Hydrogen Atoms Research Articles

Asymmetric photoenzymatic incorporation of fluorinated motifs into olefins.

Enzymes capable of assimilating fluorinated feedstocks are scarce. This situation poses a challenge for the biosynthesis of fluorinated compounds used in pharmaceuticals, agrochemicals, and materials. We developed a photoenzymatic hydrofluoroalkylation that integrates fluorinated motifs into olefins. The photoinduced promiscuity of flavin-dependent ene-reductases enables the generation of carbon-centered radicals from iodinated fluoroalkanes, which are directed by the photoenzyme to engage enantioselectively with olefins. This approach facilitates stereocontrol through interaction between a singular fluorinated unit and the enzyme, securing high enantioselectivity at β, γ, or δ positions of fluorinated groups through enzymatic hydrogen atom transfer-a process that is notably challenging with conventional chemocatalysis. This work advances enzymatic strategies for integrating fluorinated chemical feedstocks and opens avenues for asymmetric synthesis of fluorinated compounds.

Photoredox Activation of Fluorinated Organozinc Reagents: Hydrofluoroalkylation of Unactivated and Electron Deficient Alkenes.

Hydrofluoroalkylation of alkenes with organozinc reagents under photocatalytic conditions is described. The fluorinated alkyl radicals were generated from organozincs by the single electron oxidation of the carbon-zinc bond. The radical addition step is followed either by hydrogen atom transfer for unactivated olefins or by a reduction/protonation sequence for strongly accepting arylidenemalononitriles.

Density functional theory and ReaxFF MD study on steam-induced nitrogen migration mechanism during char gasification

The formation of nitrogen-containing species during char gasification is crucial for emission of nitrogenous pollutants. In this work, the detailed nitrogen migration mechanism during char gasification is studied. Density functional theory (DFT) coupled with ReaxFF MD methods are used to conduct an in-depth analysis on the intrinsic reaction mechanism during Char(N) and steam interaction. DFT results show that orbital electrons of carbon atoms on char surface are driven towards nitrogen atoms by nitrogen functional groups. The electron density of adjacent carbon atoms is weakened, which has a positive charge. Orbital electron properties show that the band energy gaps of three Char(N) models are 3.063 eV, 1.092 eV and 3.328 eV, indicating the reactivity order for three Char(N) models is as follows: Char(N)-2＞Char(N)-1＞Char(N)-3. DFT calculation indicates that the interaction between Char(N) and steam reduces unsaturated carbon atoms and lower the char decomposition activity, which will inhibit the yield of HCN. In contrast, through hydrogen transfer reactions, nitrogen atoms are easily combined with hydrogen atoms, which is more conducive to the formation of ammonia. ReaxFF MD modeling proves that HCN is the main product for Char(N) decomposition under inert atmosphere. Under steam atmosphere, nitrogen atoms in char are more likely to be converted into amino products. The induction of steam provides a large number of active hydrogen radicals, which is able to attack the nitrogen atoms of char and form N-H bonds, thus promoting the formation of ammonia.

Non-covalent interaction, topology, molecular properties, spectral and quantum chemical analysis of 2,5-dinitrophenol

Density functional theory (DFT) using the Becke-3-Parameter-Lee-Yang-Parr (B3LYP) functional and Ab-initio (HF) with the 6–311++G(d,p) basis set were employed to investigate the geometry, electronic structure, and absorption spectra of 2,5-Dinitrophenol(25DNP). The vibrational spectrum was utilized to identify functional groups. The ultraviolet–visible (UV–Vis) spectrum was simulated in the gas phase using TD-DFT to determine the range and percentage of transmission. The computed HOMO and LUMO energies indicate that charge transfer occurs within the molecule. The compound exhibits a molecular first hyperpolarizability (second-order optical nonlinearity) value of 1.690 × 10−30 esu, which is approximately five times greater than that of urea. For hyperpolarizability calculations, the hybrid Hartree-Fock exchange-correlation functional was used in conjunction with the 6–311++G(d,p) basis set. Fukui indices were employed to identify local reactive sites in the chemical system during electrophilic, nucleophilic, radical, and dual descriptor attacks. Docking simulations were performed using the Lamarckian Genetic Algorithm (LGA) and local search approach, ensuring proper establishment of the ligand molecules' starting position, orientation, and torsion. According to the molecular electrostatic potential (MEP) map, positive potential sites are found around hydrogen atoms, while negative potential sites are near electronegative atoms, providing insights into regions where the molecule may interact with other molecules, both internally and externally. Similarly, Mulliken charges and Fukui indices within the organic complex sustain the intermolecular hydrogen bonds.

