Raman scattering study of water clusters around polyrotaxane and pseudopolyrotaxane supramolecular assemblies

We have measured Raman spectra of collective O-H stretching vibration of water clusters in polyrotaxane and pseudopolyrotaxane aqueous solutions and the aqueous solutions of their constituent molecules. The intensities of the collective bands of water clusters in the polyrotaxane and pseudopolyrotaxane solutions were approximately equal to that of their solvents. On the other hand, those in the solutions of linear polymeric chains and cyclic molecules were smaller. These results indicate that the water molecules in the solvents cannot approach to interact with the hydrophobic parts of the constituent molecules sterically when the constituent molecules form the inclusion complexes. Thus, the polyrotaxane and pseudopolyrotaxane molecules are observed as inert in terms of molecular interaction with water, although the constituent molecules have hydrophobic parts in their structure.