Showing papers on "Enthalpy published in 2002"
TL;DR: In this paper, the authors presented selected values of thermodynamic quantities for the aqueous ionization reactions of 64 buffers, many of which are used in biological research. But the selection of the values of the thermodynamics quantities for each buffer is discussed.
Abstract: This review contains selected values of thermodynamic quantities for the aqueous ionization reactions of 64 buffers, many of which are used in biological research. Since the aim is to be able to predict values of the ionization constant at temperatures not too far from ambient, the thermodynamic quantities which are tabulated are the pK, standard molar Gibbs energy ΔrG∘, standard molar enthalpy ΔrH°, and standard molar heat capacity change ΔrCp∘ for each of the ionization reactions at the temperature T=298.15 K and the pressure p=0.1 MPa. The standard state is the hypothetical ideal solution of unit molality. The chemical name(s) and CAS registry number, structure, empirical formula, and molecular weight are given for each buffer considered herein. The selection of the values of the thermodynamic quantities for each buffer is discussed.
574 citations
TL;DR: In this paper, the authors measured the corrosion rates in the presence of mimosa tannin as a low carbon steel corrosion inhibitor in sulfuric acid media, in the range of temperatures from 20 to 60°C.
396 citations
TL;DR: In this article, the Gibbs free energy, enthalpy, and entropy functions from solution thermodynamics were used to describe the adsorption process of a mixture of gas mixtures in micropores.
Abstract: Thermodynamic equations are developed for adsorption of multicomponent gas mixtures in microporous adsorbents based on the principles of solution thermodynamics. The conventional spreading pressure and surface area variables, which describe 2-D films, must be abandoned for adsorption in micropores, in which spreading pressure cannot be measured experimentally or calculated from intermolecular forces. Adsorption is divided into two steps: (1) isothermal compression of the gas, (2) isothermal immersion of clean adsorbent in the compressed gas. Thermodynamic functions (Gibbs free energy, enthalpy, and entropy) from solution thermodynamics provide a complete thermodynamic description of the system. Applications are described for characterization of adsorbents, gas storage at high pressure, mixture adsorption, enthalpy balances, molecular simulation, adsorption calorimetry, and shape selectivity in catalysis.
319 citations
TL;DR: In this paper, a comprehensive model was developed for the calculation of speciation, phase equilibria, enthalpies, heat capacities and densities in mixed-solvent electrolyte systems.
310 citations
TL;DR: In this article, a calorimetric method of obtaining directly the fragility of liquids from the fictive temperatures of variably quenched glasses, is outlined, and the authors find that the most fragile liquids known are: glycerol, dibutylphthallate, 9-bromophenanthrene, salol, orthoterphenyl, propylene carbonate, decalin and its nitrogen derivative decahydroisoquinoline.
Abstract: A calorimetric method of obtaining directly the fragility of liquids from the fictive temperatures of variably quenched glasses, is outlined. “Steepness indexes” m, have been determined for a group of molecular liquids of diverse character, and vary in the range 50–150. The values obtained mostly agree well with those from earlier studies using dielectric relaxation, heat capacity spectroscopy, and viscosity data. In our method there is the advantage that the fragility is determined from the relaxation process that is basic to the calorimetric glass transition temperature measurement, namely, that of the enthalpy. The calorimetric measurements also yield the liquid and glass heat capacities, and entropies of fusion, permitting relationships between thermodynamic and kinetic responses to be examined simultaneously. We study glycerol, dibutylphthallate, 9-bromophenanthrene, salol, orthoterphenyl, propylene carbonate, decalin and its nitrogen derivative decahydroisoquinoline, and find the latter two to be the most fragile liquids known, m =145 and 128 respectively. Surprisingly, of the liquids studied, decalin has the smallest increase in heat capacity at the glass transition. By contrast, the strongest liquid, glycerol, has the largest increase. However, the thermodynamic fragility of decalin, assessed from the scaled rate of increase of the excess entropy above Tg, is found to be high, due to the unusually small value of the excess entropy at Tg. Conversely, the entropy-based fragility for glycerol is the lowest. Thus the correlation of kinetic and entropy-based thermodynamic fragilities reported in recent work is upheld by data from the present study, while the basis for any correlation with the jump in heat capacity itself is removed.
