Gibbs energy difference states

The Gibbs energy difference of the denatured and native states corresponds to the work required for the transition of a system from the native to the denatured state, i.e., the work of disruption of the native cooperative structure. Therefore, this quantity is usually considered as a measure of the stability of the cooperative structure, i.e., the stability of a small globular protein or cooperative domain. As for the large proteins, their stability cannot be expressed by a single value, but only by a set of values specifying the stability for each domain within these molecules and the interaction between the domains. 

Thus the Gibbs energy difference between the native and denatured protein states is given as... 

The Gibbs energy difference between the native and denatured states is represented by Eq. (8), a function with an extremum (Fig. 6). Its maximum value is reached at the temperature Tm, which can be determined from the condition... 

Since the Gibbs energy difference of the native and denatured states determines the stability of a cooperative unit, it follows from Eq. (11) that the stability of a small globular protein (or a single domain) is maximal at the temperature at which the entropies of the native and denatured states are equal. At this temperature, the structure is stabilized only by the... 

Fio. 6. The Gibbs energy difference of the native and denatured states of myoglobin and ribonuclease A calculated per mole of amino acid residues under the same conditions as indicated in Fig. 4. The dot-and-dash lines represent functions obtained in the assumption that the denaturation heat capacity increment is temperature independent. 

Gibbs energy of activation A G (standard free energy of activation A G ) (Id mol-1) — The standard Gibbs energy difference between the -> transition state of a reaction (either an elementary reaction or a stepwise reaction) and the ground state of the reactants. It is calculated from the experimental rate constant k via the conventional form of the absolute reaction rate equation ... 

Standard enthalpies of formation Ah and standard Gibbs energies of formation Agj are important for the calculation of enthalpies of reaction and chemical equilibria. For their estimation, the standard state at To = 298.15 K and Po = 101325 Pa in the ideal gas state is used. In process simulation programs, standard enthalpies and standard Gibbs energies of formation in the ideal gas state are usually taken as reference points for enthalpy calculation so that enthalpy and Gibbs energy differences are consistent with respect to chemical reactions. 

As depicted in Fig. 1.4, the difference between the initial and final Gibbs energy levels (state D minus state A) AGs dictates the solubility of the drug in the solvent. The difference between the initial energy levels and the intermediate RTM state energy level (state C minus state A) represents the energy required to bring the system... 

These parameters permit calculation of the standard Gibbs energy difference between the states of the protein. For a simple two-state transition of the type... 

For analysing equilibrium solvent effects on reaction rates it is connnon to use the thennodynamic fomuilation of TST and to relate observed solvent-mduced changes in the rate coefficient to variations in Gibbs free-energy differences between solvated reactant and transition states with respect to some reference state. Starting from the simple one-dimensional expression for the TST rate coefficient of a unimolecular reaction a— r... 

The difference between the electronic energies of the final and initial states must include the energy of ionization of the ion B(z-1)+ in vacuo (where its ionization potential is complemented by the entropy term TA5/), the interaction energy of the ions Bz+ and B(z-1)+ with the surroundings, i.e. the solvation Gibbs energies, and finally the energy of an electron at the Fermi level in the electrode. These quantities can be expressed most simply... 

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