Pairwise hydrophobic interactions

The distinction between pairwise and bulk hydrophobic interactions is often made, although some authors doubt the existence of an intrinsic difference between the two ". Pairwise hydrophobic interactions denote the interactions behveen two isolated nonpolar solutes in aqueous solution. They occur in the regime where no aggregation takes place, hence below the critical aggregation concentration or solubility limit of the particular solute. If any breakdown of the hydrophobic hydration shell occurs, it will be only transient. 

Interactions between nonpolar compounds are generally stronger in water than in organic solvents. At concentrations where no aggregation or phase separation takes place, pairwise hydrophobic interactions can occur. Under these conditions, the lowest energy state for a solute molecule is the one in which it is completely surrounded by water molecules. However, occasionally, it will also meet other solute molecules, and form short-lived encounter complexes. In water, the lifetime of these complexes exceeds that in organic solvents, since the partial desolvation that accompanies the formation of these complexes is less unfavourable in water than in organic solvents. 

Pairwise hydrophobic interactions can be used to alter the reactivity of organic molecules in water. For instance, the rate of hydrolysis reactions may be influenced significantly by the presence of hydrophobic cosolutes. The effect on reactivity has been analysed by comparirg the interactions between initial state and cosolute with those between transition state and cosolute. ... 

Shimizu S, Chan HS. Configuration-dependent heat capacity of pairwise hydrophobic interactions. J. Am. Chem. Soc. 2001 123 2083-2084. 

Ludermann, S. Schreiber, H. Abseher, R. Steinhauser, O. (1996) The Influence of Temperature on Pairwise Hydrophobic Interactions of Methane-like Particles A Molecular Dynamics Study of Free Energy, Journal of Chemical Physics 104, 286-295... 

Graziano, G., On the heat capacity change of pairwise hydrophobic interactions, /. Chem. Phys., 2005,123,... 

Models of hydrophobic hydration including the iceberg hypothesis and its more modern variants have led to several qualitative predictions for pairwise hydrophobic interactions. The first and simplest prediction based on free-energy arguments is that nonpolar solutes should tend to associate... 

Fig. 1.4. Paramagnetic relaxation enhancement profiles for apomyoglobin unfolded at pH 2.3 with spin labels at the positions indicated by the arrows. The fitted, curves show the initial (pale gray) fits and the fits obtained after correction for differences in pairwise cluster interaction free energies (dark gray lines).The location of hydrophobic clusters defined from regions of high AABUF are indicated by bars at the top of the figure. Reproduced with permission from [17]...

The GOLD score (G-score) is based on the work of Jones et al. and concentrates on H-bonding interactions. The H-bonding term contains desolvation of donors and acceptors. A pairwise dispersion term involves the contribution of hydrophobic interactions and a molecular mechanical equation is used to calculate the internal energy of the ligand. Therefore, this scoring function performs well when polar interactions are dominant and has difficulty with ligands that are primarily non-polar in nature. 

Are Hydrophobic Interactions Between Coarse-Grained Moieties Pairwise Additive ... 

The previous work describes pairwise interactions that result from protecting the aromatic surface. Is it possible to achieve pairwise interactions by employing unprotected hydrophobic surfaces In addressing this goal, our design of pairwise stacking/hydrophobic interactions was based on the idea that a rigid scaffold may... 

Pressure-induced denaturation of proteins and related problems are possibly linked to hydrophobicity. As a result, there has been considerable interest in studying the pressure dependence of hydrophobic interactions, highlighted by two studies. The first, by Rick, involved calculation of the pairwise... 

Here we present and discuss an example calculation to make some of the concepts discussed above more definite. We treat a model for methane (CH4) solute at infinite dilution in liquid under conventional conditions. This model would be of interest to conceptual issues of hydrophobic effects, and general hydration effects in molecular biosciences [1,9], but the specific calculation here serves only as an illustration of these methods. An important element of this method is that nothing depends restric-tively on the representation of the mechanical potential energy function. In contrast, the problem of methane dissolved in liquid water would typically be treated from the perspective of the van der Waals model of liquids, adopting a reference system characterized by the pairwise-additive repulsive forces between the methane and water molecules, and then correcting for methane-water molecule attractive interactions. In the present circumstance this should be satisfactory in fact. Nevertheless, the question frequently arises whether the attractive interactions substantially affect the statistical problems [60-62], and the present methods avoid such a limitation. 

Thus the pairwise energy, equation (12), sums a hydrophobic/hydropathic component [equation (13)] and a Lennard-Jones type dispersion component [equation (14)]. Peculiar to HINT is the sign-flip function T jj of equation (13) which examines each atom-atom interaction and corrects the sign (T jj = 1) for polar interactions, e.g. those involved between acid and base functions and in hydrogen bonds. 

---