Partial molar volumes-insights into molecular structure

Abstract

Abstract The applications of a new model describing the solute - solvent interactions of organic hydrophobic compounds to the calculation of experimental volumetric data are discussed. The proposed model is based on the interpretation of volumetric properties of aqueous solutions: partial molar volume V2o, molecular volume V2M and volume of solvation shell V1,solv. Calculations were made on reported V2o data for amides, N-alkyl amides and N,N-dialkylamides. The structural parameters of the compounds were obtained by use of the molecular mechanics methods, INSIGHT (Biosym, San Diego, USA) or SYBYL (Tripos Ass. St. Louis, USA), whereas for calculations of the molecular surface areas and molecular volumes the algorithm GEPOL version 12.1 was applied. It was demonstrated, that the ratio of V2M - V2o to the V1,solv, defined as a relative density of solvation shell, α, is a convenient parameter when used to compare solutes with different structure and polarity. It was also shown that the patterns characterizing the dependence of α on the structure and polarity of the compounds are the same although the derived results depend on the applied method of calculation of structural parameters of a solute and “a priori” assumed dimension of solvation shell.