Hydrogen Atoms Research Articles

Bromide-promoted cascade annulation of isocyanobiaryls with aldehydes through photoredox catalysis.

Herein, we report a cascade annulation of readily available isocyanobiaryls with simple aldehydes via photoredox catalysis, providing a straightforward approach towards valuable 6-hydroxyalkylated phenanthridines. Mechanistic studies indicated the generation of a key acyl radical from aldehydes by hydrogen atom abstraction with a bromine radical. This protocol exhibits exceptional chemoselectivity, excellent tolerance of various functional groups and mild reaction conditions. Its synthetic utility was demonstrated by a gram-scale reaction and various facile manipulations of the free hydroxyl group to furnish diverse phenanthridine derivatives.

Functionalized Terthiophene as an Ambipolar Redox System: Structure, Spectroscopy, and Switchable Proton-Coupled Electron Transfer.

Organic redox systems that can undergo oxidative and reductive (ambipolar) electron transfer are elusive yet attractive for applications across synthetic chemistry and energy science. Specifically, the use of ambipolar redox systems in proton-coupled electron transfer (PCET) reactions is largely unexplored but could enable "switchable" reactivity wherein the uptake and release of hydrogen atoms are controlled using a redox stimulus. Here, we describe the synthesis and characterization of an ambipolar functionalized terthiophene (TTH) bearing methyl thioether and phosphine oxide groups that exhibits switchable PCET reactivity. Electrochemical studies established that the functionalized TTH can be reversibly oxidized and reduced, prompting the synthesis and characterization of cationic and anionic radicals on a single TTH platform. Combined structural, spectroscopic, and computational investigations revealed the influence of the methyl thioether and phosphine oxide moieties on the TTH electronic structure that results in the stabilization of both cationic and anionic radicals. Upon single-electron oxidation, the functionalized TTH serves as a hydrogen atom acceptor and undergoes PCET with 1,4-dihydroquinone to generate a TTH hydroxyphosphonium species. The process was found to be reversible upon single-electron reduction, with functionalized TTH acting as a hydrogen atom donor in a PCET reaction with 2,3-dimethylanthraquinone. The thermochemistry of the O-H bond formed and cleaved in functionalized TTH during the reaction sequence was investigated, revealing that a bond weakening of 30 kcal/mol underpins the switchable PCET reactivity. Overall, these studies provide an electrochemical, structural, spectroscopic, and thermochemical foundation for the use of ambipolarity to control PCET reactions in organic redox systems.

Arrangement of Azidomethyl Group in Lupinine Azide: Structural and Spectroscopic Properties

Quinolizidine derivatives are an important class of substances that are used in the pharmaceutical industry. In previous studies, the synthesis of these substances is carried out using lupinine azide (IUPAC: 1-(azidomethyl)octahydro-2H-quinolizine), which is often used to obtain new biologically active compounds. In this regard, its structural characterization is critically important. In this work, the conformational diversity of the molecular structure of this compound has been studied. It is shown that the structure with the axial position of the methyl azide group contains a number of low-energy conformer states with energies higher than the ground state by 0.15–0.60 kcal/mol. Such structural ambiguity should manifest itself in the chemical reactions and biological activity of lupinine azide. The spectroscopic properties of the conformers were studied by modeling chemical shifts for carbon and hydrogen atoms, as well as by simulating IR absorption spectra. An analysis of the most specific spectroscopic features of all of the conformers was carried out. Based on the correlation of the theoretical results and the experimental spectroscopic data, a conclusion was made for the first time regarding the most probable conformational states in the solution.

Molecular Engineering of Amino Acid Crystals with Enhanced Piezoelectric Performance for Biodegradable Sensors.

