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Thiazole derivatives are biologically relevant molecules, used also in pharmaceutical applications. Herein, we report results for electron attachment to 2-bromo-5-nitrothiazole (BNT) in the gas phase. Employing two crossed electron–molecule beam experiments, we determined the efficiency curves of various fragment anions as a function of the initial electron energy between about 0 and 10 eV as well as the emission angle and kinetic energy distributions of Br− and NO2− ions formed from a resonance near 4 eV. The experiments were supported by quantum chemical calculations, exploring possible dissociation pathways along with their reaction energies. We also compared the electron attachment characteristics of BNT with those of the native thiazole molecule by performing electron attachment experiments and calculations for this molecule as well. Compared to thiazole, which is primarily degraded only by electrons with kinetic energies between about 5 and 10 eV, BNT is susceptible to low-energy electrons near 0 eV with enhanced cross section for (dissociative) electron attachment. However, although BNT offers two localization sites with high electron affinity (Br and NO2 moieties), we do not find the corresponding anions as the dominant negatively charged species formed upon electron attachment. Instead, the reaction channels with an abstraction of Br and NO2 as neutral radicals prevail, accompanied by the opening of the thiazole ring due to the relatively weak C–S bond. [ABSTRACT FROM AUTHOR]

Vibrational relaxation of HOD(v12, v3) molecules by collisions with Ar was studied at 298 K (v12 denotes coupled bending, v2, and OD stretching, v1, vibrational modes and v3 denotes OH stretching mode). The vibrationally excited HOD molecules were generated by exothermic abstraction reactions of OD radicals with 13 different RH reactants and observed by infrared emission from a fast-flow reactor as a function of Ar pressure and reaction time. State-specific relaxation rate constants were obtained by comparison of the time evolution of the experimental vibrational distributions with numerical kinetic calculations for vibrational populations. The relaxation mechanism was based on the relaxation scheme of H2O studied earlier with the addition of specific channels for HOD(v12, v3). Unlike H2O, energy in stretching and bending vibrations of HOD cannot be separated due to close ν1 and 2ν2 energies, which leads to fast collisional equilibration between these Fermi-resonant levels. For relaxation of the only pure bending state (10), a rate constant of (1.5 ± 0.3) × 10−13 cm3 molecule−1 s−1 was obtained. The relaxation rate of higher v12 states linearly increases with quantum number and very likely includes transfer of population from OD stretch levels, v1, to a lower energy bend level. The average rate constants for the loss of population from (01), (02), and (03) stretching states are (1.1 ± 0.3) × 10−14, (3.2 ± 1.0) × 10−14, and (5.6 ± 1.2) × 10−14 cm3 molecule−1 s−1, respectively. [ABSTRACT FROM AUTHOR]

Reliable thermodynamic and kinetic properties of free radical polymerization reactions are essential for synthesizing both primary polymeric materials and specialty polymers. The computational generation of these data from quantum chemistry requires a time-efficient method capable of capturing the essential physics. One such method, fixed-node diffusion Monte Carlo (FN-DMC) (using single Slater–Jastrow trial wavefunctions), has demonstrated the capability to recover 90%–95% of missing dynamic correlation energy for typical systems. In this study, methyl radical addition to ethylene serves as a simple model to test FN-DMC's ability to calculate enthalpies of reaction and activation energies with different time steps, antisymmetric trial wavefunctions, basis set sizes, and effective core potentials. The FN-DMC computational protocol thus defined for methyl radical addition to ethylene is subsequently benchmarked against Weizmann-1 and experimental reaction enthalpies from Lin et al.'s test set of 21 radical addition and 28 hydrogen abstraction enthalpies. Our findings reveal that FN-DMC consistently generates reaction enthalpies with chemical accuracy, exhibiting mean absolute deviation of 3.5(7) and 1.4(8) kJ/mol from the Weizmann-1 reference for radical addition and hydrogen abstraction reactions, respectively. Given its favorable computational scaling and high degree of parallelizability, we, therefore, recommend more comprehensive testing of FN-DMC with effective core potentials to address more extensive and intricate polymerization reactions and reactions with other radicals. [ABSTRACT FROM AUTHOR]

The gas-phase reaction Cl + NH3 → HCl + NH2 is a prototypical hydrogen abstraction reaction, whose minimum energy path involves several intermediate complexes. In this work, a full-dimensional, spin–orbit corrected potential energy surface (SOC PES) is constructed for the ground electronic state of the Cl + NH3 reaction. About 52 000 energy points are sampled and calculated at the UCCSD(T)-F12a/aug-cc-pVTZ level, in which the data points located in the entrance channel are spin–orbit corrected. The spin–orbit corrections are predicted by a fitted three-dimensional energy surface from about 7520 energy points in the entrance channel at the level of CASSCF (15e, 11o)/aug-cc-pVTZ. The fundamental-invariant neural network method is utilized to fit the SOC PES, resulting in a total root mean square error of 0.12 kcal mol−1. The calculated thermal rate constants of the Cl + NH3 → HCl + NH2 reaction on the SOC PES with the soft-zero-point energy constraint agree reasonably well with the available experimental values. [ABSTRACT FROM AUTHOR]

Resonant electron capture by aza and diaza derivatives of phenanthrene (7,8-benzoquinoline and 1,10-phenanthroline) and anthracene (acridine and phenazine) at incident free electron energies (Ee) in the range of 0–15 eV was studied. All compounds except 7,8-benzoquinoline form long-lived molecular ions (M−) at thermal electron energies (Ee ∼ 0 eV). Acridine and phenazine also form such ions at epithermal electron energies up to Ee = 1.5–2.5 eV. The lifetimes (τa) of M− with respect to electron autodetachment are proportional to the extent of aza-substitution and increase on going from molecules with bent geometry of the fused rings (azaphenanthrenes) to linear isomers (azaanthracenes). These regularities are due to an increase in the adiabatic electron affinities (EAa) of the molecules. The EAa values of the molecules under study were comprehensively assessed based on a comparative analysis of the measured τa values using the Rice–Ramsperger–Kassel–Marcus theory, the electronic structure analysis using the molecular orbital approach, as well as the density functional calculations of the total energy differences between the molecules and anions. The only fragmentation channel of M− ions from the compounds studied is abstraction of hydrogen atoms. When studying [M–H]− ions, electron autodetachment processes were observed, the τa values were measured, and the appearance energies were determined. A comparative analysis of the gas-phase acidity of the molecules and the EAa values of the [M–H]· radicals revealed their proportionality to the EAa values of the parent molecules. [ABSTRACT FROM AUTHOR]

We report the proton-coupled electron transfer (PCET) reactivity of an octahedral Ta(V) aniline complex supported by an acridane-derived redox active NNN pincer ligand. The reversible binding of aniline to a Ta(V) dichloride induces significant coordination-induced bond weakening (CIBW) of the aniline N–H bonds. This enables a rare two-fold hydrogen atom abstraction, resulting in a terminal imido complex and a two-electron oxidation of the NNN pincer ligand, all while maintaining the metal's oxidation state. The bond dissociation free energies (BDFEs) of the aniline and a transient radical amido complex are estimated through stoichiometric reactions with different hydrogen atom abstractors and donors, further supported by density functional theory calculations. [ABSTRACT FROM AUTHOR]

