Ercan Türkkan

Density functional theory – electron paramagnetic resonance study of gamma-irradiated single crystal of amphi-chloroglyoxime

The density functional theory was studied to examine the suggested type of model radicals RI, RII and RIII that have been formed upon gamma-irradiation of single crystals of amphi-chloroglyoxime (ACG). RI, RII and RIII type model radicals were obtained by abstraction of Cl and H atoms from ACG. The possible conformations of these model radicals were obtained using the semi-empirical Austin Model 1 method. Subsequently, hyperfine coupling constants and atomic spin density calculations of these conformations were performed using the Becke-3-Lee-Yang-Parr functional in combination with a split-valence Gaussian basis set. Theoretically calculated values were compared with the experimental values. Calculated isotropic and anisotropic hyperfine coupling constant values of conformations of model radical RII were in good agreement with experimental values. However, the agreement was rather poor in the case of the model radicals RI and RIII. Thus, the findings from the present study clearly suggest that the experimentally observed radical should be the model radical RII.

Experimental and Theoretical Electron Paramagnetic Resonance (EPR) Study on the Temperature-Dependent Structural Changes of Methylsulfanylmethane

Methylsulfonylmethane (or dimethyl sulfone), a naturally produced and vitally important organosulfur compound in living organisms, was irradiated with gamma rays, and the produced radicals were investigated using electron paramagnetic resonance spectroscopy at different temperatures. The structure and behavior of the radical changed when the temperatures varied. The hyperfine splitting of the CH3 group was small, and the 33S splitting was relatively high between 80 and −50 °C. When the temperature was between −50 and −160 °C, the 33S splitting became small and the CH3 splitting was higher. However, the group kept rotating; therefore, only the isotropic splitting values were measured, and the g-values were anisotropic. When the temperature decreased below −180 °C, the CH3 group stopped rotating, and the hydrogen splitting values became nonequivalent due to an inhomogeneous electron distribution. The observed structures can be explained by referring to both the experimental and theoretically calculated values reported.

EPR study of a gamma-irradiated (2-hydroxyethyl)triphenylphosphonium chloride single crystal

In this study, gamma-irradiated single crystals of (2-hydroxyethyl)triphenylphosphonium chloride [CH2CH2OH P(C6H5)3Cl] were investigated with electron paramagnetic resonance (EPR) spectroscopy at room temperature for different orientations in the magnetic field. The single crystals were irradiated with a 60Co-γ-ray source at 0.818 kGy/h for about 36 h. Taking the chemical structure and the experimental spectra of the irradiated single crystal of the title compound into consideration, a paramagnetic species was produced with the unpaired electron delocalized around 31P and several 1H nuclei. The anisotropic hyperfine values due to the 31P nucleus, slightly anisotropic hyperfine values due to the 1H nuclei and the g-tensor of the radical were measured from the spectra. Depending on the molecular structure and measured parameters, three possible radicals were modeled using the B3LYP/6-31+G(d) level of density-functional theory, and EPR parameters were calculated for modeled radicals using the B3LYP/TZVP method/basis set combination. The calculated hyperfine coupling constants were found to be in good agreement with the observed EPR parameters. The experimental and theoretically simulated spectra for each of the three crystallographic axes were well matched with one of the modeled radicals (discussed in the text). We thus identified the radical C˙H2CH2 P(C 6H5)3 Cl as a paramagnetic species produced in a single crystal of the title compound in two magnetically distinct sites. The experimental g-factor and hyperfine coupling constants of the radical were found to be anisotropic, with the isotropic values g iso = 2.0032, G, G, G and G for site 1 and g iso=2.0031, G, G G and G for site 2.

Molecular structure and vibrational spectra of alpha-benzoinoxime by density functional method

In the present study, an exhaustive conformational search of the Alpha-benzoinoxime has been performed. The FT-IR spectrum of this compound was recorded in the region 4000–400 cm−1. The FT-Raman spectrum was also recorded in the region 3500–50 cm−1. Vibrational frequences of the title compound were calculated by B3LYP method using 6–311++G(d, p) basis set. The calculated vibrational frequences were analysed and compared with experimental results.

An electron paramagnetic resonance and density-functional theory study on the methyl isotropic hyperfine coupling constants in gamma-irradiated 2,6-di-tert-butyl-4-methylphenol

Single crystal of gammairradiated 2,6-di-tert-butyl-4-methylphenol (BHT) was investigated using an electron paramagnetic resonance (EPR) technique at different orientations in the magnetic field at room temperatures. Taking into consideration the chemical structure and the experimental spectra of the irradiated single crystal of BHT, we assumed that one phenoxyltype paramagnetic species was produced having an unpaired electron localized at the methyl fragment side of the phenyl ring. Depending on this assumption, one possible radical was modeled using the B3LYP/6-311+G(d) level of density-functional theory. EPR parameters were calculated for these modeled radical using the B3LYP/TZVP and B3LYP/EPR-III level. The averaged value of isotropic hydrogen hyperfine coupling constants of rotating methyl functional group of phenoxyl radical is calculated for the first time. Theoretically calculated values of the modeled radical are in reasonably good agreement with the experimental data determined from the spectra (differences in averaged coupling constant values smaller than 5%, and differences in isotropic g values fall into 1 ppt).

Theoretical EPR study of 6-Mercaptopurine

6-Mercaptopurine is important antineoplastics agent and it is used for immuno – suppressive and anti – inflammatory. Experimental EPR parameters of 6-Mercaptopurine molecules powder were studied in the literature. The aim of this study EPR parameters of 6 – Mercaptopurine molecules were calculated with theoretical calculations and define the possible radicals of 6 – Mercaptopurine molecules. Firstly the X-ray structure of 6-Mercaptopurine molecules were found in the literature (1). EPR parameters and possible radicals of 6 – Mercaptopurine molecules were calculated from this X-ray structure. Possible radicals of gamma-irradiated 6-Mercaptopurine molecules were constituted. EPR parameters of possible radicals were calculated with B3LYP/6-311++ G (d,p) basis set in DFT methods for 6 – Mercaptopurine molecules.

EPR study of gamma-irradiated 2-Bromo-4′-methoxyacetophenone single crystals

ABSTRACT The gamma-irradiated single crystals of 2-Bromo-4′-methoxyaceto-phenone (2B4MA) were investigated using electron paramagnetic resonance (EPR) technique. Density-functional theory calculations were employed to investigate and identify the radicals that have been assumed to be formed upon irradiation of 2B4MA single crystals. The EPR spectra of 2B4MA were recorded at different orientations in the magnetic field at room temperature. Taking into account the chemical structure and experimental spectra of irradiated single crystal of 2B4MA, it was assumed that at least two different radicals were produced in the sample. Following this assumption, six possible radicals were modeled and EPR parameters were calculated by using the DFT, B3LYP/6-311+G(d), for the modeled radicals individually. The calculated hyperfine coupling constants and g-tensors were used as initial values for simulation studies. The three crystallographic axes on the simulated spectra were well matched with experimental spectra for the two modeled radicals. Thus, we identified the R1 type radical and R4 type radical as paramagnetic species produced in gamma-irradiated 2B4MA.

(2-Hy-droxy-eth-yl)triphenyl-phospho-nium chloride.

In the crystal structure of the title compound, C20H20OP+·Cl−, the cations and anions are linked by intermolecular C—H⋯Cl and O—H⋯Cl hydrogen bonds into chains running parallel to the b axis. In the cation, the hydroxyethyl group is disordered over two orientations with site-occupancy factors of 0.554 (4) and 0.446 (4).