Thermodynamic compensation effect

Ruvolo-Rilho, A. Curti, P.S. Chemical Kinetic Model and Thermodynamic Compensation Effect of Alkaline Hydrolysis of Waste Poly(ethylene terephthalate) in Nonaqueous Ethylene Glycol Solution. Ind. Eng. Chem. Res. 2006, 45, 7985-7996. 

Figure 16.8 shows the existence of so-called thermodynamic compensation effect , i.e. a linear dependence of on A5 j. Thermodynamic compensa-... 

Fig. 16.8 Thermodynamic compensation effect of n-alkanes on carbon nanotubes (CNT), carbon nanoflbers (CNF) and high-surface-area-graphites (HSAG) (adapted from Ref. [20])...

The relationship of thermodynamic functions of selective bonding of Hb to a series of carboxylic CP in the variation of the degree of ionization of carboxylic groups is expressed by the effect of enthalpy-entropy compensation (Fig. 18). The compensation effect of enthalpy and entropy components is the most wide-spread characteristic of many reactions in aqueous solutions for systems with a cooperative change in structure [78],... 

Another simple approach assumes temperature-dependent AH and AS and a nonlinear dependence of log k on T (123, 124, 130). When this dependence is assumed in a particular form, a linear relation between AH and AS can arise for a given temperature interval. This condition is met, for example, when ACp = aT" (124, 213). Further theoretical derivatives of general validity have also been attempted besides the early work (20, 29-32), particularly the treatment of Riietschi (96) in the framework of statistical mechanics and of Thorn (125) in thermodynamics are to be mentioned. All of the too general derivations in their utmost consequences predict isokinetic behavior for any reaction series, and this prediction is clearly at variance with the facts. Only Riietschi s theory makes allowance for nonisokinetic behavior (96), and Thorn first attempted to define the reaction series in terms of monotonicity of AS and AH (125, 209). It follows further from pure thermodynamics that a qualitative compensation effect (not exactly a linear dependence) is to be expected either for constant volume or for constant pressure parameters in all cases, when the free energy changes only slightly (214). The reaction series would thus be defined by small differences in reactivity. However, any more definite prediction, whether the isokinetic relationship will hold or not, seems not to be feasible at present. 

As experimentally demonstrated above, in the complexation thermodynamics involving cationic species as guests and ionophores as hosts, the entropic change TAAS, induced by altering cation, ligand, or solvent, is proportional to the enthalpic change AAH. This correlation immediately leads to an empirical Eq. 14 with a proportional coefficient a, integration of which affords an extrathermodynamic relationship between TAS and AH. Thus, Eq. 15 is the quantitative expression of the observed compensation effect ... 

The effects of mercury compression and the compressive heating of the hydraulic oil are thermodynamically compensated. Therefore, the need to make blank runs is unnecessary for all but the most exacting analysis. Blank runs made on cells filled with mercury show less than 1 % of full-scale signal over the entire operating range from 0 to 60000psi. 

The anomalies pointed out above, including compensation effects, may be accounted for in general bases of the assumption that the chemical elementary steps on the enzyme are accompanied by the arrangement of the conformational structure of protein globules and surrounding water molecules. The kinetic and thermodynamic parameters of such structural rearrangements make a contribution to the experimentally measured and whose reflect cooperative properties of the water-protein matrix. 

For a full account of the origin and analyses of the kinetic and thermodynamic enthalpy-entropy compensation effect, see Y Inoue, T Wada. In GW Gokel, ed. Advances in Supramolecular Chemistry. Greenwich, CT JAI Press, 1997, 55-96. 

Usually, there is a compensation effect, that is AHd —TAS11 so that AGd 0. Experimentally, AS1 is positive (especially for macrocyclic ligands), and so is very often A Hr (which means that usually, the Ln-L bonds are weaker than the Ln-OH2 ones) so that complexation reactions in water are entropy driven and, moreover, a linear relationship between AH and A. S 1 holds for the Ln(III) series of cations. One has, however, to be cautious when this approach is applied to polydentate ligands. The thermodynamic parameters may also reflect other factors such as the formation of stable 5-membered chelate rings. When another solvent is considered, the solvation enthalpy is much smaller than in water and the above considerations may no more hold. 

The focus of this review article will be on the interaction between macromolecules and small-molecule ligands. The discussion will first center on the thermodynamic and kinetic characteristics that are used to measure the extent of binding. Subsequently, we discuss the interactions at the atomic level that drive complex formation. Then, a discussion follows of some tools available to predict macroscopic properties from microscopic properties. We then briefly discuss macromolec-ular motions as well as various aspects of receptor-ligand that have attracted renewed attention, such as conformational selection versus induced-fit, enthalpy-entropy compensation effect, and protein allostery. 

The enthalpy-entropy compensation effect has long been a hot topic in chemical literature, because in principle no explicit relationship between the enthalpy change and the entropy change can be derived from fundamental thermodynamics. Nevertheless, the compensatory enthalpy-entropy relationship has often been observed in both activation and thermodynamic quantities determined for a very wide variety of reactions and equilibria. 

Rekharsky MV, Inoue Y, Chiral recognition thermodynamics of f-cyclodextrin The thermodynamic origin of enantioselectivity and the enthalpy-entropy compensation effect, J. Am. Chem. Soc. 2000 122 4418-4435. 

Comparison of AH with AHy and AS with ASx shows that integral values of thermodynamic characteristics of the ionic association process for HCOOH are not only less informative than van t Hoffs characteristics, but they contradict the physical model of the process in this case. Indeed, corresponding dependencies of compensative effect are described by equations ... 

Thus, if the compensative effect for integral thermodynamic functions is interpreted, one should conclude that characteristic temperature (this is tana = AH/AS) is a negative value, but that is, of course, devoid of physical sense. 

The thermodynamic parameters related to local minima and the transition state, which are responsible for the interaction between MeCNa" " (MeC) and water molecules, are given in Tables 21.1 and 21.2. Due to the well known nature of compensation effects the values of relative Gibbs free energy of interaction are much smaller than corresponding relative enthalpies. It is also expected that interaction of MeCNa+ and MeC Na with the first water molecule is larger than the interaction... 

It is essential to elaborate on the AS (Hupu) versus 0 and AH (Hupd) versus 0 plots. An analysis of the data shown in Figures 3 and 4 reveals that the enthalpy and entropy variations are mirror images. Such thermodynamic dependences are well known in catalysis 45-46) and show that variation of the entropy of adsorption is always counterbalanced by alteration of the enthalpy of adsorption. This phenomenon is recognized as a compensation effect 45) and the data presented in the present paper indicate that it is also observable for electrochemical systems. 

Finally, the third factor is the resultant catalytic effect described by equation 8.65, which is a consequence of a compensation effect that alters ki and Ki in the same direction. Thus as sites become better (more active), there are fewer of them present for reaction. The net result is that a nonuniform surface appears to behave catalytically much more similarly to a uniform surface than expected based on its thermodynamic properties, and it provides justification for the common usage of L-H-type and H-W-type rate expressions. 

The anomalies in the thermodynamic and kinetic parameters of enzymatic processes, including compensation effects, can be explained in general features fiom the assumption that chemical elementary steps on enzymes are accompanied by the rearrangement of the structure of protein globules and surrounding water. Thus, the experimentally measmed xp and reflect not only properties of chemical reactirms but also the cooperative properties of the water-protein matrix (G.I. Likhtenshtein, R. Lumri). 

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