Hydrogen Atoms Research Articles

Unraveling the Geometry-Driven C═C Epoxidation and C-H Hydroxylation Reactivity of Tetra-Coordinated Nonheme Iron(IV)-Oxo Complexes.

The electronic structure and reactivity of tetra-coordinated nonheme iron(IV)-oxo complexes have remained unexplored for years. The recent synthesis of a closed-shell iron(IV)-oxo complex [(quinisox)FeIV(O)]+ (1) has set up a platform to understand how such complexes compare with the celebrated open-shell iron-oxo chemistry. Herein, using density functional theory and ab initio calculations, we present an in-depth electronic structure investigation of the C═C epoxidation [oxygen atom transfer (OAT)] and C-H hydroxylation [hydrogen atom transfer (HAT)] reactivity of 1. Using a solvent-coordinated geometry of 1 (1') and other potential tetra-coordinated iron(IV)-oxo complexes bearing rigid ligands (2 and 3), we established the geometric origin of spin-state energetics and reactivity of 1. Complex 1 featuring a strong Fe-O bond exhibits OAT and HAT reactivity in its quintet state. The lowest quintet OAT pathway has a lower barrier by ∼4 kcal/mol than the quintet HAT pathway, corroborating the experimentally observed gas-phase OAT reactivity preference. A conventional HAT reactivity preference for 2 and a comparable OAT and HAT reactivity for 3 are observed. This further supports the geometry-driven reactivity preference for 1. Noncovalent interaction analyses reveal a pronounced π-π interaction between the substrate and ligand in the OAT transition state, rationalizing the origin of the observed reactivity preference for 1.

Liquefaction pathway of corn stalk cellulose in the presence of polyhydric alcohols under acid catalysis

In this paper, the experiment of cellulose from corn stalk using 1, 2-propylene glycol (PG) and diethylene glycol (DEG) liquefaction catalyzed by phosphoric acid at atmosphere pressure was carried out. The effect of reaction time on the structural changes of cellulose in the liquefaction process of polyhydric alcohols was investigated, aiming at understanding the mechanism of cellulose liquefaction reaction under the action of acid catalyzed polyhydric alcohols. It was found that the liquefaction yield increased first and then decreased with the extension of reaction time, and reached the highest at 150 min (99.34 %). In the phase of increasing liquefaction yield, cellulose was degraded and translated into glucose, which was then converted into plenty of glycosides with PG/DEG. These glycosides were further converted into low molecular weight (LMW) substances such as hydrocarbons, acids, alcohols, esters, ketones, and ethers. At this time, the biofuel contained 70 %–85 % compounds with carbon number less than 25 and 5 %–10 % compounds with carbon number more than 25. As the prolongation of reaction time (after 150 min), quantities of unstable free radicals formed by cellulose degradation could combine with each other or with hydrogen atoms provided by PG/DEG to produce relatively stable macromolecular substances. That is, the polydispersity (Mw/Mn, abbreviated Ð = 1.28) of the generated biofuel at this stage no longer decreased. However, liquefaction residue produced at 240 min had changed essentially, which was completely different from the liquefaction residue produced in the early stage of liquefaction. In conclusion, this paper revealed the partial reaction process of cellulose by studying the structural changes in the liquefaction process of polyhydric alcohols, which laid a theoretical foundation for exploring the liquefaction mechanism of cellulose.

Ultrahigh Pt-mass-activity catalyst for alkaline hydrogen evolution synthesized by microwave method in air

Platinum (Pt) metal is widely acknowledged as a highly efficient electrocatalyst for hydrogen evolution reaction (HER) in acidic electrolyte. However, its performance in alkaline environments is significantly lower owing to the sluggish water dissociation step. Herein, we synthesized an ultrahigh Pt-mass-activity alkaline HER catalyst using microwave reduction method in air. Our catalyst, PtRu@CNT, comprises PtRu alloy nanoparticles uniformly loaded on carbon nanotubes, with Pt and Ru contents of 12.3 wt% and 4.5 wt%, respectively. The PtRu alloy nanoparticles have an average diameter of about 3 nm and a face-centered cubic structure, and the introduction of Ru has led to a modified electronic structure in Pt. As a result, an impressively low HER overpotential of 13 mV was achieved, significantly lower than commercial 20 wt% Pt/C (61 mV). PtRu@CNT exhibited a high turnover frequency based on metal mass of 3.06 s−1 at 100 mV, about 6 times higher than commercial Pt/C (0.46 s−1 at 100 mV), highlighting its excellent intrinsic activity. The HER mechanism of PtRu@CNT is a Volmer-Tafel mechanism, where the rate-limiting step changed to the recombination of hydrogen atoms from initial water dissociation, attributed to the presence of Ru. The alkaline HER activity of PtRu@CNT ranks among the best of currently reported Pt-based catalysts.

