Improving sono-activated persulfate oxidation using mechanical mixing in a 35-kHz ultrasonic reactor: Persulfate activation mechanism and its application

This study investigated the degradation of ibuprofen (IBP), an activated persulfate (PS), when subjected to ultrasonic (US) irradiation and mechanical mixing (M). The effects of several critical factors were evaluated, including the effect of rpm on M, PS concentration, and initial pH, and that of temperature on IBP degradation kinetics and the PS activation mechanism. The resulting IBP oxidation rate constant was significantly higher at 400 rpm. As the PS load increased, the IBP oxidation rate constant increased. The value of the IBP reaction rate increased with decreasing pH; below pH 4.9, there was no significant difference in the IBP oxidation rate constant. The IBP oxidation activation energy when using the US/M-PS system was 18.84 kJ mol⁻¹. In the US/M-PS system, PS activation was the primary effect of temperature at the interface during the explosion of cavitation bubbles. These encouraging results suggest that the US-PS/M process is a promising strategy for the treatment of IBP-based water pollutants.     

Reactivity of 2‐aryl‐1,3‐dithiane anions towards neopentyl,neophyl and phenyl iodides. New evidence for an SRN1 mechanism

The reactions of 2‐(4‐Z‐phenyl)‐1,3‐dithiane anions (Z = H, OMe, Cl, CN) with neopentyl, neophyl and phenyl iodides were studied in DMSO, taking into consideration the effect of the Z substituent on the dithiane anions reactivity as well as on the product distribution. These substitution reactions proceed by an S_RN1 mechanism with radicals and radical anions as intermediates. Two competitive pathways are possible for the radical anion of the substitution product, namely electron transfer (ET) to the substrate giving the substitution product and C–S bond fragmentation to yield a distonic radical anion. ET is the main pathway for the reactions between dithiane anions bearing electron‐donor substituents and neopentyl or its analogue iodides affording the substitution products in moderate yields (41–53%). Copyright © 2011 John Wiley & Sons, Ltd.     

Spectroscopic Study of 2-(2-pyridyliminomethyl)phenol as a Novel Fluorescent Probe for Superoxide Anion Radicals and Superoxide Dismutase Activity

A novel spectrofluorometric method, using 2-(2-pyridyliminomethyl)phenol as a fluorescent probe, was developed for the determination of superoxide anion radical (O₂ ^•−) and superoxide dismutase activity (SOD). The new fluorescent probe was synthesized and characterized with elemental analysis and IR spectra. It was oxidized by O₂ ^•− to form a less fluorescence product. Based on this reaction, a spectrofluorometric method was proposed and successfully used to determine superoxide anion radicals and SOD activity. The effects of interferences were studied. The reaction was simple, precise and sensitive. It was applied to determine SOD activity in garlic, papaya and spinach successfully.     

Comparison of Trifluoroacetyl Monostyryl and Distyryl Dyes: Effects of Chromophore Elongation on the Spectral Properties and Chemical Reactivity

The trifluoroacetyl distyryl derivative 1-[4-(2-{4-[2-(4-dibutylaminophenyl)-vinyl]-phenyl}-vinyl)-phenyl]-2,2,2-trifluoroethanone was compared with the related monostyryl derivative 1-{4-[2-(4-dibutylaminophenyl)-vinyl]-phenyl}-2,2,2-trifluoroethanone with respect to spectral properties and sensitivity to amines. Both trifluoroacetyl derivatives had their absorbance maximum at around 445 nm. The fluorescence of the distyryl dye, however, was observed at significantly longer wavelengths than that of the monostyryl dye, indicating the effect of structural extension of the chromophore system. Furthermore, the distyryl dye exhibited significantly smaller quantum yields in polar solvents than the monostyryl dye.Both dyes were capable of chemically reacting with amines in that their trifluoroacetyl function was converted into a hemiaminal. Consequently, absorbance and fluorescence of both dyes were shifted to shorter wavelengths. The positions of the fluorescence maxima of the spectra when converting from trifluoroacetyl to hemiaminal form were shifted by an almost identical amount for both mono- and distyryl derivative. The hemiaminal form of the distyryl derivative, however, exhibited much larger quantum yields in both polar and nonpolar solvents than the hemiaminal form of the monostyryl dye. The structural extension of the chromophore affected the sensitivity to amines by enhancing the chemical reactivity of the distyryl dye over the monostyryl derivative.     

