Radiation chemistry of solid-state carbohydrates using EMR

We review our research of the past decade towards identification of radiation-induced radicals in solid state sugars and sugar phosphates. Detailed models of the radical structures are obtained by combining EPR and ENDOR experiments with DFT calculations of g and proton HF tensors, with agreement in their anisotropy serving as most important criterion. Symmetry-related and Schonland ambiguities, which may hamper such identification, are reviewed. Thermally induced transformations of initial radiation damage into more stable radicals can also be monitored in the EPR (and ENDOR) experiments and in principle provide information on stable radical formation mechanisms. Thermal annealing experi-ments reveal, however, that radical recombination and/or diamagnetic radiation damage is also quite important. Analysis strategies are illustrated with research on sucrose. Results on dipotassium glucose-1-phosphate and trehalose dihydrate, fructose and sorbose are also briefly discussed. Our study demonstrates that radiation damage is strongly regio-selective and that certain general principles govern the stable radical formation

The 4th international comparison on EPR dosimetry with tooth enamel Part 1: Report on the results

This paper presents the results of the 4th International Comparison of in vitro electron paramagnetic resonance dosimetry with tooth enamel, where the performance parameters of tooth enamel dosimetry methods were compared among sixteen laboratories from all over the world. The participating laboratories were asked to determine a calibration curve with a set of tooth enamel powder samples provided by the organizers. Nine molar teeth extracted following medical indication from German donors and collected between 1997 and 2007 were prepared and irradiated at the Helmholtz Zentrum München. Five out of six samples were irradiated at 0.1, 0.2, 0.5, 1.0 and 1.5 Gy air kerma; and one unirradiated sample was kept as control. The doses delivered to the individual samples were unknown to the participants, who were asked to measure each sample nine times, and to report the EPR signal response, the mass of aliquots measured, and the parameters of EPR signal acquisition and signal evaluation. Critical dose and detection limit were calculated by the organizers on the basis of the calibration-curve parameters obtained at every laboratory. For calibration curves obtained by measuring every calibration sample three times, the mean value of the detection limit was 205 mGy, ranging from 56 to 649 mGy. The participants were also invited to provide the signal response and the nominal dose of their current dose calibration curve (wherever available), the critical dose and detection limit of which were also calculated by the organizers

Uncovering Radiation Chemistry in the Solid State Through Periodic Density-Functional Calculations: Confrontation with Experimental Results and Beyond

Three questions are crucial to unravel the radiation chemistry of any solid-state molecular system: what is the structure of the radicals formed, how are they formed and why? Molecular modeling methods based on Density Functional Theory – in confrontation with experimental Electron Paramagnetic Resonance (EPR) results – can help in finding an answer to all three questions. In this contri-bution, one view on how to perform such computational research is presented, with emphasis on the application of a periodic approach to biomolecules such as amino acids and carbohydrates. General strategies are outlined and common pit-falls are indicated. Topics include: effect of level of theory, model space and tem-perature on calculated EPR properties, formation mechanisms of radiation-induced radicals, and reaction path simulations for radiochemical transformations. In three case studies, these principles are applied to several radiation-induced radi-cals of sucrose