Internal Hydrogen Research Articles

Carbon Atom Reactivity with Amorphous Solid Water: H2O-Catalyzed Formation of H2CO.

We report new computational and experimental evidence of an efficient and astrochemically relevant formation route to formaldehyde (H2CO). This simplest carbonylic compound is central to the formation of complex organics in cold interstellar clouds and is generally regarded to be formed by the hydrogenation of solid-state carbon monoxide. We demonstrate H2CO formation via the reaction of carbon atoms with amorphous solid water. Crucial to our proposed mechanism is a concerted proton transfer catalyzed by the water hydrogen bonding network. Consequently, the reactions 3C + H2O → 3HCOH and 1HCOH → 1H2CO can take place with low or without barriers, contrary to the high-barrier traditional internal hydrogen migration. These low barriers (or the absence thereof) explain the very small kinetic isotope effect in our experiments when comparing the formation of H2CO to D2CO. Our results reconcile the disagreement found in the literature on the reaction route C + H2O → H2CO.

An Fe–Ni–Cr–H interatomic potential and predictions of hydrogen-affected stacking fault energies in austenitic stainless steels

While Fe–Ni–Cr austenitic stainless steels exhibit relatively good resistance to hydrogen embrittlement, they still suffer from significant degradation of ductility, fatigue and fracture properties in gaseous hydrogen environments. Experimental studies in the literature suggest that hydrogen reduces stacking fault energy in austenitic stainless steels. This phenomenon causes a large separation of partial dislocations and lower propensity for cross-slip. Whereas lower stacking fault energy does not correlate well with loss of ductility in the absence of hydrogen, lower stacking fault energy trends toward greater loss of ductility when hydrogen is present. Calculations of stacking fault energy are challenging for austenitic stainless steels. One main issue is that in alloys, stacking fault energy is not a single value but rather varies depending on local composition. Herein, we first report an Fe–Ni–Cr–H quaternary interatomic potential and then use this potential to perform time-averaged molecular dynamics simulations to calculate stacking fault energies for tens of thousands of realizations of local compositions for selected stainless steels alloys with and without internal hydrogen. From statistical analyses, our results suggest that hydrogen reduces stacking fault energy, which likely impacts deformation mechanisms of Fe–Ni–Cr austenitic stainless steels when exposed to hydrogen environments. We then perform validation MD simulation tests to show that hydrogen indeed statistically increases the stacking fault widths due to statistically reduced stacking fault energies.

Numerical analysis for characterizing hydrogen embrittlement behaviors induced in STS316L stainless steel using an in-situ small-punch test

In-situ small-punch (SP) tests have recently been used to characterize the susceptibility to hydrogen embrittlement (HE) of various steels. Most techniques for HE evaluation have been based on the use of initially hydrogen pre-charged specimens. However, in internal hydrogen conditions, consistent results are not obtained for the embrittlement and fracture behavior in comparison to those under external hydrogen conditions. In this study, an in-situ SP test was used to evaluate the HE susceptibility in 316L austenitic stainless steel. The test was carried out in 10-MPa gas environments at room temperature (RT) and below with different punch velocities. The results showed that at 10-MPa H2 gas, STS316L steel exhibited good resistance to HE at RT and −10 °C. However, the susceptibility to HE depended on the test temperature and punch velocity. A numerical simulation of the SP test was used to systematically compensate for the insufficient explanation of the crack formation that occurred during in-situ SP testing and to investigate the interaction of the punch velocity and the stress field in regard to the HE effect. The numerical analysis results support the experimental findings and provide a detailed explanation of factors such as the friction coefficient, strain rate, and stress state which lead to crack formation through their interaction in hydrogen-embrittled steel.

