Some quantitative relationships for ionization reactions at high pressures

1975 ◽  
Vol 28 (5) ◽  
pp. 945 ◽  
Author(s):  
BS El'yanov ◽  
SD Hamann
Keyword(s):  
High Pressures ◽  
Good Description ◽  
Ionization Constants ◽  
Linear Free Energy Relationship ◽  
Free Energies ◽  
Ion Hydration ◽  
Linear Free Energy ◽  
Linear Relationships ◽  
Wide Range ◽  
Ionization Equilibria

A simple formula is proposed to describe the pressure dependence of the variable Φ in El?yanov and Gonikberg's linear free energy relationship for ionization reactions in solution at high pressure. ��� The expression, given in equations (10) and (12), provides a good description of the influence of pressure on ionization equilibria in aqueous solutions. It permits El'yanov's general linear relationships between Φ and ionization free energies, enthalpies and entropies, pH and Hammett's p parameter, to be expressed in terms of the pressure in convenient analytical forms. ��� The formula is shown to be consistent with the simple electrostatic theory of ion hydration, allowing for the effect of pressure on the dielectric constant of water. Combined with the theory, it provides a general means of predicting ionization constants over a wide range of pressures and temperatures simply from knowledge of the changes in molar volume, enthalpy and entropy which accompany the reactions at atmospheric pressure.

Linear free energy relationship and some quantitative regularities of the of pressure on chemical reactions

1975 ◽  
Vol 28 (5) ◽  
pp. 933 ◽  
Author(s):  
BS El'yanov
Keyword(s):  
Free Energy ◽  
Chemical Reactions ◽  
High Pressures ◽  
Ionization Constants ◽  
Linear Free Energy Relationship ◽  
Volume Changes ◽  
Effect Of Pressure ◽  
Buffer Solutions ◽  
Linear Free Energy ◽  
The Relationship

A study has been made of the applicability of a linear free energy relationship describing the effect of pressure on the equilibrium and rate constants of chemical reactions. Some properties of the relationship have been analysed and corollaries, including linear dependences, obtained which make it possible to calculate reaction enthalpies and entropies, volume changes and Hammett's p-constants at high pressures. Ionization reactions have been used as examples to illustrate the conclusions arrived at. The linear free energy relationship has been shown to describe the effect of pressure up to 8000 bars on the ionization constants of acids and on the pH of buffer solutions.

scholarly journals Rationalisation of the activities of phenolic (vitamin E-type) antioxidants

2003 ◽  
Vol 17 (4) ◽  
pp. 753-762
Author(s):  
Christopher J. Rhodes ◽  
Thuy T. Tran ◽  
Philip Denton ◽  
Harry Morris
Keyword(s):  
Free Energy ◽  
Vitamin E ◽  
Gibbs Free Energy ◽  
State Theory ◽  
Linear Free Energy Relationship ◽  
Free Energies ◽  
Gibbs Free Energy Change ◽  
Linear Free Energy ◽  
Free Energy Of Activation ◽  
Enthalpy And Entropy

Using Transition-State Theory, experimental rate constants, determined over a range of temperatures, for reactions of vitamin E type antioxidants are analysed in terms of their enthalpies and entropies of activation. It is further shown that computational methods may be employed to calculate enthalpies and entropies, and hence Gibbs Free Energies, for the overall reactions. Within the Linear Free Energy Relationship (LFER) assumption, that the Gibbs Free Energy of activation is proportional to the overall Gibbs Free Energy change for the reaction, it is possible to rationalise, and even to predict, the relative contributions of enthalpy and entropy for reactions of interest, involving potential antioxidants.

