Radical Decomposition Research Articles

Electrochemical and photochemical characteristics of organic dyes and biological molecules at conducting polymer-modified electrodes of indium oxide-polypyrrole nanohybrids

The use of In2O3 nanomaterials is increasing due to their many applications in a range of areas, such as biomedicine, semiconductor and photocatalyst. There are very poor studies of In2O3 nanoparticles for electrocatalyst, in this article, we have investigated the catalytic function of the polypyrrole (PPy) is hybrids with In2O3 nanoparticle. Also, we have synthesized by In2O3 nanoparticles in 20 nm, crystalline were produced. The In2O3-PPy nanohybrid can be exhibits electrocatalytic oxidation if exposed to Mebendazole (MBZ), as per catalytic studies for DPV. Subsequent the synthesis, the analysis performed for In2O3-PPy nano hybrid modified glassy carbon electrode (GCE) via a differential pulse voltammetry (DPV) technique showed linear responses towards the MBZ drug in the concentration range of 3 × 10−7 − 9 × 10−8 M with the sensitivity of 3.02 µA/µM cm−2. The detection limit (DL) and quantification limit (QL) were 1.406 × 10-8 and 4.518 × 10-8 M µA-1 respectively. We have prepared in In2O3-PPy nanohybrid electrode is considered as suitable for the electrochemical sensor detection of MBZ in liquid samples such as anti-helthiminic drug milk. However, in this In2O3-PPy nano hybrid was increased the formation of reactive hydroxide ions (OH). It is superoxide radical decomposition of methylene blue (MB) degradation. Further, future advances, such as the development of a superficial and versatile fabrication technique, can significantly enhance the catalytic and easily modifiable working electrode performance in donor–acceptor types of In2O3-PPy nanohybrids.

Laminar burning velocity measurements of C1-C4 alkane-air mixtures at elevated mixture temperatures

This study presents, the measurements of the laminar burning velocity (LBV) for C1-C4 alkane fuels with air at higher mixture temperatures, using an externally heated diverging channel (EHDC) method. The experimental results are shown for mixture conditions ranging from ϕ = 0.7 to 1.3, with a mixture temperature of 350–660 K at ambient pressure conditions. The temperature exponent (α) is obtained using the power-law correlation to explain the influence of LBV variation with the mixture temperature at different mixture equivalence ratios, ϕ. The maximum value of mixture burning velocity is recorded for marginally rich mixture conditions, (ϕ = 1.1) at different temperatures. The lowest value of temperature exponent (α) is observed at ϕ = 1.1. The data obtained from the current measurements are then compared with the literature results, and mechanism predictions are made using the kinetic models of USC Mech II, FFCM-1, Aramco Mech 2.0, Qin Mech, San Diego Mech, GRI Mech 3.0, and LLNL. The normalized sensitivity analysis for these straight chain C1-C4 alkane fuels reveals that the decomposition of formyl radical in reaction R163: HCO + M ↔ H + CO + M, which exhibits further major root of H atom, leading to enhancement of the LBV of these fuels at elevated mixture temperature conditions.

Construction of Cupriavidus necator displayed with superoxide dismutases for enhanced growth in bioelectrochemical systems

It is of great significance to utilize CO2 as feedstock to synthesize biobased products, particularly single cell protein (SCP) as the alternative food and feed. Bioelectrochemical system (BES) driven by clean electric energy has been regarded as a promising way for Cupriavidus necator to produce SCP from CO2 directly. At present, the key problem of culturing C. necator in BES is that reactive oxygen species (ROS) generated in cathode chamber are harmful to bacterial growth. Therefore, it is necessary to find a solution to mitigate the negative effect of ROS. In this study, we constructed a number of C. necator strains displayed with superoxide dismutase (SOD), which allowed the decomposition of superoxide anion radical. The effects of promoters and signal peptides on the cell surface displayed SOD were analyzed. The proteins displayed on the surface were further verified by the fluorescence experiment. Finally, the growth of C. necator CMS incorporating a pBAD-SOD-E-tag-IgAβ plasmid could achieve 4.9 ± 1.0 of OD600 by 7 days, equivalent to 1.7 ± 0.3 g/L dry cell weight (DCW), and the production rate was 0.24 ± 0.04 g/L/d DCW, around 2.7-fold increase than the original C. necator CMS (1.8 ± 0.3 of OD600). This study can provide an effective and novel strategy of cultivating strains for the production of CO2-derived SCP or other chemicals in BES.Graphical

Direct Observation of the Ethyl Radical in the Pyrolysis of Ethane.

