Hydrophobicity free energy

In this relationship. S is alkane solubility, A is the cavity surface area and a is the hydrophobic free energy per unit area. Extensive fitting of this equation [24] yields a value of 88 kJ mol A for the proportionality constant a. This value corresponds to an unfavourable free energy of about 3.6 kJ mol for the transfer of a CH2 group to aqueous solution. 

K. A. Sharp, A. Nicholls, R. Friedman, and B. Honig. Extracting hydrophobic free energies from experimental data relationship to protein folding and theoretical models. Biochemistry, 30 9686-9697, 1991. 

Table 3.1. Values of the constants a and b in the relation M p/iRT) = a-b nc for the hydrophobic free energy of an homologous series of compounds. (T = 298 K)...

In asi-casein, it is arguable that because the hydrophobic interaction surfaces are well separated from Ca2+ ion-binding sites, the electrostatic and hydrophobic free energies of association can be treated as separate and additive, leading to the Z2 dependence of the rate of aggregation under many circumstances. Likewise, the nearly bifunctional nature of the aggregation reaction is consistent with the formation of linear polymers, as observed in the absence of Ca2+ (Thurn etal., 1987b), and may involve the apposition of hydrophobic surfaces formed from the N- and C-terminal peptides. 

Extracting Hydrophobic Free Energies From Experimental Data Relationship to Protein Folding and Theoretical Models. 

J. A. Reynolds, D. B. Gilbert, and C. Tanford, Proc. Natl. Acad. Sci. U.S.A., 71,2925 (1974). Empirical Correlation between Hydrophobic Free Energy and Aqueous Cavity Surface Area. 

These ideas can be formalised in terms of statistical mechanics to some extent, and an outline of the main ideas is given in the following section. We remark parenthetically that there are profound difficulties confronting the definition of an aggregate. The nature of the hydrophobic free energy of transfer of a hydrocarbon from water to the hydrophobic core of a micelle can be measured, but its temperature dependence is not understood because it depends on water, an unknown quantity. For the same reasons, solution theory, does not even tell us whether mole fractions or mole volumes are the correct ratios to use to determine entropy. However, provided certain assumptions are allowed [62-65], then simple rules emerge. The rules are if v is the hydrocarbon chain volume, a the head-group area, and 1 of an optimal... 

For surfactants, the hydrophobic free energy of transfer of the lipophilic hydrocarbon tail from water to oil provides the driving force for aggregation. But the hydrophilic head-groups prefer an aqueous environment and an interface between the polar region and the lipophilic domains results. With hydrocarbon tails, like alkanes, there are a large number of accessible tail conformations, so that the hydrophobic region is usually fluid-like aroimd room temperature. The interface can be a dynamic one of a well-defined... 

Hirono, S., Qian, L. and Moriguchi, I. (1991). High Correlation Between Hydrophobic Free Energy and Molecular Surface Area Characterized by Electrostatic Potential. Chem.Pharm. 5m//., 59,3106-3109. 

Water does not spread spontaneously on hydrocarbons and the aqueous films on hydrocarbons are rather unstable. " The cause for these effects is a strong attractive hydrophobic force, which is found to appear in aqueous films in contact with hydrophobic surfaces. The experiments showed that the nature of the hydrophobic surface force is different from the van der Waals and double layer interactions. - It turns out that the hydrophobic interaction decays exponentially with the increase of the film thickness, h. The hydrophobic free energy per unit area of the film can be described by means of the equation " ... 

Figure 1. Accessible surface areas of residue side chains plotted against hydrophobicity—free energy change for the transfer from 100% ethanol...

The hydrophobic free energy contribution to the stability of protein-protein complexes can also be estimated making similar assumptions to the ones described above (9). In this case as well (Table V) it appears that hydrophobic interactions contribute greatly to the overall stability of the complexes. This is particularly interesting in the case of the trypsin-pancreatic trypsin inhibitor complex since very few residues are involved in the interaction of the two molecules. 

Table IV. Hydrophobic Free Energy Contribution to Protein Stability (5)...

Table V. Hydrophobic Free Energy of Protein—Protein Interactions (9)...

Complex kd(M) Total Free Energy (AG) (kcal/mol) Buried Surface Area (A2) Hydrophobic Free Energy ° (kcal/mol)... 

Reduction in the area of exposed hydrophobic surfaces can also enhance thermodynamic stability. Chothia has estimated a proportionality constant of 24 cal/ mol of hydrophobic free energy per square angstrom of solvent-exposed surface area (32). Substitutions at Ile-3 of T4 lysozyme enhance the stability by amounts that agree surprisingly well with this prediction (33). However, there is some debate over the choice of the proper hydrophobicity scale to quantitate the contributions of each hydrophobic residue, and it is perhaps an oversimplification to expect such a simple relationship to hold for all amino acids (34). 

Reynolds J A, Gilbert D B and Tanford C 1974 Empirical correlation between hydrophobic free energy and aqueous cavity surface area Proc. Natl Acad. Sci. USA 71 2925-7... 

The hydrophobic free energy associated with the transfer of the hydrocarbon tail from water to the hydrocarbon mixture in the micellar core. This contribution can be obtained from available solubility data. 

While the meaning of distance from the amine receptor to the micelle surface is degraded by its temporally dynamic and spatially convoluted nature, we can estimate the relative microlocation of a given member of a sensor series on a scale between the limits of bulk water and the less polar micelle interior in terms of the hydrophobicity constant (P) (24) of the variable component of the family 2a-f i,e. the tail group. In other words, we can use hydrophobic free energy as the independent variable instead of a space coordinate for the mapping of membrane bounded proton densities. Such... 

Equation (5.15) brings li t to certain semi-quantitative aspects of initiator efficiency. PCX entry into itxiically stabilized particles, it has been shown that an estimate of the value of z can be obtained fKxn hydrophobic free energy considerations [21], yielding ... 

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