Ionic mechanisms in pulse irradiated poly(vinyl chloride) system containing stabilizing additives

The pulse radiolysis studies of poly(vinyl chloride), PVC, film containing stabilizers i.e., Tinuvin P, Irgastab PVC 11, and Irganox 1076 have been carried out with the main aim of investigating ionic reactions in these systems. The evidences are presented concerning the formation of ionic transients in model solvents i.e. 2‐propanol and sec‐butyl chloride as well as in PVC film. In PVC‐stabilizer system under consideration the additives can contribute to the positive charge transfer processes whereas Tinuvin P, in addition may scavenge effectively electrons (the rate constant for e^?_solv scavenging in 2‐propanol equals 5.9 × 10⁹ mol^?1 dm³ s^?1) influencing the negative charge scavenging by PVC matrix itself and the HCl formation during the radiolysis of PVC. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Pulse Radiolysis and Inactivation of Trypsin

A study of the mechanism of aqueous trypsin inactivation by radiation was carried out by pulse radiolysis and steady irradiation in the presence of various scavengers. The initial products consist of OH radical and H atom adducts to tryptophan residues, and of electron adduct to cystine residues. Essentially, all OH react with trypophan with k(OH + trypsin) = (8.2 ± 1.2) × 10¹⁰ M^?1 sec^?1. The electron adduct to the disulphide bond accounts for about 60 per cent of the electron yield, with k(e_aq + trypsin) = (3.5 ± 0.8) × 10¹⁰ M^?1 sec^?1. Measurements of tryptophan residue loss and sulphydryl formation under different irradiation conditions show that the initial reactions are substantially reversible, except for the destruction of tryptophan under aerobic conditions. Many primary radicals induce inactivation with low independent probabilities, indicating that only a small fraction of the possible reaction sites for each species influence the integrity of the active center.     

Some Biochemical Processes Induced by Radiation as Studied by Pulse Radiolysis

The main types of biochemically important electron transfer substances can be made to undergo reactions under irradiation which in some ways mimic those which occur in nature. In the case of NAD⁺, pulse radiolysis shows that electrons add to the pyridine ring forming an NAD· radical with a characteristic absorption in the visible range which is capable of transferring its electron to oxygen. Using simpler pyridinyl compounds it has been found that, as well as the absorptions in the visible range, the radicals exhibit absorptions in the infrared range which correlate well with transitions which may be deduced from the known charge-transfer bands of the parent compound. The NAD· radical can be made by one-electron oxidation of NADH as well as by reduction of NAD⁺, and the reaction with oxygen enables NADH to be converted into NAD⁺ by an unambiguous free radical route. Cytochrome-c can be reduced either by hydrated electrons or CO₂^?. In solution buffered to neutral pH, the reduction gives rise immediately to normal reduced cytochrome-c, but in mildly alkaline solution, an unstable reduced form appears whose conformation changes over a fraction of a second to that of normal reduced cytochrome-c. As well as the hydrated electron and CO₂^?, the superoxide anion radical O₂^? has also been found to reduce cytochrome-c. This reaction is very slow (k ～ 10⁵ M^?1 sec^?1).     

A Comparison of the γ-Radiolysis of TODGA and T(EH)DGA Using UHPLC-ESI-MS Analysis

Solutions of TODGA and T(EH)DGA in n-dodecane were subjected to γ-irradiation in the presence and absence of an aqueous nitric acid phase and analyzed using UHPLC-ESI-MS to determine the rates of radiolytic decay of the two extractants, as well as to identify radiolysis products. The DGA concentrations decreased exponentially with increasing dose, and the measured degradation rate constants were uninfluenced by the presence or absence of an acidic aqueous phase, or by chemical variations in the alkyl side-chains. The DGA degradation was attributed to reactions of the dodecane radical cation, whose kinetics were measured for TODGA using picosecond electron pulse radiolysis to be k₂ = (9.72 ± 1.10) × 10⁹ M^?1 s^?1. The identified radiolysis products suggest that the bonds most vulnerable to radiolytic attack are those in the diglycolamide center of these molecules and not on the side-chains.     

