1. Exploring antioxidative properties of xanthohumol and isoxanthohumol : an integrated experimental and computational approach with isoxanthohumol pKa determinationJelena Tošović, Zala Kolenc, Gregor Hostnik, Urban Bren, 2025, izvirni znanstveni članek Opis: This study explores the antioxidative activities of xanthohumol (XN) and isoxanthohumol (IXN), prenylated flavonoids from Humulus lupulus (family Cannabaceae), utilizing the oxygen radical absorption capacity (ORAC) and ferric reducing antioxidant power (FRAP) assays along with computational Density Functional Theory methods. Experimentally, XN demonstrated significantly higher antioxidative capacities than IXN. Moreover, we determined IXN pKa values using the UV/Vis spectrophotometric method for the first time, facilitating its accurate computational modeling under physiological conditions. Through a thermodynamic approach, XN was found to efficiently scavenge HOO• and CH3O• radicals via Hydrogen Atom Transfer (HAT) and Radical Adduct Formation (RAF) mechanisms, while CH3OO• scavenging was feasible only through the HAT pathway. IXN exhibited its best antioxidative activity against CH3O• via both HAT and RAF mechanisms and could also scavenge HOO• through RAF. Both Single Electron Transfer (SET) and Sequential Proton Loss-Electron Transfer (SPLET) mechanisms were thermodynamically unfavorable for all radicals and both compounds.
Ključne besede: antioxidative activity, bio-active membranes, xanthohumol, isoxanthohumol, ORAC and FRAP assays, pKa determination, density functional theory, DFT
Objavljeno v DKUM: 31.01.2025; Ogledov: 0; Prenosov: 5
 Celotno besedilo (2,80 MB) |
2. Preučevanje interakcij med tanini in lizocimom : diplomsko delo univerzitetnega študijskega programa I. stopnjeAnja Zaverla, 2024, diplomsko delo Opis: Razvoj odpornosti bakterij na antibiotike je eden izmed večjih izzivov človeštva, ki zahtevajo tako iskanje novih protibakterijskih učinkovin, kot tudi izboljšanih načinov uporabe protibakterijskih sredstev. Raziskovalci nove protibakterijske učinkovine iščejo tudi med naravnimi spojinami s protimikrobnimi in protibakterijskimi učinki. Rastline vsebujejo tanine, ki so polifenolni sekundarni metaboliti, ki jih raziskujemo zaradi njihovih številnih potencialnih za zdravje ugodnih učinkov. Glede na njihovo kemijsko strukturo jih delimo na proantocianidine (kondenzirane tanine) in hidrolizirajoče tanine. Slednji se nadalje razdelijo na dve glavni podskupini (galotanin in elagitanini).
V diplomskem delu smo proučevali vezavo elagitaninov na lizocim – modelni protein. Po dializi v pufru s pH = 5 smo lizocim titrirali z galno kislino, metil galatom in veskalaginom. Opazovali smo, kako prisotnost elagitaninov vpliva na fluorescenco lizocima. Vpliv dodatka taninov na sekundarno strukturo lizocima smo opazovali s cirkularnim dikroizmom (CD-spektroskopija), medtem ko smo termodinamiko vezave opazovali z izotermno titracijsko kalorimetrijo (ITC). Z opazovanjem temperaturne odvisnosti fluorescenčnega spektra lizocima smo ugotovili, da prisotnost taninov ne vpliva na temperaturo tališča proteina. S pomočjo Stern-Volmerjeve enačbe ob upoštevanju učinka notranjega filtra smo poskusili pridobiti konstante vezave taninov na lizocim. S CD-spektroskopijo smo ugotovili, da ima veskalagin večji vpliv na denaturacijo proteina, kot metil galat in galna kislina. Ugotovili smo, da je interakcija veskalagina in lizocima mnogo bolj eksotermna, kot interakcija metil galata ali galne kisline z lizocimom. Poleg tega smo z ITC-jem potrdili, da gre pri interakcijah taninov z lizocimom za razmeroma šibke interakcije.
