Molecular hydration of propofol dimers in supersonic expansions: formation of active centre-like structures

Abstract

Spectroscopic studies of molecular aggregates are a powerful tool to understand the weak interactions between molecules. Here, propofol₂(H₂O)_6,7 clusters were formed in supersonic expansions and their electronic and infrared spectroscopy was explored using several mass-resolved laser-based spectroscopic techniques. Using REMPI, their S₁ ← S₀ electronic spectrum was obtained with vibrational resolution, while the UV/UV hole burning revealed the presence of a single isomer of propofol₂(H₂O)₆ and of two isomers of propofol₂(H₂O)₇. Employment of IR/UV double resonance yielded the IR spectrum in the OH stretch region. Comparison with the spectra predicted for the structures calculated at the M06-2X/6-31+G(d) level demonstrated that the two propofol molecules interact mainly through C–H⋯π contacts between the lipophilic sides of the molecules, while the hydroxyl moieties are in close contact, forming a kind of “active centre” with which the water molecules interact, forming polyhedral structures.