In recent years, visible light-induced ligand-to-metal charge transfer (LMCT) has emerged as an attractive approach for synthesizing a range of functionalized molecules. Compared to conventional photoredox reactions, photoinduced LMCT activation does not depend on redox potential and offers diverse reaction pathways, making it particularly suitable for the activation of inert bonds and the functional modification of complex organic molecules. This review highlights the indispensable role of photoinduced LMCT in synthetic chemistry, with a focus on recent advancements in LMCT-mediated hydrogen atom transfer (HAT), C–C bond cleavage, decarboxylative transformations, and radical ligand transfer (RLT) reactions. [ABSTRACT FROM AUTHOR]

In this work, hemp-derived biochar (BC) was synthesized and then activated with KOH to achieve activated carbon (AC). The selenium (Se 1, 3, 5 wt%) was loaded over AC and characterized using various techniques to investigate the physicochemical, electrochemical, and photocatalytic performance for dye degradation and H 2 generation as dual function photocatalyst. BC, AC, and the influence of different loading of Se (1 wt%, 3 wt%, 5 wt%) were examined for the degradation of crystal violet (CV) dye under sunlight. Amongst 3% Se-AC showed the maximum degradation efficiency (98.2%) of CV dye within 75 min and the electrons (e−) had a major contribution to the degradation of CV during the active radical trap test. The photocatalytic H 2 production performance was tested and the maximum H 2 rate 3095 μmol/g/h and light to hydrogen efficiency (LTH) 2.36% were achieved for 3% Se-AC. The post-reaction characterization showed competitive stability. A possible reaction mechanism was proposed for photocatalytic H 2 production and it is suggested that the Se loading played a key role in charge transfer enhancement due to high polarizability, d-electron richness, and its bond energy with hydrogen atoms (Se-H ads is 273 kJ/mol) is comparable to the platinum (Pt) (Pt-H ads is 251 kJ/mol). [Display omitted] • Dual function Se Loaded hemp-derived activated carbon (AC) is synthesized. • Se loading to improve the electrochemical and photocatalytic properties. • Tested material for dye degradation and H 2 generation in clean/degraded water. • Achieved 98.2% Crystal Violet degradation in 75 min with 3% Se-Loaded AC. • High H 2 -rates (3095 μmol/g/h), and LTH (2.36%) were achieved for 3% Se-Loaded AC. [ABSTRACT FROM AUTHOR]

Antibiotic contamination constitutes a serious environmental and public health risk. In order to fill the gap in the study of plasma degradation of erythromycin (ERY), this paper systematically investigated the mechanism of ERY degradation by dielectric barrier discharge (DBD) plasma. The underlying reaction mechanisms were investigated by experiments and molecular dynamics simulations. Plasma emission spectra revealed active hydroxyl radicals (·OH) and argon (Ar) spectral lines. The degradation efficiency of plasma treatment for ERY was found to be strongly influenced by treatment parameters, including applied voltage, treatment duration, and gas flow rate. In particular, a maximum degradation of 90% was achieved for a 250 mg/L ERY solution under conditions of 18 kV voltage, 850 sccm gas flow rate, and 60 min of treatment. The presence of ·OH and hydrogen peroxide (H2O2) in the reaction and their important role in the degradation were proved experimentally. Fracture of the ERY lactone ring induced by hydrogen abstraction reactions with reactive oxygen species (ROS) was observed by molecular dynamics simulations. In the in vitro antimicrobial assays targeting Staphylococcus aureus, the treated solutions demonstrated low toxicity, underscoring the practical applicability of dielectric barrier discharge (DBD) plasma technology in addressing antibiotic contamination in aquatic environments. [ABSTRACT FROM AUTHOR]

It is known that the presence of redox-inactive metals in the active center of an enzyme has a significant effect on its activity. In this regard and for other reasons, the effect of redox-inactive metals on redox processes, such as electron transfer, oxygen and hydrogen atom transfer, as well as the breaking and formation of O–O bonds in reactions catalyzed by transition metals, has been widely studied. Many questions about the role of redox-inactive metals in the mechanisms of these reactions remain open. In this paper, the mechanism of catalysis by bi- and triple hetero-binuclear heteroligand complexes including Ni and redox-inactive alkali metals ((A) {Ni(acac)2∙L2} and (B) {Ni(acac)2∙L2∙PhOH} (L2 = MSt (M = Li, Na, or K)) in the process of the selective oxidation of ethylbenzene by molecular oxygen into α-phenyl ethyl hydroperoxide is considered. The activity of A and B complexes towards O2, ROOH, and RO2• radicals was studied. Based on kinetic data, we suggest that the high catalytic efficiency of B triple complexes in oxidation processes may be associated with the role of outer-sphere regulatory interactions, with the formation of stable supramolecular structures due to intermolecular H bonds. This assumption was confirmed using the AFM method. Prospects for studying catalysis by complexes ({Ni(acac)2∙L2} and {Ni(acac)2∙L2∙PhOH}) that are models of NiARD (Ni-Acyreductone dioxygenase) are discussed. [ABSTRACT FROM AUTHOR]

Catalytic transformations of alkenes via the metal-hydride hydrogen atom transfer (MHAT) mechanism have notably advanced synthetic organic chemistry. This Account focuses on MHAT/radical-polar crossover (MHAT/RPC) conditions, offering a novel perspective on generating electrophilic intermediates and facilitating various intramolecular reactions. On using cobalt hydrides, the MHAT mechanism displays exceptional chemoselectivity and functional group tolerance, making it invaluable for the construction of complex biologically relevant molecules under mild conditions. Recent developments have enhanced regioselectivity and expanded the scope of MHAT-type reactions, enabling the formation of cyclic molecules via hydroalkoxylation, hydroacyloxylation, and hydroamination. Notably, the addition of an oxidant to traditional MHAT systems enables the synthesis of rare cationic alkylcobalt(IV) complexes, bridging radical mechanisms to ionic reaction systems. This Account culminates with examples of natural product syntheses and an exploration of asymmetric intramolecular hydroalkoxylations, highlighting the ongoing challenges and opportunities for future research to achieve higher enantioselectivity. This comprehensive study revisits the historical evolution of the MHAT mechanism and provides a groundwork for further innovations on the synthesis of structurally diverse and complex natural products. 1 Introduction 2 Intramolecular Hydroalkoxylation and Hydroacyloxylation Reactions 3 Intramolecular Hydroamination Reactions 4 Intramolecular Hydroarylation Reactions 5 Deprotective Cyclization 6 Asymmetric Intramolecular Hydroalkoxylation 7 Conclusion [ABSTRACT FROM AUTHOR]

