Browsing by Author "Karadjova V."
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Item A correlation between structural and vibrational spectroscopic data of some beryllium sulfates and selenates (review)(2016-01-01) Karadjova V.The present paper summarizes experimental results on the study of some beryllium compounds and is a part of a dissertation entitled ``Synthesis, structure and properties of some beryllium salts - sulfates and selenates``. The solubility diagrams of the three-component systems BeSeO4-K2SeO4-H2O, BeSO4-Rb2SO4-H2O, and BeSeO4-MSeO4-H2O (M = Co, Ni, Cu, Zn) at 25°C are presented and the crystallization field widths of the solid phases are determined. The experimental results are discussed with respect to the complex formation processes in the ternary solutions and the solubility of the salt components in their binary solutions. New compounds, Rb2Be(SO4)2·2H2O and K2Be(SeO4)2·2H2O, have been obtained as a result of co-crystallization processes in the systems pointed above. The crystal structures of BeSeO4·4H2O, M2Be(SO4)2·2H2O (M = K, Rb), and K2Be(SeO4)2·2H2O are determined from single crystal X-ray diffraction data. It has been established that the beryllium selenate tetrahydrate crystallizes in the orthorhombic space group Cmca (D18 2h). The double beryllium compounds are isostructural and crystallize in the monoclinic space group P21/c (C52h). Vibrational (infrared and Raman) spectra are recorded in the regions of the normal vibrations of the different motives building up the structures of the beryllium compounds studied. The vibrational spectra are discussed in the light of both the crystal structures of the beryllium salts and the chemical properties of the different entities. Special attention is paid to the influence of different crystal chemical factors on the strength of the hydrogen bonds formed in the beryllium compounds. These are the Be-O interactions (synergetic effect), the proton acceptor capacity of the selenate and sulfate ions, the proton acceptor capacity of the different oxygen atoms as determined according to the Brown's bond valence theory, the compositions of the beryllium tetrahedra (acidity of the water molecules), the anti-cooperative effect (proton donor and proton acceptor competitive effect), the repulsion potential of the lattice sites of water molecules location, the size of M+ cations. The intramolecular O-H bond distances are derived from the νOD vs. rOD correlation curve [H.D. Lutz, C. Jung, J. Mol. Struct., 404, 1997, 63-66]. Water librations of protiated and deuterated samples are also discussed. Crystal matrix infrared spectroscopy was applied to analyze: (i) the distribution of SO42- ions included in the structure of K2Be(SeO4)2·2H2O at two crystallographically different positions; (ii) the molecular symmetry of SeO42- ions in BeSeO4·4H2O determined from the vibrational behavior of matrix-isolated SO42- guest ions; (iii) the strength of the hydrogen bonds (with the application of the isotopic dilution method and that of the matrix-isolated HDO molecules).Item Characterization of beryllium selenates by X-ray powder diffraction, DTA and DSC(2004-11-01) Koleva V.; Karadjova V.; Georgiev M.BeSeO4.2H2O and BeSeO4 have been studied röntgenographically: BeSeO4.2H2O forms orthorhombic / crystals with lattice constants: a = 5.843(2) Å; b = 9,790(3) Å; c = 4.692(1) Å; V = 268.4(1) Å3. The crystals of BeSeO 4 are tetragonal: a = 4.648(1) Å; c = 7.084 (3) Å; V= 153.1(1) Å3, SG I4̄. The thermal dehydration of BeSeO 4.4H2O has been studied by TG, DTA and DSC methods. The dehydration occurs in four steps and intermediate hydrates BeSeO 4.2H2O, BeSeO4.H2O and BeSeO 4.0.5H2O are formed. The enthalpies of dehydration of the observed dehydration processes have been determined. The higher value of ΔHdeh of BeSeO4.4H2O as compared to those of other metal selenate tetrahydrates is discussed in terms of the strong Be-H2O interaction. The enthalpies of formation of BeSeO 4.4H2O and BeSeO4.2H2O have been calculated. