Localization of radiation damages in X-rays irradiated cis-syn-cis-dicyclohexano-18-crown-6 and its inclusion complex with BaCl2

Abstract

For the first time, structures of radical intermediates generated upon low temperature (77K) X-rays radiolysis of “free” dicyclohexano-18-crown-6 (cis-syn-cis-isomer, DCH18C6) and its inclusion complex with barium chloride (DCH18C6·BaCl2) were identified using EPR spectroscopy. A set of radicals originated from polyether and cyclohexyl rings was detected in DCH18C6·BaCl2 complex and “free” crown ether DCH18C6 irradiated at 77K. Cyclohexyl, macrocyclic OCHCH2 and acyclic CHC(H)O radicals were suggested to be formed at early stages of radiolysis in both investigated compounds, and the fraction of macrocyclic OCHCH2 radicals was predominant immediately after irradiation at 77K. Additionally, an effect of barium cation on post-radiation reactions of the radicals in irradiated DCH18C6·BaCl2 complex upon its subsequent thermal annealing at temperature above 333K was found. In particular, the analysis of EPR spectrum of the irradiated complex annealed at 333–413K implied a presence of signal from acyclic cyclohexanonyl radicals, which may presumably resulted from rearrangement of cyclic α-alkoxycyclohexyl radical precursors. This post-radiation reaction may contribute to accumulation of acyclic radiolytic products in the irradiated complex when comparing with radiolysis of free DCH18C6. The results obtained are essential for understanding the peculiarities of radiation resistance of extraction and sorption systems based on the crown ether under real conditions of radioactive waste reprocessing.