Ionization of purine nucleosides and nucleotides and their components by 193-nm laser photolysis in aqueous solution: model studies for oxidative damage of DNA

Candeias, Luis P.; Steenken, S.

doi:10.1021/ja00028a043

Cited by 213 publications

(244 citation statements)

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“…However, for this base we see no signal for the solvated electron above the background level of the neutral buffer and no longlived IR transient features indicating that no significant photoionization occurs for this base. This result is consistent with the yields for photoionization of cytosine at 193 nm, being 3 times less than for guanine (12).…”

Section: Resultssupporting

confidence: 80%

“…It is known that ionization occurs to much lesser extent with other DNA bases (12). To study this topic using our IR spectroscopic probe, we have performed analogous experiments on 5Ј-dCMP.…”

Section: Resultsmentioning

confidence: 99%

“…The rate of deprotonation, k 1 , has been the subject of controversy. The deprotonation was thought to be very fast (12,13), but measurements of the rate using transient UV pump, visible probe have been prevented because the weak absorbance of the radical base species overlaps with that of the solvated electron that is generated at the same time. However, recent pulse radiolysis experiments carried out by Kobayashi and Tagawa (24) have reported the rate constant k 1 to be 1.8 ϫ 10 7 s Ϫ1 at pH 7.…”

Section: Resultsmentioning

confidence: 99%

“…UV radiation to initiate DNA base ionization has proven extremely useful for studying direct DNA damage (4-6, 12) along with pulse radiolysis (13). Traditionally, reactions in DNA are monitored by either following the kinetics on the nanosecond time scale using UV͞visible absorption spectroscopy (5,6,12,13) or determining the resulting base damage (single-or double-strand breaks) using hot piperidine treatment or excision enzyme analysis followed by gel electrophoresis (14,15). Conversely, ESR spectroscopy has provided structural information on ionization products.…”

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confidence: 99%

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Monitoring the direct and indirect damage of DNA bases and polynucleotides by using time-resolved infrared spectroscopy

Kuimova

Cowan

Matousek

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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The nucleotide 5 -dGMP and polynucleotide poly(dGdC)⅐poly(dGdC) have been irradiated by using a 200-fs, 200-nm laser pulses and spectrally characterized by using time-resolved infrared spectroscopy. Under the experimental conditions, 200-nm excitation generates both electronic excited states and radical cations through photoionization; the former decay rapidly to vibrationally hot ground state. By using infrared signatures we have been able to follow these processes, and at time scales of >1 ns we observe an infrared marker band at 1,702 cm ؊1 within both 5 -dGMP and the polynucleotide assigned to a photoionized product of guanine. This transient has also been reproduced through indirect chemistry through the reaction with photogenerated carbonate radical with 5 -dGMP. The ability to use time-resolved infrared spectroscopy in this way paves the way for developing solution-phase studies to investigate both direct and indirect radiation chemistry of DNA.DNA damage ͉ electron transfer ͉ guanine radical cation O f the large number of ionizing events per day that are known to be a potential threat to the living cell through DNA damage, only a few are believed to lead to irreparable damage (1). This small number of irreversible events is significant because it is the fundamental step that ultimately leads to mutation and the onset of cancer (2). Oxidative stress is known to be a primary cause of such damage occurring through the formation of radical ions of nucleic acid bases, and the ease with which each individual base is ionized to produce the corresponding base radical cation is determined by its ionization potential, the order being G Ͻ A Ͻ C Ϸ T (3). Thus, within a randomly photoionized DNA strand through hole transfer from one base to the next, damage tends to favor formation of the G base radical (4-6). There is considerable research effort in trying to understand the precise mechanism of long-range electron transfer as a function of the sequence-dependent structure and how this mechanism relates to DNA damage (7-11). UV radiation to initiate DNA base ionization has proven extremely useful for studying direct DNA damage (4-6, 12) along with pulse radiolysis (13). Traditionally, reactions in DNA are monitored by either following the kinetics on the nanosecond time scale using UV͞visible absorption spectroscopy (5, 6, 12, 13) or determining the resulting base damage (single-or double-strand breaks) using hot piperidine treatment or excision enzyme analysis followed by gel electrophoresis (14, 15). Conversely, ESR spectroscopy has provided structural information on ionization products. These studies used either UV͞visible irradiation or pulse radiolysis to produce ionized DNA species in frozen glass at cryogenic temperatures (16)(17)(18)(19) and in solution (20). However, this method did not permit ultrafast time scales to be studied. It is known that the chemical processes involved in DNA damage stretch across a wide range of time domains from femtoseconds to seconds, and being able to observe the earliest event...

