Very low energy electrons transform the cyclobutane-pyrimidine dimer into a highly reactive intermediate

Area of Science:

• Physical Chemistry
• Chemical Physics
• Biophysical Chemistry

Background:

• Cyclobutane-pyrimidine dimer (CPD) is a major photoproduct in DNA, leading to mutations.
• Understanding CPD reactivity is vital for DNA repair mechanisms and photoprotection strategies.

Purpose of the Study:

• To investigate the decomposition pathways of CPD induced by low-energy electrons.
• To compare the sensitivity of CPD to electron impact with its constituent thymine molecules.

Main Methods:

• Dissociative electron attachment (DEA) experiments were conducted on CPD.
• Electron energy was precisely controlled near 0 eV to probe low-energy interactions.
• Fragment ion analysis was performed to identify decomposition products.

Main Results:

• Electrons with near-zero kinetic energy efficiently decompose CPD into various fragment ions and neutral species.
• The dominant reaction pathway involves the splitting of CPD into two thymine-like units.
• CPD exhibits significantly higher sensitivity to low-energy electrons compared to individual thymine molecules.
• A large dipole moment (6.2 D) suggests the involvement of dipole-bound states in electron attachment.

Conclusions:

• Low-energy electron interaction with CPD initiates efficient dissociation, mimicking explosive-like behavior.
• The observed fragmentation pathway is relevant to the enzymatic repair of CPD by photolyase.
• Dipole-bound states likely facilitate dissociative electron attachment, highlighting a unique electron interaction mechanism for DNA photoproducts.