Search

Self-propelled active particles are inherently out of equilibrium as they collect energy from their surroundings and transform it into directed motion. A recent theoretical study suggests that binary mixtures of active particles with distinct effective diffusion coefficients exhibit dynamical demixing when their diffusion coefficients differ by more than one order of magnitude. Here, we show that this difference may be reduced drastically in the presence of external fields even when the response to the field is the same for both species. We investigate this demixing as a function of the ratio of the diffusion coefficients and discuss the implications of the results for active systems. [ABSTRACT FROM AUTHOR]

Alow-temperature scanning tunneling microscopewas employed to study the differential conductance in an atomic junction formed by an adsorbed Co atom on a Cu(100) surface and a copper-covered tip.A zero-bias anomaly (ZBA) reveals spin scattering off the Co atom, which is assigned to a Kondo effect. The ZBA exhibits a characteristic asymmetric lineshape when electrons tunnel between tip and sample, while upon the tip-Co contact it symmetrizes and broadens. Through density functional theory calculations and the non-equilibrium non-crossing approximation, we showthat the lineshape broadening is mainly a consequence of the additional coupling to the tip, while non-equilibrium effects only modify the large-bias tails of the ZBA. [ABSTRACT FROM AUTHOR]

The present paper aims at deriving classical expressions which permit calculation of the equilibrium constant for weakly interacting molecular pairs using a complete multidimensional potential energy surface. The latter is often available nowadays as a result of the more and more sophisticated and accurate ab initio calculations. The water dimer formation is considered as an example. It is shown that even in case of a rather strongly bound dimer the suggested expression permits obtaining quite reliable estimate for the equilibrium constant. The reliability of our obtained water dimer equilibrium constant is briefly discussed by comparison with the available data based on experimental observations, quantum calculations, and the use of RRHO approximation, provided the latter is restricted to formation of true bound states only. [ABSTRACT FROM AUTHOR]

The problem of determining the Eckart molecule-fixed frame for an arbitrary molecule with nuclei displaced from the equilibrium positions is considered. The solution of the problem is formulated by minimizing the sum of mass-weighted squared deviations (MWSD) of the nuclei of a displaced configuration from the nuclei of the equilibrium configuration. A mathematical proof of the equivalence of Eckart conditions and the minimum of MWSD is given. It is shown that the extrema of the sum of MWSD coincide with eigenvalues of a special 4 × 4 symmetric matrix. Its minimal eigenvalue corresponds to the desired solution, and the respective eigenvector can be treated as the quaternion containing the necessary information for rotating the original coordinate system and aligning its axes with the molecule-fixed coordinate system. A detailed scheme for an efficient numerical implementation of the method is provided, and a numerical example is given. [ABSTRACT FROM AUTHOR]

The Single Chain Mean Field theory is used to link coarse-grained models of amphiphilic molecules with analytical models for membrane elasticity, where phenomenological parameters are deduced from explicit molecular models and force fields. We estimate the elastic constants based on the free energy of the amphiphilic bilayer in planar and cylindrical geometries on the example of four amphiphilic molecules that differ in length and stiffness. We study how these variations affect the equilibrium bilayer structure, the equilibrium free energy, and the elastic constants. Bending rigidities are obtained within the typical range of experimental values for phospholipid membranes in a liquid state. [ABSTRACT FROM AUTHOR]

In this paper, a coupled mechanical-chemical model is established based on the thermodynamic framework, in which the contribution of chemical expansion to free energy is introduced. The stress-dependent chemical potential equilibrium at the gas-solid interface and the stress gradient-dependent diffusion equation as well as a so-called generalized force which is conjugate to the oxidation rate are derived from the proposed model, which could reflect the influence of stresses on the oxidation reaction. Based on the proposed coupled mechanical-chemical model, a user element subroutine is developed in ABAQUS. The numerical simulation of the high temperature oxidation in the thermal barrier coating is carried out to verify the accuracy of the proposed model, and then the influence of stresses on the oxidation reaction is investigated. In thermally grown oxide, the considerable stresses would be induced by permanent volumetric swelling during the oxidation. The stresses play an important role in the chemical potential equilibrium at the gas-solid interface and strongly affect the oxidation reaction. The gradient of the stresses, however, only occurs in the extremely thin oxidation front layer, which plays a very limited role in the oxidation reaction. The generalized force could be divided into the stress-dependent and the stress-independent parts. Comparing with the stress-independent part, the stress-dependent part is smaller, which has little influence on oxidation reaction. [ABSTRACT FROM AUTHOR]

Abstract In many equilibrium systems, it is customary to use a simplified, apparent equilibrium reaction instead of the complete reaction model. The resulting apparent equilibrium constants are altered or controlled by changes of the chemical system, usually modifying the total concentration of auxiliary reagents, but the variation of other parameters such the intensity of light in photo-controlled reactions, types and concentration of solvents or composition of mixed solvents, the ionic strength of the chemical media, etc. is also possible. The main goal of this work is to propose a chemical equilibrium modelling based strategy to control the conditions governing equilibrium systems in order to tune the apparent constants. Indeed, by extracting the analytic relationship between the parameters of the complete model and apparent model, the magnitude of the apparent constant(s) can be predicted. At first, a basic strategy for calculating the tunable range of apparent constants of chemical equilibria is proposed. Next, three case studies for tuning the apparent constants are investigated in detail: inclusion complexes with cyclodextrin, aqueous micellar solutions for investigating the solvent effects and the boric acid/Mannitol system that allows the tuning of the apparent protonation constant. In all examples tuning the apparent constant is possible by regulating the chemical composition. Graphical abstract Image 1 Highlights • For many equilibrium systems it is customary to use a simplified apparent, instead of a complete complex equilibrium system. • By the thermodynamic laws and equilibrium models, the exact analytic relationship between complete and apparent models of equilibrium systems can be extracted. • The extracted relationship formula determine the external parameter (s) for controlling the apparent models of equilibrium systems. • By controlling the conditions, the apparent constant of equilibrium systems could be tuned in the desired value. [ABSTRACT FROM AUTHOR]

