RELATIONSHIPS BETWEEN COMPUTED MOLECULAR-PROPERTIES AND SOLUTE SOLVENT INTERACTIONS IN SUPERCRITICAL SOLUTIONS

We focus specifically on solute-solvent interactions in supercritical solutions, as reflected in the enhancement factor E = y2P/P2sat, where Y2 and P2sat are the solubility and vapor pressure of the solute and P is the pressure of the system. For a series of 12 organic solutes in supercritical CO2, We find that E can be represented well in terms of three key solute molecular properties: (a) surface area, (b) the sum of the variances of the positive and negative electrostatic potentials on the surface, and (c) a ''balance' parameter which indicates the degree to which the solute molecule can interact to a similar extent through both its positive and negative regions. These three solute properties were computed at an ab initio self-consistent field minimum basis set level. On the basis of limited data, the same type of relationship appears to be applicable for a given solute-cosolvent combination. When various solvents or cosolvents are used, the enhancement factor of a weakly polar solute correlates well with the solvent/cosolvent molecular sizes. For polar solutes, however, an explicit dependence upon electrostatic interaction tendencies must be included.