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: 45
 Celotno besedilo (2,80 MB) |
2. Implementacija hitre Fouriereve transformacije v digitalnem vezjuMatic Kuhar, 2024, diplomsko delo Opis: Diplomsko delo obravnava implementacijo Fouriereve transformacije v digitalnem vezju. Proučuje teoretične osnove Fouriereve transformacije in njeno praktično uporabo pri digitalni obdelavi signalov. Poseben poudarek je na praktičnem delu naloge, ki predstavlja programiranje oziroma kreiranje programa za algoritem FFT z opisnim programskim jezikom Verilog, ki je lahko implementiran v digitalno vezje. Naloga opisuje razvoj in optimizacijo algoritma FFT, vključno z evalvacijo zmogljivosti razvitega sistema v realnih aplikacijah.
Ključne besede: Implementacija FFT, algoritem FFT, digitalno vezje, DFT, Verilog
Objavljeno v DKUM: 22.10.2024; Ogledov: 0; Prenosov: 24
Celotno besedilo (2,14 MB) |
3. QM-CSA: a novel quantum mechanics-based protocol for evaluation of the carcinogen-scavenging activity of polyphenolic compoundsVeronika Furlan, Jelena Tošović, Urban Bren, 2024, izvirni znanstveni članek Opis: In this study, a novel quantum mechanics-based protocol for the evaluation of carcinogenscavenging activity (QM-CSA) is developed. The QM-CSA protocol represents a universal and
quantitative approach to evaluate and compare the activation-free energies for alkylation reactions
between individual polyphenolic compounds and chemical carcinogens of the epoxy type at physiological conditions by applying two scales: the absolute scale allowing for the comparison with
guanine and the relative scale allowing the comparison with glutathione as a reference compound.
The devised quantum mechanical methodology was validated by comparing the activation-free
energies calculated with 14 DFT functionals in conjunction with two implicit solvation models (SMD
and CPCM) and the experimental activation-free energies for reactions between nine investigated
chemical carcinogens and guanine. According to the obtained results, the best agreement with experimental data was achieved by applying DFT functionals M11-L and MN12-L in conjunction with the
flexible 6-311++G(d,p) basis set and implicit solvation model SMD, and the obtained uncertainties
were proven to be similar to the experimental ones. To demonstrate the applicability of the QM-CSA
protocol, functionals M11-L, and MN12-L in conjunction with the SMD implicit solvation model were
applied to calculate activation-free energies for the reactions of nine investigated chemical carcinogens
of the epoxy type with three catechins, namely EGCG, EGC, and (+)-catechin. The order of CSA in
this series of catechins in comparison to guanine and glutathione was determined as (+)-catechin >
EGC > EGCG. The obtained results, for the first time, demonstrated the evaluation and comparison
of CSA in a series of selected catechins with respect to glutathione and guanine. Moreover, the
presented results provide valuable insights into the reaction mechanisms and configurations of the
corresponding transition states. The novel QM-CSA protocol is also expected to expand the kinetic
data for alkylation reactions between various polyphenolic compounds and chemical carcinogens of
the epoxy type, which is currently lacking in the scientific literature
Ključne besede: activation-free energies, chemical carcinogens, polyphenols, guanine, glutathione, quantum mechanical calculations, M11-L and MN12-L DFT functionals
Objavljeno v DKUM: 04.09.2024; Ogledov: 39; Prenosov: 21
Celotno besedilo (10,13 MB) |
4. Absorpcija rentgenske svetlobe v hidridih elementov skupin 3p in 4pRobert Hauko, 2017, doktorska disertacija Opis: V območju energij roba K smo izmerili fotoabsorpcijske spektre plinastih hidridov elementov skupine 3p (PH3, H2S, HCl). Analizo smo razširili na že prej izmerjene hidride skupine 4p (GeH4, AsH3, H2Se, HBr) ter na žlahtna plina Ar in Kr in spekter SiH4, ki ni v dosegu naših meritev. Oblike robov in ostre strukture tik nad robom zrcalijo eno- in večelektronske prehode na molekulske in modificirane atomske orbitale. V analizo pod-robnih struktur smo vključili tudi objavljene homologne spektre skupine 2p (CH4, NH3, H2O and HF), vključno z žlahtnim plinom Ne, ki imajo robove v področju trde ultravijolične svetlobe. Strukturo roba smo modelirali z linearno kombinacijo resonančnih komponent, ki opisujejo vzbuditve v posamezna vezana stanja in v kontinuum. Relativne energije in verjetnosti posameznih prehodov, ki smo jih izračunali s programsko kodo ORCA, se dobro ujemajo z izmerjenimi vrednostmi. Robovi homolognih spektrov težjih hidridov so si zelo podobni, v vseh simetrija molekule narekuje prehode na najnižje nezasedene orbitale. V zaporedju 2p prevlada močan učinek jedrskega potenciala. Prehodi na višje, kvaziatomske nivoje, so zelo podobni prehodom v prostem atomu. Pri analizi valenčnih sovzbuditev nad absorpcijskim robom smo s postopkom dekonvolucije kompenzirali povečano naravno širino struktur pri skupini 4p. Podobnost oblik ostrih struktur v analognih parih spektrov kaže na enak sklopitveni mehanizem zunanjih elektronskih konfiguracij v obeh zaporedjih spektrov. Pokazali smo, da lahko višjeenergijski del sovzbuditvenega spektra dobro modeliramo s sovzbuditvenima spektroma Ar oz. Kr. Celotni presek za enojno ionizacijo ob prehodu drugega elektrona v vezano stanje kaže v obeh skupinah rahlo upadanje v odvisnosti od naboja centralnega atoma, pri čemer prevladuje prehod valenčnega elektrona na kvaziatomske orbitale. To je v nasprotju z rezultati meritev pri globokih sovzbuditvah, kjer prevladujejo prehodi na molekulske orbitale. Naša spoznanja potrjujejo nekatere novejše meritve v emisijski spektroskopiji. Celotna analiza in dobro ujemanje parametrov, ki smo jih izračunali v dvostopenjskem računu, z izmerjenimi, kaže na to, da lahko tudi valenčne sovzbuditve v molekulah hidridov skupin 3p in 4p dovolj dobro opišemo s približkom nenadnega prehoda: vzbujanju notranjega elektrona sledi relaksacija molekule z otresanjem valenčnega elektrona v višja vezana ali prosta stanja.
