Search

Designing catalyst to achieve ammonia synthesis at mild conditions is a meaningful challenge in catalysis community. Defective g-C3N4 nanosheet supported single-cluster ruthenium and iron catalysts were investigated for their ammonia synthesis performance. Based on density functional theory (DFT) calculations and microkinetic simulations, Ru3 single-cluster anchored on defective g-C3N4 nanosheet (Ru3/Nv-g-C3N4) has a turnover frequency (TOF) 5.8 times higher than the Ru(0001) step surface at industrial reaction conditions of 673 K and 100 bar for ammonia synthesis. In other words, similar TOFs could be achieved on Ru3/Nv-g-C3N4 at much milder conditions (623 K, 30 bar) than on Ru(0001) (673 K, 100 bar). Our computations reveal the reaction proceeds parallelly on Ru3/Nv-g-C3N4 through both dissociative and alternative associative mechanisms at typical reaction conditions (600–700 K, 10–100 bar); N-N bond cleavage of *N2 and *NNH from the two respective pathways controls the reaction collectively. With increasing temperatures or decreasing pressures, the dissociative mechanism gradually prevails and associative mechanism recedes. In comparison, Fe3/Nv-g-C3N4 catalyst shows a much lower catalytic activity than Ru3/Nv-g-C3N4 by two orders of magnitude and the reaction occurs solely through the dissociative pathway. The finding provides a prospective candidate and deepens the mechanistic understanding for ammonia synthesis catalyzed by single-cluster catalysts (SCCs). [ABSTRACT FROM AUTHOR]

In vitro kinetic measurements allow mechanistic characterization of binding interactions and are particularly valuable throughout drug discovery, from confirmation of on-target binding in early discovery to fine-tuning of drug-binding properties in pre-clinical development. Early chemical matter often exhibits transient kinetics, which remain challenging to measure in a routine drug discovery setting. For example, characterization of irreversible inhibitors has classically relied on the alkylation rate constant, yet this metric fails to resolve its fundamental constituent rate constants, which drive reversible binding kinetics and affinity complex inactivation. In other cases, extremely rapid association processes, which can approach the diffusion limit, also remain challenging to measure. To address these limitations, a practical kinetic rebinding assay is introduced that may be applied for kinetic screening and characterization of compounds. The new capabilities afforded by this probe-based assay emerge from mixed-phase partitioning in a flow-injection configuration and have been implemented using label-free biosensing. A finite element analysis-based biosensor model, simulating inhibition of rebinding within a crowded hydrogel milieu, provided surrogate test data that enabled development and validation of an algebraic model for estimation of kinetic interaction constants. An experimental proof-of-principle demonstrating estimation of the association rate constant, decoupled from the dissociation process, provided further validation. [ABSTRACT FROM AUTHOR]

High-performance polymer materials that can exhibit distinguished mechanical properties have been developed based on material design considering energy dissipation by sacrificial bond dissociation. We now propose co-continuous network polymers (CNPs) for the design of tough polymer materials. CNP is a new composite material fabricated by filling the three-dimensionally continuous pores of a hard epoxy monolith with any cross-linked polymer having a low glass transition temperature (Tg). The structure and mechanical properties of the CNPs containing epoxy resins, thiol-ene thermosets, and polyacrylates as the low-Tg components were investigated by differential scanning calorimetry, dynamic mechanical analysis, tensile tests as well as scanning electron microscopic observations and non-destructive 3D X-ray imaging in order to clarify a mechanism for exhibiting an excellent strength and toughness. It has been demonstrated that the mechanical properties and fractural behavior of the CNPs significantly depend on the network structure of the filler polymers, and that a simultaneous high strength and toughness are achieved via the sacrificial fracture mechanism of epoxy-based hard materials with co-continuous network structures. [ABSTRACT FROM AUTHOR]

Gas-hydrate occurrences along the Chilean margin have been widely documented, but the processes associated with fluid escapes caused by the dissociation of gas hydrates are still unknown. We report a seabed morphology growth related to fluid migration offshore Lebu associated with mud cones by analysing oxygen and deuterium stable water isotopes in pore water, bathymetric, biological and sedimentological data. A relief was observed at − 127 m water depth with five peaks. Enrichment values of δ18O (0.0–1.8‰) and δD (0.0–5.6‰) evidenced past hydrate melting. The orientation of the relief could be associated with faults and fractures, which constitute pathways for fluid migration. The benthic foraminifera observed can be associated with cold seep areas. We model that the mud cones correspond to mud growing processes related to past gas-hydrate dissociation. The integration of (i) the seismic data analysis performed in the surrounding area, (ii) the orientation of our studied relief, (iii) the infaunal foraminifera observed, (iv) the grain size and (v) the total organic matter and isotope values revealed that this area was formerly characterised by the presence of gas hydrates. Hence, this part of the Chilean margin represents a suitable area for investigating fluid-migration processes. [ABSTRACT FROM AUTHOR]

Singly and multiply charged molecular ions are found in diverse environments and hold relevance for a wide range of research areas like combustion chemistry, accelerator physics, atmospheric sciences, plasma physics, astrophysics etc. Molecular dications are of special significance as they can be generated and studied comparatively easily in laboratory experiments. And they have enabled exploration of new and exciting phenomenon such as hydrogen migration, inter-atomic Coulombic decay, plasmonic excitations, orbital tomography etc. The lifetime of a molecular dication is one of its fundamental characteristics, whose measurement contributes to strengthening ab initio calculations and in predicting the concentration of its dissociation products. Most of the already reported lifetimes of molecular dications are in the range of nanoseconds to seconds and metastable states with lifetimes of the order of picoseconds have only been theoretical predicted and an experimental verification is pending. We present a method of measuring subrotational lifetimes of molecular dications formed in three-body sequential breakup of polyatomic molecular precursors. Specifically, we have measured the subrotational lifetime of SO 2 + , which is formed as an intermediate in the three-body sequential fragmentation of SO 2 3 + . The lifetime against dissociation is determined to be a fraction of the rotational period of SO 2 + and is of the order of few picoseconds. The method proposed is general and is not restricted to triatomic precursors. [ABSTRACT FROM AUTHOR]

