Mimicking anaesthetic–receptor interaction: a combined spectroscopic and computational study of propofol⋯phenol

Abstract

Propofol is a general anaesthetic that exerts its action by interaction with the GABA_A receptor. Crystallographic studies suggest that there is a direct interaction between propofol and the phenolic residue of a tyrosine in the channel. In this study we create propofol⋯phenol clusters by their co-expansion in jets. The complex is probed using a set of mass-resolved spectroscopic strategies: 2-color REMPI, UV/UV hole-burning, IR/UV double resonance and the novel technique IR/IR/UV triple resonance. The existence of at least six different isomers in the expansion is demonstrated. All the isomers are stabilized by interactions between their aromatic rings. Additionally, in some conformers the OH moieties form hydrogen bonds in some of the isomers, with propofol and phenol alternating their donor–acceptor roles, while in others the –OH⋯OH angle points to a dipole–dipole interaction. Interpretation of the data in the light of dispersion-corrected DFT calculations shows that shallow barriers separate all the isomers, both in the ground and excited electronic states. Comparison of the structures of the complex with the X-ray diffraction data is also offered.