Functionalized α-cyclodextrins as potentiometric chiral sensors

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Abstract
Octylated cyclodextrins have been systhesized 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 kpot(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 kpot (+)/(–), 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.