Influence of adduct stereochemistry and hydrogen-bonding solvents on photoinduced charge transfer in a covalent benzo[a]pyrene diol epoxide-nucleoside adduct on picosecond time scales

Donald O'Connor, Vladimir Y. Shafirovich, Nicholas Geacintov

Research output: Contribution to journalArticle

Abstract

Photoinduced electron transfer occurs with different rate constants upon picosecond laser pulse excitation of the stereoisomeric (+)-trans- and (-)-cis-benzo[a]pyrene diol epoxide-N2-deoxyguanosine covalently linked adducts (BPDE-N2-dG, both with 10S absolute configuration) in polar solvents (N,N′-dimethylformamide (DMF), and the hydrogen-bonding liquids H2O, D2O, formamide (FA), and N-methylformamide (NMF)). In the case of (+)-trans-BPDE-dG in DMF, photoinduced electron transfer occurs in the normal Marcus region, from dG to the pyrenyl residue singlet with a rate constant ks = (9.1 ± 0.9) × 109 s-1, which is followed by a slower recombination (kr = (1.8 ± 0.5) × 109 s-1) in the inverted Marcus region. In the cis-stereoisomeric adduct, both rate constants are enhanced by a factor of ∼5. The presence of the hydrogen-bonding network in NMF and FA exerts opposite effects on these rate constants, decreasing ks and increasing kr by factors of 2-5. In aqueous solutions these effects are even more pronounced, and radical ions are not observed since kr ≫ ks. A kinetic isotope effect on the decay of the pyrenyl singlets in H2O and D2O (ks(H2O)/ks(D2O) = 1.3-1.5) suggests that a proton-coupled electron transfer mechanism may be operative in aqueous solutions.

Original languageEnglish (US)
Pages (from-to)9831-9839
Number of pages9
JournalJournal of Physical Chemistry
Volume98
Issue number39
StatePublished - 1994

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Stereochemistry
nucleosides
epoxy compounds
Benzo(a)pyrene
Epoxy Compounds
Pyrene
stereochemistry
methylformamide
pyrenes
Nucleosides
adducts
Charge transfer
Rate constants
Hydrogen bonds
charge transfer
Dimethylformamide
electron transfer
hydrogen
Electrons
aqueous solutions

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Engineering(all)

Cite this

@article{07e8996241314885976a11f320aae2d1,
title = "Influence of adduct stereochemistry and hydrogen-bonding solvents on photoinduced charge transfer in a covalent benzo[a]pyrene diol epoxide-nucleoside adduct on picosecond time scales",
abstract = "Photoinduced electron transfer occurs with different rate constants upon picosecond laser pulse excitation of the stereoisomeric (+)-trans- and (-)-cis-benzo[a]pyrene diol epoxide-N2-deoxyguanosine covalently linked adducts (BPDE-N2-dG, both with 10S absolute configuration) in polar solvents (N,N′-dimethylformamide (DMF), and the hydrogen-bonding liquids H2O, D2O, formamide (FA), and N-methylformamide (NMF)). In the case of (+)-trans-BPDE-dG in DMF, photoinduced electron transfer occurs in the normal Marcus region, from dG to the pyrenyl residue singlet with a rate constant ks = (9.1 ± 0.9) × 109 s-1, which is followed by a slower recombination (kr = (1.8 ± 0.5) × 109 s-1) in the inverted Marcus region. In the cis-stereoisomeric adduct, both rate constants are enhanced by a factor of ∼5. The presence of the hydrogen-bonding network in NMF and FA exerts opposite effects on these rate constants, decreasing ks and increasing kr by factors of 2-5. In aqueous solutions these effects are even more pronounced, and radical ions are not observed since kr ≫ ks. A kinetic isotope effect on the decay of the pyrenyl singlets in H2O and D2O (ks(H2O)/ks(D2O) = 1.3-1.5) suggests that a proton-coupled electron transfer mechanism may be operative in aqueous solutions.",
author = "Donald O'Connor and Shafirovich, {Vladimir Y.} and Nicholas Geacintov",
year = "1994",
language = "English (US)",
volume = "98",
pages = "9831--9839",
journal = "Journal of Physical Chemistry",
issn = "0022-3654",
publisher = "American Chemical Society",
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T1 - Influence of adduct stereochemistry and hydrogen-bonding solvents on photoinduced charge transfer in a covalent benzo[a]pyrene diol epoxide-nucleoside adduct on picosecond time scales

AU - O'Connor, Donald

AU - Shafirovich, Vladimir Y.

AU - Geacintov, Nicholas

PY - 1994

Y1 - 1994

N2 - Photoinduced electron transfer occurs with different rate constants upon picosecond laser pulse excitation of the stereoisomeric (+)-trans- and (-)-cis-benzo[a]pyrene diol epoxide-N2-deoxyguanosine covalently linked adducts (BPDE-N2-dG, both with 10S absolute configuration) in polar solvents (N,N′-dimethylformamide (DMF), and the hydrogen-bonding liquids H2O, D2O, formamide (FA), and N-methylformamide (NMF)). In the case of (+)-trans-BPDE-dG in DMF, photoinduced electron transfer occurs in the normal Marcus region, from dG to the pyrenyl residue singlet with a rate constant ks = (9.1 ± 0.9) × 109 s-1, which is followed by a slower recombination (kr = (1.8 ± 0.5) × 109 s-1) in the inverted Marcus region. In the cis-stereoisomeric adduct, both rate constants are enhanced by a factor of ∼5. The presence of the hydrogen-bonding network in NMF and FA exerts opposite effects on these rate constants, decreasing ks and increasing kr by factors of 2-5. In aqueous solutions these effects are even more pronounced, and radical ions are not observed since kr ≫ ks. A kinetic isotope effect on the decay of the pyrenyl singlets in H2O and D2O (ks(H2O)/ks(D2O) = 1.3-1.5) suggests that a proton-coupled electron transfer mechanism may be operative in aqueous solutions.

AB - Photoinduced electron transfer occurs with different rate constants upon picosecond laser pulse excitation of the stereoisomeric (+)-trans- and (-)-cis-benzo[a]pyrene diol epoxide-N2-deoxyguanosine covalently linked adducts (BPDE-N2-dG, both with 10S absolute configuration) in polar solvents (N,N′-dimethylformamide (DMF), and the hydrogen-bonding liquids H2O, D2O, formamide (FA), and N-methylformamide (NMF)). In the case of (+)-trans-BPDE-dG in DMF, photoinduced electron transfer occurs in the normal Marcus region, from dG to the pyrenyl residue singlet with a rate constant ks = (9.1 ± 0.9) × 109 s-1, which is followed by a slower recombination (kr = (1.8 ± 0.5) × 109 s-1) in the inverted Marcus region. In the cis-stereoisomeric adduct, both rate constants are enhanced by a factor of ∼5. The presence of the hydrogen-bonding network in NMF and FA exerts opposite effects on these rate constants, decreasing ks and increasing kr by factors of 2-5. In aqueous solutions these effects are even more pronounced, and radical ions are not observed since kr ≫ ks. A kinetic isotope effect on the decay of the pyrenyl singlets in H2O and D2O (ks(H2O)/ks(D2O) = 1.3-1.5) suggests that a proton-coupled electron transfer mechanism may be operative in aqueous solutions.

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