On the molecular-based thermodynamics of dilute solutions along orthobaric conditions: Concise review of the fundamental microscopic constraints, rigorous formal results, and macroscopic modeling implications

Abstract

We review the fundamentals underlying a rigorous and general molecular-based formalism for the microscopic interpretation of the solvation phenomena involving dilute solutes along the vapor–liquid envelope of a pure solvent up to its critical point. This approach bridges the path between the microstructure of the system, described in terms of correlation function integrals, and the macroscopic solvation properties resulting from the solute–solvent intermolecular interaction asymmetries. We focus on the solvation phenomena associated with the behavior of the Henry’s law constant, vapor–liquid solute distribution coefficient, and the corresponding Ostwald constant whose proper description in the compressible regime of a solvent becomes crucial to the determination of the solute’s Krichevskii parameter. Toward that end, we aim at the widespread use of linear orthobaric-density representations for the behavior of the thermodynamic quantities of infinitely dilute species in near-critical pure solvents. Then, we (i) confront their behavior against that from model systems for which we have full and accurate knowledge of the outcome, such as those for the solvation of an ideal gas solute in a real solvent, and that of a self-solvated species representing thermodynamically the Lewis-Randall solution ideality, (ii) identify the non-monotonic orthobaric-density slope of the vapor–liquid solute distribution coefficient involving the ideal gas solute in either light- or heavy-aqueous solutions, a condition that disallows the central hypothesis underpinning the conventional linear regression approach and the accuracy of the defining Krichevskii parameters, (iii) present a novel path leading to the calculation of the Krichevskii parameter of any solute according to a universal thermodynamic expression connecting rigorously the solute–solvent intermolecular asymmetry, as described by the Henry’s law constant of a solute at infinite dilution in a pure solvent, to the desired Krichevskii parameter, and (iv) establish a direct route leading to the accurate determination of the solvent effect on the Krichevskii parameter of a solute, based solely on the contrasting standard solvation Gibbs free energies of the solute at normal conditions and the corresponding Krichevskii parameters of an ideal gas solute in the desired pair of solvents. Finally, we discuss the assessment of the reliability of current modeling approximations, their internal consistency, and the conformity of limiting behaviors as fundamental constraints in the accurate description of solvation phenomena involving infinitely dilute solutions over wide ranges of state conditions and solute–solvent intermolecular interaction asymmetries.