Hydrogen Atoms Research Articles

Unique Applications of para-Hydrogen Matrix Isolation to Spectroscopy and Astrochemistry.

Cryogenic solid para-hydrogen (p-H2) exhibits pronounced quantum effects, enabling unique experiments that are typically not possible in noble-gas matrices. The diminished cage effect facilitates the production of free radicals via in situ photolysis or photoinduced reactions. Electron bombardment during deposition readily produces protonated and hydrogenated species, such as polycyclic aromatic hydrocarbons, that are important in astrochemistry. In addition, quantum diffusion delocalizes hydrogen atoms in solid p-H2, allowing efficient H atom reactions with astrochemical species and introducing new concepts in astrochemical models. Some H atom reactions display anomalous temperature behaviors, highlighting the rich chemistry in p-H2. The investigation on quantum diffusion of heavier atoms and molecules is also important for our understanding of the chemistry in interstellar ice. Additionally, matrix shifts of electronic transitions of polycyclic aromatic hydrocarbons in p-H2 are less divergent than those in solid Ne such that systematic measurements in p-H2 might help in the assignment of diffuse interstellar bands.

Direct observation of nanometer size hydride precipitations in superconducting niobium.

Superconducting niobium serves as a key enabling material for superconducting radio frequency (SRF) technology as well as quantum computing devices. Niobium has a high propensity for the uptake of hydrogen. At room temperature, hydrogen commonly occupies tetragonal sites in the Nb lattice as the metal (M)-gas (H) phase. When the temperature is decreased, however, a solid solution of Nb-H begins to precipitate. In this study, we show the first identified topographical features associated with nanometer-size hydride phase (Nb1-xHx) precipitates on the surface of the metallic superconducting niobium using cryogenic-atomic force microscopy (AFM). Further, high energy grazing incidence X-ray diffraction reveals information regarding the structure and stoichiometry of these precipitates. Finally, through time-of-flight secondary ion mass spectroscopy (ToF-SIMS), we locate atomic hydrogen sources near the top surface. This systematic study clarifies nanometer scale hydrides precipitated on the surface of the SRF Nb cavity that exhibit performance degradation at a high accelerating field regime.

Non-Adiabatic Excited-State Time-Dependent GW (TDGW) Molecular Dynamics Simulation of Nickel-Atom Aided Photolysis of Methane to Produce a Hydrogen Molecule

Methane photolysis is a very important initiation reaction from the perspective of hydrogen production for alternative energy applications. In our recent work, we demonstrated using our recently developed novel method, non-adiabatic excited-state time-dependent GW (TDGW) molecular dynamics (MD), how the decomposition reaction of methane into a methyl radical and a hydrogen atom was captured accurately via the time-tracing of all quasiparticle levels. However, this process requires a large amount of photoabsorption energy (PAE ∼10.2 eV). Moreover, only one hydrogen atom is produced via a single photon absorption. Transition metal atoms can be used as agents for photochemical reactions, to reduce this optical gap and facilitate an easier pathway for hydrogen production. Here, we explore the photolysis of methane in the presence of a Ni atom by employing TDGW-MD. We show two possibilities for hydrogen-atom ejection with respect to the location of the Ni atom, towards the Ni side or away from it. We demonstrate that only the H ejection away from the Ni side facilitates the formation of a hydrogen molecule with the quasiparticle level corresponding to it having an energy close to the negative ionization potential of an isolated H2 molecule. This is achieved at a PAE of 8.4 eV which is lower compared to that of pristine methane. The results obtained in this work are an encouraging step towards transition metal-mediated hydrogen production via photolysis of hydrocarbons.