295 citations
TL;DR: An approximation of lipid-DNA binding as dominated by two factors-ionic and hydrophobic interactions-yielded a model that was consistent with experimental data and suggested that lipid cationic headgroups and aliphatic tails distribute evenly and lay down on DNA surface without the formation of micelles.
Abstract: Alkylammonium binding to DNA was studied by isothermal titration calorimetry. Experimental data, obtained as functions of alkyl chain length, salt concentration, DNA concentration, and temperature, provided a detailed thermodynamic description of lipid−DNA binding reactions leading to DNA condensation. Lipid binding, counterion displacement, and DNA condensation were highly cooperative processes, driven by a large increase in entropy and opposed by a relatively small endothermic enthalpy at room temperature. Large negative heat capacity change indicated a contribution from hydrophobic interactions between aliphatic tails.An approximation of lipid−DNA binding as dominated by two factorsionic and hydrophobic interactionsyielded a model that was consistent with experimental data. Chemical group contributions to the energetics of binding were determined and could be used to predict energetics of other lipid binding to DNA. Electrostatic and hydrophobic contributions to Gibbs free energy, enthalpy, entropy, an...
217 citations
TL;DR: In this article, the reversible Mg 2 FeH 6 and the mixed Mg2 FeH6 and MgH 2 hydride systems were investigated on a micro- or nanoscale level.
175 citations
TL;DR: In-situ Raman measurements of silica speciation in aqueous fluids in equilibrium with solid quartz are reported to 14 kbar and 900 °C as discussed by the authors, and the enthalpy of the polymerization reaction 2H 4 SiO 4 ↔H 6 Si 2 O 7 +H 2 O at 5 kbar pressure is Δ H =12.6±1.3 kJ/mol.
155 citations
TL;DR: In this article, a thermodynamic model for screening of ferroelectric surfaces based on Ginzburg-Devonshire theory is developed so that the enthalpy and entropy of charge compensation can be derived from the temperature dependence of surface potential contrast.
Abstract: Variable temperature scanning surface potential microscopy is used to determine thermodynamic and kinetic parameters associated with polarization screening on BaTiO3(100) surfaces. The temperature dependence of the surface potential is indicative of the interplay between the fast dynamics of atomic polarization and slower dynamics of screening charge. The screening charge relaxation kinetics are found to be weakly dependent on temperature with activation energy Ea∼4 kJ/mole. Equilibrium domain potential difference depends linearly on temperature; the zero potential contrast is observed at ∼110 °C. At room temperature the sign of domain potential is determined by the screening charges rather than polarization charge. A thermodynamic model for screening of ferroelectric surfaces based on Ginzburg–Devonshire theory is developed so that the enthalpy and entropy of charge compensation can be derived from the temperature dependence of surface potential contrast. In the case of BaTiO3 in air, the charge compensa...
136 citations
TL;DR: In this paper, the fictive temperature of a hyperquenched glass is determined based on heat capacity measurements and the recovered enthalpy of heating is estimated, which equals the released amount of the excess inherent structure energy stored in the glass.
132 citations
TL;DR: In this paper, the kinetics epoxidation of rubber seed oil (RSO) by peroxyacetic acid generated in situ were studied at various temperatures, and it was found that epoxification with almost complete conversion of unsaturated carbon and negligible oxirane cleavage can be attained by the in situ technique.
TL;DR: In this article, the authors investigated the microscopic mechanism of the proton transport process in liquid methanol at 300 K and found that the defect structure associated with an excess proton is a hydrogen-bonded cationic chain whose length generally exceeds the average chain length.
Abstract: The transport of protons through aqueous, partially aqueous, or nonaqueous hydrogen-bonded media is a fundamental process in many biologically and technologically important systems. Liquid methanol is an example of a hydrogen-bonded system that, like water, supports anomalously fast proton transport. Using the methodology of ab initio molecular dynamics, in which internuclear forces are computed directly from electronic structure calculations as the simulation proceeds, we have investigated the microscopic mechanism of the proton transport process in liquid methanol at 300 K. It is found that the defect structure associated with an excess proton in liquid methanol is a hydrogen-bonded cationic chain whose length generally exceeds the average chain length in pure liquid methanol. Hydrogen bonds in the first and second solvation shells of the excess proton are considerably shorter and stronger than ordinary methanol–methanol hydrogen bonds. Along this chain, proton transfer reactions occur in an essentially random manner described by Poisson statistics. Structural diffusion of the defect structure is possible if the proton migrates toward an end of the defect chain, which causes a weakening of the hydrogen bonds at the opposite end. The latter can, therefore, be easily ruptured by ordinary thermal fluctuations. At the end of the chain where the proton resides, new hydrogen bonds are likely to form due to the strong associative nature of the excess proton. It is through this “snake-like” mechanism that the defect structure is able to diffuse through the hydrogen-bond network of the liquid. The estimated activation enthalpy of this proposed mechanism is found to be in reasonable agreement with the experimentally determined activation enthalpy.
