Thymine dimer splitting in the T<>T-G trinucleotide model system: a semiclassical dynamics and TD-DFT study

Area of Science:

• Photochemistry
• Molecular Dynamics
• Biophysics

Background:

• Thymine-thymine dimers (T<>T) are DNA lesions formed by UV radiation.
• Understanding T<>T dimer photochemistry is crucial for DNA repair mechanisms.
• Previous studies have explored T<>T dimer photodissociation, but the precise mechanism remains under investigation.

Purpose of the Study:

• To elucidate the mechanism of thymine-thymine cyclobutane dimer (T<>T) bond cleavage.
• To investigate the role of guanine trinucleotide in T<>T dimer photodissociation.
• To determine the timescale of T<>T dimer splitting.

Main Methods:

• Semiclassical dynamics simulations were employed.
• A model system comprising a T<>T dimer flanked by guanine trinucleotide was utilized.
• Pulsed laser excitation of the guanine molecule was simulated.

Main Results:

• Pulsed laser excitation of guanine induced electron transfer to the T<>T dimer.
• The dimer dissociated via sequential cleavage of the C5C5' and C6C6' bonds.
• Electrons transferred back to guanine as the dimer split into monomers on the femtosecond timescale.

Conclusions:

• Electron transfer from guanine initiates rapid T<>T dimer photodissociation.
• The C5C5' and C6C6' bond cleavage occurs sequentially.
• The femtosecond timescale of dimer splitting highlights the efficiency of this photochemical pathway.