Search results for "Free energy"
showing 10 items of 170 documents
Modelling of thermo-chemical properties over the sub-solidus MgO–FeO binary, as a function of iron spin configuration, composition and temperature
2014
Thermo-chemical properties and T–X phase relations diagram of the (Mg,Fe)O solid solution are modelled using mixing Helmholtz energy, ΔF(T,x)mixing, calculated by quantum mechanical and semi-empirical techniques. The sub-solidus MgO–FeO binary has been explored as a function of composition, with iron either in high-spin (HS) or low-spin (LS) configuration. Only the HS model provides physically sound results at room pressure, yielding a correct trend of cell edge versus composition, whereas LS’s issues are at variance with observations. Mixing Helmholtz energy has been parametrized by the following relationship: ΔF(T,x)mixing = x × y × [U0(T) + U1(T) × (x – y) + U2(T) × (x − y)2]−T × S(x,y)c…
The conductance of lithium-7 fluoride in dioxane-water mixtures at 25�C
1990
Conductance data for lithium-7 fluoride in dioxane-water mixtures covering the range 78.35>D>36 in dielectric constant are presented. These data and other previous data on lithium-7 chloride and lithium-7 iodide were analyzed by the Fuoss 1980 conductance equation in order to find the limiting conductance Δo, the pairing distance R and the conductometric association constant Kλ. Setting Ka=Kλ/VM (where VM is the molar volume of the solvent), the thermodynamic pairing constant and the corresponding change of the free energy Δg were calculated. Correlation among the values found for R and Δg=Δh−TΔs and the properties characteristic of the ions and solvents are discussed.
Negative thermal expansion of quartz glass at low temperatures: An ab initio simulation study
2017
Abstract Using a mixed classical Molecular dynamics (MD)/ab initio simulation scheme combined with a quasi-harmonic approximation, we calculate the linear thermal expansion coefficient αL(T) in vitreous silica glasses. The systems are first cooled down by classical MD simulations. Then they are structurally relaxed by ab initio DFT calculations. The vibrational properties are calculated employing the frozen phonon method, and these results are finally used to calculate the Helmholtz free energy as a function of volume. In agreement with experiments, our simulations predict that αL(T) is negative at low temperatures up to T ≈ 150 K. In this low-temperature regime, the simulation results are …
Thermodynamics of the spin transition in [FexZn1−x(2-pic)3]Cl2 · EtOH
1992
Abstract With a new type of calorimeter we reinvestigated the specific heat Cp of the mixed crystals [FexZni1−x(2-pic)3]Cl2 · EtOH in the temperature range from 15 to 300 K. On the basis of a phenomenological thermodynamic model the anomaly in the Cp(T) curve of the mixed crystal (x = 0.73) can be quantitatively described as a result of the spin transition (1A1(low spin, LS) → 5T2(high spin, HS)). The parameters of the Gibbs free energy were independently derived from the temperature dependence of the HS fraction γ in [FexZn1−x(2-pic)3]Cl2 · EtOH. The pure iron complex (x = 1) exhibits a two-step spin transition. In the temperature range between the two steps the entropy obtained from the C…
Calculation of shear influences on the phase separation of polymer blends exhibiting upper critical solution temperatures
1994
Calculations were performed on the basis of a generalized Gibbs energy of mixing G γ, which is the sum of the Gibbs energy of mixing of the stagnant system and E s, the energy stored in the system during stationary flow. With increasing shear rate γ, the demixing temperatures shift to lower values (shear-induced mixing; diminution of the heterogeneous area), then to higher values (shear-induced demixing), and finally to lower values again before the effects fade out. The details of the rather complex phase diagrams resulting for a given shear rate are primarily determined by a band in the T/χ plane (χ = mole fraction) within which (∂2 E s/∂χ2) T UCST where they submerge. Bound to a suitable…
Transduction of redox Gibbs free energy into modulated electrochemical work
1988
Abstract This work supplies an electrochemical model in order to account for some oscillatory phenomena. The model can be applied both to living bodies and to electrochemical cells. We suppose that one of the products of an electrochemical reaction in solution has a high vapour pressure and study the influence of its mass transfers on its oscillations and on that of the current,induced by the former ones. Mass transfers that we consider are either that from the solution to theatmosphere above it or both that due to bubble nucleation and that from the solution to the bubbles alreadynucleated. Two different oscillation conditions are determined. One derives from the resistance due to theinter…
Calculation of organic solvent–water partition coefficients of iron–sulfur protein models
2002
Abstract A method is presented that permits semiquantitative estimation of the partitioning of many solutes between many pairs of media. As an example, the organic solvent–water partition coefficients P are calculated. The only needed parameters are the dielectric constant and molecular volume of the organic solvent. Fe 4 S 4 Cys n models of high-potential FeS proteins are studied. The Gibbs free energies of solvation and partition coefficients for Fe 4 S 4 Cys n are calculated. The organic solvent–water partition coefficients for 1-octanol P o , cyclohexane P ch and chloroform P cf decrease 4.41, 6.22 and 4.60 log units per cysteine (Cys) ligand, respectively. P o results are compared with…
Universal model for the calculation of all organic solvent–water partition coefficients
1998
Abstract We present the basis for building a universal organic solvation model to calculate solubility in any organic solvent and in water, as well as the organic solvent–water partition coefficient ( P ). Log P values are of the same order of magnitude as reference calculations but for a few cases which are discussed. Normalized log P contributions are sensitive to the rest of the atoms. When comparing porphin with phthalocyanine, the latter results in an amphipathic molecule. For C 70 , the contribution of a–e carbons to log P correlates with the distances from the nearest pentagon. The method has been also applied to benzobisthiazole oligomers and phenyl alcohols.
Nickel(II), copper(II) and zinc(II) metallo-intercalators: structural details of the DNA-binding by a combined experimental and computational investi…
2014
We present a thorough characterization of the interaction of novel nickel(II) (1), copper(II) (2) and zinc(II) (3) Schiff base complexes with native calf thymus DNA (ct-DNA), in buffered aqueous solution at pH 7.5. UV-vis absorption, circular dichroism (CD) and viscometry titrations provided clear evidence of the intercalative mechanism of the three square-planar metal complexes, allowing us to determine the intrinsic DNA-binding constants (K(b)), equal to 1.3 × 10(7), 2.9 × 10(6), and 6.2 × 10(5) M(-1) for 1, 2 and 3, respectively. Preferential affinity, of one order of magnitude, toward AT compared to GC base pair sequences was detected by UV-vis absorption titrations of 1 with [poly(dG-d…
Complex miscibility behaviour for polymer blends in flow
1995
Abstract Experimental observations of the effect of shear flow on the miscibility of binary polymer blends are compared to calculations based on a generalized Gibbs energy of mixing Gγ˙. This mixing free energy characterizes the steady state established at shear rateγ˙, as the sum of G z , the equilibrium Gibbs energy and E s , the energy the system stores while flowing.