The altar wall paintings of the catholicon "The Nativity of the Virgin", Rila Monastery, Bulgaria: Identification of the painting materials by means of vibrational spectroscopic techniques complemented by EDX, XRD and TGA analysis.

The purpose of the present study is to deepen our knowledge about the painting materials and technology characteristics of iconography during the Bulgarian National Revival. Our efforts have focused on studying the murals in the catholicon (main church) "The Nativity of the Virgin" of the Rila Monastery, which is one of Bulgarian leading historical monuments. A series of micro samples from the altar mural paintings were analyzed by a combination of attenuated total reflectance Fourier transform infrared (ATR-FTIR), micro-Raman spectroscopy, scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Optical microscopy (OM). The data analysis showed that the painter's palette is made up of nine mineral pigments: smalt, chrome yellow, emerald green, vermilion, red lead, green earths, yellow ochre, sienna and calcite. The impression of rich colorful palette was achieved by using various pigment mixtures. The presence of egg binder in many paint samples suggested that the murals were executed by the traditional egg tempera technique, with the only exception of the smalt paint of the background where carbohydrate glue is present as binder.

Spectroscopic and in silico study on the conversion of N,N'-disubstituted hydrazone derivatives of 5-nitrobenzimidazole-2-thione into anion and radical anion products: Implications in hepatotoxicity.

The conversion of N,N'-disubstituted hydrazone derivatives of 5-nitrobenzimidazole-2-thione into radical anion and dianion products was studied through infrared (IR) spectroscopy and computational methods. The electrochemical reduction of 3,3'-(5-nitro-2-thioxo-1H-benzo[d]imidazole-1,3(2H)-diyl)bis(N'-(2-methoxybenzylidene))propane-hydrazide was performed directly in the IR cell and the spectral changes were monitored over time in order to identify the spectral bands originating from the reduction product. In order to clarify whether the reduction leads to the generation of radical anion or deprotonated radical dianion, a second spectroscopic experiment was carried out where deprotonation was achieved by treatment with sodium methoxide. Both experiments resulted in distinctly different spectral features, giving evidence that the reduction to radical anion is not accompanied by deprotonation. In order to explain the experimentally observed differences in the hepatotoxicity within the series of N,N'-disubstituted derivatives of 5-nitrobenzimidazole-2-thione, several molecular electronic parameters such as frontier molecular orbitals, spin and charge distribution over fragments, and electron affinities of the studied hydrazone derivatives were compared to those of a previously studied ester derivative. Based on the estimated electronic parameters, it was shown that the type of the side chains (ester, hydrazone etc.) attached to the N-atoms in the nitrobenzimidazole derivatives do not change significantly the propensity of the compounds towards nitro reduction, but however the generated radical anions are characterized by different reactivity accounting for the different hepatotoxicity.

Analytical studies of the Alexandrovo Thracian tomb wall paintings.

A profound study of samples obtained from Thracian tomb wall paintings at Alexandrovo, Bulgaria (dating back to the fourth century BC) were carried out by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and Attenuated Total Reflectance Fourier transform infrared spectroscopy (ATR FTIR), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS). The current work provides a glimpse of the ingenious construction and painting techniques used in Thracian tomb at Alexandrovo. The results suggest that beeswax was used as a paint binder and also revealed presence of various nano-materials.