Methylcyclohexane dehydrogenation to toluene and hydrogen (MTH) is an important reaction for H2 energy based systems. Hence, it is important to have a reliable equation for the dependence of the reaction equilibrium constant on temperature. A number of such equations have been proposed in the literature, but it is unclear which of them is more accurate in representing the equilibrium of methylcyclohexane dehydrogenation to toluene. To resolve this uncertainty, we analyzed their validity based on existing experimental data. Experimentally derived equilibrium constants were found to be generally bigger than those calculated by classical thermodynamics at 300-400 °C and 3, 10, and 15 bar. Equilibrium constants calculated based on tabulated free energy of the reaction, were closer to the experimental values than those based on standard heat capacities of the reacting materials. Part of the deviation is caused by the non-ideality of the reacting components at these conditions, which is reflected by their calculated compressibility factors. The equilibrium conversions calculated based on the proposed equilibrium constants have been compared to those obtained in a set of methylcyclohexane to toluene reactions carried out in continuous flow packed bed and membrane reactors and this comparison revealed that only the experimentally derived equilibrium constants provide reasonable results. [ABSTRACT FROM AUTHOR]

Abstract The adsorption of herbicides belonging to the group of halogenated phenoxyacids on the activated carbon was studied. They are differentiated in terms of quantity and type of functional groups (such as chloride, bromide, fluoride) and their position on an aromatic ring. The experimental equilibrium data were analyzed using adsorption isotherm equations taking into account energetic heterogeneity of the adsorption systems. The calculated concentration profiles from the kinetic data were discussed applying two diffusion models, MOE, f-MOE and multi-exponential equations. The dependences between the properties of adsorbates, adsorption uptake and rate were analyzed. The adsorption affinity of pesticides was correlated with adsorbate hydrophobicity, character of functional group, molecular structure. The applicability of kinetic models and equations was investigated; the assumptions of the models were analyzed with regard to consistency with adsorption mechanism. Similarity of adsorption mechanism was found for all adsorbates confirmed by similarity of kinetic curves and corresponding distributions of rate coefficients. The differences in kinetic profiles were attributed to differentiation of herbicide's molecules - number and type of functional groups and their positions on aromatic ring. Graphical abstract Image 1 Highlights • Strong influence of adsorbate structure and properties on adsorption. • Significant impact of energetic heterogeneity of systems. • Adsorption processes are very slow - developed internal structure of adsorbent. • Kinetic can be described by the FOE/SOE/MOE and f-MOE equations. • The best optimization results gives the multi-exponential equation. [ABSTRACT FROM AUTHOR]

We analyze the minimum electrophilicity principle of conceptual density functional theory using the framework of the finite temperature grand canonical ensemble. We provide support for this principle, both for the cases of systems evolving from a non-equilibrium to an equilibrium state and for the change from one equilibrium state to another. In doing so, we clearly delineate the cases where this principle can, or cannot, be used. [ABSTRACT FROM AUTHOR]

The rate of electron transfer between a molecular species and a metal, each at a different local temperature, is examined theoretically through the implementation of a bithermal (characterized by two temperatures) Marcus formalism. Expressions for the rate constant and the electronic contribution to a heat transfer mechanism which is induced by the temperature gradient between a molecule and metal are constructed. The system of coupled dynamical equations describing the electronic and thermal currents are derived and examined over diverse ranges of reaction geometries and temperature gradients. It is shown that electron transfer across the molecule-metal interface is associated with heat transfer and that the electron exchange between metal and molecule makes a distinct contribution to the interfacial heat conduction even when the net electronic current vanishes. [ABSTRACT FROM AUTHOR]

We introduce diagrammatic technique for Hubbard nonequilibrium Green functions. The formulation is an extension of equilibrium considerations for strongly correlated lattice models to description of current carrying molecular junctions. Within the technique intra-system interactions are taken into account exactly, while molecular coupling to contacts is used as a small parameter in perturbative expansion. We demonstrate the viability of the approach with numerical simulations for a generic junction model of quantum dot coupled to two electron reservoirs. [ABSTRACT FROM AUTHOR]

The coupling of the charge carriers passing through a molecule bridging two bulky conductors with local vibrational modes of the molecule gives rise to distinct features in the electronic transport properties on one hand and to nonequilibrium features in the vibrations' properties, e.g., their population, on the other. Here we explore theoretically a generic model for a molecular junction biased by an arbitrary dc voltage in the weak-coupling regime. We succinctly summarize parts of our past work related to the signature of the electron-vibration interaction on the full-counting statistics of the current fluctuations (i.e., the cumulant generating-function of the current correlations). In addition, we provide a novel account of the response to an ac field exerted on the junction (on top of the dc bias voltage); in particular, we study the nonequilibrium distribution and the displacement fluctuations of the vibrational modes. Remarkably, we find a behavior pattern that cannot be accounted for by classical forced oscillations. The calculations use the technique of nonequilibrium Green's functions and treat the electron-vibration coupling in perturbation theory, within the random-phase approximation when required. [ABSTRACT FROM AUTHOR]

