Hydrogen Atoms Research Articles

Mechanism of Ni-Catalyzed Photochemical Halogen Atom-Mediated C(sp3)-H Arylation.

Within the context of Ni photoredox catalysis, halogen atom photoelimination from Ni has emerged as a fruitful strategy for enabling hydrogen atom transfer (HAT)-mediated C(sp3)-H functionalization. Despite the numerous synthetic transformations invoking this paradigm, a unified mechanistic hypothesis that is consistent with experimental findings on the catalytic systems and accounts for halogen radical formation and facile C(sp2)-C(sp3) bond formation remains elusive. We employ kinetic analysis, organometallic synthesis, and computational investigations to decipher the mechanism of a prototypical Ni-catalyzed photochemical C(sp3)-H arylation reaction. Our findings revise the previous mechanistic proposals, first by examining the relevance of SET and EnT processes from Ni intermediates relevant to the HAT-based arylation reaction. Our investigation highlights the ability for blue light to promote efficient Ni-C(sp2) bond homolysis from cationic NiIII and C(sp2)-C(sp3) reductive elimination from bipyridine NiII complexes. However interesting, the rates and selectivities of these processes do not account for the productive catalytic pathway. Instead, our studies support a mechanism that involves halogen atom evolution from in situ generated NiII dihalide intermediates, radical capture by a NiII(aryl)(halide) resting state, and key C-C bond formation from NiIII. Oxidative addition to NiI, as opposed to Ni0, and rapid NiIII/NiI comproportionation play key roles in this process. The findings presented herein offer fundamental insight into the reactivity of Ni in the broader context of catalysis.

Two-in-One Role of Benzophenone in Photoinduced C(sp3)-H Monofluoralkenylation: Hydrogen-Atom Transfer and Single-Electron Transfer.

A new protocol for monofluoralkenylation of C(sp3)-H bonds with gem-difluoroalkenes was reported. In this protocol, benzophenone serves as a photocatalyst with dual roles of hydrogen-atom transfer and single-electron transfer. The excited state of benzophenone abstracts a hydrogen atom from a C(sp3)-H bond to generate a corresponding carbon radical, which subsequently undergoes a radical addition/SET/β-F elimination process rather than radical-radical cross-coupling of previous work. This reaction shows high regioselectivity for the α-carbon atoms of ethers, thioethers, and amines, enabling the preparation of monofluoroalkenes.

Modelling on a Biomimetic [Cu-O-Cu]2+-mediated Methane-to-Methanol Conversion Unveils the Site for Methane Activation.

The Cu-O-Cu core exhibits methane-to-methanol conversion, mirroring the reactivity of the copper-containing enzyme pMMO. Herein, we computationally examined the reactivity of a biomimetic Cu-O-Cu core towards methane-to-methanol conversion. The oxygen atom of the Cu-O-Cu core abstracts hydrogen present in the C-H bond of methane. The spin density at the bridging oxygen helps to abstract hydrogen from the C-H bond. We modulated the spin density of the bridging oxygen by substituting only a single copper atom of the Cu-O-Cu core by metals (M) such as Fe, Co, and Ag. These substitutions result in bimetallic [Cu-O-M]2+ models. We observed that the energy barriers for the C-H activation step and the subsequent rebound step vary with the metal M. [Cu-O-Ag]2+ exhibits the highest reactivity for M2M conversion, while [Cu-O-Fe]2+ displays the lowest reactivity. To understand the different reactivity of these models towards M2M conversion, we employed distortion-interaction analysis, orbital analysis, spin density analysis, and quantum theory of atoms in molecules analysis. Orbital analysis reveals that all four adducts follow a hydrogen atom transfer mechanism for C-H activation. Further, spin density analysis reveals that a higher spin density on the bridging oxygen leads to a lower C-H activation barrier.

