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Issue 10, 2010
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The effect of π-stacking, H-bonding, and electrostatic interactions on the ionization energies of nucleic acid bases: adenineadenine, thyminethymine and adeninethymine dimers

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Abstract

A combined theoretical and experimental study of the ionized dimers of thymine and adenine, TT, AA, and AT, is presented. Experimentally observed and computed adiabatic and vertical ionization energies (IEs) for monomers and dimers as well as thresholds for the appearance of the protonated species are reported and analyzed. Non-covalent interactions strongly affect the observed IEs. The magnitude and the nature of the effect is different for different isomers of the dimers. The computations reveal that for TT, the largest changes in vertical IEs (0.4 eV) relative to the monomer occur in asymmetric H-bonded and symmetric π-stacked isomers, whereas in the lowest-energy symmetric H-bonded dimer the shift in IEs is much smaller (0.2 eV). The origin of the shift and the character of the ionized states is different in asymmetric H-bonded and symmetric stacked isomers. In the former, the initial hole is localized on one of the fragments, and the shift is due to the electrostatic stabilization of the positive charge of the ionized fragment by the dipole moment of the neutral fragment. In the latter, the hole is delocalized, and the change in IE is proportional to the overlap of the fragments’ MOs. Relative to TT, the shifts in AA and AT are much smaller due to a less efficient overlap, smaller dipole of A and the large energy gap between ionized states of A and T monomers in the case of AT dimer. The ionization of the H-bonded dimers results in barrierless (or nearly barrierless) proton transfer, whereas the π-stacked dimers relax to structures with the hole stabilized by the delocalization or electrostatic interactions.

Graphical abstract: The effect of π-stacking, H-bonding, and electrostatic interactions on the ionization energies of nucleic acid bases: adenine–adenine, thymine–thymine and adenine–thymine dimers

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Publication details

The article was received on 24 Sep 2009, accepted on 19 Nov 2009, published on 06 Jan 2010 and first published online on 06 Jan 2010


Article type: Paper
DOI: 10.1039/B919930F
Citation: Phys. Chem. Chem. Phys., 2010,12, 2292-2307
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    The effect of π-stacking, H-bonding, and electrostatic interactions on the ionization energies of nucleic acid bases: adenineadenine, thyminethymine and adeninethymine dimers

    K. B. Bravaya, O. Kostko, M. Ahmed and A. I. Krylov, Phys. Chem. Chem. Phys., 2010, 12, 2292
    DOI: 10.1039/B919930F

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