Antipyrilquinoneimine dye formation by coupling aniline derivatives with 4-aminoantipyrine in the presence of ruthenium nanoparticles

The coupling of 4-aminoantipyrine (4-AAP) with aniline derivatives catalyzed by ruthenium nanoparticles (Rnp) has been studied by UV-Vis spectroscopy in aqueous medium. The rate constant for antipyrilquinoneimine dye formation depends on the nature of the aniline substituent and the pH, ionic strength and temperature of the reaction medium. The maximum rate constant of the dye formation reaction is observed at pH 3.6. Aniline derivatives with electron donating substituents show higher rate constant values than those with electron withdrawing substituents, with increasing rate constant values in the order: N,N-dimethyl aniline > o-toluidine > o-chloroaniline > m-chloroaniline. With pseudo first order kinetics, the total order is 1.0 + 1.0 + 1.0 = 3.0, which includes the orders with respect to amine, 4-AAP and Rnp. Studies on these effects help to complete the kinetic analysis as well as propose the reaction pathway. Furthermore, TEM measurement confirms that the nanoscalar size of the Rnp is 7 nm.     

Electrocatalytic oxidation of methanol on carbon ceramic electrode modified by platinum nanoparticles incorporated in poly (o-phenylenediamine) film

Carbon ceramic electrode, a new electrode substrate, was prepared by sol–gel procedure and used for the electropolymerization of o-phenylenediamine and incorporation of platinum nanoparticles into the resulting poly(o-phenylenediamine) (PoPD) film. The modified electrode was used for electrooxidation of methanol in 0.3 M H₂SO₄ as supporting electrolyte. The presence of PoPD film increased considerably the efficiency of deposited Pt nanoparticles toward the electrocatalytic oxidation of methanol. The effective parameters on the electrooxidation of methanol, i.e., amounts of polymer and Pt catalyst, medium temperature, working potential limit in anodic direction, and potential scan rate, were investigated, and the results were discussed.     

Nitrosation kinetics of phenolic components of foods and beverages

The kinetics of the reactions between sodium nitrite and phenol or m-, o-, or p-cresol in potassium hydrogen phthalate buffers of pH 2.5–5.7 were determined by integration of the monitored absorbance of the C-nitroso reaction products. At pH > 3, the dominant reaction was C-nitrosation through a mechanism that appears to consist of a diffusion-controlled attack on the nitrosatable substrate by NO⁺/NO₂H₂⁺ ions followed by a slow proton transfer step; the latter step is supported by the observation of basic catalysis by the buffer which does not form alternative nitrosating agents as nitrosyl compounds. The catalytic coefficients of both anionic forms of the buffer have been determined. The observed order of substrate reactivities (o-cresol ≈ m-cresol > phenol ≫ p-cresol) is explained by the hyperconjugative effect of the methyl group in o- and m-cresol, and by its blocking the para position in p-cresol. Analysis of a plot of ΔH^# against ΔS^# shows that the reaction with p-cresol differs from those with o- and m-cresol as regards the formation and decomposition of the transition state. The genotoxicity of nitrosatable phenols is compared with their reactivity with NO⁺/NO₂H₂⁺. © 1997 John Wiley & Sons, Inc.     