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality globally, with oxidative stress playing a pivotal role in its progression. Free radicals produced via oxidative stress contribute to lipid peroxidation, leading to subsequent inflammatory responses, which then result in atherosclerosis. Antioxidants inhibit these harmful effects through their reducing ability, thereby preventing oxidative damage. In this study, we introduce computational models simulating hydrophilic and hydrophobic serum environments. We optimized the Ferric Reducing Ability of Plasma (FRAP) assay at a microscale level to evaluate the antioxidant activity of L-ascorbic acid (vitamin C) and catechin, a phytochemical found in green tea, in normal and hypertriglyceridemic serum. Hypertriglyceridemic serum, characterized by increased hydrophobic lipid content, provides a model to examine the impact of serum triglycerides on antioxidant activity. Additionally, we employed computational models using the Gaussian software to simulate the hydrogen atom transfer (HAT) mechanism, calculating free energy changes and bond dissociation energy (BDE) to assess the antioxidant potency of the studied compounds in both hydrophilic and hydrophobic environments. The computational results align with the experimental finding offering a unique combinatorial approach to assess antioxidant activity in both normal and hypertriglyceridemic serum, with potential implications for clinical interventions. [ABSTRACT FROM AUTHOR]

The study investigated the degradation of 3-methoxy-1-propanol (3M1P) by OH• using the M06-2X/6-311++G(d, p) level, with CCSD(T) single-point corrections. We focused on hydrogen atom abstraction from various alkyl groups within the molecule. The rate coefficient for 3M1P degradation was calculated from the sum of the rate coefficients corresponding to the removal of H-atoms from primary (–CH3), secondary (–CH2–), tertiary (–CH<), and alcohol (–ΟH) groups. The primary attack by hydroxyl radicals occurs at the hydrogen atom bonded to carbon atoms adjacent to the oxygen atom in the ether group, leading to the formation of alkyl radicals. The computed overall rate constant is 1.85 × 10‒11 cm3 molecule‒1 sec‒1 at atmospheric pressure and room temperature, which is consistent with the experimental value of (2.15 ± 0.28)×10‒11 cm3 molecule‒1 sec‒1. This strong agreement confirms the reliability of the computational approach, which provides insights into the atmospheric reactivity and degradation pathways of 3M1P. The tropospheric lifetime of 3M1P is around 15 h, indicating rapid degradation in the atmosphere, potentially contributing to photochemical smog formation. The average ozone production from 3M1P emissions is ~ 2.1 ppb, with estimated photochemical ozone creation potential (POCP) values of 44 and 43 for north-west European and USA-urban conditions, respectively. These values indicate a moderate risk of photochemical smog production and potential harm to human health and the environment due to 3M1P emissions. Successive pathways involve the addition of molecular oxygen to the energized adducts [3M1P]•, forming [3M1P–O2]• peroxy radicals, which primarily react with nitric oxide to produce nitrogen dioxide and the [3M1P–O]• alkoxy radicals. The major degradation products include methyl formate, 3-hydroxypropyl formate, glycolaldehyde, and 3-methoxypropanal. [ABSTRACT FROM AUTHOR]

We employed density functional theory (DFT) calculations to elucidate the mechanism and origin of enantioselectivity in the C–H hydroxylation reaction catalyzed by a chiral manganese porphyrin complex. Our study reveals that the chiral manganese porphyrin forms a two-point hydrogen bonding interaction with the substrate. Specifically, the hydrogen atom abstraction of the methylene pro-(S) C–H bond at the heterocyclic C-3 position is 1.9 kcal mol−1 favored over the hydrogen atom abstraction of the pro-(R) C– H bond. This preferential reactivity results in the predominant formation of (S)-hydroxylated products. Our DFT calculations are consistent with the experimental findings of high enantioselectivity in the chiral manganese porphyrin catalyzed C(sp³ )–H hydroxylation of lactam derivatives. The observed enantioselectivity arises from the formation of two-point hydrogen bonding between lactam derivatives and manganese porphyrin catalysts. Moreover, our computations indicate varying degrees of substrate distortion upon attack by high-valent manganese oxygen complexes at different hydrogen atoms. [ABSTRACT FROM AUTHOR]

In this study, we investigate the protonation effects on the structure, relative stability and basicity of complexes formed by the interaction of monomers and dimers of BeX2 and MgX2 (X = H, F) with NH3, CH2NH, HCN, and NC5H5 bases. Calculations were performed using the M06‐2X/aug‐cc‐pVTZ formalism, along with QTAIM, ELF and NCI methods for electron density analysis and MBIE and LMO‐EDA energy decomposition analyses for interaction enthalpies. The protonation of the MH2– and M2H4–Base complexes occurs at the negatively charged hydrogen atoms of the MH2 and M2H4 moieties through typical hydride abstraction reactions, while protonation at the N atom of the base is systematically less exothermic. The preference for the hydride transfer mechanism is directly associated with the significant exothermicity of H2 formation through the interaction between H− and H+, and the high hydride donor ability of these complexes. The basicity of both, MH2 and M2H4 compounds increases enormously upon association with the corresponding bases, with the increase exceeding 40 orders of magnitude in terms of ionization constants. Due to the smaller exothermicity of HF formation, the basicity of fluorides is lower than that of hydrides. In Be complexes, the protonation at the N atom of the base dominates over the fluoride abstraction mechanism. However, for the Mg complexes the fluoride abstraction mechanism is energetically the most favorable process, reflecting the greater facility of Mg complexes to lose F−. [ABSTRACT FROM AUTHOR]

In this study, the antioxidant and prooxidant potency of protocatechuic aldehyde (PCA) was evaluated using density functional theory (DFT). The potency of direct scavenging of hydroperoxyl (HOO•) and lipid peroxyl radicals (modeled by vinyl peroxyl, H2C=CHOO•) involved in lipid peroxidation was estimated. The repair of oxidative damage in biomolecules (lipids, proteins and nucleic acids) and the prooxidant ability of PCA phenoxyl radicals were considered. The repairing potency of PCA was investigated for damaged tryptophan, cysteine, leucine, DNA base guanine and linolenic acid. The thermodynamics and kinetics of the single electron transfer (SET) and formal hydrogen atom transfer (fHAT) mechanisms underlying the studied processes were investigated under physiological conditions in aqueous and lipid environments using the SMD/M06-2X/6-311++G(d,p) level of theory. Sequestration of catalytic Fe2+ and Fe3+ ions by PCA, which prevents HO• production via Fenton-like reactions, was modeled. Molecular docking was used to study the inhibitory capability of PCA against xanthine oxidase (XO), one of the enzymes producing reactive oxygen species. The attained results show that PCA has the capability to scavenge lipid peroxyl radicals, repair damaged tryptophan, leucine and guanine, chelate catalytic iron ions and inhibit XO. Thus, PCA could be considered a possible multifunctional antioxidant. [ABSTRACT FROM AUTHOR]

We recently achieved an oxidation-initiated photoenzymatic enantioselective hydrosulfonylation of olefins through the utilization of a new Gluconobacter ene-reductase mutant (GluER-W100F-W342F). Our method simplifies the reaction system by eliminating the need for a cofactor regeneration mixture and, in contrast with previous photoenzymatic systems, does not depend on the formation of an electron donor–acceptor (EDA) complex between the substrates and enzyme cofactor. Moreover, the GluER variant exhibits good substrate compatibility and excellent enantioselectivity. Mechanistic investigations indicate that a tyrosine-mediated HAT process is involved and support the proposed oxidation-initiated mechanism. In this Synpacts article, we discuss the conceptual framework that led to the discovery of this reaction and reflect on the key aspects of its development. 1 Introduction 2 Conceptual Background 2.1 Intramolecular Photoenzymatic Reactions via Single-Electron Reduction 2.2 Intermolecular Photoenzymatic Reactions via Single-Electron Reduction 3 The Development of the Process 4 Conclusion [ABSTRACT FROM AUTHOR]

