Radiation Products at
77 K in Trehalose
Single Crystals: EMR and DFT Analysis
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Abstract
The radicals obtained in trehalose dihydrate single crystals
after
77 K X-irradiation have been investigated at the same temperature
using X-band electron paramagnetic resonance (EPR), electron nuclear
double resonance (ENDOR), and ENDOR-induced EPR (EIE) techniques.
Five proton hyperfine coupling tensors were unambiguously determined
from the ENDOR measurements and assigned to three carbon-centered
radical species (T1, T1*, and T2) based on the EIE spectra. EPR angular
variations revealed the presence of four additional alkoxy radical
species (T3 to T6) and allowed determination of their g tensors. Using
periodic density functional theory (DFT) calculations, T1/T1*, T2,
and T3 were identified as H-loss species centered at C4, C1′,
and O2′, respectively. The T4 radical is proposed to have the
unpaired electron at O4, but considerable discrepancies between experimental
and calculated HFC values indicate it is not simply the (net) H-loss
species. No suitable models were found for T5 and T6. These exhibit
a markedly larger g anisotropy than T3 and T4, which were not reproduced
by any of our DFT calculations