Reactions of O‐aryl S‐aryl dithiocarbonates with secondary alicyclic amines in aqueous ethanol. Kinetics and mechanism

The reactions of O‐(4‐methylphenyl) S‐(4‐nitrophenyl), O‐(4‐chlorophenyl) (4‐nitrophenyl), O‐(4‐chlorophenyl) S‐phenyl, and O‐(4‐methylphenyl) S‐phenyl dithiocarbonates ( 1 , 2 , 3 , and 4 , respectively) with a series of secondary alicyclic (SA) amines are subjected to a kinetic investigation in 44 wt% ethanol‐water, at 25.0 °C and an ionic strength of 0.2 M. The reactions are followed spectrophotometrically. Under amine excess, pseudo‐first‐order rate coefficients (k_obs) are found. For some of the reactions, plots of k_obs vs. free amine concentration at constant pH are linear but others are nonlinear upwards. This kinetic behavior is in accordance with a stepwise mechanism with two tetrahedral intermediates, one zwitterionic (T^±) and the other anionic (T^?). In some cases, there is a kinetically significant proton transfer from T^± to an amine to yield T^?. Values of the rate micro constants k₁ (amine attack to form T^±), k_?1 (its back step), k₂ (nucleofuge expulsion from T^±), and k₃ (proton transfer from T^± to the amine) are determined for some reactions. The Brønsted plots for k₁ are linear with slopes β₁ = 0.2–0.4 in accordance with the slope values found when T^± formation is the rate‐determining step. The sensitivity of log k₁ and log k_?1 to the pK_a of the amine, leaving and non‐leaving groups are determined by a multiparametric equation. For the reactions of 1 – 4 with 1‐formylpiperazine and those of 3 and 4 with morpholine the k₂ and k₃ steps are rate determining. Copyright © 2010 John Wiley & Sons, Ltd.     

The influence of steric effects on the kinetics and mechanism of SNAr reactions of 1‐phenoxy‐nitrobenzenes with aliphatic primary amines in acetonitrile

Rate constants are reported for the reactions of 1‐phenoxy‐dinitrobenzenes, 3 , 1‐phenoxy‐dinitrotrifluoromethylbenzenes, 4 , with n‐propylamine, and 1‐methylheptylamine in acetonitrile as solvent. The results are compared with results reported previously for n‐butylamine, pyrrolidine, and piperidine. Decreasing ring activation leads to lower values of k₁ for nucleophilic attack although this may be mediated by reduced steric congestion around the reaction centre. Specific steric effects, leading to rate retardation, are noted for the ortho‐CF₃ group. In general, reactant‐bearing ortho‐CF₃ group were subject to base catalysis irrespective of the amine nucleophile and values of k_Am/k_?1 are reduced as the size of the amine get bulkier. This is likely to reflect increases in values of k_?1 coupled with decreases in values of k_Am as the proton transfer from zwitterionic intermediates to catalysing amine becomes less thermodynamically favourable.     

Chlorination of ammonia and aliphatic amines by Cl2: DFT study of medium and substituent effects

The mechanism of chlorination of ammonia and aliphatic amines by Cl₂ was studied by quantum‐chemical calculations using a series of DFT functionals. Three different reaction pathways were considered for the reaction between Cl₂ and NH₃ in the gas phase. Several intermediates and transition state structures, not described earlier, were located on the corresponding potential energy surface. It is calculated that the reaction field effects (SCIPCM) on the chlorination is much less pronounced than the effect of a specific solvent interaction which was modeled by an explicit water molecule. It is also found that the calculated energy barrier and the reaction free energy of the chlorination of different amines are dependent on the alkyl‐substituent effects. With increase in the basicity of amine, the chlorination reaction becomes more feasible. Calculated geometries of intermediates and overall reaction energetics are significantly influenced by the method for a treatment of electron correlation (DFT vs. MP2), and by the fraction of HF exchange (χ) in DFT functionals. With increase in the χ in the corresponding functional, the DFT results approach those obtained at the MP2 level, and are closer to experimental values, as well. Copyright © 2008 John Wiley & Sons, Ltd.     