Investigations of Two Bidirectional Carbon Monoxide Dehydrogenases from Carboxydothermus hydrogenoformans by Protein Film Electrochemistry

Carbon monoxide dehydrogenases (CODHs) catalyse the reversible conversion between CO and CO₂. Several small molecules or ions are inhibitors and probes for different oxidation states of the unusual [Ni‐4 Fe‐4 S] cluster that forms the active site. The actions of these small probes on two enzymes—CODH I_Ch and CODH II_Ch—produced by Carboxydothermus hydrogenoformans have been studied by protein film voltammetry to compare their behaviour and to establish general characteristics. Whereas CODH I_Ch is, so far, the better studied of the two isozymes in terms of its electrocatalytic properties, it is CODH II_Ch that has been characterised by X‐ray crystallography. The two isozymes, which share 58.3 % sequence identity and 73.9 % sequence similarity, show similar patterns of behaviour with regard to selective inhibition of CO₂ reduction by CO (product) and cyanate, potent and selective inhibition of CO oxidation by cyanide, and the action of sulfide, which promotes oxidative inactivation of the enzyme. For both isozymes, rates of binding of substrate analogues CN^? (for CO) and NCO^? (for CO₂) are orders of magnitude lower than turnover, a feature that is clearly revealed through hysteresis of cyclic voltammetry. Inhibition by CN^? and CO is much stronger for CODH II_Ch than for CODH I_Ch, a property that has relevance for applying these enzymes as model catalysts in solar‐driven CO₂ reduction.     

The absorption rate of CO2/SO2/NO2 into a blended aqueous AMP/ammonia solution

The Inter-governmental Panel on Climate Change (IPCC) reported that human activities result in the production of greenhouse gases (CO₂, CH₄, N₂O and CFCs), which significantly contribute to global warming, one of the most serious environmental problems. Under these circumstances, most nations have shown a willingness to suffer economic burdens by signing the Kyoto Protocol, which took effect from February 2005. Therefore, an innovative technology for the simultaneously removal carbon dioxide (CO₂) and nitrogen dioxide (NO₂), which are discharged in great quantities from fossil fuel-fired power plants and incineration facilities, must be developed to reduce these economical burdens. In this study, a blend of AMP and NH₃ was used to achieve high absorption rates for CO₂, as suggested in several publications. The absorption rates of CO₂, SO₂ and NO₂ into aqueous AMP and blended AMP+NH₃ solutions were measured using a stirred-cell reactor at 293, 303 and 313 K. The reaction rate constants were determined from the measured absorption rates. The effect of adding NH₃ to enhance the absorption characteristics of AMP was also studied. The performance of the reactions was evaluated under various operating conditions. From the results, the reactions with SO₂ and NO₂ into aqueous AMP and AMP+NH₃ solutions were classified as instantaneous reactions. The absorption rates increased with increasing reaction temperature and NH₃ concentration. The reaction rates of 1, 3 and 5 wt% NH₃ blended with 30 wt% AMP solution with respect to CO₂/SO₂/NO₂ at 313 K were 6.05～8.49×10^?6, 7.16–10.41×10^?6 and 8.02～12.0×10^?6 kmol m^?2s^?1, respectively. These values were approximately 32.3–38.7% higher than with aqueous AMP solution alone. The rate of the simultaneous absorption of CO₂/SO₂/NO₂ into aqueous AMP+NH₃ solution was 3.83–4.87×10^?6 kmol m^?2s^?1 at 15 kPa, which was an increase of 15.0–16.9% compared to 30 wt% AMP solution alone. This may have been caused by the NH₃ solution acting as an alternative for CO₂/SO₂/NO₂ controls from flue gas due to its high absorption capacity and fast absorption rate.     

