Hydrogen Atoms Research Articles

The effect of Coulomb potential on phase-of-phase attoclock spectroscopy: hydrogen atom as an example

The effect of Coulomb potential on phase-of-phase attoclock spectroscopy: hydrogen atom as an example

Synthesis of Unnatural Amino Acids via β‐Aminoaldehyde C–H Arylation using HAT‐Metallaphotoredox Catalysis

Unnatural amino acids play a crucial role in advancing protein engineering and drug development. In this study, we present the synthesis of a series of γ aryl‐keto‐α‐amino acids through the direct C–H arylation of readily accessible β‐aminoaldehydes and aryl bromides, promoted by hydrogen atom transfer combined with metallaphotoredox catalysis. This direct and mild methodology provides access to enantiopure L‐ and D‐ amino acids, either N‐protected or unprotected, with broad functional group compatibility, including pyridine heterocycles. These features highlight the potential relevance of this strategy for pharmaceutical synthesis and biotechnological research.

Metal-Free Photoinduced Cascade Cyclization of Alkyne-Tethered N-Alkoxybenzamides

AbstractIn this work, a photoinduced synthesis of isoxazolidine-fused isoquinolin-1-ones and 3,4-dihydro[1,2]oxazino[2,3-b]isoquinolin-10(2H)-one from alkyne-tethered N-alkoxybenzamides is reported. The gram-scaled synthesis and structural elaboration of isoxazolidine-fused isoquinolin-1-ones are also realized. The reaction is promoted by an equimolar amount of tetrabutylammonium chloride, under metal- and catalyst-free conditions. In the reaction, it is believed that the alkyne-tethered N-alkoxybenzamide starting materials serve as photosensitizers, and the photoexcited substrate induces the formation of a chloro radical. The N-radical results from hydrogen atom abstraction by the chloro radical at the N–H bond of the substrates.

A Review of Decontamination of Aspergillus spp. and Aflatoxin Control for Grains and Nuts with Atmospheric Cold Plasma

Aspergillus spp. and their produced aflatoxins are responsible for contaminating 25–30% of the global food supply, including many grains, and nuts which when consumed are detrimental to human and animal health. Despite regulatory frameworks, Aspergillus spp. and aflatoxin contamination is still a global challenge, especially in cereal-based matrices and their derived by-products. The methods for reducing Aspergillus spp. and aflatoxin contamination involve various approaches, including physical, chemical, and biological control strategies. Recently, a novel technology, atmospheric cold plasma (ACP), has emerged which can reduce mold populations and also degrade these toxins. ACP is a non-thermal technology that operates at room temperature and atmospheric pressure. It can reduce mold and toxins from grains and seeds without affecting food quality or leaving any chemical residue. ACP is the conversion of a gas, such as air, into a reactive gas. Specifically, an electrical charge is applied to the “working” gas (air) leading to the breakdown of diatomic oxygen, diatomic nitrogen, and water vapor into a mixture of radicals (e.g., atomic oxygen, atomic nitrogen, atomic hydrogen, hydroxyls), metastable species, and ions (e.g., nitrate, nitrite, peroxynitrate). In a cold plasma process, approximately 5% or less of the working gas is ionized. However, cold plasma treatment can generate over 1000 ppm of reactive gas species (RGS). The final result is a range of bactericidal and fungicidal molecules such as ozone, peroxides, nitrates, and many others. This review provides an overview of the mechanisms and chemistry of ACP and its application in inactivating Aspergillus spp. and degrading aflatoxins, serving as a novel treatment to enhance the safety and quality of grains and nuts. The final section of the review discusses the commercialization status of ACP treatment.

Mannich Bases: Promising Scaffolds for the Treatment of Infectious Diseases.

