Primary stage of the reaction between ozone and chloride ions in aqueous solution: Can chloride ion oxidation by ozone proceed via electron transfer mechanism?

It is found that chloride-ion oxidation by ozone via electron transfer mechanism does not occur due to its extremely high endoergicity and negligibly low rate. It is concluded that all processes supposedly associated with this reaction, particularly ozone decomposition in sodium chloride solution initiated by Cl^· atoms, do not take place either. It is shown that experimental data on the products and kinetic regularities of the interaction of O₃ with Cl⁻ contradict the assumption that the electron transfer reaction is its primary stage. In fact, chloride-ion oxidation by ozone proceeds via the mechanism of oxygen atom transfer. It is noted that in order to estimate the possibility of using an ozonated physiological saline in medicine, the formation of chloride-ion oxidation products and ozonation byproducts must be taken into account.     

Degradation of 4-chlorophenol in aqueous solution by γ-radiation and ozone oxidation

The application of radiation technology in the en-vironmental protection was listed as one of the mostimportant research fields by the International AtomicEnergy Agency (IAEA) for the peaceful use of nuclearenergy. It has great research value and potential appli-cation. Because of their broad-spectrum antimicrobialproperties, Cholophenols (CPs) have been used aspreservative agents for wood, paints, vegetable fibersand leather and as disinfectants. In addition, they havebeen widely employed…     

Electrode grafting by oxidation of an amine catalyzed by a ferrocenyl “antenna” through intramolecular electron transfer

Two aminoferrocene complexes were studied by electrochemical techniques. Molecules retain the redox properties of both ferrocene and amine groups, but fundamentally different behaviours were observed depending on whether the linker between the two redox end groups was saturated (ethyl bridge) or not (ethynyl bridge). The possibility of an intramolecular electron transfer from the amine to the ferricenium moiety through the π-conjugated linker was demonstrated and the ethynyl bridge is expected to have a dual effect by facilitating both the oxidation of the amine into the cation radical and the production of aminyl radical, due to its strong electron withdrawing effect. Because of this synergy of properties, grafting of the conjugated aminoferrocene complex can occur just by oxidizing the ferrocene group without the presence of a base in solution.     

Kinetics and mechanism of the oxidation of L-ascorbic acid by the N,N′-ethylenebis(salicylideneiminato)manganese(III) complex in aqueous solution

Summary The kinetics of oxidation of l-ascorbic acid by the N,N-ethylenebis(salicylideneiminato) manganese(III) complex have been studied over the 4.5–9.3 pH range. An intermediate ascorbate complex was formed which had an inhibiting effect on the rate of the redox reaction. The rapid formation of this intermediate was followed using the stopped-flow technique, whereas its slow decomposition was monitored using a conventional spectrophotometer. The formation of this intermediate was strongly pH dependent. Addition of sodium perchlorate and sodium dodecyl sulphate (anionic surfactant) affected the reaction rate. A probable mechanism comprising both the intermediate formation and the overall redox reaction is discussed.     

The electron transfer reaction of [RuIII(edta)(pyz)]− with sulfite in aqueous solution

The reduction of [Ru^III(edta)(pyz)]^– (edta=ethylenediaminetetraacetate, pyz=pyrazine) with sulfite has been investigated spectrophotometrically in aqueous solution and found to be first order in both the complex and sulfite. The values of the observed rate constant depend on the pH, since it controls the spaciation of oxoanions of sulfur(IV). The effect of alkali cations (K⁺, Na⁺ and Li⁺) is attributed to triple-ion formation through an alkali cation bridging between two negatively charged reactants and facilitating the electron-transfer process. Kinetic data and activation parameters are interpreted in terms of an outer-sphere electron transfer mechanism. The reaction has also been analysed using the Marcus cross-section relationship for outer-sphere electron transfer reactions.     