Sorption of Th(IV) on MX-80 bentonite: effect of pH and modeling

MX-80 bentonite was characterized by XRD and FTIR in detail. The sorption of Th(IV) on MX-80 bentonite was studied as a function of pH and ionic strength in the presence and absence of humic acid/fulvic acid. The results indicate that the sorption of Th(IV) on MX-80 bentonite increases from 0 to 95% at pH range of 0–4, and then maintains high level with increasing pH values. The sorption of Th(IV) on bentonite decreases with increasing ionic strength. The diffusion layer model (DLM) is applied to simulate the sorption of Th(IV) with the aid of FITEQL 3.1 mode. The species of Th(IV) adsorbed on bare MX-80 bentonite are consisted of “strong” species o \textYOHTh^{4 +} \equiv {\text{YOHTh}}^{4 + } at low pH and “weak” species o \textXOTh(OH)₃ \equiv {\text{XOTh(OH)}}_{3} at pH > 4. On HA bound MX-80 bentonite, the species of Th(IV) adsorbed on HA-bentonite hybrids are mainly consisted of o \textYOThL₃ \equiv {\text{YOThL}}_{3} and o \textXOThL₁ \equiv {\text{XOThL}}_{1} at pH < 4, and o \textXOTh(OH)₃ \equiv {\text{XOTh(OH)}}_{3} at pH > 4. Similar species of Th(IV) adsorbed on FA bound MX-80 bentonite are observed as on FA bound MX-80 bentonite. The sorption isotherm is simulated by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models, respectively. The sorption mechanism of Th(IV) on MX-80 bentonite is discussed in detail.     

Efficient resonance energy transfer from dye to Au@SnO2 core–shell nanoparticles

The present study reports the shell thickness dependence fluorescence resonance energy transfer between Rhodamine 6G dye and Au@SnO₂ core–shell nanoparticles. There is a pronounced effect on the PL quenching and shortening of the lifetime of the dye in presence of Au@SnO₂ core–shell nanoparticles. The calculated energy transfer efficiencies from dye to Au@SnO₂ are 64.4% and 78.3% for 1.5 nm and 2.5 nm thickness of shell, respectively. Considering the interactions of single acceptor and multiple donors, the calculated average distances (r_n) are 75.8 and 71.5 Å for 1.5 nm and 2.5 nm thick core–shell Au@SnO₂ nanoparticles, respectively.     

Green synthesis of copper oxide nanoparticles CuO NPs from Eucalyptus Globoulus leaf extract: Adsorption and design of experiments

The study is concerned with synthesizing copper oxide nanoparticles with leaf extract Eucalyptus Globoulus. The results of scanning electron microscopy (SEM) and dynamic light scattering (DLS) revealed that the green synthesized copper oxide nanoparticles are spherical and have a mean particle size of 88 nm, with a negative zeta potential of ?16.9 mV. The XRD graph showed the crystalline and monoclinic phases of CuO nanoparticles. The average crystalline size around 85.80 nm was observed by the Debye–Scherrer formula. The adsorption characteristics of the nano-adsorbents were investigated using methyl orange, and the adsorption efficiency at room temperature attained 95 mg/g. Copper oxide nanoparticles (CuO NPs) adsorb methyl orange dye most effectively at pH 4.5 when the dye is applied in quantities of 0.04 g/50 mL. Box–Behnken design (BBD) in response surface methodology (RSM) was used to optimize various process parameters, such as pH solution (X₁: 2 – 11), adsorbing dose (X₂: 0.01 – 0.08 g/L), [MO] dye concentration (X₃: 10 – 80 mg/L). Overall, the adjusted coefficient of determination (R²) value of 0.99 demonstrated that the used model was quite appropriate, and the chosen RSM was effective in optimization the decolorization conditions of MO.     

Spectral studies of N-nonyl acridine orange in anionic, cationic and neutral surfactants

The spectroscopic and photophysical properties of N-nonyl acridine orange – a metachromatic dye useful as a mitochondrial probe in living cells – are reported in water and microheterogeneous media: anionic sodium dodecylsulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB) and neutral octylophenylpolyoxyethylene ether (TX-100). The spectral changes of N-nonyl acridine orange were observed in the presence of varying amount of SDS, CTAB and TX-100 and indicated formation of a dye–surfactant complex. The spectral changes were also regarded to be caused by the incorporation of dye molecules to micelles. It was proved by calculated values K_b and f in the following order: K_b TX-100 > K_b CTAB > K_b SDS and f_TX-100 > f_CTAB > f_SDS. NAO binds to the micelle regardless the micellar charge. There are two types of interactions between NAO and micelles: hydrophobic and electrostatic. The hydrophobic interactions play a dominant role in binding of the dye to neutral TX-100. The unexpected fact of the binding NAO to cationic CTAB can be explained by a dominant role of hydrophobic interactions over electrostatic repulsion. Therefore, the affinity of NAO to CTAB is smaller than TX-100. Electrostatic interactions play an important role in binding of NAO to anionic micelles SDS. We observed a prolonged fluorescence lifetime after formation of the dye–surfactant complex τ_SDS > τ_TX-100 > τ_CTAB > τ_water, the dye being protected against water in this environment. TX-100 is found to stabilize the excited state of NAO which is more polar than the ground state. Spectroscopic and photophysical properties of NAO will be helpful for a better understanding of the nature of binding and distribution inside mammalian cells.     