Non-Metal Doping as a First-Principles Study for Promoting the Hydrogen Evolution of Two-Dimensional Electride Y2C Electrocatalysts

The two-dimensional electrochemical Y2C’s low work function and strong charge transfer qualities limit its applicability in catalysis due to its poor catalytic activity. In this paper, based on density functional theory calculations, we use two techniques to increase the HER catalytic activity of the Y2C monolayer: substitution doping (XC) and adsorption doping (XT) of non-metal (X = N, P, O, S, and F). The results showed that the absolute values of hydrogen free energies (ΔGH*) of the substitutional dopants of PC, SC and adsorptive dopants of NT, OT, ST, and PT had increased catalytic activity compared with those of the pristine Y2C monolayer (−0.673 eV). It was highlighted that the adsorption doping of PT can further reduce the adsorption free energy of the pristine Y2C monolayer to −0.19 eV, which is close to the optimal zero value, and the binding energy of the hydrogen atoms on the Y2C surface significantly increased from −0.913 to −0.438 eV, which is more favorable for the desorption of hydrogen atoms. These results demonstrate that the doping of non-metals activates the adsorption of hydrogen atoms on monolayer Y2C and provides a feasible method for hydrogen generation.

Photocatalytic [3+2] Cycloaddition of Alkyl/aryl Iodides and Internal Alkynes by Merging Halogen and Hydrogen Atom Transfer

Photocatalytic [3+2] Cycloaddition of Alkyl/aryl Iodides and Internal Alkynes by Merging Halogen and Hydrogen Atom Transfer

FEATURES OF PHASE DIAGRAMS OF A TWO-FREQUENCY PENDULUM IN JAN-TELLER POTENTIAL AND HEAT CAPACITY OF WATER

A simulation of rotational vibrations of a water molecule was carried out using a model of a two-frequency pendulum in a simple Jahn–Teller potential (JTP), which has a minimum potential at a certain angle of deviation of the pendulum from the axis (the bending angle of the intermolecular hydrogen bond of the water molecule). It has been established that at low initial speeds for a given potential a new type of oscillations is observed - transverse oscillations of the pendulum inside the circular gutter JTP, at medium speeds - two-frequency independent oscillations (IO) along two axes, and at large ones - ellipse-like oscillations (ELO) at a single frequency. The work examines phase diagrams (PD) and mixed PD (MPD) in two coordinates for these two-dimensional oscillations. A significant difference between these diagrams in the JTP and standard PD is shown. The appearance of additional ellipses, loops and waves on the PD due to the appearance of transverse vibrations in the nuclear fuel gutter was discovered. To obtain ellipses in phase diagrams from all transverse oscillations of the pendulum, it is proposed to construct a PD versus radius (PDR) for the oscillation trajectory. It is shown that ellipses on the PDR for transverse oscillations of the pendulum are clearly observed at low initial speeds, but for medium and high speeds the transverse part of speed is not independently distinguished from the total speed. The presence of stable transverse vibrations in the JTP gutter for rotational vibrations of hydrogen atoms of water molecules around the axes of intermolecular bonds can be considered as new degrees of freedom for its new collectivized transverse vibrations in this potential. Their existence may lead to an explanation for the contribution of these types of oscillations to the anomalously large heat capacity of water in the liquid phase. However, for the presence of such new degrees of freedom for transverse vibrations of water molecules, it is necessary that their vibrations always take place in the region of “small” velocities - in the JTP gutter. To do this, it is necessary to increase this range of vibrations so that the maximum value of the potential on the axis of the intermolecular bond would be large. This should ensure the existence of transverse rotational oscillations in the JTP gutter for water molecules in all liquid phase temperatures.

Coulomb effect on elastic electron scattering by hydrogen atom and hydrogen-like ions in their metastable 2s state in the 511–770 KeV energy range

This paper reports on a study investigating the elastic scattering of hydrogen atoms in their metastable state (2S-2S) when subjected to electron impact, with a focus on the Coulomb effect within an energy range spanning from 511 keV to 770 keV . The analysis employs semi-relativistic wave functions to depict the hydrogen states. The validity of using Darwin wave functions is confirmed by ensuring that the condition Zα << 1 is met, where α represents the structure constant. Both incident and scattered free electrons are described using Dirac spinors. Notably, the semi-relativistic calculations converge with those of the non-relativistic case at low electron velocities. Additionally, in the presence of the Coulomb effect, the electron wave function is approximated by a Dirac function modulated by the confluent hypergeometric function. The paper presents the relativistic differential cross-section (RDCS) as a function of the final scattering angle for various energies of the incident electron, revealing intriguing insights into diffusion probabilities in specific directions. Moreover, the impact of the atomic number Z on the elastic scattering of hydrogen atoms and hydrogen-like ions by electron impact under the influence of the Coulomb effect is thoroughly examined.

