OH Radicals Research Articles

Theoretical study of the reaction of organic peroxyl radicals with alkenes and their accretion products involved in the atmospheric nucleation

Organic peroxy radicals, including alkyl peroxy radicals (RO2) and acyl peroxy radicals (RC(O)O2), are crucial intermediates in the atmospheric photochemical reactions of volatile organic compounds and directly or indirectly affect the distribution of other species (e.g., HO2 radicals, NOx, OH radicals, and alkenes). However, the atmospheric reactions of organic peroxyl radicals with alkenes (RO2 + alkene reactions) are not fully understood. The present study used theoretical calculations to investigate the reaction mechanisms of various organic peroxy radicals with different alkenes, with the aim of clarifying the influence of molecular structure on RO2 + alkene and RC(O)O2 + alkene reactions. Furthermore, we investigated the nucleation mechanisms of the subsequent oxidation products. The results show that the reaction rate constants for RC(O)O2 + alkene reactions are 1–6 orders of magnitude higher than those for RO2 + alkene reactions. The addition products formed by organic peroxy radicals with alkenes not only undergo monomolecular reactions to generate epoxides, but also participate in O2 addition to yield the accretion products ROOR’. H2SO4 molecules synergistically interact with low-volatility ROOR’ to grow clusters up to the 1–2 nm scale, and the ROOR’ molecules can form pure organic clusters larger than 1 nm, even in the absence of H2SO4 molecules. Our study provides a new perspective on the formation of accretion products in the atmosphere and their involvement in new particle formation.

Investigating the Atmospheric Fate and Kinetics of OH Radical-Initiated Oxidation Reactions for Epoxybutane Isomers: Theoretical Insight.

Epoxides, which belong to the category of oxygenated volatile organic compounds (OVOCs), are emitted into the atmosphere by an array of sources and can impact both human and environmental well-being significantly. This study involves comprehensive computational analyses aimed at investigating the mechanism, thermodynamic aspects, and reaction kinetics associated with hydrogen abstraction reactions of cis-2,3-epoxybutane, trans-2,3-epoxybutane, and 1,2-epoxybutane by OH radicals. The potential energy diagrams involving all of the species for each specific pathway were constructed at the CCSD(T)/aug-cc-pVTZ//M06-2X/cc-pVTZ level of theory. The rate coefficients for all possible pathways were calculated using the Rice-Ramsperger-Kassel-Marcus master equation (RRKM-ME) corrected by Eckart tunneling within the 200-350 K temperature range and 1 atm pressure. The overall rate coefficients of the reaction of cis-2,3-epoxybutane, trans-2,3-epoxybutane, and 1,2-epoxybutane with OH radicals at 298.15 K were found to be 0.32 × 10-12, 0.33 × 10-12, and 0.66 × 10-12 cm3 molecule-1 s-1, respectively. We also studied the atmospheric lifetime and photochemical ozone creation potential (POCP) of all three compounds. In addition, we have provided extensive degradation pathways for the product radicals formed from the initial reaction with OH radicals in the presence of O2 and NO. The study showed that the product radicals can result in various harmful end products, including grade 1 and grade 2 carcinogens, as listed by the World Health Organization (WHO).

Hydrogen combustion analysis via infrared and visible optical diagnostics combined with CFD in a dual fuel engine at low load

