A Simple and Highly Selective Determination of Telmisartan at Sodium Dodecyl Sulfate Modified Pyrolytic Graphite Surface

Electrochemical transformations catalyzed by cytochrome P450s and peroxidases

Cytochrome P450s (Cyt P450s) and peroxidases are enzymes featuring iron heme cofactors that have wide applicability as biocatalysts in chemical syntheses. Cyt P450s are a family of monooxygenases that oxidize fatty acids, steroids, and xenobiotics, synthesize hormones, and convert drugs and other chemicals to metabolites. Peroxidases are involved in breaking down hydrogen peroxide and can oxidize organic compounds during this process. Both heme-containing enzymes utilize active Fe^IVO intermediates to oxidize reactants. By incorporating these enzymes in stable thin films on electrodes, Cyt P450s and peroxidases can accept electrons from an electrode, albeit by different mechanisms, and catalyze organic transformations in a feasible and cost-effective way. This is an advantageous approach, often called bioelectrocatalysis, compared to their biological pathways in solution that require expensive biochemical reductants such as NADPH or additional enzymes to recycle NADPH for Cyt P450s. Bioelectrocatalysis also serves as an ex situ platform to investigate metabolism of drugs and bio-relevant chemicals. In this paper we review biocatalytic electrochemical reactions using Cyt P450s including C-H activation, S-oxidation, epoxidation, N-hydroxylation, and oxidative N-, and O-dealkylation; as well as reactions catalyzed by peroxidases including synthetically important oxidations of organic compounds. Design aspects of these bioelectrocatalytic reactions are presented and discussed, including enzyme film formation on electrodes, temperature, pH, solvents, and activation of the enzymes. Finally, we discuss challenges and future perspective of these two important bioelectrocatalytic systems.

Sensitive and Selective Voltammetric Sensor Based on Anionic Surfactant-Modified Screen-Printed Carbon for the Quantitative Analysis of an Anticancer Active Fused Azaisocytosine-Containing Congener

3-(4-Nitrophenyl)-8-(2,3-dimethylphenyl)-7,8-dihydroimidazo[2,1-c][1,2,4]triazin-4(6H)-one (NDIT) is one of the most promising candidates for anticancer agents. Hence, a sensitive and selective sodium dodecyl sulfate-modified screen-printed carbon sensor (SPCE/SDS) was used for its quantitative analysis. The SPCE/SDS, in contrast to the SPCE, showed excellent behavior in the electrochemical reduction of NDIT by differential-pulse adsorptive stripping voltammetry (DPAdSV). Cyclic voltammetric (CV) studies reveal an irreversible, two-stage and not purely diffusion-controlled reduction process in 0.01 M HNO₃. The sensor was characterized by CV and electrochemical impedance spectroscopy (EIS). Under the optimized conditions (t 45 s, ΔE 175 mV, ν 150 mV/s, and t_m 5 ms), the DPAdSV procedure with the SPCE/SDS presented a very wide linear range from 1 to 2000 nM and a low detection limit of 0.29 nM. A 1000-fold excess concentration of potential interferents commonly present in biological samples did not significantly alter the peak current of NDIT. The practical application of the proposed DPAdSV procedure with the SPCE/SDS was successfully checked by analyzing spiked human serum samples.

Determination of active ingredients in antihypertensive drugs using a novel green HPLC method approach

A novel, sensitive, fast, and pratic RP-HPLC methods were presented for the quantitative amounts of Telmisartan (TEL) and Olmesartan (OLM) in the presence of Amlodipin (AML) in a binary mixture of pharmaceutical preparation. Waters Spherisorb ODS-2 C18 column was used for separation. These methods were valid over linearity ranges of 2.5-30 μμg/mlL, 2-85 μμg/mlL, and 2-35 μμg/mlL for OLM, TEL, and AML, respectively. The mobile phase system consisted of acetonitrile:methanol: phosphate buffer at pH 3.0 (65:5:30 v/v/v), and the flow rate was 1,5 mlL/min for OLM and AML. The mobile system's other mixture (TEL and AML) was acetonitrile:methanol: phosphate buffer at pH 2.5 (65:5:30 v/v/v), and the flow rate was 1,5 mlL/min. These procedures were successfully applied to bulk, laboratory synthetic mixture, and medicinal dosage forms to use active ingredients quantitatively. The studied methods were validated according to ICH guidelines. In the developed HPLC method, the limit of detection values was found to be 0.020 μμg/mlL for TEL, 0.025 μμg/mlL for OML, and 0.070 μμg/mlL for AML. The correlation coefficients for the HPLC method were found to be 0.9938 for TEL, 0.9996 for OML, and 0.9982 for AML. The calibration range is between 2.5 and -30, 5-35, and 2-85 μμg/mlL for OLM, AML, and TEL, respectively. The proposed HPLC method is a convenient, effective, sensitive, green, and time-saving method for the rapid determination of TEL and OLM in the presence of AML.

