The Free-Radical Cleavage of the Disulfide Bond (Studied by Pulse Radiolysis)

Reaction of H atoms with glutathione leads rapidly to H + RSSR → RS · + RSH. The first observed product is RS, the spectrum of which is obtained. The spectrum of the RS?SR radical was obtained by direct attack of e^?_aq on glutathione. The rate constants of these processes were also measured. k_e?aq + RSSR = (2.7 ± 0.3) × 10⁹ M^?1 sec^?1 k_{H + RSSR} = (1.0 ± 0.2) × 10¹⁰ M^?1 sec^?1 When the OD of RS?SR is plotted vs pH a titration curve is obtained. This is due to the protonation of RS?SR with a rate constant of 2.6 × 10¹⁰ M^?1 sec^?1 which is probably followed by a cleavage to RS and RSH. In both cases the RSSHR radical cannot be detected. The spectrum attributed to the RSSHR radical is more likely to be that of RS.     

Decay of the HO2 and O−2 Radicals Catalyzed by Superoxide Dismutase. A Pulse Radiolytic Investigation

The pulse radiolysis technique has been employed in the investigation of the dismutation of superoxide radicals, O^?₂ and HO₂, in the presence of superoxide dismutase in aqueous solutions. The decay of superoxide radicals in the presence of the enzyme was found to be first order in both enzyme and superoxide concentrations. An apparent second order reaction rate constant was found to be about 2 × 10⁹ M^?1 sec^?1, decreasing slightly as the pH is increased from 5 to 9.5. A mechanism which accounts for all our observations is proposed. It includes two steps: (1) formation of a product (EO^?₂ or E^?) from one enzyme (E) molecule and one O^?₂ radical ion; (2) regeneration of E by a reaction of this product with an additional O^?₂ ion radical. The reaction rate constants k = (1.4 ± 0.2) × 10⁹ and k = (1.9 ± 0.6) × 10⁹ M^?1 sec^?1 were measured at pH = 7 in an oxygenated 0.16 M sodium formate solution.     

Solvation of Substituted Phenoxide Ions in T-Butyl Alcohol-Water Mixtures,from Kinetic Studies of Proton Exchange

Rate constants (k_2W or k_2A) for proton exchange between a phenol, its conjugate base, and a water or t -butyl alcohol molecule have been measured in a t -butyl alcohol-water mixture by nuclear magnetic resonance. Since k_2W and k_2A are both high (k_2W > 10⁸ sec^?1 M^?1), the ratio k_2W/k_2A measures the selective solvation of the O^?-site (of the phenoxide ions) by water and t -butyl alcohol. In 11.47 mole % t -butyl alcohol — 88.53 mole % water, k_2W/k_2A is found to be 14 ± 3 when the ionic reactant is ortho -bromophenoxide ion, and 32 ± 8 when it is meta -nitrophenoxide ion. The results suggest that substituents have a marked effect on the selective solvation of the O^?-site.     

The interaction of hydrogen sulfide with lead- and barium–cadmium–zinc-stabilized poly(vinyl chloride)

Poly(vinyl chloride) polymers stabilized with tribasic lead sulfate discolor upon exposure to hydrogen sulfide gas as a result of lead sulfide formation. The discoloration occurs for samples in both cord and sheet forms and is shown to be a function of total H₂S exposure, reaching a limiting value that is determined by the amount of lead stabilizer used in the polymer formulation. The permeation and diffusion constants for H₂S through PVC stabilized with tribasic lead sulfate and with a liquid Ba–Cd–Zn formulation are found to be P_Pb = (6.0 ± 0.2) × 10^?9, P_BaCdZn = (5.2 ± 0.2) × 10^?9 (both in cm³ gas?cm film/cm² area?sec?cm Hg), D_Pb = (1.3 ± 0.2) × 10^?7 cm²/sec, and D_BaCdZn = (6.4 ± 0.6) × 10^?8 cm²/sec, all measured at 21°C. The stabilizing efficiencies of the formulations were assessed by HCl evolution measurements, which show that exposure to H₂S decreases the initial polymer stability for both Pb-stabilized and Ba–Ca–Zn-stabilized formulations. Protection of stabilized PVC formulations from diffusing hydrogen sulfide is thus advisable for long-term stability as well as for color integrity.     