Biosynthesis of the Non-canonical C17 Sesquiterpenoids Chlororaphen A and B from Pseudomonas chlororaphis.

Chlororaphens A and B are structurally unique non-canonical C17 sesquiterpenoids from Pseudomonas chlororaphis that are made by two SAM-dependent methyltransferases and a type I terpene synthase. This study addresses the mechanism of their formation in isotopic labelling experiments and DFT calculations. The results demonstrate an astonishing complexity with distribution of labellings within a cyclopentane core that is reversely connected to two acyclic fragments in chlororaphen A and B. In addition, the uptake of up to 14 deuterium atoms from D2O was observed. These findings are explainable by a repeated late stage multistep rearrangement sequence. The absolute configurations of the chlororaphens and their biosynthetic intermediates were elucidated in stereoselective labelling experiments.

Flavonoid as a Potent Antioxidant: Quantitative Structure-Activity Relationship Analysis, Mechanism Study, and Molecular Design by Synergizing Molecular Simulation and Machine Learning.

In this work, a quantitative structure-antioxidant activity relationship of flavonoids was performed using a machine learning (ML) method. To achieve lipid-soluble, highly antioxidant flavonoids, 398 molecular structures with various substitute groups were designed based on the flavonoid skeleton. The hydrogen dissociation energies (ΔG1, ΔG2, and ΔG3) related to multiple hydrogen atom transfer processes and the solubility parameter (δ) of flavonoids were calculated using molecular simulation. The group decomposition results and the calculated antioxidant parameters constituted the ML data set. The artificial neural network and random forest models were constructed to predict and analyze the contribution of the substitute groups and positions to the antioxidant activity. The results showed the hydroxyl group at positions B4', B5', and B6' and the branched alkyl group at position C3 in the flavonoid skeleton were the optimal choice for improving antioxidant activity and compatibility with apolar organic materials. Compared to the pyrogallol group-grafted flavonoid, the designed potent flavonoid decreased ΔG1 and δ by 2.2 and 15.1%, respectively, while ΔG2 and ΔG3 kept the favorable lower values. These findings suggest that an efficient flavonoid prefers multiple ortho-phenolic hydroxyl groups and suitable sites with hydrophobic groups. The combination of molecular simulation and the ML method may offer a new research approach for the molecular design of novel antioxidants.

Deuterium Editing of Small Molecules: A Case Study on Antitumor Activity of 1,4-Benzodiazepine-2,5-dione Derivatives.

Substituting hydrogen with deuterium in drug molecules is an appealing bioisosteric strategy for the generation of novel chemical entities in drug development. Optimizing lead compounds through deuteration has proven to be challenging and unpredictable, particularly for compounds with multiple metabolic sites. This study presents the pioneering achievement of substituting up to 19 hydrogen atoms with deuterium on 1,4-benzodiazepine-2,5-dione derivatives, shedding light on the structure-metabolism relationship and the impact of multiple deuterations on drug-like properties. Notably, the deuterated compound 3f exhibited remarkable antitumor activity in vivo and demonstrated favorable drug-like properties as a drug candidate.

Explicitly Correlated Gaussians with Tensor Pre-factors: Analytic Matrix Elements

We consider a specific form of explicitly correlated Gaussians—with tensor pre-factors—which appear naturally when dealing with certain few-body systems in nuclear and particle physics. We derive analytic matrix elements with these Gaussians—overlap, kinetic energy, and Coulomb potential—to be used in variational calculations of those systems. We also perform a quick test of the derived formulae by applying them to p- and d-waves of the hydrogen atom.

1,3-Difunctionalization of [1.1.1]propellane through iron-hydride catalyzed hydropyridylation

Current methodologies for the functionalization of [1.1.1]propellane primarily focus on achieving 1, 3-difunctionalized bicyclo[1.1.1]pentane or ring-opened cyclobutane moiety. Herein, we report an innovative approach for the 1, 3-difunctionalization of [1.1.1]propellane, enabling access to a diverse range of highly functionalized cyclobutanes via nucleophilic attack followed by ring opening and iron-hydride hydrogen atom transfer. To enable this method, we developed an efficient iron-catalyzed hydropyridylation of various alkenes for C − H alkylation of pyridines at the C4 position, eliminating the need for stoichiometric quantities of oxidants or reductants. Mechanistic investigations reveal that the resulting N-centered radical serves as an effective oxidizing agent, facilitating single-electron transfer oxidation of the reduced iron catalyst. This process efficiently sustains the catalytic cycle, offering significant advantages for substrates with oxidatively sensitive functionalities that are generally incompatible with alternative approaches. The strategy presented herein is not only mechanistically compelling but also demonstrates broad versatility, highlighting its potential for late-stage functionalization.

