Ultrafast Excited State Dynamics Of 5-Halogen Cytidines And DNA System

As an epigenetic signal,methylated cytosine has been shown to play an important role in gene regulation and is often referred to as the"fifth base of DNA".5-halogenated cytidines is one of the endogenous damage products in living organism,and it exhibits very important biological functions in the process of nucleic acid methylation.However,the effect of halogen substitution on the excited state of canonical nucleosides has not attracted much attention.In view of the shortage of existing work,we investigated the excited state dynamics of 5-fluorocytidine,5-chlorocytidine and 5-bromocytidine in this work.After excitation at 295 nm,local excited states with sub-picosecond lifetimes and intramolecular charge transfer states with several to tens of picoseconds lifetimes are discovered.Our results clarify the excited state relaxation pathway of 5-halocytidines,which provides a solid theoretical basis for the application of such molecules in subsequent DNA or protein systems.Then we turn our attention to larger molecular system homopolymers poly?C?.We observed two different non-radiative decay channels.The first channel includes two bright electronic states ???.The second one contains the lower-energy ??? state and a long-lived state.Finally,we focused on d?GC?₉·d?GC?₉ double stranded oligomer and study its excitation state dynamics.The results show that both B-type DNA and Z-type DNA have similar proton coupled electron transfer?PCET?spectral information after absorbing ultraviolet photons.This result not only provides information on the excited state dynamics of the two DNA configurations,but also provides a new perspective for the further design of PCET-based photocatalytic materials.