Dual Fuel (DF) combustion concept has demonstrated to be a valid solution to ensure the utilization of diesel engines in heavy duty and naval applications. The substitution of part of diesel fuel with a cleaner gaseous one can reduce among others: carbon dioxides (CO2), nitrogen oxides (NOx) and surely particulate matter (PM). Nevertheless, the difficulties encountered by the reduced pilot liquid jet to reach out the furthest areas of the combustion chamber, especially at partial load, lead to unburned emissions of the premixed charge. They can be a serious issue to overcome when the premixed fuel is represented by a carbonaceous fuel like natural gas (NG). For this reason, hydrogen, that is carbon-free, represents the new progression to clean mobility. This work aims at deepening the in-cylinder phenomena through a synergetic methodology that involves experimental optical diagnostics and 3D numerical investigations. The experimental activity is carried out on a single cylinder research engine (SCRE) equipped with an optical apparatus allowing the visualization of the combustion process, later processed via high speed visible (VIS) and infrared (IR) imaging. Several filters applied on the IR camera permit to detect specific species such as CO2. Subsequently, these outcomes are used to validate numerical models, and in turn, the numerical results help to validate the species detected qualitatively via optical diagnostics and to identify which ones majorly affect the physical and chemical processes. Numerical simulations are performed with ANSYS Forte ® code on a geometry which accurately reproduces the shape of the combustion chamber. Combustion models include a turbulent-kinetic interaction model with a mechanism of 124 species and 660 reactions to deal with the autoignition phase and diesel surrogate oxidation, while to account for the flame propagation through the premixed charge the G-equation is considered. The reference test cases are characterized by two different engine speeds, 1500 and 2000 rpm, and a low load level, corresponding to 2 bar of brake mean effective pressure (BMEP) on light-duty vehicle. The hydrogen energy shares are between 83.2 and 81.8%. Results demonstrate that IR images and OH radical are key for the detection of ignition process of both diesel and hydrogen. The flame propagation in the air/H2 charge can be observed with the help of CFD elaborations. Finally, emission levels are adequately predicted by the chosen oxidation models.

Ultrasensitive detection of H2O2 via electrochemical sensor by graphene synergized with MOF-on-MOF nanozymes.

An electrochemical sensor was developed for the detection of hydrogen peroxide (H2O2),utilizing the synergistic effects of graphene (Gr) and MOF-on-MOF nanozymes (FeCu-NZs). Initially, Fe-MOF with peroxide-like activity is synthesized using a solvothermal method. Subsequently, the organic ligand on its surface binds Cu2+, enhancing the enzyme-like activity further. The resulting FeCu-NZs exhibit a distinctive electrochemical signal in response to H2O2. Moreover, integrating FeCu-NZs with Gr significantly amplifies the electrochemical signal and effectively reduces the sensor's detection limit. The developed sensor exhibited linear ranges of 0.1-3800 μM, with a limit of detection (LOD) of 0.06 μM. Additionally, FeCu-NZs catalyze H2O2 to generate abundant •OH radicals, and colorimetric detection of H2O2 is facilitated using the color rendering principle of 3,3',5,5'-tetramethylbenzidine (TMB). Notably, this detection method was applied to determine H2O2 concentrations in real samples, achieving a recovery exceeding 95.7%. In summary, this research provides a practical platform for the construction of traditional nanozymes and the integration of electrochemical systems, which have broad applications in food analysis, environmental monitoring, and medical diagnosis.

High-resolution HO2 radical detection by optical feedback linear cavity-enhanced absorption spectroscopy

High-resolution HO2 radical detection by optical feedback linear cavity-enhanced absorption spectroscopy

PVP-assisted in-situ self-assembly hierarchical BiOCl with oxygen vacancies for efficient photocatalytic oxidation of cyclohexane under air in solvent-free conditions

Cyclohexane (CHA) selective oxidation reactions are crucial in designing advanced organic intermediates but suffering from very challenges as the products of KA oil (cyclohexanol and cyclohexanone) are more readily oxidized to CO2. Herein, we report that a polyvinylpyrrolidone (PVP) coating of fluffy self-assembled morphology of BiOCl by nanosheets with exposed {001} facets are synthesized via the solvothermal method. Moreover, the as-synthesized hierarchical BiOCl exhibits a significant presence of in-situ produced oxygen vacancies during photocatalysis, thereby facilitating efficient CHA oxidation to KA oil with air as an oxidant in solvent-free at room temperature. The crystallinity, micromorphology, and electronic structure of BiOCl can be significantly influenced by the concentration of NH4Cl and PVP. In the photocatalytic oxidation, oxygen vacancies act as traps to inhibit electrons and holes recombination and adsorb-activate the oxygen molecule, producing h+ and ·O2− radical to achieve 466.7 μmol of KA oil (340.8 μmol of cyclohexanone and 125.9 μmol of cyclohexanol) with a selectivity of 93.9 %. The ∙OH radicals play a predominant role in the production of CHA-one. After conducting 5 experimental cycles, a consistent yield of 92 % towards KA oil and unchanged selectivity can still be maintained. The excellent photocatalytic performance can be attributed to the enhanced photo-absorption and narrow energy gap, abundant oxygen vacancies, high exposed {001} facets, smaller size and large specific surface area, and efficient electron-hole separation. The present work sheds light on the synergistic effect of PVP coating and in-situ formed oxygen vacancies on enhancing photocatalytic activity of Bi-based materials.