DFT molecular modeling investigation and optical properties characterization of CR-39 films

Abstract In this study, the structural and optical characteristics of CR-39 films were investigated both theoretically and experimentally. A number of parameters for the CR-39 structure were theoretically computed by the density functional theory (DFT) method at B3LYP/6–311 G (p, d) level of theory. FTIR and UV/Vis spectroscopy were used to determine the structure compositions and the optical parameters of the CR39 film, respectively. The computed and experimental findings show good concordance. It was found that the CR-39 compound’s total energy, dipole moment, and energy difference between the LUMO and HOMO were, respectively, −994.575 a.u., 2.772 Debye, and 7.045 eV. The MEP showed a progressive change in color, with blue signifying a low electron density and red denoting a high electron density linked to nucleophilic reactivity and electrophilic reactivity. Further, the positive charges on all hydrogen atoms, which range from 0.16506 to 0.22032 a.u., imply that they are acceptors. The positive H34 is strongly produced when electrons from the negatively charged C17 are taken up. Because they are donor atoms, part of the carbon atoms in the structure is negative, while the other atoms are positive. The highest electronegative atoms H23 and H24 were substituted, resulting in the extremely negative carbon atom C7 (−0.32436). According to the experimentally determined absorption coefficient and energy gap values, CR-39 films may find application in optoelectronic devices.

Flavin-Catalyzed, Photochemical Conversion of Dehydroalanine into 4,5-Dihydroxynorvaline.

The chemical synthesis of unnatural amino acids (UAA) is a key strategy for preparing designed peptides, including pharmaceutically active compounds. Alterations of existing amino acid residues such as dehydroalanine (Dha) are particularly important since selected positions can be addressed without the necessity of a complete de novo synthesis. The intriguing UAA 4,5-dihydroxynorvaline (Dnv) is found in a variety of naturally occurring peptides and biologically active compounds. However, no method is currently available to modify an existing peptide with this residue. We report the use of flavin catalysts and visible light irradiation for this challenge, which serves as a versatile strategy for converting Dha into Dnv. Our study shows that excited flavins are competent hydrogen atom abstraction catalysts for ethers and acetals, which allows masked 1,2-dihydroxyethylene functionalization from 2,2-dimethyl-1,3-dioxolane. The masked diol was successfully coupled to Dha residues, and a series of Dnv-containing products is reported. A mild and orthogonal protocol for deprotection of the acetal group was also identified, allowing free Dnv-modified peptides to be obtained. This method provides a straightforward strategy for Dnv functionalization, which is envisioned to be crucial for accessing natural products and synthetic analogues with pharmaceutical activity.

Inelastic Triatom-Atom Quantum Close-Coupling Dynamics in Full Dimensionality: All Rovibrational Mode Quenching of Water Due to the H Impact on a Six-Dimensional Potential Energy Surface.

The rovibrational level populations, and subsequent emission in various astrophysical environments, are driven by inelastic collision processes. The available rovibrational rate coefficients for water have been calculated using a number of approximations. We present a numerically exact calculation for the rovibrational quenching for all water vibrational modes due to collisions with atomic hydrogen. The scattering theory implements a quantum close-coupling (CC) method on a high level ab initio six-dimensional (6D) potential energy surface (PES). Total rovibrational quenching cross sections for excited bending levels were compared with earlier results on a 4D PES with the rigid-bender close-coupling (RBCC) approximation. General agreement between 6D-CC and 4D-RBCC calculations are found, but differences are evident including the energy and amplitude of low-energy orbiting resonances. Quenching cross sections from the symmetric and asymmetric stretch modes are provided for the first time. The current 6D-CC calculation provides accurate inelastic data needed for astrophysical modeling.

Harmonizing Visible‐Light in Green Synthesis: Unrevealing the Brilliance of Metal‐Free Cross‐Coupling of Unsaturated Hydrocarbons for C−C Bonds Formation

AbstractVisible‐light induced, photoredox catalysis has opened a wide range in the transformation of organic compounds in recent times. In synthetic organic chemistry HAT (hydrogen atom transfer) and SET (single electron transfer) mechanisms are a very noteworthy routes that has opened a window in favor of C−C single bond formations. Usually, a major role of unsaturated hydrocarbons is to participate in carbon‐carbon bond formation as they carry reactive π‐bond. Under visible‐light, metal‐free cross‐coupling reactions are particularly favorable because of their atom economy, increased efficiency, and environmentally friendly procedures that result in the construction of C−C bonds. The review emphasizes the latest advancements of visible‐light mediated, cross‐coupling reactions of unsaturated hydrocarbons in metal‐free conditions for constructing carbon‐carbon single bonds.