Abstract We consider the notion of equilibration for an isolated quantum system exhibiting Anderson localization. The system is assumed to be in a pure state, i.e., described by a wave-function undergoing unitary dynamics. We focus on the simplest model of a 1D disordered chain and we analyse both the dynamics of an initially localized state and the dynamics of quantum states drawn at random from the ensemble corresponding to the minimum knowledge about the initial state. While in the former case the site distribution remains confined in a limited portion of the chain, the site distribution of random pure state fluctuates around an equilibrium average that is delocalized over the entire chain. A clear connection between the equilibration observed when the system is initialized in a fully localized state and the amplitude of dynamical fluctuations of a typical random pure state is established. [ABSTRACT FROM AUTHOR]

There are large discrepancies existing in equilibrium Mg isotope fractionation calculations and experimental investigations for cases related to mineral vs. solution. To clarify this confusing issue, a newly designed cluster-model-based quantum chemistry method, i.e., volume variable cluster model (VVCM), is used to provide equilibrium Mg isotope fractionation factors between Mg-bearing carbonates (calcite, aragonite, dolomite and magnesite), amorphous calcium carbonates (ACCs), brucite and aqueous species (i.e., Mg 2+ (aq) , MgHCO 3 + (aq) and MgOH + (aq) ). We find that local configuration sampling of aqueous species is essential to provide precise fractionations between mineral and solution. The phonon-based periodic boundary method is also used for several minerals and it obtains very similar fractionations with VVCM results. Our results are very close to those of Pinilla et al. (2015) although via completely different approaches. Both of them have included the effect of local configuration disorder. However, both of them are significantly different from some of experimental results for cases of carbonates vs. solutions. The existence of various Mg-bearing species in fluids of experiments, the direct incorporation of hydrated Mg 2+ into the solids, the Mg 2+ concentration effect, and the existence of intermediate precursors (e.g., ACCs) are several possible causes for the mismatches. Relative to coexisting aqueous Mg 2+ , we find that ACCs will enrich heavy Mg isotopes, i.e., ~1.45‰ at 25 °C, agreeing with previous experimental estimation. Equilibrium Mg isotope fractionation factors between brucite and solutions are also predicted. Besides, we applied VVCM to predict the Mg isotope fractionations between high-temperature phases, i.e., forsterite, diopside, enstatite, tremolite and spinel. The predicted β factors are in the order of spinel > tremolite > diopside > enstatite > forsterite. This study provides a base for understanding the accumulating Mg isotope data. [ABSTRACT FROM AUTHOR]

While predominance area diagrams (PADs) are useful for the determination of the stable phases in the metal-sulfur-oxygen system, they are constructed at constant temperature. Varying the temperature results in shifting of the equilibrium lines and the stability areas thereof. Since the available tools in hands of an extractive metallurgist are temperature and oxygen potential, a more useful diagram would be one that shows the stability areas of different phases as a function of temperature and percent of oxygen in the roast gas. Such diagrams, called ‘roaster’ diagrams, derive directly from PADs. Although such diagrams are used by extractive practitioners, this type of diagram is unavailable in the open literature. In this paper, the relationship between the PADs and roaster diagrams is discussed and PADs and roaster diagrams for the Zn-S-O and Pb-S-O ternary systems are constructed. This information will serve as the foundation for more complex four-component systems to follow in subsequent publications. [ABSTRACT FROM AUTHOR]

Fully atomistic molecular dynamics (MD) simulations are employed to study the swelling behavior of poly(methyl methacrylate- co - n -butyl methacrylate) (P(MMA- co - n -BMA)) immersed in water. The chemical potential of water is calculated using the thermodynamic integration method to estimate the equilibrium swelling (ES) point. The solvation free energy, radial distribution functions (RDFs) and water structures are investigated to study the swelling process. The simulation results indicate an average water uptake of approximately 26.96 wt%. The van der Waals (VDW) interaction and carbonyl oxygens play critical roles in the swelling process. Hydrophilic-hydration water preferentially forms and binds with carbonyl oxygen atoms through hydrogen bonding when water molecules permeate into P(MMA- co - n -BMA). As the water content increases, hydrophobic-hydration water and intermediate water occupy more of the interior space away from the carbonyl oxygens. The amount of hydrophilic-hydration water remains constant once the swelling reaches equilibrium, which implies the saturation of the hydrogen bonding interaction between the carbonyl oxygen atoms and water. The results are significant for the structural design of nanocapsule shells for the controlled release of antifoulant. [ABSTRACT FROM AUTHOR]