Kinetic and mechanism of oxidation of thiocarbohydrazide and its metal complex by acid bromate in aqueous and partial aqueous media

The kinetics of oxidation of thiocarbohydrazide in the free and zinc(Ⅱ)-bound states byacid bromate have been studied in aqueous and water-acetic acid(1:1,V/V)media under varyingconditions,both in the absence and presence of added bromide ion.The rates of oxidations show firstorder kinetics in[bromate]in all the cases,but exhibit different kinetic behaviour in[substrate]and[H~+].Oxidation of TCH in aqueous medium shows zero order in[TCH]and nearly second order in[H~+],while oxidation in aqueous acetic acid shows two ranges in[H~+].The rate shows first and fractionalorder kinetics in[TCH]in the first and second acid ranges.Kinetics observed in the presence of Br~-are similar to those observed for oxidation of TCH in second acid range.In addition,the reactionshows fractional order in[Br~-].Oxidation of TCH in Zn(Ⅱ)-bound state exhibits first order kinetics in[substrate]and second order in[H~+].Increase in ionic strength of the medium decreases the rate in allthe cases.Increase in acetic acid composition of the solvent increases the rate.Mechanisms consistentwith the observed results have been considered and the rate laws deduced.The rate limiting steps havebeen identified and the coefficients of these steps have been calculated at different temperatures.Therelated activation parameters have also been computed.The validity of the deduced rate laws has alsobeen tested by recalculating the rate constants from them as[TCH]and[H~+]are varied.     

Characterization of the inclusion complex of β-cyclodextrin with sorbic acid in the solid state and in aqueous solution

Crystal structure of β-cyclodextrin (β-CD) complexes with sorbic acid, usually as food preservative, has been determined by single-crystal X-ray diffraction at 113 K. The space group of β-cyclodextrin-sorbic acid complex is P1 with unit cell dimensions of a = 15.284(3) Å, b = 15.402(3) Å, c = 17.981(4) Å, α = 99.67(3)°, β = 112.83(3)°, γ = 102.48(3)° and Z = 1. The result indicates that the β-CD molecules form head-to-head dimers which pack in the intermediate mode. Each dimer contains two guest molecules whose methyl groups are located at the dimer interface while the carboxyl groups protrude from the β-CD primary faces. Water molecules (25.5) are distributed outside the cyclodextrin cavity over 31 sites. Furthermore, nuclear magnetic resonance spectroscopy (¹H NMR) has been employed to investigate the inclusion behavior between the host β-CD and guest sorbic acid in aqueous solution. The results obtained enabled us to structurally characterize the β-CD inclusion complex with sorbic acid.     

Hydration numbers of α-alanine in an aqueous urea solution

Literature data on the apparent molar volumes ϕ of alanine in water and aqueous urea solutions at 298 K are analyzed. It is shown that the slope of the ϕ dependence on the alanine concentration is not dependent on the urea concentration. The standard partial volume of alanine increases linearly with the increase in the urea concentration (wt.%). The structural characteristics of hydrated complexes of alanine (hydration number, molar volume of water inside and outside the hydration sphere, and proper volume of alanine in solution) are given. The hydration number of alanine decreases by a factor of two in passing from water to a saturated (20m) urea solution. The effects of urea additions on the hydration numbers of alanine and glycine are compared.     

Gauging away the electron–electron interaction by the local phase of complex wave functions in two-electron systems

The electron–electron interaction is eliminated in the expectation values of the electronic Hamiltonian for two-electron systems. The part of the Hamiltonian referring to the repulsive interaction is gauged away by the local phase of the complex wave functions, much like a gauge field transformation, thereby leading to a one-electron Hamiltonian. Despite the appearance of complex wave functions, the expectation values of the total momentum operator vanish and Löwdin’s criterion holds for the stationary states.     

Involvement of ·OH radicals in the mechanism of excitation of the uranyl ion in the chemiluminescent oxidation of U(IV) by atmospheric oxygen in aqueous solutions of perchloric acid

The chemiluminescence (CL) kinetics in U(IV) oxidation by atmospheric oxygen in aqueous HClO₄ has been investigated. The CL quantum yield (η_CL, E/(mol U(IV))) in this reaction is 1.4 × 10^?8. The elementary event generating the CL emitter, which is the electronically excited uranyl ion *(UO ₂ ²⁺ ), is electron transfer from the uranyl ion UO ₂ ⁺ to the oxidizer (^·OH radical). The Ag⁺ ion quenches CL, and the Cu²⁺ ion enhances CL.     