Ključne besede: elagitanini, protein, konstanta vezave, sekundarna struktura, spektroskopija, termodinamični parametri vezave
Objavljeno v DKUM: 17.09.2024; Ogledov: 0; Prenosov: 45
Celotno besedilo (4,11 MB) |
3. Razvoj stacionarne faze za separacijo naravnih spojin : diplomsko delo univerzitetnega študijskega programa I. stopnjeJaka Kodelja, 2024, diplomsko delo Opis: Diplomsko delo prikazuje razvoja nove stacionarne faze za izolacijo šestih elagitaninov (ET), galne (GK) in elagične kisline (EK) iz vodnega izvlečka kostanjevega lesa, z uporabo treh različnih polimerov, v vlogi stacionarne faze. Polimere, poli (stiren-ko-divinilbenzen) (PS/DVB), poliakrilat (PA) ter poli (vinilpirolidon-ko-divinilbenzen) (PVP/DVB) smo polimerizirali s suspenzijsko polimerizacijo, z uporabo iniciatorja α,α'-azobisisobutironitrila (AIBN) in stabilizatorjema polivinilpirolidonom (PVP) ter polivinil alkoholom (PVA). S temi polimeri smo napolnili v kromatografsko kolono za hitro kromatografijo ter preverili njihovo učinkovitost za ločevanja ET z uporabo preparativnega HPLC. Uspešnost ločbe smo preverili z analiznim HPLC. Pri tem smo spreminjanjali deleža acetonitrila (ACN) v mobilni fazi, dokler nismo dobili uspešne izolacije ET, GK in EK. Pogosto se je zgodilo, da so se vse komponente kostanjevega izvlečka izločile iz kolone v mrtvem času, ne glede na vrsto uporabljene stacionarne faze ali gradienta. Za takšno stacionarno fazo smo ocenili, da ni ustrezna za ločevanje danih spojin. Pri ločbi se je najbolj izkazala stacionarna faza PVP/DVB. To stacioanrno fazo smo nato uporabili za razvoj metode, s katero smo poskušali dobiti čim boljšo ločbo posameznih elagitaninov. Poleg tega smo opazovali tudi, kako na uspešnost ločbe vpliva povprečna velikost delcev stacionarne faze.
Ključne besede: elagitanini, veskalin, kastalin, veskalagin, kastalagin, galna kislina, elagična kislina, ruburin A, ruburin D, čiščenje, izolacija, HPLC, preparativni HPLC, polimerizacija, suspenzijska polimerizacija
Objavljeno v DKUM: 16.09.2024; Ogledov: 16; Prenosov: 36
Celotno besedilo (6,17 MB) |
4. How deprotonation of cohumulone and colupulone influence their UV/Vis and CD spectrumAnja Petek, Urban Bren, Gregor Hostnik, 2024, izvirni znanstveni članek Opis: Cohumulone and colupulone are representatives of
- and
-acids, respectively. These compounds are important antimicrobial hop (Humulus lupulus) constituents, where cohumulone is an important source of the bitter taste of beer. In this study, we examined the pH dependence of UV/Vis spectra of both compounds while CD spectra of cohumulone were also measured at various wavelengths. This facilitated the examination of the protolytic equilibrium of both compounds, where the second p
value of cohumulone was determined for the first time. Additionally, comparing experimental spectra with spectra calculated using time-dependent density functional theory (TD-DFT) enabled the determination of the most likely deprotonation positions and corresponding species most likely present in the aqueous solution at various pH values. Last but not least, comparing calculated and experimental CD spectra of cohumulone facilitated the determination of the absolute stereoconfiguration of cohumulone.
Ključne besede: cohumulone, colupulone, UV/Vis spectrum, CD-spektrum, absolute configuration
Objavljeno v DKUM: 29.08.2024; Ogledov: 77; Prenosov: 0 |
5. Hydrothermal conversion of oilseed cakes into valuable products : influence of operating conditions and whey as an alternative process liquid on product properties and their utilizationAleksandra Petrovič, Tjaša Cenčič, Sabina Vohl, Gregor Hostnik, Matjaž Finšgar, Lidija Čuček, 2024, izvirni znanstveni članek Ključne besede: hydrothermal carbonization, hydrochar, process liquid, oilseed press cake, cheese whey, catalyst
Objavljeno v DKUM: 29.08.2024; Ogledov: 64; Prenosov: 14
Celotno besedilo (7,20 MB) |
6. Chelation of iron(II) ions by ellagitannins - effects of hexahydroxydiphenoyl and nonahydroxytriphenoyl groupsFranjo Frešer, Urban Bren, Gregor Hostnik, 2024, izvirni znanstveni članek Opis: Tannins represent secondary plant metabolites that are used to control bacterial populations by chelation of essential metal ions. Their presence in food also affects the bioavailability of iron. This study investigates the influence of ellagitannins (vescalin, castalin, vescalagin, castalagin) structure and pH on the stoichiometry and formation constants of ellagitannin-Fe(II) coordination compounds. We demonstrated that ellagitannins are stable for at least one hour at pH values lower than 7.25. The spectra of neutral compounds were measured and explained with the help of TDDFT calculations. Furthermore, the pH-dependence of the ellagitannins UV–Vis spectra was examined to obtain insight into their protolytic equilibrium. Using Job’s method in the pH range 3.50–5.51, the stoichiometry of the formed ellagitannin-Fe(II) ions complexes was determined. A model explaining interactions between ellagitannins and Fe(II) ions, that took into account the protolytic equilibrium of ellagitannins, was fitted globally to all four Job plots, whereby the corresponding formation constants were obtained.