Solvation of ions. XXII. Solvation of cations by hard N,N-dimethylformamide and soft N,N-dimethylthioformamide

1974 ◽  
Vol 27 (5) ◽  
pp. 933 ◽  
Author(s):  
R Alexander ◽  
DA Owensby ◽  
AJ Parker ◽  
WE Waghorne
Keyword(s):  
Electrochemical Cell ◽  
Linear Free Energy Relationship ◽  
Free Energies ◽  
Univalent Cations ◽  
Liquid Junction Potential ◽  
Liquid Junction ◽  
Linear Free Energy ◽  
Solvation Of Ions ◽  
Solvation Mechanisms ◽  
Junction Potential

The free energies of transfer of some univalent cations from N,N-dimethylformamide to N,N- dimethylthioformamide at 25� are Li+, 64.0; Na+, 50.2; K+, 37.2; Cs+, 23.4; TI+, -4.2 and Ag+, - 87.0 kJ g-ion-1. The values are based on the assumption of negligible liquid junction potential in an electrochemical cell. Certain ones of these values can be interpreted in terms of general interactions of hard and soft cations with hard and soft basic solvents. A linear free energy relationship, ΔGtr(M+) = mΔGtr(K+), is roughly obeyed by many cations for transfer to a variety of solvents. Deviations from this relationship, for example ΔGtr(Ag2+) to acetonitrile, ΔGtr (Ph4As+) to water and ΔGtr (Ag+) to N,N-dimethylthioformamide, allow specific solvation mechanisms to be detected.

scholarly journals A conformationally adaptive macrocycle: conformational complexity and host–guest chemistry of zorb[4]arene

2018 ◽  
Vol 14 ◽  
pp. 1570-1577 ◽  
Author(s):  
Liu-Pan Yang ◽  
Song-Bo Lu ◽  
Arto Valkonen ◽  
Fangfang Pan ◽  
Kari Rissanen ◽  
...  
Keyword(s):  
Free Energy ◽  
Conformational Changes ◽  
Large Amplitude ◽  
Linear Free Energy Relationship ◽  
Stimuli Responsive ◽  
Binding Behavior ◽  
Linear Free Energy ◽  
Wide Range ◽  
Heat Capacity Changes ◽  
Guest Chemistry

Large amplitude conformational change is one of the features of biomolecular recognition and is also the basis for allosteric effects and signal transduction in functional biological systems. However, synthetic receptors with controllable conformational changes are rare. In this article, we present a thorough study on the host–guest chemistry of a conformationally adaptive macrocycle, namely per-O-ethoxyzorb[4]arene (ZB4). Similar to per-O-ethoxyoxatub[4]arene, ZB4 is capable of accommodating a wide range of organic cations. However, ZB4 does not show large amplitude conformational responses to the electronic substituents on the guests. Instead of a linear free-energy relationship, ZB4 follows a parabolic free-energy relationship. This is explained by invoking the influence of secondary C–H···O hydrogen bonds on the primary cation···π interactions based on the information obtained from four representative crystal structures. In addition, heat capacity changes (ΔC p) and enthalpy–entropy compensation phenomena both indicate that solvent reorganization is also involved during the binding. This research further deepens our understanding on the binding behavior of ZB4 and lays the basis for the construction of stimuli-responsive materials with ZB4 as a major component.

Incorporation of Radioactive Metals and Trace Metals into Phosphate “Anhydrous” Autunite: Thermodynamic Evaluation

2002 ◽  
Vol 757 ◽  
Author(s):  
Huifang Xu ◽  
Yifeng Wang
Keyword(s):  
Environmental Remediation ◽  
Order Approximation ◽  
Fission Products ◽  
Monovalent Cation ◽  
Nuclear Waste Repository ◽  
Linear Free Energy Relationship ◽  
Thermodynamic Evaluation ◽  
Spent Fuel ◽  
Free Energies ◽  
Linear Free Energy

ABSTRACTThe prediction of heavy metal solubility in the presence of phosphate is the key for designing a successful environmental remediation strategy or for the performance assessment of a nuclear waste repository. In order to evaluate the possibility for solubilities and incorporation of U and its fission products, such as Cs, Np, Pu, it is important to have the Gibbs free energies of formation of possible end-member phases. In this paper, we use a linear free energy relationship to calculate the Gibbs free energies of formation of divalent cation “anhydrous” autunite phases [M2+(UO2)2(PO4)2] and monovalent cation “anhydrous” autunite phases [M+2(UO2)2(PO4)2]. Based on predicted Gibbs free energies of formation for autunite phases, an equilibrium calculation indicates that it is feasible to incorporate NpO2+ into the autunite phases. If concentration of Cs+ is high, Cs+ will be incorporated into the autunite phases. However, it is not feasible to incorporate low concentration Cs+ released from spent fuel into the uranyl phosphate phases with layered structure and interlayer water (such as autunite phases, boltwoodite phases, and uranophane phases) as previously proposed. The predicted data can be considered as a first order approximation.

