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    EPR study of gamma irradiated 2,5-di-tert-butyl-hydroquinone single crystals
    (PERGAMON-ELSEVIER SCIENCE LTD, 2011) Sayin, U.; Dereli, O.; Turkkan, E.; Yuksel, H.; Birey, M.
    gamma-irradiated single crystals of 2,5-di-tert-butyl-hydroquinone (DTBHQ) were investigated using the electron paramagnetic resonance (EPR) technique. The spectra of the crystals at different orientations in the magnetic field between temperatures of 120 and 450 K, were found to be temperature dependent. Taking into consideration the chemical structure and the experimental spectra of the irradiated single crystals of DTBHQ we assumed that one or more paramagnetic species were produced, each having an unpaired electron delocalized in the phenyl ring. Pursuant to this assumption, four possible radicals were modeled using the B3LYP/6-31+G(d) level of density-functional theory. EPR parameters were calculated for these modeled radicals using the B3LYP method and TZVP basis set. The calculated hyperfine-coupling constants were used as starting points for simulations. The experimental and simulated spectra for each of the three crystallographic axes were well matched for the modeled radical R4; we thus identified the hydroquinone anion radical as a paramagnetic species produced in DTBHQ. The experimental g-factor of the hydroquinone anion radical were found to be anisotropic with the average value g(iso)=2.0096. The hyperfine coupling constants of the H-alpha proton was found anisotropic with the average value (a(H7)(alpha))(iso) = 6.3 G and H-beta proton was found isotropic with the average value (a(H8)(beta))= 3.5 G. (C) 2010 Elsevier Ltd. All rights reserved.
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    EPR study of gamma-irradiated diaminoglyoxime single crystals
    (ELSEVIER SCIENCE BV, 2011) Ates, L.; Dereli, O.; Turkkan, E.; Sayin, U.; Sevgi, F.; Tapramaz, R.; Birey, M.
    Gamma irradiated single crystals of diaminoglyoxime (DAG), were investigated with electron paramagnetic resonance (EPR) spectroscopy at room temperature and at different orientations in the magnetic field. Taking the chemical structure and the experimental spectra of the irradiated DAG single-crystal into consideration we assumed that iminoxy type paramagnetic species were produced where the unpaired electron is delocalized on N atoms. Depending on this assumption, an iminoxy radical was modeled and EPR parameters were calculated using the MP2/6-311++G(d,p)-level of theory and then the calculated hyperfine-coupling constants were used as initial guess for simulations. The experimental and simulated spectra for each of the three crystallographic axes well matched with the modeled radical. We thus identified an iminoxy radical as a paramagnetic species produced in DAG. The experimental g-factor and theoretically calculated hyperfine coupling constants of this radical were found to be anisotropic, with the average values g(iso) = 2.0150, a(N(4)) = -2.71 mT, a(N(3)) = 1.46 mT, a(N(9)) = 0.29 mT, a(N(12)) = 0.51 mT, a(H(10)) = -0.53 mT, a(H(11)) = -0.55 mT, a(H(13)) = -0.36 mT and a(H(14)) = -0.42 mT, respectively. (C) 2011 Elsevier B.V. All rights reserved.
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    EPR Study of Gamma-Irradiated Single Crystal 4-Phenylsemicarbazide
    (Pergamon-Elsevier Science Ltd, 2010) Sayın, U.; Türkkan, E.; Dereli, Ö.; Yüksel, H.; Birey, M.
    Single crystals of 4-phenylsemicarbazide (4PSC) were investigated using an electron paramagnetic resonance (EPR) technique, with gamma irradiation of the crystals at different orientations in the magnetic field between temperatures of 120 and 450 K, and the spectra were found to be temperature independent. Taking into consideration the chemical structure and the experimental spectra of the irradiated single crystal 4PSC, we assumed that one or more paramagnetic species were produced, each having an unpaired electron delocalized in the phenyl ring. Pursuant to this assumption, six possible radicals were modeled using the B3LYP/6-311+G(d) level of density-functional theory. EPR parameters were calculated for these modeled radicals using the B3LYP method and TZVP basis set. The calculated hyperfine coupling constants were used as starting points for simulations. The experimental and simulated spectra for each of the three crystallographic axes were well matched for the modeled radical R6. We thus identified the R6 (C6H5NH) radical as a paramagnetic species produced in 4PSC. The experimental g-factor and hyperfine coupling constants of the C6H5NH radical were found to be anisotropic, with the average values g = 2.00431, a(NH)(N(8)) = 8.85 G, a(NH)(H(9)) = 16.85 G, a(o,p)(H(14,16,20)) = 6.47 G, and a(m)(H(18,19)) = 2.80 G.
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    In Vitro Analysis of AHPlus and MM-Seal by ESR and Thermoanalytical Methods
    (POLISH ACAD SCIENCES INST PHYSICS, 2015) Ceylan, Y.; Usta, A.; Usta, K.; Cobankara, F. Kont; Yildirim, C.; Birey, M.
    The free radicals and their concentration in resin materials may impact biocompatibility and polymerization properties of dental materials. The aim of this study was to determine whether there are free radicals and to obtain useful information about thermal stability of materials using electron spin resonance (ESR) spectroscopy, TGA (Thermogravimetry Analysis) and DTA (Differential Thermal Analysis) methods. Epoxy resin-based sealers AHPlus and MM-Seal samples, freshly mixed and set, were prepared to be analysed with ESR and thermal methods. The free radicals were found in dental materials. As radical concentration in AHPlus have changed very slowly, the concentration in MM-Seal have decreased dramatically. Also, MM-Seal was found to decompose in three steps with the increasing temperature, while decomposition of the AHPlus occurred in two steps.