Redox reactions of basic fuchsin in homogeneous aqueous media

The pulse-radiolysis technique has been employed to understand the reaction mechanism and to characterize the transient species involved in the redox processes taking place in the radiation chemistry of basic fuchsin (BF⁺). One-electron reduction and oxidation reactions of BF⁺ have been carried out in homogeneous aqueous solutions employing various reducing (e _aq ^– , (CH₃)₂COH, CO ₂ ^– ) and oxidizing (N ₃, Br, Cl ₂ ^– Br ₂ ^– ) radicals. The absorption spectra of the transients formed in the above reactions have been attributed to semi-reduced and semi-oxidized species of BF⁺, respectively. The kinetic and spectroscopic properties of these transients have been evaluated. The reaction with H and OH radicals have also been performed and compared with those of specific one-electron reducing and oxidizing radicals. These reactions have been inferred predominantly by addition to BF⁺. Protolytic equilibria involving semi-reduced species of basic fuchsin have been studied over the pH range from 2 to 10 and the pK _a has been determined to be 3.9.     

Iron Catalysis of SO2 Oxidation in the Atmosphere

The mechanisms of SO₂ oxidation catalyzed by iron ions in the droplet phase of the convective cloud in the lower atmosphere were examined. The relations of the catalytic SO₂ decrease to the concentration of the iron ions and to the intensity of fluxes to the droplet of the OH _(g) and HO _2(g) radicals were characterized. The determining role of the replacement of the low-reactive HO _2(g)(O^– _2(aq)) radical by the reactive SO^– _5(aq) radical in the sulfite medium during daytime was revealed. This process occurred due to the coupling of the decay of the radicals and their regeneration in the liquid-phase reactions O^– _2(aq) + FeOH²⁺ _(aq) Fe²⁺ _(aq) + OH^– _(aq) + O_2(aq), HSO^– _5(aq) + Fe²⁺ _(aq) FeOH²⁺ _(aq) + SO^– _4(aq)HSO ₃ ^- _(aq),O_{2 (aq)} SO^– _5(aq).     

Reactions of Peroxy Radicals with Hydrocarbons and Alcohols: Transition State Geometry and the Polar Effect

The reaction EtOO + EtH EtOOH + Et was studied by the intersecting parabolas method and calculated using density functional theory. The interatomic C–H, O–H, and C–O distances of the transition state for this reaction were calculated using these methods. The formulas for calculating these distances from experimental data were obtained. Similar calculations and comparisons were carried out for the reaction EtOO + MeCH₂OH EtOOH + MeCHOH. The polar effect of the hydroxy groups on the transition state manifested itself in a decrease in the activation energy and in the formation of a nonlinear structure of the transition state. An empirical formula for estimating the C–H–O angle in the transition state from the enthalpy and activation energy was derived.     

Competitive Mechanism of the Nonbranched Radical Chain Oxidation of Hydrogen Involving the Free Cyclohydrotetraoxyl Radical [OO•••H•••OO]•, which Inhibits the Chain Process

A nonbranched radical chain mechanism, which does not pass into non-steady-state critical regimes, was proposed for the uncatalyzed oxidation of hydrogen. This mechanism includes competitive reactions with the participation of H, HO, and HO ₂ free radicals and the inactive cyclohydrotetraoxyl radical HO ₄ stabilized by inner hydrogen bonding, wherein the cyclohydrotetraoxyl radical inhibits the chain process. A simple rate equation, which describes the nonmonotonic (with a maximum) dependence of the rate of the nonbranched chain process of hydrogen peroxide and water formation on the concentration of molecular oxygen, was derived using the quasi-steady-state approximation. The nonchain reaction paths of free-radical hydrogen oxidation were considered. It was assumed that the cyclic free radical HO ₄ can be an intermediate in the series of conversions of biologically harmful energy of cosmic radiation in the upper atmosphere.     