Ključne besede: rentgenski absorpcijski spektri, plinasti hidridi, spektri 3p na robu K, spektri 4p na robu K, izračuni DFT, večelektronske vzbuditve, spektri sovzbuditev, otresanje
Objavljeno v DKUM: 25.05.2017; Ogledov: 2177; Prenosov: 192
Celotno besedilo (2,97 MB) |
5. Davek na finančne transakcijeJerneja Čučnik, 2015, diplomsko delo Opis: V diplomskem delu bom bralcu najprej predstavila kronološki pregled razvoja Predloga Direktive Sveta o skupnem sistemu davka na finančne transakcije in spremembi Direktive 2008/7/ES. In sicer bom predstavila vložitev predloga, razprave na uvedbo tega davka v Ekonomsko-socialnem odboru in v Evropskem svetu. Prav tako bom izpostavila ključne časovne točke izoblikovanja predloga obravnavane direktive.
Že v naslednjem poglavju bom bralcu vsebinsko predstavila Predlog direktive Sveta o skupnem sistemu davka na finančne transakcije in spremembi Direktive 2008/7/ES. Bralec se bo seznanil s pravno podlago za sprejem tega predloga, podrobno obrazložitvijo in analizo predloga po posameznih poglavjih. Obravnavala bom vsebino, področje uporabe in opredelitev pojmov, obračunavanje davka, davčno osnovo in stopnje. V nadaljevanju bom predstavila plačilo davka na finančne transakcije, povezane obveznosti ter preprečevanje davčne utaje, izogibanja davkom in zlorabe na področju davkov.
Na koncu diplomskega dela pa bom s pomočjo člankov prikazala še stališča Republike Slovenije o obravnavani temi in razloge za njih.
Ključne besede: davek na finančne transakcije, DFT, robinhoodovski davek, področje in uporaba davka, davčna stopnja, Predlog direktive Sveta o skupnem sistemu davka na finančne transakcije in spremembi Direktive 2008/7/ES
Objavljeno v DKUM: 11.05.2016; Ogledov: 1908; Prenosov: 152
Celotno besedilo (357,10 KB) |
6. Silylation of cellobiose as a model reaction for the synthesis of silylated cellulose : a DFT and PM3 approachStefan Spirk, Heike M. A. Ehmann, Volker Ribitsch, Karin Stana-Kleinschek, 2011, objavljeni znanstveni prispevek na konferenci Opis: The object of the present study is the isodesmic reaction of cellobiose (the repeating unit in cellulose) with different kinds of silanes, R-SiH3, to form silylated cellobiose (Cello-SiH3) and the corresponding alcohols (R-OH). The size and the chemical reactivity of the substituent R is varied as well as the position where O-silylation at the cellobiose takes place. In contrast to experimental observations where the O6 position is favored for silylation, for the computed reactions, energy differences are smaller than 3 kcal/mol for the different positions at the B3LYP/6-311G* as well as at the B3LYP/6-311+G* level of theory. Depending on the silane, reaction energies in a range from -17 kcal/mol (R=NHSiH3) and +18 kcal/mol (R=F) have been calculated. In addition, semi-empirical calculations on the PM3 level of theory have been performed. These results are set into contrast with the results derived from DFT calculations to assess whether semi-empirical methods may be useful for the description of larger systems containing silylated cellobiose units.
Ključne besede: silylation of cellobiose, silanes, DFT, PM3
Objavljeno v DKUM: 01.06.2012; Ogledov: 2480; Prenosov: 76
 Povezava na celotno besedilo |
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8. Nadzor sistema za instrumentalno pristajanje : diplomsko delo strokovnega študijaBojan Dubrovnik, 1999, diplomsko delo Ključne besede: ILS, digitalno procesiranje signalov vzorčenja, sistem za instrumentalno pristajanje, DFT, FFT, diskretna Fourierjeva transformacija, A/D pretvorba, enoploščni PC sistem, SBC, serijski prenos, DDM, monitor, navigacija, nadzorni sistem
Objavljeno v DKUM: 26.07.2007; Ogledov: 2576; Prenosov: 0 |
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