Magnetic porous manganese ferrite nanoparticles (MnxFe3-xO4) with diverse ingredient Mn/Fe mole ratios were synthesized to degrade sulfamethoxazole (SMX) antibiotic residues involving peroxymonosulfate (PMS) dissociation to produce free radical SO4•−, •OH and singlet oxygen 1O2 in the absence of heat and light. With the increase in proportion of manganese, the degradation efficiency of SMX increased from 19 to 70% in 30 min. The removal efficiency of SMX increased following the concentration increase of PMS (from 1 ~ 10 mM). After 60 min, the total organic carbon went down by 20%, and the concentration of NH4+ and NO3− accumulated obviously simultaneously. EPR study and chemical probe method, depending on scavenging revealed that SO4•−, •OH and 1O2 were generated and contributed to the degradation system. Based on the capture of eleven decomposition by-products by LC/MS, two different degradation pathways of SMX were determined, mainly consisting of cleavage of the S–N bond, hydroxylation of benzene and heterocyclic ring, oxidation of amino group and ring-opening cleavage processes. The nanoparticle reuse tests showed that the porous magnetic manganese ferrite nanoparticles could still maintain a high degradation efficiency after five oxidative degradation reactions. The magnetic porous manganese ferrite nanocrystals could activate the PMS to oxidize SMX antibiotic residue without additional energy. [ABSTRACT FROM AUTHOR]

Simultaneous removal of NOx and SO2 is carried out by an oxidation-absorption process, which NO oxidized by active hydroxyl radicals (·OH) derived from catalytic decomposition of vaporized H2O2 over Fe3O4/TiO2 and then adsorbed by NaOH solution along with SO2. Fe3O4/TiO2 synthesized by wet impregnation method with an additional reduction under H2 atmosphere was characterized by XRD, FTIR, BET, XPS, and VSM analysis. Effects of H2O2 concentration, H2O2 injection rate, reaction temperature, gas flow rate, and flue gas component on simultaneous removal were investigated. The experimental results show that NO can be effectively oxidized by highly reactive ·OH radicals generated from H2O2 decomposition over Fe3O4/TiO2 catalyst, and removal efficiencies of 93.31% for NO, 85.90% for NOx, and 100% for SO2 were obtained. The surface zero-valent iron (Fe0) and divalent iron (Fe2+) are the key factors of the catalytic oxidation with hydroxyl radical. H2O2 adsorption and dissociation mechanism on catalyst surface was studied using DFT calculation. The calculation results demonstrate that H2O2 prefers to dissociate on iron containing surface, and ·OH radicals generation follow by Haber-Weiss (H–W) mechanism. The stable oxidative product of HNO2 and HNO3 were generated through NO/NO2 and H2O2 co-adsorption on the FeO/TiO2 (0 0 1) surface. [ABSTRACT FROM AUTHOR]

5-Hydroxy-1,3,6-trimethyluracil has been studied using 1H, 13C, and 15N NMR as well as UV spectroscopy. The constants and thermodynamic characteristics of its acid-base equilibrium in aqueous solutions have been determined. The stepwise mechanism of 5-hydroxy-6-methyluracil dissociation in aqueous solutions has been elucidated. [ABSTRACT FROM AUTHOR]

The correlation between chemical structure and predissociation dynamics has been evaluated for a series of linear and branched alkyl iodides with increasing structural complexity by means of femtosecond time-resolved velocity map imaging experiments following excitation on the second absorption band (B-band) at around 201 nm. The time-resolved images for the iodine fragment are reported and analyzed in order to extract electronic predissociation lifetimes and the temporal evolution of the anisotropy while the experimental results are supported by ab initio calculations of the potential energy curves as a function of the C-I distance. Remarkable similarities are observed for all molecules consistent with a major predissociation of the initially populated bound Rydberg states 6A″ and 7A′ through a crossing with the purely repulsive states 7A″, 8A′ and 8A″ leading to a major R + I*(2P1/2) (R = CH3, C2H5, n-C3H7, n-C4H9, i-C3H7 and t-C4H9) dissociation channel. The reported electronic predissociation lifetimes are found to decrease for an increasing size of the linear radical, reflecting the shifts observed in the position of the crossings in the potential energy curves, and very likely a greater non-adiabatic coupling between the initially populated Rydberg states and the repulsive states leading to dissociation induced by other coordinates associated to key vibrational normal modes. The loss of anisotropy is fully accounted for by the parent molecular rotation during predissociation and the rotational temperature of the parent molecule in the molecular beam is reasonably derived. [ABSTRACT FROM AUTHOR]

A method for isotope-selective infrared laser photodissociation of molecules characterized by a small (less than 0.25 cm−1) isotopic shift in the infrared absorption spectra is demonstrated by the example of the CF3Br molecule. The method is based on infrared laser excitation of molecules in a pulsed gas-dynamically cooled molecular flow interacting with a solid surface. The dissociation of molecules has been studied under three different conditions of their optical excitation: (i) in an undisturbed molecular flow, (ii) in a flow incident on the surface, and (iii) in the shock wave region formed in front of the surface upon its interaction of the incident molecular flow. It is shown that the dissociation yield upon the excitation of molecules in the shock wave and in the flow incident on the surface is 5–10 times higher than the dissociation yield upon excitation in the undisturbed flow, whereas the dissociation threshold in the former case is 3–5 times lower than that in the latter case. This allows the observation of the isotope selective dissociation at low energy densities of the exciting laser pulse (Φ ≤ 1.5–2.0 J/cm2). The enrichment factor Kenr(79Br/81Br) for the dissociation product Br2 is 0.85 ± 0.07 and 1.20 ± 0.09 for excitation of molecules in the incident flow and in the shock wave, respectively. [ABSTRACT FROM AUTHOR]