ALMA and GMRT Studies of Dust Continuum Emission and Spectral Lines Toward Oort Cloud Comet C/2022 E3 (ZTF)

Abstract The atomic and molecular compounds of cometary ices serve as valuable knowledge into the chemical and physical properties of the outer solar nebula, where comets are formed. From the cometary atmospheres, the atoms and gas-phase molecules arise mainly in three ways: (i) the outgassing from the nucleus, (ii) the photochemical process, and (iii) the sublimation of icy grains from the nucleus. In this paper, we present the radio and millimeter wavelength observation results of Oort cloud non-periodic comet C/2022 E3 (ZTF) using the Giant Metrewave Radio Telescope (GMRT) band L and the Atacama Large Millimeter/Submillimeter Array (ALMA) band 6. We do not detect continuum emissions and an emission line of atomic hydrogen (HI) at rest frequency 1420 MHz from this comet using the GMRT. Based on ALMA observations, we detect the dust continuum emission and rotational emission lines of methanol (CH3OH) from comet C/2022 E3 (ZTF). From the dust continuum emission, the activity of dust production (Afρ) of comet ZTF is 2280±50 cm. Based on LTE spectral modelling, the column density and excitation temperature of CH3OH towards C/2022 E3 (ZTF) are (4.50±0.25)×10^{14} cm^{−2} and 70±3 K. The integrated emission maps show that CH3OH was emitted from the coma region of the comet. The production rate of CH3OH towards C/2022 E3 (ZTF) is (7.32±0.64)×10^{26} molecules s^{−1}. The fractional abundance of CH3OH with respect to H2O in the coma of the comet is 1.52%. We also compare our derived abundance of CH3OH with the existence modelled value, and we see the observed and modelled values are nearly similar. We claim that CH3OH is formed via the subsequential hydrogenation of formaldehyde (H2CO) on the grain surface of comet C/2022 E3 (ZTF).

Thermally induced transformation tert-butyl peroxyethyl esters of carboxylic acids

The features of thermolysis of tert-butyl peroxyethyl esters of carboxylic acids (CH₃)₃COOCH(CH₃)OC(O)R are investigated. Based on the identification of reaction products and the analysis of kinetic parameters, the fact of simultaneous transformation of four bonds (O–O, C–O, C–C and C–H) in a molecule with the formation of two molecules was proved for the first time [RC(O)OH and CO] and two free radicals [(CH₃)₃CO• and •CH₃], which, under experimental conditions, do not enter into a cross-break reaction, but detach the hydrogen atom from the solvent. Evidence of the coordinated (simultaneous) transformation of four bonds is the low (compared with the energy of bond dissociation) values of the activation energy and the pre-exponential multiplier, as well as negative values of the activation entropy.

Molecular Interactions and Structural Transformations in Water Complexes with Azoles in Solid Films: IR and DFT Study

AbstractAzoles are widely used as bioactive substances, herbicides, catalysts, corrosion inhibitors, polymeric compositors, organometallic ligands, and optical elements’ components. The interaction with water plays a crucial role in many applications of azoles. The objective of this study is to observe the molecular interaction and structural transformations of 1,2‐ and 1,3‐diazoles’, 1,2,3‐ and 1,2,4‐triazoles’ complexes with water molecules. We have selected the most valuable for application and theoretical interest azoles with different molecular structures, which have allowed us to consider the basic features of their aqueous complexes. We used the IR study method allowing to fix water intermediates in the solid phase. We have also employed the hybrid B3LYP functional DFT method with GD3BJ dispersion correction. At the cluster formation, the hydrogen atom transfer arises, providing a labile spatial arrangement of the water system. The formation of azoles’ complexes with a hydronium ion having relatively low binding energy allows the reshaping of the complexes’ structure at the hydrogen atom cluster‐to‐cluster transition. The complex formation is accompanied by the hydrogen atom transfer with the participation of both water and azole hydrogen atoms. This transfer provides the mobile spatial arrangement of clusters and hydrogen atom transition from donor to acceptor centers.

