51-28-5

New highly selective method is suggested for synthesis of 2,4-dinitrophenol by nitration of phenol with nitric acid in an aqueous-alcoholic medium at the boiling point of the reaction mixture. The yield of 2,4-dinitrophenol is as high as 80%. Pleiades Publishing, Ltd., 2012.

The structural and functional properties of zinc(ii) complexes of two nitrogen rich polydentate ligands, HTPDP = 1,3-bis(bis-pyridin-2-ylmethylamino)propan-2-ol and HTPPNOL = N,N,N′-tris-(2-pyridylmethyl)-1,3-diaminopropan-2-ol, are compared. HTPDP is a hepta-dentate ligand with four pyridyl groups attached to a 1,3-diaminopropan-2-ol backbone while HTPPNOL contains only three pyridyl groups. In reactions with Zn(ClO4)2, HTPDP forms a dinuclear zinc compound [Zn2(TPDP)(OAc)](ClO4)2, 1. On the other hand, mononuclear [Zn(HTPPNOL)](ClO4)2, 2, and tetranuclear [Zn4(TPPNOL)2(OAc)3](ClO4)3, 3, complexes were isolated with the ligand HTPPNOL. Kinetic measurements with the substrate bis(2,4-dinitrophenyl)phosphate (BDNPP) revealed that compound 1 (kcat = 31.4 × 10?3 min?1) is more reactive than 3 (kcat = 7.7 × 10?3 min?1) at pH = 8.5, whilst the mononuclear compound 2 is inactive. Compound 1 displays a typical steady-state kinetic behaviour, while compound 3 exhibits steady-state behaviour only ～120 s after starting the reaction, preceded by a burst-phase. 31P NMR studies confirm that 1 can promote the hydrolysis of both ester bonds in BDNPP, generating the monoester DNPP and inorganic phosphate in the process. In contrast, DNPP is not a substrate for 3. The crystal structure of the complex formed by 3 and DNPP reveals the formation of a tetranuclear zinc complex [Zn4(TPPNOL)2(DNPP)2](ClO4)2, 4, in which the phosphate moiety of DNPP adopts an unusual tridentate μ-η1:η1:η1 coordination mode.

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The present study reports for the first time the use of a thiol-functionalized graphene oxide nanocatalyst with impressive activity (>105-fold) in dephosphorylation reactions. The innovative and recyclable nanocatalyst has potential in designing artificial enzymes with targeted multifunctionalities and in detoxification of organophosphorus agents.

p-Sulfonatocalixarene water soluble macrocyclic host receptors are known to form cooperative ternary complexes with complementary organic guest and metal cations. This property may be explored to enhance the interaction of weak nitrogen ligands with metal cations in a confined space showing some resemblance to metal-containing enzymes. However, the best of our knowledge, catalytic potential of this property remains unexplored. In this work the Ni2+ catalyzed hydrolysis of a picolinate ester (2,4-dinitrophenyl picolinate, 1) was used as a model reaction to evaluate the effect of sulfonatocalixarene macrocycles in the kinetics of this reaction. The results show that the host molecules promote the reaction through simultaneous complexation of the metal cation and the substrate and, in the case of the larger calixarenes containing more basic phenol groups, substantially higher rate enhancements are observed owing to additional assistance provided by base/nucleophilic catalysis. However, due the ionic nature of these receptors auto-inhibition of the reaction is observed at higher concentrations due counterion (Na+) binding that competes with the catalytically active Ni2+ -complexes.

We report the reactivity of three binuclear non-heme Fe(III) compounds, namely [Fe2(bbppnol)(μ-AcO)(H2O)2](ClO 4)2 (1), [Fe2(bbppnol)(μ-AcO) 2](PF6) (2), and [Fe2(bbppnol)(μ-OH)(Cl) 2]?6H2O (3), where H3bbppnol = N,N′-bis(2-hydroxybenzyl)-N,N′-bis(2-methylpyridyl)-1, 3-propanediamine-2-ol, toward the hydrolysis of bis-(2,4-dinitrophenyl)phosphate as models for phosphoesterase activity. The synthesis and characterization of the new complexes 1 and 3 was also described. The reactivity differences observed for these complexes show that the accessibility of the substrate to the reaction site is one of the key steps that determinate the hydrolysis efficiency.

The kinetic study of the reaction of 1-pyrrolidino-2,4-dinitrobenzene, 1-pipridino-2,4-dinitrobenzene and 1-morpholino-2,4-dinitrobenzene with NaOH in the presence and absence of the amine leaving group was carried out in aqueous solutions at 25 deg C, giving 2,4-dinitrophenol as the only product.A mechanism involving the formation of ? complexes by addition of HO- or the amine to the unsubstituted positions of the aromatic ring is proposed.These complexes were found to react faster than the original substrates.

Purple acid phosphatases (PAPs) are the only dinuclear metallohydrolases for which the necessity for a heterovalent active site (FeIII-MII; M = Fe, Zn or Mn) for catalysis has been established. A major goal for the synthesis of PAP biomimetics is to design a ligand in which the two coordination sites exhibit discrimination between the trivalent and divalent metal ions. With this goal in mind the ligand 2-{[bis(2-methoxyethyl)amino]methyl}-6-{[(2-hydroxybenzyl)(2-pyridylmethyl)amino]methyl}-4-methylphenol (BMMHPH2), with two distinct coordination sites, N2O2 (α) and NO3 (β), has been prepared. Although not exactly mimicking the active site of PAP, the ligand facilitated the formation of the complex [FeIIIZnII(BMMHP)(CH3COO)2](BPh4), which exhibited regioselectivity in the two metal binding sites. The phosphoesterase-like activity of the complex in 50:50 acetonitrile/water was investigated by using the substrate bis(2,4-dinitrophenyl) phosphate (BDNPP) yielding kinetically relevant pKa values of 6.89, 7.37 and 9.00, a KM of 10.8±2.1 mM and a kcat of 3.20±0.38×10-3 s-1 (at pH = 7.5). Attempts to prepare a diiron analogue resulted in a centrosymmetric dimer, [FeIII2(BMMHPH)2(μ-OH)2](BPh4)2, with one six-coordinate FeIII atom in each of the α-sites, connected by two μ-hydroxido groups. In this Fe(μ-OH)2Fe diamond core the FeIII ions are weakly antiferromagnetically coupled, with J = -1.76±0.03 cm-1. The β-sites were vacant. Attempts to replace the ZnII ion with MgII resulted in the formation of a centrosymmetric trimer, i.e. [FeIII2MgII(BMMHPH)2(CH3COO)2(CH3O)2](BPh4)2.

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The active site of mammalian purple acid phosphatases (PAPs) have a dinuclear iron site in two accessible oxidation states (FeIII2 and FeIIIFeII), and the heterovalent is the active form, involved in the regulation of phosphate and phosphorylated metabolite levels in a wide range of organisms. Therefore, two sites with different coordination geometries to stabilize the heterovalent active form and, in addition, with hydrogen bond donors to enable the fixation of the substrate and release of the product, are believed to be required for catalytically competent model systems. Two ligands and their dinuclear iron complexes have been studied in detail. The solid-state structures and properties, studied by X-ray crystallography, magnetism, and M?ssbauer spectroscopy, and the solution structural and electronic properties, investigated by mass spectrometry, electronic, nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and M?ssbauer spectroscopies and electrochemistry, are discussed in detail in order to understand the structures and relative stabilities in solution. In particular, with one of the ligands, a heterovalent FeIIIFeII species has been produced by chemical oxidation of the FeII2 precursor. The phosphatase reactivities of the complexes, in particular, also of the heterovalent complex, are reported. These studies include pH-dependent as well as substrate concentration dependent studies, leading to pH profiles, catalytic efficiencies and turnover numbers, and indicate that the heterovalent diiron complex discussed here is an accurate PAP model system.