Comments on the reactivity of methoxy pentadecyl phenyl isocyanate isomers

The reactions of 2-methoxy-4-pentadecyl phenyl isocyanate and 4-methoxy-2-pentadecyl phenyl isocyanate with excess 2-ethyl hexanol originally reported by Ghatge and co-workers to follow zero order kinetics have been re-examined on the basis of their data and shown to follow more realistically the product catalyzed pseudo first order kinetics. The new rate constant, k_s (sec^?1) for the spontaneous reaction and k_p (li. mole^?1 sec^?1) for the product catalyzed reaction are found to be: k_s = 0.57 × 10^?6 and k_p = 34 × 10^?6 for 2-methoxy-4-pentadecyl phenyl isocyanate and k_s = 1.2 × 10^?6 and k_p = 82 × 10^?6 for 4-methoxy-2-pentadecyl phenyl isocyanate.     

Equilibrium and kinetic studies on the extraction of gadolinium(III) from nitrate medium by di‐2‐ethylhexylphosphoric acid in kerosene using a single drop technique

The liquid–liquid extraction of Gd(III) from aqueous nitrate medium was studied using di‐2‐ethylhexylphosphoric acid (HDEHP) in kerosene. On the basis of the slope analysis data, the composition of the extracted species was found to be [Gd A₃(HA)] with the extraction equilibrium constant (K_ex) = (1.48 ± 0.042) × 10^?12 mol dm^?3. The results of the effect of temperature on the value of the equilibrium extraction constant indicated the endothermic character of the extraction system. The kinetics of the forward extraction of Gd³⁺ from nitrate medium by HDEHP in kerosene was investigated using the single drop column technique. The rate of flux (mass transfer per unit area) was found to be proportional to [Gd(III)], [H₂A₂]_(o), [NO₃^?], and [H⁺]^?1 in the liquid drop organic phase. The forward extraction rate constant, k_f, was 2.24 × 10^?3 m s^?1 using the equation: Copyright © 2005 Society of Chemical Industry     

Proton Transfer in Liquid Ammonia Solutions Containing Water and Hydroxide Ion

The rate of proton transfer in ammonia solutions containing water and hydroxide ion was determined as a function of temperature and concentration by means of PMR spectroscopy. A first order dependence on hydroxide ion and second order dependence on water concentration was found with a rate constant of k₃ = 6.1 ± 1.2 × 10³ M^?2 sec^?1 at 25°C and ΔE^? = 4.5 ± 0.5 kcal/mole. The value of k₃ is in good agreement with that reported by other workers.     

Anionic polymerization of styrene in triglyme-benzene mixtures

Living anionic polymerization of styrene was kinetically investigated in triglyme-benzene mixtures. At low concentrations of triglyme the overall propagation rate constant, k_p, was much larger than at the same concentration of monoglyme (DME) in DME-benzene mixtures. The Szwarc-Schulz plot did not have negative slopes for lithium and sodium salts at triglyme contents of 5～20vol%, and no contribution of free anions to the propagation was observed for the sodium salt. The sodium ion pair was more highly reactive than the lithium ion pair; thus at 25°C, the ion pair rate constant, k′_p, for the lithium salt was 43, 102, 135 and 165 M^?1sec^?1 at triglyme concentrations of 5, 10, 15, and 20%, respectively, while that for the sodium salt was 410, 920, and 1460 M^?1sec^?1 in 5, 10, and 15% triglyme, respectively. The dissociation constant, K, for the lithium salt was 2·4×10^?11, 1·9×10^?10 and 1·3×10^?9 M in 10, 15, and 20% triglyme, respectively and the free ion rate constant, k″_p, was 2～2·5×10⁴ M^?1sec^?1 for the lithium salt.     