Carborazine doped nanographene (CBNG) sheet as a promising NO2 gas sensor: A theoretician’s approach

Nanographenes (NGs) are a distinct section of graphene in which the dangling bonds are saturated with hydrogen atoms (C42H18). This confinement in size results in unique properties and potential applications. The density functional theory (DFT) is used to investigate the reactivity and electronic sensitivity of a model carborazine (B2C2N2) ring doped nanographene (CBNG) for detecting NO2 gas. In CBNG/NO2 complex, one oxygen atom of the NO2 molecule is positioned at a distance of 2.93Ả from the center of the B2C2N2 ring, with an adsorption energy −6.2 kcal/mol. The adsorption energy of NO2 on CBNG is apparently larger than those of other gas molecules, which fall between the suitable range of strong physical adsorption and weak chemical adsorption. Upon NO2 adsorption, the band gap of CBNG sheet reaches 62.4 %. The outcome of the present study may be exploited in the industry, particularly in the synthesis of effective NO2 gas sensors.

Olive pomace waste conversion to bio-fuel by application of integrated configuration of pyrolysis/hydrodeoxygenation process

Bio-oil obtained from non-catalytic pyrolysis of biomass, consists of a large number of oxygenated compounds. Hence, it is essential for the bio-oil to go through upgrading processes such as hydrodeoxygenation (HDO) to reform these compounds to aliphatic and aromatic hydrocarbons. This study works towards this purpose by initially deriving raw bio-oil from olive pomace waste biomass in a non-catalytic pyrolysis process at temperature of 400–700 ºC. Then for reducing the oxygen content of derived bio-oil, HDO of the raw bio-oil over NiMo/Al2O3 catalyst was performed in a batch reactor, in varying operational parameters: temperature of 200–250 °C, reaction time of 1–3 h, hydrogen pressure of 2–6 bar and catalyst: bio-oil ratio of 1:20, 1:10, 1:5. The results revealed that the catalytic HDO is an appropriate procedure, as fatty acids as the main oxygenated components in bio-oil were reduced from 81.8 % to 56.7 %, aldehydes and ketones were entirely removed, and there was a noticeable rise in aliphatic hydrocarbons from 2.8 % to 33.9 % at temperature of 250 ºC, hydrogen pressure of 6 bar and reaction duration of 3 h. In addition, by raising the catalyst to bio-oil ratio to 1:5, the content of fatty acids reached 47.6 %. Furthermore, a comparison was made between the O/C and H/C ratios of the obtained biofuels and the raw bio-oil, which results exhibited that this method worked successfully in substituting oxygen atoms of the raw bio-oil with hydrogen atoms.

Potential of homogeneous persulfate activation as a strategy for the oxidative treatment of tetramethylammonium hydroxide: Superiority of sulfate radical over hydroxyl radical in the oxidation of methylammoniums