Mannich bases, synthesized through the reaction of an aldehyde, a primary or secondary amine, and a compound bearing an acidic hydrogen atom, represent a versatile class of scaffolds in medicinal chemistry. This review explores their broad spectrum of biological activities, emphasizing their potential in combating infectious diseases. With demonstrated efficacy against bacteria, fungi, and parasites, Mannich bases stand out as promising candidates for the development of novel therapeutic agents. Their versatility arises from the ability of their electronic, steric, and conformational parameters to modulate receptor interactions, significantly expanding their applicability in drug design. The review provides an in-depth analysis of the structure-activity relationship (SAR) of Mannich bases, highlighting how specific structural modifications enhance their biological activity. Additionally, it examines the lipophilic properties of these compounds, offering key insights into their influence on pharmacokinetics and pharmacodynamics. This understanding is essential for optimizing the development of novel therapeutics, particularly for addressing challenging infectious diseases. By integrating these aspects, this review underscores the pivotal role of Mannich bases in overcoming current challenges in drug resistance and shaping the future of drug discovery and development.

Gauge-invariant description of a Dirac electron moving in a noncommutative gauge-field background

Abstract We provide a gauge invariant description of the quantum dynamics of an electron in a constant noncommutative (NC) gauge field background using the Dirac equation in an NC plane. We show that the physical force imparted on the electron is the standard Lorentz force but with modified NC magnetic fields that pick up two different first order corrections in the relativistic and non-relativistic (NR) domains. Taking NR limit of our Dira equation we show that noncommutativity affects the cyclotron frequency but leaves the Hall conductivity and cyclotron motion trajectory unaffected to first order in the NC parameter. The hyperfine splitting of Hydrogen atom (H-atom) spectrum also shows a first order correction.

Looking at the Distant Universe with the MeerKAT Array: The H i Mass Function in the Local Universe

Abstract We present measurements of the neutral atomic hydrogen (H i) mass function (HiMF) and cosmic H i density (ΩH I) at 0 ≤ z ≤ 0.088 from the Looking at the Distant Universe with MeerKAT Array (LADUMA) survey. Using LADUMA Data Release 1 (DR1), we analyze the HiMF via a new “recovery matrix” method that we benchmark against a more traditional modified maximum likelihood (MML) method. Our analysis, which implements a forward modeling approach, corrects for survey incompleteness and uses extensive synthetic source injections to ensure robust estimates of the HiMF parameters and their associated uncertainties. This new method tracks the recovery of sources in mass bins different from those in which they were injected and incorporates a Poisson likelihood in the forward modeling process, allowing it to correctly handle uncertainties in bins with few or no detections. The application of our analysis to a high-purity subsample of the LADUMA DR1 spectral line catalog in turn mitigates any possible biases that could result from the inconsistent treatment of synthetic and real sources. For the surveyed redshift range, the recovered Schechter function normalization, low-mass slope, and “knee” mass are ϕ * = 3.5 6 − 1.92 + 0.97 × 1 0 − 3 Mpc−3 dex−1, α = − 1.1 8 − 0.19 + 0.08 , and log ( M * / M ⊙ ) = 10.0 1 − 0.12 + 0.31 , respectively, which together imply a comoving cosmic H i density of Ω H I = 3.0 9 − 0.47 + 0.65 × 1 0 − 4 . Our results show consistency between recovery matrix and MML methods and with previous low-redshift studies, giving confidence that the cosmic volume probed by LADUMA, even at low redshifts, is not an outlier in terms of its H i content.

In situ Doping Coupling With Vacancy Regulation Induced Strong Metal‐Support Interaction in Ni/CaTiO3 to Boost Supercharged Photothermal CO2 Methanation

AbstractThe “Solar Sabatier” reaction has emerged as a promising sustainable method for the CO2 hydrogenation. The development of advanced metal‐support catalysts based on Strong Metal‐Support Interaction (SMSI) offers significant advantages in the activation of CO2 and the regulation of selectivity. Herein, a novel composite Ni/CaTiO3 catalyst consisting of Ni and Ni‐doped CaTiO3 is synthesized and utilized in the CO2 methanation. A noteworthy finding is that the incorporation of Ni into the CaTiO3 matrix is instrumental in the formation of oxygen vacancies and the establishment of SMSI between Ni and CaTiO3. The enhanced SMSI resulting from the surface‐doped Ni atoms not only facilitated effective interface contact between metallic Ni and the CaTiO3 surface but also significantly improved the migration efficiency of hydrogen atoms reduced the reaction barrier for CO2 methanation and optimized the rate‐limiting step, all of which are advantageous for the CO2 methanation. Consequently, the optimized catalysts exhibited extraordinary performance, achieving a CO2 conversion rate of 87.77%, CH4 generation rate of 3.12 mol gNi−1 h−1, and ≈100% CH4 selectivity under ambient pressure conditions. This investigation lays the groundwork for the design of highly active “Solar Sabatier” catalysts and offers a novel understanding of the mechanisms underlying effective SMSI.