Flash photolysis investigation on primary processes of the sensitized polymerization of vinyl monomers: 2. Experiments with benzoin and benzoin derivatives

Benzene solutions of benzoin (B), benzoin acetate (BA), benzoinmethyl ether (BME) and benzoinisopropyl ether (BIPE) were irradiated with 0.1 or 25 nsec flashes of 347.1 nm light at room temperature. With B and BA optical absorptions due to radical precursors were detected. The first order decay constants of these absorptions are 1.1 × 10⁸ sec^?1 (B) and 5.3 × 10⁷ sec^?1 (BA). The radical spectra decayed according to second order laws. In the case of B only one mode of decay was observed which accounts for the major part of the reaction (benzaldehyde formation by disproportionation of unlike radicals). During the experiments with BA, BME and BIPE two modes of radical-radical reactions were detected. Styrene was found to react with the rapidly decaying species with k_M = (1.3 ± 0.2) × 10⁵ M^?1 sec^?1, but did not react with the slowly decaying species. By considering the end product analyses of other authors it was concluded that the rapidly decaying mode of the absorption decay is due to the combination of benzoyl radicals forming benzil. The slowly decaying mode was assigned to the combination of alkoxybenzyl radicals (in the case of BME and BIPE) or of acetonbenzyl radicals (in the case of BA) forming pinacol derivatives. The rate constants of the reaction of naphthalene with triplet excited benzoin (7.7 ± 0.8) × 10⁹ M^?1 sec^?1 and benzoin acetate (5.0 ± 0.5) × 10⁹ M^?1 sec^?1 were determined.     

Mechanism of copper(II) adsorption by polyvinyl polyacrylate

The mechanism of copper adsorption by polyvinyl polyacrylate (PVPA) was examined using ESR and magnetic measurements. The copper adsorption by PVPA obeyed Langmuir adsorption isotherm with the maximum adsorption amounts of 4.17 mmol g^?1 adsorbent, being larger than those of uranium adsorption. Though copper in the solution was completely adsorbed by the resin above pH 4, the ESR intensity was remained low level and only increased above pH 8. The ESR spectrum of Cu(II) ion in PVPA are axial type with tetragonally distorted octahedral symmetry, having parameters of g_⊥ = 2.361, g_? = 2.057, |A_⊥| = 14.0 m cm^?1 (pH 5), and g_⊥ = 2.329, g_? = 2.058, |A_⊥| = 16.2 m cm^?1, |A_?| = 2.7 m cm^?1 (pH 9). The absorption peaks originated from Cu(II)–Cu(II) dimer was also observed (pH 5). The paramagnetic susceptibility of PVPA adsorbed Cu(II) ion at pH 5 explained by the dimer model with |J| = 220 K. These results suggested that most of copper was adsorbed and formed dimer in PVPA, being similar to that in Cu(II)‐acetate monohydrate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5372–5377, 2006     

Hydrogen peroxide sensor based on riboflavin immobilized at the nickel oxide nanoparticle-modified glassy carbon electrode

A simple and sensitive electrochemical sensor based on nickel oxide nanoparticles/riboflavin-modified glassy carbon (NiONPs/RF/GC) electrode was constructed and utilized to determine H₂O₂. By immersing the NiONPs/GC-modified electrode into riboflavin (RF) solution for a short period of time (5–300 s), a thin film of the proposed molecule was immobilized onto the electrode surface. The modified electrode showed stable and a well-defined redox couples at a wide pH range (2–10), with surface-confined characteristics. Experimental results revealed that RF was adsorbed on the surface of NiONPs, and in comparison with usual methods for the immobilization of RF, such as electropolymerization, the electrochemical reversibility and stability of this modified electrode has been improved. The surface coverage and heterogeneous electron transfer rate constants (k _s) of RF immobilized on a NiO _x –GC electrode were approximately 4.83 × 10^?11 mol cm^?2, 54 s^?1, respectively. The sensor exhibits a powerful electrocatalytic activity for the reduction of H₂O₂. The detection limit, sensitivity and catalytic rate constant (k _cat) of the modified electrode toward H₂O₂ were 85 nM, 24 nA μM^?1 and 7.3 (±0.2) × 10³ M^?1 s^?1, respectively, at linear concentration rang up to 3.0 mM. The reproducibility of the sensor was investigated in 10 μM H₂O₂ by amperometry, the value obtained being 2.5 % (n = 10). Furthermore, the fabricated H₂O₂ chemical sensor exhibited an excellent stability, remarkable catalytic activity and reproducibility.     