A method to simultaneously determine the chemical kinetics ( kC T ) and Langmuir’s adsorption equilibrium ( K L ) constants in porous catalyst particles where chemical reactions following Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetics (first order on the concentration of the adsorbed species) proceed under the existence of diffusion mass transfer limitations was proposed. Two parameters characterize this steady state diffusion-adsorption-reaction system: the well known Thiele modulus ϕ and the dimensionless adsorption equilibrium constant K , which is defined as the product between K L and the fluid phase concentration of the reactant ( C f ) . It was shown that the non-linear adsorption equilibrium is the reason that, given ϕ , the larger the K , the flatter the concentration profile and, consequently, the volume average chemical reaction rate and the effectiveness factor are higher. Although the Weisz-Prater (W-P) criterion has been previously extended to non-linear kinetics to evaluate the relative magnitude of diffusion limitations inside porous catalyst particles, this method allows determining the kinetic and adsorption parameters by using the W-P parameter, as assessed from a few laboratory experiments. Differently from the classical W-P criterion (first order kinetics), a single value of W-P parameter below which the chemical control could be secured does not exist for LHHW kinetics. Those “limit” values depend on K and increase with it. The fact that ϕ is independent from C f , while K certainly depends on it, makes it easier to simultaneously determine K L and kC T under reaction conditions. When K is small (e.g., lower than 0.1), the model converges to the solutions typical in textbooks, where linear adsorption equilibrium is taken into account, which under steady state conditions only allow estimating the kC T K L product, but not the individual constants. [ABSTRACT FROM AUTHOR]

A breakdown of the normalmodes (harmonic) approximation for partition function and equilibrium constant that occur with increasing temperature is reported. That breakdown happens when thermal energy of the molecule reaches regions of potential energy curve/surface where it inflects and, as a result, it cannot be approximated with the harmonic potential. This inflection point effect is shown now on the example of H+H2+ ... H++H2 reaction. A key role of ro-vibrational coupling is revealed. Additionally, equilibrium constant of H+H2+ ... H++H2 reaction is calculated with a new methodology composed of TI/PIMC method combined with rigid rotor harmonic approximation. Finally, breakdown of harmonic approximation is shown for two-dimensional model. [ABSTRACT FROM AUTHOR]

In this note we give an explicit formula for the Moore-Penrose inverse W† of a weighted composition operator W on L2(Σ) and then we obtain the stability constant KW of W on Lp(S), where 1 ⩽ p ⩽ ∞. Moreover, we determine, under certain conditions, the essential norm of W acting on L∞(Σ). [ABSTRACT FROM AUTHOR]

Special nanostructures of porous anodic alumina (PAA), such as the petal-like micropattern and nanofibers of alumina, cannot be explained by the classical field-assisted dissolution and dynamic equilibrium models. Here, by combination of oxygen bubble mould and plastic flow model, a reasonable explanation for these special nanostructures is proposed. The petal-like micropatterns of PAA and nanofibers of alumina are all clarified by the oxygen bubble mould and the plastic flow model. The self-ordering nanochannels of PAA are attributed to the oxide plastic flow around a gas bubble mould at each pore bottom. The petal-like micropatterns and nanofibers of alumina are attributed to chemical corrosion enhanced by the micro-gas-flow and micro-liquid-flow. [ABSTRACT FROM AUTHOR]

The study presents p-T-x-y phase equilibria measurements of an oxygenated compound (furan) and one of its potential solvents of extraction (toluene). The experimental technique of the equipment recently developed is based on a static analytic method. Measurements were done at 3 temperatures (313.02, 333.02, and 352.99 K) and pressures from 13 to 375 kPa. The experimental data measured were successfully correlated using a "gamma-phi" approach with the nonrandom two-liquid activity coefficient model. [ABSTRACT FROM AUTHOR]

Cystine plays an important role in human physiology, it is the precursor of cysteine. Cystine is the molecular form preferred by the immunity cellules system, included macrophages. Although slightly soluble, it can be a ligand towards cations because it is a sulfur-containing amino acid. Because of the physiological importance of calcium(II) and magnesium(II), complex formation between these cations and cystine was studied potentiometrically by employing electrochemical cells involving glass electrodes. The investigation was performed at two temperatures (25 and 37) °C and in two ionic media (1.00 and 0.15 mol·dm NaCl). In both ionic media, the adoption of a constant ionic medium allows extension of the investigation to a large range of reagent concentration. As the formation of weak complexes was foreseen, the low solubility of cystine is an advantage. Experimental data can be explained in any case by assuming the formation of mononuclear complexes in the presence of both calcium(II) and magnesium(II). The relative stability constants were determined. [ABSTRACT FROM AUTHOR]

Aqueous solutions of La(CHCO), NaCHCO and La(ClO) were studied using Raman spectroscopy. In dilute NaCHCO solution, acetate is fully hydrated and forms only minor amounts of ion pairs. The characteristic Raman bands are discussed and assigned. In fairly dilute La(ClO) solutions, the La(aq) ion occurs as the nonahydrate. The separation of the carboxylate bands, ν - ν (Δ-value), in NaCHCO(cr) compared to La(CHCO)·1.5HO(cr) correlates with the bonding type of acetate which is 'ionic' in the former but bidentate chelating/tridentate chelating in the latter. Other acetate bands such as the deformation mode of the CO moiety, δ CO, and the two rocking vibrations (ρ), as well as the C-C stretch show marked differences in their band positions in NaCHCO(cr) compared to the ones in La(CHCO)·1.5HO(aq). In a ternary solution of La(CHCO)/LaCl with a molar ratio La(aq): $$ {\text{CH}}_{3} {\text{CO}}_{2}^{ - } $$ (aq) = 3.87: 1.00), the bands of the bound acetate on La were characterized and compared to those of fully hydrated acetate, $$ {\text{CH}}_{3} {\text{CO}}_{2}^{ - } \left( {\text{aq}} \right) $$ . In this solution, almost all acetate is ligated to La in a bidentate fashion and two complex species could be identified (molar ratios La: $$ {\text{CH}}_{3} {\text{CO}}_{2}^{ - } $$ = 1:1 and 1:2, respectively). In La(CHCO) solutions in HO and DO strong acetato complexes are formed and the bands of the bound acetate were characterized and compared with the ones of the fully hydrated acetate modes. A dilution series down to 0.0037 mol·L in La(CHCO)(aq) and to 0.0150 mol·L in La(CHCO)(DO) showed that two acetate complexes are formed in these solutions. Again, it was shown that in these solutions the bound acetates on La exist as bidentate ligands. DFT frequencies of the acetate on clusters {La(OH)OCCH)} and {La(OH)(OCCH)} compared well with the measured values. By determining the ligation number, $$ \bar{n} $$ , it can be established that in dilute solutions, below 0.04 mol·L, a complex with a 1:1 stoichiometry (La: $$ {\text{CH}}_{3} {\text{CO}}_{2}^{ - } $$ ) exists in equilibrium with 'free' acetate while in more concentrated solutions a 1:2 complex also forms. La(aq) hydrolysis is slight and very small equilibrium concentrations of CHCOOH were detected (C-C stretch at 893 cm). From quantitative Raman measurements, K was determined to be 160 ± 10 at 22 °C. [ABSTRACT FROM AUTHOR]

