Bimolecular Rate Research Articles

Oxidation Kinetics and Thermodynamics of Resonance-Stabilized Radicals: The Pent-1-en-3-yl + O2 Reaction.

The kinetics and thermochemistry of the pent-1-en-3-yl radical reaction with molecular oxygen (CH2CHCHCH2CH3 + O2) has been studied by both experimental and computational methods. The bimolecular rate coefficient of the reaction was measured as a function of temperature (198–370 K) and pressure (0.2–4.5 Torr) using laser photolysis–photoionization mass-spectrometry. Quantum chemical calculations were used to explore the potential energy surface of the reaction, after which Rice–Ramsperger–Kassel–Marcus theory/master equation simulations were performed to investigate the reaction. The experimental data were used to adjust key parameters, such as well depths, in the master equation model within methodological uncertainties. The master equation simulations suggest that the formation rates of the two potential RO2 adducts are equal and that the reaction to QOOH is slower than for saturated hydrocarbons. The initial addition reaction, CH2CHCHCH2CH3 + O2, is found to be barrierless when accounting for multireference effects. This is in agreement with the current experimental data, as well as with past experimental data for the allyl + O2 reaction. Finally, we conducted numerical simulations of the pent-1-en-3-yl + O2 reaction system and observed significant amounts of penta-1,3-diene being formed under engine-relevant conditions.

A Machine Learning Approach for Prediction of Rate Constants.

We report a machine learning approach to train and predict bimolecular thermal rate constants over a large temperature range. The approach uses Gaussian process (GP) regression to evaluate the difference between accurate quantum results and Eckart-corrected conventional transition state theory, mostly for collinear reactions. Training is done on a database of rate constants for 13 reaction/potential surface combinations, and testing is performed on a set of 39 reaction/potential surface combinations. Averaged over all test reactions, the GP method is within 80% of the accurate answer, whereas transition state theory (TST) is only within 330% and Eckart-corrected TST (ECK) is within 110%. In the tunneling region, GP is generally (with a few exceptions) more accurate and sometimes much more accurate. In the high-temperature recrossing region, GP is significantly more accurate than either TST or ECK, neither of which addresses the possibility of recrossing. The GP predictions for the 3D reactions O(3P) + H2, OH + H2, O(3P) + CH4, and H + CH4, for which accurate quantum results are available, provide further encouragement to the machine learning approach.

Assessing the contribution of hydroxylation species in the photochemical transformation of primidone (pharmaceutical)

Pharmaceutical and personal care products (PPCPs) are a group of emerging contaminants that have frequently been detected in aqueous environments. Phototransformation driven by solar irradiation is one of the most important natural processes for the elimination of PPCPs. In this study, primidone (PMD) was chosen as a model “photorefractory” compound. A series of experiments were conducted to assess if reactive intermediates (RIs), such as hydroxyl radical (HO), singlet oxygen (1O2), and triplet states of dissolved organic matter (3DOM⁎), inhibited or enhanced the photochemical transformation of PMD under simulated solar irradiation. The results indicate that HO plays a key role in the photodegradation of PMD and that dissolved oxygen can affect the degradation rate of PMD by promoting HO formation. Our results demonstrated that PMD can not only react with free HO (HO-free) but also react with lower-energy hydroxylation agents (HO-like). The contributions of HO-free and HO-like to PMD degradation in various dissolved organic matter (DOM) solutions were estimated by a methane-quenching experiment. The results indicated that the HO-like species were important in the photodegradation of “photorefractory” compounds. The bimolecular reaction rate constant of the reaction of free HO with PMD was measured as (5.21 ± 0.02) × 109 M−1 s−1 by using electron pulse radiolysis. Furthermore, PMD was used as a probe to estimate the steady-state concentration of HO-free in various DOM solutions. Using the multivariate statistical strategies of orthogonal projection to latent structures discriminant analysis (OPLS-DA) and hierarchical clustering, 28 photochemical transformation products (TPs) of PMD were successfully identified from the DOM matrix.

Furan Carboxamides as Model Compounds To Study the Competition between Two Modes of Indirect Photochemistry.

