Search results for " free energy"
showing 10 items of 137 documents
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.
Phase diagrams of the system tetrahydrofuran/γ-butyrolactone/poly(ether imide) and determination of interaction parameters
1998
Abstract The thermodynamic interactions in the ternary mixture tetrahydrofuran/γ-butyrolactone/poly(ether imide) (THF/γ-BL/PEI) are investigated from 30 to 50°C. This is a membrane-forming system with a high He-selectivity. Cloud point measurements show that the two binary polymer solutions THF/PEI and γ-BL/PEI exhibit miscibility gaps which close towards the centre of the ternary phase diagram where the mixtures become homogeneous (cosolvency). Vapour pressures were determined for the subsystem THF/γ-BL. For the theoretical calculations the Gibbs energy of mixing is formulated according to the Flory-Huggins theory and the interaction parameter χ THF γ-BL calculated from the vapour pressure…
Shear influence on the phase separation of oligomer blends
1994
Shear influences on the phase separation behaviour of four different blends of ethylene glycol/propylene glycol oligomers, exhibiting upper critical solution temperatures, were investigated. Cloud point curves at rest (turbidity measurements) are reported for all systems, spinodal conditions (light scattering) and tie-lines (analysis of the coexisting phases) are given for some examples. Phase diagrams under shear were obtained from rheological data. They demonstrate that the demixing temperatures of systems where both glycols bear OH end-groups are lowered up to ca. 1°C by shear rates of 1000s−1; the critical composition, generalized to the non-equilibrium conditions of flow, is markedly s…
Structure and Thermodynamics of Binary Mixtures (Solutions)
2014
The concepts of chapter 2 are generalized to binary liquid mixtures (solutions). With the help of the concept of number and concentration fluctuations contact to the thermodynamics of solutions and physical chemistry of solutions is made. The perturbative RPA is shown to be equivalent to Flory’s theory of regular solutions. The phase diagrams of regular solutions and metal-salt solutions are discussed and explained in terms of the theories.