Pulse radiolysis of thionicotinamide in aqueous solutions: formation of resonance stabilized species on one electron oxidation

Pulse radiolysis studies on thionicotinamide (TNA) have been carried out in aqueous solutions at pH 6.8 and 1. The initial species formed by OH radical reaction with TNA at pH 6.8 was found to react with the parent molecule to give a dimer radical species (_max = 420-440 nm). Reaction of Br₂ ^- radicals with TNA was found to give a transient species having _max at 380 nm. This spectrum has been assigned to a resonance stabilized species with free electron delocalised over the -N-C-S bond. Reactions of OH and Cl2₂ ^- radicals with TNA at pH 1 were found to give identical transient species with _max at 420 nm, which decayed by first-order kinetics at a rate of about 8.0 × 10³ s^-1. This species is suggested to be the protonated form of the resonance-stabilized species formed at pH 6.8 in the reaction of Br₂ ^- with TNA. The rate constant for the reaction was 4 × 10⁹ dm³ mol^-1 s^-1. Semi-reduced species formed by the reaction of e-_aq with TNA (k = 1.6 × 10¹⁰ dm³ mol^-1 s^-1) was found to be a good reductant which could transfer electron to methyl viologen. CO₂ ^- radicals also reacted with TNA to give a reducing species. Although, the absorption peaks in the two cases were at the same wavelengths viz. 380 and 480 nm, the ratios of the peak heights were different suggesting the formation of different species. Hydrogen atoms and (CH₃)₂COH radicals were found to transfer an electron to TNA at pH 1, as seen by quantitative electron transfer to methyl viologen from the transient species.     

Killing of Invasive Species of Ship’s Ballast Water in 20t/h System Using Hydroxyl Radicals

A pilot-scale experiment of 20t/h for the treatment of ships ballast water was done in this paper. With the method of strong ionization discharge of dielectric barrier, O₂ in air and H₂O at gas state are ionized and dissociated into large numbers of OH radicals, and then dissolved into a part of ballast water to form dissolved OH with the concentration of 24.3 mg/L. When the dissolved OH concentration is 0.63 mg/L, the kill efficiencies of bacteria, mono-algae, protozoan reached 100% within 2.67 s. The contents of chl-a, chl-b, chl-c and carotenoid were decreased to 35–64% within 8.0 s and not be tested after 5 min. At the same time, the ballast water quality was greatly improved. Therefore, the treatment of ships ballast water using OH radicals is a kind of advanced oxidation technology, which is considered as zero pollution, zero emission and zero residual in the process of the production, of OH radicals and the treatment of ballast water.Key Project of National Foundation Research from Science and Technology Ministry of China, (2002CCC00900). Key and General Projects of National Natural Science Foundation of China (NSFC: 60031001, 60371035).     

Dissociation equilibrium between uncharged and charged local anesthetic lidocaine in a surface-adsorbed film

The dissociation equilibrium between uncharged local anesthetic lidocaine (LC) and charged local anesthetic LC (LCH⁺) in a surface-adsorbed film was investigated by measuring the surface tension and pH of aqueous solutions of a mixture of hydrochloric acid and LC. The surface tension values decreased slightly with increasing total molality m_t at 0X₂0.5, where X₂ is the mole fraction of LC in the mixture, while they decreased rapidly with increasing m_t at 0.5<X₂1. It was shown from the pH measurements that almost all LC molecules were changed into LCH⁺ ions by protonation at 0X₂0.5 and both forms coexisted only at 0.5<X₂1. The quantities of the respective LC and LCH⁺ transferred from the aqueous solution to the adsorbed film, i.e., their surface densities, were calculated by applying the thermodynamic equations derived to the surface tension and pH data. A greater quantity of LC than LCH⁺ existed in the adsorbed film at the coexisting composition. The partitioning behavior of LC and LCH⁺ in the adsorbed film was characterized by three composition regions: (1) slight partitioning of low surface-active LCH⁺ in the region at 0X₂0.5, (2) preferential partitioning of LC at 0.5<X₂<around 0.7, and (3) negative partitioning of LCH⁺ at around 0.7X₂1. The present results clearly indicate that uncharged local anesthetics transfer into hydrophobic environments such as cell membranes more than charged ones.     