We report the first direct detection of ethyl radical in the pyrolysis of ethane. Observation of this vital intermediate was made possible in this extremely reactive environment by the use of a microreactor coupled with synchrotron radiation and photoelectron photoion coincidence (PEPICO) spectroscopy, despite its short lifetime and low concentration. Together with ab-initio master equation-calculated rates and fully coupled computational fluid dynamics simulations, our measurements show that even under the low pressures and short residence times in our experiment, ethyl formation can only be explained by bimolecular reactions; the most important is the catalytic attack of ethane by H atoms, which are then regenerated by decomposition of the nascent ethyl radicals. Our results complete the observation of all hypothesized intermediates in this industrially important process and highlight the need for further studies under additional conditions using similar methods to improve existing models and optimize process chemistries.

Direct Observation of the Ethyl Radical in the Pyrolysis of Ethane

AbstractWe report the first direct detection of ethyl radical in the pyrolysis of ethane. Observation of this vital intermediate was made possible in this extremely reactive environment by the use of a microreactor coupled with synchrotron radiation and photoelectron photoion coincidence (PEPICO) spectroscopy, despite its short lifetime and low concentration. Together with ab‐initio master equation‐calculated rates and fully coupled computational fluid dynamics simulations, our measurements show that even under the low pressures and short residence times in our experiment, ethyl formation can only be explained by bimolecular reactions; the most important is the catalytic attack of ethane by H atoms, which are then regenerated by decomposition of the nascent ethyl radicals. Our results complete the observation of all hypothesized intermediates in this industrially important process and highlight the need for further studies under additional conditions using similar methods to improve existing models and optimize process chemistries.

Thermal Decomposition Path-Studied by the Simultaneous Thermogravimetry Coupled with Fourier Transform Infrared Spectroscopy and Quadrupole Mass Spectrometry-Of Imidazoline/Dimethyl Succinate Hybrids and Their Biological Characterization.

The thermal decomposition path of synthetically and pharmacologically useful hybrid materials was analyzed in inert and oxidizing conditions for the first time and presented in this article. All the imidazoline/dimethyl succinate hybrids (1-5) were studied using the simultaneous thermogravimetry (TG) coupled with Fourier transform infrared spectroscopy (FTIR) and quadrupole mass spectrometry (QMS). It was found that the tested compounds were thermally stable up to 200-208 °C (inert conditions) and up to 191-197 °C (oxidizing conditions). In both furnace atmospheres, their decomposition paths were multi-step processes. At least two major stages (inert conditions) and three major stages (oxidizing conditions) of their decomposition were observed. The first decomposition stage occurred between T5% and 230-237 °C. It was connected with the breaking of one ester bond. This led to the emission of one methanol molecule and the formation of radicals capable of further radical reactions in both used atmospheres. At the second decomposition stage (Tmax2) between 230-237 °C and 370 °C (inert conditions), or at about 360 °C (oxidizing conditions), the cleavage of the second ester bond and N-N and C-C bonds led to the emission of CH3OH, HCN, N2, and CO2 and other radical fragments that reacted with each other to form clusters and large clusters. Heating the tested compounds to a temperature of about 490 °C resulted in the emission of NH3, HCN, HNCO, aromatic amines, carbonyl fragments, and the residue (Tmax2a) in both atmospheres. In oxidizing conditions, the oxidation of the formed residues (Tmax3) was related to the production of CO2, CO, and H2O. These studies confirmed the same radical decomposition mechanism of the tested compounds both in inert and oxidizing conditions. The antitumor activities and toxicities to normal cells of the imidazoline/dimethyl succinate hybrids were also evaluated. As a result, the two hybrid materials (3 and 5) proved to be the most selective in biological studies, and therefore, they should be utilized in further, more extended in vivo investigations.