Radiolytic and hydrolytic degradation of the hydrophilic diglycolamides

The stability of different hydrophilic diglycolamides against acid degradation and radiolysis was studied. Tetraethyldiglycolamide (TEDGA) was found to undergo degradation in nitric acid at high reaction rates at elevated temperatures with a maximum of a ~8% decrease per hour at 65°C in 4 mol L^–1 HNO₃. The radiolysis was studied for tetramethyldiglycolamide (TMDGA), TEDGA, methyl-tetraethyldiglycolamide (Me-TEDGA), and dimethyl-tetraethyldiglycolamide (Me₂-TEDGA). The degradation rates decreased with increasing molecular weight, following the trend TMDGA > TEDGA > Me-TEDGA ≥ Me₂-TEDGA. Degradation products were identified by mass spectrometric techniques and were found to be comparable to those previously reported for the radiolysis of lipophilic diglycolamides in dodecane. Significant insight into the degradation mechanism in water was gained using pulse radiolysis experiments. The ^?OH radical was identified as the most important reactive species and predominant mechanism of radical reaction is one of electron transfer rather than H-atom abstraction.     

The Formation of CrO2+2 in the Reaction of Cr2+ + O2 in Aqueous Acid Solutions

The reduction rate of Cr³⁺ by e_aq was determined, k₈ = 1.7 × 10¹⁰ M^?1 s^?1. The reaction of Cr²⁺ with O₂ was studied, k₂ = 1.6 × 10⁸ M^?1 s^?1. The spectrum of CrO²⁺₂ was obtained both with the pulse radiolysis method and by mixing Cr²⁺ with excess of O₂. It was shown that CrO²⁺₂ decays slowly to yield HCrO^?₄. The results suggest that the reaction of Cr²⁺ with O₂ is a two electron transfer process.     

Probing Superoxide Dismutases through Radiation Chemistry

Superoxide dismutases (SODs) are metalloenzymes that likely evolved to remove superoxide (O₂^.−) from cells. These enzymes span a range of three uniquely different protein structures and four different metals to enable a similar overall chemistry, the catalytic and accelerated conversion of superoxide to oxygen and hydrogen peroxide. Superoxide dismutases have the attractive feature that the substrate (O₂^.−) for the catalytic reaction is easily generated using radiation chemistry, allowing the ability to follow catalysis on a fast time scale under a wide variety of conditions. This review will show how the utility of radiation chemistry was realized and enabled mechanistic understanding immediately upon discovery of these enzymes. It will then highlight some applications of pulse radiolysis, carried out in this laboratory, that illustrate mechanistic details of the enzyme function for a variety of wild-type and mutant superoxide dismutases.     

Removal of Dichromate Anions with Nanofiltration‐Complexation by using Amino Calix[4]arene Derivative

Abstract

Herein the removal and recovery of chromium anions from aqueous solutions by using nanofiltration pilot‐scale equipment (Osmonics Sepa CF Membrane Cell) with a water‐soluble amino calix[4]arene derivative was studied. To understand the selectivity, the authors also examined the retention of chromium anions in the presence of Cl^?, NO₃ ^?, SO₄ ^2?, HSO₄ ^?, CO₃ ^2?, PO₄ ^3?, H₂PO₄ ^? anions in nanofiltration‐complexation. From the results water‐soluble amino calix[4]arene was effective and selective ligand for dichromate anions over nitrate anions, in a nanofiltration‐complexation system at pH 2.5. Moreover, the recovery and reusability studies of dichromate and nitrate anions and also ligand were performed.     

Laboratory-scale coal reactivity testing for entrained gasification

A relatively simple and rapid micro-gasification test has been developed for measuring gasification reactivities of carbonaceous materials under conditions which are more or less representative of an entrained gasification process, such as the Shell coal gasification process. Coal particles of < 100 μm are heated within a few seconds to a predetermined temperature level of 1000–2000 °C, which is subsequently maintained. Gasification is carried out with either CO₂ or H₂O. It is shown that gasification reactivity increases with decreasing coal rank. The CO₂ and H₂O gasification reactions of lignite, bituminous coal and fluid petroleum coke are probably controlled by diffusion at temperatures 1300–1400 °C. Below these temperatures, the CO₂ gasification reaction has an activation energy of about 100 kJ mol^?1 for lignite and 220–230 kJ mol^?1 for bituminous coals and fluid petroleum coke. The activation energies for H₂O gasification are about 100 kJ mol^?1 for lignite, 290–360 kJ mol^?1 for bituminous coals and about 200 kJ mol^?1 for fluid petroleum coke. Relative ranking of feedstocks with the micro-gasification test is in general agreement with 6 t/d plant results.     