Novel Fe2O3/Bi2O3/CeO2 heterojunction photocatalyst for wastewater treatment: Characterization, photocatalytic performance and mechanism study

A novel ternary Fe2O3/Bi2O3/CeO2 (FeB/CeO2) heterojunction nanocomposite with different Fe2O3/Bi2O3 amounts on CeO2 (5, 10, 20, 30 and 40 wt%) was synthesized through a simple wet impregnation process. The properties of the synthesized nanocomposite were validated thorough XPS, XRD, FE-SEM, TEM, and EDS-Mapping analyses. This photocatalyst exhibited exceptional efficiency in the of Tetracycline’s (TC) photodegradation in comparison to individual Fe2O3, Bi2O3, and CeO2. The effect of Fe2O3/Bi2O3 loading on CeO2 and the influence of operational factors on TC decomposition including photocatalyst dosage (0.05–0.2 g/L), TC concentration (10–40 mg/L), and pH (1–11) were examined with the optimal conditions yielding an experimental degradation efficiency of 99.35 %. Moreover, scavenger tests showed that O2− and OH radicals served as the main oxidative radical species. The study further delved into proposing potential degradation pathways of TC in accordance with liquid chromatography tandem-mass spectrometry analysis. Notably, the stability of the synthesized photocatalyst was assessed through five degradation cycles, affirming its sustained effectiveness.

Specificity of DNA damage formation induced by femtosecond near-infrared laser filamentation in water

We investigated the deoxyribonucleic acid (DNA) damage induced by laser filamentation, which was generated by focusing femtosecond near-infrared Ti:Sapphire laser light in water at several repetition rates ranging from 1000 Hz to 10 Hz. Using plasmid DNA (pUC19), the single-strand break, double-strand break, nucleobase lesions, and the fragmented DNA were analyzed and quantified by agarose gel electrophoresis. Additionally, the H2O2 concentration after irradiation was determined. We observed that (1) the DNA damage per laser shot and (2) the enzyme-sensitive base lesions per total DNA damage decreased as the laser repetition rate increased. Furthermore, (3) extraordinarily short DNA fragments were likely to be produced, compared with those produced using X-rays, and (4) most OH radicals could be eliminated by recombination to generate H2O2, preventing them from damaging the DNA. The Monte-Carlo simulation of the strand break formation implies that the observed dependency of strand break efficiency on the laser repetition rate is mainly due to diffusion of DNA molecules. These findings quantitatively and qualitatively revealed that an intense laser pulse induces a specific DNA damage profile that is not induced by X-rays, a sparsely ionizing radiation source.

Theoretical Investigation on Water-Free, Water- and Self-Assisted H-Abstraction Reactions from Dimethylamine by Hydroxy Radicals.

Accurate branching ratios of the H-abstraction reactions from dimethylamine (DMA) by OH radicals are important in understanding the atmospheric fate of DMA. In this work, the reaction kinetics of the water-free, water-assisted, and self-assisted H-abstraction reactions between DMA and OH radicals are accurately determined using the multipath canonical variational theory with the small-curvature tunneling correction, to explore the catalytic effects of the reactant (DMA) and product (water). To choose a suitable method that well describes the current reaction systems, various combinations with seven DFT methods and six basis sets are first evaluated, and the M08-HX/ma-TZVP method is identified as the most appropriate, with a mean unsigned deviation of 0.9 kcal mol-1 against the gold-standard CCSD(T)/CBS(T-Q) method. Based on the determined potential energy surfaces with the considerations of ground-state structures and specific-reaction parameters of zero-point energies, rate constants and branching ratios are calculated in a wide temperature range. The calculations show that the participation of water and DMA can lead to three-body complexes with a lower energy and influence the energy barriers, but neither of them shows the catalytic effect on the H-abstraction reactions in terms of kinetics. Additionally, the branching ratio analysis demonstrates that the product distribution is significantly altered in the presence of DMA and water.

