Partial molar volumes-insights into molecular structure

The applications of a new model describing the solute - solvent interaction s of organic hydrophobic compounds to the calculation of experimental volum etric data are discussed. The proposed model is based on the interpretation of volumetric properties of aqueous solutions: partial molar volume V-2(o) , molecular volume V-2(M) and volume of solvation shell V-1,V-solv. Calcula tions were made on reported V-2(o) 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 molecu lar surface areas and molecular volumes the algorithm GEPOL version 12.1 wa s applied. It was demonstrated, that the ratio of V-2(M) - V-2(o) to the V- 1,V-solv, defined as a relative density of solvation shell, alpha, is a con venient parameter when used to compare solutes with different structure and polarity. It was also shown that the patterns characterizing the dependenc e of ct on the structure and polarity of the compounds are the same althoug h the derived results depend on the applied method of calculation of struct ural parameters of a solute and "a priori" assumed dimension of solvation s hell. (C) 1999 Elsevier Science B.V. All rights reserved.