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DNA’s Day in the Sun: How the Double Helix Avoids Photodamage

Event Details

Event Dates: 

Friday, September 30, 2016 - 4:00pm

Seminar Location: 

  • JILA Auditorium

Speaker Name(s): 

Bern Kohler

Speaker Affiliation(s): 

Ohio State University
Seminar Type/Subject

Scientific Seminar Type: 

  • Phys Chem/Chem Phys Seminar

Event Details & Abstract: 

The microscopic events that limit damage to DNA by UV radiation have been intensively studied during the past decade. Femtosecond pump-probe experiments show that UV absorption creates charge-separated states in single-stranded DNA based on the detection of vibrational marker bands of nucleobase radical ions. These states are only observed when two or more DNA nucleobases are stacked and in van der Waals contact. In double-stranded DNA, femtosecond time-resolved IR (TRIR) experiments reveal a distinctive photoinduced proton-coupled electron transfer (PCET) deactivation mechanism in which an electron moves between nucleobases on the same strand, attracting a proton from the opposite strand. In biology, PCET usually couples long-range electron transfer to short-range proton transfer, but in DNA electron and proton donors and acceptors are in intimate contact. This architecture favors efficient charge recombination explaining why tautomeric base pair radical ions can be high-yield intermediates during excited state decay without compromising photostability. Photoinduced electron transfer and PCET may have conferred photoredox activity on primitive ribozymes in the RNA world. Today, these phenomena are providing new insights into charge carrier formation and transport in DNA sequences and other nanoscale systems.