The pH-independent hydrolysis of bis(2,4-dinitrophenyl) carbonate, DNPC, in aqueous acetonitrile was studied spectrophotometrically from 20 to 45 °C. The binary solvent composition covers [H2O] from 0.02 to 51.39 M, corresponding to the water mole fraction, χw, from 0.100 to 0.971. The dependence of log (kobs), the observed rate constant, on χw is sigmoidal and is similar to the dependence of the solvent polarity scale ET(30) on χw for the same solvent mixture. As a function of decreasing χw, the Gibbs free energy of activation gradually increases, but ΔH? and ΔS? show a complex, quasi-mirror image dependence on χw. Plots of log (kobs) versus log [water] do not allow calculation of a single kinetic order with respect to water over the entire range of [water]. The structure of the transition state was probed by a proton inventory study carried out at χw = 0.453, 0.783, and 0.871, respectively. Plots of observed rate constants versus the atom fraction of deuterium in the solvent curve downward, and the results were fitted to a transition-state model that contains DNPC and two water molecules. Thus, the sigmoidal dependence of log (kobs) on log [water] is not due to an increase in the number of water molecules in the transition state as a function of increasing [water]. The similarity of plots of log (kobs) versus χw and ET(30) versus χw suggest similar solute- solvent interaction mechanisms, namely H-bonding and dipolar interactions. Kinetic results are discussed in terms of effects of the structure of acetonitrile-water mixtures on the solvation of reactant and transition states.

The reactions of a series of secondary alicyclic (SA) amines with O-phenyl and O-ethyl O-(2,4-dinitrophenyl) thiocarbonates (1 and 2, respectively) and of a series of pyridines with the former substrate are subjected to a kinetic investigation in water, at 25.0 °C, ionic strength 0.2 M (KCl). Under amine excess over the substrate, all the reactions obey pseudo-first-order kinetics and are first-order in amine. The Broensted-type plots are biphasic, with slopes (at high pKa) of β1 = 0.20 for the reactions of SA amines with 1 and 2 and β1 = 0.10 for the pyridinolysis of 1 and with slopes (at low pKa) of β2 = 0.80 for the reactions of SA amines with 1 and 2 and β2 = 1.0 for the pyridinolysis of 1. The pKa values at the curvature center (pK a0) are 7.7, 7.0, and 7.0, respectively. These results are consistent with the existence of a zwitterionic tetrahedral intermediate (T?) and a change in the rate-determining step with the variation of amine basicity. The larger pKa0 value for the pyridinolysis of 1 compared to that for 2 (pKa0 = 6.8) and the larger pKa0 value for the reactions of SA amines with 1 relative to 2 are explained by the greater inductive electron withdrawal of PhO compared to EtO. The larger pKa0 values for the reactions of SA amines with 1 and 2, relative to their corresponding pyridinolysis, are attributed to the greater nucleofugalities of SA amines compared to isobasic pyridines. The smaller pKa0 value for the reactions of SA amines with 2 than with O-ethyl S-(2,4-dinitrophenyl) dithiocarbonate (pKa0 = 9.2) is explained by the greater nucleofugality from T? of 2,4-dinitrophenoxide (DNPO-) relative to the thio derivative. The stepwise reactions of SA amines with 1 and 2, in contrast to the concerted mechanisms for the reactions of the same amines with the corresponding carbonates, is attributed to stabilization of T? by the change of O- to S-. The simple mechanism for the SA aminolysis of 2 (only one tetrahedral intermediate, T?) is in contrast to the more complex mechanism (two tetrahedral intermediates, T? and T-, the latter formed by deprotonation of T? by the amine) for the same aminolysis of the analogous thionocarbonate with 4-nitrophenoxide (NPO-) as nucleofuge. To our knowledge, this is the first example of a remarkable change in the decomposition path of a tetrahedral intermediate T? by replacement of NPO- with DNPO- as the leaving group of the substrate. This is explained by (i) the greater leaving ability from T? of DNPO- than NPO- and (ii) the similar rates of deprotonation of both T? (formed with DNPO and NPO).

Herein, we report the synthesis and characterization of three new Ni(II) complexes, namely: [Ni2(H2LEt)(μ-OAc)2(H2O)]BPh4?ClO4 (1), (H2LEt = 2-[(N-benzyl-N-2-pyridyl methylamine)]-4-methyl-6-[N-2(pyridylmethyl)aminomethyl)]-6((2-aminoethyl)amino)methyl phenol); [Ni2(H2LProp)(μ-OAc)2(H2O)](ClO4)2 (2), (H2LProp = 2-[(N-benzyl-N-2-pyridylmethylamine)]-4-methyl-6-[N-(2-pyridylmethyl)aminomethyl]-6-((2-aminopropyl) amino)methylphenol); and [Ni2(LBut)(μ-OAc)2(H2O)](HCl)2 (3), (LBut = 2-[(N-benzyl-N-2-pyridylmethylamine)]-4-methyl-6-[N-(2-pyridylmethyl)aminomethyl]-6-((2-aminobuthyl) amino)methylphenol). All of them were characterized through spectroscopic techniques (elemental analysis, IR, UV–Vis spectroscopy), ESI-MS, electrochemistry and potentiometric titration. Density functional theory (DFT) was used to better understand the electronic and molecular structure of these complexes. The hydrolytic activity of complexes 1–3 towards the 2,4-BDNPP substrate was analyzed and complex 2 presented the highest catalytic efficiency (kcat/KM) of the three, possibly due to a greater interaction with the substrate. The complexes were also screened for their antibacterial activities using both Gram-positive and Gram-negative bacterial strains by minimum inhibitory concentration and minimum bactericidal concentration methods.

The reaction of N-n-butyl-2,6-dinitroaniline with NaOH in 60% dioxane-water at reflux gives 7-nitro-2-n-propylbenzimidazole-3-oxide quantitatively.

The kinetics of the hydrolysis of 1-X-2,4-dinitrobenzene (X=Cl,F) were studied in the presence of β-cyclodextrin.The overall rate of hydrolysis is catalyzed by the added compound, and the observed catalysis is pH dependent.For the reaction of the fluoro derivative the catalytic factor at 0.01 M β-cyclodextrin changes from 7 at 10 -3 M NaOH to 2.5 at 10 -1 M NaOH.Part of the catalysis is due to nucleophilic reaction of β-cyclodextrin with the substrate and part of it is attributed to the reaction of an inclusion complex formed between the substrate and the β-cyclodextrin.The catalytic factor corresponding to the reaction in the cavity is 1.4 and 2 for the fluoro and chloro derivative, respectively

Catalytic particles based on supramolecular systems have demonstrated significant improvement in the field of catalysis. In this work, histidine-functionalized self-assembling peptide amphiphiles (PAs) were synthesized in order to form self-assembly high-aspect-ratio nanofibers with internal order that can present imidazolyl groups capable of ester hydrolysis. Self-assembly of the molecules making up the catalytic particle was studied by transmission electron microscopy and circular dichroism. The reactive sites were designed with histidine residues to catalyze the hydrolysis of 2,4-dinitrophenyl acetate (DNPA). Enzymatic hydrolysis of DNPA was observed in the presence of the nanofibers by UV-vis spectroscopy and the Michaelis-Menten enzyme kinetics model. Significantly faster hydrolysis rate was observed in the presence of self-assembled nanofibers relative to spherical aggregates expected to have less order as well as single molecule catalysts. Copyright

Described herein is the synthesis, structure, and monoesterase and diesterase activities of a new mononuclear [LaIII(L 1)(NO3)2] (1) complex (H2L 1 = 2-bis[{(2-pyridylmethyl)-aminomethyl}-6-[N-(2-pyridylmethyl) aminomethyl)])-4-methyl-6-formylphenol) in the hydrolysis of 2,4-bis(dinitrophenyl)phosphate (2,4-BDNPP). When covalently linked to 3-aminopropyl-functionalized silica, 1 undergoes disproportionation to form a dinuclear species (APS-1), whose catalytic efficiency is increased when compared to the homogeneous reaction due to second coordination sphere effects which increase the substrate to complex association constant. The anchored catalyst APS-1 can be recovered and reused for subsequent hydrolysis reactions (five times) with only a slight loss in activity. In the presence of DNA, we suggest that 1 is also converted into the dinuclear active species as observed with APS-1, and both were shown to be efficient in DNA cleavage.

