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

Area of Science:

• Physical Chemistry
• Polymer Science
• Spectroscopy

Background:

• Polyrotaxanes and pseudopolyrotaxanes are supramolecular structures with unique host-guest properties.
• Understanding molecular interactions in aqueous solutions is crucial for material design.
• Hydrophobic interactions play a significant role in molecular self-assembly and solvation.

Purpose of the Study:

• To investigate the molecular interactions between water molecules and polyrotaxane/pseudopolyrotaxane inclusion complexes.
• To determine if the hydrophobic components of constituent molecules in inclusion complexes affect water cluster behavior.
• To compare water cluster dynamics in polyrotaxane/pseudopolyrotaxane solutions with those of their individual components.

Main Methods:

• Raman spectroscopy was employed to measure the collective O-H stretching vibration of water clusters.
• Measurements were conducted on aqueous solutions of polyrotaxanes, pseudopolyrotaxanes, and their constituent linear polymeric chains and cyclic molecules.
• Spectra were analyzed to compare the intensities of collective water bands across different solution types.

Main Results:

• The intensities of collective water cluster bands in polyrotaxane and pseudopolyrotaxane solutions were similar to those of the solvent.
• Solutions containing linear polymeric chains and cyclic molecules showed lower intensities of collective water bands.
• This suggests steric hindrance prevents water molecules from interacting with hydrophobic parts within the inclusion complexes.

Conclusions:

• Polyrotaxane and pseudopolyrotaxane molecules act as inert structures regarding molecular interaction with water, despite possessing hydrophobic moieties.
• The formation of inclusion complexes effectively shields the hydrophobic parts of the constituent molecules from water.
• Raman spectroscopy provides insights into the solvation environment and molecular interactions within these supramolecular systems.