This work explores the adsorption and dissociation of AsH3 on Ni- and Cu-doped graphene by density functional theory (DFT) method. The most stable configurations, adsorption energy, and dissociation pathways are calculated thoroughly. In addition, the electron density difference (EDD), charge transfer, partial density of states (PDOS), and frontier orbitals are performed to describe the adsorption and dissociation process. The first dehydrogenation step on PG-Cu is easier than on PG-Ni due to the lower energy barrier. But further dissociation is becoming difficult in both systems. The third dehydrogenation steps are the rate determining steps for the whole reactions on PG-Ni and PG-Cu, as the energy barrier is 2.01 and 1.72 eV. In conclusion, PG-Ni and PG-Cu has similar AsH3 sensitivity, but the dissociation of AsH3 on PG-Cu is easier than on PG-Ni. It indicates that PG-Cu has better catalytic activity as an AsH3 removal catalyst than PG-Ni. This work may provide useful information for further experimental studies to develop efficient and long-term AsH3 removal catalysts. [ABSTRACT FROM AUTHOR]

Most fundamental studies of electrocatalysis are based on the experimental and simulation results obtained for bulk model materials. Some of these mechanistic understandings are inapplicable for more active nanostructured electrocatalysts. Herein, considering the simplest and most typical electrocatalytic process, the hydrogen evolution reaction, an alternative reaction mechanism is proposed for nanomaterials based on the identification of a new intermediate, which differs from those commonly known for the bulk counterparts. In-situ Raman spectroscopy and electrochemical thermal/kinetic measurements were conducted on a series of nanomaterials under different conditions. In high-pH electrolytes with negligible hydronium (H3O+) concentration in bulk phase, massive H3O+ intermediates are found generating on the catalytic surface during water dissociation and hydrogen adsorption processes. These H3O+ intermediates create a unique acid-like local reaction environment on nanostructured catalytic surfaces and cut the energy barrier of the overall reaction. Such phenomena on nanostructured electrocatalysts explain their widely observed anomalously high activity under high-pH conditions. Most of the current understanding on electrocatalysis is obtained on bulk catalysts but has not been fully verified on nanostructured materials. An alternative alkaline hydrogen evolution reaction mechanism is proposed here for nanostructured catalysts. [ABSTRACT FROM AUTHOR]

Valsartan is used for treating high blood pressure, congestive heart failure and to increase the chances of living longer after a heart attack and to reduce the mortality rate for people with left ventricular dysfunction following a heart attack. Regression analysis of the pH-spectra with REACTLAB and of the pH-titration curve with ESAB determined two close consecutive dissociation constants. MARVIN and ACD/Percepta predicted two protonation sites. In water a soluble anion L2− forms two sparingly soluble species LH−, LH2. Although adjusted pH less affected the spectral changes in the chromophore, p K a 1 T = 3.70 ± 0.12, p K a 2 T = 4.82 ± 0.08 at 25 °C and p K a 1 T = 3.44 ± 0.08, p K a 2 T = 4.67 ± 0.02 at 37 °C in an aqueous phosphate buffer were determined. By regression analysis of potentiometric pH-titration curves and p K a 1 T = 3.51 ± 0.01, p K a 2 T = 4.63 ± 0.01, at 25 °C and p K a 1 T = 3.44 ± 0.03, p K a 2 T = 4.51 ± 0.03 at 37 °C in an aqueous medium were estimated. Positive enthalpy values ΔH0(pKa1) = 10.33 kJ·mol−1, ΔH0(pKa2) = 17.70 kJ·mol−1 showed that the dissociation process was endothermic. The standard state Gibbs energy changes are ΔG0(pKa1) = 20.03 kJ·mol−1, ΔG0(pKa2) = 26.43 kJ·mol−1 at 25 °C and the ΔS0 at 25 °C and 37 °C are (ΔS0(pKa1) = − 32.56 J·K−1·mol−1, ΔS0(pKa2) = − 29.26 J·K−1·mol−1 at 25 °C and ΔS0(pKa1) = − 30.01 J·K−1·mol−1, ΔS0(pKa2) = − 25.92 J·K−1·mol−1 at 37 °C. [ABSTRACT FROM AUTHOR]

1-Ethyl-3-methylimidazolium acetate (EMIMAc) is an ionic liquid (IL) often investigated as a solvent, especially in the context of biopolymers and biomass pretreatment. A reduced solvent efficacy occurs upon the addition even of low amounts of water to EMIMAc. Molecular mechanisms have not yet been fully understood. It is expected that the functionality as hydrogen bond donor and acceptor is key for the solvent–solute interactions. In this work, we analyze the solvent efficacy of EMIMAc in terms of hydrogen–deuterium (H/D) exchange at the C(2)-position in mixtures with water or acetic acid added as proton donors. Low-field NMR spectroscopy and deuterated solvents are used for a time-resolved evaluation of H/D exchange reactions. The H/D exchange is also modeled to explore changes in the reaction kinetics as a function of the mixture composition. The significant difference in calculated rate constant values among the concentration regimes shows that the chosen model equations of a possible pseudo-first-order and second-order reaction mechanism including water dissociation do not cover all interaction phenomena that influence the exchange in the individual concentration ranges. However, the modeling also indicates that the investigated interaction of EMIM + and Ac - remains constant for concentrated IL mixtures containing 70 mol % of EMIMAc in water up to diluted mixtures as low as 30 mol % EMIMAc. This exemplifies the change between ions strongly associated in networks in concentrated mixtures suitable for biomass pretreatment and the much less associated anion–cation pairs in diluted mixtures which leads to the decreased efficiency of EMIMAc with increasing water content. [ABSTRACT FROM AUTHOR]

The use of bamboo for the fabrication of cellulose nanoparticles (CNs) in a facile and mild process is limited because of the existence of strong hydrogen bonding between the cellulose chains. Inspired by the synergistic effects of mechanochemistry, efficient cleavage of the strong hydrogen bonds and green manufacture of CNs with a high yield of 90.8% were realized through a shearing-assisted solvent pretreatment and a subsequent mechanochemical synergy process. In the one-pot tandem reaction, chemical action, thermodynamic interaction, and mechanical force induced by mechanochemistry created synergy to accelerate the dissociation of hydrogen bonds and ultimately regulate the disintegration of cellulose into nanofibers. The CNs showed special granular morphology and cellulose II crystal form. This method of process intensification diminished laborious intermediate purification steps and improved effectively the reaction efficiency. Thus, the study provides a facile and green approach for the large-scale production of CNs, and is expected to carry significant benefits in terms of economy and sustainability. [ABSTRACT FROM AUTHOR]