In this paper, we describe a novel synthesized ionically tagged water-soluble artificial enzyme (PI) that can efficiently cleave phosphate esters, with enhanced an ionic liquid effect through cooperative effects for the substrate activation and further nucleophilic reaction. The dephosphorylation reaction with PI was evaluated in the presence and absence of 2-methyl-4(5)-nitroimidazole, showing impressive rate enhancements of up to 2 × 106-fold, ascribed to the imidazolide species known as excellent nucleophiles, and formed favorably at lower pH values in the presence of PI.

The critical micelle concentration of solutions of cetyltrimethylammonium bromide and of tetradecyltrimethylammonium bromides were determined by a kinetic method.This involved the determination of the rates of the hydroxydehalogenation of some activated aromatic substrates over a wide range of detergent concentrations.Measurements were made in solutions containing significant quantities of added hydroxyl ion and substrates which were themselves amphiphilic.Conventional methods cannot be applied with confidence to such systems.The effects of changing hydroxyl ion concentrations, added sodium bromide, changing the nature of the aromatic substrate (whether neutral or charged), the identity of the micellar counterion and the temperature were investigated.It was found that added bromide or hydroxyl ions resulted in a lower CMC whereas increased temperature led to an increase in the CMC.The nature of the micellar counterion (Br, F, OH, SO4) had little effect on the CMC.The presence of a charged aromatic substrate led to a considerable lowering of the CMC, whereas the neutral aromatic substrate used showed very little effect.

The characteristics of two distinct perylene chemiluminescence (CL) decay curves generated by the reaction between bis(2,4-dinitrophenyl) oxalate (DNPO) and H2O2 in the absence of base catalysts were investigated. When the intensity of peroxyoxalate chemiluminescence (PO-CL) vs. time was measured under relatively low H2O2 and high DNPO concentrations in ethyl acetate, a slowly decaying curve appeared. However, upon increasing the H2O2 concentration under the same DNPO-CL reaction conditions, two distinct emission maxima were observed: a fast decaying CL curve and a slowly decaying CL curve. The fast decaying CL curve appeared alone when the H2O2 concentration greatly exceeded the DNPO concentration in ethyl acetate. To learn more about the properties of both CL decay curves, we further investigated the effects of adding H2O or phenols having different nucleophilicity [2,4-dinitrophenol (DNP), 2,4-dichlorophenol (DCP), pentachlorophenol (PCP), and 2,4,6-trichlorophenol (TCP)] and the stability of DNPO used in the CL reaction. The slowly decaying curve was predominant with the addition of H2O and relatively strong nucleophile. Based on the observed results, we propose that the likely high-energy intermediates generated in DNPO-CL reactions without added base catalysts are hydroperoxyoxalate ester and a six-membered cyclic peroxide.

The kinetics of the hydrolysis of bis(2,4-dinitrophenyl) phosphate (BDNPP) were studied in basic solutions in the presence of La3, Sm 3, Tb3+ and Er3. Bis-Tris propane (BTP) buffer was used to stabilize the Ln3 hydroxide complexes in solution. Two equivalents of the 2,4-dinitrophenolate ion (DNP) were liberated for each equivalent of BDNPP and the reaction showed first-order kinetics. Potentiometric titrations showed the formation of dinuclear complexes such as [Ln2(BTP)2(OH)n](6-n), with values of n varying as a function of pH, for all studied metals. Hence the catalytic effect depends on the formation of dinuclear lanthanide ion complexes with several hydroxo ligands. Copyright

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The hydrolytic activity of the 1,3,5-triaminocycloxexane derivatives TACH, TACI and TMCA complexed to Zn(II) and Cu(II) towards a model phosphoric ester and plasmid DNA has been evaluated by means of spectroscopic and gel-electrophoresis techniques. At conditions close to physiological, a prominent cleavage effect mediated by the nature of the ligand and metal ion was generally observed. TACI complexes are the most active in relaxing supercoiled DNA, the effect being explained by the affinity of the hydroxylated ligand for the nucleic acid. As indicated by the dependence of cleavage efficiency upon pH, Zn(II)-complexes act by a purely hydrolytic mechanism. In the case of Cu(II)-complexes, although hydrolysis should be prominent, involvement of an oxidative pathway cannot be completely ruled out.

Cleavage of an activated phosphodiester by Zn(NO3)2· 6H2O was accelerated (9 × 103-fold) by cooperative effect of a metal ion and hydrogen bonds in the presence of a bismelamine derivative bearing a 2,2′-bipyridine moiety in MeCN.

The kinetics of alkaline hydrolysis of 2-chloro-3,5-dinitrobenzotrifluoride 1 and 1-chloro-2,4-dinitrobenzene 2 were studied in various acetonitrile-water (AN-H2O) mixtures (10-90% w/w) at different temperatures. Thermodynamic parameters ΔH# and ΔS# show great variation, whereas ΔG# appears to vary little with the solvent composition presumably due to compensating variations. The results are discussed in terms of the solvent parameters such as preferential solvation, dielectric constant, polarity/polarizability, and hydrogen bond donor and acceptor parameters. It has been found that the factors controlling the reaction rates are the desolvation of OH-, the solvophobicity of the medium, and free water molecules in rich AN mixed solvent. The data showed that the solvatochromic parameters of (AN-H2O) mixed solvent are destroyed in the presence of excess OH-.

The preparation of 2,2,2-trifluoroacetaldehyde O-(aryl)oxime, a previously inaccessible precursor of trifluoroacetonitrile, via reaction of hydroxylamine and trifluoroacetaldehyde hydrate is reported. This precursor released CF3CN in quantitative yield under mildly basic conditions. The precursor was successfully used in the synthesis of trifluoromethylated oxadiazoles. The facile, cost-effective, scalable, and recyclable procedure makes these trifluoroacetonitrile precursors generally applicable.

Degradation of nonbiodegradable organic compounds into harmless substances is one of the main challenges in environmental protection. Electrically-activated persulfate process has served as an efficient advanced oxidation process (AOP) to degrade organic compounds. In this study, we synthesized three nitrogen-doped carbon materials, namely, nitrogen-doped activated carbon plus graphene (NC), and nitrogen-doped activated carbon (NAC), nitrogen-doped graphene (NGE), and three nitrogen-doped carbon material-graphite felt (GF) cathodes. The three nitrogen-doped carbon materials (NC, NGE, NAC) were characterized using X-ray diffraction, Raman spectroscopy, X-ray electron spectroscopy, and nitrogen desorption-adsorption. The electron spin resonance technique was used to identify the presence of hydroxyl radicals (OH), sulfate radicals (SO4-) and singlet oxygen (1O2) species. The results showed that NC was more conducive for the production of free radicals. In addition, we applied NC-GF to an electro-activated persulfate system with the degradation of p-nitrophenol and investigated its performance for contaminant degradation under different conditions. In general, the nitrogen-doped carbon electrode electro-activated persulfate process is a promising way to treat organic pollutants in wastewater.