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Item DETERMINATION OF SOME PROHIBITED SUBSTANCES IN FOOD SUPPLEMENTS USING HPLC WITH MS OR UV DETECTION - VIEW ON CURRENT DEVELOPMENT(2021-01-01) Zaharieva Z.; Foteva T.; Karadjova V.; Danalev D.Nowadays bioanalytical techniques including liquid and gas chromatography combined with different types of detectors are largely introduced in a practice. They are largely used for detection and control of substances and for monitoring of the whole production process. The type of detector depends on necessary levels of detection, but also on the matrix where aimed compounds have to be determined. Herein are summarized data from the last ten years related to determination of six main prohibited substances sildenafil, tadalafil, vardenafil, dapoxetine, yohimbine and sibutramine as well as their derivatives in food supplements using high performance liquid chromatography combined with mass spectrometric or UV detection. All these compounds are in a large interest because they are introduced often in products freely distributed in the internet market.Item Glass Formation and Properties of Multicomponent Glasses of the As2Se3-Ag2Te-GeTe System(2024-01-01) Karadashka I.; Ivanova V.; Jordanov V.; Karadjova V.Chalcogenide alloys of As2Se3-Ag2Te-GeTe were synthesized using the melt-quenching technique. By the visual and XRD analyses, the state of obtaining alloys was proven (glass, crystalline, glass + crystalline), and the glass formation region in the system was established. The thermal characteristics of some samples were determined—temperatures of glass transition (Tg); crystallization (Tcr); and melting (Tm). The basic physicochemical parameters, such as density (d) and Vickers microhardness (HV), were measured. Compactness (C), as well as some thermomechanical characteristics, such as module of elasticity (E), volume (Vh), and formation energy (Eh) of micro-voids, were calculated, and the influence of the composition on these characteristics was investigated. The addition of silver telluride resulted in a decrease in Tg and HV values and an increase in d and Vh values. No thermochemical effects of crystallization or melting were detected in some of the alloys. The obtained results were in agreement with the available literature data for similar systems.Item INVESTIGATION OF THE EFFECT OF ULTRA-LOW TEMPERATURES IN CRYOPRESERVATION ON THE ACTIVITY OF THE ENZYMES LACTATE DEHYDROGENASE AND GAMMA-GLUTAMYL TRANSFERASE(2022-01-01) Andreeva M.; Karadjova V.; Stefanov R.The aim of the present study was to investigate the effect of ultra-low cryopreservation temperatures on the activity of the enzymes lactate dehydrogenase and gamma-glutamyl transferase in ejaculates of Ovis aries animals. For this purpose, 25 ejaculates from breeders of the species Ovis aries were examined. Cryopreservation of sperm was performed by the Cassou method (1964). Enzyme activity was determined in sperm cells (intracellular activity) and in sperm plasma (extracellular activity) before freezing and after thawing of ejaculates. After cryopreservation, the extracellular enzyme activity of lactate dehydrogenase decreased from 334.87 ± 20.54 U L-1 to 243.54 ± 21.85 U L-1, and there was a decrease in the intracellular activity of the enzyme from 793.02 ± 36.74 U L-1 to 506.52 ± 44.46 U L-1. Gamma-glutamyl transferase enzyme activity was also affected by cryopreservation. Its extracellular activity decreased from 58.84 ± 2.66 U L-1 to 38.52 ± 2.03 U L-1, and its intracellular activity from 6.08 ± 0.27 U L-1 to 3.16 ± 0.14 U L-1. In conclusion, ultra-low cryopreservation temperatures reduce the activity of lactate dehydrogenase and gamma-glutamyl transferase enzymes in the ejaculates of Ovis aries animalsItem NEW DERIVATIVES OF GALANTHAMINE CONTAINING PEPTIDE FRAGMENT(2020-01-01) Vezenkov L.; Cena H.; Danalev D.; Karadjova V.; Tsekova D.; Bardarov V.; Vassilev N.New derivatives of galanthamine containing a peptide fragment with an antiaggregation activity are synthesized. Herein the process of synthesis, purification and characterization of the newly obtained compounds is described. Syntheses were performed by consecutive attachment of Boc-protected amino acids to either norgalanthamine or HGly-Ogal using TBTU/DIPEA and TCTU/DIPEA methods. The purification of final products was realized by treating with EtOAc or by HPLC. The newly compounds were characterized by TLC, NMR, m.p. and MS. Two pharmacological effects are expected to be combined in a single molecule: the anticholinesterase and the antiaggregation onesItem ON THE p(x) APPROXIMATION IN THE NON-ISOTHERMAL REACTION KINETICS BY A GENERALIZED EXPONENTIAL INTEGRAL The Concept(2021-01-01) Hristov J.; Karadjova V.A non-Arrhenius model based on the Mittag-Leffler function has been conceived as a basic concept. This approach allows modelling both sub-Arrhenius and super-Arrhenius behaviours and giving rise to modified temperature integrals.Item 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.Item Synthesis and biological studies on (KLAKLAK)2-NH2 analog containing unnatural amino acid β-ala and conjugates with second pharmacophore(2021-12-01) Jaber S.; Nemska V.; Iliev I.; Ivanova E.; Foteva T.; Georgieva N.; Givechev I.; Naydenova E.; Karadjova V.; Danalev D.