An analytical study on the nave mural paintings of the church “The Nativity of the Virgin” of Rila monastery, Bulgaria, painted by Zahari Zograph was carried out. Vibrational spectroscopy was applied to identify the pigments and organic materials used in the mural paintings. To complement the spectral information, elemental composition of the samples was determined by SEM-EDX. The data showed that smalt with carbohydrate binder was applied for the blue background, green colour was executed by green earths and red-orange colour – by red lead. Azurite is the pigment used to paint the blue colour of the saints’ hoods. The mordant for gilding was prepared of drying oil, resin and siccative metal oxides as evidenced by SEM-EDX, ATR-FTIR and pyrolysis GC-MS analysis. The use of azurite is related to Zahari Zograph’s works as it was not found in any of the previously studied murals in the church painted by other artists.

This presented research examined the wall paintings in the Church-Ossuary Presentation of the Blessed Virgin, part of the most important Rila Monastery complex in Bulgaria, painted by the painters from Mount Athos in 1795. The painting materials used to create the unique murals were studied for the first time by optical microscopy (OM), attenuated total reflectance Fourier transform infrared (ATR–FTIR), scanning electron microscopy energy dispersive X-ray spectroscopy (SEM–EDS), and enzyme-linked immunosorbent assay (ELISA). The vibrational and elemental analysis showed that the color palette of the paintings is composed of pigments traditional for Orthodox church wall paintings such as natural pigments, including yellow ochre, red ochre, green earth, and calcite, as well as other historical pigments of synthetic origin, including smalt, red lead, cinnabar, and verdigris. The analysis of the binders by the ATR–FTIR spectroscopy and enzyme-linked immunosorbent assay (ELISA) analysis implied the use of the post-Byzantine egg tempera technique. Only the blue backgrounds in the murals were painted using a smalt-based paint mixed with a carbohydrate binder. Based on the current analysis and comparison with the successive paintings in the other churches of the Rila Monastery, it could be concluded that the technology of the painting process followed by the Athonite artists during the work in the Church-Ossuary became a point of reference for many Bulgarian icon-painters later.

Coupling the electron-rich benzimidazole system with a nitro group could provide a suitable scaffold for the development of drugs exerting selective cytotoxicity through hypoxia-activation or enzymatic activation of the nitro group. The bioreductive potential of 1-alkylated 5(6)-nitro-1H-benzimidazoles was studied by electrochemical methods and density functional theory (DFT) calculations. An investigation directly in the infrared (IR) cell and cyclic voltammetry was conducted to examine the creation of nitro radical anions. Computational analysis of the frontier molecular orbitals of the compounds illustrated that upon reduction the unpaired electron is accepted mainly by the nitro group. The deprotonation of the 1-alkylated 5(6)-nitro-1H-benzimidazoles was also characterized by IR spectroscopy and DFT calculations. The calculated electron affinities indicate that the propensity of the 1-alkylated 5(6)-nitro-1H-benzimidazoles to nitroreduction is higher than that of the structurally related 1-methyl-2-methyl-4-nitroimidazole and slightly lower than that of nitrobenzene and the radiosensitizer misonidazole. The studied 1-alkylated 5(6)-nitro-1H-benzimidazoles show promise to be used as bioreductive agents and the relationships found can be used to obtain nitrobenzimidazole derivatives with enhanced electron affinities.

The present work introduces the Bulgarian Spectral Database for Painting Materials, a freely accessible web-based resource containing FTIR and Raman spectra, together with complementary analytical information, for materials commonly found in Bulgarian artworks. The database encompasses a collection of over 200 reference materials and more than 100 entries derived from authentic samples obtained from wall paintings, dating from the 5th century BC to the 20th century. The largest section of the database consists of inorganic reference materials, including natural and synthetic mineral pigments, fillers, and additives commonly identified in historical mural paintings, complemented by organic binders and natural dyes. Reference model mixtures simulating historical painting techniques are also included. The database provides interactive visualization and downloadable spectra in plain text formats (.txt) compatible with all spectroscopic software. The integration of spectral data obtained from artworks represents a distinctive feature of the resource. The database is a practical tool for material identification, comparative studies, and conservation research in the field of cultural heritage science. It also provides a robust foundation for comparative studies and facilitates interdisciplinary research across the Balkan region and beyond.

Background: DNase I inhibitors may be useful as biochemical tools and as potential leads for investigating pathological processes associated with excessive DNA degradation. Squaramides represent attractive scaffolds for drug discovery owing to their rigid, highly polarized structure and versatile hydrogen-bonding properties. Methods: Four novel pyridine-containing squaramides (5a–5d), comprising two symmetric and two asymmetric derivatives, were synthesized and structurally characterized by spectroscopic methods and, for 5a and 5b, single-crystal X-ray diffraction. Their DNase I inhibitory activity and cytotoxicity were evaluated experimentally. Comparative structure–activity analysis, molecular docking, molecular descriptor calculations, and in silico ADME profiling were additionally performed. Results: All compounds inhibited bovine pancreatic DNase I, with IC₅₀ values ranging from 34.42 ± 5.86 to 61.95 ± 9.61 μM. Compound 5a showed the highest inhibitory activity within the present series (IC₅₀ = 34.42 ± 5.86 μM). Comparison with five previously reported structurally related derivatives identified preliminary structure–activity trends, with 5a exhibiting the highest activity among the nine compounds considered. Molecular docking predicted a common preferred binding region within the major DNA-contact/catalytic region of DNase I and suggested possible noncovalent ligand–enzyme interactions. Molecular descriptor calculations revealed differences in the electronic properties of selected compounds, while in silico ADME analysis predicted generally favorable physicochemical and absorption-related properties together with potential pharmacokinetic liabilities. No measurable cytotoxicity was observed against the investigated cancer cell lines at the tested concentrations. Conclusions: Pyridine-containing squaramides represent a promising scaffold for further investigation as DNase I inhibitors, with 5a providing a useful starting point for subsequent structural optimization and mechanistic studies.