Use of a Modified Cyclodextrin Host for the Enantioselective Detection of a Halogenated Diether as Chiral Guest via Optical and Electrical Transducers

Abstract

In an alkaline rebreathing circuit, the inhalation anesthetic sevoflurane degrades into at least two products, one of them being the chiral halodiether 1,1,1,3,3-pentafluoro-2-(fluoromethoxy)-3-methoxypropane (halodiether B). Using octakis(3-O-butanoyl-2,6-di-O-n-pentyl)-y-cyclodextrin (Lipodex E) as chiral host diluted in the polysiloxane PS255, an exceptional large chiral separation factor alpha of 9.7 at 30 degrees C was found for halodiether B by capillary gas chromatography (cGC). Hence, the interaction of the single enantiomers and the racemic mixture of the halodiether B with Lipodex E was selected as a model system to study the enantioselective recognition by thickness shear mode resonators (TSMR), surface acoustic wave sensors, surface plasmon resonance (SPR), and reflectometric interference spectroscopy. Further investigations of the recognition process by using chemical sensors confirmed the preferential enrichment of the S-enantiomer resulting in 9-fold higher signals. Based on the distinction between enantioselective and nonenantioselective sorption, thermodynamic complexation constants of the single enantiomers with Lipodex E could be determined. The difference in Gibbs free energy -deltaE2,E1(deltaG) of the complexation of the enantiomers of halodiether B with pure Lipodex E was determined at 30 degrees C by TSMR and SPR to be 5.7 or 5.9 kJ/mol, respectively, agreeing well with that determined by cGC, i.e., 5.7 kJ/mol at 30 degrees C.