Temperature -and pressure-dependent branching ratios for 2,6-dimethylheptyl radicals (C9H19) + O2 reaction: An ab initio and RRKM/ME approach on a key component of bisabolane biofuel

Chemical kinetics mechanisms contain elementary reactions and associated Arrhenius rate parameters are necessary to understand the modeling of hydrocarbon autoignition chemistry. The complexity of such mechanisms is increased due to interest in operating next-generation combustion strategies in the low-temperature region (≤1000 K), which is governed by O2-addition to alkyl radicals (R), subsequent radical isomerization and decomposition steps thereafter. In this work, we report theoretically the reaction of molecular oxygen to the four isomers of 2,6-dimethylheptyl radicals (C9H19). The stationary points on potential energy surfaces (PES), rate constants, and branching ratios from C9H19 isomers initiated by O2 has been investigated by a combination of ab initio/density functional theory (CBS-QB3) and advanced statistical rate theory i.e., microcanonical variational transition state theory (μCVTST) and Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation (ME) simulations. The temperature- and pressure-dependent rate constants and branching ratios over temperature range 400 K–1000 K (with an interval of 50 K) and with different pressures 0.001, 0.01, 0.1, 1, 10 and 100 bar were computed. The RRKM/ME calculations reveal for addition of O2 to the primary radical, 2,6-dimethylhept-1-yl + O2 reaction, the formation of 2-iso-butyl-4-methyl-tetrahydrofuran (a five membered cyclic ether) + OH via concerted C–C and O–O bond scission of primary-secondary QOOH and formation of ROO-1 is the kinetically favorable pathway below 600 K. For 2,6-dimethylhept-2-yl + O2, three competitive favorable channels lead to the formation of 5-iso-propyl-2,2-dimethyl-tetrahydrofuran + OH, a five membered cyclic ether formed coincident with OH in a chain-propagating step from decomposition of tertiary-secondary hydroperoxyalkyl (QOOH), formation of a six membered cyclic ether i.e., 2,2,6,6-tetramethylpyran and ROO-2, however at higher temperature (>900 K) and 2–6-dimethyl-2-heptene is contributed equally over other products. For 2,6-dimethylhept-3-yl + O2 reaction, leading to 5-iso-propyl-2,2-dimethyltetrahydrofuran + OH (same products as in ROO-2) from decomposition of secondary–tertiary hydroperoxyalkyl (QOOH). For 2,6-dimethylhept-4-yl + O2 reaction, it reveals the formation of chain-propagation channels leading to iso-butene + methyl-isobutanal + OH. The results of this study reveals the importance of temperature- and pressure-dependent branching ratios, which is necessary to understand the low temperature internal combustion mechanism. The unimolecular rate constants were also compared with the previously reported values for 2,6-dimethylheptyl radical + O2 and similar reaction system i.e., 2,5-dimethylhexyl radical + O2. The updated rate constants and branching ratios may also serve as general prototypes for low-temperature oxidation of branched alkanes of next-generation biofuels with similar structural motifs, such as bisabolane and farnesane.

Photoenhanced Radical Formation in Aqueous Mixtures of Levoglucosan and Benzoquinone: Implications to Photochemical Aging of Biomass-Burning Organic Aerosols.

