Proton-coupled photoinduced electron transfer, deuterium isotope effects, and fluorescence quenching in noncovalent benzo[a]pyrenetetraol-nucleoside complexes in aqueous solutions

V. Y. Shafirovich, S. H. Courtney, N. Ya, Nicholas Geacintov

Research output: Contribution to journalArticle

Abstract

A proton-coupled, photoinduced electron transfer mechanism is responsible for the extraoridinarly efficient dynamic and static quenching (94-99%) of the fluorescence of the pyrenyl residue (Py) in the benzo[a]pyrene metabolite 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene (BPT) by the 2'-deoxynucleosides dG, dC, and dT in aqueous solutions. Time-correlated fluorescence single-photon counting techniques indicate that noncovalent[1BPT-dN] complexes decay with lifetimes 200-300 faster than those of free singlet excited 1BPT molecules. An unusual solvent kinetic isotope effect is observed: these lifetimes are longer by factors of 1.5-2.0 in D2O than in H2O. Nanosecond time scale transient absorption techniques show that BPT.+ radical cations are formed with yields ∅(R) = 0.07 and 0.02 in 0.1 M aqueous dC and dT solutions, respectively, with similar yields of 3BPT triplet excited states. In the case of dG, the products of the quenching reaction are BPT.- radical anions (∅(R) = 0.25) and 3BPT (∅(T) = 0.35) in dimethyl sulfoxide (DMSD); in aqueous solutions, however, only 3BPT triplet excited states are observed on nanosecond time scales. This lack of ion radical products is accounted for in terms of a more rapid recombination of the intermediate [BPT.-···dG.+] radical-ion pair, which is facilitated by hydrophobic interactions in water. The striking difference in the directions of electron transfer from 1BPT to the pyrimidines dC and dT on the one hand, and from the purine derivative dG to 1BPT on the other, can be rationalized in terms of the redox potentials of the relevant donor-acceptor pairs. In the case of dC and dT, the thermodynamics of electron transfer are unfavorable unless coupled to a rapid proton transfer step; this effect accounts for the strong quenching in water and the kinetic solvent isotope effect, as well as for the observed lack of fluorescence quenching by dC and dT in the polar organic solvent DMSO.

Original languageEnglish (US)
Pages (from-to)4920-4929
Number of pages10
JournalJournal of the American Chemical Society
Volume117
Issue number17
StatePublished - 1995

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Deuterium
Nucleosides
Isotopes
Protons
Quenching
Fluorescence
Electrons
Dimethyl Sulfoxide
Pyrene
Excited states
Ions
Pyrimidines
Water
Benzo(a)pyrene
Hydrophobic and Hydrophilic Interactions
Photons
Thermodynamics
Genetic Recombination
Kinetics
Oxidation-Reduction

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

@article{98eaf85287c44ff7ba75e45aa55b2cde,
title = "Proton-coupled photoinduced electron transfer, deuterium isotope effects, and fluorescence quenching in noncovalent benzo[a]pyrenetetraol-nucleoside complexes in aqueous solutions",
abstract = "A proton-coupled, photoinduced electron transfer mechanism is responsible for the extraoridinarly efficient dynamic and static quenching (94-99{\%}) of the fluorescence of the pyrenyl residue (Py) in the benzo[a]pyrene metabolite 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene (BPT) by the 2'-deoxynucleosides dG, dC, and dT in aqueous solutions. Time-correlated fluorescence single-photon counting techniques indicate that noncovalent[1BPT-dN] complexes decay with lifetimes 200-300 faster than those of free singlet excited 1BPT molecules. An unusual solvent kinetic isotope effect is observed: these lifetimes are longer by factors of 1.5-2.0 in D2O than in H2O. Nanosecond time scale transient absorption techniques show that BPT.+ radical cations are formed with yields ∅(R) = 0.07 and 0.02 in 0.1 M aqueous dC and dT solutions, respectively, with similar yields of 3BPT triplet excited states. In the case of dG, the products of the quenching reaction are BPT.- radical anions (∅(R) = 0.25) and 3BPT (∅(T) = 0.35) in dimethyl sulfoxide (DMSD); in aqueous solutions, however, only 3BPT triplet excited states are observed on nanosecond time scales. This lack of ion radical products is accounted for in terms of a more rapid recombination of the intermediate [BPT.-···dG.+] radical-ion pair, which is facilitated by hydrophobic interactions in water. The striking difference in the directions of electron transfer from 1BPT to the pyrimidines dC and dT on the one hand, and from the purine derivative dG to 1BPT on the other, can be rationalized in terms of the redox potentials of the relevant donor-acceptor pairs. In the case of dC and dT, the thermodynamics of electron transfer are unfavorable unless coupled to a rapid proton transfer step; this effect accounts for the strong quenching in water and the kinetic solvent isotope effect, as well as for the observed lack of fluorescence quenching by dC and dT in the polar organic solvent DMSO.",
author = "Shafirovich, {V. Y.} and Courtney, {S. H.} and N. Ya and Nicholas Geacintov",
year = "1995",
language = "English (US)",
volume = "117",
pages = "4920--4929",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
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TY - JOUR