A Spectrophotometric Study of Trivalent Actinide Complexes in Solution. IV. Americium with Chloride Ligands

The light absorption spectra of americium(III) in ethanolic and concentrated aqueous lithium chloride solutions, and in long-chain alkylammonium chloride solutions in aromatic diluents were obtained, as well as those of certain solid double salts and complexes. A strong 5f⁶ → 5f⁵6d¹ transition was observed in the aqueous solutions at 235 nm (42,500 cm^?1), and from the dependence of the intensity of this and the 503 nm (19,880 cm^?1) band, on the effective chloride activity, the stability constants of the inner sphere complexes: AmCl²⁺, logβ₁^* = ?2.21± 0.08, and AmCl₂⁺, log β₂^* = ?4.70 ± 0.08, were determined. The spectrum of the long-chain amine extracts is comparable to that of solids of the composition AmCl₃ · 2N(C₄H₉)₄Cl · × LiCl, and the nature of the extracts and of this and similar solids is discussed.     

Kinetics of Estrone Ozone/Hydrogen Peroxide Advanced Oxidation Treatment

Ozone/hydrogen peroxide batch treatment was utilized to study the degradation of the steroidal hormone estrone (E1). The competition kinetics method was used to determine the rate constants of reaction for direct ozone and E1, and for hydroxyl radicals and E1 at three pH levels (4, 7, and 8.5), three different molar O₃/H₂O₂ ratios (1:2, 2:1, and 4:1) and a temperature about 20°C. The average second-order rate constants for direct ozone-E1 reaction were determined as 6.2?×?10³?±?3.2?×?10³ M^?1s^?1, 9.4?×?10⁵?±?2.7?×?10⁵ M^?1s^?1, and 2.1?×?10⁷?±?3.1?×?10⁶ M^?1s^?1 at pH 4, 7, and 8.5, respectively. It was found that pH had the greatest influence on the reaction rate, whereas O₃/H₂O₂ ratio was found to be slightly statistically significant. For the hydroxyl radical-E1 reaction, apparent rate constants ranged from 1.1?×?10¹⁰ M^?1s^?1 to 7.0?×?10¹⁰ M^?1s^?1 with an average value of 2.6?×?10¹⁰ M^?1s^?1. Overall, O₃/H₂O₂ is shown to be an effective treatment for E1.     

Light‐scattering study of poly(hydroxy ester ether) in N,N‐dimethylacetamide solution

Static and dynamic light‐scattering techniques were used to study biodegradable thermoplastic poly(hydroxy ester ether) in N,N‐dimethylacetamide (DMAc). A weight‐average molecular weight M_W = 6.4 × 10⁴ g/mol, radius of gyration R_G = 9.4 nm, second‐virial coefficient A₂ = 1.05 × 10^?3 mol mL/g², translational diffusion coefficient D = 1.34 × 10^?7 cm²/s, and hydrodynamic radius R_H = 8.3 nm are reported. In addition, the effect of H₂O on the polymer chain's conformation and architecture in a DMAc/H₂O solution is evaluated. Results suggest that H₂O makes the mixed solvent poorer as well as promotes polymer chain branching via intramolecular transesterification. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1737–1745, 2001     

Kinetics of the metal exchange reaction of a Cu(II)-poly(vinyl alcohol) complex with Zn(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid in aqueous solution

The kinetics of the metal exchange reaction between Cu(II)-poly(vinyl alcohol) [Cu(II)-PVA] and Zn(II)-ethylenediamine-N,N,N′,N′-tetraacetic acid [Zn(II)-EDTA] has been studied by mixing both solutions in a spectrophotometer at pH 10.0 to 11.0, ionic strength μ=0.10(KNO₃), and 15 to 35°C. The reaction is initiated by the formation of unstable Cu(II)-H-PVA through attack of H⁺ ion on the Cu(II)-PVA complex, and both reactions, ligand exchange and metal exchange, proceed simultaneously. The metal exchange step may be rate determining. The rate equation and rate constants of this reaction were determined as follows: ?d[Cu(II)-PVA]/dt=k _0(H)[PVA^?][Cu(II)-PVA] [Zn(II)-EDTA], wherek _0(H)=k ₁+(k′₂+k′₃)[H⁺],k ₁=5.98±1.64M ^?1 s^?1, andk ₂+k ₃=k′₂ K _Cu(II)-H-PVA ^?H +k′₃ K _Zn(II)-EDTA ^H =(5.91±0.89)×10⁷ M ^?2 s^?1.     