The photochemical aging of biomass-burning organic aerosols (BBOAs) by exposure to sunlight changes the chemical composition over its atmospheric lifetime, affecting the toxicological and climate-relevant properties of BBOA particles. This study used electron paramagnetic resonance (EPR) spectroscopy with a spin-trapping agent, 5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO), high-resolution mass spectrometry, and kinetic modeling to study the photosensitized formation of reactive oxygen species (ROS) and free radicals in mixtures of benzoquinone and levoglucosan, known BBOA tracer molecules. EPR analysis of irradiated benzoquinone solutions showed dominant formation of hydroxyl radicals (•OH), which are known products of reaction of triplet-state benzoquinone with water, also yielding semiquinone radicals. In addition, hydrogen radicals (H•) were also observed, which were not detected in previous studies. They were most likely generated by photochemical decomposition of semiquinone radicals. The irradiation of mixtures of benzoquinone and levoglucosan led to substantial formation of carbon- and oxygen-centered organic radicals, which became prominent in mixtures with a higher fraction of levoglucosan. High-resolution mass spectrometry permitted direct observation of BMPO-radical adducts and demonstrated the formation of •OH, semiquinone radicals, and organic radicals derived from oxidation of benzoquinone and levoglucosan. Mass spectrometry also detected superoxide radical adducts (BMPO-OOH) that did not appear in the EPR spectra. Kinetic modeling of the processes in the irradiated mixtures successfully reproduced the time evolution of the observed formation of the BMPO adducts of •OH and H• observed with EPR. The model was then applied to describe photochemical processes that would occur in mixtures of benzoquinone and levoglucosan in the absence of BMPO, predicting the generation of HO2• due to the reaction of H• with dissolved oxygen. These results imply that photoirradiation of aerosols containing photosensitizers induces ROS formation and secondary radical chemistry to drive photochemical aging of BBOA in the atmosphere.

Isopropylcyclohexane pyrolysis at high pressure and temperature: Part 1- theoretical study

The thermal decomposition of isopropylcyclohexane (IPCH) has been investigated at the CBS-QB3 and CASSCF/MRCI levels of theory. The pyrolysis of IPCH follows a radical chain mechanism, which mainly includes the C–C bond scission, H-atom abstraction, dissociation of alkene and alkyl-cyclohexene, decomposition, and isomerization of alkyl-cyclohexane radicals, decomposition and isomerization of alkenyl radicals, and stepwise dehydrogenation of cyclic intermediates. The rate constants for all elementary reactions have been evaluated with conventional transition state theory (TST/VTST) in the temperature range of 800–2000 K. The energy barriers and rate constants have been compared with previous theoretical reports of other cyclohexanes (like cyclohexane, methylcyclohexane, and ethylcyclohexane) to see the effect of isopropyl group in the cyclohexane dissociation. The final products of IPCH thermal decomposition are methane (CH4), ethylene(C2H4), propylene (C3H6), 1,3-butadiene (1,3-C4H6), and 1,3-pentadiene (1,3-C5H8), benzene, cyclopentadiene etc. The main goal of this work has been to come up with a detailed description of the IPCH thermal decomposition using high-level quantum chemical methods and provide reliable kinetic information to help in understanding the results from shock tube investigations discussed in part 2 of this work.

New insights into persulfate decomposition by soil minerals: radical and non-radical pathways

Persulfate (PS)-based in situ chemical oxidation (ISCO) has been widely used for pollutant remediation in soil and groundwater. However, the underlying mechanism of interactions between mineral and PS was not fully explored. In this study, several soil model minerals including goethite, hematite, magnetite, pyrolusite, kaolin, montmorillonite, and nontronite were selected to investigate their potential effects on PS decomposition and free radical evolution. It was found the decomposition efficiency of PS by these minerals varied significantly, and both the radical and non-radical decomposition processes were included. Pyrolusite has the highest reactivity for PS decomposition. However, PS decomposition is prone to form SO42- through non-radical pathway, and thus, the amounts of free radicals (e.g., •OH and SO4•-) produced are relatively limited. However, PS mainly decomposed to produce free radicals in the presence of goethite and hematite. In the presence of magnetite, kaolin, montmorillonite, and nontronite, PS both decomposed to produce SO42- and free radicals. Furthermore, the radical process exhibited the high degradation performance for model pollutant such as phenol with relatively high utilization efficiency of PS, while non-radical decomposition has limited contribution to phenol degradation with extremely low utilization efficiency of PS. This study deepened the understanding of interactions between PS and minerals during the PS-based ISCO in soil remediation.