Optimized preparation of Ni-Febm bimetallic particles by ball milling NiSO4 and iron powder for efficient removal of triclosan

The excessive usage and emissions of triclosan (TCS) pose a serious threat to aquatic environments. Iron-based bimetallic particles (Pd/Fe, Ni/Fe, and Cu/Fe, etc.) were widely used for the degradation of chlorophenol pollutants. This study proposed a novel synthesis method for the preparation of Ni/Fe bimetallic particles (Ni-Febm) by ball milling microscale zero valent iron ZVI (mZVI) and NiSO4. Ball-milling conditions such as ball-milling time, ball-milling speed and ball-to-powder ratio were optimized to prepare high activity Ni-Febm bimetallic particles. During the ball-milling process, Ni2+ was reduced to Ni0 and formed a coupled structure with ZVI. The amount of Ni0 on ZVI significantly affected the activity of Ni-Febm bimetallic particles. The highest activity Ni-Febm bimetallic particles with Ni/Fe ratio of 0.03 were synthesized under optimized conditions, which could remove 86.56% of TCS (10 μM) in aerobic aqueous solution within 60 min. In addition, higher particle dosage, lower pH condition and higher reaction temperature were more conducive for TCS degradation. The higher corrosion current and lower electron transfer impedance of Ni-Febm bimetallic particles were the main reasons for its high activity. The hydrogen atom (•H) on the surface of Ni-Febm bimetallic particles was mainly contributed to the removal of TCS, as reductive transformation products of TCS were detected by LC-TOF-MS. Notably, a small amount of oxidation products were discovered. The total dechlorination rate of TCS was calculated to be 39.67%. After eight reaction cycles, the residual Ni-Febm bimetallic particles could still degrade 28.34% of TCS within 6 h. Low Ni2+ leaching during reaction indicated that Ni-Febm bimetallic particles did not pose potential environmental risks. The prepared environmental-friendly Ni-Febm bimetallic particles with high activity have great potential in the degradation of other chlorinated organic compounds in wastewater.

Photogeneration of Chlorine Radical from a Self-Assembled Fluorous 4CzIPN•Chloride Complex: Application in C-H Bond Functionalization.

The chlorine radical is a strong HAT (Hydrogen Atom Transfer) agent that is very useful for the functionalization of C(sp3)-H bonds. Albeit highly attractive, its generation from the poorly oxidizable chloride ion mediated by an excited photoredox catalyst is a difficult task. We now report that 8Rf8-4CzIPN, an electron-deficient fluorous derivative of the benchmark 4CzIPN photoredox catalyst belonging to the donor-acceptor carbazole-cyanoarene family, is not only a better photooxidant than 4CzIPN, but also becomes an excellent host for the chloride ion. Combining these two properties ultimately makes the self-assembled 8Rf8-4CzIPN•Cl- dual catalyst highly reactive in redox-neutral Giese-type C(sp3)-H bond alkylation reactions promoted by the chlorine radical. Additionally, because of its fluorous character, the efficient separation/recovery of 8Rf8-4CzIPN could be envisioned.