Super-resistance of PFOS in water: Is it beatable?

In this study, we present research on PFOS occurrence in surface and groundwater in Croatia. PFOS was detected and quantified at ultra-low concentrations (even ng/L) by means of LC-QTOF-MS analysis. PFOS was treated with solar photocatalysis using different reactor types, different irradiation intensities and photocatalytic formulations. Most experiments ended with only a slight change in PFOS concentrations, proving its super-resistance toward UV irradiation and oxidative species, e.g. OH radicals. In certain experiments, PFOS degradation extents were approximately 20% after 120 min of the photocatalytic process. Additionally, photocatalysis was coupled with ultrasound to increase PFOS degradation products, we discussed the tentative degradation mechanism and proposed a solution how to possibly beat its super-resistance.

Cytotoxic and radical activities of metal-organic framework modified with iron oxide: Biological and physico-chemical analyses

Metal-organic framework (MOF) modified with iron oxide, Fe3O4-MOF, is a perspective drug delivery agent, enabling magnetic control and production of active hydroxyl radicals, •OH, via the Fenton reaction. This paper studies cytotoxic and radical activities of Fe-containing nanoparticles (NPs): Fe3O4-MOF and its components – bare Fe3O4 and MOF (MIL-88B). Luminous marine bacteria Photobacteriumphosphoreum were used as a model cellular system to monitor bioeffects of the NPs. Neither the NPs of Fe3O4-MOF nor MOF showed cytotoxic effects in a wide range of concentrations (<10 mg/L); while Fe3O4 was toxic at >3·10−3 mg/L. The NPs of Fe3O4 did not affect the bacterial bioluminescence enzymatic system; their toxic effect was attributed to cellular membrane processes. The integral content of reactive oxygen species (ROS) was determined using a chemiluminescence luminol assay. Bacteria mitigated excess of ROS in water suspensions of Fe3O4-MOF and MOF, maintaining bioluminescence intensity closer to the control; this resulted in low toxicity of these NPs. We estimated the activity of •OH radicals in the NPs samples with physical and chemical methods – spin capture technology (using electron paramagnetic resonance spectroscopy) and methylene blue degradation. Physico-chemical interpretation of cellular responses is provided in terms of iron content, iron ions release and •OH radical production.

Combustion chemical reaction mechanism and kinetic analysis of RP-3 aviation kerosene/low carbon alcohol blends

Adding small molecules of low-carbon alcohol fuel to aviation kerosene can improve the reaction activity and shorten the ignition delay time. Low-carbon alcohols accumulate important intermediates at low temperatures and undergo rapid cracking and oxidation at high temperatures to produce reactive radicals such as OH, H2O2, C2H4, and CH3. These reactive radicals play a key role in accelerating chain reactions and reducing emissions of pollutants such as CO, HC, and PM. In order to accurately predict the combustion characteristics of large-molecule hydrocarbons and small-molecule low-carbon alcohols, in this study, a generalized new mechanism for chemical kinetic analysis of RP-3 aviation kerosene/low-carbon alcohol blended fuel was developed. Based on this blending mechanism, the ignition characteristics and chemical reaction kinetic analysis under different alcohol types and blending ratios were investigated. It was shown that at 1300 K, n-butanol could enhance the fuel oxidation most effectively, accelerating the peak time of O and OH radicals by nearly 12% and the peak time of the CH4 component by nearly 13% compared with that of ethanol. While the ethanol blending ratio of 30%, improved the peak rate of O, OH radicals by nearly 4%, the CH4 mole concentration peak enhancement was nearly 9%, proving that with the increase of the blending ratio, the rate of accumulation of reactive radicals increased, the reaction rate of the blended fuel was accelerated.

