Enthalpies of ligand binding

Another approach to issues of solvation thermodynamics utilizes the differential hydrogen bonding properties of light and heavy water [32, 33). The use of thermodynamic solvent isotope effects, or the evaluation of the enthalpy of ligand binding in light and heavy water, allows evaluation of the extent to which desolvation aids... 

Table 5. Solvation-associated enthalpies of ligand binding [35],...

Mills, J.L., Liu, G., Skerra, A., and Szyperski, T. 2009. NMR structure and dynamics of the engineered fluorescein-binding lipocalin FluA reveal rigidification of beta-barrel and variable loops upon enthalpy-driven ligand binding. Biochemistry, 48,7411-7419. 

This difference in behavior is felt to be due to the fact that Cr(co)e must first dissociatively lose a CO ligand, a fairly energetic process with an activation enthalpy of 40 kcal. (25.), prior to binding the formate ion. The once formed Cr(C0)502CH proceeds to Cr(C0)sH with subsequent production of H2 and C02 as described in the Scheme. Support for this interpretation was obtained by replacing Cr(C0)e with a chromium carbonyl species containing a labile ligand,... 

As displayed in Fig. 4, for this family of proteins, the entropy of binding is either favorable or weakly unfavorable, while the enthalpy of binding is negative, resulting in micromolar affinity. The only exception is a PA-IIL ligand consisting of two fucose residues separated by a flexible linker that... 

For soft cations, such as Ag+ and Pb2+, covalent contributions are much more important, and consequently the observed order of complex stabilities is quite different from that for alkali cations NH > O > S for Pb2+ and NH, S > O for Ag+. Dissection of the overall effect into enthalpy and entropy contributions (Table 15) reveals the complicated nature of the heteroatom effect. For K+ and Ba2+, the more favourable entropy contribution for N and S ligands is more than offset by the unfavourable change in enthalpy of binding. 

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