Electrochemical synthesis of dimethyl carbonate from methanol,CO2 and propylene oxide in an ionic liquid

BACKGROUND: Dimethyl carbonate (DMC) can be used effectively as an environmentally benign substitute for highly toxic phosgene and dimethyl sulfate in carbonylation and methylation, as well as a promising octane booster owing to its high oxygen content. Two‐step transesterification from epoxide, methanol, and CO₂ is widely used in the bulk production of DMC. However, major disadvantages of this process are high energy consumption, and high investment and production costs. A one pot synthesis of DMC from carbon dioxide, methanol, and epoxide was, therefore, developed. But the yields of DMC are below 70% due to the thermodynamic limitation. RESULTS: Electrochemical synthesis of DMC was conducted with platinum electrodes from methanol, CO₂ and propylene oxide in an ionic liquid was conducted. The bmimBr (1‐butyl‐3‐methylimidazolium bromide)‐methanol‐propylene oxide system with CO₂ bubbling allows DMC to be effectively synthesized and a high yield (75.5%) was achieved. CONCLUSION: In this electrolysis, redox reactions of substrates, CO₂, methanol, and propylene oxide, on Pt electrodes were carried out, producing the activated particles, CH₃O^?, CH₃OH⁺, CO₂^? and PO^?, resulting in the effective synthesis of DMC with a 75.5% yield in an ionic liquid (bmimBr). Finally, a mechanism for this synthesis reaction was proposed, which is very different from those reported in the literature. Copyright © 2011 Society of Chemical Industry     

Gas transport properties of siloxane polyurethanes

Polyurethanes (PUs) were synthesized from toluenediisocyanates (TDIs) and a polymeric diol having polydimethylsiloxane and polyoxyethylene blocks of the ABA type, ended with OH groups. Prepolymers, prepared in toluene solution using ratios [NCO]/[OH] ≥ 2, were crosslinked with triisopropanolamine (TIPA) (ratio [OH]/[NCO] = 1.1) (two-step process). PUs were also obtained with a one-step process using, contemporaneously, TDI, block copolymer, and, as crosslinking agent, TIPA or the glyceride of ε-hydroxyhexanoic acid. Polydimethylsiloxane (PDMSO) was prepared as a reference material. The course of the reaction between block copolymer and TDI was studied by differential scanning calorimetry in the absence and presence of benzoyl chloride (BzCl). Without BzCl, with ratios [NCO]/[OH] > 2, uncontrolled crosslinking side reactions occur. The properties of the PU films obtained with the two methods were studied both for the density of crosslinking and for gas transport properties. The two-step polymers are less crosslinked than the others and are characterized by higher diffusion coefficients and by higher permeability to gases. The permeability order is 10^?9 (N cm³ cm^?1 cm^?1 cm Hg^?1 s^?1) for CH₄, O₂, CO, and N₂ and is 10 times higher for CO₂. The selectivity for the couple O₂/N₂ is higher than that obtained with PDMSO films. Considerable selectivities are shown for the couples CO₂/N₂ and CO₂/CO. © 1995 John Wiley & Sons, Inc.     

Influences of free-air CO2 enrichment (FACE), nitrogen fertilizer and crop residue incorporation on CH4 emissions from irrigated rice fields