Rate and equilibrium constants of the reactions of nicotine and structurally related compounds with benzhydrylium ions have been determined UV-Vis spectroscopically using stopped-flow and laser-flash techniques. The pyridine nitrogen of nicotine was identified as the site of thermodynamically and kinetically controlled attack. Quantum chemical calculations showed that the introduction of a pyrid-3-yl moiety into the 2-position of N-methylpyrrolidine (to give nicotine) reduces the Lewis basicity of the pyrrolidine ring by 24 kJ mol−1, whereas the analogous introduction of a phenyl ring decreases this quantity by only 11 kJ mol−1. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this article we introduce new possibilities of bounding the stability constants that play a vital role in the reduced basis method. By bounding stability constants over a neighborhood we make it possible to guarantee stability at more than a finite number of points and to do that in the offline stage. We additionally show that Lyapunov stability of dynamical systems can be handled in the same framework. [ABSTRACT FROM AUTHOR]

A two-dimensional model of a multilayer material and a procedure for simulating its properties based on global optimization methods are proposed. This model is applied for the case of a two-dimensional crystal. Global minima of the interaction energy of the material's atoms are found, and geometric characteristics of its corresponding equilibrium states are described. The resulting lattices, in particular graphene's lattices, agree with experimental data, which confirms the validity of the proposed approach. This approach can be extended to a wider class of layered structures, and it can be used for determining the mechanical properties of materials. [ABSTRACT FROM AUTHOR]

The crystal structure of DyMnO3 (Ln: lanthanide) in the equilibrium state has been reported to be orthorhombic when La3+ to Dy3+, and hexagonal when Ho3+ to Lu3+, are used as Ln3+. However, Kumar et al. reported a two-phase structure of orthorhombic and hexagonal phases is formed in DyMnO3 when it was solidified from an undercooled melt under containerless conditions. To investigate the reason for the formation of this two-phase structure in DyMnO3, the nucleation temperature Tn and the post-recalescence temperature Tpr were measured for the Dy2O3-Mn2O3 system as a function of the substitution ratio for Mn and Dy, x = NMn/(NDy+NMn). As a result, the phase constitution was found to depend on Tn and the amount of undercooling ΔT(=Tpr - Tn); h-DyMnO3 is formed when ΔT is small, and o-DyMnO3 is formed when ΔT is large. Furthermore, when Tn is higher than 1530 K, which is the equilibrium temperature at oxygen partial pressure of atmospheric gas at 105 Pa for the chemical reaction of DyMnO3 + 1/3Mn3O4 + 1/3O2 = DyMn2O5, h-DyMnO3 is formed at x=0.5, while h-DyMnO3 is suppressed at x>0.5, irrespective of Tn. [ABSTRACT FROM AUTHOR]

We explore thermodynamic properties of a vapor in the range of state parameters where the contribution to thermodynamic functions from bound states of atoms (clusters) dominates over the interaction between the components of the vapor in free states. The clusters are assumed to be light and sufficiently "hot" for the number of bonds to be minimized. W e use the technique of calculation of the cluster partition function for the cluster with a minimum number of interatomic bonds to calculate the caloric properties (heat capacity and velocity of sound) for an ideal mixture of the lightest clusters. The problem proves to be exactly solvable and resulting formulas are functions solely of the equilibrium constant of the dimer formation. These formulas ensure a satisfactory correlation with the reference data for the vapors of cesium, mercury, and argon up to moderate densities in both the sub- and supercritical regions. For cesium, we extend the model to the densities close to the critical one by inclusion of the clusters of arbitrary size. Knowledge of the cluster composition of the cesium vapor makes it possible to treat nonequilibrium phenomena such as nucleation of the supersaturated vapor, for which the effect of the cluster structural transition is likely to be significant. [ABSTRACT FROM AUTHOR]

Pulling a sphere and vibrating it around an equilibrium position by amplitude-modulation in the near-field of a single finite circular piston transducer is theoretically demonstrated. Conditions are found where a fluid hexane sphere (with arbitrary radius) chosen as an example, centered on the axis of progressive propagating waves and submerged in non-viscous water, experiences an attractive (steady) force pulling it towards the transducer, as well as an oscillatory force forcing it to vibrate back-and-forth. Numerical predictions for the dynamic force illustrate the theory and suggest an innovative method in designing dynamic acoustical tractor beams. [ABSTRACT FROM AUTHOR]

