Tracking Hole Transport in DNA Hairpins Using a Phenylethynylguanine Nucleobase

Area of Science:

• Molecular Biology
• Biophysics
• Organic Chemistry

Background:

• Understanding charge transport in DNA is crucial for developing molecular electronics and biosensors.
• Modified nucleobases offer unique properties for probing biological processes.
• Stilbene derivatives serve as effective electron donors and acceptors in molecular systems.

Purpose of the Study:

• To investigate the hole transport dynamics in DNA hairpins containing a modified guanine (EG) nucleobase.
• To utilize the unique spectroscopic features of EG radical cation (EG+•) for direct observation of transient hole occupation.
• To assess the role of EG as a hole trap or intermediate transport site.

Main Methods:

• Synthesis of DNA hairpins with a stilbene donor/acceptor and a modified guanine (8-(4'-phenylethynyl)deoxyguanosine, EG).
• Spectroscopic characterization of EG+•, including absorption near 460 nm and Raman-active ethynyl stretch.
• Application of ultrafast absorption and stimulated Raman spectroscopies to monitor hole transport dynamics.

Main Results:

• EG exhibits nearly indistinguishable oxidation potential from natural guanine (G).
• EG+• has distinct spectroscopic signatures, separable from stilbene radical ions.
• EG functions as a shallow hole trap or intermediate site, influencing transport when deeper traps are present.
• Hole transport dynamics in EG-containing DNA are similar to G-containing systems, with minor rate and yield perturbations.

Conclusions:

• EG is a valuable tool for site-specific monitoring of hole occupancy in DNA.
• The deployment of EG enables detailed, base-specific insights into charge transport mechanisms.
• This approach advances the study of charge transport in DNA for potential applications in molecular electronics.