Search

Your search keyword '"Stoyanova, Radostina"' showing total 254 results
Start Over Author "Stoyanova, Radostina" Publication Year Range Last 10 years
254 results on '"Stoyanova, Radostina"'

6. Phase Engineering via Aluminum Doping Enhances the Electrochemical Stability of Lithium‐Rich Cobalt‐Free Layered Oxides for Lithium‐Ion Batteries

Author

De Sloovere, Dries, primary, Mylavarapu, Satish Kumar, additional, D'Haen, Jan, additional, Thersleff, Thomas, additional, Jaworski, Aleksander, additional, Grins, Jekabs, additional, Svensson, Gunnar, additional, Stoyanova, Radostina, additional, Jøsang, Leif Olav, additional, Prakasha, Kunkanadu Rajappa, additional, Merlo, Maximiliano, additional, Martínez, Elías, additional, Nel‐lo Pascual, Marc, additional, Jacas Biendicho, Jordi, additional, Van Bael, Marlies K., additional, and Hardy, An, additional

Published
2024
Full Text
View/download PDF

8. New Iron(III)-Containing Composite of Salinomycinic Acid with Antitumor Activity—Synthesis and Characterization.

Author

Ivanova, Juliana, Kukeva, Rositsa, Stoyanova, Radostina, Zhivkova, Tanya, Abudalleh, Abedulkadir, Dyakova, Lora, Alexandrova, Radostina, Pashkunova-Martic, Irena, Theiner, Johannes, Dorkov, Peter, Hejl, Michaela, Jakupec, Michael A., Keppler, Bernhard, and Grabchev, Ivo

Subjects
ELECTRON paramagnetic resonance spectroscopy, ELECTROSPRAY ionization mass spectrometry, ANTINEOPLASTIC agents, DIFFERENTIAL thermal analysis, X-ray powder diffraction, NON-small-cell lung carcinoma, ELEMENTAL analysis, IRON chlorides
Abstract

In this study we demonstrated for the first time synthetic procedures for composites of salinomycin (SalH) and two-line ferrihydrite. The products were characterized by various methods such as elemental analysis, attenuated total reflectance–Fourier-transform spectroscopy (ATR-FTIR), electron paramagnetic resonance spectroscopy (EPR), powder X-ray diffraction analysis (XRD), electrospray-ionization mass spectrometry (ESI-MS), thermogravimetric analysis with differential thermal analysis (DTA) and mass spectrometry (TG-DTA/MS). The EPR spectra of the isolated compounds consisted of signals associated with both isolated Fe3+ ions and magnetically coupled Fe3+ ions. Powder XRD analyses of the isolated products showed two intense and broad peaks at 9° and 15° 2Θ, corresponding to salinomycinic acid. Broad peaks with very low intensity around 35°, assigned to two-line ferrihydrite, were also registered. Based on the experimental results, we concluded that salinomycin sodium reacted with Fe(III) chloride to form composites consisting of two-line ferrihydrite and salinomycinic acid. One of the composites exerted pronounced antitumor activity in the sub-micromolar concentration range against human cervical cancer (HeLa), non-small-cell lung cancer (A549), colon cancer (SW480), and ovarian teratocarcinoma (CH1/PA1) cells. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

21. Experimental and DFT Study of Monensinate and Salinomycinate Complexes Containing {Fe 3 (µ 3 –O)} 7+ Core.

Author

Petkov, Nikolay, Tadjer, Alia, Encheva, Elzhana, Cherkezova-Zheleva, Zara, Paneva, Daniela, Stoyanova, Radostina, Kukeva, Rositsa, Dorkov, Petar, and Pantcheva, Ivayla

Subjects
COORDINATION compounds, IRON, IRON oxidation, OXIDATION states, X-ray diffraction, MOSSBAUER spectroscopy
Abstract

Two trinuclear oxo-centred iron(III) coordination compounds of monensic and salinomycinic acids (HL) were synthesized and their spectral properties were studied using physicochemical/thermal methods (FT–IR, TG–DTA, TG–MS, EPR, Mössbauer spectroscopy, powder XRD) and elemental analysis. The data suggested the formation of [Fe3(µ3–O)L3(OH)4] and the probable complex structures were modelled using the DFT method. The computed spectral parameters of the optimized constructs were compared to the experimentally measured ones. In each complex, three metal centres were joined together at the axial position by a μ3–O unit to form a {Fe3O}7+ core. The antibiotics monoanions served as bidentate ligands through the carboxylate and hydroxyl groups located at the termini. The carboxylate moieties played a dual role bridging each two metal centres. Hydroxide anions secured the overall neutral character of the coordination species. Mössbauer spectra displayed asymmetric quadrupole doublets that were consistent with the existence of two types of high-spin iron(III) sites with different environments—two Fe[O5] and one Fe[O6] centres. The solid-state EPR studies confirmed the +3 oxidation state of iron with a total spin St = 5/2 per trinuclear cluster. The studied complexes are the first iron(III) coordination compounds of monensin and salinomycin reported so far. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