Context. Propenal (CH2CHCHO) and propanal (CH3CH2CHO) have been detected in various regions of the interstellar medium (ISM), from star-forming regions to a comet's dusty coma. These molecules attract considerable attention due to their structural similarity to aldose sugars and their potential role in prebiotic astrochemistry. Their reactions with H atoms may significantly contribute to the chemical diversity in the ISM and link these molecules with each other and other isomers. Aims. In this study, we aimed to investigate the astrophysically relevant low-temperature reactions of propenal and propanal molecules with H atoms to explore possible reaction pathways between these molecules and their isomers. Methods. Propenal and propanal were isolated in solid para-H2 at 3.1 K. This medium, with its weak interactions, provides spec-troscopic data close to gas-phase values and allows for studying highly reactive short-lived species. Additionally, H atoms can be conveniently generated, they diffuse, and they react with the isolated molecules. The reactions were monitored using infrared (IR) spectroscopy. Quantum-chemical computations were employed to determine possible reaction paths and aid in spectral assignments. Results. The reaction of CH2CHCHO and CH3CH2CHO with H atoms in the first step results in the production of CH2CH •CO/•CH2CHCO, CH3CH2•CO, and CH3•CHCHO radicals. Further H-atom reactions of CH3•CHCHO and R•CO radicals lead to the formation of methylketene (CH3CHCO) as the product of both the reaction of propenal and propanal. The two-step addition of H atoms to CH2CHCHO was found tentatively to produce CH3CH2CHO. Conclusions. The radicals observed in the experiments are likely produced in dark molecular clouds on icy grains, increasing interstellar chemical complexity. The experiments suggest that H-atom reactions with propanal and propenal are important channels for methylketene production. The observed reactions imply that consecutive H-atom addition and H-atom abstraction reactions of propenal and propanal can catalyze interstellar H2 formation. [ABSTRACT FROM AUTHOR]

Although Type‐I photodynamic therapy has attracted increasingly growing interest due to its reduced dependence on oxygen, the design of effective Type‐I photosensitizers remains a challenge. In this work, we report a design strategy for Type‐I photosensitizers by the involvement of hydrogen atom transfer (HAT). As a proof of concept, a HAT‐involved Type‐I PS, which simultaneously generates superoxide and carbon‐centered radicals under light‐irradiation, was synthesized. This photosensitizer is comprised of a fluorene‐substituted BODIPY unit as an electron acceptor covalently linked with a triphenylamine moiety as an electron donor. Under light‐irradiation, photo‐induced intramolecular electron transfer occurs to generate the BODIPY anion radical and triphenylamine cation radical. The former transfers electrons to oxygen to generate O2−⋅, while the latter loses a proton to produce a benzyl carbon‐centered radical which is well characterized. The resulting carbon‐centered radicals efficiently oxidize NADH by HAT reaction. This photosensitizer demonstrates remarkable photocytotoxicity even under hypoxic conditions, along with outstanding in vivo antitumor efficacy in mouse models bearing HeLa tumors. This work offers a novel strategy for the design of Type‐I photosensitizers by involvement of HAT. [ABSTRACT FROM AUTHOR]

Transition metal‐catalyzed radical‐based enantioconvergent reactions have become a powerful strategy to synthesize enantiopure compounds from racemic starting materials. However, existing methods primarily address precursors with central chirality, neglecting those with axial chirality. Herein, we describe the enantioconvergent reductive coupling of racemic allenes with aldehydes, facilitated by a photoredox, chromium, and cobalt triple catalysis system. This method selectively affords one product from sixteen possible regio‐ and stereoisomers. The protocol leverages CoIII−H mediated hydrogen atom transfer (MHAT) and Cr‐catalyzed radical‐polar crossover for efficient stereoablation of axial chirality and asymmetric addition, respectively. Supported by mechanistic insights from control experiments, deuterium labeling, and DFT calculations, our approach offers synthetic chemists a valuable tool for creating enantioenriched chiral homoallylic alcohols, promising to advance radical‐based strategies for synthesizing complex chiral molecules. [ABSTRACT FROM AUTHOR]

Allylic C−H amination has emerged as a powerful tool to construct allylamines, common motifs in molecular therapeutics. Such reaction implies an oxidative path for C−H activation but furnishes reductive amines, inferring mild oxidants' inactivity for C−H oxidation but strong oxidants' detriment to products. Herein we report a heterogeneous catalytic approach that manipulates halogen‐vacancies of perovskite photocatalyst and exploits halogenated‐solvents (i.e. CH2Cl2, CH2Br2) as mild oxidants for selective C−H allyl amination with 19,376 turnovers. CsPbBr3 nanocrystals induce cooperative hydrogen‐atom‐transfer (HAT, C−H oxidation, and halogen‐vacancy CsPbBr3−x formation) and halogen‐atom‐transfer (XAT, CsPbBr3−x‐induced solvent reduction) under a radical chain mechanism. Terminal/internal olefins are amenable to forge aromatic/aliphatic, cyclic/acyclic, secondary/tertiary allylamines (70 examples), including drugs or their derivatives. [ABSTRACT FROM AUTHOR]

Context: Dopamine β -monooxygenase (D β M) is an essential enzyme in the organism that regioselectively converts dopamine into R-norepinephrine, the key step of the reaction, studied in this paper, is a hydrogen atom transfer (HAT) from dopamine to a superoxo complex on D β M, forming a hydroperoxo intermediate and dopamine radical. It was found that the formation of a hydrogen bond between dopamine and the D β M catalyst strengthens the substrate-enzyme interaction and facilitates the HAT which takes place selectively to give the desired enantiomeric form of the product. Six reactions leading to the hydroperoxo intermediate were analyzed in detail using theoretical and computational tools in order to identify the most probable reaction mechanism. The reaction force analysis has been used to demonstrate that the nature of the activation energy is mostly structural and largely due to the initial approach of species in order to get closer to each other to facilitate the hydrogen abstraction. On the other hand, the reaction electronic flux revealed that electronic activity driving the reactions is triggered by polarization effects and, in the most probable reaction among the six studied, it takes place in a concerted and non-spontaneous way. Chemical events driving the reaction have been identified and the energy absorbed or delivered by each one was quantified in detail. Methods: The dopamine and a computational model of the copper superoxo complex on D β M were optimized at B3LYP-D3(BJ)/6-311 G(d,p) level theory in the Gaussian 16 software package. Optimization and IRC calculations were performed in the gas phase and through the PCM solvation model to mimic the protein medium. Non-covalent interactions were plotted using the NCI-plot software. The interaction of dopamine with copper superoxo complex on D β M is studied in order to characterize the mechanism of the hydrogen atom transfer step in the conversion of dopamine into norepinephrine. [ABSTRACT FROM AUTHOR]