Photocatalytic oxidation of methane to C1 oxygenates promoted by Fe−N−Ti electron bridge

Highly efficient oxidation of methane (CH4) to liquid oxygenates with O2 over non-noble heterogeneous catalysts under mild conditions remains a huge challenge owing to the ultra-inert C−H bond of CH4 molecule. In this work, we have successfully constructed photocatalysts of N-Fe2Ti3O9/TiO2 by thermal treatment of a bimetallic amino-functionalized metal-organic framework, i.e., Fe-NH2-MIL-125, aiming at photocatalytic oxidation of CH4 to one-carbon (C1) oxygenates using O2 at room temperature. Impressively, the optimized photocatalyst of 10 wt%N-Fe2Ti3O9/TiO2 exhibited superior activity in photocatalytic oxidation of CH4 with a formation rate of C1 liquid oxygenates of 5897 μmol·gcat.–1·h–1. The selectivity of the primary products (CH3OH and CH3OOH) was up to 91.7 % over 10 wt%N-Fe2Ti3O9/TiO2. Mechanistic studies demonstrated that the presence of Fe−N−Ti electron bridge could trigger robust charge redistribution in 10 wt%N-Fe2Ti3O9/TiO2 to form electron-deficient Fe sites and electron-rich Ti sites. The formed electron-deficient Fe sites could oxidize H2O molecules to ·OH radicals. Meanwhile, electron-rich Ti sites greatly enhanced the chemisorption and activation of CH4 molecules, thereby synergistically promoting the generation of C1 liquid oxygenates.

Anti-Oxidative and Anti-Apoptotic Oligosaccharides from Pichia pastoris-Fermented Cress Polysaccharides Ameliorate Chromium-Induced Liver Toxicity.

Oxidative stress impairs the structure and function of the cell, leading to serious chronic diseases. Antioxidant-based therapeutic and nutritional interventions are usually employed for combating oxidative stress-related disorders, including apoptosis. Here, we investigated the hepatoprotective effect of oligosaccharides, produced through Pichia pastoris-mediated fermentation of water-soluble polysaccharides isolated from Lepidium sativum (cress) seed mucilage, on chromium(VI)-induced oxidative stress and apoptosis in mice. Gel permeation chromatography (GPC), using Bio-Gel P-10 column, of the oligosaccharides product of fermentation revealed that P. pastoris effectively fermented polysaccharides as no long chain polysaccharides were observed. At 200 µg/mL, fractions DF73, DF53, DF72, and DF62 exhibited DPPH radical scavenging activity of 92.22 ± 2.69%, 90.35 ± 0.43%, 88.83 ± 3.36%, and 88.83 ± 3.36%, respectively. The antioxidant potential of the fermentation product was further confirmed through in vitro H2O2 radical scavenging assay. Among the screened samples, the highest H2O2 radical scavenging activity was displayed by DF73, which stabilized the free radicals by 88.83 ± 0.38%, followed by DF53 (86.48 ± 0.83%), DF62 (85.21 ± 6.66%), DF72 (79.9 4± 1.21%), and EPP (77.76 ± 0.53%). The oligosaccharide treatment significantly alleviated chromium-induced liver damage, as evident from the increase in weight gain, improved liver functions, and reduced histopathological alterations in the albino mice. A distinctly increased level of lipid peroxide (LPO) free radicals along with the endogenous hepatic enzymes were evident in chromium induced hepatotoxicity in mice. However, oligosaccharides treatment mitigated these effects by reducing the LPO production and increasing ALT, ALP, and AST levels, probably due to relieving the oxidative stress. DNA fragmentation assays illustrated that Cr(VI) exposure induced massive apoptosis in liver by damaging the DNA which was then remediated by oligosaccharides supplementation. Histopathological observations confirmed that the oligosaccharide treatment reverses the architectural changes in liver induced by chromium. These results suggest that oligosaccharides obtained from cress seed mucilage polysaccharides through P. pastoris fermentation ameliorate the oxidative stress and apoptosis and act as hepatoprotective agent against chromium-induced liver injury.

