ENANTIOSELECTIVE OPTODES

Enantioselective optical sensors (optodes) for protonated 1-phenylethylamine, propranolol and norephedrine have been developed based on the use of four different lipophilic (R,R)-tartrates as carriers. The sensing scheme is based on the selective extraction of the organo-ammonium ions into a poly(vinylchloride) lipid membrane, and on the concomitant release of a proton from a protonated dye, contained in the PVC membrane, into the sample solution. Upon deprotonation, the dye undergoes a colour change which is optically detected. The sensor is fully reversible, with detection limits varying from 0.007 to 0.7 mM for 1-phenylethylamine, 0.006 to 0.07 mM for propranolol, and 0.7 to 7.0 mM for norephedrine at near neutral pH. Response times are about 2 min for membrane thicknesses of ca. 1-mu-m. The differences in the free energy of the two enantiomeric complexes (DELTA-DELTA-G) were calculated as well as the enantiomer selectivity coefficients (K(opt)) from the calibration curves. Although the best selectivity coefficient was found for norephedrine (0.5) using (1R,2S,5R)-dimenthyl (R,R)-tartrate as the receptor (carrier), (R,R)-di-tert.-butyl tartrate is found to be by far the most effective in all other cases. An ether of (R,R)-di-tert.-butyl tartrate, namely its O,O'-dichlorovinyl derivative, is reported for the first time as being a useful enantioselective ion carrier.