Although Type‐I photodynamic therapy has attracted increasingly growing interest due to its reduced dependence on oxygen, the design of effective Type‐I photosensitizers remains a challenge. In this work, we report a design strategy for Type‐I photosensitizers by the involvement of hydrogen atom transfer (HAT). As a proof of concept, a HAT‐involved Type‐I PS, which simultaneously generates superoxide and carbon‐centered radicals under light‐irradiation, was synthesized. This photosensitizer is comprised of a fluorene‐substituted BODIPY unit as an electron acceptor covalently linked with a triphenylamine moiety as an electron donor. Under light‐irradiation, photo‐induced intramolecular electron transfer occurs to generate the BODIPY anion radical and triphenylamine cation radical. The former transfers electrons to oxygen to generate O2−⋅, while the latter loses a proton to produce a benzyl carbon‐centered radical which is well characterized. The resulting carbon‐centered radicals efficiently oxidize NADH by HAT reaction. This photosensitizer demonstrates remarkable photocytotoxicity even under hypoxic conditions, along with outstanding in vivo antitumor efficacy in mouse models bearing HeLa tumors. This work offers a novel strategy for the design of Type‐I photosensitizers by involvement of HAT. [ABSTRACT FROM AUTHOR]

Transition metal‐catalyzed radical‐based enantioconvergent reactions have become a powerful strategy to synthesize enantiopure compounds from racemic starting materials. However, existing methods primarily address precursors with central chirality, neglecting those with axial chirality. Herein, we describe the enantioconvergent reductive coupling of racemic allenes with aldehydes, facilitated by a photoredox, chromium, and cobalt triple catalysis system. This method selectively affords one product from sixteen possible regio‐ and stereoisomers. The protocol leverages CoIII−H mediated hydrogen atom transfer (MHAT) and Cr‐catalyzed radical‐polar crossover for efficient stereoablation of axial chirality and asymmetric addition, respectively. Supported by mechanistic insights from control experiments, deuterium labeling, and DFT calculations, our approach offers synthetic chemists a valuable tool for creating enantioenriched chiral homoallylic alcohols, promising to advance radical‐based strategies for synthesizing complex chiral molecules. [ABSTRACT FROM AUTHOR]

Allylic C−H amination has emerged as a powerful tool to construct allylamines, common motifs in molecular therapeutics. Such reaction implies an oxidative path for C−H activation but furnishes reductive amines, inferring mild oxidants' inactivity for C−H oxidation but strong oxidants' detriment to products. Herein we report a heterogeneous catalytic approach that manipulates halogen‐vacancies of perovskite photocatalyst and exploits halogenated‐solvents (i.e. CH2Cl2, CH2Br2) as mild oxidants for selective C−H allyl amination with 19,376 turnovers. CsPbBr3 nanocrystals induce cooperative hydrogen‐atom‐transfer (HAT, C−H oxidation, and halogen‐vacancy CsPbBr3−x formation) and halogen‐atom‐transfer (XAT, CsPbBr3−x‐induced solvent reduction) under a radical chain mechanism. Terminal/internal olefins are amenable to forge aromatic/aliphatic, cyclic/acyclic, secondary/tertiary allylamines (70 examples), including drugs or their derivatives. [ABSTRACT FROM AUTHOR]

Substituted azaarenes are one of the most ubiquitous moieties in natural products and drug molecules. An efficient organophotocatalytic method for direct coupling of diverse cyclic and acyclic alkyl carbons of alcohols, ethers, alkyl halides and alkanes with different azaaryl systems has been developed. It uses low loading of easily synthesizable efficient acridinium based photocatalyst and blue LED to generate highly reactive radicals on saturated hydrocarbons through sequential single electron transfer (SET) and hydrogen atom transfer (HAT) process. These in situ generated nucleophilic carbon radicals then undergo instantaneous regio‐selective coupling with azaarenes through Minisci type coupling to generate an array of important pharmacophores through sp2C−sp3C bond formation. With inexpensive organophotocatalysts, higher yield and wide substrate scope, this method provides a greener, efficient and versatile alternative to the previously reported syntheses. [ABSTRACT FROM AUTHOR]

The valorization of toluene offers a dual solution by addressing its environmental impact while also facilitating the synthesis of a diverse array of valuable fine chemicals and pharmaceutical intermediates, thus ensuring both ecological sustainability and economic viability. We report herein a synergistic approach that harmonizes hydrogen atom transfer (HAT) process with the generation of reactive oxygen species (ROS) under mild condition and low catalyst loading, which enables the efficient synthesis of a broad spectrum of esteemed benzoic acid derivatives and aryl ketones through the photocatalytic oxidation of toluene derivatives. Mechanistic elucidation reveals that the HAT reagent anthraquinone has both the capabilities to abstract hydrogen atoms and the ability to generate singlet oxygen (1O2) during energy transfer with triplet oxygen (3O2), and the combination of these two potencies significantly improves the catalytic efficiency of the reaction. This study not only introduces the amalgamation of HAT with ROS generation but also delineates a systematic approach for the selection of HAT reagents with energy transfer proficiency for ROS generation in catalytic oxidation reactions. [ABSTRACT FROM AUTHOR]

The document titled "Green Chemistry" published by the Royal Society of Chemistry in 2024 showcases cutting-edge research for a greener, sustainable future. It includes critical reviews, tutorial reviews, communications, and papers on various topics such as CO2 switchable solvents, photo- and electro-chemical synthesis, and green synthesis of aromatic aldehydes. The journal aims to connect the world with chemical sciences and invest profits back into the chemistry community, emphasizing interdisciplinary science to preserve the environment. [Extracted from the article]

Both preventing the production of waste and achieving high atom economy are fundamental principles of green chemistry. Herein, the first example of a 100% atom economical construction of hydroxyalkylated N-heteroarenes, done through recyclable decatungstate-photocatalyzed tandem cyclization/self-hydrogenation of isocyanides with equimolar amounts of aldehydes without exogenous hydrogen reagent and under byproduct-free conditions, was developed. Mechanistic studies revealed that three sequential hydrogen atom transfer processes might be involved in this reaction and all the leaving hydrogens as hydrogen sources were incorporated into the target hydroxyalkylated products. [ABSTRACT FROM AUTHOR]

The hydroalkylation reaction of olefins with alkanes is a highly desirable synthetic transformation toward the construction of C(sp3)-C(sp3) bonds. However, such transformation has proven to be challenging for unactivated olefins, particularly when the substrates lack directing groups or acidic C(sp3)-H bonds. Here, we address this challenge by merging NiH-catalyzed radical relay strategy with a HAT (hydrogen atom transfer) process. In this catalytic system, a nucleophilic alkyl radical is generated from a C(sp3)-H compound in the presence of a HAT promotor, which couples with an alkyl metallic intermediate generated from the olefin substrate with a NiH catalyst to form the C(sp3)-C(sp3) bond. Starting from easily available materials, the reaction not only demonstrates wide functional group compatibility but also provides hydroalkylation products with regiodivergence and excellent enantioselectivity through effective catalyst control under mild conditions. [ABSTRACT FROM AUTHOR]

