How Does Guanine-Cytosine Base Pair Affect Excess-Electron Transfer in DNA?

Area of Science:

• Biophysics
• Molecular Biology
• Organic Chemistry

Background:

• Charge and proton transfer in DNA are vital for biological processes.
• Excess-electron transfer (EET) in DNA is closely linked to DNA repair mechanisms.
• Current understanding of EET dynamics in DNA remains limited.

Purpose of the Study:

• To investigate the dynamics of excess-electron transfer (EET) in DNA.
• To elucidate the role of guanine:cytosine (G:C) base pairs in modulating EET.
• To provide kinetic data for understanding DNA damage and repair.

Main Methods:

• Synthesis of functionalized DNA oligomers using a photosensitizer (trimer of 3,4-ethylenedioxythiophene, 3E) and an electron acceptor (diphenylacetylene, DPA).
• Femtosecond laser flash photolysis coupled with transient absorption measurements.
• Direct kinetic measurements of EET dynamics.

Main Results:

• Guanine:cytosine (G:C) base pairs influence EET dynamics through two mechanisms.
• Mechanism 1: Excess-electron quenching via proton transfer with guanine after cytosine radical anion formation (C•-).
• Mechanism 2: EET hindrance by G:C base pairs acting as barriers within consecutive thymines (T's).

Conclusions:

• G:C base pairs play a significant role in regulating EET in DNA.
• The findings offer valuable insights into DNA repair pathways.
• Direct kinetic measurements provide a foundation for further studies on EET in oligonucleotides related to DNA damage/repair.