Cation-anion interaction effect on the nonlinear optical behavior of pyridinium-based ionic liquids

Influence of the cation–anion interaction (expressed as internal hydrogen bonds) on the nonlinear optical properties (dipole moment, polarizability, anisotropy of polarizability and first-order hyperpolarizability) for the ionic liquids pyridinium hydrogen sulfate (PHS) and pyridinium bis(dihydrogen phosphate) (P2HP) was investigated in this paper. It was achieved analyzing vibrational modes (FT-IR) and electronic transitions (UV–vis) in PHS and P2HP. Molecular geometry of the title compounds was optimized by means of density functional theory calculations at B3LYP/6–311++G(2d,2p) level.Structural analysis exposed stronger internal hydrogen bonds (H7···O3 and H18···O4) between cationic and anionic fragments in the pyridinium hydrogen sulfate than these (H26···O4 and H25···O12) in pyridinium bis(dihydrogen phosphate). These observations are confirmed by FT-IR and UV–vis methods, where: (i) the infrared bands due to H···O and N–C interactions in P2HP appear at lower frequencies than the same ones in the spectrum of PHS and (ii) the n → π* electron transitions in PHS are more pronounced in comparison with these in P2HP. Based on the weaker cation–anion interaction in P2HP with respect to PHS, the former one is characterized with a remarkably higher first-order hyperpolarizability value. Hence, the ionic liquid P2HP was referred as a better nonlinear optical material than PHS.

Concise Modular Synthesis and NMR Structural Determination of Gallium Mycobactin T.

A modular synthesis of mycobactin T and its N-acetyl analogue is reported in a route that facilitates permutation of the lipid tails. A key feature is the generation of N(α)-Cbz-N(ε)-benzyloxy-N(ε)-Boc-lysine (A4) with methyl(trifluoromethyl)dioxirane in 59% yield. Selective hydroxamate N-acylation was achieved with acyl fluorides, enabling installation of lipids tails in the final step. O-Benzyl-dehydrocobactin T (B4) was prepared by modifying a known five-step sequence with an overall yield of 49%. 2-Hydroxyphenyl-4-carboxyloxazoline (C3) was prepared from 2-hydroxybenzoic acid and l-serine methyl ester in three steps with an overall yield of 55%. Ester coupling of A4 and B4 with EDCI afforded MbI-1 in 73% yield. Catalytic hydrogenation with Pd/BaSO4 and 50 psi of H2 simultaneously effected alkene reduction and debenzylation to afford MbI-2 in 96% yield. Fragment C3 was converted into acyl fluoride C4, which coupled with MbI-2 to afford MbI-3 in 51% yield. Finally, Boc-removal with HCl/EtOAc and treatment of the resultant hydroxylamine with stearyl fluoride furnished mycobactin T in 65% yield. Overall, the yield is 4% over 14 steps. The gallium mycobactin T-N-acetyl derivative (GaMbT-NAc) structure was determined by 1H NMR. The structure shows an octahedral Ga and two internal hydrogen bonds between peptidic N-Hs and two of the oxygen atoms coordinating Ga.

The KOALA experiment for (anti)proton–proton elastic scattering

The KOALA experiment measures the differential cross section of (anti)proton–proton elastic scattering over a wide range of four-momentum transfer squared |t| from 0.0008 to 0.1 (GeV/c)2. These data are essential input for the PANDA experiment to reach the desired absolute precision for the integrated luminosity determination. The KOALA experiment is based on fixed target kinematics and uses an internal hydrogen cluster jet target. The wide range of |t| is achieved by measuring the total kinetic energy of the recoil protons near 90°. The recoil detector consists of silicon and germanium single-sided strip sensors with an energy resolution of approximately 20keV and 30keV (FWHM), respectively. A forward detector consisting of two layers of plastic scintillators measures the elastically scattered beam particles in the forward direction close to the beam axis. By requiring a coincidence of the forward detector with the recoil detector, the large background at small recoil angles is suppressed, thereby improving the identification of elastic scattering events in the low |t| range. The KOALA setup has been installed and commissioned with proton beam at COSY in order to validate the detector by measuring the proton–proton elastic scattering. The results from this commissioning are presented here.

Palaeosciences in 2050: Some Thoughts

One of the advantages of writing about futuristic scenarios, is that an elderly author has little chance of facing criticism. The Indian born author, George Orwell knew this fact well, when he published his famous novel of life and times 1984 in the summer of 1949. He painted a rather dark, sombre picture of life in 1984 keeping in mind the dark clouds of intrigue and conspiracy that hung over the post WWII world at the time. 1984 came and went and was not as eventful as George Orwell had imagined and most of his predictions went unnoticed. Encouraged by this, I venture to see 2050 as a very crowded planet (with well over 9 billion inhabitants) competing for resources, conscious of the need to preserve and conserve the earth for future generations, sentiments that were not a priority in 1950 when we were rebuilding after 2 world wars. The factor that would dominate all activity is the restriction of the amount of carbon emissions by human actions. The Paris agreement of 2015 points to limiting temperature increase on our planet to below 2o C from start of industrial revolution. Reliance on fossil fuels will be reduced; rise of renewable energy and lower carbon economy will take shape. By 2050, we will have a very electrified world with more electric vehicles replacing internal combustion engines and hydrogen replacing natural gas. These issues will dominate on how and on what topics we will do our research and what challenges need to be tackled. The changes will help mankind towards sustainability, alleviating climate hazards and improving quality of life on our planet. But will that be enough to reverse the course of the planet?