Singlet oxygen (1O2) and triplet chromophoric dissolved organic matter (3CDOM*) are photochemically produced reactive intermediates responsible for the photodegradation of several micropollutants in the sunlit surface waters. However, elucidating the mechanism of reactions involving both 1O2 and 3CDOM* can be complicated by the deeply interconnected nature of these two reactive species. In this work, we synthesized a series of model compounds inspired by the chemical structure of fenfuram, a fungicide used in the 1980s, and used them to investigate structure-reactivity relationships in photodegradation reactions involving 1O2 and 3CDOM*. A combination of steady-state and time-resolved approaches was employed to successfully predict the extent of 1O2-induced degradation. Conversely, the prediction of triplet-induced reactivity was complicated by the presence of repair mechanisms whose extent and relative importance were difficult to predict. The results of our work indicate that bimolecular rate constants measured via time-resolved techniques alone are not sufficient to accurately predict environmental half-lives, as intrinsic differences in the reaction mechanism can amplify the importance of secondary degradation pathways.

Energy and electron transfer reactions on silica gel and titania\u2013silica mixed oxide surfaces

The energy and electron transfer reactions of anthracene co-adsorbed with an electron donor on silica gel and titania–silica mixed oxides have been studied by a combination of steady-state reflectance, emission spectroscopy, and nanosecond diffuse reflectance laser flash photolysis. Bimolecular rate constants for energy and electron transfer between anthracene and azulene have been measured; kinetic analysis of the decay of the anthracene triplet state and radical cation show that the kinetic parameters depend on the titania content of the sample and the azulene loading. The rate of energy and electron transfer reactions increases as a function of azulene loading and decreases with increasing titania content in titania–silica mixed oxides. These findings indicate that the observed rate of reaction is determined by the rate of diffusion of anthracene on the titania–silica surfaces, whereas, in contrast, the observed rate of reaction on silica gel is predominantly governed by the rate of diffusion of azulene.Graphic abstract

Time-course of human cholinesterases-catalyzed competing substrate kinetics

Competing substrate kinetic analysis of human butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) from the time-course of enzyme-catalyzed substrate hydrolysis, using spectrophotometric assays is described. This study is based on the use of a chromogenic reporter “visible” substrate (substrate A), whose complete hydrolysis time course is retarded by a competing “invisible” substrate (substrate B). For BChE, four visible substrates were used, two thiocholine esters, benzoylthiocholine and butyrylthiocholine, and two aryl-acylamides, o-nitro trifluoro acetaminide and 3-(acetamido)-N,N,N-trimethylanilinium. Three different competing invisible substrates were used, phenyl acetate, acetylcholine and butyrylcholine. For AChE, two visible substrates were used, acetylthiocholine and 3-(acetamido)-N,N,N-trimethylanilinium. For AChE, acetylcholine was competing with visible substrates.The ratio (R) of bimolecular rate constants, kcat/Km, for all couples of substrates, invisible/visible (B/A) covered all possible limit situations, R ≪ 1, R ≈ 1 and R ≫ 1.The kinetic approach, based on the method developed by Golicnik and Masson allowed determination of binding and catalytic parameters of cholinesterases for both visible and invisible substrates. This analysis was applied to michaelian and non-michaelian catalytic behaviors (activation and inhibition by excess substrate). Reevaluation of catalytic parameters obtained for acetylcholine and butyrylcholine more than 50 years ago was made.The method is fast, reliable, and particularly suitable for poorly soluble substrates and for substrates B when no direct spectrophotometric assays exist. Moreover, replacing substrate B by a reversible inhibitor, mechanism of cholinesterase inhibition was possible to study. It is therefore, useful for screening libraries of new substrates and inhibitors, and/or screening of new cholinesterase mutants. This method can be applied to any other enzymes.

Sorbic Acid as a Triplet Probe: Reactivity of Oxidizing Triplets in Dissolved Organic Matter by Direct Observation of Aromatic Amine Oxidation.

Sorbic acid (2,4-hexadienoic acid; HDA) isomerization is frequently used to probe triplet-state dissolved organic matter (3CDOM*) reactivity, but there remain open questions about the reaction kinetics of 3CDOM* with HDA due to the difficulties of directly measuring 3CDOM* quenching rate constants. Using our recently developed approach based on observing the radical cation of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) formed through oxidation of TMPD by 3CDOM*, we studied 3CDOM* quenching kinetics with HDA monitored via transient absorption spectroscopy. A competition kinetics-based approach utilizing formation yields of TMPD•+ was developed, validated with model sensitizers, and used to determine bimolecular rate constants between 3CDOM* oxidants and HDA for diverse DOM isolates and natural waters samples, yielding values in the range of (2.4-7.7) × 108 M-1 s-1. The unquenchable fraction of TMPD-oxidizing triplets showed that, on average, 41% of 3CDOM* oxidants cannot be quenched by HDA. Conversely, cycloheptatriene quenched nearly all TMPD•+-forming triplets in CDOM, suggesting that most 3CDOM* oxidants possess energies greater than 150 kJ mol-1. Comparing results with our companion study, we found slight, but noticeable differences in the 3CDOM* quenching rate constants by HDA and unquenchable triplet fractions determined by oxidation of TMPD and energy transfer to O2 (1O2 formation) methods.