The reaction of •OH with O2, the decay of O and the pKa of HO – interrelated questions in aqueous free‐radical chemistry

In the reactions of ozone with organic compounds in aqueous solution, O is an abundant intermediate. A basic aspect of its conversion into ^?OH is addressed here. The reactions O^?? + O₂ ? O (1), H⁺ + O^?? ? ^?OH (8), ^?OH + O₂ ? HO (6), and H⁺ + O ? HO (5) are interconnected by a thermodynamic cycle. For equilibria (1) and (8) reliable equilibrium constants, and hence Gibbs energies are available (ΔG⁰(1) = ?32 kJ mol^?1, ΔG⁰(8) = 67 kJ mol^?1). For reaction (6), a Gibbs energy of ΔG⁰(6) = 47 kJ mol^?1 (K₆ = 10^?8.2 M) has now been calculated by G1. From the thermodynamic cycle one hence arrives at ΔG⁰(5) = ?12 kJ mol^?1. This relates to pK_a(HO) = ?2.1. Thus, the HO radical is a very strong acid. This value agrees with a value of ?2.0 obtained from the Bielski and Schwarz relationship for pK_a values of O_xH_y compounds. Reaction (6) must be very slow, 0.1 < k₆ < 10⁴ M^?1 s^?1. Copyright © 2010 John Wiley & Sons, Ltd.     

Oxidation of substituted triazines by sulfate radical anion (SO) in aqueous medium: a laser flash photolysis and steady state radiolysis study

Laser flash photolysis has been used to determine the bimolecular rate constants and the spectral nature of the intermediates obtained by the reaction of sulfate radical anion (SO) with 1,3,5‐triazine (T), 2,4,6‐trimethoxy‐1,3,5‐triazine (TMT), 2,4‐dioxohexahydro‐1,3,5‐triazine (DHT), and 6‐chloro N‐ethyl N'‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine (atrazine, AT). The rate constants determined were in the range 4.6 × 10⁷–3 × 10⁹ dm³ mol^?1 s^?1 at pH 6. The transient absorption spectra obtained from the reaction of SO with T, TMT, DHT and AT has an absorption maximum in the region 320–350 nm and was found to undergo second‐order decay. The intermediate species is assigned to N‐yl C(OH) radical of T (TOH^?), carbon centered neutral radical of TMT, an OH‐adduct of AT and an N‐centered radical in the case of DHT. The interpretations on the experimental results obtained from TMT are supported by DFT calculation using Gaussian 03. Steady state radiolysis technique has also been used to investigate the degradation of AT induced by SO. The degradation profile indicated that about 99% of AT has been decomposed after an absorbed gamma‐radiation dose of 7.5 kGy. The degradation yield of AT (expressed as G(‐AT)) was found to be 0.26 µ mol J^?1. The degradation reactions initiated by SO may thus be employed as a potential alternative for ^?OH‐induced degradation of triazines. Copyright © 2007 John Wiley & Sons, Ltd.     

Effects of gas saturation and sparging on sonochemical oxidation activity in open and closed systems,Part I: H2O2 generation

Cavitational/sonochemical activity can be significantly enhanced or reduced depending on the gases dissolved in the liquid. Although many researchers have suggested the order of importance of dissolved gas conditions that affect the degree of sonoluminescence (SL), sonochemiluminescence (SCL), and compound degradation, the most suitable gas condition for sonochemical oxidation reactions is currently unknown. In this study (Part I), the effects of gas saturation and sparging on the generation of H₂O₂ were investigated in a 28-kHz sonoreactor system. Four gas modes, saturation/closed, saturation/open, sparging/closed, and sparging/open, were applied to Ar, O₂, N₂, and binary gas mixtures. The change in dissolved oxygen (DO) concentration during ultrasonic irradiation was measured and was used as an indicator of whether the gaseous exchange between liquid and air altered the gas content of the liquid. Considerable difference in the DO concentration was observed for the gas saturation/open mode, ranging from –11.5 mg/L (O₂ 100 %) to +4.3 mg/L (N₂ 100 %), while no significant difference was observed in the other gas modes. The change in the gas content significantly reduced the linearity for H₂O₂ generation, which followed pseudo-zero-order kinetics, and either positively or negatively affected H₂O₂ generation. Ar:O₂ (75:25) and Ar:O₂ (50:50) resulted in the highest and second-highest H₂O₂ generation for both gas saturation and sparging, respectively. In addition, gas sparging resulted in much higher H₂O₂ generation for all gas conditions compared to gas saturation; this was because of the significant change in the cavitational active zone and concentrated ultrasonic energy, which formed a bulb-shaped active zone, especially for the Ar/O₂ mixtures adjacent to the transducer at the bottom. The sparging flow rate and position also significantly affected H₂O₂ generation; the highest H₂O₂ generation was obtained when the sparger was placed at the bottom adjacent to the transducer, with a flow rate of 3 L/min.In Part II, the generation of nitrogen oxides, including nitrite (NO₂^–) and nitrate (NO₃^–), was investigated using the same ultrasonic system with three gas modes: saturation/open, saturation/closed, and sparging/closed.     

