Enthalpy-entropy compensation effect

MOLECULAR RECOGNITION IN CHEMISTRY AND BIOLOGY AS VIEWED FROM ENTHALPY-ENTROPY COMPENSATION EFFECT ... 

Enthalpy—Entropy Compensation Effect as Extrathermodynamic Relationship. 64... 

ENTHALPY-ENTROPY COMPENSATION EFFECT AS EXTRATHERMODYNAMIC RELATIONSHIP... 

It is thus demonstrated that the inclusion behavior of cyclodextrins is similarly analyzed and interpreted in terms of the enthalpy-entropy compensation effect, although the major weak forces involved are quite different from those working in... 

It is advised therefore that the extrathermodynamic analysis based on the enthalpy-entropy compensation effect should be restricted to the (suprajmolecular recognition phenomena governed by cooperative weak interactions. 

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. 

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. 

This study also revealed the validity of the enthalpy-entropy compensation effect even for such an exotic reaction as the transfer of a CyD complex from H2O to D2O (see Fig. 8.8) ... 

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. 

Inoue, Y. Wada, T. Molecular Recognition in Chemistry and Biology as Viewed from Enthalpy-Entropy Compensation Effect. In Advances in Supramolecular Chemistry Gokel. G.W.. Ed. JAI Press Greenwich, CT, 1997 Vol. 4. 55-96. 

This equation assumes that there is negligible error in the InCr term. This is reasonable because a 10% error in Cp propagates according to equation 23 to a 1% error in InCp at oligonucleotide concentrations in the range of 10" m (7). The enthalpy-entropy compensation effect is evident in the high quality of predictions made for AGS7 and Tm (31,41, 53). 

Y. Inoue and T. Wada, Molecular recognition in chemistry and biology as viewed from enthalpy-entropy compensation effect, in Advances in Supramolecular Chemistry,... 

This is actually the most common situation, and is referred to as the enthalpy-entropy compensation effect (see Chapter 4). 

Before exploring why enthalpy-entropy compensation effects exist, it is instructive to delineate the temperature dependence of LFERs. Because temperature dependence has been mostly explored with regard to kinetics, we present this discussion below in terms of activation parameters, but it also applies to reaction free energies. 

Let s examine an Sn2 reaction between an amine and an alkyl halide to illustrate enthalpy-entropy compensation effects due to differential solvation (Eq. 8.67). The transition state is polar relative to the reactants, so the enthalpy of activation should be lower in increasingly polar solvents. In addition, the developing charges in the transition state will cause the solvent to be more constrained than when solvating the neutral amine or alkyl halide, and this effect will be greater with the more polar solvent. Hence, a higher polarity solvent leads to a lower AH, but also makes AS more unfavorable as a result, these are compensating effects. 

For the cyano-Ru(II) complexes in neat water, the heats derived from the intercepts of plots with Equation [11] afforded values of the energy content of the MLCT states similar to those derived from emission data. Both for intra- and intermolecular electron transfer reactions of cyano-Ru(II) complexes in aqueous solutions in the presence of salts, the structural volume change correlates with the entropy change of the reaction. An enthalpy-entropy compensation effect occurs upon perturbation of the water structure by the addition of the salts. 

Many correlations between the complexation enthalpy and the Gibbs energy of complexation have been proposed, for example the SbCls complexes [78], the diiodine complexes [4] or the hydrogen-bonded complexes [84]. They have been explained either by a quasi-isoentropic behaviour of the complexation reaction or by an enthalpy-entropy compensation effect (Equation 1.90) ... 

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