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 π-π-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 μM to 0.3 mM, leading to a detection limit of 1.71 μM and 2.23 μM 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.
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•A chiral sensor based on CBPE modified by 3-neomenthylindene (NMI) was developed.•Large differences in energy between π-π-stacking of NMI with L-, D-TRP were observed.•Compared with D-TRP, the sensor indicates favorable chiral recognition towards L-TRP.•The sensor correctly determined L- and D-TRP in real objects and enantiomeric mixture.•The recognition of L-TRP based dietary supplements using PLS-DA was successful.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The paper is based on the theoretical aspects of studying the success of oil production projects. To conduct clustering based on the empirical data from the producing well stock, a classifier has ...been compiled describing the types of interventions in 2013-2018. The selection of indicators was carried out on the basis of theoretical qualitative analysis. The following statistical indicators were included in the study information base: well profile, well diameter, field, horizon, and oil flow rate. The dynamics of the oil flow rate is translated into a comparable form using time synchronization. Since the initial attribute space is represented in various units of measurement, in order to ensure comparability, at the stage of formation of information array, standardization of indicators was carried out to the maximum. The interventions revealed the following combinations of factors which showed the greatest effect in terms of growth and total oil production: well profile, well diameter, field, as well as critical factors that can be interpreted as factors of ineffective interventions. The obtained factors were verified by various methods of multivariate statistical data analysis. The author suggests conclusions and recommendations for the most efficient interventions in oil wells.
We developed an enantioselective voltammetric sensor based on a carbon-paste electrode modified by enantiomorphic crystals of bromotriphenylmethane for the recognition and determination of tryptophan ...enantiomers. Enantiomorphic crystals of bromotriphenylmethane were obtained under the condition of Viedma ripening. The electrochemical and analytical characteristics of the sensor were studied. The proposed sensor was used to recognize and determine the enantiomers of L- and D-tryptophan in model solutions of pharmaceutical preparations and in human urine and blood plasma samples. The sensor is easy to manufacture and exhibits high reproducibility and stability. It was shown that, in using chemometric data processing, the presence of even slight differences between the voltammograms of enantiomers recorded using the proposed carbon-paste electrode is sufficient for their reliable recognition.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Antibacterial drugs have become an integral part of the food industry and agriculture in the present-day world. The presence of even trace amounts of antibiotics in foods of animal origin can lead to ...the development of allergic reactions and direct toxic effects in a human body. In this regard, it is necessary to create sensitive and selective procedures for determining antibacterial drugs in order to prevent their excessive consumption. In this work, a glassy carbon voltammetric sensor based on layer-by-layer deposited electroreduced graphene oxide and fullerene functionalized with
S-N
,
N
'-bis(1-phenylethyl)malonamide is proposed for the determination of levofloxacin (
Lev
, S-(-)-ofloxacin) by differential pulse voltammetry. The calibration graph is linear in two ranges, 1.0 × 10
–6
–6.0 × 10
–5
M and 6.0 × 10
–5
–5.0 × 10
–4
M Lev, with sensitivity coefficients of 107 and 58.0 μA/mM, respectively. The limit of detection and limit of quantification are 1.8 × 10
–7
and 6.04 × 10
–7
M, respectively. The selectivity of the sensor to Lev relative to some fluoroquinolone antibiotics: ciprofloxacin, lomefloxacin, and enrofloxacin, was assessed. The sensor was used to determine Lev in meat and milk using differential pulse voltammetry.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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 x 10.sup.-7 to 0.5 x 10.sup.-3 M for L-tryptophan and from 5 x 10.sup.-6 to 0.5 x 10.sup.-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.
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Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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.
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