So far, the kinetic approach for determination of the rate constants of reversible reaction is still using the equilibrium concentration. Basically, this is thermodynamic concept. This technique is not only needs a long time for the experiments but also gives only the exact value of the forward rate constant. The exact value of backward rate constant must be determined based on the postulated reaction mechanism. This study presents a simple technique on the determination of the exact value of both forward and backward rate constants using irreversible approach on three data at the early stages of a reaction and then used for the determination of equilibrium constant. This theoretical study is supported with statistical analysis on the experimental data adapted from the literatures. The results showed that the technique is valid and reliable. [ABSTRACT FROM AUTHOR]

The synthesis of fused and nonfused core-modified 40π nonaphyrins are reported. Spectroscopic and X-ray structural studies reveal a twisted figure-eight conformation in the freebase form that is nonaromatic. Structural changes occur, from figure-eight to open extended conformation, upon protonation, thereby adopting 4nπ Hückel antiaromatic character, which is reflected in spectroscopic and theoretical studies. Such a structural change also induces ring inversions of specific heterocyclic rings by 180°. [ABSTRACT FROM AUTHOR]

For 2k = n + 1, we exhibit nonpolynomial solutions to the Hessian equationon all of ℝn. [ABSTRACT FROM AUTHOR]

According to HF and DFT quantum chemical calculations and H NMR data, the chair- chair conformational equilibrium of 5-methyltetrahydro-1,3-oxazine shifts toward the conformer with equatorial orientation of the methyl group on C and axial orientation of the NH proton. 3,5-Dimethyltetrahydro-1,3-oxazine exists preferentially as chair conformer with equatorial orientation of the 5-methyl group; orientation of the N-methyl group almost does not affect the conformational equilibrium. [ABSTRACT FROM AUTHOR]

Equilibrium constants and the associated thermodynamic parameters are reported for the equilibria established between the cationic carbene (N-methyl-3-pyridinium)chlorocarbene tetrafluoroborate (MePyr+CCl BF4-, 3) and 1,3,5-trimethoxybenzene (TMB) to form a carbene-TMB complex, as well as between carbene 3 and chloride ion to form the zwitterion, N-methyl-3-pyridinium dichloromethide (10). These equilibrium constants and thermodynamic parameters are contrasted with analogous data for several related carbenes, and the influence of the pyridinium unit in carbene 3 is thereby highlighted. Computational studies augment and elucidate the experimental results. [ABSTRACT FROM AUTHOR]

Chemical equilibrium and CO 2 fluid inclusion barometry are complementary techniques, as they register different geological processes. Chemical equilibrium barometry records the pressure at the site where the xenoliths were incorporated into the transporting magma, but it is not a sensible technique to document magma ascent. CO 2 fluid inclusion pore pressure in xenoliths does not register the P–T conditions in the source area, but it allows illustrating a fairly detailed record of different geological processes that occurred during the magma transport to the surface and as the eruption proceeded. Mantle xenoliths from Ventura–Espíritu Santo and Santo Domingo volcanic fields contain dominant CO 2 pseudosecondary and secondary fluid inclusions trapped in cpx and ol. Cpx chemical equilibrium pressures indicate a maximum pressure of 10 kbar for the source area. Pore pressures obtained in CO 2 pseudosecondary and secondary fluid inclusions show a distribution with three maximum peaks at ca. 8, 5–7, and less than 3 kbar. A comparison with geophysical models for the area where the xenoliths-bearing volcanoes are located shows that the three peaks in the pore pressures correspond to three physico-chemical transitions within the continental crust. Likewise, the pore pressure suggests that rapid magma ascent is momentarily interrupted by these discontinuities, a fact that allows the formation of new fluid inclusions and the re-equilibration of some of the inclusions already present in the primary minerals of the xenoliths. [ABSTRACT FROM AUTHOR]

Five models are discussed giving the equilibrium constant for the catenation of two ring oligomers as a function of their Effective Molarity (EM), the physico-chemical parameter expressing the ease of cyclization of a chain. The first three models (A-C) are derived from the revision of previous theories of catenation, that neglect excluded volume effects. A fourth model (D) is obtained from the results of Monte Carlo simulations by Deguchi and co, that can also account for excluded volume effects. Finally, a fifth model (E) is introduced which has the same functional form of models A, B, D, but is parameterized using the available experimental catenation constant. [ABSTRACT FROM AUTHOR]

Unveiling point defects concentration in transition metal oxide thin films is essential to understand and eventually control their functional properties, employed in an increasing number of applications and devices. Despite this unquestionable interest, there is a lack of available experimental techniques able to estimate the defect chemistry and equilibrium constants in such oxides at intermediate‐to‐low temperatures. In this study, the defect chemistry of a relevant material such as La1−xSrxFeO3−δ (LSF) with (x = 0.2, 0.4 and 0.5 (LSF20, LSF40 and LSF50 respectively) is obtained by using a novel in situ spectroscopic ellipsometry approach applied to thin films. Through this technique, the concentration of holes in LSF is correlated to measured optical properties and its evolution with temperature and oxygen partial pressure is determined. In this way, a systematic description of defect chemistry in LSF thin films in the temperature range from 350 °C to 500 °C is obtained for the first time, which represents a step forward in the understanding of LSF20, LSF40 and LSF50 for emerging low temperature applications. [ABSTRACT FROM AUTHOR]