Organophosphate (OP) pesticides are responsible for numerous human deaths every year. Nucleophilic substitution is an important method to mitigate the toxicity of obsolete stocks of OPs. Herein, the degradation of O,O-diethyl-2,4-dinitrophenyl phosphate (DEDNPP) and pesticide diethyl-4-nitrophenyl phosphate (Paraoxon) promoted by 1,2,4-triazole (TAZ) was investigated by means of kinetic studies, nuclear magnetic resonance (NMR) analyses, and theoretical calculations. Results showed fast degradation of OPs is promoted by the anionic form of the nucleophile (TAZ(-)) in pH > 8.5 (optimal at pH = 11). Rate enhancements of 106 and 105-fold in relation to neutral hydrolysis of DEDNPP and Paraoxon were observed, respectively, consistent with alpha-nucleophiles reactivity. TAZ(-) regioselectively promotes the degradation of DEDNPP via P-O bond break, forming a quickly hydrolyzable phosphorylated intermediate, regenerating the nucleophile. Calculations using M06-2X/6-311++G(d,p) level of theory revealed that the equivalent nitrogen atoms of TAZ(-) are the main nucleophilic center of the molecule. This study expands the knowledge on the reactivity of iminic compounds as detoxificant agents of OPs, indicating the efficiency and selectivity of TAZ(-) in aqueous medium, encouraging the design of novel TAZ-based catalysts.

In2S3/α-Fe2O3 composites were synthesized using the methods of hydrothermal treatment and reflux. Characterization such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), and Photoluminescence (PL) was used to characterize the crystallinity and morphology of the composites, which proved the successful synthesis of the In2S3/α-Fe2O3 heterostructures. The 4-nitrophenol (PNP) degradation experiments by visible light were studied to evaluate the photocatalytic activity of the In2S3/α-Fe2O3 composites. The composites showed much higher photocatalytic degradation activities and TOC removal rate than both pure In2S3 and α-Fe2O3. The PNP degradation rate of composites was about 4.7 and 11.9 times that of pure In2S3 and α-Fe2O3, respectively. The degradation process was detected by high performance liquid chromatography and mass spectrometry, and the degradation pathway was explained. Based on the trapping experiments, e? and ?OH were the main active species and a Z-scheme photocatalytic mechanism of In2S3/α-Fe2O3 was proposed, which showed the double advantage of high redox ability and efficient electron-hole pairs separation.

Titanium dioxide (TiO2) nanoparticles (NPs) have been doped with varying amounts (0.005, 0.010 and 0.015 M) of silver nanoparticles (Ag NPs) using hydrothermal method. Further, in this work, a green approach was followed for the formation of Ag?TiO2 NPs using Aloe vera gel as a capping and reducing agent. The structural property confirmed the presence of anatase phase TiO2. Increased peak intensity was observed while increasing the Ag concentration. Further, the morphological and optical properties have been studied, which confirmed the effective photocatalytic behavior of the prepared Ag?TiO2 NPs. The photocatalytic performance of Ag?TiO2 has been considered for the degradation of picric acid in the visible light region. The concentration at 0.010 M of the prepared Ag?TiO2 has achieved higher photocatalytic performance within 50 min, which could be attributed to its morphological behavior. Similarly, anticancer activity against lung cancer cell lines (A549) was also determined. The Ag?TiO2 NPs generated a large quantity of reactive oxygen species (ROS), resulting in complete cancer cell growth suppression after their systemic in vitro administration. Ag?TiO2 NPs was adsorbed visible light that leads to an enhanced anticancer sensitivity by killing and inhibiting cancer cell reproduction through cell viability assay test. It was clear that 0.015 M of Ag?TiO2 NPs were highly effective against human lung cancer cell lines and showed increased production of ROS in cancer cell lines due to the medicinal behavior of the Aloe vera gel.

The first catalytic procedure for the electrophilic nitration of phenols was developed using iodosylbenzene as an organocatalyst based on iodine(III) and aluminum nitrate as a nitro group source. This atom-economic protocol occurs under mild, non-Br?nsted acidic and open-flask reaction conditions with a broad functional-group tolerance including several heterocycles. Density functional theory (DFT) calculations at the (SMD:MeCN)Mo8-HX/(LANLo8+f,6-311+G) level indicated that the reaction proceeds through a cationic pathway that efficiently generates the NO2+ ion, which is the nitrating species under neutral conditions.

Kinetics and mechanism of nitration of aromatic compounds using trichloroisocyanuric acid (TCCA)/NaNO2, TCCA-N,N-dimethyl formamide (TCCA-DMF)/NaNO2, and TCCA-N,N-dimethyl acetamide (TCCA-DMA)/NaNO2 under acid-free and Vilsmeier-Haack conditions. Reactions followed second-order kinetics with a first-order dependence on [Phenol] and [Nitrating agent] ([TCCA], [(TCCA-DMF)], or [(TCCA-DMA)] >> [NaNO2]). Reaction rates accelerated with the introduction of electron-donating groups and retarded with electron-withdrawing groups, but did not fit well into the Hammett's theory of linear free energy relationship or its modified forms like Brown-Okamoto or Yukawa-Tsuno equations. Rate data were analyzed by Charton's multiple linear regression analysis. Isokinetic temperature (β) values, obtained from Exner's theory for different protocols, are 403.7?K (TCCA-NaNO2), 365.8?K (TCCA-DMF)/NaNO2, and 358?K (TCCA-DMA)/NaNO2. These values are far above the experimental temperature range (303-323?K), indicating that the enthalpy factors are probably more important in controlling the reaction.

Photocaging facilitates non-invasive and precise spatio-temporal control over the release of biologically relevant small- and macro-molecules using light. However, sub-cellular organelles are dispersed in cells in a manner that renders selective light-irradiation of a complete organelle impractical. Organelle-specific photocages could provide a powerful method for releasing bioactive molecules in sub-cellular locations. Herein, we report a general post-synthetic method for the chemical functionalization and further conjugation of meso-methyl BODIPY photocages and the synthesis of endoplasmic reticulum (ER)-, lysosome-, and mitochondria-targeted derivatives. We also demonstrate that 2,4-dinitrophenol, a mitochondrial uncoupler, and puromycin, a protein biosynthesis inhibitor, can be selectively photoreleased in mitochondria and ER, respectively, in live cells by using visible light. Additionally, photocaging is shown to lead to higher efficacy of the released molecules, probably owing to a localized and abrupt release.

The invention relates to a nitration method for an aryl phenol or aryl ether derivative. The method comprises the steps of stirring an aryl phenol or aryl ether compound, nitrate, trimethylchlorosilane (TMSCl) and a copper salt in an acetonitrile solution in air at room temperature, simultaneously, monitoring extent of reaction through a TLC dot plate, removing a solvent from a mixture by a rotaryevaporator after a substrate is consumed completely, and carrying out purification through a silica-gel column, thereby obtaining a nitroolefin derivative. Meanwhile, the selective mono-nitration orbis-nitration of the substrate can be achieved through controlling equivalent weight of the nitrate. Compared with the prior art, the nitration method disclosed by the invention has the advantages that the consumption of strong-acid substances is avoided, the reaction conditions are mild, the yield is high, the applicable range of the substrate is wide, reaction activity is free of obvious attenuation after an amplified reaction, and an excellent yield is still obtained, so that the method has an obvious industrial application value.