Ag decoration as a strategy to enhance the methanol and ethanol sensing on the biphenylene sheet

Efficient, miniaturized, and highly sensitive sensors to detect volatile organic compounds (VOCs) have become vital tools to minimize pulmonary diseases and other sicknesses. Therefore, the adsorption capabilities of methanol and ethanol were investigated on the recently synthesized biphenylene (BPN) monolayer using the Ag decoration. Although the pristine BPN has suitable VOCs adsorption, the lower adsorption strength and the small charge transfer affect the sensor performance. On the other hand, the Ag decoration increases the gas sensitivity, with moderate chemisorption values of –0.67eV and –0.83eV for methanol and ethanol, respectively, and transitory chemical bond character (neither ionic nor covalent) between Ag atoms and the –OH radical. In addition, significative work function changes (Δϕ > 0.23 eV), huge charge transfer, and rapid recovery times at room temperature, τ = 0.18s and τ = 87.9s for methanol and ethanol, respectively, indicate a great VOCs sensitivity. The feasibility of the Ag-BPN and Ag-BPN + VOCs systems by ab initio molecular dynamics (AIMDs) was analyzed, which confirms that both systems are stable at 500K. Therefore, the DFT calculations employed here can guide experimentalists in exploring new miniaturized sensor devices based on BPN.

Effects of equivalent ratio and initial temperature on the explosion characteristics of ethanol, acetone, and ethyl acetate

In this paper, the effects of equivalence ratio (0.8–2.0) and temperature (30°C–120°C) on ethanol, acetone, and, ethyl acetate vapors explosion characteristics through experimental and numerical studies were investigated. The explosion overpressure and flame propagation velocity were recorded through the pressure transducer and high-speed camera. The results showed that the flame propagation velocity, peak explosion overpressure, and peak growth rate of explosion overpressure increased first and then decreased with the increase of equivalence ratio. The cracks on the flame surface enhanced with the increase of the equivalence ratio. As the initial temperature increased, peak explosion overpressure, the flame propagation velocity, and peak growth rate of explosion overpressure gradually increased. The sensitivity analysis of laminar burning velocity indicated that with the change of equivalence ratio and initial temperature, the shared elementary reactions that increased the reactivity were H + O2 &amp;lt;=&amp;gt; O + OH, HCO + M &amp;lt;=&amp;gt; H + CO + M, and CO + OH &amp;lt;=&amp;gt; CO2 + H, and the shared elementary reaction that reduced the reactivity was H + OH + M &amp;lt;=&amp;gt; H2O + M. The main factor affecting laminar burning velocity was the mole fraction of H and OH radicals.

A study on anticancer and antioxidant ability of selected brown algae biomass yielded polysaccharide and their chemical and structural properties analysis by FT-IR and NMR analyses

The study was conducted to determine the chemical and structural properties of polysaccharides extracted from the marine macroalgae Nemalion cari-cariense. Furthermore, evaluate the anticancer and free radical scavenging activity of purified N. cari-cariense polysaccharide. Approximately 41.6% (w/w) of crude polysaccharide was extracted from N. cari-cariense macroalgae biomass. After deproteinization, the purified polysaccharide's major chemical composition was found to be 92.6%, with all protein content removed. The purified polysaccharide had ash and moisture % of 23.01% and 4.03%, respectively. The C, H, and N of the test polysaccharide were analyzed using GC-MS, with results of 39.21%, 5.87%, and 4.29%, respectively. Furthermore, this analysis also revealed the monosaccharide composition such as glucose, galactose, mannose, xylose, and rhamnose glucose, galactose, mannose, xylose, and rhamnose 54.62%, 29.64%, 2.8%, 5.9%, and 6.8% respectively. The molecular weight of purified polysaccharide was found as 49 kDa through PAGE analysis. The FT-IR analysis revealed that the presence of functional groups exactly attributed to polysaccharide and 1H and 13C-NMR analyses confirmed the structural properties of N. cari-cariense polysaccharide. The free radicals scavenging ability of purified N. cari-cariense polysaccharide was investigated by various assays such as total antioxidant assay (22.3%–72.5% at 50–250 μg mL−1), DPPH assay (23.6%–76.9% at 10–160 μg mL−1), OH radical scavenging assay (13.6%–70.2% at 50–250 μg mL−1 dosage, and SO radical scavenging assay (27.6–68.41% at 50–250 μg mL−1 concentration). The polysaccharide demonstrated 82.63% anticancer activity towards the A549 lung cancer cell line at 1000 μg mL−1 dosage. The findings suggest that this polysaccharide has biological applications.