Hydrogen radical-shuttle (HRS)-enabled photoredox synthesis of indanones via decarboxylative annulation

Hydrogen atom transfer (HAT) process is a powerful and effective strategy for activating C-H bonds followed by further functionalization. Intramolecular 1,n (n = 5 or 6)-HATs are common and frequently encountered in organic synthesis. However, intramolecular 1,n (n = 2 or 3)-HAT is very challenging due to slow kinetics. Compared to proton-shuttle process, which is well established for organic synthesis, hydrogen radical-shuttle (HRS) is unexplored. In this work, a HRS-enabled decarboxylative annulation of carbonyl compounds via photoredox catalysis for the synthesis of indanones is developed. This protocol features broad substrate scope, excellent functional group tolerance, internal hydrogen radical transfer, atom- and step-economy. Critical to the success of this process is the introduction of water, acting as both HRS and hydrogen source, which was demonstrated by mechanistic experiments and density functional theory (DFT) calculations. Importantly, this mechanistically distinctive HAT provides a complement to that of typical proton-shuttle-promoted, representing a breakthrough in hydrogen radical transfer, especially in the inherently challenging 1,2- or 1,3-HAT.

Biodiesel (methyl oleate) synthesis in the presence of pyridinium and aminotriazolium acidic ionic liquids: Kinetic, thermodynamic studies

Kinetics and thermodynamics of biodiesel (methyl oleate) synthesis using the protic ionic liquids pyridinium hydrogen sulfate (PHS), pyridinium nitrate (PN) and 4-amino-1H-1,2,4-triazolium nitrate (ATN) as catalysts are studied in the current work for the first time. Rate of the biodiesel production is directly related to acidity of the ionic liquids used and their internal hydrogen bonding extent. A detailed thermodynamic analysis on the title reaction is conducted as well. To optimize the reaction conditions, influence of the reaction temperature (25–55 °C), initial alcohol-to-acid molar ratio (1.0–15.0) and catalyst loading (5–15 wt% with respect to the substrate mass) is investigated in details. Catalyst reusability is evaluated for five cycles. Based on the experimental data, a plausible mechanism of biodiesel synthesis is offered. Catalytic performance of the PHS sample in the biodiesel synthesis is remarkably higher than that of the nitrate anion-based ionic liquids. Reaction temperature of 55 °C, an initial reactants molar ratio of 7.0 and a catalyst loading of 10 wt% are established as optimal conditions for the process of biodiesel production. Values of 43.09 kJ/mol and 91.29 × 105 l/mol × min are calculated as activation energy and pre-exponential factor, respectively. ΔSr° and ΔHr° for the process of biodiesel synthesis are found to be 42.32 J/mol × K and 9.64 kJ/mol, respectively. Moreover, ΔH≠ (40.49 kJ/mol) and ΔS≠ (−162.31 J/mol × K) are established as well. The respective ΔGr° (−4.241 kJ/mol) and ΔG≠ (93.727 kJ/mol) at reaction temperature of 55 °C are obtained.

Crystal structure, chemical bonds nature and thermodynamic functions for the new ionic liquid pyridinium bis(dihydrogen phosphate)

