Host-guest interactions: Part 3-Volumes of urea+ligand+water mixtures

Abstract

The density measurements of urea (U) in aqueous &beta;- cyclodextrin(CYC) and 18-crown-6-ether (CR) of 0.0100 and 0.0170 mol dm^-3 of each have been made. Densities of urea have also been measured in CYC+CR+W ternary mixture with CYC:CR mole ratio of 1:1 (0.0170:0.0170). From density data, apparent molar volumes of urea (<em>V_ɸU</em>) have been computed. From -the variation in apparent molar volumes, It has been found that the presence of 0.0170 mol dm^-3 of CYC leads to some hydrophobic hydration of CYC by urea, whereas the presence of varying amounts of CR reduce the volume of urea in comparison to its volume in pure water. On the contrary, when both CYC and CR (0.0170 mol dm^-3 of each) are present in the same ternary mixture, the volume behaviour of urea becomes non-specific.