TL;DR: Direct comparison reveals that the temperature-independent thermodynamic parameters could provide a reasonable approximation only when the temperature of interest has a small deviation from the mean melting temperature over the experimental range.
Abstract: A clear difference in the enthalpy changes derived from spectroscopic and calorimetric measurements has recently been shown. The exact interpretation of this deviation varied from study to study, but it was generally attributed to the non-two-state transition and heat capacity change. Although the temperature-dependent thermodynamics of the duplex formation was often implied, systemic and extensive studies have been lacking in universally assigning the appropriate thermodynamic parameter sets. In the present study, the 24 DNA/DNA and 41 RNA/DNA oligonucleotide duplexes, designed to avoid the formation of hairpin or slipped duplex structures and to limit the base pair length less than 12 bp, were selected to evaluate the heat capacity changes and temperature-dependent thermodynamic properties of duplex formation. Direct comparison reveals that the temperature-independent thermodynamic parameters could provide a reasonable approximation only when the temperature of interest has a small deviation from the mean melting temperature over the experimental range. The heat capacity changes depend on the base composition and sequences and are generally limited in the range of −160 to ≈−40 cal·mol−1·K−1 per base pair. In contrast to the enthalpy and entropy changes, the free energy change and melting temperature are relatively insensitive to the heat capacity change. Finally, the 16 NN-model free energy parameters and one helix initiation at physiological temperature were extracted from the temperature-dependent thermodynamic data of the 41 RNA/DNA hybrids.
TL;DR: In this paper, the molecular geometries, infrared vibrational spectra, and thermodynamic properties of octanitrocubane (ONC) are calculated using the density functional theory (DFT) method at the B3LYP/6-31G* level, and the calculated IR frequencies of ONC are scaled.
Abstract: The molecular geometries, infrared vibrational spectra, and thermodynamic properties of octanitrocubane (ONC) are calculated using the density functional theory (DFT) method at the B3LYP/6-31G* level. The IR frequency scaling factor 0.9501 suitable for polynitrocubanes is obtained at the B3LYP/6-31G* level, and the calculated IR frequencies of ONC are scaled. The accurate heat of formation 726.47 kJ/mol of ONC in gas phase is obtained via designed isodesmic reaction in which the cubane cage skeleton has been kept. The sublimation enthalpy, density, and heat of formation for ONC crystal are also calculated, and they are 220.63 kJ/mol, 2.189 g/cm3, and 505.84 kJ/mol, respectively. In addition, the estimated detonation velocity and detonation pressure of ONC are 10.26 mm/ms and 520.86 kbar, respectively. Finally, the pyrolysis mechanism of ONC is studied using various theoretical methods, i.e., MP2, DFT, and selected MINDO/3 semiempirical MO, based on the unrestricted Hartree–Fock model. The calculated results show that the pyrolysis initiation reaction of ONC, i.e., rate-controlling step, is to form a diradical by the single C–C bond breaking in the cube. The second C–C bond breaking is easily followed to form a nitrocyclooctatetraene. The calculated activation energy for the pyrolysis initiation reaction of ONC, obtained from B3LYP/6-31G* method, is 155.30 kJ/mol, which this rather large activation energy indicates that ONC is a new type of energetic material with less sensitivity and better thermal stability, and has highly exploitable values.
TL;DR: In this paper, a microscopic model for associating fluids that accurately captures the thermodynamics of liquid water is extended to aqueous solutions with nonpolar species, and the predicted solubility of non-polar solutes is slight over a wide range of temperatures, and exhibits a minimum as a function of temperature.