Untersuchungen zur Polymerisationsauslösung mit Azo-2,4,4-trimethylvaleronitril

The polymerization of styrene in bulk was studied kinetically at 25°C with Azo-2,4.4-trimethylvaleronitrile (ATN) as initiator. The decomposition constant of the initliator at 25°C in benzene is k_z = 8,47 ? 10^?6 sec^?6. For the transfer constant, an apparent value of C₁ = 0,59 was determined, which can be explained by a condrable termination of the growing chains by initiator radicals. A quantitative discussion is possible by the ratio of the rate constants k′_ab/k_w ? k_st, which was determined by different methods. A good congruence of these values was obtained. k′_ab/k_w ? k_st, was also determined for the solution polymerization of vinyl chloride in 1,2-dichloroethane. An increase of these values was observed with decreasing monomer concentration.     

Diffusion of methyl esters of higher fatty acid in polypropylene

Diffusion coefficients of several methyl esters of linear higher fatty acid (C₁₀?C₁₈) into polypropylene (PP) were determined, over the temperature range of 50 to 110°C, using a mass uptake technique. The relations between an amount of mass uptake and t^1/2 were linear within 10 min, indicating Fickian diffusion. The diffusion coefficients were in the range of 4.6×10^?8 to 6.2×10^?12 cm² sec^?1, increased with temperature, and decreased with increasing n-alkyl chain length of fatty acid. The plots of In D vs. the molecular weight of methyl esters were approximately linear. The temperature dependence of diffusion followed an Arrhenius relationship, and the activation energies were in the range of 133 ? 147 KJ mol^?1 and increased with an increase in n-alkyl chain length of corresponding fatty acid. The diffusion coefficients were discussed with the interaction between methyl esters of higher fatty acid and PP. The diffusion coefficients of methyl esters, at the simultaneous diffusion process, were always higher than that derived from the single diffusion process, except for methyl decanoate with lower molecular weight. The difference in diffusion coefficients in single and simultaneous diffusion was discussed thermodynamically. © 1994 John Wiley & Sons, Inc.     

Gibbs free energy of formation of Bi2O3 from EMF cells with δ-Bi2O3 solid electrolyte

Determination of thermodynamic data on the formation of Bi₂O₃ was established by emf measurements as a function of temperature in the range 660–820°C on the system Metal, Bi(1)|Bi₂O₃|Pt, O₂. From the results using a tungsten electrode the following relation was found: ΔG⁰ = ?(134.7 ± 1.2) + (64.0 ± 1.2) × 10^?3 T kcal mole^?1 (validity range: 940–1080 K). Standard thermodynamic data at 298 K were calculated as ΔG⁰ = ?119.2 ± 2.1 kcal mole^?, ΔH⁰ = ?139.0 ± 1.2 kcal mole^?1, and ΔS⁰ = ?66.3 ± 1.2 eu.     

Transient Species in the Laser Photolysis at 265 Mμ of the Halogenobenzenes in Solution

Pulsing cyclohexane or methanol-water solutions of chlorobenzene and fluorobenzene with the Nd laser at 265 mμ (half-height width 30 nsec) gives rise to intermediates, absorbing in the 290–300 mμ region, attributed to the corresponding triplet states. The decay of the triplet states is roughly first order with rate constants of (2.1 ± 0.1) × 10⁶ sec^?1 and (1.5 ± 0.1) × 10⁶ sec^?1 respectively. No transient absorption was observed with bromo- and iodobenzene under the same conditions. Solutions of the two latter compounds containing KI or KBr show the appearance of I^?₂ or IBr^? following laser excitation.