A crystal structure (confirmed via single X-ray diffraction analysis) of the new ionic liquid pyridinium bis(dihydrogen phosphate) ([H–Pyr]+([H2PO4]–)2) is presented in this work for the first time. Optimized molecular geometry of [H–Pyr]+([H2PO4]–)2 is determined by means of density functional theory (DFT) at B3LYP/6-311++G(2d,2p) level and a good correlation between experimental and calculated structural parameters (bond lengths and angles) is revealed. Different types of intramolecular hydrogen bonds between [H–Pyr]+ and [H2PO4]– fragments are found to stabilize the title compound structure. Moreover, a hydrogen bond between the dihydrogen phosphate anions is also detected. The Quantum theory of atoms in molecules and natural bond orbital analysis have been performed to elucidate the chemical bonds nature and electron density delocalization, respectively in [H–Pyr]+([H2PO4]–)2. The standard thermodynamic functions specific heat capacity (Cp,m∘), enthalpy and entropy for the title compound are calculated. Polynomial equations for solid and liquid phases describe the temperature dependence of Cp,m∘for [H–Pyr]+([H2PO4]–)2 sample. A relationship between the internal hydrogen bonding, chemical bonds nature and the standard thermodynamic functions is presented.

Structure and Glass Transition Temperature of Amorphous Dispersions of Model Pharmaceuticals with Nucleobases from Molecular Dynamics.

Glass transition temperature (Tg) is an important material property, which predetermines the kinetic stability of amorphous solids. In the context of active pharmaceutical ingredients (API), there is motivation to maximize their Tg by forming amorphous mixtures with other chemicals, labeled excipients. Molecular dynamics simulations are a natural computational tool to investigate the relationships between structure, dynamics, and cohesion of amorphous materials with an all-atom resolution. This work presents a computational study, addressing primarily the predictions of the glass transition temperatures of four selected API (carbamazepine, racemic ibuprofen, indomethacin, and naproxen) with two nucleobases (adenine and cytosine). Since the classical non-polarizable simulations fail to reach the quantitative accuracy of the predicted Tg, analyses of internal dynamics, hydrogen bonding, and cohesive forces in bulk phases of pure API and their mixtures with the nucleobases are performed to interpret the predicted trends. This manuscript reveals the method for a systematic search of beneficial pairs of API and excipients (with maximum Tg when mixed). Monitoring of transport and cohesive properties of API–excipients systems via molecular simulation will enable the design of such API formulations more efficiently in the future.

Wear Resistance of Spark Ignition Engine Piston Rings in Hydrogen-Containing Environments

We describe the external and internal hydrogen interaction on contacting surfaces in the “cylinder–piston rings” friction coupling. Under the influence of high temperatures and pressure, the oil in the combustion chamber at a temperature up to 1473 K decomposes and forms small amounts of water. External hydrogen (H2) is subsequently formed. Hydrogen removal from the piston rings reduces the heterogeneity of the structure, residual stresses, and uneven physical and chemical properties of the near-surface layers, which reduces the stress concentration and, as a consequence, results in an improvement in the performance characteristics of the surface layers of the friction couple “cylinder-piston rings” of the spark ignition engine.

Structures of guaiacol and the guaiacol-argon van der waals complex from rotational spectroscopy of guaiacol isotopologues

High-resolution rotational spectra were recorded for guaiacol and eight isotopologues as well as the guaiacol-argon van der Waals complex using a resonant-cavity Fourier transform microwave spectrometer. The monomer spectra were assigned to an anti-syn conformation with an internal hydrogen bond from the hydroxyl group to the methoxy oxygen. Atomic coordinates of the carbon and hydroxyl hydrogen atoms were determined from the experimental moments of inertia using the Kraitchman method, and these coordinates are in excellent agreement with the corresponding coordinates in the MP2/6-311++G(d,p) model structure. The recorded rotational transitions showed no evidence for methyl internal rotation tunneling, and a potential energy scan (ωB97XD/6-311++G(d,p)) identified a 1006.0 cm−1 barrier to methyl internal rotation. The rotational spectrum of guaiacol-argon was used determine the location of the argon with respect to the anti-syn monomer conformation: RCM = 3.533 Å, θ = 105.4 °, and χ = -100.0 °. The argon is positioned towards the hydroxyl and methoxy groups because of relatively strong van der Waals interactions between argon and the oxygen atoms.

