Voltammetric measurement of catechol-O-methyltransferase inhibitor tolcapone in the pharmaceutical form on the boron-doped diamond electrode.

This study presents an electroanalytical approach to measure the catechol-O-methyltransferase (COMT) inhibitor tolcapone (TOL) using a boron-doped diamond (BDD) electrode. The application of cyclic voltammetry (CV) technique revealed that TOL exhibited a distinct, diffusion-controlled, irreversible anodic peak at a potential of approximately +0.71 V (vs. Ag/AgCl) in a 0.1 mol L-1 phosphate buffer solution (PBS) with a pH of 2.5. The oxidation of TOL is highly dependent on the pH and supporting electrolytes. Based on the data obtained from the pH investigation, a proposed mechanism for the electro-oxidation of TOL is suggested. Using the square wave voltammetry (SWV) technique, a satisfactory linear relationship was observed at approximately +0.66 V in a 0.1 mol L-1 PBS with a pH of 2.5. The presented method exhibited linearity within the concentration range between 1.0-50.0 µg mL-1 (3.7 × 10-6-1.8 × 10-4 mol L-1), with a limit of detection (LOD) of 0.29 µg mL-1 (1.1 × 10-6 mol L-1). The BDD electrode demonstrated good selectivity against inorganic ions and filler materials interference. Finally, the suitability of the developed approach was assessed by measuring TOL in tablet formulations, resulting in favorable recoveries ranging from 103.4% to 106.2%.

Simultaneous estimation of total phenolic and alkaloid contents in the tea samples by utilizing the catechin and caffeine oxidation signals through the square-wave voltammetry technique.

This work outlines the simultaneous estimation of the total phenolic and alkaloid contents in the tea samples by using catechin (C) and caffeine (CAF) oxidation signals at a non-modified boron-doped diamond (BDD) electrode. Two irreversible oxidation peaks, about + 1.03 (for C) and + 1.45 V (for CAF) vs Ag/AgCl in acetate buffer solution at pH 4.7, were seen in the cyclic voltammetric profile of the binary mixtures of C and CAF. In optimal conditions and utilizing the square-wave mode, the BDD electrode allows for simultaneous quantification of C and CAF within the concentration ranges of 5.0-100.0 µg mL-1 (1.72 × 10-5 - 3.45 × 10-3 mol/L) and 1.0-50.0 µg mL-1 (5.15 × 10-6 - 2.57 × 10-4 mol/L) respectively. The corresponding detection limits are 1.22 µg mL-1 (4.21 × 10-6 mol/L) for C and 0.11 µg mL-1 (5.66 × 10-7 mol/L) for CAF. Other phenolic compounds (like tannic acid, gallic acid, epicatechin, and epigallocatechin gallate) and other alkaloids (theophylline and theobromine) present in tea samples were examined for selectivity assessment. Ultimately, the applicability of the proposed approach was demonstrated by estimating the total phenolic and alkaloid contents in the black and green tea samples, expressed as C and CAF equivalents. The results obtained were contrasted against those acquired using UV-Vis spectrometry.

Strengthening of Reinforced Concrete Non-Circular Columns with FRP.

Fiber reinforced polymer (FRP) strengthening in circular columns is known to be more effective than in rectangular and square columns because of the uniform distribution of confining pressure. This study explores the effectiveness of using carbon-FRP anchors to improve the confinement of square reinforced concrete (RC) columns strengthened with FRP. Sharp corners in non-circular columns cause stress concentration on the corners, reducing the effectiveness of strengthening. To address this, the study examines the impact of three different anchor configurations on two sizes of FRP-strengthened square columns. The results show that the proposed anchors distribute stresses to a greater extent, resulting in a more uniform distribution of stresses and better confinement. For the best performance, it is proposed that the anchor fans surround the corners of the cross section. Experimental findings and finite element analysis results using the Concrete Damage Plasticity model in the ABAQUS material library match.

Ferrocement, Carbon, and Polypropylene Fibers for Strengthening Masonry Shear Walls.

