| Autor: |
Böhnke H; Institute of Physical Chemistry , Christian-Albrechts-University Kiel , Olshausenstr. 40 , 24098 Kiel , Germany., Röttger K; Institute of Physical Chemistry , Christian-Albrechts-University Kiel , Olshausenstr. 40 , 24098 Kiel , Germany.; School of Chemistry , University of Bristol , Cantock's Close , Bristol BS8 1TS , U.K., Ingle RA; School of Chemistry , University of Bristol , Cantock's Close , Bristol BS8 1TS , U.K., Marroux HJB; School of Chemistry , University of Bristol , Cantock's Close , Bristol BS8 1TS , U.K., Bohnsack M; Institute of Physical Chemistry , Christian-Albrechts-University Kiel , Olshausenstr. 40 , 24098 Kiel , Germany., Schwalb NK; Institute of Physical Chemistry , Christian-Albrechts-University Kiel , Olshausenstr. 40 , 24098 Kiel , Germany., Orr-Ewing AJ; School of Chemistry , University of Bristol , Cantock's Close , Bristol BS8 1TS , U.K., Temps F; Institute of Physical Chemistry , Christian-Albrechts-University Kiel , Olshausenstr. 40 , 24098 Kiel , Germany. |
| Abstrakt: |
The fluorescent analogue 2-aminopurine (2AP) of the canonical nucleobase adenine (6-aminopurine) base-pairs with thymine (T) without disrupting the helical structure of DNA. It therefore finds frequent use in molecular biology for probing DNA and RNA structures and conformational dynamics. However, detailed understanding of the processes responsible for fluorescence quenching remains largely elusive on a fundamental level. Although attempts have been made to ascribe decreased excited-state lifetimes to intrastrand charge-transfer and stacking interactions, possible influences from dynamic interstrand H-bonding have been widely ignored. Here, we investigate the electronic relaxation of UV-excited 2AP·T in Watson-Crick (WC) and Hoogsteen (HS) conformations. Although the WC conformation features slowed-down, monomer-like electronic relaxation in τ ∼ 1.6 ns toward ground-state recovery and triplet formation, the dynamics associated with 2AP·T in the HS motif exhibit faster deactivation in τ ∼ 70 ps. As recent research has revealed abundant transient interstrand H-bonding in the Hoogsteen motif for duplex DNA, the established model for dynamic fluorescence quenching may need to be revised in the light of our results. The underlying supramolecular photophysical mechanisms are discussed in terms of a proposed excited-state double-proton transfer as an efficient deactivation channel for recovery of the HS species in the electronic ground state. |