Ključne besede: Ellagitannins, Fe(II) ions chelation, protolytic equilibrium, Job’s method, model fitting
Objavljeno v DKUM: 22.08.2024; Ogledov: 52; Prenosov: 12
Celotno besedilo (3,98 MB) |
7. Antimicrobial properties of different hop (Humulus lupulus) genotypesZala Kolenc, Tomaž Langerholc, Gregor Hostnik, Miha Ocvirk, Sara Štumpf Horvat, Maša Pintarič, Iztok Jože Košir, Andreja Čerenak, Alenka Garmut, Urban Bren, 2023, izvirni znanstveni članek Opis: The antimicrobial activity of hop extracts obtained from different hop genotypes were investigated against Staphylococcus aureus and Lactobacillus acidophilus. In this study the pure xanthohumol, purified β-acids rich fraction, as well as α-acids with β-acids rich fraction were used to test antimicrobial activity against Staphylococcus aureus and Lactobacillus acidophilus; whereby, the antimicrobial activity of different hop extracts against Lactobacillus acidophilus was studied for the first time. Microbial susceptibility to purified hydroacetonic extracts from different hop varieties was investigated by the broth microdilution assay to determine the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). The hop hydroacetonic extracts were more effective against Staphylococcus aureus than against Lactobacillus acidophilus. Strong inverse correlations of MIC and MBC values were obtained with xanthohumol, cohumulone, n+adhumulone, colupulone and n+adlupulone contents, suggesting that the identified chemical hop compounds are directly responsible for antimicrobial effects. Moreover, the effect of the growth medium strength on the MIC values of hop extracts against Staphylococcus aureus was systematically investigated for the first time. The current study also reveals the effect of different hop extracts on Staphylococcus aureus, which responds to their presence by lag phase extension and generation time prolongation.
Ključne besede: hop extract, xanthohumol, Staphylococcus aureus, Lactobacillus acidophilus, minimum inhibitory concentration, minimum bactericidal concentration
Objavljeno v DKUM: 09.05.2024; Ogledov: 203; Prenosov: 25
Celotno besedilo (2,03 MB)
Gradivo ima več datotek! Več... |
8. The Influence of Chestnut Extract and Its Components on Antibacterial Activity against Staphylococcus aureusSara Štumpf Horvat, Gregor Hostnik, Tomaž Langerholc, Maša Pintarič, Zala Kolenc, Urban Bren, 2023, izvirni znanstveni članek Opis: Increasing antimicrobial resistance has caused a great interest in natural products as alternatives or potentiators of antibiotics. The objective of this study was to isolate individual tannins from crude chestnut extract as well as to determine the influence of both crude extracts (tannic acid extract, chestnut extract) and individual pure tannins (gallic acid, vescalin, vescalagin, castalin, castalagin) on the growth of Gram-positive Staphylococcus aureus bacteria. Their antibacterial activity was monitored by measuring the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) as well as the duration of the lag phase, growth rate and generation time. The effect of growth medium strength on the MIC of different tannins was also investigated. Bacterial growth was followed spectrophotometrically, and MIC values were determined by the microdilution method. The MIC values of various isolated compounds allowed us to determine the bioactive compounds and their contribution to antimicrobial activity. It was found that MIC values increase with increasing growth medium strength and that the lag phase lengthens with increasing tannin concentrations, while the growth rates decrease. Comparing the results of the two studies, the antimicrobial activity of tannins against S. aureus was not as pronounced as in the case of E. coli, which may indicate that a different mechanism of action is responsible for the antimicrobial effects of tannins on Gram-positive than on Gram-negative bacteria, or that a different mechanism is more pronounced.
