Capturing the radical ion-pair intermediate in DNA guanine oxidation

Area of Science:

• Photochemistry
• Chemical Biology
• Spectroscopy

Background:

• Radical ion pairs are key intermediates in DNA oxidative damage and photoinduced electron transfer.
• Their detection is challenging due to instability and low concentrations.

Purpose of the Study:

• To detect and characterize transient radical ion pairs in DNA oxidation reactions.
• To elucidate the mechanism of guanine oxidation and proton-coupled charge transfer.

Main Methods:

• Utilized cryogenic stabilization to enhance the detection of transient species.
• Employed time-resolved laser flash photolysis spectroscopy.
• Coupled cryogenic stabilization with spectroscopy for direct observation.

Main Results:

• Successfully captured the guanine radical cation-chloride anion (G^+•⋯Cl^-) ion pair.
• Identified a unique spectral signature with a peak at 570 nm, distinct from G^+• alone.
• Observed ion-pair spectral sensitivity to protonation equilibria in guanine-cytosine (G:C) base pairs.

Conclusions:

• Provided direct evidence for an addition/charge separation mechanism in guanine oxidation.
• Tracked intrabase-pair proton transfer dynamics in DNA oligonucleotides using spectral changes.
• Highlighted the importance of proton-coupled charge transfer in DNA.