T1 - Proton-coupled photoinduced electron transfer, deuterium isotope effects, and fluorescence quenching in noncovalent benzo[a]pyrenetetraol-nucleoside complexes in aqueous solutions

AU - Shafirovich, V. Y.

AU - Courtney, S. H.

AU - Ya, N.

AU - Geacintov, Nicholas

PY - 1995

Y1 - 1995

N2 - A proton-coupled, photoinduced electron transfer mechanism is responsible for the extraoridinarly efficient dynamic and static quenching (94-99%) of the fluorescence of the pyrenyl residue (Py) in the benzo[a]pyrene metabolite 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene (BPT) by the 2'-deoxynucleosides dG, dC, and dT in aqueous solutions. Time-correlated fluorescence single-photon counting techniques indicate that noncovalent[1BPT-dN] complexes decay with lifetimes 200-300 faster than those of free singlet excited 1BPT molecules. An unusual solvent kinetic isotope effect is observed: these lifetimes are longer by factors of 1.5-2.0 in D2O than in H2O. Nanosecond time scale transient absorption techniques show that BPT.+ radical cations are formed with yields ∅(R) = 0.07 and 0.02 in 0.1 M aqueous dC and dT solutions, respectively, with similar yields of 3BPT triplet excited states. In the case of dG, the products of the quenching reaction are BPT.- radical anions (∅(R) = 0.25) and 3BPT (∅(T) = 0.35) in dimethyl sulfoxide (DMSD); in aqueous solutions, however, only 3BPT triplet excited states are observed on nanosecond time scales. This lack of ion radical products is accounted for in terms of a more rapid recombination of the intermediate [BPT.-···dG.+] radical-ion pair, which is facilitated by hydrophobic interactions in water. The striking difference in the directions of electron transfer from 1BPT to the pyrimidines dC and dT on the one hand, and from the purine derivative dG to 1BPT on the other, can be rationalized in terms of the redox potentials of the relevant donor-acceptor pairs. In the case of dC and dT, the thermodynamics of electron transfer are unfavorable unless coupled to a rapid proton transfer step; this effect accounts for the strong quenching in water and the kinetic solvent isotope effect, as well as for the observed lack of fluorescence quenching by dC and dT in the polar organic solvent DMSO.

AB - A proton-coupled, photoinduced electron transfer mechanism is responsible for the extraoridinarly efficient dynamic and static quenching (94-99%) of the fluorescence of the pyrenyl residue (Py) in the benzo[a]pyrene metabolite 7,8,9,10-tetrahydroxytetrahydrobenzo[a]pyrene (BPT) by the 2'-deoxynucleosides dG, dC, and dT in aqueous solutions. Time-correlated fluorescence single-photon counting techniques indicate that noncovalent[1BPT-dN] complexes decay with lifetimes 200-300 faster than those of free singlet excited 1BPT molecules. An unusual solvent kinetic isotope effect is observed: these lifetimes are longer by factors of 1.5-2.0 in D2O than in H2O. Nanosecond time scale transient absorption techniques show that BPT.+ radical cations are formed with yields ∅(R) = 0.07 and 0.02 in 0.1 M aqueous dC and dT solutions, respectively, with similar yields of 3BPT triplet excited states. In the case of dG, the products of the quenching reaction are BPT.- radical anions (∅(R) = 0.25) and 3BPT (∅(T) = 0.35) in dimethyl sulfoxide (DMSD); in aqueous solutions, however, only 3BPT triplet excited states are observed on nanosecond time scales. This lack of ion radical products is accounted for in terms of a more rapid recombination of the intermediate [BPT.-···dG.+] radical-ion pair, which is facilitated by hydrophobic interactions in water. The striking difference in the directions of electron transfer from 1BPT to the pyrimidines dC and dT on the one hand, and from the purine derivative dG to 1BPT on the other, can be rationalized in terms of the redox potentials of the relevant donor-acceptor pairs. In the case of dC and dT, the thermodynamics of electron transfer are unfavorable unless coupled to a rapid proton transfer step; this effect accounts for the strong quenching in water and the kinetic solvent isotope effect, as well as for the observed lack of fluorescence quenching by dC and dT in the polar organic solvent DMSO.

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