Use of the Spin-Trapping Method for the Study of Stable Radicals Produced in Solid Dihydrothymine

ESR spin-trapping method has been used for the study of radiation-induced radicals in· powdered dihydrothymine. Four approximately equal small proton couplings (AH\u27 = 0.35 mT), a larger proton coupling (AH = 0.195 mT) and a nitrogen coupling (AN = = 0.295 mT) are attributed to the nitroxide radical formed by reaction of the spin trap with 6-dihydrothymyl radical upon dissolving of dihydrothymine. In the pyrimidine bases of nucleic acid and a number of related compounds irradiated in solid state and dissolved, no signs of the trapped radicals were observed

Slabo izražene pojave u epr spektru paramagnetičnog centra sličnog šupljini u citozin hidrokloridu

The fine phenomena in the EPR spectra of the hole-like paramagnetic centre formed in cytosine(thiocytosine)-HCl crystals upon irradiation are studied with EPR spectroscopy. The spin Hamiltonian including the electronic Zeeman term, hyperfine coupling, quadrupole coupling and the nuclear Zeeman term has been used in the second-order perturbation treatment for the interpretation of the experimental observations. It is shown that the quadrupolar term causes a detectable shift of the EPR lines and also induces the "forbidden\u27\u27 transitions. From the shift of the "allowed\u27\u27 transitions and the positions of the ``forbidden\u27\u27 transitions, the chlorine quadrupolar coupling tensor [P], has been determined.Proučavane su slabo izražene, neredovite pojave u EPR spektrima paramagnetičnog centra sličnog šupljini u ozračenim kristalima citozin hidroklorida s primjesama tiocitozina. Za objašnjenje ponašanja upotrijebljen je spinski Hamiltonijan koji se sastoji od elektronskog Zeemanovog člana, nuklearnog Zeemanovog člana, člana hiperfine i člana kvadrupolne sprege jezgre s elektronom. Pokazano je da kvadrupolni član koji potječe od klora ne samo unosi pomak EPR spektralnih linija, nego uzrokuje i pojavu dodatnih, “zabranjenih” prijelaza. Iz mjerenja slabo izraženih pomaka linija i položaja “zabranjenih” linija izračunat je kvadrupolni tenzor

Oxidation-induced Spin Probes in Low-density Lipoproteins

PBN trapping indicated the presence of at least two types of radicals induced in LDL upon slow oxidation, as observed with EPR spectroscopy. The EPR spectra are very similar to those of the spin probes or spin labels, which are routinely used in the studies of macromolecular systems and supramolecular assemblies. The parameters of the spectral line shapes, treated in two different theoretical models, did not provide conclusive evidence for the phase transition in the LDL particles, known to be present at about 25 °C. It is concluded that both types of trapped radicals, or at least one of them, are associated with the apolipoproteins, with the spin probe sticking into the lipid domain of phospholipids

Slabo izražene pojave u epr spektru paramagnetičnog centra sličnog šupljini u citozin hidrokloridu

The fine phenomena in the EPR spectra of the hole-like paramagnetic centre formed in cytosine(thiocytosine)-HCl crystals upon irradiation are studied with EPR spectroscopy. The spin Hamiltonian including the electronic Zeeman term, hyperfine coupling, quadrupole coupling and the nuclear Zeeman term has been used in the second-order perturbation treatment for the interpretation of the experimental observations. It is shown that the quadrupolar term causes a detectable shift of the EPR lines and also induces the "forbidden\u27\u27 transitions. From the shift of the "allowed\u27\u27 transitions and the positions of the ``forbidden\u27\u27 transitions, the chlorine quadrupolar coupling tensor [P], has been determined.Proučavane su slabo izražene, neredovite pojave u EPR spektrima paramagnetičnog centra sličnog šupljini u ozračenim kristalima citozin hidroklorida s primjesama tiocitozina. Za objašnjenje ponašanja upotrijebljen je spinski Hamiltonijan koji se sastoji od elektronskog Zeemanovog člana, nuklearnog Zeemanovog člana, člana hiperfine i člana kvadrupolne sprege jezgre s elektronom. Pokazano je da kvadrupolni član koji potječe od klora ne samo unosi pomak EPR spektralnih linija, nego uzrokuje i pojavu dodatnih, “zabranjenih” prijelaza. Iz mjerenja slabo izraženih pomaka linija i položaja “zabranjenih” linija izračunat je kvadrupolni tenzor

ERP spektroskopija suprahiperfinog međudjelovanja bakarnog paramagnetskog centra u kristalima citozin monohidrata