Simultaneous determination of hydrochlorothiazide, amlodipine, and telmisartan with spectrophotometric and HPLC green chemistry applications

For the quantifiable amounts of Telmisartan (TLM) and Hydrochlorothiazide (HYD) in the presence of Amlodipine (AML) in a ternary mixture of synthetic laboratory mixture, a novel, sensitive, quick, and practical reversed-phase high-performance liquid chromatography (RP-HPLC) method was given. In order to separate, a Waters Spherisorb ODS-2 C18 column was used. For HYD, TLM, and AML, these techniques were viable over linearity ranges of 4-12 μg/mL, 4-25 μg/mL, and 5-40 μg/mL, respectively. The mobile phase system was acetonitrile:methanol: phosphate buffer at pH 2.5 (65:5:30 v/v/v), and the flow rate was 1.5 mL/min. Novel spectrophotometric methods were applied for active substances to determine simultaneously. The first method is absorptivity centering using factorized spectrum, and the second method is dual amplitude difference coupled with absorbance subtraction. These approaches have been effectively applied to bulk, laboratory synthetic mixtures to employ active components quantitatively. Correlation coefficients were found to be higher than 0.99 and the limit of detection values lower than 0.49 μg/mL in both spectrophotometric methods. The methodologies were validated following ICH recommendations. In the developed HPLC method, the limit of detection values was found to be 0.01 μg/mL for HYD and 0.02 μg/mL for AML and TLM. The correlation coefficients for the HPLC method were found to be 0.9971 for HYD, 0.9990 for AML, and 0.9983 for TLM. The suggested HPLC technique is a simple, effective, sensitive, environmentally friendly, and time-saving approach for determining TLM and HYD in the presence of AML.

Electrochemically Activated Screen-Printed Carbon Sensor Modified with Anionic Surfactant (aSPCE/SDS) for Simultaneous Determination of Paracetamol, Diclofenac and Tramadol

In this work, an electrochemically activated screen-printed carbon electrode modified with sodium dodecyl sulfate (aSPCE/SDS) was proposed for the simultaneous determination of paracetamol (PA), diclofenac (DF), and tramadol (TR). Changes of surface morphology and electrochemical behaviour of the electrode after the electrochemical activation with H₂O₂ and SDS surface modification were studied by scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The influence of various parameters on the responses of the aSPCE/SDS such as pH and concentration of the buffer, SDS concentration, and techniques parameters were investigated. Using optimised conditions (E_acc. of −0.4 V, t_acc. of 120 s, ΔE_A of 150 mV, ν of 250 mV s⁻¹, and t_m of 10 ms), the aSPCE/SDS showed a good linear response in the concentration ranges of 5.0 × 10⁻⁸–2.0 × 10⁻⁵ for PA, 1.0 × 10⁻⁹–2.0 × 10⁻⁷ for DF, and 1.0 × 10⁻⁸–2.0 × 10⁻⁷ and 2.0 × 10⁻⁷–2.0 × 10⁻⁶ mol L⁻¹ for TR. The limits of detection obtained during the simultaneous determination of PA, DF, and TR are 1.49 × 10⁻⁸ mol L⁻¹, 2.10 × 10⁻¹⁰ mol L⁻¹, and 1.71 × 10⁻⁹ mol L⁻¹, respectively. The selectivity of the aSPCE/SDS was evaluated by examination of the impact of some inorganic and organic substances that are commonly present in environmental and biological samples on the responses of PA, DF, and TR. Finally, the differential pulse adsorptive stripping voltammetric (DPAdSV) procedure using the aSPCE/SDS was successfully applied for the determination of PA, DF, and TR in river water and serum samples as well as pharmaceuticals.