Linear orthobaric-density approach to the Krichevskii parameter of a solute from its vapor-liquid distribution coefficient: What can we learn about its accuracy from systems whose precise behavior is known?

Abstract

We invoke the thermodynamic description of the solvation behavior of two limiting-case model solutes in highly-compressible environments of a real solvent to address the issue identified in the subtitle of this manuscript. We probe the effect of small experimental uncertainties in the vapor-liquid distribution constant of a dilute solute on the regressed limiting orthobaric-density slope by interrogating how this slope deviates from the theoretically-expected known values. The approach becomes feasible because we have developed the solvation thermodynamics of two limiting-case solute-solvent intermolecular asymmetries, i.e., the ideal gas solute and the solute behaving as another real solvent species, whose exact results provide unambiguous answers. We also uncover the non-monotonic dependence of the orthobaric-density slope of the vapor-liquid distribution constant involving the ideal gas solute in either light- or heavy-water solutions, a behavior that conspires against the key hypothesis behind the linear regression approach and the accuracy of the resulting Krichevskii parameters. Moreover, we reveal the significant water H/D−substitution effect on the orthobaric-density range of validity of the linear density representation for the vapor-liquid distribution constant of a solute.