Anesthetic-membrane interactions evaluated by Taft's polarity parameters

Abstract Interactions between volatile anesthetics and dipalmitoylphosphatidylserine liposomes were investigated spectroscopically. A thiacarbocyanine dye and methylene blue were used as polarity probes. The spectral changes caused by inhalation anesthetics (halothane and isoflurane) were correlated with Taft's generalized polarity parameters. Anesthetics decreased the generalized polarity scale (π) and increased the generalized proton acceptor scale (β) of the water—liposome interface. The decrease of π was attributed to the access of anesthetics with a smaller π value to the liposomal membrane. The increase of β was attributed to the perturbation of hydrogen bonds at the water—liposome interface. Application of Taft's parameters enabled quantitative evaluation of the effects of these anesthetics. The present results support our previous conclusion that anesthetics release bound water molecules from the water—liposome interface.