Transformed thermodynamic properties

Explains the distinction between biochemical and chemical equations, and the calculation and meaning of transformed thermodynamic properties for ATP and other phosphorylated compounds. 

Tables of Standard Transformed Thermodynamic Properties at 298.15 K for Biochemical Reactants at Specified pH and Ionic Strength... 

When the pH is specified, we enter into a whole new world of thermodynamics because there is a complete set of new thermodynamic properties, called transformed properties, new fundamental equations, new Maxwell equations, new Gibbs-Helmholtz equations, and a new Gibbs-Duhem equation. These new equations are similar to those in chemical thermodynamics, which were discussed in the preceding chapter, but they deal with properties of reactants (sums of species) rather than species. The fundamental equations for transformed thermodynamic potentials include additional terms for hydrogen ions, and perhaps metal ions. The transformed thermodynamic properties of reactants in biochemical reactions are connected with the thermodynamic properties of species in chemical reactions by equations given here. 

The relationships between the thermodynamic properties of chemical reactions and the transformed thermodynamic properties of biochemical reactions have been treated in several reviews (Alberty, 1993a, 1994c, 1997b, 2001 e). Recommendations for Nomenclature and Tables in Biochemical Thermodynamics from an IUPAC-IUBMB Committee were published in 1994 and republished in 1996. This report is available on the Web http llwww.chem.qmw.ac.uhlimbmbl thermodl. 

These tables apply to single sets of values of pH and ionic strength. A more general approach is to use the functions of ionic strength and pH for each reactant that give the values of standard transformed thermodynamic properties at 298.15 K. For reactants for which A,//0 is known for all species, functions of temperature, pH, and ionic strength can be used to calculate standard transformed thermodynamic properties at temperatures in the approximate range 273.15 to 313.15 K, as discussed in Section 4.9. 

Equations for the Standard Transformed Thermodynamic Properties of a Reactant... 

Construction of Tables and Plots of Transformed Thermodynamic Properties of Inorganic Phosphate at 298.15 K... 

The standard formation properties of species are set by convention at zero for the elements in their reference forms at each temperature. The standard formation properties of in aqueous solution at zero ionic strength are also set at zero at each temperature. For other species the properties are determined by measuring equilibrium constants and heats of reaction. Standard transformed Gibbs energies of formation can be calculated from measurements of K, and so it is really these Maxwell relations that make it possible to calculate five transformed thermodynamic properties of a reactant. 

Now we are in a position to calculate the standard transformed thermodynamic properties of reactants from the standard properties of the species that make them up. In this chapter the transformed thermodynamic properties are calculated only at 298.15 K. Caleulations at other temperatures are presented in the next chapter. The first step is to adjust the properties at zero ionic strength to the desired ionic strength in the range 0-0.35 M. Equations 1.3-5 and 1.3-6 Chapter 1 show how these calculations can be made using the extended Debye-HUckel equation. Substituting equation 1.3-5 in equation 3.5-3 in two places yields... 

When enzyme-catalyzed reactions are studied at a series of temperatures or there are calorimetric data, it is possible to calculate in addition Aj H ° and Ar 5 provided that the temperature dependencies of the p fs have been determined. In this chapter we have emphasized calculations at 298.15 K, including Ar H ° and Ar 5 but we have not fully utilized the enthalpy information. In Chapter 4, we will use the enthalpy information to calculate transformed thermodynamic properties at other temperatures. This will make it possible to utilize more Maxwell relations that show how various transformed thermodynamic properties are necessarily interrelated. 

R. A. Alberty, Calculation of transformed thermodynamic properties of biochemical reactants at specified dpH and pMg, Biophys. Chem. 43.239-254 (1992). 

Calculations of Standard Transformed Thermodynamic Properties of Enzyme-catalyzed Reactions... 

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