Thermodynamics describes the macroscopic behaviour of matter. Its relation to intermolecular interactions is in principle well-known through statistical mechanics, be it in its rigorous way via molecular dynamics or Monte-Carlo simulations or integral equations or via more simplistic approaches such as Debye-Hückel-like models. On the other hand amino-acid solutions and particularly protein solutions exhibit numerous types of interactions between the charged and uncharged parts of the molecules, hydrophobic and hydrophilic parts and between these entities and the solvent, usually water. The story is even more complicated by sterical hindrances, partial exposition of the amino acid residues to the surrounding solvent and the flexibility of the molecules allowing more or less different conformations of the macromolecules. Added salt and buffer further enhances the complexity. In such very complex systems, it seems hopeless to relate thermodynamic properties to molecular interactions. And a microscopic analysis of the molecular interactions is today only possible in few cases . So what to do? First, data are necessary. Fortunately, there are several handbooks containing experimental thermodynamic data on amino acid and protein solutions [2,3,4,5,6]. In part, these monographs contain also useful information about modelling strategies and the relation between the microscopic and the macroscopic level. Numerous studies are devoted to specific ion effects and the interactions between ions and proteins, not only in protein channels . 1 Adam G., Laeuger P., Stark G. Physikalische Chemie und Biophysik, 4-te, vollst. Ueberarb. u. erweit. Aufl.- Springer: Berlin, Heidelberg, New York.- 2003.- 617 p. 2 Makhatadze G.I. , Privalov P.L. Thermodynamic Properties of Proteins, in James E. Mark (ed.) Phys.Prop.Polym.Handb., AIP Press: Woodbury, New York.-1996.- 91 p. 3 Biochemical and Physical Properties. Landolt Boernstein. Group 7. Biophysics. Ser. Proteins.2003. Springer. 4 Cohn E.G., Edsall S.T. Proteins, Amino Acids and Peptides as Ions and Dipolar Ions. - New York: Reinfold Publ.Corp. 1943.- 700 p. 5 The Chemistry and Biochemistry of Amino Acids. Ed. G.C. Barrett. New York: Chapman Hall, London, 1985.- 700 p. 6 Timasheff S.N., Fasman G.D. Structure and Stability of Biological Macromolecules. New York: Marcel Dekker. 1969.- 700 p. 7 Eisenberg B. Ionic channels in biological membranes electrostatic analysis of a natural nanotube // Contemporary Physics. 1998.- V. 39. P. 447 - 466. In the present book only selected subtopics of this huge area can be illustrated. Well-known authors summarize some relevant aspects of how to gain information from thermodynamics or how to infer important thermodynamic data from molecular interactions. They summarize the present state of art in their respective fields. In the first chapter a general survey is given about the relevance of hydrophobic interactions in protein science. As Czaplewski et al. show, basic thermodynamic data can only be interpreted by modelling correctly these interactions. A multitude of experimental and simulation evidences are discussed proving that hydrophobic interactions are major driving forces for the formation and stability of the structures of proteins and protein complexes. In the next two chapters Prausnitz et al. and Li et al. illustrate how phase diagrams of protein solutions can be modeled and phase equilibria can be predicted. Prausnitz' concept is based on the potential of mean force acting between proteins. Special emphasis is given to the influence of salts on these solvent-averaged potentials. Li et al. give an extensive overview of different approaches, interaction models and statistical-mechanical models to simulate such phase diagrams and present many examples of their usefulness. The remaining three chapters are devoted to more specific que
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