Browsing by Author "Tsekova D."

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    Heterogeneous nucleation of hen-egg-white lysozyme - molecular approach
    (2000-01-01) Nanev C.N.; Tsekova D.
    The heterogeneous nucleation of hen-egg-white lysozyme (HEWL) crystals has been repeatedly investigated using a double-(thermal)-pulse technique, thus detaching nucleation from growth stage. n(t) dependencies of the nucleus number n, on templates of poly-L-lysine, vs time, t were plotted and the steady-state nucleation rates I were determined. They were compared with the results obtained earlier for surfaces rendered hydrophobic (by means of hexamethyl-disilazane) as well as for bare glass surfaces. In the present paper we determine the number of HEWL molecules in the (heterogeneously formed) critical nucleus. It turned out that it is build of 3 (to 4) HEWL molecules on glass substrate and 8 molecules for both hexamethyl-disilazane and poly-L-lysine templates. The energy Ak required for heterogeneous formation of a critical nucleus on poly-L-lysine has been calculated, on the basis of the steady-state nucleation rates I. Intermolecular binding energy in the HEWL crystal lattice has been estimated again (approximately 10-9 erg/molecule). This time the basis was the adhesion of HEWL crystals to poly-L-lysine substrate (compare D. Tzekova, S. Dimitrova, C.N. Nanev, J. Cryst. Growth, 196 (2), 226 (1999)).
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    Improvement of Stevia rebaudiana Bertoni In Vitro Propagation and Steviol Glycoside Content Using Aminoacid Silver Nanofibers
    (2022-10-01) Sichanova M.; Geneva M.; Petrova M.; Miladinova-Georgieva K.; Kirova E.; Nedev T.; Tsekova D.; Iwanov I.; Dochev K.; Ivanova V.; Trendafilova A.
    The food industry is interested in replacing artificial sweeteners with natural sugars that possess zero calories and carbohydrates and do not cause spikes in blood sugar levels. The steviosides leaves, synthesized at Stevia rebaudiana Bertoni, are 300 times sweeter than common table sugar. Stevia propagation is limited due to the poor viability of the seeds, the long time and low germination rate, and the poor rooting ability of vegetative cuttings. Because of this, an alternative biotechnological method for its reproduction is being studied, such as multiple shoot production through direct organogenesis using nanofibers, formed from a derivative of amino acid valine as a carrier of the biologically active agent silver atoms/particles (NF-1%Ag and NF-2%Ag). The stevia explants were cultured on a medium containing NF-1%Ag and NF-2%Ag at concentrations of 1, 10, 50, and 100 mg L−1. The NF-1%Ag and NF-2%Ag treatment caused hormetic effects on stevia plantlets. At low concentrations of from 1 to 50 mg L−1 of nanofibers, the stimulation of plant growth was observed, with the maximum effect being observed at 50 mg L−1 nanofibers. However, at the higher dose of 100 mg L−1, inhibition of the values of parameters characterizing plant growth was recorded. The presence of nanofibers in the medium stimulates stevia root formatting.
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    Influence of the Abiotic Elicitors Ag Salts of Aspartic Acid Derivatives, Self-Organized in Nanofibers with Monomeric and Dimeric Molecular Structures, on the Antioxidant Activity and Stevioside Content in Micropropagated Stevia rebaudiana Bert.
    (2023-10-01) Sichanova M.; Geneva M.; Petrova M.; Miladinova-Georgieva K.; Kirova E.; Nedev T.; Tsekova D.; Ivanova V.; Trendafilova A.
    The use of nanomaterials in biotechnology for the in vitro propagation of medical plants and the accumulation of certain biologically active metabolites is becoming an efficient strategy. This study aimed to evaluate the influence of the concentration (0, 1, 10, 50, and 100 mg L−1) of two types of nanofibers on the growth characteristics, the antioxidant status, and the production of steviol glycosides in micropropagated Stevia rebaudiana Bert. plantlets. The nanofibers were synthesized by aspartic acid derivatives (L-Asp) Ag salts self-organized into nanofibers with two different molecular structures: monomeric, containing one residue of L-Asp with one hydrophilic head which bonds one Ag ion (NF1-Ag salt); and dimeric, containing two residues of L-Asp with two hydrophilic heads which bond two Ag ions (NF2-Ag salt). An increase in the shoots from the explants’ number and length, biomass accumulation, and micropropagation rate was achieved in the plants treated with the NF1-Ag salt in concentrations from 1 to 50 mg L−1 after 30 days of in vitro proliferation compared to the NF2-Ag salt. In contrast, the plants grown on MS media supplemented with NF2-Ag salt exhibited an increase in the level of stevioside, rebaudioside A, and mono- (CQA) and dicaffeoylquinic (DCQA) acids as compared to the NF1-Ag salt.
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    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 ones
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    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 aggregation