The electrochemical and analytical characteristics of enantioselective sensors based on glassy carbon electrodes modified by chelate complexes (bis(L-phenylalaninate) copper(II), glycinato-L-phenylalaninate copper(II), tris(L-phenylalaninate) cobalt(II), bis(L-phenylalaninate) zinc) are studied. It is found that the most promising sensor for determining tryptophan enantiomers is the sensor modified by copper(II) (bis)L-phenylalaninate. In determining tryptophan enantiomers, this sensor provides a linear concentration range from 6.25 × 10 -7 to 0.5 × 10 -3 M for L-tryptophan and from 5 × 10 -6 to 0.5 × 10 -3 M for D-tryptophan. The sensor is more sensitive to L-tryptophan. The proposed sensor was used for the recognition and determination of tryptophan enantiomers in human urine and plasma samples, and also in a mixture of enantiomers. The statistical assessment of the results of determinations by the spiked-found method indicates the absence of a significant systematic error.

A voltammetric sensor based on a composite of polyarylene phthalide and graphitized carbon black Carboblack C modified with chelate complexes of L-argenato-L-alaninate of copper (II) has been developed for the recognition and selective determination of tryptophan enantiomers. The conditions for modifying the sensor are optimized, the effective surface area (A = 4.38 ± 0.06 mm2) and the effective resistance (Ret = 1.29 ± 0.08 kΩ) are calculated. The optimal conditions for recording voltammograms of tryptophan enantiomers are selected: the range of operating potentials is 0.5-1.2 V, the potential sweep rate is 20 mV/s, the holding time of the electrode in the test solution is 5 s. The electrochemical and analytical characteristics of the sensor were studied when registering differential pulse voltammograms of tryptophan enantiomers. It is shown that the dependence of the analytical signal on the concentration is linear in the range from 1.25·10-6 to 1·10-3 M with detection limits of 0.90·10-6 M for L-Trp and 0.66·10-6 M for D-Trp. The developed sensor shows the greatest sensitivity to D-Trp. The sensor has been successfully tested to determine the content of L- and D-Trp in enantiomer solutions in the presence of excipients that are part of medicines and biologically active additives. The proposed sensor allows the determination of tryptophan enantiomers in human urine and blood plasma. To evaluate the analytical capabilities of the sensor, the "entered-found" method was used. When determining tryptophan enantiomers in model solutions, the relative standard deviation does not exceed 2.3 %, and the relative error is 1.7 %. When determining D- and L-Trp in biological fluids, the relative standard deviation ranges from 0.3-1.7 %, and the relative error ranges from 0.3-5.6 %. The research results show that there is no significant systematic error.

The use of chiral modifiers is among the simplest and most popular strategies for synthesizing enantioselective voltammetric sensors that are applied for the analysis and discrimination of enantiomerical drugs in various media. The type and structure of the chiral modifier are the key factors for the creation of enantioselectivity to a specified analyte. We suggest a novel approach to the prediction of the quality of a chiral modifier for preparing highly enantioselective sensors. The suggested approach is based on the molecular mechanics modeling of the adsorption of analyte enantiomers on chiral modifiers and on the comparison of the corresponding adsorption energies (ΔEads). The efficiency of our approach is demonstrated using the example of cyclodextrins and chiral single‐wall carbon nanotubes as chiral modifiers, and a wide range of chiral analytes. We found that the experimental enantioselectivity (ϑexp) measured using voltammetry linearly correlates with ΔEads. The suggested approach also showed good predictive power in application to enantioselective chromatography, which further validates its general applicability.

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Разработан вольтамперометрический сенсор на основе стеклоуглеродного электрода, модифицированного композитом полиэлектролитного комплекса хитозана и сукцинилхитозана с аминокислотным комплексом меди (II) [Cu(L-Phe)(Gly)] для распознавания и определения энантиомеров тирозина. По данным циклической вольтамперометрии и спектроскопии электрохимического импеданса рассчитаны площадь эффективной поверхности предложенного композитного сенсора (А = 2.05± 0.13 мм 2 ) и значения сопротивления переноса электронов (R et = 14.7 ± 0.3 кОм). Изучены электрохимические и аналитические характеристики разработанного сенсора при регистрации линейных вольтамперограмм энантиомеров тирозина.