Browsing by Author "Givechev I."

Now showing 1 - 6 of 6
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    Calibration of GC/MS method and validation of the modified sample preparation for determination of polycyclic aromatic hydrocarbons
    (2018-01-01) Givechev I.; Danalev D.; Yaneva S.; Tanev D.
    A modified procedure of EN 16619:2015 method for determination of four polycyclic aromatic hydrocarbons (PAH's) was proposed. A change in internal standard and in sample preparation procedure was made for two low fat food matrices (wheat flour and smoked pork leg). As a result a new calibration was obtained with very good linearity (correlation coefficient R2 = 0.999). Recovery rates for spiked samples from both matrices were also calculated and were found in a good fit with the European legislation specifications. The average values of the recovery rates amounted to 99.32 % (1.83 % relative standard deviation) for wheat flour and 97.25 % (2.50 % relative standard deviation) for smoked pork leg.
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    Development and validation of GC/MS method for simultaneous determination of 16 polycyclic aromatic hydrocarbons (PAHs) in pork meat matrix
    (2021-03-01) Givechev I.; Tanev D.; Danalev D.
    The major processes for introducing polycyclic aromatic hydrocarbons (PAHs) in food are smoking and grilling of different products. But in addition, PAHs can permeate in the food chain due to their high lipophilicity and ability to be accumulated in specific tissue, through contaminated animal feed. Further, when some parts of these animals are marketed as food, the accumulated PAHs can go to the human organism. Some of them are classified as highly toxic, carcinogenic and mutagenic for animal and human organisms so they are under consideration of International and European legislation. This work reports development and validation of simple and fast GC/MS method for 16 PAHs determination. Comparison of two methods for sample preparation in pork meat matrix standard extraction/saponification procedure and modified QuEChERS method is also done. In addition, this paper report the calibration step of instrument and a recovery study for 16 PAHs in model pork meat, using modified QuEChERS procedure for sample pretreatment. The calibration step with accessible and suitable for use in real laboratory conditions internal standard (chrysene D12) is done in the range 10–100 ppb using toluene as solvent. The obtained results show very good linearity (R2 5 0.99 to 1.00). For the recovery study six model samples were spiked with 16 PAHs and they all are subjected to QuEChERS procedure. The recovery is calculated and the obtained data (71–120%) is in a good correlation with requirements of international legislation. Finally, LOD values for all 16 investigated compounds of modified GC/MS method and for the instrument were determined.
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    First steps of development of a method for simultaneous determination of cholesterol and fatty acids in food matrices
    (2018-01-01) El Mazbouh H.; Givechev I.; Tanev D.; Yaneva S.; Danalev D.
    Cholesterol and fatty acids are compounds with a key role in the human organism. Their levels must be strictly controlled and maintained in the human body to ensure its proper biochemical functioning. Herein, we report first steps of development of a method for cholesterol determination in food using GC/FID. The calibration, the linearity and the choice of an appropriate internal standard are discussed. The obtained correlation coefficient is R2 = 0,9992. A very good analytical yield of cholesterol 100 % is achieved following a specific procedure of sample preparation. LOQ is 50 ppm, while LOD is 15 ppm.
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    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.
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    Synthesis, antiproliferative and antimicrobial activities of (KLAKLAK)2-NH2 analogue containing nor-Leu and its conjugates with a second pharmacophore
    (2023-01-01) Jaber S.; Nemska V.; Iliev I.; Ivanova E.; Foteva T.; Georgieva N.; Givechev I.; Tanev D.; Naydenova E.; Danalev D.
    Peptides are a promising alternative of conventional medical drugs for the treatment of different diseases because they have no or have very few side effects owing to the natural mechanisms for their elimination. There are a lot of examples of drugs on the pharmaceutical market based on modified amino acids and peptides. Herein, we report the synthesis and studies on the antimicrobial peptide (KLAKLAK)2-NH2 where Leu is replaced by the unnatural amino acid nor-Leu. In addition, a second pharmacophore with well proven anticancer properties is introduced to the peptide moiety. All structures were synthesized by conventional solid phase peptide synthesis. The antiproliferative and antimicrobial activities were studied using MTT-dye reduction assay and disk-diffusion test, respectively. Biological activity assays showed that the introduction of nor-Leu in the primary structure of the parent compound does not lead to an increase in the antiproliferative activity. However, the combination with the second pharmacophore 1,8-naphtalimide in a hybrid structure 1,8-NphtG-(KNleAKNleAK)2-NH2 leads to a significant increase in the antiproliferative properties. The antimicrobial tests showed that all tested compounds exhibit antimicrobial activity. The peptide and the second pharmacophore had a synergistic effect. In combination with complete hydrolytic stability for 72 h in model systems, the compound 1,8-NphtG-(KNleAKNleAK)2-NH2 is the best candidate for a medical drug in the treatment of mammary gland type A adenocarcinoma (MCF-7) in combination with antimicrobial properties.
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    Synthesis, antitumor and antibacterial studies of new shortened analogues of (KLAKLAK)2-NH2 and their conjugates containing unnatural amino acids
    (2021-02-02) Jaber S.; Iliev I.; Angelova T.; Nemska V.; Sulikovska I.; Naydenova E.; Georgieva N.; Givechev I.; Grabchev I.; Danalev D.
    (1) Background: (KLAKLAK)2 is a representative of the antimicrobial peptide group which also shows good anticancer properties. (2) Methods: Herein, we report synthesis using SPPS and characterization by HPLC/MS of a series of shortened analogues of (KLAKLAK)2. They contain single sequence KLAKLAK as C-terminal amides. In addition, substitution of some natural amino acids with unnatural β-Ala and nor-Leu is realized. In addition, these structures are conjugated with second pharmacophore with well proven anticancer properties 1,8-naphthalimide or caffeic acid. Cytotoxicity, antiproliferative effect and antimicrobial activity of newly synthesized structures were studied. (3) Results: The obtained experimental results reveal significant selective index for substances with common chemical structure KLβAKLβAK-NH2. The antibacterial properties of newly synthesized analogues at two different concentrations 10 μM and 20 μM, were tested against Gram-negative microorganisms Escherichia coli K12 407. Only two of the studied compounds KLAKLAK-NH2 and the one conjugated with second pharmacophore 1,8-naphthalimide and unnatural amino acid nor-Leu showed moderate activity against tested strains at concentration of 20 μM. (4) Conclusions: The obtained results reveal that the introducing of 1,8-naphthalimideGlyand Caf- increase the cytotoxicity and antiproliferative activity of the peptides but not their selectivity. Only two compounds KLAKLAK-NH2 and 1,8-naphthalimideGKnLAKnLAK-NH2 show moderate activity against Escherichia coli K12 at low concentration of 20 μM.