Functionalized α-cyclodextrins as potentiometric chiral sensors

Octylated cyclodextrins have been synthesized and characterized by mass spectrometry (+ fast atom bombardment, + field desorption) and 500 MHz ¹H nuclear magnetic resonance spectroscopy. These highly lipophilic, enantiomerically pure molecules have been incorporated into solvent polymeric membranes and investigated as electrochemical sensors for chiral molecules incorporating aryl rings. Bis(1-butylpentyl) adipate (BBPA) and ortho-nitrophenyl octyl ether (o-NPOE) were used as plasticizers. Electrodes using BBPA as the plasticizer were stable and well defined with a limit of detection for ephedrine of -log[c] = 6.5. Interference from serum levels of Na⁺, K⁺ and Ca²⁺ is minimal; the best value obtained for -log k^pot (the over-all selectivity coefficient) was 3.9 with BBPA as plasticizer and 1 × 10^-3 mol dm^-3 NH₄Cl as inner filling solution. The electrodes were highly enantioselective in binding ephedrine (enantioselectivity k _(+)/(-)^pot, 2.7). The o-NPOE-based electrodes, although enantioselective with minimal interference from serum levels of Na⁺, K⁺ and Ca²⁺, behaved in a time-dependent manner.