Browsing by Author "Dochev K."

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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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    pH-dependent hydrogels obtained by low molecular weight derivatives of aspartic acid and glutamic acid (L-Asp and L-Glu)
    (2024-01-01) Tsekova D.; Kondova V.; Dochev K.; Anchev B.
    We report here the synthesis of two new anionic gemini surfactants, derivatives of L-Asp and L-Glu with analogous structure and their applications as low molecular weight gelators. Conditions for formation of pH-dependent hydrogels and their stability are presented and discussed. Although both compounds possess very close molecular structures, only one of them – the derivative of L-Asp, can form stable hydrogels. Loading of such a hydrogel with silver nanoparticles and the conditions of their release are also studied and described. Different methods to analyze molecular and supramolecular structures, such as NMR, FTIR, UV–VIS and SEM, are used to characterize the compounds and also to understand and follow the processes of loading and release of silver nanoparticles. It was found that a stable hydrogel can be formed only in acidic solution, while release can happen only at basic condition – over pH ≥ 9. The results obtained show that such pH-dependent hydrogels can be used for slowly and gradually supply of active compounds at necessity, expressed through changing the pH of the living tissue.