26. High-Performance Full Sodium Cells Based on MgO-Treated P2-Type Na 0.67 (Mn 0.5 Fe 0.5) 1−x Co x O 2 Cathodes.

Author

Taskiran, Nermin, Altundag, Sebahat, Koleva, Violeta, Altin, Emine, Arshad, Muhammad, Avci, Sevda, Ates, Mehmet Nurullah, Altin, Serdar, and Stoyanova, Radostina

Subjects
TRANSITION metal oxides, TRANSITION metal ions, SURFACE area measurement, SODIUM ions, CATHODES, CHEMICAL formulas, SODIUM
Abstract

Herein, we design a cathode material based on layered Na2/3(Mn1/2Fe1/2)O2 for practical application by combining the Co substitution and MgO treatment strategies. The oxides are prepared via solid-state reactions at 900 °C. The structure, morphology, and oxidation state of transition metal ions for Co-substituted and MgO-treated oxides are carefully examined via X-ray diffraction, IR and Raman spectroscopies, FESEM with EDX, specific surface area measurement, and XPS spectroscopy. The ability of oxides to store sodium reversibly is analyzed within a temperature range of 10 to 50 °C via CV experiments, galvanostatic measurements, and EIS, using half and full sodium ion cells. The changes in the local structure and oxidation state of transition metal ions during Na+ intercalation are monitored via operando XAS experiments. It is found that the Co substituents have a positive impact on the rate capability of layered oxides, while Mg additives lead to a strong increase in the capacity and an enhancement of the cycling stability. Thus, the highest capacity is obtained for 2 at.%-MgO-treated Na2/3(Mn1/2Fe1/2)0.9Co0.1O2 (175 mAh/g, with a capacity fade of 28% after 100 cycles). In comparison with Co substituents, the Mg treatment has a crucial role in the improvement of the lattice stability during the cycling process. The best electrode materials, with a chemical formula of 2 at.%-MgO treated Na2/3(Mn1/2Fe1/2)0.9Co0.1O2, were also used for the full cells design, with hard carbon as an anode. In the voltage window of 2–4 V, the capacity of the cells was obtained as 78 mAh/g and 51 mAh/g for applied current densities of 12 mA/g and 60 mA/g, respectively. [ABSTRACT FROM AUTHOR]

Published
2023
Full Text
View/download PDF

34. Novel Salinomycin-Based Paramagnetic Complexes—First Evaluation of Their Potential Theranostic Properties

Author

Pashkunova-Martic, Irena, primary, Kukeva, Rositsa, additional, Stoyanova, Radostina, additional, Pantcheva, Ivayla, additional, Dorkov, Peter, additional, Friske, Joachim, additional, Hejl, Michaela, additional, Jakupec, Michael, additional, Hohagen, Mariam, additional, Legin, Anton, additional, Lubitz, Werner, additional, Keppler, Bernhard K., additional, Helbich, Thomas H., additional, and Ivanova, Juliana, additional

Published
2022
Full Text
View/download PDF

41. МАРИЯНА ВИТАНОВА, ВАНЯ МИЧЕВА, ЙОАННА КИРИЛОВА, КАЛИНА МИЧЕВА-ПЕЙЧЕВА, НАДЕЖДА НИКОЛОВА. ЕТНОЛИНГВИСТИЧЕН РЕЧНИК НА БЪЛГАРСКАТА НАРОДНА МЕДИЦИНА / MARIYANA VITANOVA, VANYA MICHEVA, YOANNA KIRILOVA, KALINA MICHEVA-PEYCHEVA, NADEZHDA NIKOLOVA. AN ETHNOLINGUISTIC DICTIONARY OF BULGARIAN FOLK MEDICINE

Author

Stoyanova, Radostina, primary

Published
2022
Full Text
View/download PDF

42. Control of the thermoelectric activity of LaCoO3 perovskites through multiple metal substitution on Co-sites

Author

Harizanova, Sonya, Zhecheva, Ekaterina, Valchev, Vasil, and Stoyanova, Radostina

Subjects
Multiple metal substitution, Co-based perovskites, Thermoelectric oxide materials
Abstract

Lanthanum cobaltate, LaCoO3, with a perovskite type of structure has been recognized as attractive thermoelectric material due to its high Seebeck coefficient (S>500 V/K at room temperature) and high thermal stability. However, the electrical resistivity of LaCoO3 is relatively гigh (about 10 Ωcm at 300 K), which lowers the thermoelectric activity (ZT

Published
2022

43. Enhancing oxygen redox activity in sodium-deficient three-layered oxides: modeling the structure or the surface?

Author

Kalapsazova, Mariya, Kukeva, Rositsa, Zhecheva, Ekaterina, and Stoyanova, Radostina

Subjects
oxygen redox activity, sodium-ion batteries, layered oxides, surface modeling
Abstract