Various mechanisms of the primary act of gas-phase monomolecular thermal decomposition of nitrobenzene were studied theoretically. The following reactions were considered: radical decomposition with dissociation of the C-N bond, nitro-nitrite rearrangement to trans-phenyl nitrite and cis-phenyl nitrite, elimination of nitrous acid, as well as formation of 6(S)-7-oxa-8-azabicyclo[4.2.0]octa-1(8),2,4-triene 8-oxide were studied theoretically. Calculations were carried out for different temperatures using a number of density functional theory methods (B3LYP, wB97XD, CAM-B3LYP, MN12L, and PBE0) and basic sets (6-31G(d,p) and 6-31+G(2df,p)). The transition state of homolytic dissociation of the C-N bond was localized using the method of search for the structure corresponding to maximum value of the Gibbs free energy along the reaction coordinate. The structure thus found was used to evaluate the rate constants and the activation parameters at different temperatures. It was shown that not only radical decomposition, but also isomerization to trans-phenyl nitrite (at low temperatures) and cis-phenyl nitrite (at high temperatures) can contribute to the effective rate constant. [ABSTRACT FROM AUTHOR]

In order to investigate the influence of dissociation reaction on thermal decomposition of ammonium nitrate (AN), biochar was selected as an adsorbent to interfere with the dissociation of AN. The TG-DSC results showed that the notable exothermic reaction of AN with the presence of 2% or 7% biochar took place. The decomposition temperature of AN decreased with increasing amount of biochar. The notable knee point was found in the TG curves. The activation energy of AN with biochar in the initial stage was higher than that of AN itself. Remote sensing Fourier transform infrared experiments found biochar induced AN decomposition at about 190 °C, which was also confirmed by the TG-MS results. After dissociation reaction, HNO3 (g) and NH3 (g) were adsorbed and crystalline of AN was formed on the surface of biochar. With the increasing temperature, NH3 escaped from the surface of biochar, while HNO3 (g) was stayed in biochar. HNO3 (g) catalyzed the thermal decomposition of AN and also reacted with biochar. The results indicated that dissociation reaction of AN played an important role during AN thermal decomposition process. When dissociation reaction was changed, the thermal decomposition reaction of AN would also change, catalysis or inhibition AN thermal decomposition. It is a useful reference to guide the AN additives selection and to understand the mechanism for the AN decomposition accident. [ABSTRACT FROM AUTHOR]

Nitro-substituted 2,3,7,7,8,12,18-hexamethyl-5-phenyl-13,17-diethylporphins with nitro groups in positions 10 and 20 of the porphyrin core and in the para-position of the benzene ring have been synthesized. The structure of the obtained compounds has been confirmed by H1 NMR, UV, and IR spectroscopy as well as mass spectrometry. The kinetics of dissociation of zinc, copper, cobalt, and manganese complexes of the obtained porphyrins in proton-donor media has been studied. The stability of the porphyrin metal complexes has been related to the electronic effects of the substituents in the tetrapyrrole cycle and spatial distortion of the latter. [ABSTRACT FROM AUTHOR]

The internal dispersion structure of silica fillers in polymer matrix is significant for design and fabricating high-performance polymer composite. In order to explore the relationship between fillers spatial dispersion states and mechanical properties, we use superficial fluorescent labeling to achieve fillers visualization in polymer matrix with laser scanning confocal microscopy. Through the effect of fluorescent silane coupling agent, the uniform red fluorescence characteristics were shown on the silica surface. The 2D-planar and 3D-spatial dispersion states of silica fillers in rubber matrix can be accurately observed with fluorescence imaging technology. The results by Avizo software statistics show that high-content silica fillers in composite tend to undergo dissociation of aggregates. These dissociated small volume aggregates which facilitate the interaction between particles and rubber matrix to dissipate mechanical energy effectively and rapidly improve rubber toughness. This successful visualization method opens a new avenue in spatial dispersion description of fillers aggregates in organic-inorganic composite. [ABSTRACT FROM AUTHOR]

Types of dimers of aluminum and cobalt complexes of tetraanthraquinoneporphyrazines were identified. Thermodynamic characteristics of dissociation of the dimers in aqueous media were obtained. The kinetics of the deactivation of the triplet state of the aluminum complexes of sulfonated phthalocyanine and tetraanthraquinoneporphyrazine was studied. [ABSTRACT FROM AUTHOR]

Copper and cobalt complexes of nitro derivatives of planar and nonplanar derivatives of 5,15-diphenyl- 3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphyrin are synthesized and their stability in proton-donor media is investigated. It is established that the kinetic parameters of the dissociation reactions of copper and cobalt complexes of the studied porphyrins depends on the degree of deformation of the porphyrin macroring and the acceptor properties of NO2 groups. [ABSTRACT FROM AUTHOR]

Structural changes induced via ionization in an RDX lattice have been studied by using optimized [(RDX)2]0 conformers comprising eight combinations of four RDX isomers using DFT. Structures, dissociation enthalpy, and free energies of the resulting [(RDX)2]·+ clusters are calculated. The gas-phase and medium polarizable continuum model (PCM) calculations of the most stable [(RDX)2]·+ cluster produced similar structural results. Electron removal caused 75% of the [(RDX)2]·+ conformers to be unstable in their neutral isomeric composition and orientation. Charge distributions and structural factors indicate that [(RDX)2]·+ are in the general form RDX·+·RDX. Ionization causes charge polarization, hydrogen transfer, N-N dissociation, and assisted HONO formation in solid RDX. The assisted HONO formation occurs via and suggests hydrogen mobility within [(RDX)2]·+, causing a stabilization by a minimum of 114 kJ/mol more than the other conformers. The RDX conformational identity is a determining factor in the emerging dissociation pathways. The energy costs of ion-neutral dissociation are comparable to the hydrogen transfer and NO2 loss processes. Ionization of the RDX surface is expected to produce NO2 and HONO precursors of the NO+ ion observed previously. [ABSTRACT FROM AUTHOR]

We consider the problem of the choice of "free" particle interaction potential and the calculation of virial corrections for interatomic and ion–atom interaction in chemical models with dissociation reactions. We perform a critical analysis of the potentials given in the available literature, propose simple formulas to calculate virial corrections with allowance for the limitations of the two-particle phase space, and present recommendations to apply these formulas. [ABSTRACT FROM AUTHOR]