This paper describes an experimental investigation into the feasibility of using ferrocement jacketing, polypropylene fibers, and carbon fiber reinforced polymer sheets (CFRP) to enhance the shear resistance of unreinforced brick masonry. The study involved testing 12 wall panels in diagonal compression, three of which were strengthened using each of the above-mentioned techniques. The results showed that all three strengthening techniques led to a significant improvement in the shear resistance and deformation capacity of the unreinforced walls. Furthermore, the results showed that the strengthened walls exhibited a significant improvement in shear resistance and deformation capacity by a factor of 3.3-4.7 and 3.7-6.8, respectively. These findings suggest that ferrocement jacketing is a viable and highly effective method for strengthening masonry structures. Test results can assist in the decision-making process to identify the most suitable design and retrofitting solution, which could indicate that not only new materials, but also traditional methods and materials (ferrocement) could be interesting and effective, also considering their lower initial cost.

Iodine adsorption and electrochemical double-layer capacitor characteristics of activated carbon prepared from low-cost biomass.

The efficient adsorption application and electric double-layer capacitor material with low-cost biomass-based activated carbon materials have been quite common recently. In this study, chestnut shell-based activated carbons were produced by chemical activation. ZnCl2, H3PO4, and KOH agents were used for chemical activation. The obtained activated carbon, iodine adsorption from aqueous solutions, and its use as an electro capacitor were investigated. The scanning electron microscope, nitrogen adsorption/desorption, and Fourier transform infrared spectroscopy were used for characterization. The values of surface area and iodine adsorption capacity of the chestnut shell-based activated carbon are 1544 m2 g-1 and 1525 mg g-1. As a result, a specific capacitance of 97 Fg-1 with chestnut shell-based activated carbon was obtained in a 1 M KCl electrolyte for the electrochemical double-layer capacitor. This study shows that activated carbon based on the chestnut shell can be used both as an electrochemical energy storage material and as an adsorbent in iodine adsorption.

Electroanalytical investigation and voltammetric quantification of antiviral drug favipiravir in the pharmaceutical formulation and urine sample using a glassy carbon electrode in anionic surfactant media.

This work describes the electrochemical investigation of a promising antiviral agent, favipiravir (FAV) utilizing a nonmodified glassy carbon (GC) electrode, along with a unique voltammetric approach that can determine FAV with a good degree of accuracy, speed, and cost-effectiveness. Using cyclic voltammetry, the compound demonstrated a single well-defined and an irreversible oxidation peak at approximately +1.12 V (vs. Ag/AgCl) in Britton-Robinson (BR) buffer at pH 10.0. The synergistic effect of anionic surfactant, sodium dodecyl sulfate (SDS) on the adsorption ability of GC electrode remarkably increased the sensitivity of the stripping voltammetric measurements of FAV. Employing square-wave adsorptive stripping voltammetry at +1.17 V (vs. Ag/AgCl) (after 60 s accumulation at open-circuit condition) in BR buffer (pH 10.0) containing 3 × 10-4 M SDS, the linear relationship is found for FAV quantification in the concentration from 1.0 to 100.0 µg mL-1 (6.4 × 10-6-6.4 × 10-4 M) with a detection limit of 0.26 µg mL-1 (1.7 × 10-6 M). The proposed approach was used successfully to determine FAV in pharmaceutical formulations and model human urine samples.

Square-wave voltammetric sensing of Lawsone (2-hydroxy-1,4-naphthoquinone) based on the enhancement effect of cationic surfactant on anodically pretreated boron-doped diamond electrode.