Ion-Pair Hydrogen Atom Transfer Catalysis Enables Cr-Catalyzed Allylation of Ketones Using Hydrocarbon Alkenes.

We report a catalytic allylation of ketones using simple hydrocarbon alkenes, enabled by a synergistic system comprising chromocene and photo-activatable ion-pair hydrogen atom transfer (IP-HAT) catalysts derived from a thiophosphoryl imide and N-heteroaromatics. This catalyst system generates highly nucleophilic, electron-rich allylchromium(III) species directly from unactivated alkenes, demonstrating broad applicability to various ketones, including aromatic, aliphatic, and multifunctional ketones. The reaction proceeds under mild conditions with high functional group tolerance. The modular design of the IP-HAT catalysts allows precise tuning of redox potential and HAT activity, with the enhanced reduction potential of the reduced N-heteroaromatics catalyst playing a pivotal role in efficiently regenerating the electron-rich chromocene(II) catalyst.

Ion‐Pair Hydrogen Atom Transfer Catalysis Enables Cr‐Catalyzed Allylation of Ketones Using Hydrocarbon Alkenes

We report a catalytic allylation of ketones using simple hydrocarbon alkenes, enabled by a synergistic system comprising chromocene and photo‐activatable ion‐pair hydrogen atom transfer (IP‐HAT) catalysts derived from a thiophosphoryl imide and N‐heteroaromatics. This catalyst system generates highly nucleophilic, electron‐rich allylchromium(III) species directly from unactivated alkenes, demonstrating broad applicability to various ketones, including aromatic, aliphatic, and multifunctional ketones. The reaction proceeds under mild conditions with high functional group tolerance. The modular design of the IP‐HAT catalysts allows precise tuning of redox potential and HAT activity, with the enhanced reduction potential of the reduced N‐heteroaromatics catalyst playing a pivotal role in efficiently regenerating the electron‐rich chromocene(II) catalyst.

Deconjugative Photoisomerization of Cyclic Enones.

The deconjugative isomerization of α,β-unsaturated carbonyl compounds enables regioisomeric products to be forged with simultaneous Umpolung of alkene reactivity. Although highly enabling, the endergonic nature of the net process coupled with governing regioselectivity outcomes, renders it challenging. Innovations in the positional isomerization of linear species, often by light-triggered activation, have re-energized this area. However, the deconjugative isomerization of cyclic enones is underdeveloped and often associated with impractical reaction conditions, limited substrate scopes, and a lack of mechanistic clarity. Herein, we report an operationally simple photochemical isomerization of cyclic enones using near-UV (372 nm) irradiation with catalytic amounts of Brønsted acid (HCl). This platform enables exocyclic deconjugative isomerization of a diverse array of enones including α-isophorone (a key intermediate in a variety of industrial processes), terpenoids and steroids. Mechanistic studies reveal the pivotal role of the solvent as a key mediator in the isomerization, where sequential hydrogen atom transfer (HAT) and reverse-HAT (RHAT) are proposed to be operational.

Zn(II)-Stabilized Radical Ligand Enabled Radical-Type C(sp3)-H Activation-Cascade Cyclization to Imidazopyridines.

A Zn(II)-stabilized radical-ligand enabled tandem cyclization via radical-type C(sp3)-H functionalization of N-benzylpyridin-2-amines with terminal alkynes producing straightforward access to a wide variety of imidazo[1,2-a]pyridines in moderate to good yields is reported. In the presence of KOtBu the Zn(II)-catalyst [ZnIILaCl2] (1a) (La = 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline) undergoes one-electron reduction to the active catalyst [ZnII(La)•-Cl2] [1a]- bearing a ligand-centered radical. Upon coordination of N-benzylpyridin-2-amine to [1a]-, the radical-ligand abstracts a hydrogen atom from the benzylic position, forming a benzylic radical intermediate which, through radical addition with the alkyne generates a vinyl radical intermediate. Subsequent cyclization via intramolecular nucleophilic attack by the pyridine nitrogen produces imidazo[1,2-a]pyridines. Control experiments and spectroscopic investigation confirm the radical-ligand assisted tandem radical-type C(sp3)-H activation, addition, and cyclization steps.