The planar complex of Cu(II) with two cytosine bases was formed by gamma irradiation of the cytosine monohydrate crystal, containing copper impurities. The paramagnetic complex was probably formed by trapping the radiation-induced migrating holes by Cu(I), that is originally present in the crystal lattice. The structure of the complex was analyzed from the superhyperfine pattern of its EPR spectra. The experimentally evaluated tensor elements of the three 14N couplings and the observation of an additional proton coupling unequivocally confirm the structure. The ab initio B3LYP density functional method calculations are in good agreement with the experiments. Both experiments and the calculations demonstrate large spin delocalization in the cytosine ring plane.Gama ozračivanjem kristala citozin monohidrata, koji je sadržavao bakarne nečistoće, pripremali smo planarni kompleks Cu(II) s dvije citozinske baze. Paramagnetski se kompleks vjerojatno stvarao vezanjem zračenjem proizvedenih šupljina i Cu(I) koji je prvotno bio u kristalnoj rešetci. Proučavali smo strukturu kompleksa analizirajući suprahiperfinu strukturu njegovog EPR spektra. Eksperimentalno određeni elementi tenzora triju vezanja 14N i opažanje dodatnog protonskog vezanja pouzdano potvrđuju strukturu. Ab initio B3LYP računi metodom funkcionala gustoće u dobrom su slaganju s mjerenjima. Eksperimenti i računi pokazuju jaku delokalizaciju spina u ravnini citozinskog prstena

ERP spektroskopija suprahiperfinog međudjelovanja bakarnog paramagnetskog centra u kristalima citozin monohidrata

The planar complex of Cu(II) with two cytosine bases was formed by gamma irradiation of the cytosine monohydrate crystal, containing copper impurities. The paramagnetic complex was probably formed by trapping the radiation-induced migrating holes by Cu(I), that is originally present in the crystal lattice. The structure of the complex was analyzed from the superhyperfine pattern of its EPR spectra. The experimentally evaluated tensor elements of the three 14N couplings and the observation of an additional proton coupling unequivocally confirm the structure. The ab initio B3LYP density functional method calculations are in good agreement with the experiments. Both experiments and the calculations demonstrate large spin delocalization in the cytosine ring plane.Gama ozračivanjem kristala citozin monohidrata, koji je sadržavao bakarne nečistoće, pripremali smo planarni kompleks Cu(II) s dvije citozinske baze. Paramagnetski se kompleks vjerojatno stvarao vezanjem zračenjem proizvedenih šupljina i Cu(I) koji je prvotno bio u kristalnoj rešetci. Proučavali smo strukturu kompleksa analizirajući suprahiperfinu strukturu njegovog EPR spektra. Eksperimentalno određeni elementi tenzora triju vezanja 14N i opažanje dodatnog protonskog vezanja pouzdano potvrđuju strukturu. Ab initio B3LYP računi metodom funkcionala gustoće u dobrom su slaganju s mjerenjima. Eksperimenti i računi pokazuju jaku delokalizaciju spina u ravnini citozinskog prstena

The mathematical simulation of the temperature fields of building envelopes under permanent frozen soil conditions

The physical-mathematical model of the thermal state of the aired technical underground taking into account the air exchange and design features of construction under permanent frozen soil conditions has been suggested. The computational scheme of the temperature fields prediction of building envelopes of projected buildings and soil under and nearby buildings has been developed. The numerical simulation of the temperature fields of building envelopes changes was conducted during a year. The results of the numerical simulation showed that the heat coming from the technical undergrounds and through the walls does not influence the temperature field of the soil neither under a building nor at a distance from it

Communication research between working capacity of hardalloy cutting tools and fractal dimension of their wear

The results of communication research between the wear resistance of the Kapplicability hard-alloy cutting tools and the fractal dimension of the wear surface,which is formed on a back side of the cutting edge when processing the materialsshowing high adhesive activity are presented in the paper. It has been established thatthe wear resistance of tested cutting tools samples increases according to a fractaldimension increase of their wear surface

Performances and stability of a 2.4 ton Gd organic liquid scintillator target for antineutrino detection

In this work we report the performances and the chemical and physical properties of a (2 x 1.2) ton organic liquid scintillator target doped with Gd up to ~0.1%, and the results of a 2 year long stability survey. In particular we have monitored the amount of both Gd and primary fluor actually in solution, the optical and fluorescent properties of the Gd-doped liquid scintillator (GdLS) and its performances as a neutron detector, namely neutron capture efficiency and average capture time. The experimental survey is ongoing, the target being continuously monitored. After two years from the doping time the performances of the Gd-doped liquid scintillator do not show any hint of degradation and instability; this conclusion comes both from the laboratory measurements and from the "in-tank" measurements. This is the largest stable Gd-doped organic liquid scintillator target ever produced and continuously operated for a long period