ТЕОРЕТИЧЕСКОЕ ИССЛЕДОВАНИЕ N1H ТАУТОМЕРА КАРНОЗИНА В ЦВИТТЕРИОННОЙ ФОРМЕ

. In the present work, the spatial and electronic structures of the lowest energy conformation of the carnosine N1H tautomer in the zwitterionic form, which has a wide range of applications, have been studied. The calculations were performed by the DFT quantum-chemical method based on the B3LYP hybrid functional and the 6-31+G(d,p) basis set in gas, water, and DMSO using the Gaussian 09 and GaussView 6.0.16 programs. The geometry parameters, values of electronic energy, dipole moments, values of partial charges on atoms, HOMO and LUMO energies, descriptors of reactivity of a molecule were calculated and NBO analysis is carried out. The molecular electrostatic potential (MEP) maps and frontier orbitals were visualized. The structural and electronic rearrangements in the molecule and changes in various parameters depending on the dielectric constant of the medium were analyzed. It was found that the influence of the solvent does not play a significant role for this structure, very similar results were obtained for the aqueous medium and DMSO. However, the optimization of the geometry of this carnosine zwitterion tautomer in the gas phase, led to the elimination of the hydrogen atom from the terminal NH3+ group and its addition to the COO- group, actually converting the zwitterionic form into a neutral one.

Cu1‐Fe Dual Sites for Superior Neutral Ammonia Electrosynthesis from Nitrate

The electrochemical nitrate reduction reaction (NO3RR) is able to convert nitrate (NO3‐) into reusable ammonia (NH3), offering a green treatment and resource utilization strategy of nitrate wastewater and ammonia synthesis. The conversion of NO3‐ to NH3 undergoes water dissociation to generate active hydrogen atoms and nitrogen‐containing intermediates hydrogenation tandemly. The two relay processes compete for the same active sites, especially under pH‐neutral condition, resulting in the suboptimal efficiency and selectivity in the electrosynthesis of NH3 from NO3‐. Herein, we constructed a Cu1‐Fe dual‐site catalyst by anchoring Cu single atoms on amorphous iron oxide shell of nanoscale zero‐valent iron (nZVI) for the electrochemical NO3RR, achieving an impressive NO3‐ removal efficiency of 94.8% and NH3 selectivity of 99.2% under neutral pH and nitrate concentration of 50 mg L‐1 NO3‐‐N conditions, greatly surpassing the performance of nZVI counterpart. This superior performance can be attributed to the synergistic effect of enhanced NO3‐ adsorption on Fe sites and strengthened water activation on single‐atom Cu sites, decreasing the energy barrier for the rate‐determining step of *NO‐to‐*NOH. This work develops a novel strategy of fabricating dual‐site catalysts to enhance the electrosynthesis of NH3 from NO3‐, and presents an environmentally sustainable approach for neutral nitrate wastewater treatment.

Photogeneration of Chlorine Radical from a Self‐Assembled Fluorous 4CzIPN•Chloride Complex: Application in C−H Bond Functionalization

AbstractThe chlorine radical is a strong HAT (Hydrogen Atom Transfer) agent that is very useful for the functionalization of C(sp3)−H bonds. Albeit highly attractive, its generation from the poorly oxidizable chloride ion mediated by an excited photoredox catalyst is a difficult task. We now report that 8Rf8‐4CzIPN, an electron‐deficient fluorous derivative of the benchmark 4CzIPN photoredox catalyst belonging to the donor‐acceptor carbazole‐cyanoarene family, is not only a better photooxidant than 4CzIPN, but also becomes an excellent host for the chloride ion. Combining these two properties ultimately makes the self‐assembled 8Rf8‐4CzIPN•Cl− dual catalyst highly reactive in redox‐neutral Giese‐type C(sp3)−H bond alkylation reactions promoted by the chlorine radical. Additionally, because of its fluorous character, the efficient separation/recovery of 8Rf8‐4CzIPN could be envisioned.

Cu1-Fe Dual Sites for Superior Neutral Ammonia Electrosynthesis from Nitrate.

