Hydrophobic hydration thermodynamic properties

Thus, for a hydrophobic solute is determined by quantifying the probability po of successfully inserting a hard-core solute of the same size and shape into equilibrium configurations of water, as illustrated in Figure 4. A virtue of this approach is that the thermodynamics of hydrophobic hydration characterized by is determined from the properties of pure water alone. The solute enters only through its molecular size and shape (see Fig. 4). 

The lack of information on the thermodynamic properties of the alkylammonium makes it impossible to calculate absolute values for the AH1, AHh, AS1, AS71 terms. Taking into account the hydrophobic nature of the Pr ion, it seems reasonable to assume that HFrh is smaller in absolute values than HXa7t. The hydration of ions being an exothermic effect, the AHh is expected to yield a negative value. The entropy of hydration is also negative and increases in absolute value when the ion is more hydrated. Thus, AS7 also will be a negative quantity. 

Guillot, B. Guisani, Y. (1995) Thermodynamics and Structure of Hydrophobic Hydration by Computer Simulation. In Properties of Water and Steam Physical Chemistry of Aqueous Systems Meeting the Needs of Industry, H. J. White J. V. Sengers D. B. Neumann and J. C. Bellows, Ed. Begell House, Inc. New York, pp 269-277. 

Guillot, B., Guissani, Y. and Bratos, S., A computer simulation study of hydrophobic hydration of rare gases and methane. I. Thermodynamic and structural properties, /. Chem. Phys., 1991,95, 3643-3648. 

Study of Hydrophobic Hydration of Rare Gases and of Methane. I. Thermodynamic and Structural Properties. 

In this review isentropic compressibility data have been compiled for aqueous solutions of the amino acids, including all those found in proteins, of various peptides of low molar mass, and of many proteins. For both the small molecule and protein systems, it is clear that this thermodynamic property is a particularly sensitive measure of hydration effects in aqueous solution. For the small solutes attempts have been made to rationalize the compressibility data in terms of the interactions that occur between the various functional groups and solvent water. For proteins it has been shown that the compressibilities are not correlated with any one structural characteristic. Various characteristics such as amino acid composition, hydrophobicity and the degree of secondary structure all influence, to some degree, the compressibility of a protein. Compressibility measurements on protein solutions also provide an important means to determine the volume fluctuation of a protein. We believe that compressibility measurements on aqueous solutions of these biologically important molecules provide a very powerful means of probing and characterizing solute -water interactions in these systems. 

Experimental studies of the thermodynamic, spectroscopic and transport properties of mineral/water interfaces have been extensive, albeit conflicting at times (4-10). Ambiguous terms such as "hydration forces", "hydrophobic interactions", and "structured water" have arisen to describe interfacial properties which have been difficult to quantify and explain. A detailed statistical-mechanical description of the forces, energies and properties of water at mineral surfaces is clearly desirable. 

To summarize, three conclusions transpire from the nanoscale thermodynamics results (a) The interfacial tension between protein and water is patchy and the result of both nanoscale confinement of interfacial water and local redshifts in dielectric relaxation (b) the poor hydration of polar groups (a curvature-dependent phenomenon) generates interfacial tension, a property previously attributed only to hydrophobic patches and (c) because of its higher occurrence at protein-water interfaces, the poorly hydrated dehydrons become collectively bigger contributors to the interfacial tension than the rarer nonpolar patches on the protein surface. 

The approach under discussion, although not commonly used, deserves special attention as it seems to be the only one taking into account the fact that hydration interactions of a biological macromolecule depend upon the concentration of the components of an aqueous solution affecting the structure and/or thermodynamic state of water in the solution 30). At the same time the authors of this model30) assume the constancy of the hydrophobicity of a protein which is a measure of the above interactions varying with the composition of an aqueous medium. This example seems to be typical of that even in the case of an obvious discrepancy between experimental results and interpretation of the results from the conventional point of view, the conventional ideas take the upper hand which in this particular case 30) means that the hydrophobicity of a solute is considered as an intrinsic property of the solute and not as a measure of the intensity of the interaction between the solute and the solvent which clearly depends on both properties of the solute and of the solvent. 

The transport properties of hydrophobic-hydrophilic ion-exchange membranes such as Nafion are likely to alter with time when operated at high current densities. The thermodynamic tendency of the system to form large hydrated ionic clusters is realized by increasing the molecular energy (kT) of the polymer chains to such an extent that the activation... 

The chemical potential difference is tabulated in Table III [17,18]. There are small but nonmegligible differences depending on both the method and the pair potential. Two distinctive features are noteworthy. CS-II is more stable than CS-I irrelevant as to whether the anharmonic free energy is taken into account for the TIP4P potential (all the properties are calculated for clathrate hydrates with this potential unless otherwise mentioned) [52]. This is also true for most of the other pair potential of water such as SPC/E [53]. The chemical potential difference is negative for most of the potential but it is positive for the CC potential [54] and other potentials with the same functional form, which is favorable to observe a hydration structure around a hydrophobic solute but is inappropriate to evaluate the thermodynamic stability of clathrate hydrates. 

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