Novel chiral voltammetric sensor for tryptophan enantiomers based on 3-neomenthylindene as recognition element

To achieve satisfactory recognition and determination of tryptophan (TRP) enantiomers a chiral voltammetric sensor based on carbon black paste electrode (CBPE) containing Carboblack C powder and 3-neomenthylindene (NMI) chiral selector is developed in this work. A possible recognition mechanism as well as chiral selectivity have been explained using the molecular dynamics simulation. It was shown that 3-neomenthylindene attracts to TRP enantiomers via Van der Waals and n-n-stacking interactions. Compared with D-TRP, the sensor indicates favorable chiral recognition towards L-TRP with a selectivity coefficient of 1.34. The higher response signal of L-TRP than D-TRP is due to the energetically more favorable interaction of 3-neomenthylindene with L-TRP, which is confirmed by a change in the total energy of the system. CBPE modified by NMI was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). The electrochemical and analytical characteristics of the sensor and conditions of the voltammogram registration were studied by differential pulse voltammetry (DPV). It was found that the oxidation of TRP enantiomers on CBPE/NMI is the diffusion-controlled process. The experimental results indicate a linear correlation between the peak currents of TRP enantiomers and their concentration in the range from 2.5 pM to 0.3 mM, leading to a detection limit of 1.71 pM and 2.23 pM for L- and D-TRP, respectively. The practical capabilities of the proposed sensor were demonstrated by analyzing human urine and blood plasma with satisfactory recoveries ranging from 95.2% to 99.0%. L-TRP was recognized in dietary supplements using projection to latent structures discriminant analysis. The present sensor also can detect the enantiomeric composition based on current signals with the different total concentrations of the mixture. The selectivity, stability, and reproducibility of the proposed sensor were studied as well.

Automated summary

A chiral voltammetric sensor based on carbon black paste electrode was developed for the recognition and determination of tryptophan enantiomers. The sensor showed better recognition towards L-TRP compared to D-TRP, with a linear correlation between peak currents of TRP enantiomers and their concentration. Experimental results demonstrated satisfactory recoveries in human urine and blood plasma, with a detection limit of 1.71 pM for L-TRP and 2.23 pM for D-TRP.