The electrochemical nitrate reduction reaction (NO3RR) is able to convert nitrate (NO3-) into reusable ammonia (NH3), offering a green treatment and resource utilization strategy of nitrate wastewater and ammonia synthesis. The conversion of NO3- to NH3 undergoes water dissociation to generate active hydrogen atoms and nitrogen-containing intermediates hydrogenation tandemly. The two relay processes compete for the same active sites, especially under pH-neutral condition, resulting in the suboptimal efficiency and selectivity in the electrosynthesis of NH3 from NO3-. Herein, we constructed a Cu1-Fe dual-site catalyst by anchoring Cu single atoms on amorphous iron oxide shell of nanoscale zero-valent iron (nZVI) for the electrochemical NO3RR, achieving an impressive NO3- removal efficiency of 94.8% and NH3 selectivity of 99.2% under neutral pH and nitrate concentration of 50 mg L-1 NO3--N conditions, greatly surpassing the performance of nZVI counterpart. This superior performance can be attributed to the synergistic effect of enhanced NO3- adsorption on Fe sites and strengthened water activation on single-atom Cu sites, decreasing the energy barrier for the rate-determining step of *NO-to-*NOH. This work develops a novel strategy of fabricating dual-site catalysts to enhance the electrosynthesis of NH3 from NO3-, and presents an environmentally sustainable approach for neutral nitrate wastewater treatment.

High cyclic stability and low plateau of Ti2V2Zr/NaH/Al hydrogen storage composite system prepared by ultrasound-assisted ball milling

NaH/Al doped with Ti2V2Zr with the aim of lowering the rehydrogenation pressure, lowering the dehydrogenation temperature, and improving the hydrogenation/dehydrogenation kinetics of NaAlH4. It was found that moderate ultrasonic-assisted wet grinding was beneficial to fine particles efficiently, improved uniformity of particle size, and reduced lattice distortion because its crystalline phase can converge more active hydrogen atoms and reduce the energy barrier of H exchange between the alloy and the matrix, thus improving the comprehensive hydrogen storage performance of the composite systems. It could reversibly store 4.81 wt% of hydrogen and completely hydrogenation under a low hydrogen pressure of 55 atm, its starting and ending dehydrogenation temperatures decrease by 81 and 89 °C, respectively, and the activation energies of the two-step dehydrogenation decrease by 26.7 and 52.7 kJ mol−1 respectively, with a dehydrogenation capacity retention of up to 99.58% over five cycles.

Energetic particle precipitation influences global secondary ozone distribution

The secondary ozone layer is a global peak in ozone abundance in the upper mesosphere-lower thermosphere (UMLT) around 90-95 km. The effect of energetic particle precipitation (EPP) from geomagnetic processes on this UMLT ozone remains largely unexplored. In this research we investigated how the secondary ozone responds to EPP using satellite observations. In addition, the residual Mean Meridional Circulation (MMC) derived from model simulations and the atomic oxygen [O], atomic hydrogen [H], temperature measurements from satellite observations were used to characterise the residual circulation changes during EPP events. We report regions of secondary ozone enhancement or deficit across low, mid and high latitudes as a result of global circulation and transport changes induced by EPP. The results are supported by a sensitivity test using an empirical model.

Visible Light‐Induced Synthesis of γ‐Amino Sulfones from Vinyl Sulfones and Amino Acids

A method for the synthesis of γ‐amino sulfones through visible light‐induced oxidative decarboxylation and radical reductive addition is described. Various readily available N‐protected natural amino acids react with aromatic/aliphatic vinyl sulfones to directly produce γ‐amino sulfone derivatives. This reaction is also applicable to α‐N(O)‐acids and other aliphatic carboxylic acids, resulting in the corresponding sulfone derivatives. The method operates without the need for sacrificial reducing agents or additional hydrogen atom donors. The sole by‐product is CO2 released from decarboxylation, rendering the process both atom‐ and step‐economical.

Crystal structure, Hirshfeld surface analysis and photophysical properties of disubstituted 4,4′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dianiline

Two independent molecules of the crystal structure of the title compound C18H14N4S were found to occupy the asymmetric unit of the space group. The flanking 4-anilines were not coplanar with the central benzothiadiazole. In the crystal, two unique types of hydrogen bonds were found: i) one set between two NH2 of two molecules in the asymmetric unit and ii) another set between hydrogen atoms of the second aniline NH2 and the nitrogen atom of benzothiadiazole. The two-dimensional fingerprint plots along with the Hirshfeld surface confirmed the most important contributions for the crystal packing were C···H, H···H and N···H interactions. The compound was also solvatochromic with both its emission wavelength and quantum yield contingent on the solvent polarity. The fluorophore had a reversible oxidation. This was used to induce both a reversible color change from yellow to blue and emission off/on with an applied potential.

