Proton Transfer Behavior in Irradiated Adenine Derivatives: ESR and
ENDOR Study of X-ray Irradiated Arabinofuranosyl Adenine Single Crystals
Jun Seog Kang
Department of Physics and Astronomy, GSU
Abstract
ESR and ENDOR were used to study free radicals produced in single crystals
of 9-b-D arabinofuranosyl adenine (ara-A) by X-irradiation and observation
at 10K. The ara-A is an isomer of adenosine differing only in the sugar
group. Previously, adenosine [Close et al., Radiat. Res. 117, 367-378
(1989)] and deoxyadenosine [Nelson et al. Radiat. Res. 149,75-86
(1998)], which have similar hydrogen-bonding environment to ara-A, were
studied, and radical R2 (the adenine anion protonated at N3) and radical
R1 (the adenine cation deprotonated at the amino) were reported. Based
on these observations, the previous work proposed a model for radical stabilization
based on the possibility of proton transfers within the hydrogen bonding
networks in the crystals.
In this work, Radical R2 was identified and its magnetic properties
were characterized. However, the experiment found no evidence for the amino-deprotonated
structure R1. Based on this evidence, that the R1 structure was not stabilized
in ara-A, a refinement to the previous proton transfer model is proposed.