This paper highlights the latest advancements in asymmetric alkylative difunctionalization of carbon–carbon double bonds by utilizing aliphatic C─H substrates as alkyl radical precursors. By integrating different hydrogen atom transfer (HAT) processes with various transition metal catalytic systems, various alkane substrates can be efficiently converted into corresponding alkyl radicals, which then participate in radical additions to carbon–carbon double bonds followed by stereoselective functionalizations with a third component. These strategies leverage inexpensive, abundant, and readily available alkane feedstocks to rapidly construct complex chiral molecules, demonstrating high step and atom economy. This paper focuses on recent progress and applications in this area, provides a comprehensive perspective on current developments, and suggests future directions in alkane‐involved asymmetric transformations. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: An amide‐substituted quinuclidine‐borane has been identified as a more efficient hydridic hydrogen atom transfer (HAT) catalyst for the hydroalkylation of unactivated olefins under visible‐light irradiation. 1H NMR titration experiments reveal that the amide moiety of the quinuclidine‐borane catalyst forms stronger hydrogen bonds with the carbonyl substrates, thereby improving the reaction yields. Furthermore, it was found that the reaction yields correlate well with the association constant between the quinuclidine‐borane catalyst and the carbonyl substrate. A scale‐up reaction using a continuous‐flow photoreactor has also been demonstrated. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: In the past two decades, the development of asymmetric radical reactions has achieved tremendous progress, which has emerged as a powerful tool for the synthesis of chiral molecules in synthetic chemistry. Among the diverse array of radical processes, the transfer of hydrogen atoms to tertiary carbon radicals offers the potential for constructing chiral tertiary carbon centers in a stereoselective fashion. Notwithstanding the challenges associated with the reactive and evanescent nature of radical species, the use of chiral reagents or mediators has enabled the stereocontrol of the asymmetric hydrogen atom transfer (AHAT), which provides novel avenues for advancing the field of asymmetric synthesis. Key Scientists: [ABSTRACT FROM AUTHOR]

The evolution of catalysis and functional group transfer reagents play a significant role in the development of anti‐Markovnikov alkene hydrofunctionalization reactions, facilitating the access to value‐added molecules. We herein report the first rational design of a modular intermolecular anti‐Markovnikov hydronitration of alkenes, enabling the direct synthesis of terminal nitroalkanes under visible light‐mediated photoredox catalysis. By employing the redox‐active organic nitrating reagent N‐nitrosuccinimide, the produced nitryl radicals, in the presence of an olefin and a hydrogen atom transfer (HAT) mediator, lead to an anti‐Markovnikov addition with complete regioselectivity. Furthermore, we present results demonstrating the use of this catalytic system for chain expansion via anti‐Markovnikov addition, utilizing substituted bromonitroalkanes as commercially available reagents. These transformations effectively address a gap in synthetic chemistry, enabling the direct synthesis of nitroalkanes from a variety of unactivated olefins in both complex molecules and unfunctionalized commodity chemicals. [ABSTRACT FROM AUTHOR]

Semiconductor‐based photoelectrochemical (PEC) organic transformations usually show radical characteristics, in which the reaction selectivity is often difficult to precisely control due to the nonselectivity of radicals. Accordingly, several simple organic reactions (e.g., oxidations of alcohols, aldehydes, and other small molecules) have been widely studied, while more complicated processes like C─C coupling remain challenging. Herein, a synergistic heterogeneous/homogeneous PEC strategy is developed to achieve a controllable radical‐induced C─C coupling reaction mediated by the copper‐coordination effect at the semiconductor/electrolyte interfaces, which additionally exerts a significant impact on the product regioselectivity. Through experimental studies and theoretical simulations, this study reveals that the copper‐chloride complex effectively regulates the formation of chloride radicals, a typical hydrogen atom transfer agent, on semiconductor surfaces and stabilizes the heterogeneous interfaces by suppressing the radical‐induced surface passivation. Taking the Minisci reaction (the coupling between 2‐phenylquinoline and cyclohexane) as a model, the yield of the target C─C coupling product reaches up to 90% on TiO2 photoanodes with a selectivity of 95% and long‐term stability over 100 h. Moreover, such a strategy exhibits a broad scope and can be used for the functionalization of various heteroaromatic hydrocarbons. [ABSTRACT FROM AUTHOR]

Diethylamine (DEA) represents a nitrogen-containing bio-oil model compound and an amine-model compound during the co-combustion of ammonia and hydrocarbons. Kinetics of the hydrogen abstraction reactions by H, O, OH, O 2 , HO 2 , CH 3 , and C 2 H 5 , and unimolecular decomposition reactions including 1,3-elimination, 1,2-hydrogen transfer, and C-N/C-C bond dissociations of DEA are theoretically investigated. Using the DLPNO-CCSD(T)/CBS(T-Q) method as a benchmark, cost-effective M06-2X/def2-TZVP method is selected for kinetic investigation. High-pressure-limit rate constants for the reactions with tight saddle points are determined by canonical variational transition-state theory with the multi-structural torsional anharmonicity and small-curvature tunneling. Hydrogen abstraction reactions at the C site connecting to the N site dominant in the low-to-mediate temperature range. Pressure dependent rate constants for the unimolecular decomposition reactions are determined by SS-QRRK/MSC-Dean approach. 1,3-elimination and C-C dissociation reactions dominant at the low-to-mediate and high temperature ranges, respectively. • Rate constants of the hydrogen abstractions from DEA are calculated. • Site-specific reactivity of the hydrogen abstractions from DEA is investigated. • Dominant pathways for the unimolecular decomposition of DEA are screened. • Multi-structural torsional anharmonicity on the consumption of DEA is examined. • Multidimensional tunneling effect on the consumption of DEA is explored. [ABSTRACT FROM AUTHOR]

Herein, we report a mild photocatalytic redox‐neutral dehydration of aryl‐1,2‐ethanediols forming the respective methyl ketones. In the proposed mechanistic cycle an initial hydrogen atom abstraction (HAT) is followed by a 1,2‐spin center shift (SCS) as key steps. Interestingly, Eosin Y was found to act as a pre‐catalyst dissociating into a catalytically active mixture under irradiation. To the best of our knowledge, this exemplifies the first synthetic utilization of Eosin Y degradation products. As a result, our reaction can be realized with a single organic photocatalyst and releases water as a sole by‐product. [ABSTRACT FROM AUTHOR]

The document from Chemical Communications, published in 2024, provides a comprehensive list of articles and research findings in the field of chemistry. Topics covered include alkene functionalization, perovskite solar cells, waste polyester upcycling, and various catalytic reactions. The journal aims to showcase original discoveries and preliminary research that contribute to scientific progress. [Extracted from the article]

Direct functionalization of alkenes with C(sp3)–H substrates offers unique opportunities for the rapid construction of pharmaceuticals and natural products. Although significant progress has been made over the past decades, the development of green, high step-economy methods to achieve these transformations under mild conditions without the need for pre-functionalization of C(sp3)–H bonds remains a substantial challenge. Therefore, the pursuit of such methodologies is highly desirable. Recently, the direct activation of C(sp3)–H bonds via photocatalytic hydrogen atom transfer (HAT), especially from unactivated alkanes, has shown great promise. Given the potential of this approach to generate a wide range of pharmaceutically relevant compounds, this review highlights the recent advancements in the direct functionalization of alkenes through photocatalytic HAT from C(sp3)–H compounds, as well as their applications in the synthesis and diversification of drugs, natural products, and bioactive molecules, aiming to provide medicinal chemists with a practical set of tools. [ABSTRACT FROM AUTHOR]