Using Linear Free Energy Relationship to Predict the Stability Constants of Aqueous Complexes of Metal-Organic Ligands

2004 ◽  
Vol 824 ◽  
Author(s):  
Huifang Xu ◽  
Yifeng Wang
Keyword(s):  
Free Energy ◽  
Metal Complexes ◽  
Stability Constants ◽  
Metal Cation ◽  
Dissociation Constants ◽  
Natural Environments ◽  
Linear Free Energy Relationship ◽  
Free Energies ◽  
Linear Free Energy ◽  
The Stability

AbstractThe Sverjensky-Molling linear free energy relationship was originally developed to correlate the Gibbs free energies of formation of an isostrutural family of solid phases to the thermodynamic properties of aqueous cations. In this paper, we demonstrate that the similar relationship also exists between metal complexes and simple metal cations in aqueous solutions. We extend the Sverjensky-Molling relationship to predict the Gibbs free energies of formation or dissociation constants for a family of metal complexes with a given complexing ligand. The discrepancies between the predicted and experimental data are generally less than 1.5 kcal/mol (or one log unit for stability constants). The use of this linear free energy correlation can significantly enhance our ability to predict the speciation, mobility, and toxicity of heavy metals in natural environments. According the obtained results, Gibbs free energies of formation of cations (δG0f, Mn+) can be used as an indicator for the hardness/softness of a metal cation (acid). The higher negative value of a metal cation, the harder acid it will be. It is logical to postulate that the coefficient a*ML characterizes the softness of a complexing ligand (base).

scholarly journals Substrate analogues as probes of the catalytic mechanism of l-mandelate dehydrogenase from Rhodotorula graminis

1994 ◽  
Vol 297 (3) ◽  
pp. 647-652 ◽  
Author(s):  
O Smékal ◽  
G A Reid ◽  
S K Chapman
Keyword(s):  
Transition State ◽  
Catalytic Mechanism ◽  
Activation Parameters ◽  
Linear Free Energy Relationship ◽  
Free Energies ◽  
Linear Free Energy ◽  
Kinetic Isotope ◽  
Substrate Analogues ◽  
Reaction Constant ◽  
Delta G

A detailed kinetic analysis of the oxidation of mono-substituted mandelates catalysed by L-(+)-mandelate dehydrogenase (L-MDH) from Rhodotorula graminis has been carried out to elucidate the role of the substrate in the catalytic mechanism. Values of Km and kcat. (25 degrees C, pH 7.5) were determined for mandelate and eight substrate analogues. Values of the activation parameters, delta H++ and delta S++ (determined over the range 5-37 degrees C), for mandelate and all substrate analogues were compensatory resulting in similar low values for free energies of activation delta G++ (approx. 60 kJ.mol-1 at 298.15 K) in all cases. A kinetic-isotope-effect value of 1.1 +/- 0.1 was observed using D,L-[2-2H]mandelate as substrate and was invariant over the temperature range studied. The logarithm of kcat. values for the enzymic oxidation of mandelate and all substrate analogues (except 4-hydroxymandelate) showed good correlation with Taft's dual substituent constant omega (where omega = omega I + 0.64 omega +R) and gave a positive reaction constant value, rho, of 0.36 +/- 0.07. This linear free-energy relationship was verified by analysing the data using isokinetic methods. These findings support the hypothesis that the enzyme-catalysed reaction proceeds via the same transition state for each substrate and indicates that this transition state is relatively nonpolar but has an electron-rich centre at the alpha-carbon position.

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