Amino acid crystals have emerged as promising piezoelectric materials for biodegradable and biocompatible sensors; however, their relatively low piezoelectric coefficients constrain practical applications. Here, we introduce a fluoro-substitution strategy to overcome this limitation and enhance the piezoelectric performance of amino acid crystals. Specifically, we substituted hydrogen atoms on the aromatic rings of L-tryptophan, L-phenylalanine, and N-Cbz-L-phenylalanine with fluorine, resulting in significantly elevated piezoelectric coefficients. Density functional theory calculations further indicate that fluorination strengthens polarization by modifying molecular dipole moments. Consequently, these fluoro-substituted crystals achieve piezoelectric coefficients of up to 50.36 pm/V, surpassing those of other organic piezoelectric materials such as polyvinylidene fluoride (PVDF), poly(l-lactic acid) (PLLA), and gelatin. When integrated into flexible, biodegradable force sensors, the fluoro-substituted crystals exhibit a broad sensing range, high sensitivity, and stable in vivo operation over extended periods. This work establishes a versatile route for boosting piezoelectricity in biomaterials, thereby broadening their scope in biomedical applications.

Features of the Defect Structure of the Compositionally Homogeneous Crystal LiNbO3:Er3+(3.1 wt%) and the Gradient Crystal LiNbO3:Er3+ and Their Manifestation in the IR Transmission Spectra in the Region of Stretching Vibrations of Hydrogen Atoms of OH−-Groups

Based on the analysis of the IR transmission spectra in the region of stretching vibrations of hydrogen atoms of OH−-groups, it was established that the oxygen-octahedral МеО6 clusters (Ме-Li+, Nb5+, vacant octahedron V, impurity ion) of the structure of the compositionally homogeneous crystal LiNbO3:Er3+(3.1 wt%) and the gradient crystal LiNbO3:Er3+(congruent composition by the main components, Er gradient of 0.55 at%/cm) have a shape close to the regular one. In this case, the value of R = [Li]/[Nb] ≈ 1, and in the structure of both crystals, there are practically no point defects in NbLi responsible for the photorefraction effect. By using the IR transmission spectra and Klauer’s method, it was found that the volume concentration of OH−-groups in the gradient crystal LiNbO3:Er3+ is almost an order of magnitude lower than in the compositionally homogeneous LiNbO3:Er3+(3.1 wt%) crystal. This fact explains the lower hydrogen conductivity of the gradient crystal LiNbO3:Er3+ and the lower photorefraction effect compared to the compositionally homogeneous LiNbO3:Er3+(3.1 wt%) crystal. The results obtained are important for the development of materials for active nonlinear laser media and for the conversion of laser radiation.

Molecular Engineering of Amino Acid Crystals with Enhanced Piezoelectric Performance for Biodegradable Sensors

Amino acid crystals have emerged as promising piezoelectric materials for biodegradable and biocompatible sensors; however, their relatively low piezoelectric coefficients constrain practical applications. Here, we introduce a fluoro‐substitution strategy to overcome this limitation and enhance the piezoelectric performance of amino acid crystals. Specifically, we substituted hydrogen atoms on the aromatic rings of L‐tryptophan, L‐phenylalanine, and N‐Cbz‐L‐phenylalanine with fluorine, resulting in significantly elevated piezoelectric coefficients. Density functional theory calculations further indicate that fluorination strengthens polarization by modifying molecular dipole moments. Consequently, these fluoro‐substituted crystals achieve piezoelectric coefficients of up to 50.36 pm/V, surpassing those of other organic piezoelectric materials such as polyvinylidene fluoride (PVDF), poly(l‐lactic acid) (PLLA), and gelatin. When integrated into flexible, biodegradable force sensors, the fluoro‐substituted crystals exhibit a broad sensing range, high sensitivity, and stable in vivo operation over extended periods. This work establishes a versatile route for boosting piezoelectricity in biomaterials, thereby broadening their scope in biomedical applications.

Optimization of metal polymer friction pair composition for hydrogen wear reduction through thermal stabilization analysis

The composition of the metal-polymer friction pair is carefully considered for interacting with water and hydrogen, ensuring the metals electrode process potential remains below waters in a neutral medium. Simultaneously, adherence to defined chemical composition ratios for the metal-polymer materials is crucial. This analysis is conducted under conditions of thermal stabilization, characterized by a minimal temperature gradient across the rim thickness within an equivalent thermal field. Using the quasi-chemical approximation, the paper derives a concentration-dependent diffusion coefficient of hydrogen (H) in iron (Fe) across a broad spectrum. This derivation includes electronic and vibrational contributions to the chemical potential. The research establishes a correlation between the equivalent diffusion coefficient and the concentration of diffusing hydrogen atoms from the metal, such as the pulley or drum rim. These findings offer novel insights into optimizing hydrogen wear behaviour in brake friction couples, contributing to advancements in materials and design considerations in the automotive field.