Tetramethylammonium hydroxide (TMAH) as the etching and chelating agent exhibits the extreme recalcitrance to advanced oxidation processes utilizing hydroxyl radical (OH). This study showed that based on the relative position of PDS/heat and PDS/UV against H2O2/UV in terms of TMAH degradation efficiency, sulfate radical (SO4−) was superior to OH in oxidizing TMAH. PDS/heat (at 60 °C) and PDS/UV at the initial pH = 7 achieved TMAH degradation efficiency of ∼ 80–90 % within 1 h whereas H2O2/UV barely eliminated TMAH, which contrasted with H2O2/UV decomposing phenol faster than the activated PDS. The high susceptibility of TMAH (in which four methyl groups bonded to nitrogen removed the lone pair of electrons) to oxidation by SO4− aligned with the pH–dependent efficiency of PDS/heat for the treatment of methylamines. PDS/heat effectively degraded methylammoniums (lacking nitrogen lone pair available for electron transfer due to amine protonation) under non–alkaline conditions, whereas acidification caused the efficiency loss of ∼ 90 % for H2O2/UV. Methylammoniums as radical scavengers retarded benzoic acid degradation by PDS/heat to a more pronounced extent than counterparts with deuterated N–methyl groups, which implied that hydrogen–atom abstraction primarily contributed to the SO4−–induced oxidation of methylammoniums. Estimation of the bimolecular reaction rate constants using laser flash photolysis and electron paramagnetic resonance spectroscopic detection of TMAH–derived carbon–centered radical supported the superiority of SO4− over OH in TMAH oxidation. These findings suggested the potential of homogeneous persulfate activation in the pH-insensitive oxidative treatment of alkylamines and quaternary ammonium cations structurally analogous to TMAH.

Effect of the electronic properties of the side charges of neutral solvent molecules on the charges of the N and H atoms of the carbazole molecule: IR experiment and DFT calculations

The IR spectral parameters of the absorption band of the valence vibration of the NH bond of the carbazole molecule in several neutral solvents (n-hexane C6H14, carbon tetrachloride CCl4, chloroform CHCl3, benzene C6H6) have been measured. It has been experimentally established that the position of the maximum of the NH vibrational band of the carbazole molecule in solvents undergoes a low-frequency shift relative to the gas phase. This shift increases in the series C6H14, CCl4, CHCl3, C6H6. The change in the magnitude of the linear shift is well described by the Kirkwood-Bauer-Magat KBM ratio in C6H14, CCl4, CHCl3. The presence of a linear shift may indicate that only universal interactions take place. The deviation of this ratio of shift magnitude for carbazole in benzene is interpreted as a manifestation of intermolecular complexation. Quantum-chemical calculations of the position of the absorption band position of the valence vibration of the NH bond of the carbazole molecule in these solvents, carried out by the electron density functional method B3LYP/6-31G using the Gaussian 09W program package, also showed a low-frequency shift relative to the gas phase.It was found that for the carbazole molecule in the condensed phase relative to the gas phase the following effects of changing the magnitude of charges on atoms N13 and H14 take place: 1 – increase in the positive sign of the charge on both atoms; 2 – the change in charge magnitude is larger on the nitrogen atom than on the hydrogen atom for both solvents (whose molecules have a dipole moment ∼0: C6H14, CCl4); 3 – the chlorine containing environment has a greater effect on the charge change in the carbazole molecule than the proton containing environment (whose molecules have a dipole moment ∼0: C6H14, CCl4).The correlation between the change of charges on atoms N13 and H14 with the value of electronegativity ξ of the side solvent atoms was established.Thus, it is shown that the charges on the 13N and 14H atoms of the carbazole molecule undergo changes in the presence of universal interactions, and the magnitude of the charge change depends on the electronic properties of the side atoms of the nearest solvent molecules. A hypothesis is proposed to explain the different frequency shift of the NH vibrational frequency of the molecule for chlorine-containing and hydrogen-containing side atoms of neutral solvent molecules, which takes into account different values of ξ for nitrogen and hydrogen atoms.

High-Valent Iron–Oxo species in heterogeneous Catalysis: Formation, Mechanism, and reactivity for the degradation of various emerging organic contaminants