To investigate the response of methane (CH₄) emissions to an elevated atmospheric carbon dioxide (CO₂) concentration (200?±?40???mol?mol^?1 higher than the ambient atmosphere), we performed a 4-year multi-factorial experiment at a subtropical rice paddy that contained sandy loam soil in the Yangtze River Delta from 2004 to 2007 using free-air CO₂ enrichment (FACE) technology. Our results revealed that the elevated atmospheric CO₂ increased the seasonal cumulative CH₄ emissions by 15?% on average during the 4-year period. The increase was insignificant and much weaker than the previous studies, which might be primarily attributed to the absence of a significant difference in the rice biomass between the two CO₂ levels in half of the field treatments. Crop residue incorporation hindered the stimulatory effects induced by the elevated CO₂, which were 37, 14 and 6?% for the fields that were incorporated with none, half or all of the wheat straws that were harvested in the preceding winter wheat season, respectively. Nitrogen fertilizers application also hindered the stimulatory effects of the elevated CO₂ on the CH₄ emissions. The CO₂ stimulatory effect was 39?% for the field without nitrogen fertilizers, and reduced to 17, 7 and 5?% for the field with nitrogen fertilization of 125, 250 and 350?kg?N?ha^?1, respectively. The regulation of nitrogen fertilizers on the CO₂ effects in this experiment does not well agree with the previous studies, which might because the soil type was different from those of the previous studies. Thus, further studies are necessary to evaluate the role of soil properties in regulating the effects of elevated atmospheric CO₂ on CH₄ emissions from managed and natural wetlands. There were no significant interactions between the atmospheric CO₂ and the incorporations of nitrogen fertilizer and crop residue. Appropriate experiments are necessary for better understanding of the interact influences of the elevated CO₂ and farm managements.     

Reaction mechanisms of lithium garnet pellets in ambient air: The effect of humidity and CO2

Li₇La₃Zr₂O₁₂ (LLZO) has been reported to react in humid air to form Li₂CO₃ on the surface, which decreases ionic conductivity. To study the reaction mechanism, 0.5‐mol Ta‐doped LLZO (0.5Ta–LLZO) pellets are exposed in dry (humidity ~5%) and humid air (humidity ~80%) for 6 weeks, respectively. After exposure in humid air, the formation of Li₂CO₃ on the pellet surface is confirmed experimentally and the room‐temperature ionic conductivity is found to drop from 6.45×10^?4 S cm^?1 to 3.61×10^?4 S cm^?1. Whereas for the 0.5Ta–LLZO samples exposed in dry air, the amount of formed Li₂CO₃ is much less and the ionic conductivity barely decreases. To further clarify the reaction mechanism of 0.5Ta–LLZO pellets with moisture, we decouple the reactions between 0.5Ta–LLZO with water and CO₂ by immersing 0.5Ta–LLZO pellets in deionized water for 1 week and then exposing them to ambient air for another week. After immersion in deionized water, Li⁺/H⁺ exchange occurs and LiOH H₂O forms on the surface, which is a necessary intermediate step for the Li₂CO₃ formation. Based on these observations, a reaction model is proposed and discussed.     

New Amine Blends for Improved CO2 Separation: A Study on Reaction Kinetics and Vapor–Liquid Equilibrium

Gas cleaning will be more eco-friendly if the absorbents used for CO₂ capture are prepared from renewable supplies such as ethanol. Ethylene diamine (EDA), N-ethylmonoethanolamine (EMEA), N-ethyldiethanolamine (EDEA), and N,N′-diethylmonoethanolamine (DEMEA) represent this class of solvents. We selected two new blends from this group: EDEA?+?EMEA and DEMEA?+?EDA. Thus, a high-capacity tertiary amine (EDEA or DEMEA) was mixed with a very reactive amine (EMEA or EDA). Using a stirred cell, we analyzed kinetics of the CO₂ reaction with these blends in aqueous solutions (2–3?M) at 308?K. On the whole, two reactions ensued in parallel: one, between CO₂ and EDEA (or DEMEA), and the other, between CO₂ and EMEA (or EDA). We evidenced that DEMEA and DEMEA?+?EDA were more reactive than EDEA and EDEA?+?EMEA. We reported the rate constant for EMEA and EDA (4700 and 28,300?M^?1?s^?1). Finally, we presented vapor–liquid equilibrium data for the DEMEA?+?EDA blend.     