Modifying Parallel Excitations into One Framework for C(sp3)─H Bond Activation with Energy Combined More Than Two Photons.

Natural photosynthesis enzymesutilize energies of several photons for challenging oxidation of water, whereas artificial photo-catalysis typically involves only single-photon excitation. Herein, a multiphoton excitation strategy is reported that combines parallel photo-excitations with a photoinduced electron transfer process for the activation of C(sp3)─H bonds, including methane. The metal-organic framework Fe3-MOF is designed to consolidate 4,4',4″-nitrilotrisbenzoic units for the photoactivation of dioxygen and trinuclear iron clusters as the HAT precursor for photoactivating alkanes. Under visible light irradiation, the dyes and iron clusters absorbed parallel photons simultaneously to reach their excited states, respectively, generating 1O2 via energy transfer and chlorine radical via ligand-to-metal charge transfer. The further excitation of organic dyes leads to the reduction of 1O2 into O2 •- through a photoinduced electron transfer, guaranteeing an extra multiphoton oxygen activation manner. The chlorine radical abstracts a hydrogen atom from alkanes, generating the carbon radical for further oxidation transformation. Accordingly, the total oxidation conversion of alkane utilizing three photoexcitation processes combines the energies of more than two photons. This new platform synergistically combines a consecutive excited photoredox organic dye and a HAT catalyst to combine the energies of more than two photons, providing a promising multiphoton catalysis strategy under energy saving, and high efficiency.

Unlocking the potential of Allium dictyoprasum C.A. Meyer ex Kunth: quantum chemical insights into radical scavenging, chemical composition, phenolic content, and antimicrobial activity

ABSTRACT Allium dictyoprasum C.A. Meyer ex Kunth (A. dictyoprasum) underwent comprehensive analysis, encompassing quantum chemical computations to assess its radical scavenging potential, chemical and elemental composition, total phenolic content, and antimicrobial activity. Experimental and theoretical investigations focused on elucidating the radical scavenging properties of polyhydroxy phenolic compounds present in the plant. Quantum chemical calculations were employed to evaluate the antioxidants employed to evaluate selected polyhydroxy phenolic molecules including flavonoids, hydrocinnamic acid derivatives, and hydroxybenzoic acid derivatives from natural sources. Thermochemical parameters of these compounds were calculated by the B3LYP/6–311 G++(d,p) level in both gas and solvent phases to elucidate the radical scavenging mechanism including hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET). Analysis of A. dictyoprasum extracts obtained via various extraction methods revealed the presence of several major compounds, including dimethyl trisulfide, 3,5-Dihydroxy-6-methyl-2,3-dihydro-4 H-pyran-4-one, 2-Methoxy-4-vinylphenol, Dimethyl phthalate, Methyl palmitate, Methyl oleate, Methyl stearate, (9Z)-9-Octadecenamide. Notably, Malic acid and Quinic acid were identified as major compounds, with concentrations of 43.31 and 17.47 mg kg−1 extract, respectively, based on LC-MS/MS analysis. The total phenolic content of the extract was measured as 17.83 mg gallic acid/mL, while its free radical scavenging activity was 80.89% per mg/mL. Elemental analysis revealed significant levels of Mg, K, Na, Fe, and P, with minor concentrations of elements such as Ti, Tl, B, and Be. Furthermore, A. dictyoprasum exhibited notable antibacterial activity against various bacteria strains, surpassing the efficacy of some commercial antibiotics.