Carbon-carbon triple bond cleavage and reconstitution to achieve aryl amidation using nitrous acid esters

C–C bond cleavage and recombination provide an efficient strategy for the modification and reconstruction of molecule structures. Herein, we present a method for achieving amidation of aryl C(sp2)–H bond through the cleavage and recombination of C–C triple bond with the involvement of nitrous acid esters. This method marks the instance of precise and controlled stepwise cleavage of C–C triple bond, offering a fresh perspective for the cleavage of such bonds. Nitrous acid ester serves as both a radical source and a hydrogen atom transfer (HAT) reagent to functionalize and utilize the two carbon atoms of the C–C triple bond. The alkoxy radical captures the hydrogen atom from the aryl C(sp2)–H bond or N-hydroxyl to induce the 1,3-oxygen radical migration, which is crucial for the subsequent cleavage of the C–C bond.

Chemical Informatics Combined with Kendrick Mass Analysis to Enhance Annotation and Identify Pathways in Soybean Metabolomics

Background: Among abiotic stresses to agricultural crops, drought stress is the most prolific and has worldwide detrimental impacts. The soybean (Glycine max) is one of the most important sources of nutrition to both livestock and humans. Different plant introductions (PI) of soybeans have been identified to have different drought tolerance levels. Objectives: Here, two soybean lines, Pana (drought sensitive) and PI 567731 (drought tolerant) were selected to identify chemical compounds and pathways which could be targets for metabolomic analysis induced by abiotic stress. Methods: Extracts from the two lines are analyzed by direct infusion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The high mass resolution and accuracy of the method allows for identification of ions from hundreds of different compounds in each cultivar. The exact m/z of these species were filtered through SoyCyc and the Human Metabolome Database to identify possible molecular formulas of the ions. Next, the exact m/z values were converted into Kendrick masses and their Kendrick mass defects (KMD) computed, which were then sorted from high to low KMD. This latter process assists in identifying many additional molecular formulas, and is noted to be particularly useful in identifying formulas whose mass difference corresponds to two hydrogen atoms. Results: In this study, more than 460 ionic formulas were identified in Pana, and more than 340 ionic formulas were identified in PI 567731, with many of these formulas reported from soybean for the first time. Conclusions: Using the SoyCyc matches, the metabolic pathways from each cultivar were compared, providing lists of molecular targets available to profile effects of abiotic stress on these soybean cultivars. Key metabolites include chlorophylls, pheophytins, mono- and diacylglycerols, cycloeucalenone, squalene, and plastoquinones and involve pathways which include the anabolism and catabolism of chlorophyll, glycolipid desaturation, and biosynthesis of phytosterols, plant sterols, and carotenoids.

Lewis Base-Enhanced C-H Bond Functionalization Mediated by a Diiron Imido Complex.

Herein, we investigate the effects of ligand design on the nuclearity and reactivity of metal-ligand multiply bonded (MLMB) complexes to access an exclusively bimetallic reaction pathway for C-H bond functionalization. To this end, the diiron alkoxide [Fe2(PhDbf)2] (1) was treated with 3,5-bis(trifluoromethyl)phenyl azide to access the diiron imido complex [Fe2(PhDbf)2(μ-NC8H3F6)] (2a) that promotes hydrogen atom abstraction (HAA) from a variety of C-H and O-H bond containing substrates. A diiron bis(amide) complex [Fe2(PhDbf)2(μ-NHC8H3F6)(NHC8H3F6)] (3) was generated, prompting the isolation of the analogous bridging amide terminal alkoxide [Fe2(PhDbf)2(μ-NHC8H3F6)(OC19H15)] (4) and the asymmetric pyridine-bound diiron imido [Fe2(PhDbf)2(μ-NC8H3F6)(NC5H5)] (6a). We found that 6a is competent for toluene amination, indicating the effect of Lewis base-enhanced C-H bond functionalization. Mechanistic investigations suggest that the bimetallic bridging imido complex is the reactive intermediate as no monometallic species is detected during the time course of the reaction.