The effect of dual-frequency ultrasound on synergistic Sonochemical oxidation to degrade aflatoxin B1

This study investigated the degradation of aflatoxin B1 (AFB1) in food by using dual-frequency ultrasound (DFUS) and the effects of sonochemical oxidation on the efficacy. It was found that the degradation of AFB1 by bath ultrasound (BU), probe ultrasound (PU), and DFUS were all consistent with first-order kinetics. The use of DFUS significantly increased the AFB1 degradation to 91.3%, and compared with BU and PU, it increased by about 177.0% and 61.5% after 30 min treatment. DFUS could generate a synergistic effect to accelerate the generation of free radicals, which promoted sonochemical oxidation to degrade AFB1. It could be speculated that hydroxyl radical (·OH) probably acted a dominant part in the AFB1 degradation by DFUS, and the hydrogen atoms (·H) might also are contributed. These results indicated that DFUS was an effective method of AFB1 degradation.

Silylation and (Hetero)aryl/alkenylation of Unactivated Alkenes via Radical-Mediated Distal 1,4-Migration with Hydrosilanes under Organophotocatalysis.

We report a novel organic photoredox catalysis to achieve unprecedented γ-(hetero)aryl/alkenyl-δ-silyl aliphatic amines via silyl-mediated distal (hetero)aryl/alkenyl migration of aromatic/alkenyl amines bearing unactivated alkenes with hydrosilanes. This protocol features mild and metal-free reaction conditions, high atom economy, excellent selectivity, and functional group compatibility. Mechanistic studies suggest that silylation and (hetero)aryl/alkenylation involve photoredox hydrogen atom transfer catalysis and subsequent 1,4-migration of a remote (hetero)aryl/alkenyl group from nitrogen to carbon.

Novel 10,11-dihydro-5H-dibenzo[b,f]azepine triazoles hybrids: Synthesis, in vitro antioxidant activity and xanthine oxidase inhibition and computational study

The study reports the synthesis and antioxidant capability of six novel 10,11-dihydro-5H-dibenzo[b,f]azepine linked 1,2,3-triazoles 6(a–f), synthesized in good yield using copper (II)-catalyzed azide-alkyne 1,3- dipolar cycloaddition reaction (Click Chemistry) under ultrasonication. The alkyne of 10,11-dihydro-5H-dibenzo[b,f]azepine has been prepared and confirmed to have monoclinic geometry using single crystal XRD. All the synthesized compounds are fully characterized using 1H and 13CNMR , IR, and HRMS. The new compounds 6(a-f) were studied for in vitro DPPH and FRAP antioxidant assay, as well as their ability to inhibit xanthine oxidase enzyme. Compound 6d showed minimum IC50 values of 3.58 ± 1.5 µg/ml and 58.66 ± 3 µM for DPPH and FRAP inhibitory effect respectively. The HAT (hydrogen atom transfer) mechanism for DPPH activity and SET (single electron transfer) mechanism for FRAP activity of compound 6d, has been studied through a DFT study on B3LYP hybrid functional at 6–31+G(d,p) basis set. The bond dissociation enthalpy and ionization potential of 6d are 77.01 kcal/mol and 162.59 kcal/mol respectively, proving it to be an excellent antioxidant. Being the best antioxidant 6d has been further used for in vitro inhibition study on xanthine oxidase enzyme isolated from buttermilk. 6d derivative has an IC50 value of 4.93±2 µg/ml much lesser than the standard drug Allopurinol, having an IC50 value of 10.29 ± 1 µg/ml. The molecular docking study is performed on 6(a-f) for XO protein PDBID:1FIQ. All compounds showed effective binding with XO enzyme and the best lead 6d showed a maximum binding energy value of -10.0 kcal/mol. A molecular dynamic simulation study of 100 ns further proved the stability of enzyme 6d complex in the biological system.