Metal‐ and Photocatalyst‐Free Aerobic Photoinduced Benzyl C(sp3)−H Bonds Oxidation

AbstractPhotoinduced the direct oxidation of benzyl C(sp3)−H bonds provides an attractive strategy for producing high‐value chemicals or intermediates. Unlike the conventional approaches that typically require transition‐metal catalysts, semiconductors, and organic photosensitizers as the photocatalysts, herein we report a bromine salt‐promoted photoinduced aerobic oxidation protocol for methylarenes. By applying NH4Br as both the bromine radical source and hydrogen atom transfer agent, photoinduced oxidation of methylarenes to the corresponding carboxylic products exhibits high conversion and selectivity. Furthermore, control experiments confirm that reactive oxygen species are proved to be essential for the success of this transformation. This strategy provides a metal‐/strong oxidant‐/photocatalyst‐free paradigm for the direct deep oxidation of methylarenes.

Enabling long-distance hydrogen spillover in nonreducible metal-organic frameworks for catalytic reaction

Hydrogen spillover is an extraordinary effect in heterogeneous catalysis and hydrogen storage, which refers to the surface migration of metal particle-activated hydrogen atoms over the solid supports. Historical studies on this phenomenon have mostly been limited to reducible metal oxides where the long-distance proton-electron coupled migration mechanism has been established, yet the key question remains on how to surmount short-distance and defect-dependent hydrogen migration on nonreducible supports. By demerging hydrogen migration and hydrogenation reaction, here we demonstrate that the hydrogen spillover in nonreducible metal-organic frameworks (MOFs) can be finely modulated by the ligand functional groups or embedded water molecules, enabling significant long-distance (exceed 50 nm) movement of activated hydrogen. Furthermore, using sandwich nanostructured MOFs@Pt@MOFs as catalysts, we achieve highly selective hydrogenation of N-heteroarenes via controllable hydrogen spillover from Pt to MOFs-shell. We anticipate that this work will enhance the understanding of hydrogen spillover and shed light on de novo design of MOFs supported catalysts for many important reactions involving hydrogen.

Low-energy atomic and molecular hydrogen ion interaction with low-work function electride 12CaO · 7Al2O3

To efficiently generate H− ions from positive atomic or molecular hydrogen beams injected onto a solid surface, it has been suggested to use a material with a low-work function as the target material. However, it is not clear under what conditions the most efficient H− production is realized for incident beam parameters or reflection angles. Therefore, we studied the interaction between low-energy atomic and molecular hydrogen beams (less than 1 keV/nucleon) with a low-work function electride 12CaO⋅7Al2O3 (C12A7). The production ratio of H− to H+ ions from the C12A7 electride was much higher than Mo targets with higher work functions, especially at smaller incident and smaller reflection angles. The H− to H+ production ratio slightly increased as the incident energies were decreased, but there was no significant difference between the electride and Mo targets. These results indicate that smaller incident angles and lower beam energies of the incident hydrogen beam are favorable for the enhancement of the production ratio of H− to H+ ions in C12A7. The higher production ratio appeared at the vertical beam energies less than on the order of 100 eV, where quantum mechanical processes may become important.

Unraveling the Structural and Vibrational Response of Zharchikhite to Pressure (II): Insights from First Principles Calculations

