Browsing by Author "Chakarov K."

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    Archaeometric Investigations on the Significance of Limestones in the Roman Provinces of the Southern Lower Danube
    (2025-03-01) Prochaska W.; Anevlavi V.; Chakarov K.; Andreeva P.; Sutev I.
    In contrast to several types of marbles used in antiquity, where different data collections do exist, similar approaches for provenance analysis are not available for limestones. In general, limestones are characterised visually and by the examination of sedimentological parameters. The usual microscopic investigation of limestones and the characterisation of limestone artefacts are often impossible because of the large samples necessary for these investigations. It is demonstrated in this paper that for the provenance analysis of limestone, the same established methods used for assigning marbles to their origin can also be successfully used in the case of limestone. We investigated a series of Roman quarries (three different quarry regions) in the north of the Haemus Mountain Range in the region of Marcianopolis and Nicopolis ad Istrum with the aim of establishing a first database (isotope analyses and trace element analyses) to correlate limestone artefacts. All in all, 42 quarry samples from the locations Marciana, Samovodene and Koevtsi were investigated. Fifteen artefacts made of limestone were analysed. Two samples from Marcianopolis were assigned to the Marciana quarry, and seven artefacts from Nicopolis ad Istrum originate from the quarries of Samovodene. For six more samples from Nicopolis ad Istrum, no match to one of the sampled and investigated quarries was found; thus, the existence of one or more quarries in the area is presumed. An extension of the database and the investigation of further limestone quarries in the area certainly will compensate for this deficiency.
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    Chemical Behavior and Bioactive Properties of Spinorphin Conjugated to 5,5′-Dimethyl- and 5,5′-Diphenylhydantoin Analogs
    (2024-06-01) Georgieva S.; Todorov P.; Tchekalarova J.; Subaer S.; Peneva P.; Chakarov K.; Hartati H.; Faika S.
    The discovery of new peptides and their derivatives is an outcome of ongoing efforts to identify a peptide with significant biological activity for effective usage as a possible therapeutic agent. Spinorphin peptides have been documented to exhibit numerous applications and features. In this study, biologically active peptide derivatives based on novel peptide analogues of spinorphin conjugated with 5,5′-dimethyl (Dm) and 5,5′-diphenyl (Ph) hydantoin derivatives have been successfully synthesized and characterized. Scanning electron microscopy (SEM) and spectral methods such as UV-Vis, FT-IR (Fourier Transform Infrared Spectroscopy), CD (Circular Dichroism), and fluorimetry were used to characterize the microstructure of the resulting compounds. The results revealed changes in peptide morphology as a result of the restructuring of the aminoacidic sequences and aromatic bonds, which is related to the formation of intermolecular hydrogen bonds between tyrosyl groups and the hydantoin moiety. Electrochemical and fluorescence approaches were used to determine some physicochemical parameters related to the biological behavior of the compounds. The biological properties of the spinorphin derivatives were evaluated in vivo for anticonvulsant activity against the psychomotor seizures at different doses of the studied peptides. Both spinorphin analog peptides with Ph and Dm groups showed activity against all three phases of the seizure in the intravenous Pentylenetetrazole Seizure (ivPTZ) test. This suggests that hydantoin residues do not play a crucial role in the structure of spinorphin compounds and in determining the potency to raise the seizure threshold. On the other hand, analogs with a phenytoin residue are active against the drug-resistant epilepsy test (6-Hz test). In addition, bioactivity analyses revealed that the new peptide analogues have the potential to be used as antimicrobial and antioxidant compounds. These findings suggest promising avenues for further research that may lead to the development of alternative medicines or applications in various fields beyond epilepsy treatment.
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    OPTIMIZATION OF THE EXTRACTION CONDITIONS FOR THE Hg2+ - DITHIZONE COMPLEX IN CHLOROFORM AND ITS DETERMINATION BY UV-VIS SPECTROPHOTOMETRY
    (2026-01-01) Ivanova V.; Minkova K.; Chakarov K.
    This study aimed to optimize a UV- Vis spectrophotometric method for determining mercury based on its extraction with dithizone in chloroform. In the present work, the effects of pH, reagent concentration, stoichiometry of the complex were investigated. In addition, the sensitivity of the method was determined by calculating the molar absorbance, assessing the linearity and shaking time. Optimal conditions were established at pH ≈ 1.0 ± 0.1, using 4.00 mL of 5.00 mg L-1 dithizone and 1.00 min shaking. Under these parameters, the method showed stable absorbance and reproducible results. The calibration was linear within 0.80 - 1.10 mg L-1 Hg, and recovery tests yielded 71 - 74 % for spiked tap and deionized water samples. The optimized procedure provides reliable preliminary mercury determination and can be further adapted for complex matrices such as sediment, soil, or coal after microwave digestion.
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    Simultaneous determination of total and speciated mercury in marine sediment: A combined analytical approach
    (2025-11-20) Ivanova V.; Chakarov K.
    This study presents a combined analytical approach for determining total mercury (THg) and mercury species (CH3Hg+ and Hg2+) in marine sediments. THg was measured using AMA-254, while speciation analysis was performed by GC-ICP-HRMS with double isotope dilution calibration approach. In the sediment sample, CH3Hg+ was 0.00054 ± 0.00011 mg kg-1 and Hg2+ was 0.118 ± 0.030 mg kg-1. The sum of mercury species closely matched THg values obtained by AMA, confirming the method's reliability with 85% recovery. The low detection limits enabled accurate quantification of mercury, even at trace levels. Combining both techniques allowed a clearer distinction between the main mercury species and improved understanding of their distribution in the sediment. This approach is reliable for accurate mercury determination and the results can contribute useful information for future environmental assessments and monitoring efforts.