A highly regioselective visible light photoredox‐catalyzed hydrogen isotope exchange (HIE) of benzylic positions in both simple and complex molecules is reported. The process follows a dual catalytic approach using an acridinium photocatalyst in combination with a thiol‐based hydrogen atom transfer catalyst, while the use of D2O as an isotope source ensures operational simplicity and cost‐effectiveness. High reactivity has been achieved for electron‐rich benzylic positions. Moreover, targeted radical formation enables unprecedented selective HIE on intramolecular competing benzylic and alpha to heteroatom positions with moderate to excellent deuterium incorporation. The utility of the reaction was demonstrated on the late‐stage HIE of several natural compounds and drug derivatives. Experimental studies and density functional theory (DFT) calculations suggested a single electron transfer (SET) mechanism followed by deprotonation to generate the benzylic radical, and revealed the importance of halogenated solvents or additives. Upon a weak complexation of the halogenated species to the substrate, an oxidation potential lowering effect is induced, as well as a stabilization of the radical‐cation species through spin delocalization. [ABSTRACT FROM AUTHOR]

This study investigates the hydrogen‐bond geometry in six two‐component solid systems composed of quinoline and chloro‐nitrobenzoic acids. New X‐ray diffraction studies were conducted using both the conventional independent‐atom model and the more recent Hirshfeld atom‐refinement method, with the latter providing precise hydrogen‐atom positions. The systems can be divided into salts (the hydrogen atom transferred to the quinoline nitrogen), cocrystals (the hydrogen atom retained by the acid), and intermediate structures. Solid‐state NMR experiments corroborated the X‐ray diffraction‐derived H−N distances. DFT calculations, using five functionals including hybrid B3LYP and PBE0, showed varying energy profiles for the hydrogen bonds, with notable differences across functionals. These calculations revealed different preferences for salt or cocrystal structures, depending on the functional used. Path‐integral molecular dynamics simulations incorporating nuclear quantum effects demonstrated significant hydrogen‐atom delocalization, forming a hydrogen‐bond continuum, and provided average N−H distances in excellent agreement with experimental results. This comprehensive experimental and theoretical approach highlights the complexity of multicomponent solids. The study emphasizes that the classification into salts or cocrystals is frequently inadequate, as the hydrogen atom is often significantly delocalized in the hydrogen bond. This insight is crucial for understanding and predicting the behavior of such systems in pharmaceutical applications. [ABSTRACT FROM AUTHOR]

The fluorinated alcohols, (CF3)3COH (RF9OH) and (CF3)2MeCOH (RF6OH), react with W(NR)2Cy2 (Cy=Cyclohexyl; R=2,6‐diisopropylphenyl or 1‐adamantyl) in C6D6 at 55 °C to give cyclohexylidene complexes. Traditional routes to terminal alkylidene complexes (neopentylidene or neophylidene) have used either triflic acid or HCl (rarely), but relatively weak fluorinated acids are sufficient and active bisalkoxide catalysts are therefore prepared directly. An α hydrogen abstraction reaction to give a cyclohexylidene complex from a biscyclohexyl complex appears to be as facile as α hydrogen abstraction to give a neopentylidene or neophylidene ligand, but isomerization of a cyclohexene formed through β hydrogen abstraction is also a possibility. The ORF9 ligands can be replaced readily with dimethylpyrrolide (Me2Pyr) or other more basic alkoxides. Single crystal X‐ray studies were carried out on W(NAr)2Cy2, W(NAr)(ORF9)2(C6H10)(ArNH2), W(NAr)(ORF6)2(C6H10)(ArNH2), W(NAd)(ORF9)2(C6H10)(AdNH2), W(NAr)(O‐i‐PrF6)3Cy, and W(NAd)(η1‐Me2Pyr)2(C6H10) (C6H10=cyclohexylidene). [ABSTRACT FROM AUTHOR]

The fluorinated alcohols, (CF3)3COH (RF9OH) and (CF3)2MeCOH (RF6OH), react with W(NR)2Cy2 (Cy=Cyclohexyl; R=2,6‐diisopropylphenyl or 1‐adamantyl) in C6D6 at 55 °C to give cyclohexylidene complexes. Traditional routes to terminal alkylidene complexes (neopentylidene or neophylidene) have used either triflic acid or HCl (rarely), but relatively weak fluorinated acids are sufficient and active bisalkoxide catalysts are therefore prepared directly. An α hydrogen abstraction reaction to give a cyclohexylidene complex from a biscyclohexyl complex appears to be as facile as α hydrogen abstraction to give a neopentylidene or neophylidene ligand, but isomerization of a cyclohexene formed through β hydrogen abstraction is also a possibility. The ORF9 ligands can be replaced readily with dimethylpyrrolide (Me2Pyr) or other more basic alkoxides. Single crystal X‐ray studies were carried out on W(NAr)2Cy2, W(NAr)(ORF9)2(C6H10)(ArNH2), W(NAr)(ORF6)2(C6H10)(ArNH2), W(NAd)(ORF9)2(C6H10)(AdNH2), W(NAr)(O‐i‐PrF6)3Cy, and W(NAd)(η1‐Me2Pyr)2(C6H10) (C6H10=cyclohexylidene). [ABSTRACT FROM AUTHOR]

Mononuclear inorganic diradical species are scarce. Here, we confirm, via X‐ray absorption spectroscopy in the gas phase combined with computational studies, the oxygen‐centered diradical character of the tetraoxidorhenium(VII) cation. A dioxido‐superoxido isomer, close in energy to the diradical, is also found, where rhenium appears in its rare oxidation state of +6. Addition of one or two hydrogen atoms to [Re,O4]+ forms hydroxido ligands, and strongly disfavors isomers with any oxygen‐oxygen bond. This adds spectroscopic characterization of the rhenium oxidation state and the nature of ligands to the known ability of [Re,O4]+ to perform two consecutive hydrogen‐atom abstraction reactions from methane, and demonstrates that pentaatomic [Re,O4]+ combines a metal center in its highest oxidation state with two oxygen‐centered radical ligands in a highly reactive species. [ABSTRACT FROM AUTHOR]

Visible‐light induced, photoredox catalysis has opened a wide range in the transformation of organic compounds in recent times. In synthetic organic chemistry HAT (hydrogen atom transfer) and SET (single electron transfer) mechanisms are a very noteworthy routes that has opened a window in favor of C−C single bond formations. Usually, a major role of unsaturated hydrocarbons is to participate in carbon‐carbon bond formation as they carry reactive π‐bond. Under visible‐light, metal‐free cross‐coupling reactions are particularly favorable because of their atom economy, increased efficiency, and environmentally friendly procedures that result in the construction of C−C bonds. The review emphasizes the latest advancements of visible‐light mediated, cross‐coupling reactions of unsaturated hydrocarbons in metal‐free conditions for constructing carbon‐carbon single bonds. [ABSTRACT FROM AUTHOR]