The equilibrium and kinetics of intermolecular hydrogen bonding in nitroarene anion radical–alcohol system: 1,3‐dinitro‐benzene anion radical – R–OH (R═CH3–, C2H5–, (CH3)2 CH–)

To explore the possibility of hydrogen bonding of a stable anion radical with DNA – component sugar, hormones, steroid, and so on (through hydroxyl group), as a first step, the possibility of hydrogen bonding of 1,3‐dinitrobenzene anion radical (1,3‐DNB^??) with aliphatic alcohols was studied. It was found that 1,3‐DNB^?? anion radical undergoes hydrogen bonding with alcohols: methanol, ethanol, and 2‐proponal. The hydrogen‐bonding equilibrium constant K_eq and the (hydrogen‐bonding) rate constants k₂ were evaluated through the use of linear scan and cyclic voltammetry theory and techniques. The K_eq was found to be in the range of 1.4–6.0 m ^?1, whereas the rate constants k₂ were found to be in the range of 1.5–3.6 m ^?1 s^?1, depending upon the hydrogen‐bonding agent and the equation used for the calculation of the rate constants. The hydrogen‐bonding number n was found to be around 0.5 or 1.0. The implication of this study in, for example, the replication of DNA, the prevention of the formation of super oxide, and so on is discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

‘Self‐terminating radical cyclizations’ – new insight into the mechanism of the termination step from computational studies

Computational methods were used to gain detailed insight into the mechanism of self‐terminating radical cyclizations, which are initiated by intermolecular addition of O‐centred radicals XO^? to alkynes. The calculations were performed for the reaction of NO, SO, and AcO^? with cyclodecyne ( 1 ) and 5‐cyclodecynone ( 2 ), respectively. Whereas radical addition and the subsequent transannular radical translocation steps are energetically highly favourable processes for the various XO^?, the terminating homolytic β‐fragmentation of the O? X bond in the intermediate α‐oxy radicals 10 – 13 shows a strong dependence on the nature of X. Using simplified model systems, the fragmentation was explored in detail, which revealed that the rate of this step is primarily determined by the strength of the O? X bond and only to a minor extent by the ability of the X moiety to stabilize an unpaired electron in the transition state. However, the cleavage is exothermic, when the released radical X^? is resonance stabilized, e.g. NO, SO, and Bn^?, respectively. In those cases where the unimolecular β‐fragmentation of the O? X bond is slow, termination could also proceed through a bimolecular radical chain process involving the α‐oxy radical intermediate 10 – 13 and the precursor of XO^?, e.g. the Barton PTOC ester 18 or Kim's dithiocarbamate 20 , respectively. Alternative termination mechanisms via oxidation of 10 – 13 can be ruled out under the usual experimental conditions of self‐terminating radical cyclizations. Copyright © 2010 John Wiley & Sons, Ltd.     

Contact electrification of polymers due to electron transfer among mechano anions,mechano cations and mechano radicals

Many studies have been reported for contact electrification based on the electron transfer from donors to acceptors. However, the chemical structures of donors and acceptors have not been identified. Here we calculated the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of model structures of mechano anions, mechano cations and mechano radicals which were produced by the heterogeneous and homogeneous scissions of covalent bonds comprising polymer main chain in vacuum at 77 K. We identified the donors are mechano anions(HOMO) and mechano radicals(HOMO), and the acceptors are mechano cations(LUMO) and mechano radicals(LUMO). The contact electrification is due to the electron transfer from the donors to the acceptors during contacting on the friction surface, and produces mosaic nano-scopic domains with opposite sign. The sign of the net charge of polymer was deduced from the number of paths of electron acceptance reaction. The relative sign of charge and position on the triboelectric series were deduced from their chemical structure.     