In this reported work, an anodically pretreated boron-doped diamond (BDD) electrode was used for the inexpensive, simple and quick detection of a natural dye, lawsone. Lawsone had a well-defined, irreversible and diffusion-controlled oxidation peak at approximately +0.19 V in phosphate buffer solution (PBS, 0.1 M, pH 2.5) using cyclic voltammetry (CV). The oxidation peak heights of lawsone were significantly increased in PBS using the cationic surfactant cetyltrimethylammonium bromide (CTAB). Under optimized experimental conditions, the calibration curve was linear over a concentration range of 0.1-5.0 µM with detection limit of 0.029 µM in 0.1 M PBS (pH 2.5) containing 0.1 mM CTAB by using square-wave voltammetry (SWV). To evaluate the practical applicability of the BDD electrode, it was used for the quantification of lawsone in commercial henna, a natural dye made from the leaves of the henna plant.

First electrochemical evaluation of favipiravir used as an antiviral option in the treatment of COVID-19: A study of its enhanced voltammetric determination in cationic surfactant media using a boron-doped diamond electrode.

Favipiravir, a promising antiviral agent, is undergoing clinical trials for the potential treatment of the novel coronavirus disease 2019 (COVID-19). This is the first report for the electrochemical activity of favipiravir and its electroanalytical sensing. For this purpose, the effect of cationic surfactant, CTAB was demonstrated on the enhanced accumulation of favipiravir at the surface of cathodically pretreated boron-doped diamond (CPT-BDD) electrode. At first, the electrochemical properties of favipiravir were investigated in the surfactant-free solutions by the means of cyclic voltammetry. The compound presented a single oxidation step which is irreversible and adsorption controlled. A systematic study of various operational conditions, such as electrode pretreatment, pH of the supporting electrolyte, concentration of CTAB, accumulation variables, and instrumental parameters on the adsorptive stripping response, was examined using square-wave voltammetry. An oxidation signal at around +1.21 V in Britton-Robinson buffer at pH 8.0 containing 6 × 10-4 M CTAB allowed to the adsorptive stripping voltammetric determination of favipiravir (after 60 s accumulation step at open-circuit condition). The process could be used in the concentration range with two linear segments of 0.01-0.1 µg mL-1 (6.4 × 10-8-6.4 × 10-7 M) and 0.1-20.0 µg mL-1 (6.4 × 10-7-1.3 × 10-4 M). The limit of detection values were found to be 0.0028 µg mL-1 (1.8 × 10-8 M), and 0.023 µg mL-1 (1.5 × 10-7 M) for the first and second segments of calibration graph, respectively. The feasibility of developed methodology was tested to the analysis of the commercial tablet formulations and model human urine samples.

Electrooxidation of tetracycline antibiotic demeclocycline at unmodified boron-doped diamond electrode and its enhancement determination in surfactant-containing media.

In this paper, for the first time, the study of voltammetric determination of tetracycline antibiotic demeclocycline was conducted. The oxidation of compound was investigated using a commercially available boron-doped diamond electrode pretreated electrochemically (anodic and subsequent cathodic). Addition of anionic surfactant, sodium dodecylsulfate (SDS) and cationic surfactant, cetyltrimethylammonium bromide (CTAB) to the demeclocycline-containing electrolyte solution at pH 2.0 and 9.0, respectively, was found to improve the sensitivity of the stripping voltammetric measurements. Employing square-wave stripping mode (after 30 s accumulation at open-circuit condition) in Britton-Robinson buffer, the limits of detection were found to be 1.17 µg mL-1 (2.3 × 10-6 M) for 4 × 10-4 SDS-containing buffer solution at pH 2, and 0.24 µg mL-1 (4.8 × 10-7 M) for 1 × 10-4 CTAB-containing buffer solution at pH 9.0. The feasibility of the developed approach for the quantification of demeclocycline was tested in urine samples.

Polypropylene as a Retrofitting Material for Shear Walls.