Role of Water in Suppressing Recombination Pathways in CH3NH3PbI3 Perovskite Solar Cells

Moisture degradation of halide perovskites is the Achilles heel of perovskite solar cells. A surprising revelation in 2014 about the beneficial effects of controlled humidity in enhancing device efficiencies overthrew established paradigms on perovskite solar cell fabrication. Despite the extensive studies on water additives in perovskite solar cell processing that followed, detailed understanding of the role of water from the photophysical perspective remains lacking; specifically, the interplay between the induced morphological effects and the intrinsic recombination pathways. Through ultrafast optical spectroscopy, we show that both the monomolecular and bimolecular recombination rate constants decrease by approximately 1 order with the addition of an optimal 1% H2O by volume in CH3NH3PbI3 as compared to the reference (without the H2O additive). Correspondingly, the trap density reduces from 4.8 × 1017 cm-3 (reference) to 3.2 × 1017 cm-3 with 1% H2O. We obtained an efficiency of 12.3% for the champion inverted CH3NH3PbI3 perovskite solar cell (1% H2O additive) as compared to the 10% efficiency for the reference cell. Increasing the H2O content further is deleterious for the device. Trace amounts of H2O afford the benefits of surface trap passivation and suppression of trap-mediated recombination, whereas higher concentrations result in a preferential dissolution of methylammonium iodide during fabrication that increases the trap density (MA vacancies). Importantly, our study reveals the effects of trace H2O additives on the photophysical properties of CH3NH3PbI3 films.

Scavenging of Retinoid Cation Radicals by Urate, Trolox, and α-, β-, γ-, and δ-Tocopherols.

Retinoids are present in human tissues exposed to light and under increased risk of oxidative stress, such as the retina and skin. Retinoid cation radicals can be formed as a result of the interaction between retinoids and other radicals or photoexcitation with light. It has been shown that such semi-oxidized retinoids can oxidize certain amino acids and proteins, and that α-tocopherol can scavenge the cation radicals of retinol and retinoic acid. The aim of this study was to determine (i) whether β-, γ-, and δ-tocopherols can also scavenge these radicals, and (ii) whether tocopherols can scavenge the cation radicals of another form of vitamin A—retinal. The retinoid cation radicals were generated by the pulse radiolysis of benzene or aqueous solution in the presence of a selected retinoid under oxidizing conditions, and the kinetics of retinoid cation radical decays were measured in the absence and presence of different tocopherols, Trolox or urate. The bimolecular rate constants are the highest for the scavenging of cation radicals of retinal, (7 to 8) × 109 M−1·s−1, followed by retinoic acid, (0.03 to 5.6) × 109 M−1·s−1, and retinol, (0.08 to 1.6) × 108 M−1·s−1. Delta-tocopherol is the least effective scavenger of semi-oxidized retinol and retinoic acid. The hydrophilic analogue of α-tocopherol, Trolox, is substantially less efficient at scavenging retinoid cation radicals than α-tocopherol and urate, but it is more efficient at scavenging the cation radicals of retinoic acid and retinol than δ-tocopherol. The scavenging rate constants indicate that tocopherols can effectively compete with amino acids and proteins for retinoid cation radicals, thereby protecting these important biomolecules from oxidation. Our results provide another mechanism by which tocopherols can diminish the oxidative damage to the skin and retina and thereby protect from skin photosensitivity and the development and/or progression of changes in blinding retinal diseases such as Stargardt’s disease and age-related macular degeneration (AMD).