Visible Light‐Promoted Enantioselective Catalytic Alkylation of α‐Ketoamides with Hydrocarbons

AbstractVisible light‐mediated enantioselective alkylation of carbonyls with hydrocarbons provides beneficial access to the synthesis of chiral alcohols in terms of atom economy. Herein, we disclosed a direct asymmetric alkylation of α‐keto pyrazoleamides with hydrocarbons as C(sp3)–H donors for the preparation of tertiary α‐hydroxy amides. Our method operates by synergistic catalysis involving Ir‐based photoredox catalyst and chiral N,N′‐dioxide‐NiBr2 complex enabled the addition reaction in good‐to‐excellent yield and enantioselectivity (up to 87% yield and 97% ee), competing successfully with the homocouplings. Based on the control experiments and spectrographic experiments, a possible radical addition mechanism triggered by Ir photoredox catalysis and bromine radical‐participated hydrogen atom transfer of hydrocarbon was proposed.

Continuous Atomic Hydrogen for Eminent Bromate Reduction via Palladium Coordination Manipulation

Continuous Atomic Hydrogen for Eminent Bromate Reduction via Palladium Coordination Manipulation

Intrinsic Curvatures of Atomic Orbitals for Hydrogen-Like Atoms

Within the quantum model for the hydrogen-like atom and taking into account the concepts of differential geometry, we calculate the intrinsic curvature of several types of atomic orbitals. Based on this concept of intrinsic curvature, a classification of atomic orbitals (AO) is given. We conclude by discussing the advantages of characterizing atomic quantum states by intrinsic curves for the AO of the hydrogen-like atom.

Harnessing Nitrous Oxide for Sustainable Methane Activation: A Computational Exploration of CNC-Ligated Iron Catalysts

This study employs DFT at the APFD/def2-TZVP level, with SMD solvation in THF, to investigate the catalytic activation of methane by [(κ3-CNC)Fe(N₂O)]2+ cation complexes. The catalytic mechanism encompasses three key steps: oxygen atom transfer (OAT), hydrogen atom abstraction (HAA), and oxygen radical rebound (ORR). The computational results identify OAT as the rate-determining step, with activation barriers of −10.2 kcal/mol and 5.0 kcal/mol for κ1-O- and κ1-N-bound intermediates in the gas and solvent phases, respectively. Methane activation proceeds via HAA, with energy barriers of 16.0–25.2 kcal/mol depending on the spin state and solvation, followed by ORR, which occurs efficiently with barriers as low as 6.4 kcal/mol. The triplet (S = 1) and quintet (S = 2) spin states exhibit critical roles in the catalytic pathway, with intersystem crossing facilitating optimal reactivity. Spin density analysis highlights the oxyl radical character of the FeIV=O intermediate as being essential for activating methane’s strong C–H bond. These findings underscore the catalytic potential of CNC-ligated iron complexes for methane functionalization and demonstrate their dual environmental benefits by utilizing methane and reducing nitrous oxide, a potent greenhouse gas.

Ethylene Glycol Partial Aqueous Oxidation on Co3O4 (001) Surfaces: Pathways to Two‐ and Four‐Electron Products in Neutral and Oxidative Conditions

AbstractThe catalytic oxidation of ethylene glycol (EG) on the Co3O4 (001) surface is investigated by AIMD simulations in the presence of a water layer for the A‐ and B‐ terminations. In addition to the surface structure and composition, the chemical state of the aqueous environment plays a crucial role in the oxidation process. Specifically, it depends on the concentration of surface hydroxyl groups, which can act both as proton donors and acceptors. Reference surfaces, which are generated by bringing the unhydrogenated A‐ and B‐terminated surfaces in contact with a stoichiometric water layer, show some spontaneous water dissociation, which produces a number of surface hydroxyl groups. On such an A‐terminated reference surface, the EG molecule is barely reactive. This holds even in a more oxidative state. On the B‐terminated surface, EG's decomposition into ethylenedioxy species occurs already in the reference state. Under the more oxidative hydrogen‐deficient conditions obtained by removing eight hydrogen atoms, the reaction proceeds to the formation of the two‐electron oxidation product glycolaldehyde. Removal of altogether 16 hydrogen atoms facilitates the formation of four‐electron oxidation products, such as glycolic acid and glyoxal and the observation of a transient H2O2 species, which subsequently evolves to form dioxygen.

