Browsing by Author "Nedkova-Shtipska M."

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    New Glass-Ceramics in the System Ca2SiO4-Ca3(PO4)2—Phase Composition, Microstructure, and Effect on the Cell Viability
    (2025-08-01) Mihailova I.; Dimitrova P.; Avdeev G.; Ivanova R.; Georgiev H.; Nedkova-Shtipska M.; Teodosieva R.; Radev L.
    The CaO-SiO2-P2O5 system is one of the main systems studied aiming for the synthesis of new bioactive materials for bone regeneration. The interest in materials containing calcium-phosphate-silicate phases is determined by their biocompatibility, biodegradability, bioactivity, and osseointegration. The object of the present study is the synthesis by the sol-gel method of biocompatible glass-ceramics in the Ca2SiO4-Ca3(PO4)2 subsystem with the composition 6Ca2SiO4·Ca3(PO4)2 = Ca15(PO4)2(SiO4)6. The phase-structural evolution of the samples was monitored using X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and surface area analysis. A powder (20–30 µm) glass-ceramic material containing fine crystalline aggregates of dicalcium silicate and plates of silicon-substituted hydroxyapatite was obtained after heat treatment at 700 °C. After heat treatment at 1200 °C, Ca15(PO4)2(SiO4)6, silicocarnotite Ca5(PO4)2(SiO4), and pseudowollastonite CaSiO3 were identified by XRD, and the particle size varied between 20 and 70 µm. The compact glass-ceramic obtained at 1400 °C contained Ca2SiO4-Ca3(PO4)2 solid solutions with an α-Ca2SiO4 structure as a main crystalline phase. SEM showed the specific morphology of the crystalline phases and illustrated the trend of increasing particle size depending on the synthesis temperature. Effects of the glass-ceramic materials on cell viability of HL-60-derived osteoclast-like cells and on the expression of apoptotic and osteoclast-driven marker suggested that all materials at low concentrations, above 1 µg mL−1, are biocompatible, and S-1400 might have a potential application as a scaffold material for bone regeneration.
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    SODA LIME SILICATE GLASSES CONTAINING IRON OXIDE - IN VITRO EVALUATION
    (2024-01-01) Mihailova I.; Harizanova R.; Shtapleva-Dimova N.; Georgiev H.; Nedkova-Shtipska M.
    Three glasses with different iron oxide concentrations (between 5 and 8.1 mol %) were obtained in the CaO - Na2O - SiO2 - Fe2O3 system by using conventional melting-quenching technique. The amorphous nature of the synthesized materials is confirmed by X-ray diffraction analysis, XRD. The physico-chemical and structural characterization of the glasses was performed by measuring their density, refractive indices, as well as by calculating the molar volume, oxygen packing density and recording the infrared spectra by Fourier Transformed Infrared Spectroscopy, FT-IR, respectively. The glasses were evaluated in vitro by examining bone-like apatite formation on their surfaces in a simulated body fluid, SBF. The structural changes in the glasses during the in-vitro test were traced by means of FT-IR and Scanning Electron Microscopy, SEM. The solutions were examined by Inductively Coupled Plasma Optical Emission Spectroscopy, ICP-OES to determine the ion exchange between the glasses and the starting SBF and the corresponding effect on the pH was also recorded.
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    STUDY OF MODEL REACTION OF SYNTHESIS OF n-BUTYL ACETATE USING IR SPECTROSCOPY IN SOLUTION
    (2023-01-01) Jaber S.; Nedkova-Shtipska M.
    FT-IR spectroscopy is an absorption method, used to obtain the infrared spectrum of a chemical compound in a sample in order to monitor specific functional groups in organic and inorganic compounds. Herein, the ability of this technique to be used for on-time monitoring of a model chemical reaction is demonstrated. Every chemical reaction is characterized by specific kinetic profile, especially when a reversible reaction as esterification has to be realized. The selection of an appropriate, easy to be applied tracking technique is an important moment in the industry. N-butyl acetate can be obtained by the esterification of n-butan-1-ol and acetic acid. The main purpose of the presented work is to study the kinetics of the model reaction of n-butyl acetate synthesis showing the ability of FT-IR technique in solution to be used. Process of on-time monitoring can help to study the external factors which influence on the both right and reversed reaction in order to obtain the best yield of aimed product. The obtained results showed that FT-IR technique could be used as an easy to be applied for on-time monitoring of esterification reaction technique and the reaction reaches equilibrium in the 90th minute. Otherwise, a yield of 100 % is observed after one hour and half since the beginning of the reaction
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    STUDY OF TRANSFORMATION OF p-AMINOPHENOL IN LIQUID PHASE WITH INFRARED SCPECTROSCOPY
    (2022-01-01) Nedkova-Shtipska M.; Jaber S.; Petrin S.; Karadjova V.; Danalev D.
    Determining the rate, mechanism and dynamic of chemical reactions, including reactions between organic and inorganic substances, biotransformations involving enzymes, catalytic processes, etc., is key to setting the most appropriate technological parameters in various industries. The conversion of a substrate into a final product can go through various stages, some of which are speed-determining, while others require specific conditions - pressure, temperature, presence of catalyst and others. Therefore, clarifying the exact mechanism and dynamics of the transformation process is extremely important for achieving good yields and purity of the final products. It is also important to ensure the overall course of the transformation reaction, while minimizing the loss of time, as these factors directly affect the budget of the final product. The aim of the present study was to apply the features of IR spectroscopy to follow the dynamics of model acetylation reaction of transformations of p-aminophenol to paracetamol. Finally, we demonstrated the possibility IR spectroscopy in solution to be used as a technique for monitoring of specific transformation reaction in solution. The main reaction was successfully followed at time by preliminary selecting of the most suitable solvent, which is compatible with the requirements of the technique used and the monitored reaction as well as the right IR bands characteristic for the process of transformation.