Photochemical formation of carbonate radical and its reaction with dissolved organic matters

The carbonate radical (CO3•−) is a strong oxidative radical that is generated via the reactions of HCO3−/CO32− with hydroxyl radical (HO•) or triplet states of dissolved organic matter (3DOM∗) in sunlit surface water. The bimolecular reaction rate constants of CO3•− with various DOM isolates (kCO3•−,DOM) were calculated as 15–239 (mg of C/L)−1 s−1 and were correlate to the bulk DOM properties, such as the content of phenolic moieties, the specific UV absorbance (SUVA), the E2/E3 value, and the fluorescence index (FI). The spectroscopic E2/E3 values was found to strongly correlated (R2 = 0.93) with kCO3•−,DOM, and an empirical equation was established. Our results also demonstrate that CO3•− is involved in the photobleaching of dissolved organic matter (DOM) and in particular reacts with electron-donor moieties, leading to faster decay rates at long wavelengths of UV–vis absorption. Furthermore, a model was developed to calculate the steady-state concentrations of CO3•− during DOM photobleaching. These results allow us to estimate the reactivity of DOM with CO3•− and to evaluate the role of CO3•− in sunlit surface water. It will also allow a better assessment of the concentration and utilization of CO3•− during the application of advanced oxidation processes.

Thermal stability and entropy generation of unsteady reactive hydromagnetic Powell-Eyring fluid with variable electrical and thermal conductivities

Theoretical analysis of thermal stability and inherent irreversibility of reactive hydromagnetic Powell-Eyring fluid flow in a fixed vertical channel with variable electrical and thermal conductivities is examined. The conducting reactive fluid is influenced by gravity and axial pressure gradient under bimolecular kinetic rate law. Ignoring the material assumptions, the governing dimensionless equations are solved by finite semi-discretization difference scheme along with integration Fehlberg Runge-Kutta method. The results for the momentum and heat equations, Bejan number, thermal runaway, entropy generation and current density are graphically presented under different thermophysical parameters. The computational results for the shear stress and heat transfer at the wall is also presented and discussed quantitatively. It was observed that the parameter which enhance the rate of entropy generation also augment Bejan number with large pitch ratio. Hence, entropy generation can be minimized at low dissipation and material variables.

Steady, Symmetric, and Reversible Growth and Dissolution of Individual Amyloid-β Fibrils.

Oligomers and fibrils of the amyloid-β (Aβ) peptide are implicated in the pathology of Alzheimer's disease. Here, we monitor the growth of individual Aβ40 fibrils by time-resolved in situ atomic force microscopy and thereby directly measure fibril growth rates. The measured growth rates in a population of fibrils that includes both single protofilaments and bundles of filaments are independent of the fibril thickness, indicating that cooperation between adjacent protofilaments does not affect incorporation of monomers. The opposite ends of individual fibrils grow at similar rates. In contrast to the "stop-and-go" kinetics that has previously been observed for amyloid-forming peptides, growth and dissolution of the Aβ40 fibrils are relatively steady for peptide concentration of 0-10 μM. The fibrils readily dissolve in quiescent peptide-free solutions at a rate that is consistent with the microscopic reversibility of growth and dissolution. Importantly, the bimolecular rate coefficient for the association of a monomer to the fibril end is significantly smaller than the diffusion limit, implying that the transition state for incorporation of a monomer into a fibril is associated with a relatively high free energy.

Radiative thermal criticality and entropy generation of hydromagnetic reactive Powell–Eyring fluid in saturated porous media with variable conductivity

Theoretical study of inherent irreversibility and thermal runaway of an exothermic reactive Eyring–Powell fluid flow through a saturated porous fixed horizontal channel with thermal radiation and variable electrical conductivity is investigated. The reactive conducting fluid under bimolecular chemical rate law is propelled by pressure gradient. Ignoring the material assumptions, the governing dimensionless equations of the flow model are solved using semi discretization finite difference techniques coupled with weighted residual method. The results in terms of flow rate, temperature, thermal runaway, Bejan number and entropy generation are presented in graphical form. From the results, it is observed that parameter which argument the entropy production rate also enhances the Bejan number. Also, minimization of entropy generation is achieved at low values of thermal radiation, dissipation rate, electric field loading and viscosity variables.

Kinetic and mechanistic insight into the OH[rad]–initiated atmospheric oxidation of 2,3,7,8-tetrachlorodibenzo-p-dioxin via OH[rad]–addition and hydrogen abstraction pathways: A theoretical investigation

The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic polychlorinated dibenzo-p-dioxin. The OH–initiated oxidation of TCDD has been studied using the density functional, canonical transition state, and canonical Rice-Ramsperger-Kassel-Marcus theories. The kinetic data were corrected for quantum tunneling by the Wigner and Eckart models. All OH addition and hydrogen atom abstraction channels were thermodynamically exergonic. The kinetic and thermodynamic data analysis at the reliable level MPWB1K/MG3S//M06-2X/MG3S indicate that the addition of OH to the carbon atom adjacent to the oxygen atom in dioxin ring leads to the formation of predominant adduct. The calculated bimolecular rate constant for the formation of predominant adduct was ~5.97–6.75 × 10−13 cm3 molecule−1 s−1, its branching ratio was ~0.955, and the overall rate constant for the OH–initiated oxidation of TCDD was ~6.25–7.08 × 10−13 cm3 molecule−1 s−1. The atmospheric lifetime of TCDD determined by OH was ~8.17–9.26 days indicating the TCDD can be categorized as medium lifetime organic pollutant.