A broad-spectrum oxidation capability Ru-CeO2 catalyst for efficient synergistic selective oxidation of benzyl alcohol

Selective oxidation of alcohols to aldehydes by molecular oxygen is one of the most important transformations in multiphase catalysis. In this paper, a catalyst with selective oxidation ability was designed and synthesized for the selective catalytic oxidation of benzyl alcohol. N-doped carbon materials were prepared by high-temperature calcination using hydrothermal reaction products of citric acid and melamine as a carbon source, and a bimetallic catalyst supported by Ru-CeO2 was constructed using the mixture as the carrier for the selective oxidation of benzyl alcohol to benzaldehyde. The results showed that the introduction of CeO2 could effectively improve the oxidizing ability and catalytic activity of the catalyst. The Ru-Ce0.05/NC170–600 catalyst was able to convert 85.5 % benzyl alcohol into benzaldehyde at 140 °C, 6 h, and 2 MPa, and the selectivity for benzaldehyde was 100 %. It was demonstrated by DFT that it was theoretically feasible to generate benzaldehyde by extracting hydrogen atoms from benzyl alcohol molecules. Further, the selective oxidation experiments on other alcohols showed that the catalyst has high activity for the oxidation of various alcohols to generate the corresponding carbonyl products, and it is a catalyst with broad-spectrum selective oxidation ability. In this study, a green synthesis route of benzaldehyde was proposed to solve the problems in the traditional process. Meanwhile, it provides a new idea for the synthesis of carbonyl products by selective oxidation of alcohols.

Direct Functionalization of Polyethylene Surfaces with High-Density Polymer Brushes.

Introducing functionality onto PE surfaces is a longstanding challenge in polymer science, driven by the need for polymer materials with improved adhesion and antifouling properties. Herein, we report surface-initiated hydrogen atom transfer-reversible addition-fragmentation chain transfer (SI HAT-RAFT) as a robust method to grow high-density brush polymers from PE surfaces. We demonstrate that, under mild conditions, direct initiation from the C-H bonds of PE surfaces allows for the graft polymerization of a variety of (meth)acrylate monomers. The resulting polymer brushes reached several hundred nanometers in thickness with densities of ca. 0.62 chains/nm2, compared to the current standard of ∼0.28 chains/nm2. Finally, we show that our method is capable of dramatically improving the adhesive properties of PE surfaces. This work enables the preparation of PE with diverse surface functionalities for potential use in biomedical, industrial, and battery applications.

Wild-Edible Allium Species from Highlands of Eastern Anatolia: Phytochemical Composition and In Vitro Biological Activities.

This study presents the phytochemical composition, antioxidant (hydrogen atom and single-atom transfer mechanisms), and digestive enzyme inhibitory (alpha-amylase, alpha-glucosidase, and pancreatic lipase) activities of ethanol-based extractions and traditional preparations (infusion) of the leaves of wild-edible Allium species (A. kharputense, A. affine, A. shirnakiense, and A. akaka) from the highlands of Eastern Anatolia. Among the eight extracts analyzed, ethanol extractions of the A. kharputense and A. akaka leaves exhibited better biotherapeutic activities and had the highest bioactive content. The dominant bioactive profile was composed of mainly allicin and phenolic compounds (chlorogenic acid, hesperidin, rutin, isoquercitrin, and quercetin) with small amounts of fatty acids. These data were similar to the biological activities and chemical composition of common Allium species and suggest the utilization of the extracts of wild-edible Allium species in the development of Allium-based biotherapeutics or nutraceuticals.

Measurements of atomic hydrogen recombination coefficients and the reduction of Al2O3 using a heat flux sensor

The knowledge of atomic hydrogen recombination coefficient (γ) is essential for plasma simulations to calculate accurate atomic hydrogen fluxes. However, γ is a complex material property, and it is affected by the experimental conditions under which it is measured. Therefore, values of γ can differ even by a few orders of magnitude for the same material. In this paper, we demonstrate measurements of hydrogen recombination coefficients at room temperature using an in-house-built catalytic sensor for two selected materials: aluminum Al-5083 (alimex) and stainless steel 316 l, under the load of low-temperature H2 plasma with an admixture of H2O or N2 gases. The plasma settings were carefully chosen to mimic properties of the so-called extreme ultraviolet-generated plasma.1 The measured γ values agree well with literature data obtained for similar plasma conditions and show a correlation with ion energy. Additionally, we show a novel application of the sensor for indirect measurements of the reduction of oxidized surfaces as a function of ion dose. In these experiments, a correlation between reduction time and background water pressure is observed.