Kinetics of the Anaerobic Reaction of para‐Substituted Phenols with Nitrogen Dioxide

para‐Substituted phenols in aqueous solution under anaerobic conditions readily react with nitrogen dioxide (NO₂^●) over a wide range of experimental conditions. The rate and rate law of the process were dependent on phenol concentration and solution pH. The kinetic order in phenol changed from one (low concentration) to zero (high concentration), a result attributable to total NO₂^● capture. Initial consumption rate (r ₀) of phenols versus pH plots showed parabolic behavior with a minimum rate at pH ca. 5. On the other hand, the maximum rate took place at high pH (pH>10) and involved the protonated phenols. The reaction rate of para‐substituted phenols with NO₂^● correlated with the bond dissociation energy and with Hammett's parameter. Based on such results and also supported by analysis of products carried out by HPLC‐MS/MS, our data conclusively show that, in spite of the fast acid–base interchanges of phenols and the interconversion of the different nitrogen oxides, the mechanisms of phenols nitration mediated by NO₂^● or HONO are clearly different.     

Underpotential deposition of cobalt onto polycrystalline platinum

An electrochemical study of cobalt electrodeposition onto a polycrystalline platinum electrode from an aqueous solution (10⁻² M CoCl₂ + 1 M NH₄Cl (pH 9.5)) was carried out through cyclic voltammetry and potential step techniques. Analysis of the voltammetric data clearly showed that a cobalt adlayer is formed during the application of potential in the underpotential deposition (upd) region. Formation of this cobalt adlayer involved the simultaneous presence of both adsorption and 2D nucleation processes. Cobalt adlayers obtained by linear voltammetry in upd region were analyzed employing diffuse reflectance spectroscopy (DRS). By using theoretical quantum studies at PM6//HF/LANL1MB level, it was possible to assign the peaks obtained by DRS at 328 and 337 nm to the cobalt adsorption on Pt(111) and Pt(100), respectively, while the signals recorded at 355 and 362 nm were related with the clean platinum surfaces Pt(100) and Pt(111). Also, quantum calculations at the PM6 level indicated that the energy formation order is Co-Pt(100) > Co-Pt(111) > Co-Pt(110) > Co-Co(surface).     

Photodegradation of toluic acid isomers by UV/TiO2

This work elucidates the photodegradation of toluic acid isomers by UV/TiO₂. Effects of the toluic acid isomers, pH and form of TiO₂ on photodegradation are identified. The rate of photodegradation of toluic acid isomers in UV/TiO₂ obey the sequence p > o > m. Additionally, the reaction rates under acidic conditions exceed those under neutral and alkaline conditions.     

Electrochemical Studies on <Emphasis Type="Italic">cis</Emphasis>-[Cr<Superscript>III</Superscript>(bipy)<Subscript>2</Subscript>(SCN)<Subscript>2</Subscript>]I<Subscript>3</Subscript> (Where bipy Denotes 2,2′-Bipyridine) in Acetonitrile

