Thermodynamics of hydrogen bond formation

The experimental determination of Aff and AS sometimes yields surprising results, as, for example, in the thermodynamics of hydrogen-bond formation in the complex of FK506 or rapamycin with FK506-binding protein (FKBP). " Binding to the wild-type and to the mutant Tyr 82 Phe 82 was... 

In order to determine to what extent these speculations have validity, it is necessary to be able to evaluate more quantitatively the relative contributions of these interactions to the free energies of protein and nucleic acid molecules in water and nonaqueous solvents. For this purpose, a substantial body of quantitative data is required concerning the properties of suitable model compounds in a variety of solvents, including their solubilities, acid-base dissociation constants, and thermodynamics of hydrogen bond formation. The dearth of pertinent data on hydrogen bonds in solvents of interest is particularly frustrating to even a semiquantitative evaluation of the scheme presented in Fig. 7. 

Thermodynamics of hydrogen-bond formation in aprotic solvents... 

A proton-transfer reaction can only occur through the initial formation of a hydrogen-bonded complex and this step, although rapid, may significantly affect the kinetic analysis of a proton-transfer reaction, since a factor involving the thermodynamics of hydrogen-bond formation will be incorporated in the rate expression. 

Flory and Garrett have analyzed the fusion of a particular collagen, rat tail tendon, in detail. (207) The appropriate thermodynamic quantities involved in fusion are given in Table 6.1. These quantities, characteristic of this naturally occurring polymer, are similar to those characteristic of synthetic polymers. Both the heat and entropy of fusion appear to be normal. The heat of fusion, on a weight basis, is similar to that of the synthetic poly(amides). Any enhanced stability endowed to the crystalline state of the polymer by virtue of hydrogen bond formation is not in evidence, unless this contribution is much smaller than beUeved. 

AG° is determined by AH°, AS° and T, which are the enthalpy, entropy and absolute temperature of the hydrogen-bond formation, respectively. To understand the thermodynamics of hydrogen-bond basicity, one must know whether this basicity is controlled by enthalpy, by entropy or by both. If it is the last case, the respective contributions of the enthalpic and entropic terms need to be determined. 

Stymne, B., Stymne, H. and Wettermark, G. (1973) Substituent effects in the thermodynamics of hydrogen bonding as obtained by infrared spectrometry. J. Am. Chem. Soc., 3490-3494. Ahrland, S. (1967) Enthalpy and entropy changes by formation of different types of complexes. Helv. Chim. Acta, 50, 306-318. 

D. J. Tobias and C. L. Brooks, Thermodynamics of amide hydrogen bond formation in... 

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