WALLABY Pilot Survey: kNN identification of perturbed galaxies through Hi morphometrics

Abstract Galaxy morphology in stellar light can be described by a series of “non-parametric” or “morphometric” parameters, such as concentrationasymmetry-smoothness, Gini, M20, and Sersic fit. These parameters can be applied to column density maps of atomic hydrogen (Hi). The Hi distribution is susceptible to perturbations by environmental effects, e.g. inter-galactic medium pressure and tidal interactions. Therefore, Hi morphology can potentially identify galaxies undergoing ram-pressure stripping or tidal interactions. We explore three fields in theWALLABY Pilot Hi survey and identify perturbed galaxies based on a k-nearest Neighbor (kNN) algorithm using an Hi morphometric feature space. For training, we used labeled galaxies in the combined NGC 4808 and NGC 4636 fields with six Hi morphometrics to train and test a kNN classifier. The kNN classification is proficient in classifying perturbed galaxies with all metrics –accuracy, precision and recall– at 70-80%. By using the kNN method to identify perturbed galaxies in the deployment field, the NGC 5044 mosaic, we find that in most regards, the scaling relations of perturbed and unperturbed galaxies have similar distribution in the scaling relations of stellar mass vs star formation rate and the Baryonic Tully-Fisher relation, but the Hi and stellar mass relation flatter than of the unperturbed galaxies. Our results for NGC 5044 provide a prediction for future studies on the fraction of galaxies undergoing interaction in this catalogue and to build a training sample to classify such galaxies in the fullWALLABY survey.

Spontaneous Reactions by Atomic Hydrogen – An Extraordinary Reactant for Atomic Layer Deposition of Platinum

Spontaneous Reactions by Atomic Hydrogen – An Extraordinary Reactant for Atomic Layer Deposition of Platinum

Remote Activation Catalysis: Interparticle Hydrogen Spillover-Assisted Cumene Synthesis from Propane and Benzene.

Hydrogen spillover, particularly when involving "interparticle" hydrogen spillover, offers a unique opportunity to enhance catalytic efficiency by remote activation of surface acidity. Building on this concept, this study aims to investigate physically mixed alumina-supported platinum nanoparticles (Pt/Al2O3) and zirconia-supported tungsten oxide (WO3/ZrO2) in promoting the direct synthesis of cumene from benzene and propane at 300 °C. The reaction with Pt/Al2O3 alone afforded propylene as the only product, indicating the successive reaction route of Pt-catalyzed dehydrogenation of propane, followed by acid-catalyzed alkylation. WO3/ZrO2 with 18 wt.% WO3 loading resulted in high benzene conversion (≈5.0%) and cumene selectivity (≈87.5%), which possesses poly tungstate species on the surface that is active for the acid-catalyzed alkylation. UV-vis-near infrared spectroscopy, X-ray photoelectron spectroscopy, and in situ Fourier-transform infrared spectroscopy analyses revealed that atomic hydrogen abstracted from propane spills over from Pt/Al2O3 particles to WO3/ZrO2 particles to form Brønsted acid sites on the poly tungstate species, whose activity for alkylation between benzene and propylene is double that of the parent WO3/ZrO2.

A Unique Intramolecular Redox Reaction by Unidirectional Migration of Three Hydrogen Atoms: Theoretical Elucidation of the 3H-Transfer Sequence.

The intramolecular migration of three hydrogen atoms from one moiety of a gaseous radical cation to the other prior to fragmentation is an extremely rare type of redox reaction. Within the scope of this investigation, this scenario requires an ionized but electron-rich arene acceptor bearing a para-(3-hydroxyalkyl) residue. The precise mechanism of such unidirectional 3H transfer processes, including the order of the individual H transfer steps, has remained unclear in spite of previous isotope labelling and recent infrared ion spectroscopy (IRIS) studies. Herein, the details of this peculiar process have been investigated for ionized 4-(N,N-dimethylaminophenyl)-2-butanol, 2, by state-of-the-art density functional theory (DFT) calculations. The energetically most favorable pathway consists of a sequence of successive 1,4-, 1,6- and 1,5-H steps. During these steps the secondary alcohol functionality is oxidized to a carbonyl group and the radical-cationic aniline ring is reduced to an ionized 2,3-dihydroaniline unit. Several alternative sequences, such as three successive 1,5-H shifts, could be excluded. A concomitant unidirectional 2H migration reaction of the ion 2 was also investigated and the intermediacy of ion-neutral complexes (INCs) enabling sequential hydride and proton transfer was confirmed by the calculations.