The molar conductivities (Λ) of solutions of bis(2,2′-bipyridine)bis(thiocyanate)chromium(III) triiodide [Cr^III(bipy)₂(SCN)₂]I₃ (where bipy denotes 2,2′-bipyridine, C₁₀H₈N₂), [ _3^-\mathrm{A}^{+}\mathrm{I}_{3}^{-} ], were measured in acetonitrile (ACN) at the temperatures 294.15, 299.15, and 305.15 K. In addition, cyclic voltammograms (CVs) of [ A⁺I₃^-\mathrm{A}^{+}\mathrm{I}_{3}^{-} ] were recorded on platinum, gold, and glassy carbon working electrodes in ACN, using n-tetrabutylammonium hexafluorophosphate (NBu₄PF₆) as the supporting electrolyte, at scan rates (v) ranging from 0.05 to 0.12 V⋅s⁻¹. Furthermore, electrochemical impedance spectroscopic (EIS) measurements were carried out in the frequency range 50 Hz<f<50 kHz using these three working electrodes. The measured molar conductivities (Λ) demonstrate that [ A⁺I₃^-\mathrm{A}^{+}\mathrm{I}_{3}^{-} ] behaves as uni-univalent electrolyte in ACN over the investigated temperature range. The Λ values were analyzed by means of the Lee-Wheaton conductivity equation in order to estimate the limiting molar conductivities (Λ _o), as well as the thermodynamic association constants (K _A), at each experimental temperature for formation of [A⁺ I₃^-\mathrm{I}_{3}^{-} ] ion-pairs. The limiting ionic conductivities ( l_±^o\lambda_{\pm}^{\mathrm{o}} ), the diffusion coefficients at infinite dilution (D _±), as well as the Stokes’ radii (r _St) were determined for both A⁺ and I₃^-\mathrm{I}_{3}^{-} ions. The thermodynamic parameters for the ionic association process, i.e. the Gibbs energy ( DG_A^o\Delta G_{\mathrm{A}}^{\mathrm{o}} ), enthalpy ( DH_A^o\Delta H_{\mathrm{A}}^{\mathrm{o}} ), and entropy ( DS_A^o\Delta S_{\mathrm{A}}^{\mathrm{o}} ), were also determined. The mobility and diffusivity of the A⁺ ion increase linearly with increasing temperature because the solvent medium becomes less viscous as the temperature increases. The K _A values indicate that significant ion association occurs that is not influenced by temperature changes. The ion-pair formation process is exothermic ( DH_A^o < 0\Delta H_{\mathrm{A}}^{\mathrm{o}}<0 ), leading to the generation of additional entropy ( $\Delta S_{\mathrm{A}}^{\mathrm{o}}>0$\Delta S_{\mathrm{A}}^{\mathrm{o}}>0 ). As a result, the Gibbs energy DG_A^o\Delta G_{\mathrm{A}}^{\mathrm{o}} is negative ( DG_A^o < 0\Delta G_{\mathrm{A}}^{\mathrm{o}}<0 ) and the formation of [A⁺I₃^-][\mathrm{A}^{+}\mathrm{I}_{3}^{-}] becomes favorable. CV studies on [A⁺I₃^-][\mathrm{A}^{+}\mathrm{I}_{3}^{-}] solutions indicated that the redox pair Cr^3+/2+ appears to be quasi-reversible on a glassy carbon electrode but is completely irreversible on platinum and gold electrodes. EIS experiments confirm that, among these three electrodes, the glassy carbon working electrode has the smallest resistance to electron transfer.     

Thermodynamics of citrate complexation with Mn<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> ions

Isothermal titration calorimetry has been used to determine the stoichiometry, formation constants and thermodynamic parameters (ΔG ^o, ΔH, ΔS) for the formation of the citrate complexes with the Mn²⁺, Co²⁺, Ni²⁺ and Zn²⁺ ions. The measurements were run in Cacodylate, Pipes and Mes buffer solutions with a pH of 6, at 298.15 K. A constant ionic strength of 100 mM was maintained with NaClO₄. The influence of a metal ion on its interaction energy with the citrate ions and the stability of the resulting complexes have been discussed.     

