Vol. 23 No. 4 (2025)
Published:
2026-04-07
Full Issue
Original Researches
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The Potentiometric Quantification of Chondroitin Sodium Sulfate Using Ion-Selective Electrodes
Chondroitin sodium sulfate is an anionic polysaccharide widely used in pharmaceutical practice as an active ingredient of mono- and multicomponent medicinal products, and its quantitative determination is an essential stage of the quality control. It has been found that the application of potentiometric titration with ion-selective electrodes can increase the accuracy and objectivity of the quantitative analysis, which is of great importance for ensuring the quality and safety of medicines.
The aim of the study was to develop and validate a potentiometric method for the quantitative determination of chondroitin sodium sulfate in the substance and in a combined medicinal product in the form of the sachet powder.
The study objects were chondroitin sodium sulfate substance and a combined medicinal product containing chondroitin sodium sulfate in combination with D-glucosamine sodium sulfate, methylsulfonylmethane, sodium hyaluronate, ascorbic and citric acids, and sorbitol. The conditions of the potentiometric titration with 0.001 M solution of cetylpyridinium chloride were studied using an ion-selective electrode based on cetylpyridinium ionic associates with some lipophilic anions. The titrant was standardized using sodium dodecyl sulfate as a primary standard, as well as the substance itself. The equivalence point was determined from the titration curve and its mathematically processed forms (differential curve, first derivative, and Gran functions).
It has been found that the plasticized membrane ion-selective electrodes based on cetylpyridinium associates with dodecyl sulfate and tetraphenylborate anions are characterized by a stable near-Nernstian response in the operating range of cetylpyridinium concentrations of 10-3-10-6 mol L-1. The analytical characteristics of the electrodes remained stable for at least 30 consecutive titrations. The selectivity of the reaction between chondroitin sodium sulfate and cetylpyridinium chloride was found, ensuring a clear determination of the equivalence point even in the presence of other mixture components. The influence of pH on the titration results was evaluated; it was shown that in the pH range of 4-8 the shape of titration curves and potential values remained constant, confirming the robustness of the method. The accuracy, precision, linearity (within 80–120% of the nominal content of the analyte), and the reproducibility of the method were characterized.
It has been experimentally demonstrated that the potentiometric method proposed is accurate, selective, and reproducible for the quantitative determination of chondroitin sodium sulfate both in pure form and in combined medicinal products. The results obtained confirm the analytical suitability of the method developed and the prospects of its implementation in the pharmaceutical analysis practice for the quality control of substances and combined medicinal products of small-scale and industrial production.
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The complexation of Water-Soluble Calix[4]Arene-Phosphine Oxides With Antiviral Drugs
The complexation of tetrahydroxycalix[4]arene-methyldimethylphosphine oxide (CMPO), tetrahydroxythiacalix[4]arene-methyldimethylphosphine oxide (TCMPO), and tetrapropoxycalix[4]arene-methyldiethylphosphine oxide (CEPO) with active pharmaceutical ingredients of antiviral drugs Remdesivir, Nevirapine, Vesatolimod, Bictegravir, Emtricitabine, and Tenofovir in the water medium was studied using the RP HPLC method. By analyzing the dependence of the drug capacity values on the concentration of calixarenes in the chromatographic mobile phase, the stability constants (KA = 1100 - 12000 M-1) of the complexes formed were determined. Quantum-chemical calculations show that the antiviral drugs form supramolecular exo-complexes with the calixarene-phosphine oxide molecules. These complexes can be stabilized by intermolecular hydrogen bonds between the proton acceptor P=O groups and the proton donor groups of antiviral drugs.
