Free enthalpy-reaction coordinate

Figure 2.1 Free enthalpy reaction coordinate diagram for an enzyme reaction.

From the idea of enzyme kinetics as a binding and a reaction step with the corresponding course of the energy curve in the Gibbs free enthalpy-reaction coordinate (AG - E) diagram, the reaction scheme represented by Eq. (2.1) can be drawn. 

These parameters (AG, A//, and A5 ) differ slightly from normal standard parameters in that the contribution of motion along the reaction coordinate toward the transition state is not included. The values are the difference in free energy, enthalpy, and entropy between 1 mole of activated complex and 1 mole of each reactant, all substances being at their standard-state concentrations (usually 1 M). 

FIGURE 1.2 Two-state diagram (states A and B) to describe chemical kinetics. The reaction coordinate can be considered as the pathway with lowest energy through the multidimensional energy hyper-surface of the reaction. represents the transition state, i.e., the state with highest free energy on the reaction coordinate. The reaction enthalpy and the enthalpy differences between the two states and the transition state are depicted by arrows. Note that for the rate coefficients and the differences, have to be considered. 

Fig. I. Reaction coordinate/free enthalpy diagram for the reaction of an educt E to a product P in the absence (path A) and in the presence (path B) of a host H. In case (A), the binding has no effect on the overall rate while case (B) shows catalysis. In case (C) educt inhibition , in case (D) product inhibition is shown. In cases (C) and (D), the differences of free enthalpy between E and E H, and P and P H, respectively, are much larger than the difference between TS and TS-H...

An energy diagram is a conceptual tool, so there is some variability in how its axes are labeled. The y-axis of the diagram is usually labeled energy (E), but it is sometimes labeled "enthalpy (/-/)" or (rarely) "free energy (G)." There is an even greater variability in how the x-axis is labeled. The terms "reaction pathway," "reaction coordinate," "course of reaction," or "reaction progress" may be used on the x-axis, or the x-axis may remain without a label. 

The amount of product formed or reactant consumed per unit of time. (p. 145) (potential-energy diagram) A plot of potential-energy changes as the reactants are converted to products. The vertical axis is potential energy (usually free energy, but occasionally enthalpy). The horizontal axis is the reaction coordinate, a measure of the progress of the reaction, (p. 148)... 

Of course, under many conditions, the preformed enolate aldol reaction appears to be significantly exothermic. The additional driving force is presumably provided by the enthalpy of coordination of the ambident aldolate ion with a cation. The importance of cation solvation in providing a driving force for the aldol reaction has been elegantly demonstrated by Noyori and coworkers.In this important experiment, the tris(dimethylamino)sulfonium (TAS" ) enolate of l-phenyl-2-propanone was prepared as shown in equation (6). The naked enolate was obtained as a yellow crystalline material, free of trimethylsilyl fluoride, by concentration of the THF solution. 

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