Electrophilic Properties Of 2 '-Deoxyadenosine Center Dot Center Dot Center Dot Thymine Dimer: Photoelectron Spectroscopy And Dft Studies

The anion radical of the 2'-deoxyadenosine center dot center dot center dot thymine (dAT(center dot-) ) pair has been investigated experimentally and theoretically in the gas phase. By employing negative-ion photoelectron spectroscopy (PES), we have registered a spectrum typical for the valence-bound anion, featuring a broad peak at the electron-binding energy (EBE) between similar to 1.5 and 2.2 eV with the maximum at similar to 10.9 eV. The measured value of the adiabatic electron affinity (AEA) for dAT was estimated to be similar to 1.1 eV. Calculations performed at the M06-2X/6-31++G(d,p) level revealed that the structure, where thymine is coordinated to the sugar of dA by two hydrogen bonds, is responsible for the observed PES signal. The AEA G and the vertical detachment energy of 0.91 and 1.68 eV, respectively, calculated for this structure reproduce the experimental values well. The role of the possible proton transfer in the stabilization of anionic radical complexes is discussed.