Application of capillary electrophoresis in anion binding studies: Complexation and separation of nitrate and nitrite by an azacryptand

Capillary electrophoresis (CE) was employed for studying the complexation of an azacryptand with nitrate and nitrite in aqueous solution. CE separation of a mixture of nitrate and nitrite with 10 mM acetate buffer (pH 3.3) showed two peaks at the retention times of 2.8 and 3.1 min for nitrate and nitrite, respectively. However, when the ligand (2 mM) was added to the running buffer, the peaks emerged in the reverse order and at shorter retention times of 2.7 and 2.5 min for nitrate and nitrite, respectively. The longer retention time for nitrate compared with nitrite indicates a stronger complex formation between the ligand and nitrate, that reduces the migration speed of nitrate as compared with the less strongly bound nitrite. The (1)H NMR titrations of L with these two anions at the pH 3.3, gave the binding constants (log K), 3.75 and 4.23, for nitrite and nitrate, respectively which were in consistence with the results obtained from the CE method.     

Novel 1,2,4-triazole analogues as mushroom tyrosinase inhibitors: synthesis,kinetic mechanism,cytotoxicity and computational studies

Molecular Diversity - We have created a novel series of mushroom tyrosinase inhibitors with 1,2,4-triazole as fundamental skeleton. The target compound 1,2,4-triazol-3-ylthio)-N-phenyl acetamide...     

甲基橙-银胶体系pH和氯离子效应的光谱研究

研究了甲基橙-银胶体系的光吸收和光致发光信号随pH值和加入氯离子的变化规律.实验发现随着pH值的增加, 分子的荧光发射峰与银胶的光吸收峰的重叠增大, 引起体系中能量转移效率的增加, 即428 nm分子荧光峰的淬灭和560 nm聚集体的特征光致发光峰增强现象的加剧.另外, 不同pH值下氯离子的加入都会使染料分子更加密集的吸附在胶体银颗粒表面, 形成分子吸附更加紧密的聚集体, 造成体系中受表面吸附分子影响的光致发光峰获得了极大的增强.同时, 因聚集体表面吸附层染料分子对入射光的大量吸收, 导致到达内核银表面的入射光强度减弱, 致使体系能量转移通道在一定程度上受阻, 表现为428 nm荧光峰的淬灭幅度减小.参照分子聚集体的形成理论, 接合体系光谱的变化, 从pH值的改变和Cl^-的加入对分子结构及加剧聚集体的形成等方面的影响来解释发光和光吸收的显著变化.     

High pressure equation of state studies using methanol-ethanol-water and argon as pressure media

We have measured the equation of state of the intermetallic compound AuIn₂ up to 20 GPa and Cd_0.8Hg_0.2 up to 50 GPa using methanol-ethanol-water solution or argon as pressure media. In the experiments performed with argon as pressure medium, we minimized non-hydrostatic conditions by thermally annealing the sample. We present data revealing compressibility anomalies in AuIn₂ at 2.7 GPa and in Cd_0.8Hg_0.2 near 8, 18 and 34 GPa with methanol-ethanol-water and argon. At pressures above 5 GPa the P-V data for AuIn₂ and Cd_0.8Hg_0.2 from experiments preformed with argon as a pressure medium start deviating from those using methanol-ethanol-water, and the equation of state based on experiments in argon is stiffer compared with that in methanol-ethanol-water. This behavior is consistent with the relative merits of the two pressure transmitting media as documented in the literature. We also provide a brief summary of the results of electronic structure calculations that associate these anomalies with electronic topological transitions.     

Numerical study on three-dimensional C-J detonation waves: detailed propagating mechanism and existence of OH radical

An unsteady three-dimensional simulation is performed for a hydrogen/air C–J detonation in a rectangular tube, where a detailed chemical reaction model is used to reveal the C–J detonation structure. In this simulation, detailed propagating detonation structures for a diagonal mode are described in three-dimensions. The detonation front structures, the line of triple points, and the strong explosions at the corners of the rectangular tube are revealed by using a three-dimensional numerical visualization. From the spatial isosurface profiles of H₂ mass fraction, it is confirmed that the triple point lines have a role of “shutter” to generate unburned gas pockets and become of a ring shape behind the detonation front due to its explosion. The explosion process and its influence on an induction delay are observed by visualizing the spatial isosurface profiles of OH mass fraction. Moreover, a high “peninsula-shaped” OH mass fraction area, which has been experimentally reported, is reproduced on the side wall of the rectangular tube.