The halide mineral Zharchikhite with the chemical formula AlF(OH)2 is studied using first-principles methods of density functional theory with the local functional VBH, generalized gradient functionals PBE, BLYP, PBEsol, with an empirical dispersion correction in the form of D3(BJ) PBE-D3, BLYP-D3, global hybrid functionals PBE0, B3LYP, PBEsol0, hybrid functionals with range separation HSE06, SC-BLYP. It is shown that all functionals overestimate O-H and underestimate O-H∙∙∙O distances. The best values are provided by SC-BLYP, B3LYP. The bulk modulus, determined from the Birch-Murnaghan equation of state, is 72.32GPa. The axes compress unevenly and the fastest is the longest one with a modulus of 217.3GPa. The linear compressibility modulus of the Al-F bond has a similar value and is twice as large for the Al-O bond. Under pressure, the lengths of H∙∙∙O hydrogen bonds decrease faster and, conversely, O-H bonds slowly increase. Also, at a rate of 0.289°/GPa, the monoclinic angle also increases with pressure. The spectra of infrared absorption and Raman scattering of light have been calculated, in which vibrations of Al-F and Al-O atoms will be active in the region up to 600cm−1; above 700cm−1 there are translational vibrations of O-H with a dominant contribution of H1 (Au symmetry) or H2 (Bu symmetry) and above 3200cm−1 100% hydrogen atoms. For them, with increasing pressure, the wave numbers decrease and the Grüneisen parameters change from −0.36 to −0.54. The large value of the derivative dν/dP can be used to solve the inverse problem - finding the pressure P from the known wave number ν(P).

Hydrogenation of hexene catalyzed by a ruthenium (II) complex with N‐heterocyclic carbene ligands

AbstractIn this study, we investigated the mechanism of the inactivated hexene hydrogenation reaction catalyzed by a ruthenium (II) complex containing “N‐heterocyclic carbene” (NHC) ligands, specifically SIMes and CBA, using DFT calculations. Our focus was on RuH(OSO2CF3)(CO)(SIMes)(CBA), which exhibits excellent catalytic behavior. We tested the B3LYP‐D3, cam‐B3LYP, and TPSSh functionals. The hydrogenation reaction is initiated by the release of SIMes rather than CBA due to the lower associated dissociation energy. Our findings indicate a reaction mechanism consisting of two consecutive steps, each involving one hydrogen atom migration. The first step, considered as the kinetically limiting transition state, exhibits a Gibbs free activation barrier of 12.9 kcal mol−1. This step involves two asynchronous processes. The first one describes the migration of the ruthenium hydride to the internal carbon of the olefine function, transitioning from π to σ coordination mode, which promotes the formation of a bond between ruthenium and the terminal olefinic carbon. The second process involves the oxidation of ruthenium from Ru(II) to Ru(IV). This oxidation is crucial as it enables the decomposition of the H2 molecule into two hydrogen atoms bonded to the ruthenium atom. The geometrical structures of the Hidden Reaction Intermediate Ru(II) complex and the quasi‐transition state of the second process have been determined by means of the RIRC technique. The second step entails the migration of one of the newly formed hydrides of the Ru(IV) complex to the terminal olefinic carbon, resulting in the release of hexane with a weak activation Gibbs free energy of .8 kcal mol−1. Lastly, we explored the use of dichloromethane as a solvent, considering the PCM model. The presence of the solvent significantly decreases the energy dissociation of SIMes from 17.9 to 9.0 kcal mol−1, providing notable benefits.

Hydrogen penetration into the NiTi superelastic alloy investigated in-situ by synchrotron diffraction experiments

Microstructural changes induced by a hydrogen permeation into the NiTi superelastic alloy were investigated in-situ using the X-ray synchrotron diffraction. A new design of an electrochemical cell enabled to uncover time and position dependent processes under a flat alloy surface exposed to the cathodic hydrogen. The diffraction data supported by thermo-elastic FEM calculations helped to quantify an evolution of compressive stresses in the B2 austenitic phase hosting hydrogen atoms. The compressive stress state initiates a formation of martensitic phases starting from the exposed surface layer and advancing into the alloy volume with increasing time of hydrogen charging. We have performed the ab-initio DFT study in order to rationalize volumetric changes associated with variations in the B2 austenite and B19’ martensite lattice parameters. The numerical results also contributed to the identification of a new hydride phase with orthorhombic crystal structure and lattice parameters a=0.8505 nm, b=0.7366 nm and c=0.4722 nm.

Unraveling the Mechanism of Hydrogen Atom Transfer by a Nickel-Hypochlorite Species and the Influence of Electronic Effects.

