Acid-base equilibria in aqueous solutions of 2-aminopurine radical cations generated by two-photon photoionization

Vladimir Shafirovich, Alexander Dourandin, Natalia P. Luneva, Nicholas Geacintov

Research output: Contribution to journalArticle

Abstract

The acid-base equilibria of the nucleic acid analogue 2-aminopurine (2AP) and 2-aminopurine riboside (2-APr) radicals generated by two-photon photoionization of the 2AP residues with intense 308 nm XeCl excimer laser pulses (fwhm = 12 ns, ca. 70 mJ cm-2 pulse-1) have been investigated using transient absorption spectroscopy techniques. It is of interest to investigate the properties of these radicals as a function of pH because of their abilities to undergo proton-coupled electron transfer reactions with other nucleic acid bases. Pronounced differences in the 2AP and 2APr radical absorption bands are observed in the 330-550 nm spectral region within the pH range of 1 to 12. These differences are attributed to the deprotonation of the 2AP and 2APr radical cations, 2AP·+ (pKa1r = 2.8 ± 0.2), and 2APr·+ (pKa1r = 2.7 ± 0.2), with the concomitant formation of the neutral radicals, 2AP(-H)· and 2APr(-H)·. At higher pH values, the 2AP(-H)· radical (pKa2r = 9.5 ± 0.2) loses a second proton at the N9 position to form the radical anion 2AP(-2H)·-; this deprotonation reaction does not occur in the case of the 2APr(-H)· radical because of the ribofuranosyl substitution at the N9 position.

Original languageEnglish (US)
Pages (from-to)271-275
Number of pages5
JournalJournal of the Chemical Society. Perkin Transactions 2
Issue number2
StatePublished - Feb 2000

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2-Aminopurine
Photoionization
Cations
Photons
Deprotonation
Nucleic Acids
Protons
Acid-Base Equilibrium
Excimer lasers
Absorption spectroscopy
Anions
Absorption spectra
Laser pulses
Substitution reactions

ASJC Scopus subject areas

  • Chemistry(all)

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Acid-base equilibria in aqueous solutions of 2-aminopurine radical cations generated by two-photon photoionization. / Shafirovich, Vladimir; Dourandin, Alexander; Luneva, Natalia P.; Geacintov, Nicholas.

In: Journal of the Chemical Society. Perkin Transactions 2, No. 2, 02.2000, p. 271-275.

Research output: Contribution to journalArticle

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abstract = "The acid-base equilibria of the nucleic acid analogue 2-aminopurine (2AP) and 2-aminopurine riboside (2-APr) radicals generated by two-photon photoionization of the 2AP residues with intense 308 nm XeCl excimer laser pulses (fwhm = 12 ns, ca. 70 mJ cm-2 pulse-1) have been investigated using transient absorption spectroscopy techniques. It is of interest to investigate the properties of these radicals as a function of pH because of their abilities to undergo proton-coupled electron transfer reactions with other nucleic acid bases. Pronounced differences in the 2AP and 2APr radical absorption bands are observed in the 330-550 nm spectral region within the pH range of 1 to 12. These differences are attributed to the deprotonation of the 2AP and 2APr radical cations, 2AP·+ (pKa1r = 2.8 ± 0.2), and 2APr·+ (pKa1r = 2.7 ± 0.2), with the concomitant formation of the neutral radicals, 2AP(-H)· and 2APr(-H)·. At higher pH values, the 2AP(-H)· radical (pKa2r = 9.5 ± 0.2) loses a second proton at the N9 position to form the radical anion 2AP(-2H)·-; this deprotonation reaction does not occur in the case of the 2APr(-H)· radical because of the ribofuranosyl substitution at the N9 position.",
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