Abstract: A recently developed microscopic model for associating fluids that accurately captures the thermodynamics of liquid water [Truskett et al., J. Chem. Phys. 111, 2647 (1999)] is extended to aqueous solutions with nonpolar species. The underlying association model incorporates the highly directional and open nature of water’s hydrogen-bond network, and, as a result, captures a number of the distinguishing properties of liquid water, such as the density anomaly. The model for aqueous mixtures developed herein predicts many of the thermodynamic signatures of hydrophobic hydration without resorting to empirical temperature-dependent parameters. The predicted solubility of nonpolar species is slight over a wide range of temperatures, and exhibits a minimum as a function of temperature, in accord with experiment. Hydration is opposed by a dominant entropy and favored by the enthalpy at low temperatures. At elevated temperatures these roles are reversed. Furthermore, the hydration entropies for hydrophobes of varying size converge over a very narrow temperature range. Comparison with experimental and simulation data for nonpolar solutes in water shows that the theory tends to exaggerate the solute’s transfer heat capacity at low temperature, and hence solubility minima and entropy convergence are predicted to occur at lower temperatures than observed. Our results support the emerging view that hydrophobic effects can be attributed in large part to the equation of state for pure water.
TL;DR: A two-state model of the water structure appears to provide a microscopic view of the hydrophobic effect and is consistently linked to macroscopic thermodynamic parameters.
Abstract: Herein we provide a new insight into the hydrophobic effect in protein folding. Our proposition explains the molecular basis of cold denaturation, and of intermediate states in heat and their absence in cold denaturation. The exposure of non-polar surface reduces the entropy and enthalpy of the system, at low and at high temperatures. At low temperatures the favorable reduction in enthalpy overcomes the unfavorable reduction in entropy, leading to cold denaturation. At high temperatures, folding/unfolding is a two-step process: in the first, the entropy gain leads to hydrophobic collapse, in the second, the reduction in enthalpy due to protein-protein interactions leads to the native state. The different entropy and enthalpy contributions to the Gibbs energy change at each step at high, and at low, temperatures can be conveniently explained by a two-state model of the water structure. The model provides a clear view of the dominant factors in protein folding and stability. Consequently, it appears to prov...
TL;DR: For both groups of compounds, ED Y's destabilize the molecule and stabilize the radical, while the opposite holds true for EW Y's, and data indicate that the strengthening effect on N-H BDEs of electron-withdrawing (EW) Y's is greater than the weakening effect ofelectron-donating (ED) Ys.
Abstract: Bond dissociation enthalpy differences, Z−X ΔBDE = BDE(4-YC6H4Z-X) − BDE(C6H5Z-X), for Z = CH2 and O are largely independent of X and are determined mainly by the stabilization/destabilization effect of Y on the 4-YC6H4Z• radicals. The effects of Y are small (≤2 kcal/mol for all Y) for Z = CH2, but they are large for Z = O, where good correlations with σp+(Y) yield ρ+ = 6.5 kcal/mol. For Z = NH, two sets of electrochemically measured N−H ΔBDEs correlate with σp+(Y), yielding ρ+ = 3.9 and 3.0 kcal/mol. However, in contrast to the situation with phenols, these data indicate that the strengthening effect on N−H BDEs of electron-withdrawing (EW) Y's is greater than the weakening effect of electron-donating (ED) Y's. Attempts to measure N−H ΔBDEs in anilines using two nonelectrochemical techniques were unsuccessful; therefore, we turned to density functional theory. Calculations on 15 4-YC6H4NH2 gave N−H ΔBDEs correlating with σp+ (ρ+ = 4.6 kcal/mol) and indicated that EW and ED Y's had comparable strengthenin...
TL;DR: In this paper, the phase equilibria of the pseudo-binary Li 2 O-TiO 2 system and the stoichiometry shift of Li 2 TiO 3 during the Li transmutation process are investigated.
TL;DR: Effects of amino acid substitutions at four fully buried sites of the ubiquitin molecule on the thermodynamic parameters (enthalpy, Gibbs energy) of unfolding were evaluated experimentally using differential scanning calorimetry to conclude that packing of non-polar groups in the protein interior is favorable and is largely defined by a favorable enthalpy of van der Waals interactions.
TL;DR: A statistical thermodynamics theory is provided that rationalizes the close relation between heat capacity and relaxation times and is based on the recent finding that enthalpy and volume changes close to the melting transition are proportional functions.
TL;DR: A first attempt at an empirical parameterization of the binding enthalpy for small ligands in terms of structural information is presented and it is found that at least three terms need to be considered: the intrinsicEnthalpy change that reflects the nature of the interactions between ligand, target, and solvent; the ent Halpy associated with any possible conformational change in the protein or ligand upon binding.