Kinetics and mechanism of the oxidation of a ferrous complex with an α,α′-diimine chelate ligand by ceric sulfate in aqueous acidic medium by UV-vis absorption spectroscopy

Kinetics of the oxidation of tris(2,2′-bipyridine)iron(II) sulfate by ceric sulfate was spectrophotometrically studied in an aqueous sulfuric acid medium. Different methods, including isolation, integration and half-life, were employed to determine the reaction order. The redox reaction was found to be first-order with respect to the reductant, tris(2,2′-bipyridine)iron(II) sulfate, and the oxidant, ceric sulfate. Complex kinetics was observed with an increase in the initial concentration of the oxidant. The influence of the dielectric constant, [H⁺] and [SO₄ ^2-] on the rate was also investigated. The increase in the dielectric constant and H⁺ ion concentration of the medium retard the rate, while an increase in the SO₄ ^2- ion concentration first accelerates the rate, and then retards the reaction. The effect of each factor, i.e., the dielectric constant, H⁺ ions and SO₄ ^2- ions, suggests that Ce(SO₄)₃ ^2- is the active species of cerium(IV). A rate law consistent with the observed kinetic data and the proposed mechanism is suggested to be: {fx631-1     

Degradation of trichloroethylene in aqueous solution by persulfate activated with Fe(III)–EDDS complex

In this study, an environmentally friendly complexing agent, S,S′-ethylenediamine-N,N′-disuccinic acid (EDDS), was applied in Fe(III)-mediated activation of persulfate (PS), and the degradation performance of trichloroethylene (TCE) was investigated. The effects of PS concentration, Fe(III)/EDDS molar ratio, and inorganic anions on TCE degradation were evaluated, and the generated reactive oxygen species responsible for TCE removal were identified. The results showed that nearly complete TCE degradation was achieved with PS of 15.0 mM and a molar ratio of Fe(III)/EDDS of 4:1. An increase in PS concentration or Fe(III)/EDDS molar ratio to a certain value resulted in enhanced TCE degradation. All of the anions (Cl^?, HCO₃ ^?, SO₄ ^2?, and NO ₃ ^? ) at tested concentrations had negative effects on TCE removal. In addition, investigations using radical probe compounds and radical scavengers revealed that sulfate radicals (SO ₄ ^·? ), hydroxyl radicals (^·OH), and superoxide radical anions (O ₂ ^·? ) were all generated in the Fe(III)–EDDS/PS system, and ^·OH was the primary radical responsible for TCE degradation. In conclusion, the Fe(III)–EDDS-activated PS process is a promising technique for TCE-contaminated groundwater remediation.     

Orientational effects of β-cyclodextrins on electron transfer between metal complexes in solution

The kinetics of the electron transfer reaction between pentammine-(4,4bipyridine)ruthenium(II) and cyclohexyldiamine-N,N,N,N-tetraacetatocobaltate(III) has been studied in unsubstituted and substituted -cyclodextrin solutions. The increased ion-pairing and the decreased electron transfer rates that result when the ruthenium complex are encapsulated by cyclodextrins are interpreted in terms of hydrogen bonding between cyclodextrin and the metal complexes markedly stabilizing the ionpair.Presented at the Symposium 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

Investigation on the photo-induced de-oxygenation process of myoglobin in aqueous solution by use of fluorescence spectroscopy

A photo-induced de-oxygenation process of myoglobin (Mb) in aqueous solution was investigated by use of fluorescence spectroscopy. The spectra are characterized by the fluorescence intensity declining gradually after each scan,and the decay of fluorescence intensity being significant in each scan,which is assigned to the release of oxygen from the opening of the heme-pockets induced by illumination. More illumination will cause more release of oxygen; if the temperature of an Mb solution is increased when it is illuminated,the rate of de-oxygenation will be higher. It was found that ligand-oxygen in Fe-porphyrin could be removed from Mb by nitrogen. This indicates that the interac-tion between oxy-Mb and other different gases can be tested by the method of fluorescence spectros-copy. In addition,fluorescence spectroscopy can be employed to probe the energy transfer between Fe-porphyrin and tryptophan or tyrosine in Mb molecules.     