Hypervalent Iodine (III)-Based Complexation for Chiroptical Supramolecular Glass, Deep Eutectic Solvent and Luminescent Switch.

Hypervalent iodine(III) have widely been utilized for organic synthetic reagents. They are also recognized as positive charge-assisted, exceptionally robust biaxial halogen bond donors, while their potential in supramolecular materials is barely explored. This work reports a cyclic diaryliodonium ion as biaxial halogen bonding donor that displays remarkable binding affinity toward phenanthroline or acridine acceptors with chiral pendants. Biaxial halogen bonding enables chiroptical evolution in solution, allowing for rational control over supramolecular chirality. Leveraging their strong binding affinity, the halogen bonding complexes manifested amorphous properties and deep eutectic behavior in the solid state. Capitalizing on these attributes, this work achieves the successful preparation of supramolecular glasses and deep eutectic solvents. Additionally, halogen bonding appended light irradiation-triggered luminescence through a hydrogen atom transfer process, showing applications in anti-counterfeit and display.

Assessing Hydrogen Embrittlement in Pipeline Steels for Natural Gas-Hydrogen Blends: Implications for Existing Infrastructure

Governments worldwide are actively committed to achieving their carbon emission reduction targets, and one avenue under exploration is harnessing the potential of hydrogen. Blending hydrogen with natural gas is emerging as a promising strategy to reduce carbon emissions, as it burns cleanly without emitting carbon dioxide. This blending could significantly contribute to emissions reduction in both residential and commercial settings. However, a critical challenge associated with this approach is the potential for Hydrogen Embrittlement (HE), a phenomenon wherein the mechanical properties of pipe steels degrade due to the infiltration of hydrogen atoms into the metal lattice structure. This can result in sudden and sever failures when the steel is subjected to mechanical stress. To effectively implement hydrogen-natural gas blending, it is imperative to gain a comprehensive understanding of how hydrogen affects the integrity of pipe steel. This necessitates the development of robust experimental methodologies capable of monitoring the presence and impact of hydrogen within the microstructures of steel. Key techniques employed for this assessment include microscopic observation, hydrogen permeation tests, and tensile and fatigue testing. In this study, samples from two distinct types of pipeline steels used in the natural gas distribution network underwent rigorous examination. The findings from this research indicate that charged samples exhibit a discernible decline in fatigue and tensile properties. This deterioration is attributed to embrittlement and reduced ductility stemming from the infiltration of hydrogen into the steel matrix. The extent of degradation in fatigue properties is correlated not only to the hydrogen content but also to the hydrogen permeability and diffusion rate influenced by steel’s microstructural features, with higher charging current densities indicating a more significant presence of hydrogen in the natural gas pipeline blend.

Addressing the Opioids Lipophilicity Challenge via a Straightforward and Simultaneous 1H NMR-Based logP/D Determination, Both Separately and in Mixtures.

A systematic study of trends in the lipophilicity of prominent representatives of the opioid family, including natural, semisynthetic, synthetic, and endogenous neuropeptide opioids, is described. This was enabled by a straightforward 1H NMR-based logP/D determination method developed for compounds holding at least one aromatic hydrogen atom. Moreover, the new method enables a direct simultaneous logD determination of opioid mixtures, overcoming the high sensitivity of this family to the measurement conditions, which is critical when a determination of the exact ΔlogD values of matched pairs is required. Interpretation of the experimental ΔlogD7.4 values of selected matched pairs, focusing inter alia on the 3-OMe and 14-OMe motifs in morphinan opioids, is suggested with the aid of DFT calculations and may be useful for the discovery of new opioid therapeutics.

Impact of Quantum Non-Locality and Electronic Non-Ideality on the Shannon Entropy for Atomic States in Dense Plasma.

The influence of the collective and quantum effects on the Shannon information entropy for atomic states in dense nonideal plasma was investigated. The interaction potential, which takes into account the effect of quantum non-locality as well as electronic correlations, was used to solve the Schrödinger equation for the hydrogen atom. It is shown that taking into account ionic screening leads to an increase in entropy, while taking into account only electronic screening does not lead to significant changes.