A study of tiamulin removal by nanosecond pulsed gas–liquid discharge underwater

AbstractIn this study, gas–liquid discharge plasma excited by nanosecond pulsed voltage is used to efficiently remove tiamulin (TIA) from water. The discharge produces a large number of reactive species (H2O2, OH radicals, NO3−, etc.) that can attack the TIA molecules. The effects of peak pulse voltage, initial TIA concentration, gas composition, and the addition of ferrous sulfate and persulfate on TIA removal were mainly investigated. The results showed that the oxygen plasma could approach 100% removal within 30 min of treatment time. The addition of the catalyst increased the TIA removal efficiency by approximately 15% during the 10‐min discharge treatment time. The toxicity of 12 intermediates was analyzed and the degradation mechanism of TIA was investigated.

Infrared signature of the hydroperoxyalkyl intermediate (·QOOH) in cyclohexane oxidation: An isomer-resolved spectroscopic study.

Infrared (IR) action spectroscopy is utilized to characterize carbon-centered hydroperoxy-cyclohexyl radicals (·QOOH) transiently formed in cyclohexane oxidation. The oxidation pathway leads to three nearly degenerate ·QOOH isomers, β-, γ-, and δ-QOOH, which are generated in the laboratory by H-atom abstraction from the corresponding ring sites of the cyclohexyl hydroperoxide (CHHP) precursor. The IR spectral features of jet-cooled and stabilized ·QOOH radicals are observed from 3590 to 7010cm-1 (∼10-20kcal mol-1) at energies in the vicinity of the transition state (TS) barrier leading to OH radicals that are detected by ultraviolet laser-induced fluorescence. The experimental approach affords selective detection of β-QOOH, arising from its significantly lower TS barrier to OH products compared to γ and δ isomers, which results in rapid unimolecular decay and near unity branching to OH products. The observed IR spectrum of β-QOOH includes fundamental and overtone OH stretch transitions, overtone CH stretch transitions, and combination bands involving OH or CH stretch with lower frequency modes. The assignment of β-QOOH spectral features is guided by anharmonic frequencies and intensities computed using second-order vibrational perturbation theory. The overtone OH stretch (2νOH) of β-QOOH is shifted only a few wavenumbers from that observed for the CHHP precursor, yet they are readily distinguished by their prompt vs slow dissociation rates to OH products.

Photochemical Synthesis and Characterization of a Uranyl Peroxide Triethylamine N‐OxideDimer

A µ‐peroxido‐bis[di‐triethylamine N‐oxide‐dichloro‐dioxouranium] complex with the formula [(UO2)2O2(ON(CH2CH3)3)4Cl2] (complex 1) was synthesized photochemically from a reaction containing uranyl chloride, triethylamine, and H2O2. The photochemical breakdown of H2O2 yielded •OH radicals that reacted with triethylamine to form triethylamine N‐oxide (TEAO) in situ, which subsequently coordinated to UO22+ cations in a monodentate fashion via the N‐oxide functional groups. Structure determination using single crystal X‐ray diffraction revealed that TEAO ligands also formed intermolecular and intramolecular hydrogen bonds with UO22+ and peroxide moieties, and the intermolecular H‐bonding interactions displayed a temperature dependence with Oyl ‐ ‐ H – C and Oper ‐ ‐ H – C distances shortening at 100(2) K by ca. 0.1 Å. Raman spectroscopy data were collected on single crystals of 1 and peak fitting of these results allowed for assignments of peaks including C‐N stretches for TEAO ligands bound to UO22+ cations at 696.8 cm‐1, 717.8 cm‐1, and 776.5 cm‐1, which are redshifted by approximately 30 cm‐1 when compared to free triethylamine. UO22+ν1 and O22‐ν1 stretches, U‐Oper stretches, and notably, U‐Cl stretches were all identified as well, with U‐Cl modes at 198.9 cm‐1 and 212.1 cm‐1 substantially redshifted compared to the uranyl chloride starting material.