Comparison of isoprene chemical mechanisms under atmospheric night-time conditions in chamber experiments: evidence of hydroperoxy aldehydes and epoxy products from NO3 oxidation

Abstract. The gas-phase reaction of isoprene with the nitrate radical (NO3) was investigated in experiments in the outdoor SAPHIR chamber under atmospherically relevant conditions specifically with respect to the chemical lifetime and fate of nitrato-organic peroxy radicals (RO2). Observations of organic products were compared to concentrations expected from different chemical mechanisms: (1) the Master Chemical Mechanism, which simplifies the NO3 isoprene chemistry by only considering one RO2 isomer; (2) the chemical mechanism derived from experiments in the Caltech chamber, which considers different RO2 isomers; and (3) the FZJ-NO3 isoprene mechanism derived from quantum chemical calculations, which in addition to the Caltech mechanism includes equilibrium reactions of RO2 isomers, unimolecular reactions of nitrate RO2 radicals and epoxidation reactions of nitrate alkoxy radicals. Measurements using mass spectrometer instruments give evidence that the new reactions pathways predicted by quantum chemical calculations play a role in the NO3 oxidation of isoprene. Hydroperoxy aldehyde (HPALD) species, which are specific to unimolecular reactions of nitrate RO2, were detected even in the presence of an OH scavenger, excluding the possibility that concurrent oxidation by hydroxyl radicals (OH) is responsible for their formation. In addition, ion signals at masses that can be attributed to epoxy compounds, which are specific to the epoxidation reaction of nitrate alkoxy radicals, were detected. Measurements of methyl vinyl ketone (MVK) and methacrolein (MACR) concentrations confirm that the decomposition of nitrate alkoxy radicals implemented in the Caltech mechanism cannot compete with the ring-closure reactions predicted by quantum chemical calculations. The validity of the FZJ-NO3 isoprene mechanism is further supported by a good agreement between measured and simulated hydroxyl radical (OH) reactivity. Nevertheless, the FZJ-NO3 isoprene mechanism needs further investigations with respect to the absolute importance of unimolecular reactions of nitrate RO2 and epoxidation reactions of nitrate alkoxy radicals. Absolute concentrations of specific organic nitrates such as nitrate hydroperoxides would be required to experimentally determine product yields and branching ratios of reactions but could not be measured in the chamber experiments due to the lack of calibration standards for these compounds. The temporal evolution of mass traces attributed to product species such as nitrate hydroperoxides, nitrate carbonyl and nitrate alcohols as well as hydroperoxy aldehydes observed by the mass spectrometer instruments demonstrates that further oxidation by the nitrate radical and ozone at atmospheric concentrations is small on the timescale of one night (12 h) for typical oxidant concentrations. However, oxidation by hydroxyl radicals present at night and potentially also produced from the decomposition of nitrate alkoxy radicals can contribute to their nocturnal chemical loss.

Study on the synergistic inhibition mechanism of multicomponent powders on methane explosions

To obtain a new multicomponent powder with superior ability to inhibit methane explosions, sodium bicarbonate (NaHCO3), aluminum hydroxide (Al(OH)3), potassium carbonate (K2CO3) and ammonium dihydrogen phosphate (NH4H2PO4) were mixed, and a 20 L spherical vessel was used to study the inhibitive effect of the multicomponent powders on methane explosions. The results reveal that the inhibiting effect of the multicomponent powder on methane explosions was greater than that of individual powders, mainly due to the rapid thermal decomposition and consumption of C-containing radicals. At a fixed powder concentration, the explosion pressure, pressure rise rate and flame propagation velocity of methane explosion were less with the multicomponent powder than the individual powders, and radical production and production rate were reduced to a larger degree. The methane explosion flame was more susceptible to the buoyancy effect under multicomponent powder inhibition. The analysis revealed the synergistic inhibition mechanism of the multicomponent powder.

