Proton-coupled photoinduced electron transfer, deuterium isotope effects, and fluorescence quenching in noncovalent benzo[a]pyrenetetraol. Nucleoside complexes in aqueous solutions
- New York Univ., NY (United States)
In this work, the origins of the fluorescence quenching mechanisms are explored in some detail employing time-correlated fluorescence single-photon counting and nanosecond time scale transient absorption techniques. Using the noncovalently interacting donor-acceptor pairs BKT and 2`-deoxynucleosides as model systems, we show here that the pyrimidine derivatives 2`-deoxythymidine (dT) and 2`-deoxycytidine (dC) are strong quenchers of the fluorescence of BPT in water, but are inactive in polar organic solvents such as DMSO. In aqueous media, the fluorescence quenching mechanism involves a photoinduced electron transfer mechanism that occurs in the opposite direction with the Py residues now acting as the electron donors. A remarkable solvent isotope effect is observed on the kinetics of the fluorescence decay of {sup 1}BPT in H{sub 2}O and in D{sub 2}O. This kinetic isotope effect, as well as a consideration of the redox potentials of the electron donor-acceptor couples, suggests that the electron transfer is coupled with a proton transfer from water molecules to the corresponding radical anions of the pyrimidine bases. Taking the thermodynamics of the proton-coupled photoinduced electron transfer reactions into account, this mechanism can explain the lack of fluorescence quenching by pyrimidine derivatives in polar organic solvents, and their strong quenching activities in aqueous solutions. 55 refs., 7 figs., 1 tab.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 53967
- Journal Information:
- Journal of the American Chemical Society, Vol. 117, Issue 17; Other Information: PBD: 3 May 1995
- Country of Publication:
- United States
- Language:
- English
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