In recent years, on account of their excellent mechanical properties, composite materials (made of epoxy-bonded carbon, glass, or aramid fibers) have been used to reinforce masonry walls against in-plane actions. These materials have proven to be an effective solution for the strengthening of unreinforced masonry (URM) walls. Lately, research has shifted to the study of different types of fibers to avoid the use of epoxy adhesives, whose long-term behavior and compatibility with masonry are poor. This paper describes an experimental program that investigated the behavior of URM shear walls strengthened with two types of commercially available polypropylene products: short fibers (fiber length = 12 mm) and polypropylene nets. This investigation aimed to evaluate the influence of polypropylene reinforcement, embedded into an inorganic matrix, in terms of the improvement of the lateral load-carrying capacity, failure mechanism, ductility, and energy dissipation capacity of URM wall panels, where nine walls were subjected to in-plane loads using a racking test setup. The study showed that using two layers of polypropylene fibers embedded into a cementitious matrix greatly increased the in-plane load capacity of the brickwork masonry. On the other hand, the test results indicated that polypropylene nets, used as a repair method for cracked shear walls, cannot improve the structural performance of the walls.

The performance of cathodically pretreated boron-doped diamond electrode in cationic surfactant media for enhancing the adsorptive stripping voltammetric determination of catechol-containing flavonoid quercetin in apple juice.

In the present paper, an electroanalytical methodology was developed for the determination of an important catechol-containing flavonoid derivative, quercetin using adsorptive stripping voltammetry at a cathodically pretreated boron-doped diamond electrode. In cyclic voltammetry, the compound showed a couple of oxidation/reduction peak at low positive potentials, and additional two oxidation peaks at more positive potentials. The sensitivity of the stripping voltammetric measurements was significantly improved when the cationic surfactant, cetyltrimethylammonium bromide (CTAB) was present in the electrolyte solution. Using square-wave stripping mode, a highly linear analytical curve was obtained for quercetin determination in 0.1 M acetate buffer solution (pH 4.7) containing 3 × 10-4 M CTAB at + 0.37 V (vs. Ag/AgCl) (after 30 s accumulation at open-circuit condition) in the range of 0.5-200 ng mL-1 (1.7 × 10-9-3.3 × 10-7 M), with a detection limit of 0.132 ng mL-1 (4.4 × 10-10 M). As an example, the practical applicability of proposed method was successfully tested with the measurement of quercetin concentration in commercial apple juice samples.

Simultaneous voltammetric determination of vanillin and caffeine in food products using an anodically pretreated boron-doped diamond electrode: Its comparison with HPLC-DAD.

This paper describes an electroanalytical method for the simultaneous determination of vanillin (VAN) and caffeine (CAF) using an anodically pretreated boron-doped diamond electrode. Selective determination of one compound in the presence of other one was also realized. Both compounds yielded a single irreversible oxidation peak using cyclic voltammetry. The nature of the electrode reaction was found to be diffusion controlled with contribution of adsorption. By using square-wave adsorptive stripping voltammetry after 60s accumulation under open-circuit voltage, method allowed simultaneous determination of VAN and CAF in phosphate buffer, pH 2.5, with detection limits of 0.234µgmL-1 (1.54×10-6M) and 0.071µgmL-1 (3.66×10-7M), respectively. The proposed method was successfully applied in the selective and simultaneous determination of VAN and CAF in commercial food and beverage samples. In addition, for the comparison, high-performance liquid chromatographic method with diode-array detection was developed for the first time for their simultaneous determination.

Graphene/Nafion composite film modified glassy carbon electrode for simultaneous determination of paracetamol, aspirin and caffeine in pharmaceutical formulations.

A graphene-Nafion composite film was fabricated on the glassy carbon electrode (GR-NF/GCE), and used for simultaneous determination of paracetamol (PAR), aspirin (ASA) and caffeine (CAF). The electrochemical behaviors of PAR, ASA and CAF were investigated by cyclic voltammetry and square-wave adsorptive anodic stripping voltammetry. By using stripping one for simultaneous determination of PAR, ASA and CAF, their electrochemical oxidation peaks appeared at +0.64, 1.04 and 1.44V, and good linear current responses were obtained with the detection limits of 18ngmL(-1) (1.2×10(-9)M), 11.7ngmL(-1) (6.5×10(-8)M) and 7.3ngmL(-1) (3.8×10(-8)M), respectively. Finally, the proposed electrochemical sensor was successfully applied for quantifying PAR, ASA and CAF in commercial tablet formulations.

