Yana Nikolova

Dr. Yana Nikolova

Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences
orcid

Research Focus & Metrics

Academic Career Length

13Years (2014-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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8 March 2022 in Molecules
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Journal Article
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MOManol Ognyanov
Manol Ognyanov
Petko DenevPetko Denev
Petko Denev
DTDesislava Georgieva Teneva
Desislava Georgieva Teneva
YGYordan Nikolaev Georgiev
Yordan Nikolaev Georgiev
STSabina Taneva
Sabina Taneva
SMSvetlana Momchilova
Svetlana Momchilova
Gamma irradiation is efficiently applied to many foods, but nevertheless there is a distinct lack of information about the changes of macro- and micronutrients (e.g., carbohydrates, lipids, organic acids, and phenolics) in dried rose hip (RH) fruits. Therefore, in this study, for the first time, the effect of gamma irradiation (10 and 25 kGy) on RH constituents is investigated. Different analytical techniques (GC-FID, HPLC-UV, HPSEC-RID, IR-FT, and SEM) are employed to examine this effect. The irradiation treatment (10 kGy) increased the glucose content by 30% and released cellobiose from RH fruits, thus revealing cellulose destruction. The extractability of total uronic acids increased from 51% (control) to 70.5% (25 kGy-irradiated), resulting in a higher pectin yield (10.8% < 12.8% < 13.4%) and molecular heterogeneity. Moreover, de-esterification was not a major effect of the irradiation-induced degradation of pectin. The sample exposure to the highest dose did not change the content of total carotenoids, β-carotene, and (un)saturated fatty acids, but it affected the tocopherols levels. Gamma rays had a negligible effect on the phenolic constituents and did not affect ORAC and HORAC antioxidant activity. In conclusion, it can be compromised that the exposition of dried RH is safe and can be successfully applied to decontaminate fruits without affecting their nutritional value and biological activity.

1 April 2014 in European Journal of Medicinal Chemistry
Verified
Journal Article
Closed access
GDGeorgi M. Dobrikov
Georgi M. Dobrikov
VVVioleta Valcheva
Violeta Valcheva
YNYana Nikolova
Yana Nikolova
Iva UgrinovaIva Ugrinova
Iva Ugrinova
EPEvdokia Pasheva
Evdokia Pasheva
Vladimir DimitrovVladimir Dimitrov
Vladimir Dimitrov

14 November 2021 in Molecules
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YNYana Nikolova
Yana Nikolova
GDGeorgi M. Dobrikov
Georgi M. Dobrikov
ZPZhanina Stoyanova Petkova
Zhanina Stoyanova Petkova
PSPavletta Shestakova
Pavletta Shestakova
A series of squaric acid amides (synthesized in 66–99% isolated yields) and a set of chiral aminoalcohols were comparatively studied as ligands in a model reaction of reduction of α-chloroacetophenone with BH3•SMe2. In all cases, the aminoalcohols demonstrated better efficiency (up to 94% ee), while only poor asymmetric induction was achieved with the corresponding squaramides. A mechanistic insight on the in situ formation and stability at room temperature of intermediates generated from ligands and borane as possible precursors of the oxazaborolidine-based catalytic system has been obtained by 1H DOSY and multinuclear 1D and 2D (1H, 10/11B, 13C, 15N) NMR spectroscopy of equimolar mixtures of borane and selected ligands. These results contribute to better understanding the complexity of the processes occurring in the reaction mixture prior to the possible oxazaborolidine formation, which play a crucial role on the degree of enantioselectivity achieved in the borane reduction of α-chloroacetophenone.

27 January 2023 in Molecules
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Journal Article
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GDGeorgi M. Dobrikov
Georgi M. Dobrikov
YNYana Nikolova
Yana Nikolova
ISIvaylo Slavchev
Ivaylo Slavchev
MDMiroslav G. Dangalov
Miroslav G. Dangalov
VDVera Deneva
Vera Deneva
NVNikolay Vassilev
Nikolay Vassilev
A series of OLED-relevant compounds, consisting of 1,3,5-triazine core linked to various aromatic arms by amino group, has been synthesized and characterized. The studied compounds exist in solution as a mixture of two conformers, a symmetric propeller and asymmetric conformer, in which one of the aromatic arms is rotated around the C-N bond. At temperatures below −40 °C, the VT NMR spectra in DMF-d7 are in a slow exchange regime, and the signals of two conformers can be elucidated. At temperatures above 100 °C, the VT NMR spectra in DMSO-d6 are in a fast exchange regime, and the averaged spectra can be measured. The ratio of symmetric and asymmetric conformers in DMF-d7 varies from 14:86 to 50:50 depending on the substituents. The rotational barriers of symmetric and asymmetric conformers in DMF-d7 were measured for all compounds and are in the interval from 11.7 to 14.7 kcal/mol. The ground-state energy landscapes of the studied compounds, obtained by DFT calculations, show good agreement with the experimental rotational barriers. The DFT calculations reveal that the observed chemical exchange occurs by the rotation around the C(1,3,5-triazine)-N bond. Although some of the compounds are potentially tautomeric, the measured absorption and emission spectra do not indicate proton transfer neither in the ground nor in the excited state.

1 November 2021 in Journal Scientific and Applied Research
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Journal Article
Open access
YNYana Nikolova
Yana Nikolova