(1) Background: Peptides are good candidates for anticancer drugs due to their natural existence in the body and lack of secondary effects. (KLAKLAK)2 is an antimicrobial peptide that also shows good anticancer properties. (2) Methods: The Solid Phase Peptide Synthesis (Fmoc-strategy) was used for the synthesis of target molecules, analogs of (KLAKLAK)2-NH2. The purity of all compounds was monitored by HPLC, and their structures were proven using mass spectrometry. Cytotoxicity and antiproliferative effects were studied using 3T3 NRU and MTT tests, respectively. For determination of antimicrobial activity, the disc-diffusion method was used. Hydrolytic stability at three pH values, which mimic the physiological pH in the body, was investigated by means of the HPLC technique. (3) Results: A good selective index against MCF-7 tumor cell lines, combined with good cytotoxicity and antiproliferative properties, was revealed for conjugates NphtG-(KLAKLAK)2-NH2 and Caf-(KLAKLAK)2-NH2. The same compounds showed very good antifungal properties and complete hydrolytic stability for 72 h. The compound Caf-(KLβ-AKLβ-AK)2-NH2 containing β-Ala in its structures exhibited good antimicrobial activity against Escherichia coli K12 407 and Bacillus subtilis 3562, in combination with very good antiproliferative and cytotoxic properties, as well as hydrolytic stability. (4) Conclusions: The obtained results reveal that all synthesized conjugates could be useful for medical practice as anticancer or antimicrobial agents.Item SYNTHESIS, ISOLATION AND BIOLOGICAL ACTIVITY STUDIES OF GALANTHAMINE DERIVATIVES INCLUDING PEPTIDE MOIETY AND TANNINS FROM MEDICINAL PLANTS(2022-01-01) Atanasov A.; Karadjova V.; Andonova A.; Tsekova D.; Lozanov V.; Parashkevova B.; Mindov I.; Todorova R.; Vezenkov L.The search of a new chemical substances influencing platelet aggregation is a very important endeavor for medical practice. Among the compounds that have antiaggregating activity are some peptides, tannins, etc. Here we present antiaggregation activity of Arg-Gly-Asp (RGD) peptide derivatives. Synthetic procedures of new peptide-galantamine derivatives including also glucose moiety designed to possess such activity are included. The in vitro effect of water extract from 20 tannins-containing plants from Bulgarian flora on aggregation of modified rat platelet-rich plasma was investigated and seven of them (Corylus avellana L, Cydonia oblonga Mill, Dryopteris filix-mas (L.) Schott, Ephedra distachya L., Geum urbanum L., Primula officinalis (L.) Hill and Punica granatum L.)were able to inhibit platelet aggregationItem SYNTHESIS, STRUCTURE AND PROOXIDANT ACTIVITY OF 3-HYDROXYFLAVONE COMPLEXES WITH Cu(II)(2022-01-01) Vakarelska-Popovska M.; Karadjova V.; Velkov Z.Hydroxyflavones chelate iron and copper ions thus preventing the formation of new active radicals in experiments in vivo. Furthermore, it is reported that some of them demonstrate in vitro prooxidant activity in the presence of metal ions. Consequently, there is no unanimity in the literature on the chemical mechanisms that engender the properties of these compounds vital for the human health. Herein, our investigations on the synthesis and DPPH activity of 3-hydroxyflavone complexes with copper ions obtained at different pH and different metal/ligand ratio are presented. Their structure was confirmed using spectral methods and elemental analyzes. A DFT quantum chemical study on the complexes structure was also performed. The resulting complexes were tested for activity against DPPH. The outcome show that the complexes exhibit prooxidant rather than antioxidant activity, which decreases with declining the relative metal ion content in the complexes.