Flow-through enzyme immobilized amperometric detector for the rapid screening of acetylcholinesterase inhibitors by flow injection analysis.

A commercially available thin-layer flow-through amperometric detector, with the sensing block customized in an original design, was applied to the screening of drug compounds known as acetylcholinesterase (AChE) inhibitors. AChE from electric eel was covalently immobilized onto a cysteamine modified gold disk adjacent to a silver disk working electrode. On-line studies were performed by flow injection analysis (FIA) in PBS buffer pH 7.4. Seven commercially available AChE inhibitors used in the medical field, namely neostigmine, eserine, tacrine, donepezil, rivastigmine, pyridostigmine and galantamine as well as two natural compounds, quercetin and berberine, were investigated. The same trend of inhibitory potency as described in the literature was observed. Of particular interest and in addition to the determination of the IC50 values, this flow-through system allowed the study of both, the stability of the enzyme-inhibitor complex and the kinetic of the enzyme activity recovery.

Voltammetric determination of mixtures of caffeine and chlorogenic acid in beverage samples using a boron-doped diamond electrode.

Herein, a boron-doped diamond (BDD) electrode that is anodically pretreated was used for the simultaneous determination of caffeine (CAF) and chlorogenic acid (CGA) by cyclic and adsorptive stripping voltammetry. The dependence of peak current and potential on pH, scan rate, accumulation parameters and other experimental variables were studied. By using square-wave stripping mode after 60 s accumulation under open-circuit voltage, the BDD electrode was able to separate the oxidation peak potentials of CAF and CGA present in binary mixtures by about 0.4V in Britton-Robinson buffer at pH 1.0. The limits of detection were 0.107 µg mL(-1) (5.51×10(-7) M) for CAF, and 0.448 µg mL(-1) (1.26×10(-6) M) for CGA. The practical applicability of this methodology was tested in commercially available beverage samples.

Determination of vanillin in commercial food product by adsorptive stripping voltammetry using a boron-doped diamond electrode.

A method for the determination of food additive vanillin was developed by adsorptive stripping voltammetry. Its determination was carried out at the anodically pre-treated boron-doped diamond electrode in aqueous solutions. Using square-wave stripping mode, the compound yielded a well-defined voltammetric response in phosphate buffer, pH 2.5 at +1.14 V (vs. Ag/AgCl) (a pre-concentration step being carried out at open-circuit condition for 60s). A linear calibration graph was obtained in the concentration range of 0.5-15.0 µg mL(-1) (3.3×10(-6)-9.8×10(-5) mol L(-1)) with a detection limit of 0.024 µg mL(-1) (1.6×10(-7) mol L(-1)). As an example, the practical applicability of the proposed method was tested for the determination of this flavouring agent in commercial pudding powder of Keshkule (Turkish milk pudding with almond flour).

Electrochemical evaluation and adsorptive stripping voltammetric determination of capsaicin or dihydrocapsaicin on a disposable pencil graphite electrode.

Capsaicin and dihydrocapsaicin are the two most abundant capsaicinoids in peppers, which are responsible for about 90% of the spiciness. A detailed study of the electrochemical properties of these compounds at pencil graphite (PG) electrode was carried out in the pH range 1.0-12.0 in aqueous solutions. The compounds underwent irreversible oxidation at PG electrode, which was an adsorption-controlled process with two protons and two electrons. The voltammetric data indicated that their oxidation proceeded via an ECE mechanism. Using the square-wave adsorptive stripping voltammetry with accumulation at a fixed potential of -0.1V for 120s, both of them yielded a well-defined voltammetric response at +0.31V (vs. Ag/AgCl) in Britton-Robinson buffer, pH 9.0. Capsaicin and dihydrocapsaicin could be determined with detection limits of 1.12 ng mL(-1) (3.7×10(-9)M) and 0.28 ng mL(-1) (9.1×10(-10)M), respectively. The practical applicability of this methodology was tested in commercial Turkish pepper products. The concentration of total capsaicinoids was determined using capsaicin as standard.