Oxidation of norbornadiene: Theoretical investigation on H-atom abstraction and related radical decomposition reactions

The chemical kinetics of hydrogen atom (H-atom) abstraction reactions from norbornadiene (NBD) by five radicals (H, O(3P), OH, CH3, and HO2), and the unimolecular reactions of three NBD derived radicals, were studied through high-level ab-initio calculations. The geometries optimization and vibrational frequencies calculation for all the reactants, transition states, and products were obtained at the M06-2X/6-311++G(d,p) level of theory. The zero-point energy (ZPE) corrected potential energy surfaces (PESs) were determined at the QCISD(T)/cc-pVDZ, TZ level of theory with basis set corrections from MP2/cc-pVDZ, TZ, QZ methods for single point energy calculations. Conventional transition state theory (TST) was used for the rate constants calculations of H-atom abstraction reactions by five radicals (H, O(3P), OH, CH3, and HO2) at temperatures from 298.15 to 2000 K, while the α-site H-atom abstraction reaction rate constant of NBD by OH radical has been obtained through variational transition state theory (VTST). The results show that the H-atom abstraction reactions from the α-carbon atom of NBD are the most critical channels at low temperatures. Total rate constants for H-atom abstraction reactions by OH radical are also the fastest among all of the reaction channels investigated at the temperature range from 298.15 to 2000 K. Rice-Ramsperger-Kassel-Marcus/Master Equation (RRKM/ME) has been used to calculate the pressure- and temperature-dependent rate constants for the unimolecular reactions of three related C7H7 product radicals which generated from H-atom abstraction reaction within temperature ranges of 300–2000 K and pressures of 0.01–100 atm. A combination of composite methods has been used to calculate the temperature-dependent thermochemical properties of NBD and related radicals. All the calculated kinetics and thermochemistry data can be utilized in the model development for NBD oxidation.

Investigation of Methylcyclopentadiene Reactivity: Abstraction Reactions and Methylcyclopentadienyl Radical Unimolecular Decomposition.

Understanding the reactivities of methylcyclopentadiene and the methylcyclopentadienyl radical is important in order to improve our comprehension of the chemical kinetics leading to the formation, decomposition, and growth of the first aromatic ring, as it has been shown that five-membered-ring species are important intermediates in the reaction kinetics of aromatic species. In this work, the rate constants of some key H-abstraction reactions from methylcyclopentadiene to produce the methylcyclopentadienyl radical and the formation of fulvene and benzene from the latter are theoretically determined. Rate constants are evaluated using the ab initio transition state theory-based master equation approach, determining structures and Hessians of all stationary points at the ωB97X-D/aug-cc-pVTZ level, energies at the CCSD(T) level extrapolated to the complete basis set limit, RRKM rate constants using conventional and variational transition state theory, and phenomenological rate constants through the solution of the one-dimensional master equation. Variational corrections are determined in both internal and Cartesian coordinates, and it is found that the choice of the coordinate system can impact the accuracy of the calculated rate constants by up to a factor of 4 for H-abstraction reactions and 2 for the unimolecular decomposition of the methylcyclopentadienyl radical. The calculated rate constants are in good agreement with the available literature data. Prompt dissociation of methylcyclopentadienyl radicals accessed following H-abstraction from methylcyclopentadiene was also investigated, and the corresponding rate constants were determined; the results show that prompt dissociation plays a key role under combustion conditions. Finally, lumping of theoretically derived rate constants to account for methylcyclopentadiene ⇄ methylcyclopentadienyl tautomerism allowed the derivation of a simplified set of rate constants suitable to be inserted into kinetic mechanisms.

