Quantum yields for the generation of hydrated electrons and single-strand breaks in poly(C), poly(A) and single-stranded DNA in aqueous solution on 20 ns laser excitation at 248 nm

Wala, Malgorzata; Bothe, Eberhard; Görner, Helmut; Schulte‐Frohlinde, D.

doi:10.1016/1010-6030(90)87116-s

Cited by 55 publications

(34 citation statements)

References 35 publications

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“…, 1975;Bensasson et al, 1983) on the triplet state (e.g. a,,,) and to extend the information concerning photoionization (Nikogosyan and Letokhov, 1983;Schulte-Frohlinde et al, 1985;Wala et al, 1990). The quantum yield of electron ejection (ac-) was measured for various uracil derivatives at defined excitation conditions.…”

Section: Introductionmentioning

confidence: 99%

TRANSIENTS OF URACIL and THYMINE DERIVATIVES and THE QUANTUM YIELDS OF ELECTRON EJECTION and INTERSYSTEM CROSSING UPON 20 ns PHOTOLYSIS AT 248 nm

Görner

1990

Photochem & Photobiology

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Transients of uracil and a series of 17 correlated pyrimidines, e.g. methylated bases, nucleosides, nucleotides, and polyuridylic acid [poly(U)] were studied after 248 nm excitation by 20 ns laser pulses. The transient absorption spectra in aqueous solution at room temperature reveal the triplet state and the hydrated electron (e-aq), while the corresponding radical cation could not be observed at pH 6-7. Fast loss of the chromophore in the 260-290 nm range within 0.1 microsecond was observed in aqueous solution in some cases [e.g. poly(U), 5'-UMP, uridine, uracil] and in others (thymine, thymidine) virtually not. This photobleaching is assigned to formation of the photohydrate. The concentration of e-aq shows a quadratic dependence on the laser pulse intensity (IL) in the range (0.2-2) x 10(7) W cm-2 and the quantum yield of electron ejection (phi c-) thus depends linearly on IL. This behaviour, suggesting that the photoionization involves a two-step absorption process, was found for poly(U) and all pyrimidine monomers examined. At a constant IL value of 2 x 10(7) W cm-2, phi c- ranges from 3 x 10(-3) for 1,3-dimethylthymine to 4 x 10(-2) for poly(U). The triplet state shows a much larger transient absorbance (delta A, typically in a broad range, e.g. 290-500 nm) than that of the neutral radical resulting from the radical cation. The triplet state in organic solvents (acetonitrile and ethanol) shows generally a significantly larger delta A value than in aqueous solution. The estimated quantum yields of intersystem crossing at room temperature are compared with those of phosphorescence at -196 degrees C.

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Section: Introductionmentioning

confidence: 99%

TRANSIENTS OF URACIL and THYMINE DERIVATIVES and THE QUANTUM YIELDS OF ELECTRON EJECTION and INTERSYSTEM CROSSING UPON 20 ns PHOTOLYSIS AT 248 nm

Görner

1990

Photochem & Photobiology

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“…For A,,, c 250 nm it has to he taken into account that the reverse photosplitting reaction occurs effectively (with @ = 0.5-1). Kochcvar and BuckleyZR have used sufficiently low fluences 01' [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] . I m and their rcsult for A,, = 193 nm is ad,,,, = 1.05 x lo-'.…”

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confidence: 99%

PHOTOLESIONS IN DNA UPON 193 nm EXCITATION

Gurzadyan¹,

Görner

1993

Photochem & Photobiology

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Aqueous solutions of plasmid (pBR322 and pTZ18R) and calf thymus DNA were excited by 20 ns laser pulses at 193 nm. The quantum yields of single-and double-strand break formation, interstrand cross-links, locally denatured sites, (6-4)photoproducts and biological inactivation (phi ssb, phi dsb, phi icl, phi lds, phi 6-4 and phi ina, respectively) were measured. The quantum yields are virtually independent of intensity, demonstrating a one-quantum process. The obtained values in aerated neutral solution in the absence of additives are phi ssb approximately 1.5 x 10(-3), phi dsb approximately 0.06 x 10(-3) (dose: 10-200 J m-2), phi icl approximately phi lds approximately 0.1 x 10(-3) and phi 6-4 = 0.5 x 10(-3). Both phi ssb and phi dsb decrease strongly with increasing concentrations of TE buffer (0.01-10 mM). Biological inactivation of the pTZ18R plasmid was determined from the transformation efficiency of Escherichia coli bacteria strains AB1157, AB1886 uvr and AB2480 uvr rec; the phi ina values are 1.4 x 10(-3), 2.1 x 10(-3) and 3 x 10(-3), respectively. The monoexponential survival curves in all cases show that a single damage site leads to inactivation (one single hit). The biological consequences of different photoproducts are discussed.

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“…From the initial linear increase of Qe-vs intensity (at low values) it has been concluded that the electrons and respective base radical cations are produced by consecutive biphotonic excitation Opitz and SchulteFrohlinde, 1987;Wala et al, 1990;Gorner, 1990a). Also for RNA and DNA Nikogosyan (1990) and his group have shown that Qe-increases with increasing ps laser pulse intensities and reaches a maximum.…”

Section: Photoionizationmentioning

confidence: 98%

“…The concentration of hydrated electrons as a function of the laser-pulse intensity shows a square dependence at low intensities and goes over to a linear dependence at high intensities (Opitz and Schulte-Frohlinde, 1987;Wala et al, 1990). This latter behaviour may lead erroneously to the conclusion that photoionization occurs monophotonically.…”

Section: Photoionizationmentioning

confidence: 98%