Protective effect of Hypericum perforatum L. on serum and hair trace elements in rats 7,12-dimethylbenz[a]anthracene-induced oxidative stress.

The study was designed to assess the effect of Hypericum perforatum L. (H.P) on serum and hair trace elements and mineral levels, oral administration of 7,12-dimethylbenz[a]anthracene (DMBA) induced oxidative stress in Sprague-Dawley female rats. Analysis of the trace element has been carried out using atomic absorption spectrophotometer method at end of 60th day. It has been found out that the DMBA group contained statistically lower Zn and Cr compared to the control group (p<0.01) and (p<0.05), Cu, Mg and Na contained higher than control group (p<0.05), (p<0.05) and (p<0.05). In DMBA+H.P group, Zn higher and Na lower than DMBA group (p<0.05), (p<0.05), in hair samples Cd, K and Zn contained lower DMBA compared to the control group (p<0.05), (p<0.05) and (p<0.05). In group DMBA+H.P, Cd was higher than DMBA group and Cr lowered accordance with control group (p<0.05). The present study demonstrated significantly positive and beneficial effect of H.P on the concentration levels of Zn and Na in serum, also on Cd levels in hair between DMBA and DMBA+H.P groups.

Electrochemical behavior of chlorogenic acid at a boron-doped diamond electrode and estimation of the antioxidant capacity in the coffee samples based on its oxidation peak.

In this study, an electroanalytical methodology for the determination of chlorogenic acid (CGA) was achieved at a boron-doped diamond electrode under adsorptive transfer stripping voltammetric conditions. The values obtained for CGA were used to estimate the antioxidant properties of the coffee sample based on CGA oxidation. By using square-wave stripping mode, the compound yielded a well-defined voltammetric response at +0.49 V with respect to Ag/AgCl in Britton-Robinson buffer at pH 3.0 (after 120 s accumulations at a fixed potential of 0.40 V). At the optimum experimental conditions, linear calibration curve is obtained within the concentration range of 0.25 to 4.0 µg mL⁻¹ with the limit of detection 0.049 µg mL⁻¹ . The developed protocol was successfully applied for the analysis of antioxidant capacity in the coffee products such as Turkish coffee and instant coffee.

Determination of 7,12-dimethylbenz[a]anthracene in orally treated rats by high-performance liquid chromatography and transfer stripping voltammetry.

A number of polycyclic aromatic hydrocarbons (PAHs) have been shown to be toxicants, and induce carcinogenic and immunotoxic effects. As a model PAH agent, 7,12-dimethylbenz[a]anthracene (DMBA) was the strongest one tested in terms of its biological activities and biotransformation. A new and simple high-performance liquid chromatographic (HPLC) method with diode-array detection at 290 nm was developed and validated for monitoring of DMBA in different matrices (serum, liver and kidney) of rats orally treated with DMBA. Furthermore, the applicability of adsorptive transfer stripping voltammetry (AdTSV) on the pencil-lead graphite electrode to these samples was illustrated using our previously reported data for bulk aqueous solutions of DMBA. HPLC and AdTSV methods, which were compatible with each other, allowed DMBA to be detected down to the levels of 3.82x10-9 M (0.98 ppb) and 6.73x10-9 M (1.73 ppb), respectively. Olive oil solutions of DMBA in dose 50 mg/kg were orally administered. 60 days after a single dose of DMBA, its concentrations in these biological samples from rats were measured by means of both methods. Because of rapid biotransformation, DMBA could not be detected in serum. Only low levels of the compounds were deposited unchanged in kidney whereas its levels were considerably higher in liver. These methods were also applied to the assay whether there is an influence of the intake of aqueous extracts of Hypericum Perforatum L. plant on the parent DMBA levels accumulated in rat tissues.