The oxidation of hydrocarbons is an important chemical transformation with relevance to biology and industry. Ni-catalyzed transformations are more scarce compared to Mn or Fe but have gained attention in recent years, affording efficient oxidations. Understanding the mechanism of action of these catalysts, including the detection and characterization of the active nickel-oxygen species, is of interest to design better catalysts. In this work, we undertake a theoretical study to unravel the mechanism of formation of the previously reported [Ni(OCl)(HL)]+ (H2) and how it activates C-H bonds. We disclose that the active species is indeed compound [Ni(O)(HL)]+, formed after homolytic cleavage of the O-Cl bond in H2 assisted by a chlorine radical. [Ni(O)(HL)]+ mediates C-H activation through an asynchronous concerted mechanism, in which the transition state is given by hydrogen atom transfer. Moreover, the electronic tuning of the ligand has a very modest impact on the stability and reactivity of the corresponding X2 species. Effective oxidation state analysis reveals an intriguing electronic structure of H2 and [Ni(O)(HL)]+, in which both the macrocycic HL ligand and the OCl and O ligands behave as redox noninnocent. Such redox activity leads to a fully ambiguous oxidation state assignation.

Hydrogen Atom Abstraction and Reduction Study of 21-Thiaporphyrin and 21,23-Dithiaporphyrin.

The metal-free porphyrins protonation has gained interest over five decades because its structure modification and hardly monoacid intermediate isolation. Here, upon the hydrogen atom abstraction processes, one step diproptonated H3STTP(BF4)2 (STTP = 5,10,15,20-tetraphenyl-21-thiaporphyrin) (3) and stepwise protonated HS2TTPSbCl6 (5) and diprotonated H2S2TTP(BF4)2 (6) (S2TTP = 5,10,15,20-tetraphenyl-21,23-thiaporphyrin) compounds were obtained using HSTTP and S2TTP with oxidants. The closed-shell protonated compounds were fully characterized using XRD, UV-vis, IR and NMR spectra. In addition, the reduced 19π compounds [K(2,2,2)]HSTTP (2) and [K(2,2,2)]S2TTP (7) were synthesized by the ligands with reductant KC8 in THF solution. These two open-shell compounds were characterized with UV-vis, IR and EPR spectroscopies. The semiempirical ZINDO/S method was employed to analyze the HOMO/LUMO gap lever and identify the electronic transitions of the UV-vis spectra of the closed- and open-shell porphyrin compounds.

Time evolution as an optimization problem: The hydrogen atom in strong laser fields in a basis of time-dependent Gaussian wave packets.

Recent advances in attosecond science have made it increasingly important to develop stable, reliable, and accurate algorithms and methods to model the time evolution of atoms and molecules in intense laser fields. A key process in attosecond science is high-harmonic generation, which is challenging to model with fixed Gaussian basis sets, as it produces high-energy electrons, with a resulting rapidly varying and highly oscillatory wave function that extends over dozens of ångström. Recently, Rothe's method, where time evolution is rephrased as an optimization problem, has been applied to the one-dimensional Schrödinger equation. Here, we apply Rothe's method to the hydrogen wave function and demonstrate that thawed, complex-valued Gaussian wave packets with time-dependent width, center, and momentum parameters are able to reproduce spectra obtained from essentially exact grid calculations for high-harmonic generation with only 50-181 Gaussians for field strengths up to 5 × 1014 W/cm2. This paves the way for the inclusion of continuum contributions into real-time, time-dependent electronic-structure theory with Gaussian basis sets for strong fields and eventually accurate simulations of the time evolution of molecules without the Born-Oppenheimer approximation.

Photocatalyzed Cascade Hydrogen Atom Transfers for Assembly of Multi-Substituted α-SCF3 and α-SCF2H Cyclopentanones.

A photocatalyzed formal (3+2) cycloaddition has been developed to construct original polysubstituted α-SCF3 cyclopentanones in a regio- and diastereoselective manner. This building block approach leverages trifluoromethylthio alkynes and branched/linear aldehydes, as readily available reaction partners, in consecutive hydrogen atom transfers and C-C bond formations. Difluoromethylthio alkynes are also compatible substrates. Furthermore, the potential for telescoped reaction starting from alcohols instead of aldehydes was demonstrated, as well as process automatization and scale-up under continuous microflow conditions. This prompted density functional theory (DFT) calculations to support a radical-mediated cascade process.

