Impact of disorder on formation of free radicals by gamma-irradiation: Multi-frequency EPR studies of trehalose polymorphs

Šaric, Iva; Jurec, Jurica; Reijerse, Edward; Maltar-Strmečki, Nadica; Rakvin, Boris; Kveder, Marina (2018) Impact of disorder on formation of free radicals by gamma-irradiation: Multi-frequency EPR studies of trehalose polymorphs. Journal of Physics and Chemistry of Solids, 123 . pp. 124-132. ISSN 0022-3697

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Abstract

Electron paramagnetic resonance (EPR) studies of the radiation-induced radicals in two anhydrous trehalose polymorphs, beta- crystalline (TREc) and glassy (TREg), were conducted with the aim to resolve whether different types of free radicals are induced in a differently disordered environment. A multifrequency approach (9.5 GHz, 94 GHz, and 244 GHz) was applied to improve the resolution of the complex EPR spectra. In addition, the thermal stability of the EPR spectra and the respective decay kinetics were analyzed in a series of thermal annealing studies in the temperature interval from 333 K to 363 K. It was found that in the crystalline matrix the transformation process of the induced radicals is more complex than in the glassy host matrix. Qualitative decomposition of the experimental spectra, assuming four contributing species, reproduced characteristic EPR spectral features in both matrices. These were interpreted as carbon-centered radicals while the possibility of the formation of alkoxy radicals due to the abstraction of a hydrogen atom could be ruled out. Only in one case, the tentative assignment of the EPR spectral components revealed the formation of the same radical species in both TREc and TREg. Furthermore, by thermal annealing TREg lost one of the radical species, whereas in TREc all 4 radical species pertained irrespective of the treatment. The results presented here, therefore, provide experimental evidence that the extent of disorder present in the material strongly affects the type and stability of radicals induced by ionizing radiation.

Item Type:

Article

Additional Information:

The authors highly acknowledge the financial support from the Alexander von Humboldt Foundation. The presented study is a result of the Research Group Linkage Program entitled the study of soft condensed matter by EPR: dynamics in glassy and crystalline matrices. Furthermore, the authors would like to thank Prof. Wolfgang Lubitz (MPI-CEC) for his continuous support for this project. Gudrun Klihm is gratefully acknowledged for her invaluable technical assistance with the high field EPR experiments. The authors thank Dr. Milan Jokic for providing glassy samples, and Dr. Mile Ivanda and Dr. Davor Ristic for the help to acquire the Raman spectra. Additionally, the Croatian Science Foundation under the project number 1108 supported this work.

Uncontrolled Keywords:

Trehalose ; Irradiation ; Multi-frequency EPR ; Glassy state

Subjects:

NATURAL SCIENCES > Physics
NATURAL SCIENCES > Physics > Condensed Matter Physics

Divisions:

Division of Physical Chemistry

Projects: