDNPP) by hydroxylamine in water, pH region 4-12, the observed first-order rate constant, kobs, initially increases as a function of pH, but is pH-independent between pH 7.2 and pH 10. The initial BDNPP cleavage by nonionic NH 2OH (a short-lived O-phosphorylated hydroxylamine, 2, followed by three possible reactions: (1) reaction of 2 with hydroxylamine, generating 2,4-dinitrophenyl phosphate (DNPP, 3), which subsequently forms DNP; (2) intramolecular displacement of the second DNP group and rapid decomposition of the cyclic intermediate to form phosphonohydroxylamine and eventually inorganic phosphate; (3) a novel rearrangement with intramolecular aromatic nucleophilic substitution involving a cyclic intermediate and migration of the 2,4-dinitrophenyl group from O to N. Values of kobs increase modestly with pH > 10, the reaction is biphasic, and the yield of DNP increases. An increase in [NH2OH] also increases the yield of DNP, due largely to accelerated hydrolysis of DNPP.

The reactions of 4-methylphenyl 4-nitrophenyl carbonate (MPNPC) and 4-methylphenyl 2,4-dinitrophenyl carbonate (MPDNPC) with a series of secondary alicyclic amines are subjected to a kinetic investigation in 44 wt% ethanol-water, at 25.0°C, ionic strength 0.2 M (KCl). Under amine excess over the substrate, pseudo-first-order rate coefficients (kobs) are obtained. Plots of kobs against [amine] are linear, with kN as slopes. A biphasic Broensted-type plot for kN is obtained for the aminolysis of MPNPC, with slopes β1 = 0.2 (high pKa) and 32 = 0.9 (low pKa). This is in accordance with a stepwise mechanism, through a zwitterionic tetrahedral intermediate (T±), and a change in the rate-determining step, from formation to breakdown of T± the amine pKa decreases. For the aminolysis of MPDNPC, a slightly curved Broensted-type plot for kN is obtained, with β1 = 0.1 (low pKa) β2 = 0.55 (high pKa). This is consistent with a concerted mechanism.

The reactions of methyl 4-nitrophenyl carbonate (MNPC) with a series of secondary alicyclic amines (SAA) and quinuclidines (QUIN), methyl 2,4-dinitrophenyl carbonate (MDNPC) with QUIN and 1-(2-hydroxyethyl)piperazinium ion (HPA), and phenyl 2,4-dinitrophenyl carbonate (PDNPC) with SAA are subjected to a kinetic investigation in aqueous solution, at 25.0°C and an ionic strength of 0.2 M. By following spectrophotometrically the nucleofuge release (330-400 nm) under amine excess, pseudo-first-order rate coefficients (kobsd) are obtained. Plots of kobsd VS [amine] at constant pH are linear, with the slope (kN) being pH independent. The Broensted-type plot (log kN vs amine pKa) for the reactions of SAA with MNPC is biphasic with slopes β1 = 0.3 (high pKa region) and β2 = 1.0 (low pKa region) and a curvature center at pKa0 = 9.3. This plot is consistent with a stepwise mechanism through a zwitterionic tetrahedral intermediate (T±) and a change in the rate-determining step with SAA basicity. The Broensted plot for the quinuclidinolysis of MNPC is linear with slope βN = 0.86, in line with a stepwise process where breakdown of T± to products is rate limiting. A previous work on the reactions of SAA with MDNPC was revised by including the reaction of HPA. The Broensted plots for the reactions of QUIN and SAA with MDNPC and SAA with PDNPC are linear with slopes β = 0.51, 0.48, and 0.39, respectively, consistent with concerted mechanisms. Since quinuclidines are better leaving groups from T± than isobasic SAA, yielding a less stable T±, it seems doubtful that the quinuclidinolysis of PDNPC is stepwise, as reported.

Phosphate-catalyzed hydrolysis of 2,4-dinitrophenyl 4-X-benzoate, and 3- or 4-Y-phenyl 3,5-dinitrobenzoates, where X and Y are substituents, has been studied spectrophotometrically. The following conclusions are based on catalytic rate constants, solvent

Elimination reactions of 2-X-4-NO2C6H3CH2C(O) OC6H3-2-Y-4-NO2 [X = H (1), NO2 (2)] promoted by R2NH/R2NH2+ in 70 mol % MeCN(aq) have been studied kinetically. The base-promoted eliminations from 1 proceeded by the E2 mechanism when Y = Cl, CF3, and NO2. The mechanism changed to the competing E2 and E1cb mechanisms by the poorer leaving groups (Y = H, OMe) and to the E1cb extreme by the strongly electron-withdrawing β-aryl group (2, X = NO2). The values of β = 0.14 and |β1g| = 0.10-0.21 calculated for elimination from 1 (Y = NO2) indicate a reactant-like transition state with small extents of proton transfer and Cα-OAr bond cleavage. The extent of proton transfer increased with a poorer leaving group, and the degree of leaving group bond cleavage increased with a weaker base. Also, the changes in the k1 and k-1/k2 values with the reactant structure variation are consistent with the E1cb mechanism. From these results, a plausible pathway of the change of the mechanism from E2 to the E1cb extreme is proposed.

A kinetic study is reported for the reaction of the anionic nucleophiles OH-, CN-, and N3- with aryl benzoates containing substituents on the benzoyl as well as the aryloxy moiety, in 80 mol % H2O-20 mol % dimethyl sulfoxide at 25.0 °C. Hammett log k vs σ plots for these systems are consistently nonlinear. However, a possible traditional explanation in terms of a mechanism involving a tetrahedral intermediate with curvature resulting from a change in rate-determining step is considered but rejected. The proposed explanation involves ground-state stabilization through resonance interaction between the benzoyl substituent and the electrophilic carbonyl center in the two-stage mechanism. Accordingly, the data are nicely accommodated on the basis of the Yukawa-Tsuno equation, which gives linear plots for all three nuceophiles. Literature reports of the mechanism of acyl transfer processes are reconsidered in this light.

Second-order rate constants have been measured spectrophotometrically for the nucleophilic reactions of three substituted phenyl acetates with butane-2,3-dione monoximate (Ox-) as an α-nucleophile and p-chlorophenoxide (ClPhO-) as co

Hydrolysis of bis(2,4-dinitrophenyl) phosphate (BDNPP) by Zn(II) with ligands bearing plural bis(imidazol-2-yl) groups was kinetically studied in aqueous solution. The binuclear Zn(II) complex of 1,3-bis(diimidazol-2-yl-hydroxymethyl)benzene (2a) was foun