B1LYP, B1PW91, B3LYP, BHandH, BHandHLYP, BLYP, BP, CAMY-B3LYP, HTBS, KMLYP, LCYBLYP, LCY-BP86, LCY-PBE, LDA, M06, M06-2X, M06-HF, M06L, mPBE, mPW, MPW1K, MPW1PW, O3LYP, OLYP, OPBE, OPBE0, PBE, PBE0, PBEsol, PW91, revPBE, revTPSS, RPBE, TPSS, TPSSH, X3LYP, and HF methods are used to calculate the electron energy Eel of the reference GeO and C2H6 compounds in Slater basis sets QZ4P, aug-TZ2P, and TZ2P, as well as DZ for C2H6. The Eel values are recalculated into the bond breaking enthalpy D0(Ge-O) and formation enthalpy ΔfH2980 of ethane, and calculation errors for Eel are obtained at the variation limit. The ADF program settings are chosen so that they make it possible to attribute these Eel errors to the structure of DFT functionals. The dependence of the Eel values on the type (size) of the basis set is studied. It is demonstrated that when Eel is calculated for GeO, the optimum combination is DFT/TZ2P, where DFT = LCY-BLYP, LCY-BP86, LCY-PBE, CAMYB3LYP; for C2H6 it is DFT/TZ2P, where DFT = PBE0, M06, mPBE, OLYP. Errors in the calculation of the geometric parameters are studied. [ABSTRACT FROM AUTHOR]

In dissociation in nuclear track emulsion of 4.5 and 1 A GeV/c12C nuclei, the formation of triplets of α particles in the Hoyle state (the second excited state 0+) is observed. This state is identified by the invariant mass, calculated from pair angles in the α triples in approximation of conservation of momentum per nucleon of the parent nucleus. An estimate of the contribution of the Hoyle state to the dissociation of 12C→ 3α is 10-15%. [ABSTRACT FROM AUTHOR]

Eight dissociation constants of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis (methylene phosphonic acid) (DOTMP, H8L) were determined for the first time by potentiometric titration in water using the CHEMEQUI program. The stability constants of Ga3+ complexes with deprotonated forms of DOTMP were determined. The stability constant of the Ga3+ complex with the fully deprotonated DOTMP ligand, lg KML equal to 27.8, is higher than the corresponding constant for the Ga3+ complex with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), the ligand most widely used in radiopharmacy; it is also higher than the constant for the Ga3+ complex with plasma protein transferrin, which makes the DOTMP ligand very promising for the use in radiopharmacy. [ABSTRACT FROM AUTHOR]

The kinetics of dehydrochlorination of 1,1,1-trichloro-2,2-bis(4-nitrophenyl)ethane with sodium nitrite in dipolar aprotic solvents have been studied. Quantum chemical simulation of the process has been performed, and its thermodynamic parameters have been determined. The effects of dissociation and solvation on the rate constant have been considered. The reaction mechanism has been identified as E2H. [ABSTRACT FROM AUTHOR]

Chrysin is a bioflavonoid which possesses a wide range of important biological activities. In present study, we used a quantum mechanical approach to shed light on the antioxidant ability and antioxidant mechanism of chrysin to scavenge hydroxyl radical (˙OH) in solution phase. The analysis of the theoretical bond dissociation enthalpy (BDE) values and spin density of the radicals to determine the delocalization possibilities at B3LYP/6-311++G** level clearly shows the importance of the A-ring and the 7-OH group in antioxidant reactivity. In the next step, the inclusion of chrysin with β-CD has been investigated extensively using theoretical methods. Density functional theory (M05-2X) employing the 6-31+G* basis set has been used to research the lowest energy geometry for all studied complexes in gas and water mediums. The results of calculations show that the A ring of chrysin with large cavity side of β-CD significantly formed the favorable β-CD/chrysin complex in both phases. Our observations also inferred that hydrogen bonds were the key interactions which stabilized the chrysin/β-CD complex. We used Bader’s atoms in molecules (AIM) theory to perform a topological study on chrysin/β-CD complex to emphasize the hydrogen bonds. According to our findings, the process of inclusion increased not only the solubility of chrysin but also its antioxidant potential. [ABSTRACT FROM AUTHOR]

To address the mechanism of C-C bond cleavage on the metal surface of the M/SiO2 (M represents metal) catalyst is desirable and vital during the catalytic depolymerization process of lignin in solvents. Density functional theory simulation is used to determine the energy of C-C bond dissociation, adsorption geometry, adsorption energy and electronic structures of three kinds of the β-1 bond contained lignin model compounds (Mo1, Mo2 and Mo3), which were adsorbed on the (100) surface of metal (Ni, Cu, W) in the catalysts. The bond dissociation energy (BDE) of Cα-Cβ was found to be lower than those of Caryl-Cα and Cβ-Caryl bond. The Cα-Cβ in Mo2 was adsorbed via a π configuration on the Ni(100) and Cu(100) surfaces, exhibiting the weak dissociation bond energy. The -OH group was anchored as a η1(O) configuration which was instable on the (100) surface of W. The model compounds might be co-adsorbed with hydrogen on the metal surface under the reaction condition. The adsorption of Mo2 on the (100) surface of Cu was changed to the η1(O) pattern, while the Cα-Cβ BDE was declined on the (100) surface of Ni and Cu involving the coverage of hydrogen. The adsorption on W(100) had no effect on the decline of Cα-Cβ BDE. The adsorption of Mo2 on the (100) surface of metals plays different roles on weakening the Cα-Cβ BDE, giving conceptual guide for the selective depolymerization of lignin to specific chemicals. [ABSTRACT FROM AUTHOR]

Solvent extraction-based processes for separating lanthanides from actinides depend strongly on the kinetics of ligand complexation and de-complexation with the metal ions. The slower metal-ligand de-complexation process is usually the rate-limiting step, requiring these kinetics to be accurately known. In this study the kinetics of europium(III)-diethylenetriaminepentaacetic (DTPA) acid complex dissociation rates were directly measured using the change in europium(III) luminescence. These dissociation rates were independently determined by minimizing the complex formation rates by using high acidity, and keeping the concentration of europium(III) low to avoid double metal complexes. [ABSTRACT FROM AUTHOR]