High-resolution BOES Spectroscopy of Raman-scattered He iiλ6545 in Young Planetary Nebulae

Abstract Young planetary nebulae (PNe) are characterized by their hot central stars and the presence of abundant neutral and molecular components, which result from significant mass loss during the asymptotic giant branch phase of stellar evolution. Far-UV He ii λ1025 line photons produced near the central star can undergo Raman scattering by hydrogen atoms, creating a broad emission feature centered at ~6545 Å. We conducted high-resolution spectroscopy of 12 young PNe from 2019 April to 2020 March using the Bohyunsan Observatory Echelle Spectrograph. Building on the study by Choi and Lee, who identified Raman-scattered He ii at 6545 Å in NGC 6881 and NGC 6886, we report new detections of this feature in NGC 6741 and NGC 6884. Profile fitting reveals that the velocity of the H i component relative to the He ii emission region ranges from 26 to 33 km s−1 in these PNe. Using photoionization modeling, we estimate the line flux of He ii λ1025 and derive Raman conversion efficiencies of 0.39, 0.21, 0.24, and 0.07 for NGC 6881, NGC 6741, NGC 6886, and NGC 6884, respectively. These results, combined with radiative transfer modeling, suggest the presence of H i components with masses around 10−2 M ⊙, moving outward from the central He ii emission region at speeds characteristic of the slow stellar wind from a mass-losing giant star.

Ruthenium‐Catalyzed Deconstruction of Polyolefins: A Strategy to Up‐cycle the Waste Polyethylene to Value‐Added Alkenes

Synthesis of value‐added products from post‐consumer waste polyolefins is fascinating as well as challenging. Here we report ruthenium‐catalyzed up‐cycling of the polyethylene to long‐chain alkene derivatives. The developed methodology mainly involves two steps i.e., dehydrogenation of polyethylene through hydrogen atom transfer and its metathesis using the HG‐II catalyst. The dehydrogenation of polyethylene using ruthenium catalysis derived up to 3.38%, of double bonds; with 90% of the recovered polyolefin material. The obtained unsaturated polyethylene was subjected to cross‐metathesis with ethylene using HG‐II catalytic system. This resulted in the synthesis of predominantly dodecene (C12) derivatives, with 58% selectivity, along with other derivatives of varying chain lengths. The overall reaction produced terminal and internal olefins in the ratio 1:0.8 respectively. The dehydrogenation of polyethylene and its deconstruction was confirmed by NMR spectroscopy, Gel Permeation Chromatography (GPC) and Differential Scanning Calorimetry (DSC). The origin of C12 selectivity has been demonstrated by control experiments. The scope of the methodology was extended to post‐consumer waste polyethylene gave high conversion of value‐added dodecene derivatives as a major product.

Ruthenium-Catalyzed Deconstruction of Polyolefins: A Strategy to Up-cycle the Waste Polyethylene to Value-Added Alkenes.

Synthesis of value-added products from post-consumer waste polyolefins is fascinating as well as challenging. Here we report ruthenium-catalyzed up-cycling of the polyethylene to long-chain alkene derivatives. The developed methodology mainly involves two steps i.e., dehydrogenation of polyethylene through hydrogen atom transfer and its metathesis using the HG-II catalyst. The dehydrogenation of polyethylene using ruthenium catalysis derived up to 3.38%, of double bonds; with 90% of the recovered polyolefin material. The obtained unsaturated polyethylene was subjected to cross-metathesis with ethylene using HG-II catalytic system. This resulted in the synthesis of predominantly dodecene (C12) derivatives, with 58% selectivity, along with other derivatives of varying chain lengths. The overall reaction produced terminal and internal olefins in the ratio 1:0.8 respectively. The dehydrogenation of polyethylene and its deconstruction was confirmed by NMR spectroscopy, Gel Permeation Chromatography (GPC) and Differential Scanning Calorimetry (DSC). The origin of C12 selectivity has been demonstrated by control experiments. The scope of the methodology was extended to post-consumer waste polyethylene gave high conversion of value-added dodecene derivatives as a major product.