We present a full quantum evaluation of the water second virial coefficient B(T) based on the Takahashi-Imada second order approximation. As the associated trace T r[e-βHAB - e-βHoAB] is performed in the coordinate representation, it does also include contribution from the whole continuum, i.e., resonances and collision pairs of monomers. This approach is compared to a Path Integral Monte Carlo evaluation of this coefficient by Schenter [J. Chem. Phys. 117, 6573 (2002)] for the TIP4P potential and shown to give extremely close results in the low temperature range (250-450 K) reported. Using a recent ab initio flexible potential for the water dimer, this new formulation leads to very good agreement with experimental values over the whole range of temperatures available. The virial coefficient is then used in the well known relation Kp(T) = -(B(T) - bM)/RT where the excluded volume bM is assimilated to the second virial coefficient of pure water monomer vapor and approximated from the inner repulsive part of the interaction potential. This definition, which renders bM temperature dependent, allows us to retrieve the 38 cm3 mol-1 value commonly used, at room temperature. The resulting values for Kp(T) are in agreement with available experimental data obtained from infrared absorption spectra of water vapor. [ABSTRACT FROM AUTHOR]

The intermetallic molecules CuSb, AgSb, and AuSb were identified in the effusive molecular beam produced at high temperature under equilibrium conditions in a double-cell-like Knudsen source. Several gaseous equilibria involving these species were studied by mass spectrometry as a function of temperature in the overall range 1349-1822 K, and the strength of the chemical bond formed between antimony and the group 11 metals was for the first time measured deriving the following thermochemical dissociation energies (D°0 , kJ/mol): 186.7 ± 5.1 (CuSb), 156.3 ± 4.9 (AgSb), 241.3 ± 5.8 (AuSb). The three species were also investigated computationally at the coupled cluster level with single, double, and noniterative quasiperturbative triple excitations (CCSD(T)). The spectroscopic parameters were calculated from the potential energy curves and the dissociation energies were evaluated at the Complete Basis Set limit, resulting in an overall good agreement with experimental values. An approximate evaluation of the spin-orbit effect was also performed. CCSD(T) calculations were further extended to the corresponding group 11 arsenide species which are here studied for the first time and the following dissociation energies (D°0 , kJ/mol): 190 ± 10 (CuAs), 151 ± 10 (AgAs), 240 ± 15 (AuAs) are proposed. Taking advantage of the new experimental and computational information here presented, the bond energy trends along group 11 and 4th and 5th periods of the periodic table were analyzed and the bond energies of the diatomic species CuBi and AuBi, yet experimentally unobserved, were predicted on an empirical basis. [ABSTRACT FROM AUTHOR]

A systematic ab initio treatment of the nitryl halides (XNO2) and the cis- and trans- conformers of the halide nitrites (XONO), where X = Cl, Br, and I, have been carried out using highly correlated methods with sequences of correlation consistent basis sets. Equilibrium geometries and harmonic frequencies have been accurately calculated in all cases at the explicitly correlated CCSD(T)-F12b level of theory, including the effects of core-valence correlation for the former. Where experimental values are available for the equilibrium structures (ClNO2 and BrNO2), the present calculations are in excellent agreement; however, the X-O distances are slightly too long by about 0.01 Å due to missing multireference effects. Accurate predictions for the iodine species are made for the first time. The vertical electronic excitation spectra have been calculated using equation-of-motion coupled cluster methods for the low-lying singlet states and multireference configuration interaction for both singlet and triplet states. The latter also included the effects of spin-orbit coupling to provide oscillator strengths for the ground state singlet to excited triplet transitions. While for ClNO2 the transitions to excited singlet states all occur at wavelengths shorter than 310 nm, there is one longer wavelength singlet transition in BrNO2 and two in the case of INO2. The long wavelength tail in the XNO2 species is predicted to be dominated by transitions to triplet states. In addition to red-shifting from X = Cl to I, the triplet transitions also increase in oscillator strength, becoming comparable to many of the singlet transitions in the case of INO2. Hence in particular, the latter species should be very photolabile. Similar trends are observed and reported for the halogen nitrites, many of which for the first time. [ABSTRACT FROM AUTHOR]

Orbital-optimized second-order perturbation theory (OOMP2) optimizes the zeroth order wave function in the presence of correlations, removing the dependence of the method on Hartree-Fock orbitals. This is particularly important for systems where mean field orbitals spin contaminate to artificially lower the zeroth order energy such as open shell molecules, highly conjugated systems, and organometallic compounds. Unfortunately, the promise of OOMP2 is hampered by the possibility of solutions being drawn into divergences, which can occur during the optimization procedure if HOMO and LUMO energies approach degeneracy. In this work, we regularize these divergences through the simple addition of a level shift parameter to the denominator of the MP2 amplitudes. We find that a large level shift parameter of 400 mEh removes divergent behavior while also improving the overall accuracy of the method for atomization energies, barrier heights, intermolecular interactions, radical stabilization energies, and metal binding energies. [ABSTRACT FROM AUTHOR]

