Initial Excited-State Structural Dynamics of dT and dA Oligonucleotide Homopentamers Using Resonance Raman...

Area of Science:

• Photochemistry
• Molecular Spectroscopy
• Biophysics

Background:

• DNA photochemical damage arises from ultraviolet light absorption and excited-state dynamics.
• Understanding these dynamics is crucial for comprehending DNA repair and photodamage mechanisms.

Purpose of the Study:

• To investigate the initial excited-state structural dynamics of nucleotide homopentamers.
• To compare these dynamics with those of monomeric nucleobases.
• To elucidate the role of large-scale dynamics in DNA photochemistry.

Main Methods:

• UV resonance Raman spectroscopy was employed to study homopentamers of adenosine monophosphate and thymidine monophosphate.
• Excited-state parameters were extracted via self-consistent simulation of resonance Raman excitation profiles and absorption spectra.
• A time-dependent formalism was used for spectral analysis.

Main Results:

• Resonance Raman spectra of homopentamers closely resembled those of their monomeric counterparts.
• Key excited-state parameters, including slopes and broadening, showed no significant differences between pentamers and monomers.
• Initial excited-state structural dynamics were found to be similar in both nucleotide polymers and isolated bases.

Conclusions:

• The similarity in dynamics suggests that large-scale polymer dynamics govern the formation of photochemical products in DNA.
• The transition-state structure, influenced by polymer dynamics, is critical for photoproduct formation.
• These findings support a model where DNA photochemistry is dictated by collective molecular motions rather than isolated base properties.