Synthesis,kinetics, and mechanism for adduct formation of tetraaza Schiff base cobalt(II) complexes with diorganotin(IV)dichlorides in dimethylformamide solvent

The kinetics and mechanism of the adduct formation of diorganotin(IV)dichlorides with Co(II) tetraaza Schiff base complexes, such as [Co(ampen)] {[N,N′‐ethylenebis‐(o‐amino‐α‐phenylbenzylideneiminato)cobalt(II)]}, [Co(campen)] {[N,N′‐ethylenebis‐(5‐chloro‐o‐amino‐α‐phenylbenzylideneiminato)cobalt(II)]}, and [Co(amaen)] {[N,N′‐ethylenebis‐(o‐amino‐α‐methylbenzylideneiminato)cobalt(II)]}, were studied spectrophotometrically. The kinetic parameters and the rate constant values show the following acceptor tendency trend for the diorganotin(IV)dichlorides: Ph₂SnCl₂> Me₂SnCl₂> Bu₂SnCl₂. Adducts have been separately synthesized and fully characterized by ¹¹⁹SnNMR, IR, UV–vis spectra, and elemental microanalysis (C,H,N) methods. The trend of the rate constants for the adduct formation of the cobalt complexes with a given tin acceptor decreases as follow: Co(amaen) > Co(ampen) > Co(campen). The linear plots of k_obs vs. the molar concentration of the diorganotin(IV)dichlorides, the high span of the second‐order rate constant k₂ values, and the large negative values of AS^≠ suggest an associative (A) mechanism for the acceptor–donor adduct formation. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 499–507, 2010     

Synthesis and characterization of WO3 nanoparticles prepared by the precipitation method: Evaluation of photocatalytic activity under vis-irradiation

WO₃ nanoparticles were synthesized by the precipitation method varying the time employed in the formation of their precursor in aqueous media and the calcination temperature. The WO₃ crystallization process and morphology of the synthesized samples were followed by the XRD, TEM and SEM techniques. The effects of the calcination temperature on the surface area and optical properties of the WO₃ nanoparticles were also investigated. Nanoparticles with morphologies such as square and rectangular plates and ovoid forms were observed for the different experimental conditions. WO₃ nanoparticles with different morphologies were tested for the photocatalytic degradation of organic dyes. In general, the photocatalysts showed a capacity to bleach the dye solution in the following sequence: indigo carmine (IC) > rhodamine B (rhB) > congo red (CR). The extent of mineralization was determined by means of total organic carbon (TOC) measurements, which showed a satisfactory TOC reduction (93%, within 75 h) only for IC. This value was even better than the one concerning the P-25 Degussa reference.     

A one-step,clean, capping-agent-free electrochemical approach to prepare Pt nanoparticles with preferential (100) orientation and their high electrocatalytic activities

A clean and simple electrodeposition method without the use of any organic additives has been reported to prepare platinum nanoparticles with preferential (100) orientation directly on the conductive substrate. The formation of platinum nanoparticles exposing (100) facets was confirmed by electrochemical methods and high-resolution transmission electron microscopy. The fraction of Pt (100) sites increases as the electrodeposition current density increases from 0.2 to 10 mA cm^− 2. Furthermore, as the Pt (100) fraction increases, the specific activity of the Pt particles for ammonia oxidation increases obviously.     

Multifunctional Zn0.3Al0.4O4.5 crystals: An efficient photocatalyst for formaldehyde degradation and EBT adsorption

The Zn_0.3Al_0.4O_4.5 nanoparticles (ZnAlONPs) with size of 70–90 nm are used as an efficient photocatalyst for formaldehyde (HCHO) degradation and effective adsorbent for the removal of eriochrome black-T (EBT) dye from synthetic aqueous solution. Degradation of HCHO reactions were studied using TiO₂ (homemade), TiO₂ (P-25) and ZnAlONPs by irradiating under 18 W daylight lamp source for photocatalytic degradation. The HCHO degradation rate is about 67, 76 and 89% for TiO₂ (homemade), TiO₂ (P25) and ZnAlONPs during 2 h reaction, respectively at initial formaldehyde gas concentration of 20 ppm. Maximum adsorption capacity was optimized by changing the parameters such as pH, EBT concentration and adsorbent dosage. A  200 mg of ZnAlONPs are useable for quick removal of EBT (>95%). Langmuir isotherm model showed a maximum adsorption capacity of 90.90 mgg⁻¹. The ZnAlONPs could be successfully reused upto 5^th adsorption/desorption cycle for EBT dye removal from water samples.     