In this study, reactive extraction of glyoxylic acid (0.93 kmol·m−3) using Amberlite-LA2 (0.24 to 1.67 kmol·m−3) in five different alcoholic diluents is performed at 298 K. The extraction ability of Amberlite-LA2 is found to be in the order of isoamylalcohol (IAA) > nonan-1-ol > octan-1-ol > decan-1-ol > dodecanol. Maximum extraction efficiency, 98.92% is obtained at 1.67 kmol·m−3of Amberlite-LA2 in IAA. The values of stoichiometric coefficient (m), overall equilibrium constant (KE) and individual constants (K11,K21, andK12) are estimated. The effect of diluent onKDis also quantified by applying LSER model using solvatochromic parameters of diluents. [ABSTRACT FROM PUBLISHER]

Microscopicredox equilibrium constants, a new species-specifictype of physicochemical parameters, were introduced and determinedto quantify thiol–disulfide equilibria of biological significance.The thiol–disulfide redox equilibria of glutathione with cysteamine,cysteine, and homocysteine were approached from both sides, and theequilibrium mixtures were analyzed by quantitative NMR methods tocharacterize the highly composite, co-dependent acid–base andredox equilibria. The directly obtained, pH-dependent, conditionalconstants were then decomposed by a new evaluation method, resultingin pH-independent, microscopic redox equilibrium constants for thefirst time. The 80 different, microscopic redox equilibrium constantvalues show close correlation with the respective thiolate basicitiesand provide sound means for the development of potent agents againstoxidative stress. [ABSTRACT FROM AUTHOR]

Amino carbamate adduct formation from the amino group of an aminoglycoside and carbon dioxide has been postulated as a mechanism for reducing nephrotoxicity in the aminoglycoside class compounds. In this study, sisomicin was used as a model compound for amino carbamate analysis. A high pH based reversed-phase high performance liquid chromatography (RP-HPLC) method is used to separate the amino carbamate from sisomicin. The carbamate is stable as the breakdown is inhibited at high pH and any reactive carbon dioxide is removed as the carbonate. The amino carbamate was quantified and the molar fraction of amine as the carbamate of sisomicin was obtained from the HPLC peak areas. The equilibrium constant of carbamate formation, K c , was determined to be 3.3 × 10 −6 and it was used to predict the fraction of carbamate over the pH range in a typical biological systems. Based on these results, the fraction of amino carbamate at physiological pH values is less than 13%, and the postulated mechanism for nephrotoxicity protection is not valid. The same methodology is applicable for other aminoglycosides. [ABSTRACT FROM AUTHOR]

ABSTRACT For low polar molecular processes, we found the reliable relationship between the logarithm changes of the rate or equilibrium constants in the pressure range 1-1000 bar, [Ln( KP = 1000/ KP = 1)/1000], and tangent modulus at P = 1 bar, ∂Ln( KP)/∂ P: ∂Ln( KP)/∂ P = 1.15·[Ln( KP = 1000/ KP = 1)/1000], R = 0.995, which allows to predict the value of activation and reaction volume at ambient pressure. Therefore, it is sufficient to determine the values of the rate or equilibrium constants only at ambient pressures and at 1000 bar for the reliable estimation of the values of activation or reaction volume. [ABSTRACT FROM AUTHOR]

The aim of this work was to determine p K a values and solubility properties of 34 active agents using the SiriusT3 apparatus. The selected drug substances belong to the groups of ACE-inhibitors, β-blockers, antidiabetics and lipid lowering substances. Experimentally obtained p K a and intrinsic solubility values were compared to calculated values (program ACD/ChemSketch) and p K a values to published data as well. Solubility-pH profiles were generated to visualise the substance solubility over the gastrointestinal pH range. The relationship between the solubility characteristic of a substance, its bioavailability and categorisation according to the Biopharmaceutics Classification System (BCS) was examined as well. The results showed a good agreement between experimentally obtained, calculated and published p K a values. The measured and calculated intrinsic solubility values indicated several major deviations. All solubility-pH profiles showed the expected shape and appearance for acids, bases or zwitterionic substances. The obtained results for the p K a and solubility measurements of the examined active agents may help to predict their physicochemical behaviour in vivo, and to understand the bioavailability of the substances according to their BCS categorisation. The easy and reproducible determination of p K a and solubility values makes the SiriusT3 apparatus a useful tool in early stages of drug and formulation development. [ABSTRACT FROM AUTHOR]

We review the chemical equilibrium equations, and conclude that both their derivation and their meaning are problematic. We find that these equations can be established for a suitably defined simple system without chemical reactions. [ABSTRACT FROM AUTHOR]

Water oxidation in Photosystem II occurs at the oxygen-evolving complex (OEC), which cycles through distinct intermediates, S0-S4. The inhibitor ammonia selectively binds to the S2 state at an unresolved site that is not competitive with substrate water. By monitoring the yields of flash-induced oxygen production, we show that ammonia decreases the net efficiency of OEC turnover and slows the decay kinetics of S2 to S1. The temperature dependence of biphasic S2 decay kinetics provides activation energies that do not vary in control and ammonia conditions. We interpret our data in the broader context of previous studies by introducing a kinetic model for both the formation and decay of ammonia-bound S2. The model predicts ammonia binds to S2 rapidly (t1/2 = 1 ms) with a large equilibrium constant. This finding implies that ammonia decreases the reduction potential of S2 by at least 2.7 kcal mol-1 (>120 mV), which is not consistent with ammonia substitution of a terminal water ligand of Mn(IV). Instead, these data support the proposal that ammonia binds as a bridging ligand between two Mn atoms. Implications for the mechanism of O-O bond formation are discussed. [ABSTRACT FROM AUTHOR]