The deprotonated guanine-cytosine base pair

Area of Science:

• Computational Chemistry
• Molecular Biophysics
• Radiation Biology

Background:

• Growing awareness of radiation's harmful effects necessitates understanding DNA damage mechanisms.
• Radical and anion formation in DNA base pairs are critical steps in radiation-induced DNA damage.
• The guanine-cytosine (G-C) base pair is a fundamental unit of DNA susceptible to such damage.

Purpose of the Study:

• To investigate the energetic properties and optimized geometries of radicals and anions derived from G-C base pairs.
• To elucidate the mechanisms of DNA damage through hydrogen abstraction from the G-C base pair.
• To identify which radical species most significantly alters G-C base pair properties.

Main Methods:

• Employed reliable theoretical methods to study 10 radicals and their anions formed by hydrogen abstraction from G-C base pairs.
• Calculated dissociation energies, vertical detachment energies, and relaxation energies.
• Determined relative energies, adiabatic electron affinities, and pairing energies.

Main Results:

• Identified a highly stable deprotonated G-C structure with a significantly reduced H...O2 distance (1.58 Å), forming an extremely short hydrogen bond.
• Observed a unique 'reverse wobble' structure with two N-H...N hydrogen bonds.
• The most stable deprotonated base pair exhibited a large adiabatic electron affinity (3.65 eV), a substantial increase from the closed-shell G-C pair (0.60 eV).

Conclusions:

• The study details specific radical and anion formations in G-C base pairs, providing insights into radiation-induced DNA damage.
• The identified stable deprotonated structures and their energetic properties offer a deeper understanding of DNA's response to radiation.
• The significant increase in electron affinity of the most stable radical indicates a profound alteration of G-C base pair characteristics.