Prednisone/Cyclodextrin Inclusion Complexation: Phase Solubility,Thermodynamic, Physicochemical and Computational Analysis

Guest–host interaction of prednisone (PN) with cyclodextrins (CDs) have been investigated using phase solubility diagrams (PSD), differential scanning calorimetry (DSC), X-ray powder diffractometry (XRPD), scanning electron microscopy (SEM) and molecular mechanical modeling (MM). Estimates of the complex formation constant (K ₁₁) show that the tendency of PN to complex with CDs follows the order: β-CD>γ-CD>HP-β-CD>α-CD. At the same pH of 7.0, β-CD forms soluble 1:1 and insoluble 1:2 PN/CD complexes (B_S-type PSDs). The thermodynamic functions for 1:1 PN/β-CD estimated at pH = 7.0 (ΔG ₁₁^o=−20.8 kJ⋅mol⁻¹) show that complexation is driven by enthalpy (−30.7 kJ⋅mol⁻¹) but retarded by entropy (ΔS ₁₁^o=−33.1 J⋅mol⁻¹⋅K⁻¹) changes. The MM modeling study indicates the formation of different isomeric 1:1 complexes with CDs. PSD, DSC, XRPD, SEM and MM studies established the formation of inclusion complexes in solution and the solid state.     

Solvent effect on the size of platinum nanoparticle synthesized in microemulsion systems

In this research work, the effect of solvent on the size of paltinum nanoparticles synthesized by microemulsion method was investigated. Platinum nanoparticles have been prepared by the reduction of H₂PtCl₆ with hydrazine in water-in-oil (w/o) microemulsions consisting of sodium bis(2-ethylhexyl) sulfo-succinate (AOT) and solvents n-hexane, cyclohexane and n-nonane. The size of the platinum nanoparticles was measured using transmission electron microscopy (TEM). It was verified that, for reduction of H₂PtCl₆ by hydrazine in microemulsion with different organic solvents, the solvents are arranged by their influence on nanoparticle sizes as follows: n-nonane > cyclohexane > n-hexane.     

Electrochemical behavior of catechol in the presence of 2-methyl-1,3-cyclopentanedione: application to electrosynthesis

Abstract  Electro-oxidation of catechol in the presence of 2-methyl-1,3-cyclopentanedione as a nucleophile was investigated in water–acetonitrile (90:10 v/v) solution. The results indicate that the o-benzoquinone electrogenerated participates in a Michael addition reaction with this nucleophile. The electrosynthesis of 2-(3,4-dihydroxyphenyl)-2-methylcyclopentane-1,3-dione was carried out. The product was characterized by NMR, MS, FT-IR, and elemental analysis. An EC mechanism was deduced from voltammetric and spectroscopic data. Also, the Michael addition reaction rate constant (k _m) was estimated using digital simulation of voltammograms. Graphical abstract   Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis of Fused Oxazolocoumarins from o‐Hydroxynitrocoumarins and Benzyl Alcohol Under Gold Nanoparticles or FeCl3 Catalysis

Synthesis of fused oxazolocoumarins has been achieved from the one‐pot tandem reactions of o‐hydroxynitrocoumarins with benzyl alcohol in toluene under catalysis in a sealed tube at 150°C. The catalysis was performed by gold nanoparticles supported on TiO₂ (0.4 mol% Au) or FeCl₃ (5%) or silver nanoparticles supported on TiO₂ (1.7 mol% Ag).