Browsing by Author "Stoyanov S."
Now showing 1 - 7 of 7
Results Per Page
Sort Options
Item A new cu(Ii) complex of pamam dendrimer modified with 1,8-naphthalimide: Antibacterial and anticancer activity(2022-08-15) Manov H.; Staneva D.; Vasileva-Tonkova E.; Kukeva R.; Stoyanov S.; Grabchev I.; Alexandrova R.; Stoyanova R.A new fluorescent PAMAM copper complex ([Cu2 (D)(NO3 )4 ]) has been synthesized and identified. The formation of the complex has been investigated by fluorescence spectroscopy which revealed two copper ions to be bound to the dendrimer ligand. That has also been confirmed upon subjecting the solid copper complex to electron paramagnetic spectroscopy. The antimicrobial activity of the copper complex against Gram-negative bacterium Pseudomonas aeruginosa in light and the dark has been studied. The results demonstrate an increase in its activity when irradiated with daylight. This activity of the copper complex is retained even after being loaded onto a cotton cloth. The antitumor activity of the copper complex and dendrimer ligand against triple-negative breast cancer MDA-MB-231 cells has been investigated as well.Item An algorithm for metallurgical waste minimization(2014-02-25) Borisov D.; Stefanov B.; Stoyanov S.The selection of the optimal process that satisfies both environmental and economic objectives simultaneously is rather difficult. Identifying the optimum from set of objectives is depending of the preferences of decision makers. Successful and widespread implementation of existing methodologies for pollution prevention and waste minimization has failed to provide significant benefits for applications in metallurgical processes. One of the main reasons for this is the lack of a comprehensive approach that integrates and guides the application of the proper tool. The existing methodologies have been developed more general and for particular stages in the process and they require different detailed and accurate information which may not be available. An algorithm developed for waste minimization from metallurgical processes is presented in this paper. The methodology incorporates both environmental and economics criteria into the metallurgical processes in order to select the best alternative for waste material flow minimization. The proposed algorithm and described criteria can be used in multi criteria decision making during alternatives evaluation both new and technological modernization of existing metallurgical installation.Item Characterization of art materials and degradation processes in the exterior wall paintings of the main church of Rila Monastery, Bulgaria(2023-09-01) Stamboliyska B.; Tapanov S.; Kovacheva D.; Atanasova-Vladimirova S.; Ranguelov B.; Yancheva D.; Velcheva E.; Stoyanov S.; Guncheva M.; Fischer D.; Lederer A.The present study focused on the characterization of the art materials and the degradation processes in the exterior (exonarthex) mural paintings of the main church of the Nativity of the Virgin in Rila monastery, Bulgaria, which is believed to be the last large-scale example of Eastern Orthodox wall painting. For the first time the art materials used to create a unique and colourful polychrome decoration of the outer gallery and the possible degradation products, caused by atmospheric influence - permanent exposure to open air and moisture - were revealed by a multi-technique approach. The mineral pigments were identified by means of attenuated total reflectance Fourier transform infrared (ATR-FTIR), micro-Raman spectroscopy, scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD). The natural yellow, red ochre, and green earth pigments, as well as some synthetic ones such as ultramarine and vermillion, were found in stable condition. Minium and emerald green pigments showed chemical transformations due to adverse environmental conditions which lead to chromatic changes of wall paintings. Black discolouration occurred due to the conversion of orange minium to black plattnerite (PbO2) and white discolouration – due to its transformation to white lead carbon oxide (PbCO3). The copper acetoarsenite (Cu(CH3COO)2.3Cu(AsO2)2) in the emerald green pigment showed partial transformation to arsen-containing mineral phases clinoclase and lindackerite, which fortunately did not affect much the colour appearance. Gypsum and calcium oxalate were found in the majority of the microsamples as decay products. Analysis of the binders by enzyme-linked immunosorbent assay (ELISA) implied the use of the Orthodox Church post-Byzantine egg-tempera technique. The registered Ca metal oxalates in accordance with ELISA results suggested binder chemical degradation induced by external factors. Most of the used painting materials are close to the those found in other Eastern Orthodox Byzantine and post-Byzantine monuments which indicates that the wall painting decoration of the main church of Rila monastery continues the post-Byzantine traditions. On the other hand, the study showed that the exonarthex wall paintings of the main charge of Rila monastery bear some new features as the religious artists supplemented the colourful scheme by emerald green as a new pigment and replaced smalt by the brighter synthetic ultramarine.Item Characterization of Zahari Zograph’s nave wall paintings in the church “The nativity of the virgin” of Rila Monastery (Bulgaria) by vibrational spectroscopy and SEM–EDX analysis(2017-12-15) Yancheva D.; Tapanov S.; Velcheva E.; Stamboliyska B.; Glavcheva Z.; Stoyanov S.; Haralampiev N.; Fischer D.; Lederer A.