Radical scavenging properties of a flavouring agent–Vanillin

Using pulse radiolysis technique, the one-electron oxidation of vanillin (V-OH) with azide radicals, at pH 6 and 9 resulted in the formation of vanillin phenoxyl radical with k = 6.7 × 10⁷ and 2.5 × 10⁹ dm³ mol^-1 s^-1, respectively. The transient absorption spectra of the vanillin phenoxyl radical (V-O) formed either at pH 6 or 9, showed a _max at 410 nm. At pH 5, the OH radicals seem to form an adduct with vanillin, _max at 430 nm and k(OH + V-OH) = 3.3 × 10⁹ dm³ mol^-1 s^-1, while at pH 9, the OH radical reaction resulted in the formation of vanillin phenoxyl radical with _max at 410 nm and k(OH + V-O-) = 6.6 × 10⁹ dm³ mol^-1 s^-1. The reactivity of NO₂radicals with vanillin is lower by orders of magnitude signifying an incomplete reaction. In general, the rate constants for the reaction of OH, N, NO radicals with vanillin were higher at pH 9 than at the lower pH. Its reactivity with other one-electron oxidants like CCl₃OO, CHCl₂OO and CH radicals and the ability to chemically repair tryptophanyl and guanosyl radicals with k = 1.5 - 4 × 10⁷ dm³ mol^-1 s^-1 indicate its antioxidative behaviour.     

Kinetics and spectral properties of electron and •OH adducts of dimethylpyridines: a pulse radiolysis study

The reactions of e_aq ^-, OH, O^- and SO^- ₄ with 2,4-, 2,6- and 3,5-dimethylpyridines have been investigated in aqueous solution by pulse radiolysis with optical detection. Both e_aq ^- and OH radicals have high reactivity toward these compounds with k = (4-8) × 10⁹ dm³ mol^-1 s^-1. The rates of O^- and SO₄ ^- reactions ((1-3) × 10⁹ dm³ mol^-1 s^-1) were lower compared to the rate observed with the OH radical. The transient absorption spectra obtained in the reaction of e_aq ^- with three isomers exhibited a weak broad band around 340-410 nm. The absorption maxima of the intermediates formed in the OH and SO₄ ^- reactions were centred around 320-330 nm ( = 2450-3500 dm³ mol^-1 cm^-1) with an additional broad peak in the range 460-520 nm which are attributed to the corresponding OH adducts. The spectra in the O^- reaction have absorption maxima between 300 and 320 nm and it reacts both by addition and H-abstraction from the CH₃ group. A reaction mechanism consistent with the observed results is proposed.     

Ascorbate-induced oxidation of formate by peroxodisulfate: product yields,kinetics and mechanism

The slow reaction between peroxodisulfate and formate is significantly accelerated by ascorbate at room temperature. The products of this induced oxidation, CO₂ and oxalate (C₂O^2– ₄), were analyzed by several methods and the kinetics of this reaction were measured. The overall mechanism involves free radical species. Ascorbate reacts with peroxodisulfate to initiate production of the sulfate radical ion (SO^– ₄), which reacts with formate to produce carbon dioxide radical ion (CO^– ₂) and sulfate. The carbon dioxide radical reacts with peroxodisulfate to form CO₂ or self-combines to form oxalate. Competition occurring between these two processes determines the overall fate of the carbon dioxide radical species. As pH decreases, protonation of the carbon dioxide radical ion tends to favor production of CO₂.     

Structure of 2,4,4,5,5‐pentamethyl‐2‐imidazoline‐1‐oxyl‐3‐oxide

The crystal and molecular structures of the stable nitroxide radical 2,4,4,5,5pentamethyl2imidazoline1oxyl3oxide was determined. The N—O bond lengths are 1.279(2) and 1.280(2), respectively. The O^-—N⁺=C—N— O fragment is nearly planar with carbon atoms of the ethyl fragment that deviated from the O—N⁺=C—N—O plane by –0.204(5) and +0.176(5). The minimum intermolecular distance between the oxygen atoms of NO groups is 4.094.     

Investigation of the intermediates formed during the degradation of Malachite Green in the presence of Fe3+ and H2O2 under visible irradiation

The photodegradation of Malachite Green (MG) was investigated in the presence of Fe³⁺ and H₂O₂ under visible irradiation ( > 470 nm) and the intermediates produced during the degradation were determined by FTIR, GC-MS and ¹H NMR. The mineralized products of nitrogen atoms in the dye molecule were analyzed by ammonia ion-selective electrode and ion chromatography. N,N-dimethylaniline, 4-dimethylamino phenol, 4-methylamino benzophenone, 4-dimethylamino benzophenone, benzeneacetic acids and 4-hydroxybenzoic acid were found during the photodegradation of MG. It can be concluded that the dye underwent two different principal degradation pathways in the initial period of the photodecomposition, one is that the dye molecule is splittingly decomposed into small species by attack of HO radicals on the central carbon, another is that the N-methyl groups are oxidized by HO radicals, leading to demethylation. Nitrogen atoms in the dye molecules are finally transformed into ammonium ions. A possible degradation mechanism is proposed.     