Abstract: A major goal in ligand and drug design is the optimization of the binding affinity of selected lead molecules. However, the binding affinity is defined by the free energy of binding, which, in turn, is determined by the enthalpy and entropy changes. Because the binding enthalpy is the term that predominantly reflects the strength of the interactions of the ligand with its target relative to those with the solvent, it is desirable to develop ways of predicting enthalpy changes from structural considerations. The application of structure/enthalpy correlations derived from protein stability data has yielded inconsistent results when applied to small ligands of pharmaceutical interest (MW < 800). Here we present a first attempt at an empirical parameterization of the binding enthalpy for small ligands in terms of structural information. We find that at least three terms need to be considered: (1) the intrinsic enthalpy change that reflects the nature of the interactions between ligand, target, and solvent; (2) the enthalpy associated with any possible conformational change in the protein or ligand upon binding; and, (3) the enthalpy associated with protonation/deprotonation events, if present. As in the case of protein stability, the intrinsic binding enthalpy scales with changes in solvent accessible surface areas. However, an accurate estimation of the intrinsic binding enthalpy requires explicit consideration of long-lived water molecules at the binding interface. The best statistical structure/enthalpy correlation is obtained when buried water molecules within 5–7 A of the ligand are included in the calculations. For all seven protein systems considered (HIV-1 protease, dihydrodipicolinate reductase, Rnase T1, streptavidin, pp60c-Src SH2 domain, Hsp90 molecular chaperone, and bovine β-trypsin) the binding enthalpy of 25 small molecular weight peptide and nonpeptide ligands can be accounted for with a standard error of ±0.3 kcal · mol−1. Proteins 2002;49:181–190. © 2002 Wiley-Liss, Inc.
TL;DR: The isocratic retention of enantiomers of chiral analytes, i.e. tryptophan, 1,2,3,4-tetrahydroisoquinoline and gamma-butyrolac tone analogs, was studied on a ristocetin A chiral stationary phase at different temperatures and with different mobile phase compositions, using the reversed-phase, polar-organic and normal-phase modes.
TL;DR: Data indicated the formation of micelles with a less ordered structure as the formamide increases in the solvent system, which is attributed to an enhanced solvation in formamide rich solvent mixtures.
TL;DR: The model system described earlier to make direct measurements of the enthalpy of helix formation at different temperatures has an enormous potential for measuring various thermodynamic properties of α-helices.
Abstract: The goal of this study is to use the model system described earlier to make direct measurements of the enthalpy of helix formation at different temperatures. For this we studied model alanine peptides in which helix formation can be triggered by metal (La3+) binding. The heat of La3+ interaction with the peptides at different temperatures is measured by isothermal titration calorimetry. Circular dichroism spectroscopy is used to follow helix formation. Peptides of increasing length (12-, 16-, and 19-aa residues) that contain a La3+-binding loop followed by helices of increasing length, are used to separate the heat of metal binding from the enthalpy of helix formation. We demonstrate that (i) the enthalpy of helix formation is −0.9 ± 0.1 kcal/mol; (ii) the enthalpy of helix formation is independent of the peptide length; (iii) the enthalpy of helix formation does not depend significantly on temperature in the range from 5 to 45°C, suggesting that the heat capacity change on helix formation is very small. Thus, the use of metal binding to induce helix formation has an enormous potential for measuring various thermodynamic properties of α-helices.
TL;DR: 1-3 are the first examples of species containing eta2-coordinated tetrahedral P4 molecules, and the Ag(P4)2+ ion has an almost planar coordination environment around the Ag+ ion.
