Partial Molar Volumes of Alkylated Uracils--Insight into the Solvation Shell? Part II

The solute–solvent interactions in aqueous solutions of alkylated uracils are discussed. The partial molar volume data are interpreted using a new model of interaction of the solute molecule with the solvent. The model is based on the assumption that the density of solvent in the hydration shell depends on the structure and polarity of the solute molecule. The relation among molecular volume, partial molar volume, and volume of the solvation shell is expressed by α parameter, α which is defined as the relative density of the solvation shell. It is found that in compounds with the same number of CH2- groups, the α values depend on substitution on the C or N atoms of the uracil skeleton. The α values also depend to some extent, on screening of the oxygen atoms by methylation of the neighboring atoms of the uracil ring. A correlation is presented between the relative density of solvation shell and polarity (defined as the ratio of the surface of polar groups and atoms exposed to the solvent to the total accessible molecular surface of the molecule) for the compounds studied. It was demonstrated that of the various solute–solvent interactions the dominant role is played by polar interactions.