The importance of anion–π interactions as a driving force for chemical and biological processes is increasingly being recognized. In this communication, we describe for the first time its key participation in light-induced reactions. We show, in particular, how transient complexes formed through noncovalent anion–π interactions between electron-poor N-aryloxyamides and multiply-charged anions (such as carbonate or phosphate) can undergo facile light-promoted N?O cleavage, affording amidyl radicals that can subsequently be trapped by (hetero)aromatics.

A new type of waste recycling strategy is described in which nitrogen oxides or nitric acid are directly employed in photocatalyzed hydroxylations and nitrohydroxylations of benzenes. Through these transformations, otherwise costly denitrification can be combined with the synthesis of valuable compounds for various applications.

Sodium perborate (SPB) was used as efficient green catalyst for NaNO2/KHSO4-mediated nitration of aromatic compounds in aqueous acetonitrile medium. Synthesis of nitroaromatic compounds was achieved under both conventional and solvent-free microwave conditions. Reaction times were comparatively shorter in the microwave-assisted than conventional reaction. The reaction kinetics for nitration of phenols in aqueous bisulfate and acetonitrile medium indicated first-order dependence on [Phenol], [NaNO2], and [SPB]. Reaction rates accelerated with introduction of electron-donating groups but retarded with electron-withdrawing groups. Kinetic results did not fit well quantitatively with Hammett’s equation. Observed deviations from linearity were addressed in terms of exalted Hammett’s constants (σˉ or σeff), para resonance interaction energy (ΔΔGp) parameter, and Yukawa–Tsuno parameter (r). This term provides a measure of the extent of resonance stabilization for a reactive structure that builds up charge (positive) in its transition state. The observed negative entropy of activation (?ΔS#) suggests greater solvation and/or cyclic transition state before yielding products.

We report a visible light-assisted one-pot method for the synthesis of polynitrophenols through radical tandem hydroxylation and nitration of arylboronic acids by utilizing copper(II) nitrate tri-nitydrate as the nitro source. This method features mild conditions, a simple procedure, and good functional group tolerance. Compared to conventional methods, this work provides a straightforward approach for the polynitration of aromatic compounds.

Synthesis and kinetics of potassium periodate(KIO4)/NaNO2/KHSO4)-initiated nitration of aromatic compounds have been studied in aqueous acetonitrile medium. Synthesis of nitroaromatic compounds is achieved under conventional and solvent-free microwave conditions. Reaction times in microwave-assisted reaction are comparatively less than in conventional reaction. The reaction kinetics for the nitration of phenols in aqueous bisulfate and acetonitrile medium indicated first-order dependence on [phenol], [NaNO2], and [KIO4]. An increase in [KHSO4] accelerated the rate of nitration under otherwise similar conditions. The rate of nitration increased in the solvent of high dielectric media (solvents with high dielectric constant (D)). Observed results were in accordance with Amis and Kirkwood plots [log k′ vs. (1/D) and [(D ? 1)/(2D + 1)]. These observations probably indicate the participation of anionic species and molecular or (dipolar) species in the rate-determining step. In addition, the plots of (log k′) versus volume% of organic solvent were also linear, which probably indicate the importance of both electrostatic and nonelectrostatic forces, solvent–solute interactions during nitration of phenols. Reaction rates accelerated with the introduction of electron-donating groups and retarded with electron-withdrawing groups, but results could not be quantitatively correlated with Hammett's equation and depicted deviations from linearity. These deviations could probably be attributed to cumulative effects arising inductive, resonance, and steric effects. Leffler's plot (ΔH# vs. ΔS#) was found linear indicating the compensation (cumulative) effect of both enthalpy and entropy parameters in controlling the mechanism of nitration.

A novel setup to analyze the heat of reaction of different single- and multiphase reactions carried out in continuous flow is presented. The measurement principle of the calorimetric system is based on true heat flow measurements and therefore ensures precise calorimetric data within 10 mW resolution. In addition to the investigation of simple mixing phenomena (ethylene glycol and water), a number of exothermic, industrially relevant chemical transformations including the nitration of phenol, the reduction of nitrobenzene, as well as several oxidation and reduction processes, were investigated as model systems. For these experiments a commercially available batch calorimeter (ChemiSens CPA202) was equipped with a glass static mixer (250 μL) optionally connected to a tubular microreactor (PFA coil) allowing overall reaction volumes of up to ca. 5.5 mL. Experiments were performed by feeding individual streams with syringe pumps (alternatively substituting one liquid feed with a gaseous feed controlled by a mass flow controller) and mixing the feeds inside the glass static mixer contained in the thermostatted reactor zone of the calorimeter. By adjusting the residence time, volume, and flow rates, chemical transformations were driven to full conversion in order to obtain meaningful calorimetric data. A comparison with literature data indicates that the calorimetric flow system described herein provides comparable data to those obtained by standard batch calorimetry.

The invention discloses a method for preparing 2-amino-4-nitrophenol through selective catalytic hydrogenation reduction. The method roughly comprises the processes of obtaining a 2,4-sodium dinitrobenzene water solution through reaction of 2,4-dinitrochlorobenzene and a 10%-30% sodium hydroxide solution, mixing the 2,4-sodium dinitrobenzene water solution with an acid and an organic solvent to obtain a mixed solution of 2,4-dinitrophenol and an organic solvent; and mixing the mixed solution of 2,4-dinitrophenol and an organic solvent with hydrogen in the presence of a noble metal catalyst, and producing 2-amino-4-nitrophenol through selective catalytic hydrogenation reduction. According to the method, the problems that 2-amino-4-nitrophenol is high in salinity, much in wastewater and high in production cost in an existing production method of 2-amino-4-nitrophenol are solved, and an environment-friendly method which is low in production cost is provided for production of high-quality 2-amino-4-nitrophenol.

Organophosphate (OP) detoxification is a worldwide problem due to the high stability of P-O bonds. Here, we designed several imidazole-coated nanocatalysts targeted towards the cleavage of OP and thus their detoxification. Specifically, Ag, Au and bimetallic AgAu nanoparticles (NPs) supported on SiO2 were functionalized with methimazole (MTZ), which comprises thiol and imidazole groups, foreseeing enabling freely available imidazole groups. Raman analyses indicate that MTZ interacts preferably via its sulfur atom over Au NPs and via the nitrogen of the imidazole ring over Ag NPs. The MTZ-derived nanocatalysts were effective towards OP cleavage. For instance, rate enhancements of 108 fold were obtained for the toxic pesticide Paraoxon, compared to the uncatalyzed reaction. Interestingly, Au-derived nanocatalysts were significantly more effective since the imidazole group is free to react with the OP, which is not possible when Ag-N interactions take place.

A novel, simple, and practical visible-light-mediated intramolecular α-C(sp3)-H imination of tertiary aliphatic amines containing β-O-aryl oximes leading to N-heterocycles has been developed. The reaction was performed well at rt with tolerance of some functional groups. Importantly, the selective C-H functionalization did not require added catalyst, oxidant, additive, acid, and base; visible light was the sole requirement.

