Polyethylene glycols affect electron transfer rate in phenosafranin-DNA complex

Area of Science:

• Biophysics
• Molecular Biology
• Photochemistry

Background:

• Long-distance electron transfer (ET) in DNA is crucial for biological processes.
• DNA typically exists in a crowded cellular environment, unlike dilute aqueous solutions.
• Molecular crowding may influence DNA's electron transfer dynamics.

Purpose of the Study:

• To investigate the impact of molecular crowding on DNA-ligand electron transfer.
• To examine how ethylene glycol (EG) and polyethylene glycols (PEGs) affect phenosafranine (PSF) emission intercalated in calf thymus (CT) DNA.

Main Methods:

• Steady-state and time-resolved (femtosecond and picosecond) fluorescence spectroscopy.
• Circular dichroism (CD) spectroscopy to assess DNA structural integrity.
• Studies conducted in the presence of varying concentrations of EG and PEGs (200, 400, 1000).

Main Results:

• Phenosafranine (PSF) fluorescence, quenched upon DNA intercalation, is restored by PEGs.
• Circular dichroism (CD) confirmed minimal DNA structural changes with PEG addition.
• Picosecond-resolved fluorescence showed reduced DNA-induced quenching time constants with PEGs, while femtosecond measurements indicated less significant changes.

Conclusions:

• Molecular crowding, via PEGs, affects 'through-space' electron transfer pathways.
• Electron hopping through the DNA core (guanine bases) remains largely unaffected by crowding.
• Crowding agents modulate DNA-ligand ET by influencing intermolecular interactions rather than DNA structure.