Density functional theory calculations were carried out to investigate Cu12TM (TM = Co, Rh, Ir, Ni, Pd, Pt, Ag, Au) bimetallic metal catalysts for the mechanism of reverse water-gas shift (RWGS) reaction. The three possible reaction pathways relevant to the RWGS reaction are explored, including the CO2 dissociation, carboxyl, and formate mechanisms. Our results indicate that the RWGS reaction prefers to follow the CO2 dissociation mechanism on Cu12TM surfaces. A detailed potential energy diagram of the kinetically favored mechanism is presented that shows that the RDS of reaction are the formation of H2O and carboxyl (HOCO), formate (HCOO) dissociation, respectively. And, Cu12TM (TM = Co, Pt) are lower than other catalysts from the energy barrier of elementary step. Moreover, the catalytic behavior of a Cu12TM cluster is changed significantly due to the modifiers, via the electron transfer from TM to Cu-based cluster, and the activation barrier decreases with doped TM. The turnover frequency of the Cu12Co is the highest value, which thus is more efficiency catalyst to RWGS reaction. To gain insights into the synergistic effect in catalytic activity of the Cu12TM bimetallic cluster, a projected density of states analysis has been performed. Our works will be important for predicting the energetic trends and designing a better catalyst of RWGS reaction. [ABSTRACT FROM AUTHOR]

Recent studies have found an unusual way of dissociation in formaldehyde. It can be characterized by a hydrogen atom that separates from the molecule, but instead of dissociating immediately it roams around the molecule for a considerable amount of time and extracts another hydrogen atom from the molecule prior to dissociation. This phenomenon has been coined roaming and has since been reported in the dissociation of a number of other molecules. In this paper we investigate roaming in Chesnavich’s CH4+ model. During dissociation the free hydrogen must pass through three phase space bottleneck for the classical motion, that can be shown to exist due to unstable periodic orbits. None of these orbits is associated with saddle points of the potential energy surface and hence related to transition states in the usual sense. We explain how the intricate phase space geometry influences the shape and intersections of invariant manifolds that form separatrices, and establish the impact of these phase space structures on residence times and rotation numbers. Ultimately we use this knowledge to attribute the roaming phenomenon to particular heteroclinic intersections. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we analyze the hydrogen combustion and heat transfer in the combustion chamber in an oxygen environment with forced cooling of the combustion chamber. We simulated the combustion of a previously unmixed mixture of fuel and oxidizer with allowance for dissociation processes. The main parameters and composition of the combustion products are determined for different geometric dimensions of the combustion chamber and the excess oxidant coefficients. An increase in the internal diameter and length of the combustion chamber with an unchanged hydrogen consumption is shown to lead to a reduction in the actual underburning. In this case, the actual underburning is significant due to the dissociation of combustion products at high temperatures. The effect of oxidizer excess on underburning and the temperature of combustion products is studied. [ABSTRACT FROM AUTHOR]

A new method enabling the qualitative determination of the dissociation constant of peptides to full-length proteins and the estimation of the effect of point mutations in peptides on the stability of a formed complex with whole proteins was presented. Based on the developed approach, a qualitative correlation was revealed between the obtained results and the dissociation constant using the formation of a biocomplex of the Bmf, Puma, Bad, Hrk, Bax, Bik, Noxa, Bid, Bim, and Bak BH3-peptides and the Bcl-xl protein and a biocomplex of the Bax BH3-peptides and the Bcl-2 protein with consideration for the replacement of amino acid residues as an example. [ABSTRACT FROM AUTHOR]

According to DFT B3LYP/6-31G(d,p) calculations, the intramolecular migration of NCX groups (X = O, S, Se, Te) in 7-(heptaphenylcycloheptatrienyl)isochalcogencyanates in the gas phase proceeds via the dissociation-recombination mechanism. Structures were found of transition states preceding the formation of tight ion pairs. High activation barriers to the migration of isochalcogencyanate groups (ΔEZPE≠ 26.7, 21.3, 20.5, 19.3 kcal mol-1) originate from the existence of stable conformation of molecules with NCX groups located in the equatorial position and are in agreement with the data of dynamic NMR. For the transition of the molecule in the form favorable for the NCX group migration an inversion of the seven-membered ring and the rotation of the phenyl group are necessary. [ABSTRACT FROM AUTHOR]

The promotion effect of O2 on the dissociative adsorption of H2O to UO2 surface is studied by first-principles method within generalized gradient approximation formalism corrected by on-site Coulomb interaction. Investigations on all UO2 low index surfaces indicate that U-terminate (001) surface is the highest energy surface. For the adsorption of O2 and H2O on the U-terminate UO2(001) surface, all O2 molecules dissociate spontaneously while H2O molecules only dissociate incompletely in some specific initial configurations. The results of co-adsorption demonstrate the promotion effect of O2 on the dissociative adsorption of H2O, and two different promotion mechanisms are studied detailedly. [ABSTRACT FROM AUTHOR]