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.Item Esterification of mixtures of pure fatty acids with methanol(2013-11-05) Cholakov G.; Yanev S.; Markov V.; Stoyanov S.Extracts from secondary biomass, e. g. spent coffee grounds (SCG), can be utilized in the production of biodiesel additives (esters of fatty acids with low molecular mass alcohols). However, they contain a significant amount of free fatty acids, so the transesterification of their glycerides has to be preceded by catalytic esterification of these acids. SCG extracts are essentially a mixture of compounds with approximately equal amounts of glycerides with saturated and unsaturated fatty acid moieties, so their iodine values are much lower than those of the typical highly unsaturated biodiesel feedstocks - e.g., sunflower oil, soybean oil, etc. In the wider context of our studies on the preparation of renewable fuel additives from SCG and other extracts from secondary biomass, this work presents results on direct esterification of mixtures of pure fatty acids, modeling the unsaturation of such extracts. They are also relevant to the utilization of biodiesel feedstocks, consisting entirely or predominantly of fatty acids like tall oil, soapstock and synthetic fatty acids, etc.Item Hepatotoxicity and antioxidant activity of some new N,N′-disubstituted benzimidazole-2-thiones, radical scavenging mechanism and structure-activity relationship(2018-03-01) Anastassova N.; Mavrova A.; Yancheva D.; Kondeva-Burdina M.; Tzankova V.; Stoyanov S.; Shivachev B.; Nikolova R.A new method for the synthesis of 1,3-disubstituted benzimidazole derivatives was developed using aza-Michael addition. The target compounds were synthesized in good yields and purity and tested on isolated hepatocytes for their toxicity and antioxidant activity. The antioxidant properties of the substances with lowest toxicity were evaluated using oxidative stress induced by tert-butyl hydroperoxide (tert-BOOH). Some of them as methyl 3-[3-(3-methoxy-3-oxopropyl)-5-benzoyl-2-thioxo-2,3-dihydro-1H-benzimidazol-1-yl]propanoate 10 and 1,3-bis[3-(hydrazinooxy)-3-oxopropyl]-5-benzoyl-1,3-dihydro-2H-benzimidazole-2-thione 15 exhibited statistically significant cytoprotective and antioxidant effects which were similar to those of quercetin. In order to estimate the influence of the structure on the biological properties, structural characterization of the studied compounds was performed by X-ray diffraction analysis and DFT methods. On the basis of the calculated reaction enthalpies of hydrogen atom abstraction (HAT mechanism) and single-electron transfer (SET mechanism) the mechanisms of the antioxidant action of the tested compounds were studied. Subsequently it was established that the HAT mechanism governs the radical scavenging of 10 and 15 in the lipid phase, while the SET mechanism is preferred in water medium for 10 and competitive to HAT for 15.Item Photophysical and antibacterial activity of light-activated quaternary eosin Y(2019-01-01) Staneva D.; Yordanova S.; Vasileva-Tonkova E.; Stoyanov S.; Grabchev I.The functional characteristics of a new eosin dye with biocidal quaternary ammonium group (E) were studied in aqueous solution and in organic solvents of different polarity. The spectral properties depend on the nature and polarity of the respective solvents. The antimicrobial activity of compound E has been tested in vitro against Gram-negative bacteria (Escherichia coli, Acinetobacter johnsoni and Pseudomonas aeruginosa), Gram-positive bacteria (Sarcina lutea and Bacillus cereus) and the antifungal activity was tested against the yeasts Candida lipolytica in solution and after treated on cotton fabric. Broth dilution test has been used for quantitative evaluation of the antimicrobial activity of compound E against the model strains. The ability of compound E to inhibit the growth of model Gram-negative P. aeruginosa strain was assessed after 16 h of incubation in presence and absence of light. These experiments were conducted in planktonic format in solution and on cotton fabric. The results suggest that the new compound is effective in treating the relevant pathogens with better results being obtained by irradiation with light. In this case the quaternary ammonium group promotes the binding of eosin Y moiety to the bacterial cell wall thus accelerating bacterial photo inactivation.