Free energy of association

A surprising result that emerged from the earlier work on hydrophobic interactions is that there is little or no tendency for nonpolar solute association at low concentration. For example, simulation results led Watanabe and Andersen to discuss the hydrophobic repulsion between krypton atoms in water.Calculated PMFs have typically supported a similar conclusion (discussed below). Aggregation of methane in water was observed to occur at higher concentrations, suggesting that there may be cooperative aspects to the solute aggregation process. This conflicts, however, with results from Shimizu and Chan who explicitly observed anticooperativity in three-body hydrophobic interactions.  

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Equilibria in Solution The stability of a protein-ligand complex in solution is measured in terms of the equilibrium constant and the standard free energy of association based on it. For association of species P and L in solution to form a complex PL, i.e., for... 

For example, 130 kj/iriol of favorable Interaction minns 80 kJ/mol of nnfavorahle interaction eqnals a net free energy of association of 50 kj/mol. 

Dixit, S. B. Chipot, C., Can absolute free energies of association be estimated from molecular mechanical simulations The biotin-streptavidin system revisited, J. Phys. Chem. A 2001,105, 9795-9799. 

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. 

Ion pair interactions are also present in natural supramolecular systems (e.g. DNA-peptides, polyamine-nucleic acids and among proteins or enzymes). Such kinds of attractive forces are strongly dependent on the ionic strength (I) of the solution if extrapolated to I = 0 the average value for the free energy of association for one cation-anion pair is about 8 KJ/mol, and... 

Chicken lysozyme residue Asp-lOlma in the HyHEL-10 epitope7 is of additional interest because it contributes to the free energy of association of substrate ligands with the enzyme 33 turkey lysozyme (TEL) has a glycine at position 101.34 Nine replacements were designed to test the importance... 

In terms of the impact and directions that these forms of molecular HPLC will take, let us consider the RP-HPLC separation of a specific polypeptide as an exemplar. If, for example, the free energy of association AG SS0C, where in this case refers to the RP mode of interaction, was... 

A summary of the complexing properties of hosts 38 and 40 in (CDC12)2 towards neutral guest species is given in Fig. 13, where the experimental free energy of association AG°a(= — RT In Ka) at 300 K has been plotted as a function of the guest van der Waals volumes [35],... 

Fig. 13. Free energy of association AG°a for complexes of 38 and 40 with neutral guests at 300 K, in (CDC12)2...

Attempts to obtain a distillation curve directly on the asphaltenes fraction resulted in essentially no FID response. This result is attributed to the high free energy of association of these molecules. Once these species are allowed to associate, it is difficult to disassociate them. The results in Figure 3 suggest that volatile molecules are contained in the asphaltene fraction and that the overlap in molecular weight and volatility between asphaltenes and maltenes is substantial. 

In water, however, the above contribution from EDA interactions tends to be over-ridden by solvation effects. In this solvent, solvophobic forces (see below) can provide a very favourable contribution to the free energy of association of host and guest. 

This measurement of allows one to calculate AG , the free energy of association of the complex. To find AH and AS separately requires a determination of Kg as a function... 

Our real interest is in AG, the solution phase free energy of association. Until now, our discussion has focused on the energy (AEj ), enthalpy (AH,), and free energy (AG )... 

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