Energy of association

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. 

TABLE IV. Comparison of Measured and Calculated Values of the Energy of Association (in kilocalories/mole). The calculated values are given in brackets and are equal to gAE2o> where AE20 is the energy of association of Nal, 39.5 kcal/mole. Values of d were obtained from Ref. 9 for all salts except LiF and KF. For LiF they were obtained from Wharton, L. et al., J. Chem. Phys. 38, 1203 (1963) and for KF from Green, G. W., and Lew, H., Can. J. Phys. 38, 482 (1960)... 

Aromatic polyesters were particularly good candidates for this new field of thermotropic main-chain polymers, since the relatively low energy of association of the ester groups led to low inter-chain forces. Further research led to the discovery that incorporation of 2,6-naphthylene or of 4,4 -biphenylyl groups, in addition to p-phenylene groups, as components of aromatic polyesters, introduced a useful new degree of randomness. Particularly useful, and the basis of the commercial products Vectra (polymer) and Vectran (fibre) from Hoechst-Celanese and Kuraray, are the copolymers formed by polymerisation of mixtures of p-acetoxybenzoic acid and 6-acetoxy-2-naphthoic acid. Within a range of... 

More advanced semiempirical molecular orbital methods have also been used in this respect in modeling, e.g., the structure of a diphosphonium extractant in the gas phase, and then the percentage extraction of zinc ion-pair complexes was correlated with the calculated energy of association of the ion pairs [29]. Semiempirical SCF calculations, used to study structure, conformational changes and hydration of hydroxyoximes as extractants of copper, appeared helpful in interpreting their interfacial activity and the rate of extraction [30]. Similar (PM3, ZINDO) methods were also used to model the structure of some commercial extractants (pyridine dicarboxylates, pyridyloctanoates, jS-diketones, hydroxyoximes), as well as the effects of their hydration and association with modifiers (alcohols, )S-diketones) on their thermodynamic and interfacial activity [31 33]. In addition, the structure of copper complexes with these extractants was calculated [32]. 

The coulombic energy of associative processes is conveniently described by... 

Table 4.5 Energies of associative processes in halides and simple snlfides. Values in eV (from Kroger, 1964 modified). ...

Logarithms of formation constants, which are proportional to the Gibbs energies of association, are often tabulated. The logarithms of formation constants and pK t values of dissociation constants are identical (Eq. 6-72) and are a measure of the standard... 

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... 

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