Removal of methamphetamine by UV-activated persulfate: Kinetics and mechanisms

In this study, removal of methamphetamine (METH) was investigated by UV activated persulfate (PS), and the influence of key factors was evaluated. Results suggested that METH degradation followed pseudo-first order reaction kinetics. The combination of UV and persulfate (UV/PS) could completely degrade 100 μg/L of METH in 30 min with a PS dosage of 200 μM at pH 7. Both hydroxyl radical (OH) and sulfate radical (SO4−) were confirmed to contribute to the degradation of METH. The bimolecular reaction rate constants of METH with OH and SO4− were 7.91 × 109 and 3.29 × 109 M−1 s−1, respectively. The degradation rate constant of METH was proportional to the PS dosage (0–800 μM) and was high at neutral pH condition. The presence of inorganic anions significantly reduced METH degradation to different degrees, with the inhibitory effect order of Cl− > NO3− > HCO3−. The degradation efficiency of METH was suppressed by the presence of humic acid due to the effect of UV absorption and free radical quenching. The degradation intermediates and products were identified by UPLC-MS/MS and possible transformation pathways were proposed. Results suggested that the combination of UV/PS is a promising treatment technique for the removal of METH in the water environment.

Effects of electrolyte on the mediated electrocatalytic glucose oxidation reaction catalyzed by flavin adenine dinucleotide glucose dehydrogenase

Flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) become a key enzyme for electrochemical oxidation of glucose. Here, we investigated the effects of electrolyte, especially at high concentration, on the bioelectrocatalytic activity of FAD-GDH from Aspergillus terreus using a ferricyanide as a redox mediator. In the low ionic strength region, an increase of bimolecular reaction rate constant (k2) between FAD-GDH and ferricyanide was observed due to the reduction of the ionic repulsive interaction between negatively charged enzyme and mediator. Above 0.5 M concentration, ion-specific increments in k2 were observed; ammonium ions most efficiently increased k2, owing to adsorption via dispersion force on the enzyme surface likely proximal to the active site.

5,7,3′,4′-Hydroxy substituted flavonoids reduce the heme of cytochrome c with a range of rate constants

Flavonoids are antioxidants known to be abundant in edible plants. Seven 5,7,3′,4′-tetrahydroxy substituted flavonoids representing each major flavonoid class were used as cytochrome c reductants to systematically investigate the redox role of their C-rings. Additional examples of flavonoids and benzenediols were investigated to better understand the role of the B-ring. Pseudo-first order rate constants (kobs) and apparent bimolecular rate constants (kapp) values were calculated from spectroscopic measurements. Of the seven flavonoids tested, five yielded measurable observed reduction rate constants. Butein (a chalcone) had the highest apparent bimolecular rate constant (kapp), followed by taxifolin (a flavanonol), catechin (a flavanol), eriodictyol (a flavanone), and luteolin (a flavone). Quercetin (a flavonol) and cyanidin (an anthocyanidin), however, reduced cytochrome c but kapp rate constants were unable to be calculated. Neither this trend nor trends in observed rate constants correlated with flavonoid pKa, solvent accessible surface area, polar surface area, reduction potential, antioxidant ability, resonance, or radical scavenging efficiency. Weak correlation, however, was found with degrees of freedom and the number of redox involved electrons. While some cytochrome c reduction rates have been reported, this study is the first to systematically investigate the role of the structure of the flavonoid C-ring across a full set of flavonoids with identical B-rings.

