Low Energy Photoionization of Phosphorothioate DNA-Oligomers and Ensuing Hole Transfer.

Phosphorothioate (PS) modified oligonucleotides (S-DNA) naturally exist in bacteria and archaea genome and are widely used as an antisense strategy in gene therapy. However, the introduction of PS as a redox active site may trigger distinct UV photoreactions. Herein, by time-resolved spectroscopy, we observe that 266 nm excitation of S-DNA d(A) and d(AA) leads to direct photoionization on the PS moiety to form hemi-bonded -P-S∴S-P- radicals, in addition to A base ionization to produce A/A(-H).