Evaluation of molten inorganic salt hydrates as reaction medium for the derivatization of cellulose

Molten inorganic salt hydrates are highly efficient solvents forcellulose. The carboxymethylation of the polymer dissolved in this new group ofcellulose solvents was investigated. The homogeneous carboxymethylation ofcellulose in molten LiClO₄3H₂O using sodiummonochloroacetate in the presence of NaOH is possible. The formation of CMC wasconfirmed by FT- Raman spectroscopy. Structure analysis by means of HPLC afterchain degradation showed the formation of CMC with a DS of 2 after a shortreaction time of 4 h. The derivatives exhibit a statisticaldistribution of substituents along the polymer chain if prepared in moltenLiClO₄3H₂O as solvent. A substituent distributioninthe order C-6 > C-2 C-3 for anhydroglucose units (AGU) was concludedfrom ¹H-NMR measurements. The synthesis of CMC in the swellingmediumLiClxH₂O (2 x 5) yields polymers with astatistical distribution of functional groups along the chain. The watercontentof the salt melts has a dramatic influence on the DS_CMC.     

Determination of Heavy Metal Ions in Chinese Herbal Medicine by Microwave Digestion and RP-HPLC with UV-Vis Detection

A new method for the simultaneous determination of heavy metal ions in Chinese herbal medicine by microwave digestion and reversed-phase high-performance liquid chromatography (RP-HPLC) has been developed. The Chinese herbal medicine samples were digested by microwave digestion. Lead, cadmium, mercury, nickel, copper, zinc, and tin ions in the digested samples were pre-column derivatized with tetra-(4-chlorophenyl)-porphyrin (T₄-CPP) to form the colored chelates which were then enriched by solid phase extraction with C₁₈ cartridge and eluted from the cartridge with tetrahydrofuran (THF). The chelates were separated on a Waters Xterra RP₁₈ column by gradient elution with methanol (containing 0.05molL^–1 pyrrolidine-acetic acid buffer salt, pH=10.0) and THF (containing 0.05molL^–1 pyrrolidine-acetic acid buffer salt, pH=10.0) as mobile phase at a flow rate of 0.5mLmin^–1 and detected with a photodiode array detector in the range of 350–600nm. In the original samples the detection limits of lead, cadmium, mercury, nickel, copper, zinc and tin are 4ngL^–1, 3ngL^–1, 6ngL^–1, 5ngL^–1, 2ngL^–1, 6ngL^–1, and 4ngL^–1, respectively. This method was applied to the determination of lead, cadmium, mercury, nickel, copper, zinc and tin in Chinese herbal medicine samples with good results.     

Enthalpies of formation of amidyl free radicals

The enthalpies of formation (#x0394;H°_f) of twenty-one amidyl radical (R) belonging to the formamidyl homological series were calculated using the published values of R—H bond dissociation energies. Among them, the H°_f values of nine radicals were first calculated and those of eight radicals were refined. Most of the H°_f values of corresponding starting molecules RH (H°_f(RH)) were obtained using the macroincrementing schemes. Based on the group additivity scheme, the structure—enthalpy of formation relationships for the radicals considered were examined, the H°_f(R) values were analyzed, and their reliability was confirmed. Parameters for calculating the H°_f values of radicals belonging to this homologous series were suggested.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1574–1577, August, 2004.     

Crystal Structures and Magnetic Properties of Cu(II) Complexes with Pyrazole‐Substituted Iminonitroxyl Radicals: New Trinuclear Heterospin Complexes

The paper describes the crystal structures and magnetic properties of complexes of copper(II) hexafluoroacetate (Cu(hfac)₂) with stable pyrazolesubstituted iminonitroxyl radicals containing the pyrazole substitutuent in the second position of the 2imidazoline cycle (L). A new group of [Cu(hfac)₂]₃(L)₂ complexes is found, in which L performs a bidentatebridge function due to the coordination of the imine N atoms of the pyrazole and imidazoline cycles. It is shown that in the solid complexes there are Cu²⁺—N = C—N—O exchange routes with highenergy ferromagnetic interactions (60–100 cm^-1).     