Improved Fuel Cell Chemical Durability of an Heteropoly Acid Functionalized Perfluorinated Terpolymer-Perfluorosulfonic Acid Composite Membrane

Commercial proton exchange membrane heavy-duty fuel cell vehicles will require a five-fold increase in durability compared to current state-of-the art light-duty fuel cell vehicles. We describe a new composite membrane that incorporates silicotungstic heteroply acid (HPA), α-K8SiW11O40▪13H2O, a radical decomposition catalyst and when acid-exchanged can potentially conduct protons. The HPA was covalently bound to a terpolymer of tetrafluoroethylene, vinylidene fluoride, and sulfonyl fluoride containing monomer (1,1,2,2,3,3,4,4-octafluoro-4-((1,2,2-trifluorovinyl)oxy)butane-1-sulfonyl fluoride) by dehydrofluorination followed by addition of diethyl (4-hydroxyphenyl) phosphonate, giving a perfluorosulfonic acid-vinylidene fluoride-heteropoly acid (PFSA-VDF-HPA). A composite membrane was fabricated using a blend of the PFSA-VDF-HPA and the 800EW 3M perfluoro sulfonic acid polymer. The bottom liner-side of the membrane tended to have a higher proportion of HPA moieties compared to the air-side as gravity caused the higher mass density PFSA-VDF-HPA to settle. The composite membrane was shown to have less swelling, more hydrophobic properties, and higher crystallinity than the pure PFSA membrane. The proton conductivity of the membrane was 0.130 ± 0.03 S cm−1 at 80 °C and 95% RH. Impressively, when the membrane with HPA-rich side was facing the anode, the membrane survived more than 800 h under accelerated stress test conditions of open-circuit voltage, 90 °C and 30% RH.

Dual functionality of ferrocene-based metallopolymers as radical scavengers and nanoparticle stabilizing agents.

The beneficial redox properties of ferrocene-based polymers have been utilized during in situ preparation of metallic nanoparticles, while such redox features also indicate a great promise in applications as free radical scavengers. Here, colloidal dispersions of an antioxidant nanozyme composed of amidine-functionalized polystyrene latex (AL) nanoparticles, negatively charged poly(ferrocenylsilane) (PFS(-)) organometallic polyions, and ascorbic acid (AA) were formulated. The AL was first functionalized with PFS(-). Increasing the polymer dose resulted in charge neutralization and subsequent charge reversal of the particles. The strength of repulsive interparticle forces of electrostatic nature was significant at low and high doses leading to stable colloids, while attractive forces dominated near the charge neutralization point giving rise to unstable dispersions. The saturated PFS(-) layer adsorbed on the surface of the AL (p-AL nanozyme) enhanced the colloidal stability against salt-induced aggregation without affecting the pH-dependent charge and size of the particles. The joint effect of PFS(-) and the AA in radical decomposition was observed indicating the antioxidant potential of the system. The immobilization of PFS(-) deteriorated its scavenging activity, yet the combination with AA improved this feature. The results indicate that p-AL-AA is a promising radical scavenger since the high colloidal stability of the particles allows application in heterogeneous systems, such as in industrial manufacturing processes, where antioxidants are required to maintain acceptable product quality.

Supramolecular Catalysts for the Radical Destruction of Hydroperoxides Based on Choline Derivatives

The effect of natural quaternary ammonium compounds (QAC) of choline (Ch) and its derivatives, acetylcholine (AСh) and L-carnitine (LCh), containing the tetraalkylammonium cation (CH3)3RN+, on the radical decomposition of hydroperoxides (ROOH) was studied. In mixtures of ACh and Ch with ROOH in chlorobenzene, mixed supramolecular nanoaggregates are formed, and accelerated decomposition of ROOH into radicals takes place; the rates of radical formation measured by the inhibitor method decrease in the series ACh Ch \( \gg \) LCh. ACh and Ch immobilized on microcrystalline cellulose retain the ability to catalyze the radical decomposition of ROOH and initiate the polymerization of styrene containing ROOH from the surface. LСh adsorbed on cellulose does not affect the decomposition of ROOH and the rate of polymerization. Scanning electron microscopy (SEM) showed that ACh and Ch adsorbed on a silicon plate accelerate the radical decomposition of ROOH and initiate oxidative condensation of egg phosphatidylcholine on the surface of the plate, while adsorbed LCh does not affect the decomposition of ROOH. LCh, unlike ACh and Ch, is an internal salt in which the R4N+ cation is neutralized by its own carboxy anion, i.e., LCh has no external counterion and, probably, for this reason, it differs from ACh and Ch in the mechanism of adsorption and interaction with ROOH.

