This book was planned and written with one central goal in mind: to demonstrate that statistical thermodynamics can be used successfully by a broad group of scientists, ranging from chemists through biochemists to biologists, who are not and do not intend to become specialists in statistical thermodynamics. The book is addressed mainly to gradu ate students and research scientists interested in designing experiments the results of which may be interpreted at the molecular level, or in interpreting such experimental results. It is not addressed to those who intend to practice statistical thermodynamics per se. With this goal in mind, I have expended a great deal of effort to make the book clear, readable, and, I hope, enjoyable. This does not necessarily mean that the book as a whole is easy to read. The first four chapters are very detailed. The last four become progressively more difficult to read, for several reasons. First, presuming that the reader has already acquired familiarity with the methods and arguments presented in the first part, I felt that similar arguments could be skipped later on, leaving the details to be filled in by the reader. Second, the systems themselves become progressively more com plicated as we proceed toward the last chapter.

This book deals with a subject that has been studied since the beginning of physical chemistry. Despite the thousands of articles and scores of books devoted to solvation thermodynamics, I feel that some fundamen tal and well-established concepts underlying the traditional approach to this subject are not satisfactory and need revision. The main reason for this need is that solvation thermodynamics has traditionally been treated in the context of classical (macroscopic) ther modynamics alone. However, solvation is inherently a molecular pro cess, dependent upon local rather than macroscopic properties of the system. Therefore, the starting point should be based on statistical mechanical methods. For many years it has been believed that certain thermodynamic quantities, such as the standard free energy (or enthalpy or entropy) of solution, may be used as measures of the corresponding functions of solvation of a given solute in a given solvent. I first challenged this notion in a paper published in 1978 based on analysis at the molecular level. During the past ten years, I have introduced several new quantities which, in my opinion, should replace the conventional measures of solvation thermodynamics. To avoid confusing the new quantities with those referred to conventionally in the literature as standard quantities of solvation, I called these "nonconventional," "generalized," and "local" standard quantities and attempted to point out the advantages of these new quantities over the conventional ones."

My personal involvement with the problem of hydrophobic interactions (HI) began about ten years ago. At that time I was asked to write a review article on the properties of aqueous solutions of nonpolar solutes. While surveying the literature on this subject I found numerous discussions of the concept of HI. My interest in these interactions increased especially after reading the now classical review of W. Kauzmann (1959), in which the importance of the HI to biochemical processes is stressed. Yet, in spite of having read quite extensively on the various aspects of the subject, I acquired only a very vague idea of what people actually had in mind when referring to HI. In fact, it became quite clear that the term HI was applied by different authors to describe and interpret quite different phenomena occurring in aqueous solutions. Thus, even the most fundamental question of the very definition of the concept of HI remained unanswered. But other questions followed, e. g.: Are HI really a well established experimental fact? Is there any relation between HI and the peculiar properties of water? Is the phenomenon really unique to aqueous solutions? Finally, perhaps the most crucial question I sought to answer was whether or not there exists hard evidence that HI are really important -as often claimed-in biological processes."

This book evolved from a graduate course on applications of statistical thermody- namics to biochemical systems. Most of the published papers and books on this subject used in the course were written by experimentalists who adopted the phenomenological approach to describe and interpret their results. Two outstanding papers that impressed me deeply were the c1assical papers by Monod, Changeux, and Jacob (1963) and Monod, Wyman, and Changeux (1965), where the allosteric model for regulatory enzymes was introduced. Reading through them I feIt as if they were revealing one of the c1everest and most intricate tricks of nature to regulate biochemical processes. In 1985 I was glad to see T. L. HilI's volume entitled Cooperativity Theory in Biochemistry, Steady State and Equilibrium Systems. This was the fIrst book to systematically develop the molecular or statistical mechanical approach to binding systems. HilI demonstrated how and why the molecular approach is so advanta- geous relative to the prevalent phenomenological approach of that time. On page 58 he wrote the following (my italics): The naturalness of Gibbs' grand partition function for binding problems in biology is evidenced by the rediscovery of what is essentially the grand partition function for this particular type of problem by various physical biochentists, including E. Q. Adams, G.

This book evolved from a graduate course on applications of statistical thermody- namics to biochemical systems. Most of the published papers and books on this subject used in the course were written by experimentalists who adopted the phenomenological approach to describe and interpret their results. Two outstanding papers that impressed me deeply were the c1assical papers by Monod, Changeux, and Jacob (1963) and Monod, Wyman, and Changeux (1965), where the allosteric model for regulatory enzymes was introduced. Reading through them I feIt as if they were revealing one of the c1everest and most intricate tricks of nature to regulate biochemical processes. In 1985 I was glad to see T. L. HilI's volume entitled Cooperativity Theory in Biochemistry, Steady State and Equilibrium Systems. This was the fIrst book to systematically develop the molecular or statistical mechanical approach to binding systems. HilI demonstrated how and why the molecular approach is so advanta- geous relative to the prevalent phenomenological approach of that time. On page 58 he wrote the following (my italics): The naturalness of Gibbs' grand partition function for binding problems in biology is evidenced by the rediscovery of what is essentially the grand partition function for this particular type of problem by various physical biochentists, including E. Q. Adams, G.