Ključne besede: tannins, antibacterial activity, MIC, MBC, Staphylococcus aureus, lag phase, generation time
Objavljeno v DKUM: 20.02.2024; Ogledov: 363; Prenosov: 77
Celotno besedilo (1,19 MB)
Gradivo ima več datotek! Več... |
9. Meritve osmolarnosti izotoničnih napitkov za hidracijo telesa pri športni aktivnosti : magistrsko deloTjaša Skarlovnik, 2023, magistrsko delo Opis: V magistrskem delu smo izmerili osmolalnosti in poskušali izmeriti toničnosti izotoničnih napitkov, ki jih je mogoče kupiti na slovenskem tržišču. Z osmometrom smo izmerili osmolalnosti vseh izotonikov, pri čemer smo ugotovili, da osmolalnost večine izotonikov sodi v območje med 270 in 330 mOsm/kg, ki ga EFSA predpisuje za izotonične napitke. Nadalje smo pripravili standardne raztopine natrijevega klorida različnih osmolalnosti, ki smo jih izpostavili rdečim krvničkam, da smo lahko s pomočjo opazovanja sipanja in absorpcije svetlobe opazovali vpliv raztopin različnih osmolalnosti na volumen in obliko celic. S tem smo naredili umeritveno krivuljo in določili spodnjo mejo izotoničnega območja. Ker je bila na zgornji meji razlika med raztopinami zelo majhna, smo za razlikovanje med raztopinami različne toničnosti v tem območju uporabili mikroskop z multimodalnim čitalcem, s katerim smo opazovali delež ježkov v posamezni raztopini ob času 20 in 60 minut po vstavitvi celic v raztopino. Delež ježkov je do raztopine z osmolalnostjo 300 mOsm/kg zanemarljivo majhen, nato se opazno poveča. V okviru proučevanja izotonikov smo najprej pomerili njihove UV/VIS spektre, da smo lahko opazovali, v katerem delu absorpcijskega spektra lahko zaznamo sipanje svetlobe. Nato smo izotonikom dodali še rdeče krvne celice in pomerili spektre, iz katerih smo s primerjavo z umeritveno krivuljo poskusili določiti toničnosti raztopin. Na prvi pogled je videti, da ima večina izotonikov manjšo toničnost, kot jo imajo standardne raztopine natrijevega klorida primerljive osmolalnosti. Vendar pa meritve otežujejo nizke vrednosti pH izotonikov, ki vplivajo na morfologijo rdečih krvničk. Da bi videli, kako je membrana rdečih krvničk prepustna za sladkorje, smo tudi preverili, kakšna je toničnost raztopin sladkorjev znane osmolalnosti. Vidimo lahko, da so membrane rdečih krvničk prepustne za določene saharide. To pomeni, da izotonični napitki, kljub ustrezni osmolalnosti, pogosto niso izotonični, saj je koncentracija sladkorjev v njih razmeroma visoka.
Ključne besede: osmolalnost, toničnost, hidracija, izotonični napitki, eritrociti
Objavljeno v DKUM: 26.07.2023; Ogledov: 588; Prenosov: 91
Celotno besedilo (3,68 MB) |
10. Tvorba koordinacijskih spojin galne kisline z bakrovimi in aluminijevimi ioni : diplomsko delo visokošolskega strokovnega študijskega programa I. stopnjeAjda Raj Miloševič, 2022, diplomsko delo Opis: V diplomskem delu smo ugotavljali, kakšna je stehiometrijo koordinacijske spojine, nastale med galno kislino in Cu(II) ioni ter galno kislino in Al(III) ion. Opazovali smo tudi vpliv pH na koncentracijo nastale koordinacijske spojine. Pomerili smo UV/Vis-spektre galne kisline, raztopine Cu(II)) ionov ter raztopie Al(III) ionov ter jih primerjali s spektri raztopin mešanice galne kisline in Cu(II) ali Al(III) ionov. Pri skupni koncentraciji serije raztopin galne kisline in Cu(II) ionov c=1∙10-3 mol∙L-1 pri valovni dolžini λ=335 nm in skupne koncentracije serije raztopin galne kisline in Al(III) ionov c=2∙10-4 mol∙L-1 pri valovni dolžini λ=297 nm smo izrisali Jobova diagrama pri uporabi pufrov z različnimi vrednostmi pH. Rezultat Jobovega diagrama je bila stehiometrijo spojin med galno kislino in kovinskimi ioni. Pri vezavi galne kisline s Cu(II) ioni nismo mogli potrditi ali gre za stehiometrijo 1:1 ali 1:2 (pH=5,50), prav tako stehiometrije nismo mogli potrditi pri vezavi galne kisline in Al(III) ionov (pH=4,50), kjer se je nakazovalo da en Al(III) ion veže en do dve molekuli galne kisline, medtem ko gre pri pH=5,50 za vezavo v razmerju 1:1
Ključne besede: galna kislina, Cu(II) ioni, Al(III) ioni, Jobov diagram, koordinacijska spojina
Objavljeno v DKUM: 03.11.2022; Ogledov: 522; Prenosov: 96
Celotno besedilo (1,49 MB) |