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Section: Resultssupporting

confidence: 80%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Monitoring the direct and indirect damage of DNA bases and polynucleotides by using time-resolved infrared spectroscopy

Kuimova

Cowan

Matousek

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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“…Direct information about the ionization process can be obtained by transient absorption spectroscopy which allows the quantification of the generated hydrated electrons (e aq -) and the identification of the resulting cations and/or derived radicals of nucleobases. [9][10][11][12][13][14][15][16] The sparse experiments of this type performed for DNA oligomers and polymers in neutral pH did not detect one photon ionization for excitation wavelengths greater than 210 nm.…”

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confidence: 99%

One- and Two-Photon Ionization of DNA Single and Double Helices Studied by Laser Flash Photolysis at 266 nm

2006

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The ionization of the DNA single and double helices (dA) 20 , (dT) 20 , (dAdT) 10 .(dAdT) 10 and (dA) 20 . (dT) 20 , induced by nanosecond pulses at 266 nm, is studied by time-resolved absorption spectroscopy. The variation of the hydrated electron concentration with the absorbed laser intensity shows that, in addition to two photon ionization, one photon ionization takes place for (dAdT) 10 (dAdT) 10 , (dA) 20 (dT) 20 and (dA) 20 but not for (dT) 20 . The spectra of all adenine containing oligomers at the microsecond time-scale correspond to the adenine deprotonated radical formed in concentrations comparable to that of the hydrated electron. The quantum yield for one photon ionization of the oligomers (ca. 10 -3 ) is higher by at least one order of magnitude than that of dAMP showing clearly that organization of the bases in single and double helices leads to an important lowering of the ionization potential. The propensity of (dAdT) 10 (dAdT) 10 , containing alternating adenine -thymine sequences, to undergo one photon ionization is lower than that of (dA) 20 (dT) 20 and (dA) 20 , containing adenine runs. Pairing of the (dA) 20 with the complementary strand leads to a decrease of quantum yield for one photon ionization by about a factor two. 20 . The choice of these base sequences was guided by previous photophysical and photochemical studies carried out in our group which allowed us to overcome experimental and conceptual difficulties related to the fragility and complexity of these systems. [18][19][20][21] We show that upon excitation at 266 nm one photon ionization is observed only for the adenine containing oligomers leading, in all cases, to the formation of deprotonated adenine radicals. The quantum yield for one photon ionization of these oligomers (ca. 10 -3 ) is at least ten times higher than that of the mononucleotide 2'-deoxoadenosine monophosphate (dAMP).Our experiments were performed using the fourth harmonic (266 nm) of a Nd/YAG laser delivering 8 ns pulses at a repetition rate of 2 Hz. The absorbed laser intensity (I) varied from 0.13 to 1. measurements, we conclude that the quantum yield for one photon ionization (φ 1hν ) of dAMP does not exceed 10 -4 . This upper limit is 30 times lower than the value found for monophotonic ionization of dAMP in ultrapure water from experiments performed with higher laser intensities without using a flow-through cell. 26The plot corresponding to each oligomer in Figure 2 are fitted correctly by the function aI + b. In all cases it is found that two photon ionization takes place (a ≠ 0). This is not surprising since the decays of the singlet excited states of such single and double strands are longer than the decays of dAMP 20,27 allowing the absorption of successive photons. Moreover, exciton-exciton 20 interaction could also be but not for (dT) 20 . This difference in the behavior of (dT) 20 compared to the adenine containing oligomers is not surprising since the gas phase IP of hydrated thymine is higher than that of the hydrated adenine. ...

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Derivatization of amino acids for enhanced ion yield in laser desorption/post-ionization mass spectrometry

Preisler

Yeung

1999

J. Mass Spectrom.

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Ionization of purine nucleosides and nucleotides and their components by 193-nm laser photolysis in aqueous solution: model studies for oxidative damage of DNA

Cited by 213 publications

References 0 publications

Monitoring the direct and indirect damage of DNA bases and polynucleotides by using time-resolved infrared spectroscopy

Monitoring the direct and indirect damage of DNA bases and polynucleotides by using time-resolved infrared spectroscopy

One- and Two-Photon Ionization of DNA Single and Double Helices Studied by Laser Flash Photolysis at 266 nm

Derivatization of amino acids for enhanced ion yield in laser desorption/post-ionization mass spectrometry

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