Tracking the interaction between single-wall carbon nanotube and SARS-Cov-2 spike glycoprotein: A molecular dynamics simulations study

COVID-19, a newly discovered type of coronavirus, is the cause of the pandemic infection that was first reported in Wuhan, China, in December 2019. One of the most critical problems in this regard is to identify innovative drugs that may reduce or manage this global health concern. Nanoparticles have shown a pivotal role in drug delivery systems in recent decades. The surface of nanoparticles could be covered by a layer composed of different biomolecules (e.g., proteins and macromolecules) following the incubation with a biological fluid. This protein-rich layer is called “Protein Corona.” In this study, an all-atom molecular dynamics simulation was used for investigating the monomeric B domain of the spike glycoprotein due to its role in the accessibility of the spike glycoprotein to single-wall carbon nanotubes (SWCNTs). The interaction energy values between the carbon nanotube and B domain of the viral spike glycoprotein were evaluated. The obtained results, based on Lennard-Jones potentials, demonstrated that SWCNTs had an affinity to the B domain of the S1 subunit in the spike glycoprotein. The adsorption of SWCNTs on the B domain surface led to a significant change in solvent-accessible surface, internal hydrogen bonds, and finally in the tertiary structure, which could provide a reasonable method to impede the interaction between the angiotensin-converting enzyme II and SARS-CoV-2 spike glycoprotein. A decrease in the mean square displacement of the B domain was shown after the adsorption of SWCNTs as a result of increasing the hydrophobic-hydrophilic properties of the B domain. The arrangement of SWCNTs on the B domain surface and their interaction using the 2-acetamido-2-deoxy-β-d-glucopyranose group (988, 991, and 992) demonstrated that a change in the affinity of the S1 subunit could be used as a barrier to viral replication. The analysis of the SWCNT-B domain complex indicated that the presence of SWCNTs is able to cause alterations in the S1 subunit of the spike protein, and these nanotubes could be employed for further in-vitro and in-vivo antiviral studies. Also, SWCNTs are able to be utilized in drug delivery systems.

Interpretation of complex, tensile-fracture phenomena in precipitation-hardened, martensitic stainless steels, 17-4PH, in presence of hydrogen

Hydrogen-induced ductility loss in two precipitation-hardened, martensitic stainless steels was investigated via tensile testing with internal hydrogen, revealing it to be more significant with a higher hydrogen content or tensile strength. A lower hydrogen content and tensile strength resulted in quasi-cleavage fracture and considerable plastic strain, suggesting that hydrogen–dislocation interaction contributed to the loss in ductility. When either the hydrogen content or the tensile strength increased, the intergranular and cleavage surfaces were incorporated into the quasi-cleavage surface, a phenomenon attributed to the hydrogen-induced reduction of cohesive strength. Such a reduction was confirmed using impact tests at cryogenic temperatures, implying that some mechanisms were responsible for the loss in ductility.

Facile Synthesis of Matrix‐Free Room‐Temperature Phosphorescent Nitrogen‐Doped Carbon Dots and Their Application as Security Inks

AbstractRoom‐temperature phosphorescent (RTP) nitrogen‐doped carbon dots (N‐CDs) have attracted great interest but their efficiency is usually dependent on a solid matrix. Developing efficient matrix‐free RTP CDs is still a great challenge. Here, a simple strategy is reported to synthesize efficient matrix free RTP N‐CDs from citric acid (CA) and basic fuchsine (BF) via a single step hydrothermal process. The synthesized N‐CDs show strong fluorescence in aqueous solution and the solid state, and the RTP lifetime is long‐lived (51.9 ms at 298 K). The phosphorescence of the N‐CDs is attributed to the formation of an internal hydrogen bonded network by the organic polymers on the surface of the N‐CDs. This reduces the nonradiative transitions of the triplet excitons and mitigates oxygen quenching. The application of N‐CDs as security inks is demonstrated.

Synthesis, crystal structure and properties of hepta(ammonium) penta(1H-imidazol-3-ium) paratungstate B tetrahydrate

An attempted isolation of the elusive diammonium tetraoxidotungstate (NH4)2[WO4] as its imidazole (Im) adduct resulted in the serendipitous formation of hepta(ammonium) penta(1H-imidazol-3-ium) paratungstate B tetrahydrate having formula [NH4]7[ImH]5[W12O42]·4H2O (1). The synthesis, vibrational spectra, crystal structure and thermal study of the mixed cationic paratungstate tetrahydrate 1 are reported. The structure of 1 consists of a centrosymmetric paratungstate [W12O42]12– anion devoid of internal hydrogen atoms, which is charge balanced by ammonium and 1H-imidazol-3-ium cations. One of the four unique NH4 + cations and one of the three crystallographically independent 1H-imidazol-3-ium cations are disordered around a center of inversion. The cations, [W12O42]12– anion and the unique lattice water molecules are joined with the aid of five varieties of hydrogen bonding interactions. A comparative study of twenty-three partaungstates is described. Thermal decomposition of 1 results in the formation of monoclinic tungsten trioxide WO3.