Numerical simulation of CO2 absorption into aqueous methyldiethanolamine solutions

The CO₂ absorption rate into aqueous N-methyldiethanolamine solutions was measured using a stirred cell with a flat gas-liquid interface. The measurements were performed in the temperature range of 293.15 to 333.15 K for various amine concentrations and CO₂ partial pressures. A numerical model of mass-transfer with complex chemical reactions based on the film theory was developed to interpret the experimental results. The model predictions have been found to be in good agreement with the experimental values of CO₂ absorption rates. A comparison is made between the enhancement factor predicted from the detailed model and the approximate solution of mass transfer equations with chemical reaction. The numerical results indicate that under the present experimental conditions, the effect of the reaction between CO₂ and OH^? on the observed mass transfer rates is negligible. The detailed mass transfer model was used for simulating the CO₂ absorption process in terms of the enhancement factor under a variety of operating conditions.     

Primary Events in the Radiolysis of Nucleic Acids and their Components

The radiolysis of dilute aqueous solutions of DNA and its components is discussed, with particular reference to the rates of reaction and the sites of reaction of the primary reactive species, OH, H and e^?_aq. Recent work on the formation and subsequent reactions of OH? and electron-adducts of pyrimidines is described.     

Oxidation of Amino Acids,Peptides and Proteins by Ozone: A Review

The kinetics and products of the reaction of ozone with specific amino acids, peptides, and proteins are reviewed based on studies reported in the literature. Ozone reacts mainly with the unprotonated amino group of the acids and the second-order ozone rate constants for these reactions, except for cysteine, methionine, and tryptophan, vary by about two-orders from 2.6?×?10⁴ to 4.4?×?10⁶ M^?1s^?1. The site of attack on cysteine and methionine by O₃ is at the sulfhydryl rather than the amino group to give sequential O-atom addition products. The order of reactivity for the oxidation of amino acids by O₃ at pH 8 is cysteine > tryptophan ≈ methionine > phenylalanine ≈ histidine > others, with half-lives mostly in the range of milliseconds to tens of seconds (1 mg L^-1 O₃ dose). Reactions of O₃ with aliphatic amino acids form nitrate, ammonia, and one or two carbon atom-containing carbonyl and carboxylic byproducts. In the ozonolysis of peptides and proteins, oxidation by O₃ occurs at the tyrosine, tryptophan, histidine, cysteine, and methionine residues. Oxidation of proteins results in changes in their folding ability and tertiary structures.     

Preparation of vinyl amine‐co‐vinyl alcohol/polysulfone composite membranes and their carbon dioxide facilitated transport properties

A vinyl amine–vinyl alcohol copolymer (VAm–VOH) was synthesized through free‐radical polymerization, basic hydrolysis in methanol, acidic hydrolysis in water, and an anion‐exchange process. In the copolymer, the primary amino groups on the VAm segment acted as the carrier for CO₂‐facilitated transport, and the vinyl alcohol segment was used to reduce the crystallinity and increase the gas permeance. VAm–VOH/polysulfone (PS) composite membranes for CO₂ separation were prepared with the VAm–VOH copolymer as a selective layer and PS ultrafiltration membrane as a support. The membrane gas permselectivity was investigated with CO₂, N₂, and CH₄ pure gases and their binary mixtures. The results show that the CO₂ transport obeyed the facilitated transport mechanism, whereas N₂ and CH₄ followed the solution–diffusion mechanism. The increase in the VAm fraction in the copolymer resulted in a carrier content increase, a crystallinity increase, and intermolecular hydrogen‐bond formation. Because of these factors, the CO₂ permeance and CO₂/N₂ selectivity had maxima with the VAm fraction. At an optimum applied pressure of 0.14 MPa and at an optimum VAm fraction of 54.8%, the highest CO₂ permeance of 189.4 GPU [1 GPU = 1 × 10^?6 cm³(STP) cm^?2 s^?1 cmHg^?1] and a CO₂/N₂ selectivity of 58.9 were obtained for the CO₂/N₂ mixture. The heat treatment was used to improve the CO₂/N₂ selectivity. At an applied pressure of 0.8–0.92 MPa, the membrane heat‐treated under 100°C possessed a CO₂ permeance of 82 GPU and a CO₂/N₂ selectivity of 60.4, whereas the non‐heat‐treated membrane exhibited a CO₂ permeance of 111 GPU and a CO₂/N₂ selectivity of 45. After heat treatment, the CO₂/N₂ selectivity increased obviously, whereas the CO₂ permeance decreased. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40043.