High-valent iron–oxo species (FeⅣ/Ⅴ=O), generated via peroxide activation with Fe-based catalysts, have shown potential in the selective and efficient degradation of organic contaminants. However, a comprehensive understanding of the oxidative degradation mechanism induced by FeⅣ/Ⅴ=O is still pending. In this research, to unravel this oxidation mechanism, an Fe-single atom catalyst (FeN4-C) was synthesized, and FeⅤ=O was formed as the predominant reactive species upon peroxymonosulfate (PMS) activation. The FeN4-C/PMS system was experimentally studied on its catalytic oxidation behavior for the degradation of 34 typical emerging organic contaminants (EOCs) in water, exhibiting a significant variation in the pseudo first-order kinetic rate constants (kobs) among the EOCs. A quantitative structure–activity relationship (QSAR) model was established based on the molecular structure feature and measured kobs of the EOCs. The model infers that EOCs with higher electron donating ability (EHOMO) are more susceptible towards FeN4-C/PMS oxidation, implying an electrophilic reaction following the single electron transfer (SET) mechanism. Further exploration of the degradation pathways for seven representative EOCs revealed that the oxidation occurs through the abstraction of either a hydrogen atom or a nonbonded (or π) electron by FeⅤ=O, enabling processes such as C-, N-, and S-oxidation, along with N- and O-dealkylation and deamination, to effectively degrade EOCs. These research findings provide a robust theoretical framework for understanding the reaction mechanisms and predicting the degradability and removal of various EOCs by FeⅣ/Ⅴ=O for water purification.

Synthesis of Laves phase hydrides YFe2H6 and YFe2H7 at high pressure: reaching a limit of interstitial hydrogen uptake

The C15 Laves phase compound YFe2 has been extensively studied for its significant hydrogen absorption in its tetrahedral interstitial sites. It can stably hold up to five hydrogen atoms per formula unit under ambient conditions. However, the maximum hydrogen capacity in such Laves phase materials remains an open question. The use of high pressure is a tool that facilitates the formation of polyhydrides with high hydrogen-to-metal ratios. By subjecting YFe2H4.2 to hydrogen pressures up to 50 GPa in a diamond anvil cell without any heating, two new interstitial compounds, YFe2H6 and YFe2H7, were synthesized. Synchrotron X-ray diffraction and ab initio calculations reveal that these new compounds have ordered hydrogen atoms occupying two types of tetrahedral interstitial sites, A2B2 and B4, and a new triangular interstitial site AB2, in an orthorhombic structure distorted from the C15 Laves phase. The magnetic properties of YFe2Hx hydrides have to be taken into account to reproduce experimental volumes, identify stable compounds on the convex hull of the YFe2-H system, and explain deviations from Vegard’s law regarding volume expansion with hydrogen concentration. These compounds cannot be retrieved at ambient pressure upon pressure release.

Measurements of the Reaction Rate Coefficients of Atomic Hydrogen with Astrochemical Anions: CN− and C3N−

We present the temperature-dependent reaction rate coefficients of CN− and C3N− with atomic hydrogen in the temperature range from 7 to 290 K, measured in a 16-pole radio-frequency ion trap. The rate of C3N− with H steadily increases toward lower temperatures, while the rate coefficients for the CN− + H system show a sudden change around 160 K. Fits to the data were performed to determine temperature-dependent reaction rate coefficients. The fits reveal a rate coefficient of 4.1(3)×10−10(T/300)−0.31(6) cm3 s−1 for C3N− + H. For CN−, we determined a rate coefficient for the temperature regime below 160 K of 3.2(4)×10−10(T/300)−0.31(11) cm3 s−1. Given our present results, higher rate coefficients than previously reported must be assumed for the modeling of cold interstellar environments involving these H atom reactions.

Cobalt single-site molecular Catalyst-mediated electrochemical Hydrodechlorination for detoxification of halogenated Antibiotics: Performance, reaction pathway and mechanism