Temperature-Dependent Rate Coefficient for the Reaction of CH3SH with the Simplest Criegee Intermediate

The kinetics of the reaction of the simplest Criegee intermediate CH2OO with CH3SH was measured with transient IR absorption spectroscopy in a temperature-controlled flow reaction cell, and the bimolecular rate coefficients were measured from 278 to 349 K and at total pressure from 10 to 300 Torr. The measured bimolecular rate coefficient at 298 K and 300 Torr is (1.01 ± 0.17) × 10-12 cm3 s-1. The results exhibit a weak negative temperature dependence: the activation energy Ea ( k = Ae- Ea/ RT) is -1.83 ± 0.05 kcal mol-1, measured at 30 and 100 Torr. Quantum chemistry calculations of the reaction rate coefficient at the QCISD(T)/CBS//B3LYP/6-311+G(2d,2p) level (1.6 × 10-12 cm3 s-1 at 298 K; Ea = - 2.80 kcal mol-1) are in reasonable agreement with the experimental results. The experimental and theoretical results of the reaction of CH2OO with CH3SH are compared to the reactions of CH2OO with methanol and hydrogen sulfide, and the trends in reactivity are discussed. The results of the present work indicate that this reaction has a negligible influence to atmospheric CH2OO or CH3SH.

Surface reaction-diffusion kinetics on lattice at the microscopic scale.

Microscopic models of reaction-diffusion processes on the cell membrane can link local spatiotemporal effects to macroscopic self-organized patterns often observed on the membrane. Simulation schemes based on the microscopic lattice method (MLM) can model these processes at the microscopic scale by tracking individual molecules, represented as hard spheres, on fine lattice voxels. Although MLM is simple to implement and is generally less computationally demanding than off-lattice approaches, its accuracy and consistency in modeling surface reactions have not been fully verified. Using the Spatiocyte scheme, we study the accuracy of MLM in diffusion-influenced surface reactions. We derive the lattice-based bimolecular association rates for two-dimensional (2D) surface-surface reaction and one-dimensional (1D) volume-surface adsorption according to the Smoluchowski-Collins-Kimball model and random walk theory. We match the time-dependent rates on lattice with off-lattice counterparts to obtain the correct expressions for MLM parameters in terms of physical constants. The expressions indicate that the voxel size needs to be at least 0.6% larger than the molecule to accurately simulate surface reactions on triangular lattice. On square lattice, the minimum voxel size should be even larger, at 5%. We also demonstrate the ability of MLM-based schemes such as Spatiocyte to simulate a reaction-diffusion model that involves all dimensions: three-dimensional (3D) diffusion in the cytoplasm, 2D diffusion on the cell membrane, and 1D cytoplasm-membrane adsorption. With the model, we examine the contribution of the 2D reaction pathway to the overall reaction rate at different reactant diffusivity, reactivity, and concentrations.

Catalytic and stoichiometric C[sbnd]H oxidation of benzylalcohols and hydrocarbons mediated by nonheme oxoiron(IV) complex with chiral tetrapyridyl ligand

Bioinspired chiral iron(II) complex [((R)-(−)-N4Py*)FeII(CH3CN)]2+ (1) (N4Py* = N,N-bis(2-pyridylmethyl)-1,2-di(2-pyridyl)ethylamine) has been shown to efficiently catalyze the benzylic CH oxidation of ethylbenzene with tert-butyl hydroperoxide (TBHP), H2O2, and meta-chloroperoxybenzoic acid (mCPBA) resulting in enantiomerically enriched 1-phenylethanol up to 12.5% ee and the corresponding acetophenone, where the [FeIV(N4Py*)(O)]2+ (2) intermediate has been detected by UV/Vis spectrometry. The stoichiometric oxidation of benzyl alcohol and various hydrocarbon derivatives including the asymmetric hydroxylation of ethylbenzene with 2 has also been investigated. Detailed kinetic, and mechanistic studies (kinetic isotop effect (KIE) of 31 and 38, and Hammett correlation with ρ = −0.32 and −0.98 for PhCH2OH and PhCH3, respectively, and the linear correlation between the normalized bimolecular reaction rates and bond dissociation energies (BDECH)) lead to the conclusion that the rate-determining step in these reactions above involves hydrogen-atom transfer between the substrate and the Fe(IV)-oxo species. The stoichiometric 2-mediated hydroxylation of ethylbenzene affords 1-phenylethanol in up to 33% ee, suggesting clear evidence for the involvement of the oxoiron(IV) species in the enantioselective step. The moderate enantioselectivity may be explained by the epimerization of the long-lived substrate radical before the rebound step (non-rebound mechanism, where kep > kreb). The kinetic resolution of the resulting chiral alcohol due to its metal-based overoxidation process into acetophenone in the catalytic metal-based ethylbenzene oxidation can be excluded.