Conduction-band-edge ionization thresholds of DNA components in aqueous solution

Area of Science:

• Physical Chemistry
• Chemical Physics
• Biophysical Chemistry

Background:

• Ionizing radiation induces DNA damage, but photoionization energies of nucleic acids in aqueous solution remain largely unknown.
• Understanding these energies is crucial for elucidating radiation-induced DNA damage mechanisms.

Purpose of the Study:

• To determine the aqueous photoionization threshold energies of 2'-deoxythymidine 5'-phosphate (5'-dTMP-) and 2'-deoxycytidine 5'-phosphate (5'-dCMP-).
• To investigate the influence of hydration on the ionization potentials of these nucleic acid components.

Main Methods:

• Combined gas-phase photoelectron spectroscopy data with molecular orbital calculations (self-consistent field and post-self-consistent field).
• Incorporated theoretical Gibbs free energies of hydration.
• Validated the approach using indole and tryptophan as test molecules.

Main Results:

• Calculated aqueous ionization energies for 5'-dTMP- and 5'-dCMP-.
• Demonstrated that hydration significantly alters ionization energy landscapes, making base ionization more favorable compared to gas-phase.
• Observed a shift in ionization energy difference between phosphate and base from ~1.3 eV (gas-phase) to ~0.5 eV (aqueous).

Conclusions:

• Hydration plays a critical role in modulating the photoionization pathways of nucleic acid components.
• The findings support experimental observations of base ionization as the primary photoionization event in hydrated DNA components.
• Provides essential data for understanding DNA radiation damage at a molecular level.