Long-range photoinduced electron transfer through a DNA helix

Area of Science:

• Photochemistry
• Molecular Biology
• Supramolecular Chemistry

Background:

• Metallointercalators are metal complexes that can insert into DNA base pairs.
• Photoinduced electron transfer (PET) is a fundamental process in chemistry and biology.
• Efficient long-distance electron transfer in DNA is crucial for understanding biological processes and developing molecular devices.

Purpose of the Study:

• To demonstrate and quantify long-distance photoinduced electron transfer (PET) in a DNA duplex.
• To investigate the role of the DNA structure in mediating electron transfer between metallointercalators.
• To synthesize and characterize a DNA-oligomeric assembly with specific donor and acceptor metal complexes.

Main Methods:

• Synthesis of a 15-base pair DNA duplex functionalized with ruthenium (Ru) and rhodium (Rh) metallointercalators at the 5' termini.
• Spectroscopic analysis, including time-resolved luminescence studies, to monitor electron transfer.
• Hybridization of modified and unmodified DNA strands to assess quenching efficiency.

Main Results:

• Demonstrated PET over distances greater than 40 angstroms between Ru(phen)2dppz2+ (donor) and Rh(phi)2phen3+ (acceptor) tethered to a DNA duplex.
• Observed intense luminescence for a Ru-modified oligonucleotide hybridized to an unmodified complement.
• Detected no significant luminescence for the Ru-modified oligomer hybridized to the Rh-modified oligomer, indicating efficient quenching with a rate limit of 10^9 s^-1.
• Showed no quenching when metal complexes did not intercalate into the DNA structure.

Conclusions:

• The DNA duplex acts as an efficient medium for coupling electron donors and acceptors over extended distances.
• The stacked aromatic heterocycles within the DNA helix facilitate long-range photoinduced electron transfer.
• This study highlights the potential of DNA as a scaffold for constructing molecular electronic components.