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The Synthesis and Spectral Properties of Merocyanine Dyes Based on 9H‑Fluorene-2,7-Dicarbonitrile
Di-, tetra-, and hexamethine merocyanine dyes bearing donor heterocyclic end groups of different electron-donating abilities and the 9H-fluorene-2,7-dicarbonitrile moiety as the acceptor end group have been synthesized. Their UV/Vis absorption spectra have been studied in solvents of varying polarity, and their electronic nature and vertical transitions have been investigated via (TD)-DFT calculations. The results indicate that the electronic structure of these merocyanines approaches the neutral polyene limit, becoming increasingly polyene-like in low-polarity solvents and upon increasing the polymethine chain length, which indicates the weak electron-acceptor ability of the 9H-fluorene-2,7-dicarbonitrile moiety. Nevertheless, longer vinylogs, especially those containing the 4H-pyran donor end group, exhibit the inverse solvatochromic behavior, which is highly unusual for such weakly dipolar merocyanines. A possible explanation for this effect has been proposed although its rigorous verification would require higher-level quantum-chemical calculations with solvent effects taken into account.
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A Scalable Synthesis of 4-Functionalized Isoxazolidines and Pyrazolidines
A practical and scalable cyclization method for the preparation of C4-functionalized isoxazolidine and pyrazolidine building blocks is described. The methodology is based on the use of commercially available 1,3-dihalide and protected hydroxylamine or hydrazine derivatives under unified NaH/DMF conditions, enabling direct assembly of both N,O- and N,N-heterocycles. The process is operationally robust and successfully implemented on an over 100 g scale. The oxidative conversion of exocyclic alkene intermediates made it possible to obtain isoxazolidin-4-one and pyrazolidin-4-one scaffolds. The resulting pyrazolidine derivatives demonstrate a broad tolerance to reductive and oxidative conditions, whereas isoxazolidines exhibit certain stability limitations. The combination of the modular C4 diversification, orthogonal nitrogen protection, and preparative scalability transforms these saturated heterocycles into practically accessible building blocks for medicinal chemistry applications.
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Antimicrobial and Antifungal Study of Thiazolotriazolium Salts: in vivo Investigation, and Molecular Docking
Three thiazolo[3,2-b][1,2,4]triazol-7-ium hexabromotellurates 1-3 were synthesized via the electrophilic heterocyclization of methallyl thioether precursors using a classical tellurium(IV) electrophilic reagent generated in situ from TeO2 and 1 M hydrobromic acid. The resulting salts were comprehensively screened for the antimicrobial activity against five clinically relevant pathogens: Staphylococcus aureus, Candida albicans, Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa. Biological assays revealed that compound 1 containing a 2-(4-pyridyl) substituent demonstrated the strongest activity profile, particularly against C. albicans (MIC = 15.625 μg mL-1) and E. coli (MIC = 31.25 μg mL-1). Compound 2, substituted with the 3-hydroxyphenyl moiety, also showed a significant antifungal efficacy, while compound 3 (with the 2-phenyl substituent) exhibited a relatively low activity. To rationalize these differences, the molecular docking was performed targeting MurB (UDP-N-acetylenolpyruvoylglucosamine reductase, PDB 1MBT) and DNA gyrase B (GyrB, PDB 4URO), two bacterial enzymes known to be essential for the viability of Gram-negative pathogens. The docking results confirmed the experimental data, showing strong π–π stacking and hydrogen bonding between compound 1 and the FAD-containing binding pocket of MurB. This work highlights the utility of the tellurium-induced annulation in producing biologically potent heterocycles and emphasizes the structure–activity relationships driven by substituents in position 2 of the fused scaffold.
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Biocatalytic Approach to Aldehydes Using Lyophilisates of Bjerkandera Adusta Fungus
An optimized biocatalytic oxidation protocol has been developed for the efficient conversion of benzylic and allylic alcohols into their corresponding aldehydes. The sustainable method uses lyophilized mycelia of Bjerkandera adusta white-rot fungus as a catalyst in the aqueous medium with 2-propanol (10% v/v) as a co-solvent, and operates under mild conditions to give high yields for a wide range of substrates. On a preparative scale, the approach allowed the synthesis of important aldehydes, including benzaldehyde, piperonal, cinnamaldehyde, cuminaldehyde, methoxybenzaldehydes, and citral.
