Multi-frequency EPR study of radiation-induced radicals in tooth enamel

Human tooth enamel powders, unheated as well as heated prior to X -irradiation at room temperature, have been investigated by means of Q - and W -band Electron Paramagnetic Resonance (EPR). Upon irradiation of enamel, carbonate-derived radicals are generated. The simplest acquired EPR spectra in this study consist mainly of a group of three different \hbox{CO}_3^{3-} signals, with a very weak \hbox{CO}_2^{-} contribution. The characterisation of the paramagnetic species in enamel is quite important for the reliability of EPR applications ( e.g. , EPR retrospective dosimetry). The spectra from the heated samples reveal a striking resemblance with spectra from certain irradiated synthetic apatite powders. The spin Hamiltonian parameters obtained from the computer simulations of the Q - and W -band spectra are compared with those reported in the literature.     

Radiation-induced radicals in glucose-1-phosphate. I. Electron paramagnetic resonance and electron nuclear double resonance analysis of in situ X-irradiated single crystals at 77 K

Electron magnetic resonance analysis of radiation-induced defects in dipotassium glucose-1-phosphate dihydrate single crystals in situ X-irradiated and measured at 77 K shows that at least seven different carbon-centered radical species are trapped. Four of these (R1-R4) can be fully or partly characterized in terms of proton hyperfine coupling tensors. The dominant radical (R2) is identified as a C1-centered species, assumedly formed by a scission of the sugar-phosphate junction and the concerted formation of a carbonyl group at the neighboring C2 carbon. This structure is chemically identical to a radical recently identified in irradiated sucrose single crystals. Radical species R1 and R4 most likely are C3- and C6-centered species, respectively, both formed by a net hydrogen abstraction. R3 is suggested to be chemically similar to but geometrically different from R4. Knowledge of the identity of the sugar radicals present at 77 K provides a first step in elucidating the formation mechanism of the phosphoryl radicals previously detected after X-irradiation at 280 K. In paper II, the chemical identity, precise conformation, and possible formation mechanisms of these radical species are investigated by means of DFT calculations and elementary insight into the radiation chemistry of sugar and sugar derivatives is obtained.     

Age-Related Carbonylation of Fibrocartilage Structural Proteins Drives Tissue Degenerative Modification

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Radiation-induced radicals in glucose-1-phosphate. II. DFT analysis of structures and possible formation mechanisms

Four radiation-induced carbon-centered radicals in dipotassium glucose-1-phosphate dihydrate single crystals are examined with DFT methods, consistently relying on a periodic computational scheme. Starting from a set of plausible radical models, EPR hyperfine coupling tensors are calculated for optimized structures and compared with data obtained from EPR/ENDOR measurements, which are described in part I of this work. In this way, an independent structural identification is made of all the radicals that were observed in the experiments (R1-R4) and tentative reaction schemes are proposed. Also, the first strong evidence for conformational freedom in sugar radicals is established: two species are found to have the same chemical composition but different conformations and consequently different hyperfine coupling tensors. Analysis of the calculated energies for all model compounds suggests that the radiation chemistry of sugars, in general, is kinetically and not necessarily thermodynamically controlled.     

Applied radiation research around a 15 MeV high-average-power linac

The Department of Subatomic and Radiation Physics of the University Gent is equipped with a 15 MeV 20 kW linear electron accelerator (linac) facility. In its present configuration the accelerator is used as a multipurpose apparatus for research in the fields of polymer chemistry, biomedical materials, medicine, food technology, dosimetry, solid state physics, agriculture and nuclear and radiation physics. We present an overview of both the various research projects around our linac facility involving radiation chemistry and physics and the specialised technologies facilitating this research.     

Palladium‐Catalyzed Carbonylative α‐Arylation to β‐Ketonitriles

A carbonylative α‐arylation process employing unactivated nitriles for the first time is described. The reaction tolerates a range of (hetero)aryl iodides and several nitrile coupling partners. No prefunctionalization of the nitriles is necessary and the resulting β‐ketonitriles are obtained in good to excellent yields. The methodology also allows for a convenient ¹³C‐labelling of the generated carbonyl moiety.     

Electron magnetic resonance and density functional theory study of room temperature X-irradiated β-D-fructose single crystals

Stable free radical formation in fructose single crystals X-irradiated at room temperature was investigated using Q-band electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and ENDOR induced EPR (EIE) techniques. ENDOR angular variations in the three main crystallographic planes allowed an unambiguous determination of 12 proton HFC tensors. From the EIE studies, these hyperfine interactions were assigned to six different radical species, labeled F1-F6. Two of the radicals (F1 and F2) were studied previously by Vanhaelewyn et al. [Vanhaelewyn, G. C. A. M.; Pauwels, E.; Callens, F. J.; Waroquier, M.; Sagstuen, E.; Matthys, P. J. Phys. Chem. A 2006, 110, 2147.] and Tarpan et al. [Tarpan, M. A.; Vrielinck, H.; De Cooman, H.; Callens, F. J. J. Phys. Chem. A 2009, 113, 7994.]. The other four radicals are reported here for the first time and periodic density functional theory (DFT) calculations were used to aid their structural identification. For the radical F3 a C3 carbon centered radical with a carbonyl group at the C4 position is proposed. The close similarity in HFC tensors suggests that F4 and F5 originate from the same type of radical stabilized in two slightly different conformations. For these radicals a C2 carbon centered radical model with a carbonyl group situated at the C3 position is proposed. A rather exotic C2 centered radical model is proposed for F6.