Out of six possible positional isomers of dinitrophenol, only 2,4-DNP has been used extensively by many researchers for developing reactive molecular probes. But the question remains unanswered: why has only the 2,4-isomer emerged as a labile protecting group? To answer this question, six molecular probes using available DNP isomers were developed and investigated to evaluate the effect of the extent of atomic orbital overlap on their reactivity. We have proved for the first time at the molecular level that the o-NO2 group contributes less compared to the p-NO2 group toward the reactivity of 2,4-DNP-based probes. Crystal structure analysis revealed that the 2p orbital of N atom and the 2p orbital of the adjacent ring C atom to which the o-NO2 is attached are inclined at >30° to each other, leading to substantial reduction in π overlap (as these two p-orbitals loose coplanar state) resulting in a very weak ?M effect of the o-NO2 group, whereas the 2p orbitals of the N atom of the p-NO2 group and the adjacent ring C atom are almost coplanar (11° inclined to each other), leading to strong π overlap. Hence, the p-NO2 group contributes largely toward the molecular reactivity through its ?M effect.

The novel bis-addition of benzaldehydes to acrylates or maleates was achieved by the direct use of samarium metal with the assistance of CuI under mild conditions under dry air, and the useful 2-hydroxylalkyl-γ-butyrolactons and lignan derivatives were thus constructed with high efficiency. The key factors that influence the reaction efficiency were investigated. The use of potassium iodide and molecular sieves as additives can improve the reaction efficiency remarkably.

The invention discloses a method for catalytic oxidation of phenolic compounds fragrant boron class compound synthesis method, the flux in the solvent in the aqueous solution, under the action of alkali, adding hydrazine hydrate or acid hydrazides catalyst, catalytic oxidation fragrant boron class compound directly for the preparation of phenolic compound. The invention of the method of preparation of the phenol compound, the catalyst is a cheap hydrazine hydrate or hydrazine compound, the oxidizing agent is atmospheric pressure of air or oxygen, the reaction does not need good and activeness metal catalyst, is extensive and stable substrate, substrate-sensitive functional group compatibility good and wide range of application. In the optimized under the reaction conditions, the yield of the target product separation up to 99%. (by machine translation)

Nitration of phenols with tertiary butyl nitrite (TBN) obeyed second-order kinetics with a first-order dependence on [TBN] and [phenol] under acid-free conditions. Reaction rates were significantly altered by a change in the dielectric constant and other physical properties of solvent. The rate of nitration increased with an increase in temperature (303-323 K) in different solvent media (acetonitrile, dichloroethane, CCl4, dimethyl formamide (DMF), and toluene). The rates of nitration (log k) could not fit into either Amis or Kirkwood plots [log k' vs. (1/D) or [(D - 1)/(2D + 1)], but the trends were better explained by the basic form of multivariate linear solvent energy relationships (MLSER) suggested by the Koppel and Palm approach on the one hand and the Kamlet and Taft approach on the other hand. These observations probably substantiate that cumulative contributions of basic solvent parameters (equilibrium as well as frictional solvent effects) and solvent-solute interactions for solvation of transition state during nitration of phenols. Reaction rates accelerated with the introduction of electron-donating groups and retarded with electron-withdrawing groups. Accordingly, the reactivity of structurally different phenols was found to follow the following sequence: p-OH > p-MeO > p-Me > H > m-Me > p-Cl > p-Br > m-Cl > p-NO2 > m-OH. The results are interpreted by Hammett's theory of linear free energy relationship. The reaction constant (Hammett's ρ) is a measure of the sensitivity of the reaction toward the electronic effects of the substituent. The rho (ρ) values obtained from the present experiments are fairly large negative values (ρ CH3) versus σ? or, Es or combined Taft's relationship. However, Charton's MLRA of the log k with polar, resonance, steric, hydrophobicity, and molar refractivity showing a very good linear relationship was obtained. It is of interest to note that when log kexp values are correlated with log kcal a perfect linearity is obtained with a correlation coefficient of unity, indicating the consonance between experimental and calculated rate constants in the present work.

The invention discloses a preparation method for 2-amino-4-nitrophenol. The preparation method for the 2-amino-4-nitrophenol, provided by the invention, comprises the following step: subjecting 2,4-dinitrophenol and hydrazine hydrate to a reduction reaction in the presence of a catalyst, thereby preparing the 2-amino-4-nitrophenol, wherein the catalyst is a combination of ferric chloride hexahydrate (FeCl3.6H2O) and activated charcoal. The preparation method disclosed by the invention has the advantages of milder reaction conditions, no byproduct, economical efficiency, environment-friendliness, simple aftertreatment and high reaction yield, thereby being adaptable to industrial production.

The invention discloses a preparation method of 2-amino-4-nitrophenol. The method consists of the steps of: (1) in a solvent and in the presence of alkali, subjecting 2, 4-dinitrochlorobenzene to hydrolysis reaction, and then carrying out acidification reaction with acid to obtain 2, 4-dinitrophenol; and (2) in the presence of a catalyst, subjecting the 2, 4-dinitrophenol obtained in step (1) and hydrazine hydrate to reduction reaction so as to obtain the 2-amino-4-nitrophenol, with the catalyst being a combination of ferric trichloride hexahydrate and activated carbon. The preparation method of the invention has the advantages of milder reaction conditions, no byproduct, economical efficiency and environmental protection, simple post-treatment, and high reaction yield, and is suitable for industrial production. (reaction formulas).

The intramolecular charge transfer (ICT) process in donor-acceptor systems has tremendous importance in various physical and biological systems. Three nitrophenolate salts were synthesized and studied here. The ICT and π → π? transition processes were identified in these derivatives using UV-Vis spectroscopy and theoretical calculations. It was observed that by simple substitution with nitro groups, one can generate and control the ICT process by regulating the charge distribution over the molecule. While for a monosubstitute nitro derivative, only one ICT band was observed, additional ICT processes can be generated at will by introducing a second nitro group. The intensity of this second ICT channel can be regulated with introduction of a third nitro group. Further, the association constants and solvation processes for these potassium nitrophenolate derivatives were found to be drastically dependent on the number of ICT channels present in the molecule. Theoretical studies (MEP analysis) support the experimental observations presented here. The results show that by simply introducing additional acceptor groups to the system, one can tune the ICT band efficiently in a conjugate system.

A kinetic study on SNAr reactions of 1-(4-nitrophenoxy)-2,4-dinitrobenzene (1a) with various anionic nucleophiles in 80 mol% water-20 mol% DMSO at 25.0 °C is reported. The Bronsted-type plot for the reaction of 1a with a series of substituted phenoxides and HOO- results in an excellent linear correlation with βnuc = 1.17. However, OH- exhibits dramatic negative deviation from the Bronsted-type plot, while N3-, C6H5S-, and butane-2,3-dione monoximate (Ox-) deviate positively from linearity. HOO- is 680-fold more reactive than OH- but does not exhibit the α-effect. In contrast, Ox- is 166-fold more reactive than isobasic 4-Cl-C6H4O- and exhibits the α-effect. Differential solvation effects have been suggested to be responsible for the α-effect in this study, i.e., Ox- exhibits the α-effect, since it is 5.7 kcal/mol less strongly solvated than 4-Cl-C6H4O- in the reaction medium, while HOO- does not show the α-effect due to a strong requirement for partial desolvation before nucleophilic attack. The highly enhanced reactivity of polarizable N3- and C6H5S- and extremely decreased reactivity of nonpolarizable OH- are in accord with the hard-soft acid and base principle.

The nitration of phenol with excess nitric acid in aqueous dioxane, in contrast to the nitration in aqueous ethanol, yields exclusively 2,4-dintrophenol, whereas at equimolar ratio of phenol and nitric acid the major reaction products are mononitrophenols (99%), among which the p-isomer prevails.