Photocatalyzed Cascade Hydrogen Atom Transfers for Assembly of Multi‐Substituted α‐SCF3 and α‐SCF2H Cyclopentanones

AbstractA photocatalyzed formal (3+2) cycloaddition has been developed to construct original polysubstituted α‐SCF3 cyclopentanones in a regio‐ and diastereoselective manner. This building block approach leverages trifluoromethylthio alkynes and branched/linear aldehydes, as readily available reaction partners, in consecutive hydrogen atom transfers and C−C bond formations. Difluoromethylthio alkynes are also compatible substrates. Furthermore, the potential for telescoped reaction starting from alcohols instead of aldehydes was demonstrated, as well as process automatization and scale‐up under continuous microflow conditions. This prompted density functional theory (DFT) calculations to support a radical‐mediated cascade process.

Photoinduced Lignin C α -C β Bond Cleavage and Chemodivergent Functionalization via Iron Catalysis.

The photocatalytic conversion of lignin into value-added chemicals especially those functionalized molecules represent one of the most important strategies for sustainable and environmental-friendly development. Cleavage of C-C bonds in lignin under mild photocatalytic conditions for refining lignin into useful molecules is meaningful but challenging. Meanwhile, the assembly of diverse functional groups into active lignin fragments during the depolymerization is of great challenging. Herein, using cheap iron catalysts under visible light irradiation, the highly selective and efficient cleavage of Cα-Cβ bond in lignin is realized via ligand-to-metal charge transfer (LMCT) and hydrogen atom transfer (HAT) processes. The subsequent divergent functionalization of generated lignin fragment-based radical intermediates enables an efficient formation of diverse functionalized molecules. This method is also effective for cleavage of Cα-Cβ bond in native lignin, yielding two identified benzaldehyde monomers in a total yield of 8.7 wt%.

Desorption of atomic hydrogen from graphene on hexagonal boron nitride

Desorption of atomic hydrogen from graphene on hexagonal boron nitride

Probing Short-Range Interactions in Isostructural Hydrate and Perhydrate of Dabrafenib by Magic-Angle Spinning Solid-State NMR.

Dabrafenib (DBF), an anticancer drug, exhibits isostructural properties in its hydrate (DBF⊃H2O) and perhydrate (DBF⊃H2O2) forms, as revealed by single-crystal X-ray diffraction. Despite the H2O and H2O2 solvent molecules occupying identical locations, the two polymorphs have different thermal behaviors. In general, determination of stoichiometry of H2O in the perhydrate crystals is difficult due to the presence of both H2O and H2O2 in the same crystal voids. This study utilizes magic-angle spinning (MAS) solid-state NMR (SSNMR) combined with gauge-included projector augmented wave calculations to characterize the influence of solvent molecules on the local environment in pseudopolymorphs. SSNMR experiments were employed to assign 1H, 13C, and 15N peaks and identify spectral differences in the isostructural pseudopolymorphs. Proton spectroscopy at fast MAS was used to identify and quantify H2O2/H2O in DBF⊃H2O2 (mixed hydrate/perhydrate). 1H-1H dipolar-coupling-based experiments were recruited to confirm the 3D molecular packing of solvent molecules in DBF⊃H2O and DBF⊃H2O2. Homonuclear (1H-1H) and heteronuclear (1H-14N) distance measurements, in conjunction with diffraction structures and optimized hydrogen atom positions by density functional theory, helped decipher local interactions of H2O2 with DBF and their geometry in DBF⊃H2O2. This integrated X-ray structure, quantum chemical calculations, and NMR study of pseudopolymorphs offer a practical approach to scrutinizing crystallized solvent interactions in the crystal lattice even without high-resolution crystal structures or artificial sample enrichment.