Abstract: The silver aluminates AgAl[OC(CF3)2(R)]4 (R = H, CH3, CF3) react with solns. of white phosphorus P4 to give complexes that bind one or two almost undistorted tetrahedral P4 mols. in an h2 fashion: [Ag(P4)2]+[Al(OC(CF3)3)4]- (1) contg. the 1st homoleptic metal-phosphorus cation, the mol. species (P4)AgAl[OCMe(CF3)2]4 (2), and the dimeric Ag(m,h2-P4)Ag bridged {(P4)AgAl[OC(H)(CF3)2]4}2 (3). Compds. 1-3 were characterized by variable-temp. (VT) 31P NMR spectroscopy (1 also by VT 31P MAS NMR spectroscopy), Raman spectroscopy, and single-crystal x-ray crystallog. Other Ag:P4 ratios did not lead to new species, and this observation was rationalized on thermodn. grounds. The Ag(P4)2+ ion has an almost planar coordination environment around the Ag+ ion due to dx2-y2(Ag) -> s*(P-P) backbonding. Calcns. (HF-DFT) on six Ag(P4)2+ isomers showed that the planar h2 form is only slightly favored by 5.2 kJ mol-1 over the tetrahedral h2 species; h1-P4 and h3-P4 complexes are less favorable (27-76 kJ mol-1). The bonding of the P4 moiety in [RhCl(h2-P4)(PPh3)2], the only compd. in which an h2 bonding mode of a tetrahedral P4 mol. was claimed, must be regarded as a tetraphosphabicyclobutane, and not as a tetrahedro-P4 complex, from the published NMR and vibrational spectra, the calcd. geometry of [RhCl(P4)(PH3)2] (10), the highly endothermic (385 kJ mol-1) calcd. dissocn. enthalpy of 10 into P4 and RhCl(PH3)2 (11), as well as atoms in mols. (AIM) and natural bond orbital (NBO) population analyses of 10 and the Ag(P4)2+ ion. Therefore, 1-3 are the 1st examples of species contg. h2-coordinated tetrahedral P4 mols. [on SciFinder (R)]
01 Jul 2002
TL;DR: A Mg/Fe hydrotalcite-like-compound was prepared and its affinity toward the removal of SeO(3)(2-) from an aqueous medium was studied as a function of pH, time, temperature, particle dose, and SeO (3)( 2-) concentration.
Abstract: A Mg/Fe hydrotalcite-like-compound (HTlc) was prepared and its affinity toward the removal of SeO32− from an aqueous medium was studied as a function of pH, time, temperature, particle dose, and SeO32− concentration. The fraction of SeO32− removal increases with decrease in both pH and temperature. The adsorption data are fitted to the Langmuir adsorption isotherm in the temperature range 303–333 K, and the thermodynamic parameters viz. standard Gibbs' free energy change (ΔG°), enthalpy change (ΔH°), and entropy change (ΔS°) are calculated. The negative value of ΔH° indicates that the adsorption process is exothermic. The apparent equilibrium constants (Ka) are also calculated and found to decrease with increase in temperature.
TL;DR: In this paper, the enthalpy of the supersaturated fcc solid solution was determined as a function of composition using calorimetry measurements and molecular dynamics simulations, and the preference for the fcc crystalline state is enhanced by the low kinetic barrier to crystallization of the amorphous solution.
TL;DR: In this article, the authors investigated the extraction behavior of La(III) from acidic nitrate-acetato medium by bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272, H2A2) in toluene either alone or in combination with trioctylphospine oxide (TOPO, B) has been investigated as a function of contact time, aqueous phase concentration of La3+, H+, NO3− and Ac− (acetate), Cyanex 272 and TOPO concentration in the
TL;DR: In this paper, the authors used long molecular dynamics simulations of methane molecules in explicit water at three different temperatures at pressures of 1 and 4000 atm to calculate entropic and enthalpic contributions to the free energy of methane-methane association.
Abstract: We use long molecular dynamics simulations of methane molecules in explicit water at three different temperatures at pressures of 1 and 4000 atm to calculate entropic and enthalpic contributions to the free energy of methane–methane association. In agreement with previous simulation studies, we find that the contact minimum is dominated by entropy whereas the solvent-separated minimum is stabilized by favorable enthalpy of association. Both the entropy and enthalpy at the contact minimum change negligibly with increasing pressure leading to the relative pressure insensitivity of the contact minimum configurations. In contrast, we find that the solvent-separated configurations are increasingly stabilized at higher pressures by enthalpic contributions that prevail over the slightly unfavorable entropic contributions to the free energy. The desolvation barrier is dominated by unfavorable enthalpy of maintaining a dry volume between methanes. However, the increasing height of the desolvation barrier with increasing pressures results from entropy changes at the barrier configurations. Further resolution of the enthalpy of association shows that major contributions to the enthalpy arise from changes in water–water interactions and the mechanical work (PΔV) expended in bringing the methanes to a separation of r. A connection of these thermodynamic features with the underlying changes in water structure is made by calculating methane–methane–water oxygen triplet correlation functions.
TL;DR: In this paper, the authors derived standard enthalpies of formation, ΔH0f (kJ/mol), for three pyrochlore phases: Ca0.93Ce1.00Ti2.