Electrochemistry of methimazole on fluorine-doped tin oxide electrodes and its square-wave voltammetric determination in pharmaceutical formulations

A simple and fast flow injection amperometry for the determination of methimazole in pharmaceutical preparations using an unmodified boron-doped diamond electrode

In this work, an automated flow injection analysis (FIA) connected to a boron-doped diamond electrode (BDDE) was originally developed for the analysis of methimazole in pharmaceutical preparations. At a modification-free BDDE, methimazole was easilly oxidized. For the analysis of the mechanisms occurring at the electrode surface, cyclic voltammetry was employed to evaluate the impact of fundamental experimental parameters, such as pH and scan rate, on the BDDE response. For the quantitative detection, the FIA amperometric approach was constructed and used as a fast and sensitive method. The suggested approach provided a broad linear range of 0.5-50 μmol/L and a low detection limit of 10 nmol/L (signal-to-noise ratio = 3). Furthermore, the BDDE was successfully utilized to quantify methimazole in genuine samples from a variety of medicines, and its performance remained steady after more than 50 tests. The findings of amperometric measurements exhibit excellent repeatability, with relative standard deviations of less than 3.9 and 4.7 % for intra-day and inter-day, respectively. The findings indicated that, compared with traditional approaches, the suggested method has the following advantages: quick analysis time, simplicity, highly sensitive output, and no need for complicated operational processes.

Analysis of solvent-accessible voids and proton-coupled electron transfer of 2,6-bis(1H-imidazol-2-yl)pyridine and its hydrochloride

The crystal structures of the solid form of solvated 2,6-bis(1H-imidazol-2-yl)pyridine (H₂dimpy) trihydrate, C₁₁H₉N₅·3H₂O·[+solvent], I, and its hydrate hydrochloride salt 2-[6-(1H-imidazol-2-yl)pyridin-2-yl]-1H-imidazol-3-ium chloride trihydrate, C₁₁H₁₀N₅⁺·Cl^-·3H₂O, II, are reported and analysed in detail, along with potentiometric and spectrophotometric titrations for evaluation of the acid-base equilibria and proton-coupled electron-transfer reactions. Compound I crystallizes in the high-symmetry trigonal space group P3₂21 with an atypical formation of solvent-accessible voids, as a consequence of the 3₂ screw axis in the crystallographic c-axis direction, which are probably occupied by uncharacterized disordered solvent molecules. Additionally, the trihydrated chloride salt crystallizes in the conventional monoclinic space group P2₁/c without the formation of solvent-accessible voids. The acid-base equilibria of H₂dimpy were studied by potentiometric and spectrophotometric titrations, and the results suggest the formation of H₃dimpy⁺ (pK_a1 = 5.40) and H₄dimpy²⁺ (pK_a2 = 3.98), with the electrochemical behaviour of these species showing two consecutive irreversible proton-coupled electron-transfer reactions. Density functional theory (DFT) calculations corroborate the interpretation of the experimental results and support the assignment of the electrochemical behaviour.

Determination of methimazole based on electropolymerized-molecularly imprinted polypyrrole modified pencil graphite sensor

Preparation of a molecularly imprinted polymer (MIP) film and its recognition property for methimazole (MMZ) was investigated. The polypyrrole (PPy) film was prepared by the cyclic voltammetric deposition of pyrrole in the presence of a supporting electrolyte (NaClO₄·H₂O) with and without MMZ through on a pencil graphite electrode (PGE). A computational study based on density functional theory was developed to evaluate the template-monomer geometry and interaction energy in the prepolymerization mixture. The performance of MIP sensor and non-imprinted polymer (NIP) film was evaluated by differential pulse voltammetry (DPV). The most important parameters controlling the performance of sensor were investigated and optimized. The prepared electrode was used for MMZ measurement by a three-step procedure, including analyte extraction in the electrode, electrode washing and electrochemical measurement of MMZ. The molecularly imprinted film exhibited a high selectivity and sensitivity toward methimazole in the experimental conditions. The calibration curve demonstrated linearity over a concentration range of 0.007-6mM with a correlation coefficient (r²) of 0.9808. The accuracy of the method was studied through spiking blank samples showed recovery of 98% with precision of 4%. Limit of detection based on S/N=3 was obtained 3×10^-6M. The proposed sensor was applied successfully to determine MMZ in biological model samples and pharmaceuticals.

Graphene Dendrimer-stabilized silver nanoparticles for detection of methimazole using Surface-enhanced Raman scattering with computational assignment

Graphene functionalized with polyamidoamine dendrimer, decorated with silver nanoparticles (G-D-Ag), was synthesized and evaluated as a substrate with surface-enhanced Raman scattering (SERS) for methimazole (MTZ) detection. Sodium borohydride was used as a reducing agent to cultivate silver nanoparticles on the dendrimer. The obtained G-D-Ag was characterized by using UV-vis spectroscopy, scanning electron microscope (SEM), high-resolution transmission electron microscope (TEM), Fourier-transformed infrared (FT-IR) and Raman spectroscopy. The SEM image indicated the successful formation of the G-D-Ag. The behavior of MTZ on the G-D-Ag as a reliable and robust substrate was investigated by SERS, which indicated mostly a chemical interaction between G-D-Ag and MTZ. The bands of the MTZ normal spectra at 1538, 1463, 1342, 1278, 1156, 1092, 1016, 600, 525 and 410 cm(-1) were enhanced due to the SERS effect. Correlations between the logarithmical scale of MTZ concentrations and SERS signal intensities were established, and a low detection limit of 1.43 × 10(-12) M was successfully obtained. The density functional theory (DFT) approach was utilized to provide reliable assignment of the key Raman bands.