RISM-SCF study of the free-energy profile of the Menshutkin-type reaction NH3+CH3Cl→NH3CH3++Cl− in aqueous solution

The free-energy profile for the Menshutkin-type reaction NH₃ + CH₃Cl → NH₃CH₃ ⁺ + Cl⁻ in aqueous solution is studied using the RISM-SCF method. The effect of electron correlation on the free-energy profile is estimated by the RISM-MP2 method at the HF optimized geometries along the reaction coordinate. Solvation was found to have a large influence on the vibrational frequencies at the reactant, transition state and product; these vibrational frequencies are utilized to calculate the zero-point energy correction of the free-energy profile. The computed barrier height and reaction exothermicity are in reasonable agreement with those of experiment and previous calculations. The change of solvation structure along the reaction path is represented by radial distribution functions between solute-solvent atomic sites. The mechanisms of the reaction are discussed from the view points of solute electronic and solvation structures. Received: 26 June 1998/Accepted: 28 August 1998 / Published online: 2 November 1998     

Coumarin-based fluorescent chemosensor for the selective quantification of Zn2+ and AcO− in an aqueous solution and living cells

In this work, we report a novel fluorescence chemosensor HM based on the coumarin fluorophore for the quantification of Zn²⁺ and AcO^?. HM specifically binds to Zn²⁺ in the presence of other competing cations, and evident changes in UV–vis and fluorescence spectra in HEPES buffer are noticed. The in situ generated HM-Zn²⁺ complex solution exhibit a high selectivity toward AcO^? via Zn²⁺ displacement approach. The detection limits of HM for Zn²⁺ and HM-Zn²⁺ for AcO^? were estimated to be 7.24 × 10^?8 M and 9.41 × 10^?8 M, respectively. HM and the resultant complex HM-Zn²⁺ exhibit low cytotoxicity and cell-membrane permeability, which makes them capable of Zn²⁺ and AcO^? imaging in living Hep G2 cells. A B3LYP/6-31G(d,p) basis set was employed for optimization of HM and HM-Zn²⁺ complex.     

Effects of an applied magnetic field on the anodic dissolution of nickel in HNO3 + Cl− solution

All types of the magnetic field effects on the anodic dissolution of metallic materials have been found in one electrochemcial system: the Ni/0.40 M HNO₃ + 5.0 mM NaCl system. The effects are similar to those of a stirring on all occasions. With the presence of the magnetic field, the current decreases in the active region. However, the current oscillations are changed to active dissolution in the prepassive region and induced in the transitive potential from the prepassive region to the passive region by the magnetic field. In the passive region, the magnetic field has little influence. Those effects are discussed with different rate-determining steps. The study of the effects of the magnetic field on this system may help us understand why the magnetic field enhances the corrosion rates in some conditions while suppressing them in others.     

Kinetics of oxidation of phenylhydrazine by a μ-oxo diiron(III,III) complex in acidic aqueous media

Phenylhydrazine (R) quantitatively reduces [Fe₂(μ-O)(phen)₄(H₂O)₂]⁴⁺ (1) (phen?=?1,10-phenanthroline) and its conjugate base [Fe₂(μ-O)(phen)₄(H₂O)(OH)]³⁺ (2) to [Fe(phen)₃]²⁺ in presence of excess 1,10-phenanthroline in the pH range 4.12–5.55. Oxidation products of phenylhydrazine are dinitrogen and phenol. The reaction proceeds through two parallel paths: 1?+?R?→?products (k ₁), 2?+?R?→?products (k ₂); neither RH⁺ nor the doubly deprotonated conjugate base of the oxidant, [Fe₂(μ-O)(phen)₄(OH)₂]²⁺ (3) is kinetically reactive though both are present in the reaction media. At 25.0°C, I?=?1.0?M (NaNO₃), the rate constants are k ₁?=?425?±?10?M^?1?s^?1 and k ₂?=?103?±?5?M^?1?s^?1. An inner-sphere, one-electron, rate-limiting step is proposed.     

Thermochemical study of the reactions of acid–base interaction in an aqueous solution of α-aminobutyric acid

The heat effects of the interaction between a solution of α-aminobutyric acid and solutions of HNO₃ and KОН are measured by means of calorimetry in different ranges of рН at 298.15 K and values of ionic strength of 0.25, 0.5, and 0.75 (KNO₃). The heat effects of the stepwise dissociation of the amino acid are determined. Standard thermodynamic characteristics (Δ_r H ⁰, Δ_r G ⁰, and Δ_r S ⁰) of the reactions of acid–base interaction in aqueous solutions of α-aminobutyric acid are calculated. The connection between the thermodynamic characteristics of the dissociation of the amino acid and the structure of this compound is considered.