Liquid-gas phase diagrams and Gibbs free energy per nucleon

1994 ◽  
Vol 50 (2) ◽  
pp. 771-774 ◽  
Author(s):  
G. T. Zheng
Keyword(s):  
Free Energy ◽  
Phase Diagrams ◽  
Gas Phase ◽  
Gibbs Free Energy

Theoretical Investigation on Tautomerization Mechanism of 6-Thioguanine

2013 ◽  
Vol 690-693 ◽  
pp. 1418-1421 ◽  
Author(s):  
Hong Jiang Ren
Keyword(s):  
Free Energy ◽  
Gas Phase ◽  
Gibbs Free Energy ◽  
Rate Constants ◽  
Reaction Mechanisms ◽  
Energy Barrier ◽  
Intramolecular Proton Transfer ◽  
Transfer Reactions ◽  
Free Energy Barrier ◽  
Proton Transfer Reactions

The tautomerization reaction mechanisms between three stable 6-thioguanine tautomers were investigated theoretically using B3LYP/6-311+G(d,p) method. The results show that the pathway P(1) is to isomerize from TG(9,10,10,11) to TG(1,9,10,10) and the needed activation Gibbs free energy barrier is 112.7 kJ/mol with the rate constant of 1.12×10-7 s-1. Another two pathways P(2) and P(3) are to isomerize from TG(1,9,10,10) to TG(1,7,10,10) and the activation Gibbs free energy barriers of the rate-determining steps are 227.4 and 281.6 kJ/mol, respectively, with the related rate constants of 8.96×10-28 s-1 and 2.86×10-37 s-1, these results implying the intramolecular proton transfer reactions are infeasible in the gas phase.

scholarly journals Host–guest interactions between p-sulfonatocalix[4]arene and p-sulfonatothiacalix[4]arene and group IA, IIA and f-block metal cations: a DFT/SMD study

2019 ◽  
Vol 15 ◽  
pp. 1321-1330 ◽  
Author(s):  
Valya K Nikolova ◽  
Cristina V Kirkova ◽  
Silvia E Angelova ◽  
Todor M Dudev
Keyword(s):  
Aqueous Solution ◽  
Free Energy ◽  
Complex Formation ◽  
Gas Phase ◽  
Gibbs Free Energy ◽  
Metal Cations ◽  
Water Soluble ◽  
Model Systems ◽  
Solvent Treatment ◽  
Explicit Solvent

The molecular recognition in aqueous solution is extremely important because most biological processes occur in aqueous solution. Water-soluble members of the calix[n]arene family (e.g., p-sulfonato substituted) can serve as model systems for studying the nature and manner of interactions between biological receptors and small ions. The complex formation behavior of water-soluble p-sulfonatocalix[4]arene and thiacalix[4]arene and group IA, IIA and f-block metal cations has been investigated computationally by means of density functional theory computations in the gas phase and in aqueous environment. The calculated Gibbs free energy values of the complex formation reaction of these ligands with the bare metal cations suggest a spontaneous and energy-favorable process for all metal cations in the gas phase and only for Na+, Mg2+, Lu3+ cations in water environment. For one of the studied cations (La3+) a supramolecular approach with explicit solvent treatment has been applied in the study of the effect of metal hydration on the complexation process. The La3+ binding to the p-sulfonatocalix[4]arene host molecule (now in the metal’s second coordination shell) is still exergonic as evidenced by the negative Gibbs free energy values (ΔG 1 and ΔG 78). The combination of implicit/explicit solvent treatment seems useful in the modeling of the p-sulfonatocalix[4]arene (and thiacalix[4]arene) complexes with metal cations and in the prediction of the thermodynamic parameters of the complex formation reactions.

High pressures and the structure of solids of geochemical and geophysical interest

1992 ◽  
Vol 56 (384) ◽  
pp. 373-383 ◽  
Author(s):  
C. H. L. Goodman
Keyword(s):  
High Pressure ◽  
Free Energy ◽  
Phase Transformations ◽  
Phase Diagrams ◽  
Gibbs Free Energy ◽  
Amorphous Materials ◽  
High Pressures ◽  
Opposite Sign ◽  
Amorphous Solids ◽  
Radius Ratio

AbstractPressures of 10 GPa and above can bring about phase transformations in many oxides, an effect of great interest to geochemists and geophysicists. We can interpret such behaviour as due to the differential compressibility of 'anion' and 'cation' leading to a progressive rise in radius ratio with pressure, and hence, on the classic crystallochemical picture, eventually to an increase in co-ordination number (though with complications which make prediction difficult). More generally, pressure affects Gibbs free energy G directly; for oxides a pressure of 5 GPa gives, very roughly, the same contribution to G as 100°C in temperature (though with opposite sign). Thus high pressure significantly affects the shape and structure of phase diagrams, showing increasingly important effects above, say, 10 GPa—but again prediction can be difficult. However these two complementary approaches to the effects of pressure, helpful though they can be conceptually, are 'crystal-based' and totally neglect another rather littleknown but potentially important effect--the formation of amorphous solids; 'polymers' and glasses. Since amorphous materials are 'non-equilibrium' they are not readily dealt with theoretically; also, since they are difficult to detect by standard crystallographic techniques, they can be overlooked experimentally. The pressure-induced formation of amorphous solids could have significant implications for both geochemistry and geophysics.

Prediction of Alkanolamine pKa Values by Combined Molecular Dynamics Free Energy Simulations and ab initio Calculations

2019 ◽  
Author(s):  
Javad Noroozi ◽  
William Smith
Keyword(s):  
Molecular Dynamics ◽  
Free Energy ◽  
Ab Initio Calculations ◽  
Gas Phase ◽  
Quantum Chemical ◽  
Phase Reaction ◽  
Pka Values ◽  
Gas Phase Reaction ◽  
Reaction Free Energy ◽  
Energy Simulations

We use molecular dynamics free energy simulations in conjunction with quantum chemical calculations of gas phase reaction free energy to predict alkanolamines pka values. <br>

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