The Study On Enantioselctive Ion Electrodes

Chirality is one of the essence of nature. Due to the different optical and biologic peroperties between the enantiomers, enantioselective assay, also entitled as chiral analysis, became very important in almost all fields of biological, chemical and pharmaceutical sciences. Popular techniques for chiral discrimination are based on chromatography and spectrometry, however most of them are equipments costly, time consuming, sample pretreatment and need sophisticated and extensive analysis procedures. It is necessary to develop a fast, low cost, simple equipment and high selective method for determining enantiopurity of drugs. In this paper, two kinds of ion selective electrodes for electrochemical analysis was introduced to identify chiral compound, one is based on ligand exchange principle and the other based on chiral salen Mn(III) complex as the recognition selector.1. Enantioseletive PVC Membrane Electrode Based on N-dodecanoyl-L-proline as Chiral CarrierAn enantioselective electrodes is presented. N-dodecanoyl-L-proline (N-DDO-L-Pro) was prepared as the chiral selector of PVC membrane electrode. It can undergo ligand exchange with the enantiomeric labile coordination complexes of [Cu(II)(L-Pro)2] or [Cu(Ⅱ)(D-Pro)2] in the testing solutions and form diastereoisomeric complex [(L-Pro)Cu(II)(N-DDO-L-Pro)] or [(D-Pro)Cu(Ⅱ)(N-DDO-L-Pro)] on surface of PVC membrane. Due to different thermodynamic stabilities of diastereoisomeric complexes, electrode can preferentially respond L-proline, exhibiting near Nernstian slope of 57 mV per decade in the concentration range of 1.0×10-4 to 1.0×10-1mol/L. The detection limit is 3.89×10-5mol/L. Moreover, the electrode can detect chiral L-proline with the enantiomeric selectictivity coefficients(Log KL,Dpot,-3.19)2. An enantioselective potentiometric sensor with the polyaniline modification for L-mandelic acid based on chiral SalenMn(Ⅲ)A novel construction for polymeric membranes used in ion-selective electrodes is presented. The polyaniline(PANI)-coated PVC membranes based on chiral SalenMn(III) for chiral determination of L-mandelic acid (L-MA) are described. An excellent performance was obtained for the membrane with a composition of 31.05% poly(vinyl chloride),6.84% chiral SalenMn(III) and 62.11% o-NPOE. The electrode exhibited good potentiometric response characteristics and displayed a linear response over a wide concentration range of 5.0×10-6 to 1×10-1 mol/L with Nernstian slope of 57.6 mV per decade and the detection limit of 1.0×10-6 mol/L. Due to different energy and thermodynamic stabilities of chiral SalenMn(III) compound formed by D-MA or L-MA coordinated to SalenMn(Ⅲ), this sensor demonstrated an enantioselective coefficient (Log KL,Dpot),-4.04. Owing to the presence of PANI hydration, the potentiometric response towards highly hydrated L-MA was promoted.