Adenine-thymine tautomerization under the influence of strong homogeneous electric fields.

The effect of strong electric fields on the tautomerization of the adenine-thymine (AT) base pair in DNA is explored using density functional theory. It was found that the AT base pair is not likely to undergo a double proton transfer reaction even in the presence of electric fields ranging from 5.14 × 108 to 5.14 × 109 V m-1. This conclusion holds true in Gibbs energies computed at 25 °C or 37 °C. Energy correction terms to the electronic energy, such as total internal energy, Gibbs energy, zero-point energy, enthalpy and entropy corrections, were investigated in detail to pinpoint the major contributors to the low probability of the AT tautomerization. It was found that the entropy corrections are the least significant, while zero-point energy and Gibbs energy corrections can be large enough to thermodynamically inhibit the DPT in AT.