Reduced parabolic model for radical addition reactions

The transition state of addition of free radicals and atoms to multiple bonds is considered as a result of intersecting of two parabolic potential curves. One of them characterizes the stretching vibration of the attacked multiple bond, and another curve characterizes the stretching vibration of the bond formed in the transition state. The force constant of the latter is calculated by an empirical equation that correlates the force constant with the bond dissociation energy. In the framework of this model, the thermally neutral activation energy (E _e0) and the elongation of the attacked and formed bonds (r _e) in the transition state were calculated from the experimental data (activation energy (E _e) and enthalpy of reaction (H _e)) for the addition of an H atom and methyl, alkoxyl, aminyl, triethylsilyl, and peroxyl radicals to the C=C bond and the addition of H and CH₃ to the C=O and CC bonds. Analysis of the data obtained showed that E _e0 depends linearly on the |H _e| + E_e sum, i.e., E_e0/kJ mol^–1 = 14.2 + 0.61 · (E_e – H _e), and the bond elongation in the transition state for addition of the most part of radicals to ethylene and acetylene vary within (0.65–0.87)·10_–10 m. The factors affecting the activation energy of the radical addition reactions are discussed.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1542–August, 2004.     

Determination of Iron in Tap and Waste Water Using Liquid–Liquid Extraction in a Flow-Injection System

A flow-injection procedure for the determination of iron(III) in water is described. The procedure is based on the formation of an ion pair between the tetraphenylarsonium (Ph₄As⁺) (TPA) or tetrabutylammonium (But₄N⁺) (TBA) cations and the tetrathiocyanatoferrate(III) complex (TTF). This ion pair is extracted with chloroform, and the absorbance of the organic phase is measured at 503nm (for Ph₄As⁺) or 475nm (for But₄N⁺). Iron concentrations higher than 0.9×10^–6molL^–1 (50µgL^–1) can be detected in the first case, with a relative standard deviation of 1.9% (n=12), a linear application rangeof between 1.34 and 54.0×10^–6molL^–1 (75–3015µgL^–1), and a sampling frequency of 30h^–1. For the ion pair with But₄N⁺, the detection limit is 0.52×10^–6molL^–1 (29µgL^–1), with a relative standard deviation of 1.6% and a linear application range between 0.73 and 54.0×10^–6molL^–1. Under the proposed working conditions, only Pd(IV), Cu(II) and Bi(III) interfere. With the application of the merging zones technique, considerable amounts of organic reagent can be saved. The TBA method was applied to the analysis of iron(III) in tap and industrial waste waters.     

Mechanisms of Reactions of H2O and NH3 Molecules with (≡Si–O)3Si⋅and (≡ Si–O)3Si–⋅ Radicals on the Silica Surface

Spin traps, which are diamagnetic centers (SiO)₂Si, are used to register low-molecular radicals OH, NH₂, and H formed by the reactions of H₂O and NH₃ molecules with the radicals (Si–O)₃Si and (Si–O)₃Si–O stabilized on the silica surface. The experimental data and the results of quantum-chemical calculations for model systems are used to determine the mechanism and thermochemical characteristics of these reactions. A new paramagnetic center (Si–O)₂SiNH₂ was identified on the silica surface, and its radiospectroscopic characteristics are determined.     

Kinetics of the displacement of aqua ligands from cis-diaqua(ethylenediamine)-platinum(II)perchlorate by adenosine 5′-monophosphate in aqueous medium

The kinetics of the interaction of adenosine 5-monophosphate (5-AMP) with cis-[Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺, [5-AMP] and temperature at pH 4.0, where the substrate complex exists predominantly as the diaqua species. Both N1 and N7 donor sites of 5-AMP are active for coordination to Pt at this pH. Base stacking and metal-induced macrochelate formation of 5-AMP plays a vital role in determining the concentration limit of 5-AMP during kinetics. Substitution occurs in two consecutive steps; both dependent on the 5-AMP concentration. Activation parameters for both steps have been calculated. The low H ₁ (42.76 ± 1.64 kJ mol^–1) and large negative values of S ₁ (–112.1 ± 5.1 J K^–1 mol^–1) as well as H ₂ (58.1 ± 1.4 kJ mol^–1) and S ₂ (–84.2 ± 4.4 J K^–1 mol^–1) indicate associative modes of activation for both ligand substitution processes in the two consecutive steps.