Hydrogenation of HOCO and formation of interstellar CO2: A not so straightforward relation

Abstract Carbon dioxide (CO2) is one of the most important interstellar molecules. While it is considered that it forms on the surface of interstellar dust grains, the exact contribution of different chemical mechanisms is still poorly constrained. Traditionally it is deemed that the CO + OH reaction occurring on top of ices is the main reaction path for its formation. Recent investigations showed that in reality the reaction presents a more complex mechanism, requiring an additional H-abstraction step. Building on our previous works, we carried out a detailed investigation of such H abstraction reactions with the hydrogen atom as a reactant for the abstraction reaction. We found an unconventional chemistry for this reaction, markedly depending on the isomeric form of the HOCO radical prior to reaction. The favored reactions are t-HOCO + H $\longrightarrow$ CO + H2O, c-HOCO + H $\longrightarrow$ CO2 + H2 and t/c-HOCO + H $\longrightarrow$ c/t-HCOOH. We estimate bounds for the rate constants of the less favored reaction channels, t-HOCO + H $\longrightarrow$ CO2 + H and c-HOCO + H $\longrightarrow$ CO + H2O, to be approximately 104 − 6 s−1. However, these estimates should be interpreted cautiously due to the significant role of quantum tunneling in these reactions and the complex electronic structure of the involved molecules, which complicates their study. Our findings underscore the need for detailed investigation into the chemistry of interstellar CO2 and pave the way for a reevaluation of its primary formation mechanisms in the interstellar medium.

Infrared Spectrum and UV-Triggered Transformations of Matrix-Isolated Meta-Fluorothiophenol Supported by Ground and Excited State Theoretical Calculations.

The infrared (IR) spectrum of meta-fluorothiophenol (mFTP) isolated in a low-temperature N2 matrix was recorded and interpreted with the aid of B3LYP vibrational frequency calculations for both cis and trans conformers. Then, photochemical transformations in the matrix-isolated compound were triggered through UV-Vis laser irradiations and their outcomes were monitored by IR spectroscopy. Upon excitation at λ = 285 nm, thiol-to-thione phototautomerization was identified as the sole reaction pathway, leading to the formation of three thione isomers. Among them, the ortho-isomer where the hydrogen atom reattaches to the fluorine-substituted side of the aromatic ring was identified as the predominant photoproduct. Identification of the photoproducts was confirmed by comparing the emerging experimental spectra with the IR absorptions predicted for the candidate structures. The photoreaction was found to be reversible, as irradiation at λ = 405 nm partially restored the reactant. The experimental results were complemented with the application of multireference/multiconfigurational (CASSCF, CASPT2, MR-CIS) and TD-DFT (TD-M062X, ωB97XD, and τ-HCTHhyb) methods to investigate the excited state properties of mFTP, including the simulation of its UV photoabsorption spectra. A comparative analysis of the results obtained by the different methods was performed. This combined experimental and theoretical approach provided valuable insights into the photochemical behavior and electronic structure of fluorinated thiophenols.

Visible-Light-Induced Divergent C-H Esterification/Alkylation of Quinoxalin-2(1H)-ones with Aldehydes under Mild Conditions.

Herein, we introduce an efficient and straightforward strategy for the selective C-H esterification and alkylation of quinoxalin-2(1H)-ones with aldehydes. A key feature of our study is the ability to perform both C-H esterification and alkylation using different types of aldehydes. The reaction system is highly compatible with a range of quinoxalin-2(1H)-ones and aldehydes, yielding C3-esterified and C3-alkylated products in moderate-to-good yields. The applicability of this approach is further enhanced by its scalability through continuous-flow synthesis, late-stage modification of significant molecules, and product derivatization. Our mechanistic investigations reveal a radical relay mechanism, triggered by a hydrogen atom transfer process.