A quantitative method of analyzing nanoparticles (NPs) for drug delivery is urgently required by researchers and industry. Therefore, we developed new quantitative analytical methods for biodegradable and amphiphilic NPs consisting of polymeric γ-PGA-Phe [phenylalanine attached to poly(γ-glutamic acid)] molecules. These γ-PGA-Phe NPs were completely dissociated into separate γ-PGA-Phe molecules by adding sodium dodecyl sulfate (SDS). The dissociated NPs were chromatographically separated to analyze parameters such as the γ-PGA-Phe content in the NPs, the impurities present [using reverse-phase (RP) HPLC with an ultraviolet (UV) detector], and the absolute MW [using size-exclusion chromatography (SEC) with refractive index detection (RI) and multiangle light scattering (MALS) detection, i.e., SEC-RI/MALS]. The chromatographic patterns of the NPs were equivalent to those of the component polymer (γ-PGA-Phe), and excellent chromatographic separation for the quantitative evaluation of NPs was achieved. To the best of our knowledge, this is the first report of the quantitative evaluation of NPs in the field of NP-based delivery systems. Furthermore, these methods were applied to optimize and evaluate the NP manufacturing process. The results showed that impurities were effectively removed from the γ-PGA-Phe during the manufacturing process, so the purity of the final γ-PGA-Phe NPs was enhanced. In addition, the appearance, clarity of solution, particle size, zeta potential, particle matter, osmolarity, and pH of the product were evaluated to ensure that the NPs were of the required quality. Our approach should prove useful for product and process characterization and quality control in the manufacture of NPs. γ-PGA-Phe NPs are known to be a powerful vaccine adjuvant, so they are expected to undergo clinical development into a practical drug-delivery system. The analytical methods established in this paper should facilitate the reliable and practical quality testing of NP products, thus aiding the clinical development of γ-PGA-Phe-based drug-delivery systems. Moreover, since these analytical methods employ commonly used reagents and chromatographic systems, the methods are expected to be applicable to other NP-based drug-delivery products too.NPs were completely dissociated into separate γ-PGA-Phe polymeric molecules, which yielded a similar chromatogram to that seen for the NPs [ABSTRACT FROM AUTHOR]

Dark and photolysis reactions in solution were investigated for 9-acridinecarboxaldehyde (ACL). ACL reacts in the dark at T = 20 °C and pH = 7.0 in an air saturated solution to the main product 9-acridinecarboxylic acid (ACA) and to the minor product 9-acridinemethanol (ACM) with a lifetime of τ = 4.3 days. The dissociation constant of the base ACLH+ was determined to be pKa±σ = 4.38 ± 0.04. The photolysis of ACL was investigated using a polychromatic Xe-light source. The quantum yield in aqueous solution at T = 20 °C in a concentration range of c0(ACL) = 0.18–16.6 μM for pH ＞ pKa and for nitrogen, air and oxygen aerated solutions was found to be Φ±σ = (0.015 ± 0.003) mol/mol, independent from concentration. The quantum yield of ACLH+, i.e. for pH < pKa, is by a factor of 2 higher (Φ = 0.029 mol/mol). Quantum yields in methanol and isopropanol are slightly lower compared to water and in acetone lower by about a factor of 20. In acetonitrile ACL was found to be practically photostable. Minimum lifetimes in sunlight for a measurement on September 5, 2017 were in the range of τ = 5–10 minutes. The diurnal photolysis of ACL in sunlight was satisfactory explained using the mean quantum yield, the absorption spectrum and photon fluxes with suitable corrections for cloudiness and the dimensions of the setup. For low concentrations ACR is formed with a yield of practically 100% in the photolysis reaction. However, with increasing concentration of ACL yields of ACR decrease and yields of ACA increase. 9(10H)-Acridinone and ACM were always detected as minor products with yields below 2%. 9-Methylacridine was never detected in any reaction of ACL. Strong indications are presented of a photolysis reaction of ACL in a river located in Lower Saxony (Germany) with a corresponding equimolar formation of ACR. ACL is therefore a direct precursor of ACR in natural surface water. [ABSTRACT FROM AUTHOR]

The structural dynamics of insulin hexamer dissociation were studied by the photoinduced temperature jump technique and monitored by time-resolved X-ray scattering. The process of hexamer dissociation was found to involve several transient intermediates, including an expanded hexamer and an unstable tetramer. Our findings provide insights into the mechanisms of protien–protein association. [ABSTRACT FROM AUTHOR]

The high temperature gas occurs behind shock or near the wall surface of vehicle in the hypersonic flight. As the temperature exceeds 2 000K, 4 000K, respectively, O2 and N2 molecules are successively dissociated. Because of variable components at different temperatures and pressures, the dissociated air is no longer a perfect gas. In this paper, a new method is developed to calculate accurate thermal physical parameters with the dissociation degree providing the thermochemical equilibrium procedure. Based on the dissociation degree, it is concluded that few numbers of equations and the solutions are easily obtained. In addition, a set of formulas relating the parameter to the dissociation degree are set up. The thermodynamic properties of dissociated air containing four-species, O2 molecule and N2 molecule, O atom and N atom, are studied with the new method, and the results are consistent with those with the traditional equilibrium constant method. It is shown that this method is reliable for solving thermal physical parameters easily and directly. [ABSTRACT FROM AUTHOR]

Electrical discharges are increasingly used to dissociate CO2 in CO and O2. This reaction is the first step in the way for the synthesis of value-added compounds from CO2 by using renewable electricity. If efficient, this technology might allow at the same time recycling CO2 and storing renewable energy in chemical form. At present, while the dissociation degree is measured in the reactor exhaust, little is experimentally known about the dissociation kinetics in the discharge and post-discharge. This knowledge is however critical to increasing the overall efficiency of the plasma process. To estimate the time dependence of the CO2 dissociation following a discharge event, we have coupled a LIF diagnostics to a nanosecond repetitively pulsed discharge in a mixture of CO2 and H2O. This paper discusses a procedure to obtain data on the time evolution of the CO2 dissociation, its limits and future perspectives. In addition, the local gas temperature is measured as well. We find that a few microseconds after the discharge pulse, CO2 is highly dissociated with a temperature around 2500 K. In about 100 µs, the temperature decreases at about 1500 K while the dissociation is reduced by about a factor of three. [ABSTRACT FROM AUTHOR]

It has been reported that dislocations with 1/31¯101 edge component of the Burgers vector are formed in {11¯04}/112¯0 low-angle grain boundaries of alumina (α-Al2O3). These dislocations dissociate into two partial dislocations with a stacking fault on the (0001) plane (Tochigi et al. in J Mater Sci 46:4428-4433, 2011). However, the dissociation reaction of these dislocations has not been determined so far. In this study, the structures of the dissociated dislocations and the (0001) stacking fault were investigated by transmission electron microscopy and theoretical calculations. It was revealed that the dissociated dislocations were generated from the 1/31¯101 perfect edge dislocation by the reaction of 1/31¯101 → 1/184¯223 + 1/182¯42¯3. Furthermore, electron energy loss spectroscopy analysis was performed to examine the atomic/electronic structure of the (0001) stacking fault. In the observed spectra, a chemical shift and intensity decrease were found at the oxygen K-edge. Theoretical spectrum analysis using first-principles calculations revealed that the characteristic features of the spectra are originated from the local atomic configurations of the (0001) stacking fault. [ABSTRACT FROM AUTHOR]