Electrocatalytic hydrodehalogenation (ECHD) offers a promising approach for detoxification of the halogenated antibiotics via hydrogenolysis of the C-X bonds (X = F, Cl or Br). Herein we demonstrated that the commercially-available cobalt phthalocyanine (CoPc) molecules with a high-loading of −[Co-N4]- moieties (Co wt%: 10.8 %) were exceptionally active for hydrogenolysis of the C-Cl bonds in florfenicol (FLO). It afforded an impressive mass activity of 6.2 gFLO h−1 g-1Co, a low Co leaching of 0.34 μg/L and a strong tolerance to interference from impurities in water, significantly surpassing reported Co/Fe/Ni-based particle and single-site counterparts. Mechanistic studies revealed that the ECHD on CoPc underwent a direct electron transfer manner rather than the atomic hydrogen (H*)-mediated indirect way, and the ECHD efficacy was affected by both the electron and proton transfer kinetics. The single-atom Co, with its d orbitals constituting the lowest unoccupied molecular orbitals of CoPc, served as the primary active site. It facilitated both electron and proton transfer, as well as the cleavage of the C-Cl bond but not the C-F bond. In a continuous-flow cell, the CoPc/C-driven ECHD reduced the antibacterial activity of a FLO-contaminated natural lake water sample by 90.8 % with an energy consumption of 0.19 kwh g-1FLO. This study highlighted great promise of the single-atom metal-bearing molecular catalyst toward the sustainable detoxification of halogenated antibiotics-contaminated water.

Tailoring β-Ti based shape memory alloy with the exceptional mechanical and functional properties towards biomedical bone implants application

In the present study, the interstitial hydrogen (H) atoms were introduced as β-stabilizing element to tailor the microstructure, martensitic phase transition, and functional properties of Ti-V-Al shape memory alloys for biomedical applications. The results revealed that the addition of interstitial H atoms into Ti-V-Al shape memory alloys induced the transition from a single αˊˊ martensite to the coexistence of β parent phase and α phase, regardless of H content. Moreover, the amount of α phase firstly increases and then decreases in the present Ti-V-Al based shape memory alloy with H content increasing. Besides, H addition resulted in larger lattice distortion, further causing the formation of nano-domains in Ti-V-Al based alloys. Besides, no endothermic and exothermic peaks were detected due to the confinement of α-phase, and the emergence of nano-domains. With increasing H atoms content, the mechanical properties such as fracture strength, hardness, recoverable strain for Ti-V-Al based shape memory alloys initially increased and then decreased. (Ti-13V-3Al)99.2H0.8 shape memory alloys exhibited the highest fracture strength of 862MPa, superior hardness of 307HV, and the fully recoverable strain under 6% pre-strain as well as the moderate elastic modulus, which was mainly attributed to the solution strengthening of interstitial H atoms and the precipitation strengthening of α phase. The best corrosion resistance of Ti-V-Al based shape memory alloys was observed with the 2.0at. % H, which was due to the formation of TiO2, Ti2O3 oxide films. Moreover, the best wear resistance with the lower wear rate of 0.9347×10-6 mm3/N mm was obtained in (Ti-13V-3Al)99.2H0.8 shape memory alloy, due to the integrated effects of higher microhardness, reinforcing effect of α phase and lubrication effect of the hydrogenated film.

Palladium-Catalyzed C(sp3)-H Activation in A Monoterpene-Based Compound Under Mild Conditions: A Combined Experimental and Theoretical Mechanistic Study.

A rare example of the palladium-catalyzed sp3 C-H bond activation in a monoterpene-based compound has been observed in the reaction of PdCl2 with a (+)-3-carene-based ligand HL (HL=N-((1aS,3S,7bR)-1,1,3-trimethyl-7-phenyl-5-(pyridin-2-yl)-1a,2,3,7b-tetrahydro-1H-cyclopropa[f]quinolin-3-yl)acetamide), which yielded the [PdLCl] complex. In contrast to the vast majority of C(sp3)-H activation reactions which require prolonged heating and mixing due to the inert character of the corresponding bond, the reaction reported herein proceeds rapidly under mild conditions. A theoretical insight into the ligand deprotonation has been performed by DFT calculations. The mechanism of the C-H activation involves (i) simultaneous coordination of the CH3 group of HL to the Pd2+ ion and decoordination of the Cl- anion with consequent formation of a Cl⋅⋅⋅H-N hydrogen bond with the amide group, (ii) approximation of the out-of-sphere Cl- anion to one of the hydrogen atoms of the CH3 group mediated by the crane motion of the amide group and (iii) the ejection of the HCl molecule, which increases the entropy of the system and serves as a driving force for the reaction.