In this contribution we unveil the interplay between metal substitution, treatment with oxygen storage materials and anionic redox activity in sodium nickel manganese oxides with three-layer stacking (P3-Na2/3Ni1/2Mn1/2O2) during single Na+ and Li+ intercalation. As metal substituents, Mg2+ and Ti4+ ions were used through partial replacement of low- and high-oxidized nickel ions, respectively: Na2/3Ni1/3Mg1/6Mn1/2O2 and Na2/3Ni1/3Ti1/6Mn1/2O2. Furthermore, the metal-substituted oxides are treated with an oxygen storage material, such as CeO2. The effect of the metal substitution and CeO2-treatment on the structure and morphology of the oxides is observed by X-ray powder diffraction, EPR spectroscopy and HR-TEM. Cyclic voltammetry was employed to investigate the reduction and oxidation processes during Na+ and Li+ intercalation. The electrochemical tests are carried out in galvanostatic mode. The electrode–electrolyte interaction is monitored by ex-situ EPR of the long-cycled electrodes.

Published
2022

44. Ca3Co4O9 Ceramics and Thin Films with Giant Dielectric Behaviour

Author

Al Thehaiban, Mohammad, Harizanova, Sonya, Rente, Bruno, K. Petrov, Peter, and Stoyanova, Radostina

Subjects
Ca3Co4O9, x-ray diffraction, thin film, giant dielectric permittivity, thermoelectric
Abstract

Ca3Co4O9 ceramic is an attractive lead-free alternative to conventional semiconductor materials, based on bismuth and tellurium with a practical application in converting waste heat to electricity, solar thermoelectric generators and refrigeration devices [1]. Ca3Co4O9 is a thermoelectric material representing the family of the so-called misfit layered oxides. It consists of a Ca2CoO3 layer which is an insulating subsystem that maintains the charge supply for the conducting CoO2 layer, where both Co3+ and Co4+ ions coexist [2]. In addition to the research carried out on the thermoelectric properties of Ca3Co4O9, several studies have reported results elucidating crystal information and electronic structure [3,4]. Recently, a giant dielectric permittivity was measured in Ca3Co4O9 ceramic at room temperature [5]. In this work, we investigated and compared the structural and electrical properties of Ca3Co4O9 (CCO) ceramics and thin films. The CCO thin films were produced from a stoichiometric, in-house made CCO ceramic by pulsed laser deposition (PLD) onto (100) oriented lanthanum aluminate (LaAlO3, LAO) substrates. Both the CCO ceramics and thin films were subsequently characterised by X-ray diffraction (XRD). To evaluate the samples’ dielectric properties, capacitor structures were formed. Their capacitances were measured and the corresponding permittivities were evaluated in a temperature range RT – 450 K. Both CCO ceramics and thin films were pure misfit phases. The thin film exhibited epitaxial growth with preferred (00l) orientation. For the CCO ceramics, the measured dielectric permittivity was increasing moronically with no maximum observed at temperatures up to 450 K (Figure 1a). The estimated value of the dielectric permittivity ~ 5,300 measured at room temperature corresponds well with the values reported elsewhere [5]. Similar behaviour of the capacitance as a function of the temperature with a maximum at 430K was measured for the thin film sample (Figure 1b). Due to the small thickness of the layer, the error associated with the dielectric permittivity evaluation procedure is very high. Nevertheless, one could speculate that it is in the same order of magnitude as those of the CCO ceramic. The observed reduction of the phase-transition temperature is associated with the residual strain in the thin film sample introduced by the substrate.

Published
2022

45. Aluminum doping and Al2O3 coating for improving the electrochemical performance of layered Na2/3Ni1/2Mn1/2O2

Author

Kalapsazova, Mariya, Zhecheva, Ekaterina, and Stoyanova, Radostina

Subjects
surface coating, sodium-ion batteries, structure modeling, layered oxides
Abstract

In the present contribution the effects of doping and coating on the electrochemical performance of layered Na2/3Ni1/2Mn1/2O2 oxide are differentiated. As structural and surface modifiers, we used electrochemically inactive Al3+ ions. The structural modification consists in selective substitution for Ni3+ with Al3+ ion in the transition metal layer. The second approach aims to modify the oxide surface, therefore the pristine oxide as well as aluminium doped one was coated with Al2O3. The distribution of Al3+ ions into the layered crystal structure and Al2O3-coated oxides were monitored by X-ray powder diffraction and EPR spectroscopy. The electrochemical tests were carried out in model two- and three-electrode Swagelok type cells in presence of 1M NaPF6:PC as electrolyte solution and pure sodium metal as counter and reference electrode. Based on the experimental data, it was found that the electrochemical performance of layered Na2/3Ni1/2Mn1/2O2 depends critically on the kind of selected substituents and surface modifiers.

Published
2022

48. Purification of Hydrogen from CO with Cu/ZSM-5 Adsorbents

Author

Mihaylov, Mihail, primary, Ivanova, Elena, additional, Zdravkova, Videlina, additional, Andonova, Stanislava, additional, Drenchev, Nikola, additional, Chakarova, Kristina, additional, Kefirov, Radoslav, additional, Kukeva, Rositsa, additional, Stoyanova, Radostina, additional, and Hadjiivanov, Konstantin, additional

Published
2021
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results