Entropy and enthalpy12/2/2023 One can further classify its application in the literature to two kinds of experiments, as follows: (a) The first kind is those involving a given experimental measurement on a homologous series of compounds. This is referred to here as the strong form of S-H compensation. In addition, it will likely be difficult to distinguish this from more trivial forms of compensation in real experimental systems.Ī linear correlation between ΔS and ΔH of some process for a series of homologous compounds, a series of perturbations of the molecules involved, or some other regular variation of experimental conditions (other than temperature). This behavior is insensitive to the details of the model, thus revealing little extra-thermodynamic or causal information about the system. This model shows that the most likely behavior to be seen is linear S-H compensation over a rather limited range of perturbations with a compensation temperature Tc = dΔH/dΔS within 20% of the experimental temperature. A general statistical mechanical model of a complex system is analyzed to explore whether and under what conditions extra-thermodynamic compensation can occur and what it reveals about the system. Some recent thermodynamic data on proteins purporting to show compensation is analyzed and shown to be better explained by other causes. The most precise and interesting one, which is considered here, is a linear relationship between ΔH and ΔS for some series of perturbations or changes in experimental variable. The questions examined here are whether the observed compensation is extra-thermodynamic (i.e., reflects anything more than the well-known laws of statistical thermodynamics) and if so, what does it reveal about the system? Compensation is rather variably defined in the literature and different usages are discussed. It has been suggested that this compensation is an intrinsic property of either complex, fluctuating, or aqueous systems. The phenomenon of entropy–enthalpy (S-H) compensation is widely invoked as an explanatory principle in thermodynamic analyses of proteins, ligands, and nucleic acids.
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