Laminar burning velocity measurements of ethyl acetate at higher mixture temperatures

In this paper, the laminar burning velocity measurements (LBV) of ethyl acetate-air mixtures are reported using an externally heated diverging channel (EHDC) method for mixture temperatures up to 600 K. The measurements are performed at 1 atmosphere pressure and mixture equivalence ratio, ϕ = 0.7–1.5. The present measurements exhibit a significantly better consistency with the predictions of the Ahfaz kinetic model compared to the other available measurements in the literature. At various mixture temperatures, the highest LBV is observed for the predictions of the Dayma mechanism. The minimum value of temperature exponent (α) variation in the present work is obtained at ϕ ≈ 1.1, alike the predictions of Ahfaz and Dayma reaction mechanisms. The effect of the highest negative sensitive reaction (R136: CH3 + H(+M) ⇔ CH4 (+M)) at ϕ = 1.5 is reduced by nearly 50 % as the mixture temperature changes from 423 K to 600 K. Further, the inhibition effect of reaction R127 (H + O2 (+M) ↔ HO2 (+M)) on burning velocity tends to reduce as the mixture turns richer. Higher LBV at 600 K is associated with the presence of vinoxy radical (CH2CHO), which undergoes radical decomposition (CH2CHO (+M) ⇔ CH2CO + H(+M)) to produce a highly reactive H radical.

The Influence of Solvents and Colloidal Particles on the Efficiency of Molecular Antioxidants.

The radical scavenging activity of three molecular antioxidants (trolox, rutin and ellagic acid) was investigated in different solvents with and without added polymer-based colloidal particles (SL-IP-2). Rutin and ellagic acid showed poor solubility in water, preventing the accurate measurement of the effective antioxidant concentration values, which were determined in ethanol/water (EtOH/H2O) mixtures. The presence of trolox and rutin changed neither the surface charge properties nor the size of SL-IP-2 in these solvents, while significant adsorption on SL-IP-2 was observed for ellagic acid leading to overcharging and rapid particle aggregation at appropriately high antioxidant concentrations in EtOH/H2O. The differences in the radical scavenging capacity of trolox and ellagic acid that was observed in homogeneous solutions using water or EtOH/H2O as solvents vanished in the presence of the particles. Rutin lost its activity after addition of SL-IP-2 due to the larger molecular size and lower exposure of the functional groups to the substrate upon interaction with the particles. The obtained results shed light on the importance of the type of solvent and particle-antioxidant interfacial effects on the radical decomposition ability of molecular antioxidants, which is of crucial importance in industrial processes involving heterogeneous systems.

Validation of ablation model for polyethylene using pulsed x-ray and proton exposures

The surface erosion of polyethylene is interrogated using pulsed x rays at the Z Machine (Sandia National Laboratories) and with proton beams at the Gamble II generator (Naval Research Laboratory) to validate a coupled model for volumetric thermal ablation, photoionization, finite-rate decomposition, and molecular recombination of radicals. The intense radiation pulses (up to ∼1014W/m2 over tens of nanoseconds) are used to generate one-dimensional vapor flows with low ionization fractions and a simplified geometry compared to typical laser ablation, allowing for evaluation of the model under local thermal equilibrium conditions. Areal momentum carried by the ensuing uniaxial hydrodynamic shock is used to indicate the extent of ablation. The threshold fluence for ablation is found to be in close correspondence with the bulk melt transition, and reasonable agreement with the model is obtained for peak temperatures in polyethylene up to 5500 K and heating rates up to 1011K/s where thermal decomposition reactions are also active.