1-Methylnaphthalene is a critical component for constructing fuel surrogates of diesel and aviation kerosene. However, the reaction pathways of 1-methylnaphthalene included in existing detailed chemical kinetic models vary from each other, leading to discrepancies in the simulation of ignition and oxidation processes. In the present study, reaction classes and pathways involved in the combustion of 1-methylnaphthalene were analyzed, and effects of rate constants of reactions related to 1-methylnaphthalene and its significant intermediates on ignition delay times and species concentration profiles were discussed, involving hydrogen abstraction and substitution reactions of 1-methylnaphthalene, oxidation, isomerization, and addition reactions of 1-naphthylmethyl, hydrogen abstraction and oxidation reactions of indene, as well as the oxidation of indenyl and naphthalene. On this basis, a new detailed chemical kinetic model for 1-methylnaphthalene was developed, which includes 1389 species and 7185 reactions. The validation of this mechanism shows that it can predict accurately the available experimental ignition delay times, species concentration profiles, and laminar flame speeds of 1-methylnaphthalene. Finally, reaction paths and sensitivity analysis of ignition delay times were performed using the proposed reaction mechanism, and the result shows that the conversion of 1-methylnaphthalene to 1-naphthaldehyde plays an important role in its ignition. [ABSTRACT FROM AUTHOR]

In this study, the DFT/M062X/PCM method was applied to investigate thermodynamic and kinetic aspects of reactions involved in possible mechanisms of antioxidant activity of caffeic acid against HOO● radicals in aqueous medium at different pH values. Kinetic parameters of the reactions involved in HAT (Hydrogen Atom Transfer), RAF (Radical Adduct Formation), and SET (Single Electron Transfer) mechanisms, including reaction energy barriers and bimolecular rate constants, were determined, and identification and characterization of stationary points along the reaction pathways within HAT and RAF mechanisms were performed. Inspection of geometrical parameters and spin densities of the radical products formed within HAT and RAF mechanisms revealed that they are stabilized by hydrogen bonding interactions and the odd electron originated through the reaction with the HOO● radical is spread over the entire molecule, resulting in significant radical stabilization. Thermodynamic and kinetic data collected in this study indicated that increasing pH of the medium boosts the antioxidant activity of caffeic acid by reducing the energy required to generate radicals within the RAF and/or HAT mechanism and, at extremely high pH, where the trianionic form of caffeic acid is a dominant species, by the occurrence of an additional fast, diffusion-limited electron-related channel. [ABSTRACT FROM AUTHOR]

This study explores the synthesis and characterization of three Schiff base compounds, namely N-(2-hydroxybenzylidene)-m-chloroaniline (1), N-(2-hydroxybenzylidene)-m-nitroaniline (2), and N-(2-hydroxybenzylidene)-m-methoxyaniline (3). Comprehensive spectroscopic analyses involving FT-IR, H1NMR, and UV-Vis were employed to elucidate their molecular structures. Theoretical calculations were conducted using the DFT/B3LYP method with the 6-311 + G (d, p) basis set, elucidating electronic transitions and providing comprehensive vibrational assignments. The study identifies key electronic features of these compounds by analyzing global chemical reactivity descriptors. Density functional theory (DFT) was employed to assess the ability of these compounds to scavenge free radicals, both in the gas phase and solvent environment, focusing on three primary mechanisms: hydrogen atom transfer (HAT), stepwise electron-transfer-proton transfer (ET-PT), and sequential proton-loss-electron transfer (SPLET). Additionally, the research explores drug-likeness properties and conducts molecular docking investigations against the ubiquinol cytochrome c reductase protein (UQCRB) to gain further insights into potential biological activities. [ABSTRACT FROM AUTHOR]

Context: Scopolin and scopoletin belong to the class of coumarins and have experimentally proven natural antioxidants. Natural antioxidants are crucial in mitigating the impact of oxidants in the human body through radical scavenging. Even though scopolin and scopoletin are proven antioxidants by experimental results, their antioxidant mechanisms still remained unexplained. In this study, Density functional theory (DFT) calculations were used to study the radical scavenging mechanisms of both scopolin and scopoletin using kinetic and thermodynamics parameters. The global parameters indicated that both scopolin and scopoletin have antioxidant properties. The band gap energy (Δ E HOMO - LUMO) revealed that scopoletin (4.18 eV) has strong antioxidant activity compared to scopolin (4.31 eV). These studies found that hydrogen atom transfer (HAT) is the primary mechanism for CH3OO• radical scavenging at the C–H bond in scopolin (91.98 kcal.mol−1) and the O–H bond in scopoletin (77.05 kcal.mol−1) due to their lowest bond dissociation energies. The calculated activation energy ( E a ) for the radical scavenging reaction, reconfirmed scopoletin ( E a =11.19 kcal.mol−1) performed as a better antioxidant compared to scopolin ( E a =20.91 kcal.mol−1). In this study, the results of DFT calculations confirmed that scopoletin exhibits a higher antioxidant capacity, and HAT mechanism is the most effective radical scavenging mechanism. Methods: The antioxidant activity of scopolin and scopoletin was determined by DFT at the B3LYP/6-31G(d) level of theory. Global parameter calculations and frontier molecular orbital analysis were conducted to assess these compounds' capacity for scavenging radicals. Hydrogen atom transfer (HAT), sequential electron transfer proton transfer (SETPT), and sequential proton loss electron transfer (SPLET) mechanisms were the three main mechanisms that were taken into consideration. The potential energy surface (PES) verified the most appropriate processes shown by the enthalpy calculations. [ABSTRACT FROM AUTHOR]

A systematic computational mechanistic and kinetics investigation has been performed on the antioxidant activity of phenyl carbamate, namely 3-morpholinopropyl phenyl carbamate (3-MPPC), against HO• and HOO• radicals. The standard density functional theory (DFT) method (M062X) is used for electronic structure calculation, and conventional transition state theory and Marcus theory are used for H-transfer and electron transfer kinetics, respectively. Four types of possible reaction mechanisms, such as hydrogen atom transfer (HAT), radical adduct formation (RAF), single electron transfer followed by proton transfer (SETPT), and sequential proton loss electron transfer (SPLET) have been considered here for investigation. 3-MPPC showed excellent HO• radical scavenging activity in the gas phase (koverall = 1.58 × 1011 M−1 s−1), water (koverall = 3.0 × 109 M−1 s−1) and pentyl ethanoate solvents (koverall = 3.8 × 109 M−1 s−1). In the case of HOO• radical scavenging activity, endothermic reactions with quite high activation energy are observed irrespective of the type of mechanisms. It was found that HAT is the most possible mechanism as it contributes approximately 97% and 93% to the overall rate (koverall) in the gas phase and the lipid medium, respectively. The RAF mechanism has a minor contribution to the scavenging of HO• radical in all the studied environments. In contrast, the SET mechanism is favorable in aqueous solution. The detailed theoretical studies will be helpful for better understanding the antioxidant activities of carbamate compounds and for further designing new potential antioxidants. [ABSTRACT FROM AUTHOR]