Alkane/Water Partition Coefficient Calculation Based on the Modified AM1 Method and Internal Hydrogen Bonding Sampling Using COSMO-RS.

We introduce a physics-based model for calculating partition coefficients of solutes between water and alkanes, using a combination of a semi-empirical method for COSMO charge density calculation and statistical sampling of internal hydrogen bonds (IHBs). We validate the model on the experimental partition data (∼3500 molecules) of small organics, drug-like molecules, and statistical assessment of modeling of proteins and ligand drugs. The model combines two novel algorithms: a bond-correction method for improving the calculation of COSMO charge density from AM1 calculations and a sampling method to deal with IHBs. From a comparison of simulated and experimental partition coefficients, we find a root-mean-square deviation of roughly one log 10 unit. From IHB analysis, we know that IHBs can be present in two states: open (in water) and closed (in apolar solvent). The difference can lead to a shift of as much as two log 10 units per IHB; not taking this effect into account can lead to substantial errors. The method takes a few minutes of calculation time on a single core, per molecule. Although this is still much slower than quantitative structure–activity relationship, it is much faster than molecular simulations and can be readily incorporated into any screening method.

Theoretical Design, Synthesis, and In Vitro Neurobiological Applications of a Highly Efficient Two-Photon Caged GABA Validated on an Epileptic Case.

In this paper, we present an additional, new cage-GABA compound, called 4-amino-1-(4′-dimethylaminoisopropoxy-5′,7′-dinitro-2′,3′-dihydro-indol-1-yl)-1-oxobutane-γ-aminobutyric acid (iDMPO-DNI-GABA), and currently, this compound is the only photoreagent, which can be applied for GABA uncaging without experimental compromises. By a systematic theoretical design and successful synthesis of several compounds, the best reagent exhibits a high two-photon efficiency within the 700–760 nm range with excellent pharmacological behavior, which proved to be suitable for a complex epileptic study. Quantum chemical design showed that the optimal length of the cationic side chain enhances the two-photon absorption by 1 order of magnitude due to the cooperating internal hydrogen bonding to the extra nitro group on the core. This feature increased solubility while suppressing membrane permeability. The efficiency was demonstrated in a systematic, wide range of in vitro single-cell neurophysiological experiments by electrophysiological as well as calcium imaging techniques. Scalable inhibitory ion currents were elicited by iDMPO-DNI-GABA with appropriate spatial–temporal precision, blocking both spontaneous and evoked cell activity with excellent efficiency. Additionally, to demonstrate its applicability in a real neurobiological study, we could smoothly and selectively modulate neuronal activities during artificial epileptic rhythms first time in a neural network of GCaMP6f transgenic mouse brain slices.

Preparation and characterization of polyvinyl alcohol/ sodium alginate/carboxymethyl cellulose composite hydrogels with oriented structure

ABSTRACT In order to control complex motion behavior in organisms, most biological tissues have highly oriented structures and anisotropic mechanical properties, such as articular cartilage, muscle, skin and blood vessel. In this study, inspired by the directional structure and excellent mechanical properties of biological soft tissues, polyvinyl alcohol/carboxymethyl cellulose hydrogels with different contents of sodium alginate were prepared by combining freeze-thaw and prestretching methods. Compared with SEM images without pre-stretch hydrogels, there are obvious ordered pore structures in the pre-stretch samples along the tensile direction, and the network structure becomes denser. XRD and FTI R results indicate that the introduction of SA and CMC increases the number of internal hydrogen bond and forms new covalent bonds. The tensile strength of the hydrogel without annealing and stretching treatments is only 0.41MPa. After annealing and stretching treatments, the tensile strength of the hydrogel is increased to 0.93MPa. Furthermore, the creep deformation of hydrogel was reduced from 1.08 mm to 0.27 mm by annealing and stretching treatments. To sum up, these results suggested that PVA/SA/CMC composite hydrogels with oriented structure might have potential applications in soft tissue repair and other biomaterials.