The thermobaric conditions of the formation, stability, and dissociation of continental gas hydrates were determined by simulation of the thermal state of the permafrost. The calculations covered the period over the last 130 000 years, taking into account the various paleo-settings, including continental glaciation, marine transgression, and high geothermal fluxes. According to the numerical calculations, relict gas hydrates may currently exist in the metastable state in the permafrost at depths of less than 100-150 m. [ABSTRACT FROM AUTHOR]

Bond dissociation enthalpies (BDEs) are computed using the Density Functional Theory (DFT) for a selected set of C-Br, C-O, and C-Br bonds susceptible to homolysis in the thermal degradation of four brominated flame retardants (BFRs): decabromo-diphenyl, decabromo-diphenylethane, 1,2-bis(2,4,6-tribromophenoxy)-ethane, and 3,4,5,6-tetrabromo-1,2-diethyl-phtalate. Based on BDEs computed at M06/cc-pVTZ level, choice based on a previous benchmark, we find debromination as the dominant decomposition pathway of brominated diphenyls and brominated phtalates, whereas scission to form brominated phenoxyls and benzyl radicals is preferred in aromatic BFRs containing ether and alkyl bridges, respectively. Trends in computed BDEs are rationalized in terms of (de)localization of spin density in the electronic structure of the resulting radicals. [ABSTRACT FROM AUTHOR]

Antibiotics are ubiquitous pollutants in aquatic systems and can exist as different dissociated species depending on the water pH. New knowledge of their multivariate photochemical behavior (i.e., the photobehavior of different ionized forms) is needed to improve our understanding on the fate and possible remediation of these pharmaceuticals in surface and waste waters. In this study, the photochemical degradation of aqueous tetracycline (TC) and its dissociated forms (TCH20, TCH−, and TC2−) was investigated. Simulated sunlight experiments and matrix calculations indicated that the three dissociated species had dissimilar photolytic kinetics and photooxidation reactivities. TC2− photodegraded the fastest due to apparent photolysis with a kinetic constant of 0.938 ± 0.021 min−1, followed by TCH− (0.020 ± 0.005 min−1) and TCH20 (0.012 ± 0.001 min−1), whereas TCH− was found to be the most highly reactive toward •OH (105.78 ± 3.40 M−1 s−1), and TC2− reacted the fastest with 1O2 (344.96 ± 45.07 M−1 s−1). Water with relatively high pH (e.g., ~ 8-9) favors the dissociated forms of TCH− and TC2− which are most susceptible to photochemical loss processes compared to neutral TC. The calculated corresponding environmental half-lives (t1/2,E) in sunlit surface waters ranged from 0.05 h for pH = 9 in midsummer to 3.68 h for pH = 6 in midwinter at 45° N latitude. The process was dominated by apparent photolysis (especially in summer, 62-91%), followed by 1O2 and •OH oxidation. Adjusting the pH to slightly alkaline conditions prior to UV or solar UV light treatment may be an effective way of enhancing the photochemical removal of TC from contaminated water.Aqueous multiple photochemical behavior of dissociated tetracycline (TCH20, TCH−, and TC2−) is first comprehensively reported on revealing the phototransformation kinetics and implications for the fate in surface waters. [ABSTRACT FROM AUTHOR]

It has been reported that dislocations with 1/31¯101 edge component of the Burgers vector are formed in {11¯04}/112¯0 low-angle grain boundaries of alumina (α-Al2O3). These dislocations dissociate into two partial dislocations with a stacking fault on the (0001) plane (Tochigi et al. in J Mater Sci 46:4428-4433, 2011). However, the dissociation reaction of these dislocations has not been determined so far. In this study, the structures of the dissociated dislocations and the (0001) stacking fault were investigated by transmission electron microscopy and theoretical calculations. It was revealed that the dissociated dislocations were generated from the 1/31¯101 perfect edge dislocation by the reaction of 1/31¯101 → 1/184¯223 + 1/182¯42¯3. Furthermore, electron energy loss spectroscopy analysis was performed to examine the atomic/electronic structure of the (0001) stacking fault. In the observed spectra, a chemical shift and intensity decrease were found at the oxygen K-edge. Theoretical spectrum analysis using first-principles calculations revealed that the characteristic features of the spectra are originated from the local atomic configurations of the (0001) stacking fault. [ABSTRACT FROM AUTHOR]

The effect of volume variation at the possible dissociation equilibria of (MX4)2- anionic complexes in halide melts of bivalent metals are analyzed in terms of the mean-sphere approximation (MSA) of the statistical theory. Within the framework of the simplified model of charged hard spheres of different diameters and valences, the complete system of equilibrium equations is obtained, i.e., equations of the law of mass action and equations of state. This system makes possible self-correlated calculations of both the equilibrium concentration of autocomplexes and the melt density. It is shown that the simplest approximation of the complex diameter as the treble diameter of simple ions overestimates the effects of volume variations when considering dissociation. Taking into account the superposition of spheres makes it possible to describe the smoother volume variations with the temperature. [ABSTRACT FROM AUTHOR]

A method has been developed for nanoparticles synthesis based on oligomers of sulfobutyl ether β-cyclodextrin (SBE-β-CD) and their structure has been studied by FTIR spectroscopy. The physicochemical properties of “guest−host” inclusion complexes formed by SBE-β-CD and its oligomers with moxifloxacin have been investigated. It has been shown that, as compared with SBE-β-CD, the synthesized oligomers have an increased affinity for moxifloxacin: the dissociation constants for the complexes of monomeric and oligomeric SBE-β-CD are (1.0 ± 0.3) × 10−4 and nearly 5 × 10−6 M, respectively. The binding efficiency increases due to the multy-point interaction of a moxifloxacin molecule with functional groups of the oligomeric carrier. SBE-β-CD oligomers are promising carriers for drugs, in particular, fluoroquinolone-based antibacterial agents, and may be used for the development of new compositions with improved solubility, bioavailability, and prolonged drug release. [ABSTRACT FROM AUTHOR]