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In this work, for the first time, an approach was suggested for determining the pKa of triazolo[5,1-c][1,2,4]triazine compounds in N,N-dimethylformamide using potentiometric titration. It was noted that change in system potential in the titration curves of triazolo[5,1-с][1,2,4]triazine are observed for compounds containing either H+ located at the nitrogen atom in position 1 or an –NH2 group. The calculated pKa values of the studied molecules correspond to the pKa values of moderately strong acids and are in the range of 2–8. The relationship was established between the acidity of the heterocyclic fragment and the presence of electron donor substituents. The obtained pKa values of the compounds correlate with the calculated possible deprotonation centers of the molecule. It was found that determining the acidity constants of substances is useful for clarifying the mechanisms of their transformations. The possibility of establishing a relationship between the structure of the compound, pKa, and probable biological activity was shown.

Polyvinyl chloride (PVC) plays an important role in industry; however, due to its uncontrolled accumulation in the environment, the methods for its utilization are of high demand. Herein we wish to report an approach for the utilization of PVC via its use as a carrier for some azole-based drugs, such as 2-mercaptobenzothiazole (multi-activity drug), 4-oxo-1,4-dihydropyrazolo[5,1-c]-1,2,4-triazine-3,8-dicarboxylic acid diethyl ester (antidiabetic drug) and 5-methyl-6-nitro-7-oxo-1,2,4-triazolo[1,5-a]pyrimidinide (antiviral drug). The abovementioned approach involves the reaction between PVC and potassium or sodium salts of these azole-based drugs either in solution or under ball-milling conditions. The as-obtained PVCs modified with azole-based drugs were isolated for the first time and characterized by means of 1H NMR-spectroscopy as well as gel-permeation chromatography (GPC).

The structural study of plant viruses is of great importance to reduce the damage caused by these agricultural pathogens and to support their biotechnological applications. Nowadays, X-ray crystallography, NMR spectroscopy and cryo-electron microscopy are well accepted methods to obtain the 3D protein structure with the best resolution. However, for large and complex supramolecular structures such as plant viruses, especially flexible filamentous ones, there are a number of technical limitations to resolving their native structure in solution. In addition, they do not allow us to obtain structural information about dynamics and interactions with physiological partners. For these purposes, small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM) are well established. In this review, we have outlined the main principles of these two methods and demonstrated their advantages for structural studies of plant viruses of different shapes with relatively high spatial resolution. In addition, we have demonstrated the ability of AFM to obtain information on the mechanical properties of the virus particles that are inaccessible to other experimental techniques. We believe that these under-appreciated approaches, especially when used in combination, are valuable tools for studying a wide variety of helical plant viruses, many of which cannot be resolved by classical structural methods.