Strain Release in Hydrogen Atom Transfer from 1,4-Disubstituted Cyclohexanes to the Cumyloxy Radical

A kinetic, product and computational study on the reactions of the cumyloxyl radical (CumO•) with 1,4-dimethyl- and 1,4-diphenylcyclohexanes is reported. The rate constants for hydrogen atom transfer (HAT) from the C-H bonds of these substrates to CumO•, together with the corresponding oxygenation product distributions reveal the role of strain release on reaction site-selectivity. Transition structures and activation barriers obtained by DFT calculations are in excellent agreement with the experimental results. Tertiary/secondary ratios of oxygenation products of 0.6, 1.0 and 3.3 were observed, for trans-1,4-dimethyl-, cis-1,4-dimethyl- and trans-1,4-diphenylcyclohexane, respectively. With cis-1,4-diphenylcyclohexane, exclusive formation of the diastereomeric tertiary alcohol products was observed. Within the two diastereomeric couples, the tertiary equatorial C-H bond in the cis- isomer is ∼6 and 27 times more reactive, respectively, than the tertiary axial ones, a behavior that reflects the release of 1,3-diaxial strain in the HAT transition state. The tertiary axial C-H bonds of the four substrates show remarkably similar reactivities in spite of the much greater stabilization of the benzyl radicals resulting from HAT from the 1,4-diphenylcyclohexanes. The lack of benzylic acceleration is discussed in the framework of Bernasconi’s “principle of non-perfect synchronization”.

Computational Investigation of the Role of Metal Center Identity in Cytochrome P450 Enzyme Model Reactivity.

Mononuclear Fe enzymes such as heme-containing cytochrome P450 enzymes catalyze a variety of C-H activation reactions under ambient conditions, and they represent an attractive platform for engineering reactivity through changes to the native enzyme. Using density functional theory, we study both native Fe and non-native group 8 (Ru, Os) and group 9 (Ir) metal centers in an active site model of P450. We quantify how changing the metal changes spin state preferences throughout the catalytic cycle. Our calculations reveal an intermediate-spin ground state for all Fe intermediates while the heavier metals prefer low-spin ground states across most intermediates in the reaction cycle. We also study the rate-determining hydrogen atom transfer (HAT) step and the subsequent rebound step. We observe comparable HAT barriers for Fe and Ru, a much higher barrier for Os, and the lowest HAT barrier for Ir. Rebound steps are barrierless for all metals, and the rebound intermediate for Fe is most significantly stabilized. Examination of ground spin states of all intermediates in the reaction cycle reveals spin-allowed pathways for the group 8 metals and spin-forbidden energetics for the group 9 Ir with potential two-state reactivity. Our work highlights the differences between the group 8 metals and the group 9 Ir, and it suggests that engineered P450 enzymes with Ru in particular result in improved enzyme reactivity toward C-H hydroxylation.

Light-Driven Stepwise Reduction of Aliphatic Carboxylic Esters to Aldehydes and Alcohols.

The reduction of carboxylic esters to aldehydes and alcohols is a fundamental functional group transformation in chemistry. However, the inertness of carbonyl group and the instability of ketyl radical anion intermediate impede the reduction of carboxylic esters via photochemical strategy. Herein, we described the reduction of aliphatic carboxylic esters with synergistic dual photocatalysis via phenolate-catalyzed single electron transfer process and thiol-catalyzed hydrogen atom transfer process. The competitive back electron transfer process was effectively inhibited by protonation of the ketyl-type radical anion. This protocol enabled the efficient reduction of carboxylic esters to alcohols under mild conditions. By interruption of the reduction with prolinol, the step-controlled reduction of carboxylic esters to aldehydes was accomplished. The developed process was also successfully applied to the preparation of deuterated alcohols and aldehydes from esters with D2O as the deuterium source.