Physical Discussion and Speculation on Hydrophobic Effects

The present example does support some speculation on an outstanding puzzle for our conceptualization of hydrophobic effects. It is known that the sum of the standard hydration entropies of K+(aq) and Cl (aq) is about twice the standard hydration entropy of Ar(aq) [67]. The case of methanol as the solvent is qualitatively different. If hydrophobic effects are conceptualized on the basis of hydration entropies and specific hydration structures then this is paradoxical according to the measured entropies K+(aq) + Cl (aq) is about as hydrophobic as Ar(aq) + Ar(aq), but the hydration structures neighboring K+(aq), Cl (aq), and Ar(aq) should be qualitatively different. This paradox has not been given a satisfactory explanation. 

The interactions that have to be considered in the three cases here are also different from each other. Nevertheless, some features of the graphs of Figs. 9.4 and 9.6 are likely to be generally observed. a e) will populate higher energies than S e), and -Ay i -) will be extremely broad relative to / (- ). / (- ) will be much more 

Return now to the assertions of the Introduction. The explanation of assertion (1) was pointed out previously. Assertion (2), that the PDT is a practical computational tool, was the subject of Sect. 9.2.3. See especially the discussion the general computational tricks work for the PDT also, emphasizing the general statistical methods of stratification and importance weighting, and their correspondence to the natural theoretical analyses of the PDT partition function. 

The reason that the PDT is an effective tool for the generation of physical models is that it treats an intensive thermodynamic property, and the distribution functions involved are simpler in the thermodynamic limit than if this were not the case [10]. An extended family of modeling tools then applies directly. The quasichemical approach is a general example. It amounts to stratification of the statistical problem 

Molecular theory of hydrophobic effects She is too mean to have her name repeated. , Annu. Rev. Phys. Chem. 2002, 53, 409 -36 

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