PARENT SESSION
1:30 PM to 3:30 PM
Wednesday, April 24, 2002
Poster Session 29 Radiation Chemistry
Room: Nevada Exhibition Center
(P34-338) Proton transfer behavior in adenine derivatives: Study of 9-
-D-arabinofuranosyl adenine crystals x-irradiated at 10K.
Kang, Junseog1, Nelson, William*,1, 1 Department of Physics and Astronomy, Atlanta, Georgia
ABSTRACT-
Previous study of several adenine derivatives showed clear evidence that the immediate hydrogen-bonding environment either enabled or prohibited stabilization of adenine radicals produced by electron loss (oxidation). In 9--D-arabinofuranosyl adenine (ara-A) the hydrogen bonding arrangement is similar to those in adenosine (AR) and (anhydrous) deoxyadenosine (AdRa) crystals. Specifically, in AR and AdRa, an amino proton of one molecule hydrogen bonds to O5' of the sugar in a second molecule, and HO5' of the sugar hydrogen bonds to N1 of the adenine in a third molecule. This arrangement appears to enable radical stabilization by allowing spin and charge separation in a two-proton transfer process following electron loss: the amino proton transfers to O5' of the sugar, and the original HO5' transfers to N1 of the third adenine. In ara-A, an amino proton of one molecule hydrogen bonds to O3' of the sugar in a second molecule, and HO3' of the sugar hydrogen bonds to N7 of the adenine in a third molecule. However, radical products of adenine oxidation were not stabilized in ara-A. We interpret this result to indicate critical importance of the relative proton-accepting properties of specific molecular sites in the adenine base since it is well-known that neutral adenine bases in acidic solution protonate much more readily at N1 than at N7. In contrast to the oxidation behavior, electron-gain (reduction) radicals were stabilized in ara-A by protonation at nitrogen (the N3 position). This behavior of ara-A is like that found for electron-gain radicals from essentially all other adenine derivatives studied as crystals. This work was supported by the Research Program Enhancement fund of Georgia State University and by PHS grant CA36810.
KEYWORDS: Proton Transfer, Adenine Oxidation/reduction, Charge Transfer, Radical Stabilization