Sunghwan Kim - Structures and energetics of the deprotonated adenine-uracil base pair, including proton-transferred systems

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  Publication Details (including relevant citation   information):

  S. Kim, M.C.   Lind, and H.F. Schaefer;

  Journal of Physical Chemistry B, 2008,   112, 3545.



  The B3LYP/DZP++ level of theory has been employed to investigate   the structures and energetics of the deprotonated adenine-uracil   base pairs, (AU-H)-. Formation of the lowest-energy structure,   [A(N9)-U] - (which corresponds to deprotonation at the N9 atom of   adenine), through electron attachment to the corresponding   neutral is accompanied by proton transfer from the uracil N3 atom   to the adenine N1 atom. The driving force for this proton   transfer is a significant stabilization from the base pairing in   the proton transferred form. Such proton transfer upon electron   attachment is also observed for the [A(N6b)-U]- and [A(C2)-U] -   anions. Electron attachment to the A-U(N3) radical causes strong   lone pair repulsion between the adenine N1 and the uracil N3   atoms, driving the two bases apart. Similarly, lone pair   repulsion in the anion A(N6a)-U causes the loss of coplanarity of   the two base units. The computed adiabatic electron attachment   energies for nine AU-H radicals range from 1.86 to 3.75 eV,   implying that the corresponding (AU-H)- anions are strongly   bound. Because of the large AEAs of the (AU-H) radicals, the C-H   and N-H bond dissociation in the AU- base pair anions requires   less energy than the neutral AU base pair. The computed C-H and   N-H bond dissociation energies for the AU- anion (i.e., the AU   base pair plus one electron) are in the range 1.0-3.2 eV, while   those for neutral AU are 4.08 eV or higher.


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