Enantioselective biomimetic sensor for discrimination of R and S-Clopidogrel promoted by β-cyclodextrin complexes employing graphene and platinum nanoparticle modified carbon paste electrode

Abstract

To mimic the enantioselectivity of an enzyme in the field of biosensor for a drug molecule is daunting task for chiral selector. Here, we report beta cyclodextrin (β-CD) as artificial enzyme model for molecular recognition of Clopidogrel (CLP) isomers on chiral carbon paste electrode. The inclusion of CLP enantiomers was initiated by β-CD and stability constants obtained for 1:1 complex of β-CD-R-CLP and β-CD-S-CLP. The stability constants calculated for β-CD-R-CLP and β-CD-S-CLP were 6.109×103M−1 and 5.023×102M−1, respectively at 25°C. The best enantioselectivity was obtained for R-CLP which was found to be 12 times higher to that of S-CLP. The thermodynamic consideration of the complex formation shows negative values of Gibbs free energy (ΔG) -21.602 kJ K−1mol−1 (R-CLP) and−15.411 kJ K−1mol−1 (S-CLP) which indicates inclusion process to be exothermic and spontaneous. The difference in ΔG values indicates effective enantiomeric recognition of the aforementioned electrode systems for CLP. The synergistic effect of graphene, platinum nanoparticle and beta cyclodextrin in the form of modified carbon paste electrode (GNS-PNP-β-CD-CPE) were studied by differential pulse voltammetric techniques. The anodic peak potential difference of 102mV was able to discriminate isomers of CLP at the surface of GNS-PNP-β-CD-CPE. Under optimum conditions, R-CLP and S-CLP exhibited good linear response in the range of 2.0×10−6 to 2.0×10−4M with low detection limit of 4.87×10−7M and 2.10×10−7M, respectively. The Michaelis-Menten constants (KM) calculated for R-CLP and S-CLP were 44.0μM and 60.0μM employing chronoamperometry. The higher value of KM for S-CLP suggests weak binding of S-CLP to the β-CD confirming catalytically different biotransformation rate of each enantiomer towards oxidation. Although the kinetic parameters do not match the level of enzymatic transformations, this study predicts the Michaelis-Menten constants for CLP using β-CD which may become useful guide for future exploration of enzyme mimics in the area of chiral electrochemical biosensor.