Engineering an enzyme-like catalytic sensor for on-site dual-mode evaluation of total antioxidant capacity.

Anovel Fe-MoOx nanozyme, engineered with enhanced peroxidase (POD)-like activity through strategic doping and the creation of oxygen vacancies, is introducedto catalyze the oxidation of TMB with high efficiency. Furthermore, Fe-MoOx is responsive to single electron transfer (SET) and hydrogen atom transfer (HAT) mechanisms related to antioxidants and can serve as a desirable nanozyme for total antioxidant capacity (TAC) determination. The TAC colorimetric platform can reach a low LOD of 0.512μM in solution and 24.316μM in the smartphone-mediated RGB hydrogel (AA as the standard). As proof of concept, the practical application in real samples was explored. The work paves a promising avenue to design diverse nanozymes for visual on-site inspection of food quality.

Computational Insights into the Intramolecular Aromatic C-C Coupling Catalyzed by the Cytochrome P450 Enzyme CYP121 from Mycobacterium tuberculosis.

CYP121 is a P450 enzyme that catalyzes the intramolecular C-C coupling of its native substrate, dicyclotyrosine (cYY). According to previous suggestions, when the cosubstrate peracetic acid was used to generate Cpd I, the substrate cYY was suggested to participate in the cleavage of the O-O bond; however, whether cYY is involved in the formation of Cpd I and how two distant aromatic carbon atoms are activated are still unclear. Here, we constructed computational models and performed QM/MM calculations to clarify the reaction mechanism. On the basis of our calculation results, cYY is not involved in the formation of Cpd I, and the C-C coupling reaction starts from hydrogen abstraction. In the second stage, the substrate should first undergo a complex conformational change, leading to two phenolic hydroxyls of cYY close to each other. In the subsequent reaction, the resultant Cpd II again abstracts a hydrogen atom from the proximal tyrosine to generate the diradical intermediate. In addition, the C-C coupling occurs in the active site, but the final aromatization may be a nonenzymatic reaction. In general, the intramolecular C-C coupling requires two basic conditions, including the active site having good flexibility and the substrate itself having a suitable and rotatable skeleton.

Directing-Group-Assisted Transition-Metal-Catalyzed Selective BH Functionalization of o-Carboranes

AbstractCarboranes are a type of molecular clusters consisting of carbon, hydrogen, and boron atoms. They possess unique characteristics, such as three-dimensional aromaticity, icosahedral geometry, and robustness. Functionalized carboranes have been utilized in various fields, including medicine, materials, and organometallic/coordination chemistry. In this context, selective functionalization of o-carboranes has received tremendous attention, specifically in the regio- and enantioselective modification of the ten chemically similar BH vertices within the carborane cage. In recent years, significant progress has been made in catalytic vertex-specific BH functionalization, as well as achieving enantioselective functionalization of the cage BH. This review provides an overview of the recent advancements in this research field.1 Introduction2 Carboxy-Assisted BH Functionalization2.1 Formation of B–C Bonds2.2 Formation of B–N Bonds2.3 Formation of B–O Bonds2.4 Formation of B–X Bonds2.5 Consecutive Formation of B–C and B–Y (Y = N, O) Bonds3 N-Based Directing-Group-Assisted B–H Functionalization3.1 Acylamino as a Directing Group3.2 Amide as a Directing Group3.3 Pyridyl as a Directing Group3.4 Imine as a Directing Group4 Phosphinyl-Assisted Cage B–H Functionalization5 Bidentate-Directing-Group-Assisted B–H Functionalization6 Other Directing-Group-Assisted B–H Functionalization7 Conclusions

A Ru-porphyrin metal-organic framework with Mn2+ paddlewheel nodes for the selective oxidation of C(sp3)-H bonds.

The activation and selective functionalization of inert C(sp3)-H bonds is fundamental for industrial applications and occupies a very important place in industry, but it remains a great challenge in current synthetic chemistry. In this paper, we report an approach for activating reactive tert-butyl peroxyl radicals by modifying Ru-porphyrin into metal-organic frameworks (MOFs) for the activation of inert C(sp3)-H bonds. Under mild conditions, the Ru-porphyrinyl MOF can activate the peroxyl radical, extracting a hydrogen atom from the inert C(sp3)-H bond. Mn2+ paddlewheels with unsaturated coordination sites were introduced into the MOF, and direct oxidative conversion using environmentally friendly oxygen provides a new pathway to activate the inert C(sp3)-H bond.