While the phase-vanishing (PV)-PTFE reaction design works well with a broad range of substrates and reaction conditions, there are occasional problems. A description of the problems and their importance, including their effects on the reaction outcome and ways to address them, are discussed. Details of an improved design, a hybrid of previously reported PV-PTFE and solvent-free PV-PTFE designs, is presented, as well as the use of silica-supported reagents.

In a PTFE tape phase-vanishing reaction (PV-PTFE), a delivery tube sealed with PTFE tape is inserted into a vessel which contains the substrate. The reagent diffuses across the PTFE tape barrier into the reaction vessel. PTFE co-polymer films have been found to exhibit selective permeability towards organic compounds, which was affected by the presence of solvents. In this study, we attempted to establish general trends of permeability of PTFE tape to different compounds and to better describe the process of solvent transport in PV-PTFE bromination reactions. Though PTFE tape has been reported as impermeable to some compounds, such as dimethyl phthalate, solvent adsorption to the tape altered its permeability and allowed diffusion through channels of solvent within the PTFE tape. In this case, the solvent-filled pores of the PTFE tape are chemically more akin to the adsorbed solvent rather than to the PTFE fluorous structure. The solvent uptake effect, which was frequently observed in the course of PV-PTFE reactions, can be related to the surface tension of the solvent and the polarity of the solvent relative to the reagent. The lack of pores in bulk PTFE prevents solvents from altering its permeability and, therefore, bulk PTFE is impermeable to most solvents and reagents. However, bromine, which is soluble in liquid fluorous media, diffused through the bulk PTFE. A better understanding of the PTFE phase barrier will make it possible to further optimize the PV-PTFE reaction design.

The second-order rate constants for reactions of 2,4-dinitrophenyl X-substituted-benzenesulfonates (4a-4f) and Y-substituted-phenyl-4-nitrobenzenesulfonates (5a-5f) with N3- ion have been measured spectrophotometrically. The reactions of 4a-4f proceed through S-O and C-O bond fission pathways competitively. Fraction of the S-O bond fission decreases rapidly as the substituent X in the benzenesulfonyl moiety changes from an electron-withdrawing group to an electron-donating group. The Hammett plots for reactions of 4a-4f are linear with ρX=1.87 and 0.56 for the S-O and C-O bond fission, respectively. The fact that the substituent X is further away from the reaction site of the C-O bond fission than that of the S-O bond fission is one reason for the smaller ρX value. The nature of the reaction mechanism (i.e., a stepwise mechanism in which expulsion of the leaving group occurs after the rate-determining step) is also responsible for the smaller ρX value obtained from the C-O bond fission. The Bronsted-type plot for the reactions of 5a-5f is linear with βlg=-0.63, which is typical for reactions reported previously to proceed through a concerted mechanism. Effects of substituents X and Y on regioselectivity and reaction mechanism are discussed in detail.

Nucleophilic substitution reactions of 5-XC4H2(S)C(O)OC6H3-2-Y-4-NO2 (1) promoted by 4-Z-C6H4O-/4-Z-C6H4OH in 20 mol % dimethyl sulfoxide (DMSO)(aq) have been studied kinetically. The reactions exhibited second-order kinetics with βacyl = -2.52 to -2.83, ρ(x) = 2.81-3.16, βnuc = 0.88-0.04 and βlg = -0.94, respectively. The results have been interpreted with an addition-elimination mechanism in which the nucleophilic attack occurs in the rate-determining step. Comparison with existing data reveals that the ratedetermining step changes from the second to the first step by the change in the nucleophile from R2NH/R2NH2+ to 4-Z-C6H4O-/4-Z-C6H4OH.

Vanadium pentoxide is used as an efficient catalyst for regioselective nitration of aromatic compounds under conventional and nonconventional conditions such as ultrasonically assisted (USAR) and microwave-assisted reactions (MWAR). The reactions underwent smoothly and afforded good yields of products with high regioselectivity. Observed longer reaction times (about 8 h) in V2O5 catalyzed reactions reduced to (0.5/30 min) under sonication and (90 s) in the case of MWAR. When ortho position is blocked, para derivatives are obtained as end products while ortho nitro products are obtained when para position is blocked.

The heterodinuclear mixed-valence complex [FeMn(ICIMP)(OAc)2Cl] (1) {H2ICIMP = 2-(N-carboxylmethyl)-[N-(N-methylimidazolyl-2-methyl) aminomethyl]-[6-(N-isopropylmethyl)-[N-(N-methylimidazolyl-2-methyl)] aminomethyl-4-methylphenol], an unsymmetrical N4O2 donor ligand} has been synthesized and fully characterized by several spectroscopic techniques as well as by X-ray crystallography. The crystal structure of the complex reveals that both metal centers in 1 are six-coordinate with the chloride ion occupying the sixth coordination site of the MnII ion. The phenoxide moiety of the ICIMP ligand and both acetate ligands bridge the two metal ions of the complex. M?ssbauer spectroscopy shows that the iron ion in 1 is high-spin FeIII. Two quasi-reversible redox reactions for the complex, attributed to the FeIIIMnII/Fe IIMnII (at -0.67 V versus Fc/Fc+) and Fe IIIMnII/FeIIIMnIII (at 0.84 V), were observed by means of cyclic voltammetry. Complex 1, with an Fe III-MnII distance of 3.58 ?, may serve as a model for the mixed-valence oxidation state of purple acid phosphatase from sweet potato. The capability of the complex to effect organophosphate hydrolysis (phosphatase activity) has been investigated at different pH levels (5.5-11) by using bis(2,4-dinitrophenyl)phosphate (BDNPP) as the substrate. Density functional theory calculations indicate that the substrate coordinates to the MnII ion. In the transition state, a hydroxide ion that bridges the two metal ions becomes terminally coordinated to the FeIII ion and acts as a nucleophile, attacking the phosphorus center of BDNPP with the concomitant dissociation of the leaving group. Copyright

A kinetic study is reported for the SNAr reaction of 1-Y-substituted- phenoxy-2,4-dinitrobenzenes (1a-1h) with OH- in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The second-order rate constant (kOH-) increases as the substituent Y in the leaving group changes from an electron-donating group (EDG) to an electronwithdrawing group (EWG). The Bronsted-type plot for the reactions of 1a-1h is linear with βlg = -0.16, indicating that the reactivity of substrates 1a-1h is little affected by the leaving-group basicity. A linear Bronsted-type plot with βlg = -0.3 ± 0.1 is typical for reactions reported previously to proceed through a stepwise mechanism in which formation of a Meisenheimer complex is the rate-determining step (RDS). The Hammett plot correlated with σY o constants results in a much better correlation than that correlated with σY - constants, implyng that no negative charge is developing on the O atom of the leaving group (or expulsion of the leaving group is not advanced at all in the TS). This excludes a possibility that the SNAr reaction of 1a-1h with OH- proceeds through a concerted mechanism or via a stepwise pathway with expulsion of the leaving group being the RDS. Thus, the current reactions have been concluded to proceed through a stepwise mechanism in which expulsion of the leaving group occurs rapidly after the RDS.

Ketene-forming elimination from 2-X-4-nitrophenyl furylacetates (1a-d) promoted by r2NH-r2NH2 + in 70 mol % MeCN(aq) has been studied kinetically. When X = Cl and NO2, the reactions exhibited second-order kinetics as well as Broensted β = 0.37-0.54 and |βlg| = 0.31-0.45. The Broensted β decreased with a poorer leaving group and |βlg| increased with a weaker base. The results are consistent with an E2 mechanism. When the leaving group was changed to a poorer one [X= H (1a) and OCH3 (1b)], the reaction mechanism changed to the competing E2 and E1cb mechanisms. A further change to the E1cb mechanism was realized for the reaction of 1a with i-Pr2NH/i-Pr2NH2 + in 70 mol % MeCN-30 mol % D2O. By comparing the kinetic results in this study with the existing data for ArCH2C(O)OC6H3-2-X-4-NO 2, the effect of the β-aryl group on the ketene-forming elimination was assessed.

An aqueous solution of sodium dodecylsulfate in the presence of dilute nitric acid at room temperature works as a mild medium for the nitration of aromatic compounds with high regioselectivity.

Notwithstanding its half-life of 70 years at 25 C, the spontaneous hydrolysis of the anion of di-2-pyridyl phosphate (DPP) is thousands of times faster (ca. 3000 at 100 C, over 10000-fold at 25 C) than expected for a diester with leaving groups of pKa 9.09. The kinetic parameters do not permit a conclusive choice between five possible mechanisms considered, but the combination of kinetics and calculational evidence supports a single-step, concerted, SN2(P) mechanism involving the attack of solvent water on phosphorus assisted by intramolecular catalysis by a (weakly basic) pyridine nitrogen acting as a general base. Catalysis is relatively efficient for this mechanism, with an estimated effective molarity (EM) of the general base of >15 M, consistent with the absence of catalysis by typical buffers. Further new results confirm that varying the nonleaving group has minimal effect on the rate of spontaneous diester hydrolysis, in striking contrast to the major effect on the corresponding reaction of triesters: though protonation of one nitrogen of DPP- increases the rate of hydrolysis by 6 orders of magnitude, in line with expectation.

Complexation of dimethyl-6,6′-(2-hydroxy-5-methyl-1,3-phenylene) bis(methylene)bis((2-hydroxyethyl)azanediyl)bis(methylene)dipicolinate (Me 2H3L4) and 2,2′-(2-hydroxy-5-methyl-1,3-phenylene) bis(methylene)bis(((6-methylpyridin-2-yl)methyl)azanediyl)diethanol (H 3L5) with Zn(II) afforded the complexes [Zn2(H 2L4)(H2O)2](ClO4) and [Zn 2(H2L5)(CH3CO2)(H 2O)](PF6)2·2H2O, which were characterized by 1H and 13C NMR spectroscopy, mass spectrometry, microanalysis, and the former by X-ray crystallography. Functional studies of the zinc complexes with the substrate bis(2,4-dinitrophenyl) phosphate (BDNPP) showed the complexes to be competent catalysts with k cat = 3.52 ± 0.03 × 10-4 and 1.27 ± 0.04 × 10-3 s-1 (Km = 6.7 ± 0.9; 13.8 ± 1.5 mM), with catalytically relevant pKas of 9.4 and 6.6, respectively. The pKa values are discussed with respect to the potential nucleophilic species and the effect of the donor environment.

Elimination reactions of (E)-2,4-(NO2)2C 6H2CH=NOC6H3-2-X-4-NO2 (1a-e) promoted by R3N/R3NH+ in 70 mol % MeCN(aq) have been studied kinetically. The reactions are second-order and exhibit Broensted β = 0.80- 0.84 and |βlg| = 0.39-0.42, respectively. For all leaving groups and bases employed in this study, the β and |βlg| values remained almost the same. The results can be described by a negligible pxy interaction coefficient, pxy = δβ/pKlg = δβlg/pK-azip 0, which describes the interaction between the base catalyst and the leaving group. The negligible pxy interaction coefficient is consistent with the (E1cb) irr mechanism. Change of the base-solvent system from R 3N/MeCN to R3N/R3NH+-70 mol % MeCN(aq) changed the reaction mechanism from E2 to (E1cb)irr. Noteworthy was the relative insensitivity of the transition state structure to the reaction mechanism change.

The dinuclear complex [Zn2(papy)2]·2CH 3OH [H2papy = N-(2-hydroxybenzyl)-N-(2-picolyl)glycine] was synthesized and characterized. The crystal structure of the complex reveals that both ZnII ions are pentacoordinate with distorted pentagonal bipyramidal coordination arrangements. The phenoxyl groups of each ligand bridge the two metal atoms, whereas each carboxylate of the ligand is terminally bound to one ZnII ion. Potentiometric studies of the Zn II:H2papy system in a methanol/water mixture show the existence of a mononuclear species at lower pH; but at a pH above 5, a dimeric species starts to dominate and transforms further into a bis(μ-phenoxo) bridged dizinc complex by deprotonation of phenolic hydrogen. A kinetic study of the hydrolysis of bis(2, 4-dinitrophenyl)phosphate at different pH, catalyzed by complex 1, indicates a maximum rate at pH 9, where the bis(μ-phenoxo)- bridged dizinc species corresponding to 1 dominates in solution. Copyright

The reactions of the title compounds with phenoxides, secondary alicyclic (SA) amines, and pyridines, in 44 wt% ethanol-water, at 25°C and an ionic strength of 0.2 M, were subjected to kinetic and product studies. From analytical techniques (HPLC and NMR), two pathways were detected (nucleophilic attack at the phosphoryl center and at the C-1 aromatic carbon) for the reactions of all the nucleophiles with the phosphate (2) and for the pyridinolysis of the thionophosphate (1). Only aromatic nucleophilic substitution was found for the reactions of 1 with phenoxides and SA amines. For the dual reactions, the nucleophilic rate constants (kN) were separated in two terms: documentclass{article}usepackage{amssymb} pagestyle{empty}begin{document}k-{rm N}^{rm P}end{document} and documentclass{article}usepackage{amssymb}pagestyle{empty}begin{document}k-{ rm N}^{{rm Ar}}end{document}, which are the rate constants for the corresponding electrophilic centers. The absence of a break in the Bronsted-type plots for the attack at P is consistent with concerted mechanisms. The Bronsted slopes, βAr 0.32-0.71, for the attack at the aromatic C-1, are in agreement with stepwise mechanisms where formation of a Meisenheimer complex is the rate-determining step. 2013 Wiley Periodicals, Inc. Int J Chem Kinet 45: 202-211, 2013 Copyright

Background The commercially important glycoside hydrolase family 3 (GH3) β-glucosidases from Aspergillus niger are anomeric-configuration-retaining enzymes that operate through the canonical double-displacement glycosidase mechanism. Whereas the catalytic nucleophile is readily identified across all GH3 members by sequence alignments, the acid/base catalyst in this family is phylogenetically variable and less readily divined. Methods In this report, we employed three-dimensional structure homology modeling and detailed kinetic analysis of site-directed mutants to identify the catalytic acid/base of a GH3 β-glucosidase from A. niger ASKU28. Results In comparison to the wild-type enzyme and other mutants, the E490A variant exhibited greatly reduced k cat and kcat/Km values toward the natural substrate cellobiose (67,000- and 61,000-fold, respectively). Correspondingly smaller kinetic effects were observed for artificial chromogenic substrates p-nitrophenyl β-d-glucoside and 2,4-dinitrophenyl β-d-glucoside, the aglycone leaving groups of which are less dependent on acid catalysis, although changes in the rate-determining catalytic step were revealed for both. pH-rate profile analyses also implicated E490 as the general acid/base catalyst. Addition of azide as an exogenous nucleophile partially rescued the activity of the E490A variant with the aryl β-glucosides and yielded β-glucosyl azide as a product. Conclusions and general significance These results strongly support the assignment of E490 as the acid/base catalyst in a β-glucosidase from A. niger ASKU28, and provide crucial experimental support for the bioinformatic identification of the homologous residue in a range of related GH3 subfamily members.