218 - Redox processes during photodynamic damage of DNA I. Results obtained by several physico-chemical methods

Berg, Hermann; Gollmick, Friedrich A.; Triebel, Hans; Bauer, Eckhard; Horn, G.; Flemming, J.; Kittler, L.

doi:10.1016/0302-4598(87)87045-9

Cited by 19 publications

(8 citation statements)

References 22 publications

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“…The conspicuous loss of absorbance at 520 nm raises an interesting possibility in regard to the photosensitized oxidation of guanine derivatives by MB. Berg et al (1978) have shown that thiopyronine (TP) reacts most readily with guanosine through its semioxidized form (TP'). In a series of papers (Berg, 1978;Berg et al, 1978;Kittler er al.. 1980) it was proposed that photosensitized single-and double-strand breaks in DNA occur via a mechanism in which the half-oxidized form of the photosensitizer reacts with guanine in DNA by electron transfer.…”

Section: Methodsmentioning

confidence: 99%

The Role of Ground State Complexation in the Electron Transfer Quenching of Methylene Blue Fluorescence by Purine Nucleotides

Dunn

Lin

Kochevar

1991

Photochem & Photobiology

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The effect of three purine nucleotides on the fluorescence of methylene blue in aqueous buffer has been investigated. Guanosine-5'-monophosphate (GMP) and xanthosine-5'-monophosphate cause fluorescence quenching while adenosine-5'-monophosphate causes a red shift in the fluorescence maximum. All three nucleotides form ground state complexes with the nucleotides as indicated by absorption spectroscopy. The fluorescence changes at nucleotide concentrations less than 30 mM are best described by a static mechanism involving the formation of non-fluorescent binary and ternary complexes in competition with dimerization of the dye. Quenching of the fluorescence decay (tau = 368 ps) at high GMP concentrations (10-100 mM) occurs at the rate of diffusion. The mechanism of fluorescence quenching may involve electron transfer within the singlet excited dye-nucleotide complex although published values of the oxidation potentials of various purine derivatives would suggest that all three nucleotides should cause quenching. Evidence for electron transfer was obtained from flash photolysis experiments in which 100 mM GMP was found to cause the appearance of a long lived transient species absorbing in the region expected for semimethylene blue.

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Section: Methodsmentioning

confidence: 99%

The Role of Ground State Complexation in the Electron Transfer Quenching of Methylene Blue Fluorescence by Purine Nucleotides

Dunn

Lin

Kochevar

1991

Photochem & Photobiology

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“…Photodynamic oxidation of nucleic acids and their components in the presence of various dyes has been extensively studied (Berg et al, 1978a;Berg, 1978b;Kittler et al, 1980;Girotti, 1983;Cadet et ul., 1983). It has been shown that guanine is the most readily disrupted residue (Sussenbach and Berends, 1964;Waskell et al, 1966;Rosenthal, 1971;Houba-Herin et ul., 1983) and that several mechanisms seem to be involved in the process, the major mechanisms being either a singlet-oxygen Type I1 mechanism, or a Type I process involving the formation of a complex between the triplet state of sensitizer and substrate, followed by an oxidation of the latter by ground-state triplet oxygen (Gollnick, 1968).…”

Section: Introductionmentioning

confidence: 99%

Photocleavage of Dna in the Presence of Synthetic Water‐soluble Porphyrins

Praseuth

Gaudemer

Verlhac

et al. 1986

Photochem & Photobiology

144

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In the presence of oxygen and visible light, various synthetic water‐soluble porphyrins cleave pBR 322 plasmid supercoiled DNA (form I) producing relaxed (form II) and linear (form III) DNA corresponding to single‐strand and double‐strand breaks respectively. Large variations are observed in the efficiency of the porphyrins containing a diamagnetic metal or no metal at all. Singlet oxygen (1O2) seems to be involved in the mechanism of cleavage consistent with the inhibitory effect of the azide anion, N–3. The higher efficiency of cationic porphyrins (as compared to anionic ones) is due to their greater affinity for DNA as shown by experiments carried out at either high ionic strength or in the presence of the surfactant, sodium dodecyl sulfate.

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“…The photoreactions of thiopyronine have been studied in detail first by Morita and Kato [24] and later by Berg et al [25]. The dye is of some importance in photobiology due to its very strong photodynamical efficiency [26].…”

Section: The Probe Function Of Heavy Atom Substimentsmentioning

confidence: 99%

“…The flash lamp was filled with xenon (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), the electric energy of the discharge being 100 J (20 kY, 0.5~the flash duration (FWHM) 3 IJ.S. A Kodak Wratten filter No.8 was inserted between the flash lamp and the photolysis cell to absorb light of wavelengths shorter than 450 nm.…”

Section: The Probe Function Of Heavy Atom Substimentsmentioning

confidence: 99%

Heavy Atom Substituents as Molecular Probes for Solvent Effects on the Dynamics of Short‐lived Triplet Exciplexes

Winter

Steiner

1980

Ber Bunsenges Phys Chem

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The influence of heavy atom substituents (Br, I) in the electron donor aniline on the electron transfer reaction with thiopyronine triplet is investigated by flash spectroscopy in solvents of different viscosity and polarity. Triplet quenching constants and radical yields are determined. The results are analysed in terms of decay constants of an intermediate triplet exciplex where the heavy atom substituents significantly enhance the intersystem crossing process leading to singlet ground state formation and thus diminishing the radical yield due to exciplex dissociation. The sensitivity of the radical yield to solvent effects is strongly enhanced by heavy atom substitution though the solvent effects proper on the exciplex dynamics are substituent independent. The heavy atom effect is used to study the solvent cage effect on exciplex dissociation by means of viscosity variation. The exciplex dissociation lifetime is proportional to solvent viscosity, however, it contains a constant contribution which may be attributed to exciplex bonding. By means of the heavy atom probes it is found that increasing solvent polarity intersystem crossing in the exciplex is favored over exciplex dissociation into radicals. A tentative explanation is given in terms of solvent polarity dependence of the electronic energy gap between exciplex and corresponding Franck-Condon ground state. (1) and (2) it follows that the radical yield is determined by three factors, characterizing the behaviour of the triplet exciplex (Eq. (4» where 'Hal is the atomic spin-orbit coupling constant of the halogen and C 2 (POSHaJ is the Hiickel spin density transferred to the position of the halogen atom by the electron transfer. The latter factor readily explains the positional dependence of the substituent effect (para > ortho > meta).(1)The rate determining step in the quenching of the excited cationic dye triplet eA +) by the electron donor (D) is the formation of a triplet exciplex with radical-pair-like electronic structure e(A'D +». The triplet exciplex has two decay channels: dissociation to the free radicals (rate constant k fr ) and intersystem crossing with back transfer of the electron to the donor leading to the formation of the ground state of the reaction partners (rate constant k isc ) ' The radical yield observed is determined by the two decay constants of the exciplex:triplet exciplexes can be detected by their phosphorescence under such conditions. In a recent paper [22] we provided indirect evidence for the formation of triplet exciplexes as intermediates in electron transfer reactions. We studied the reaction of thionine triplet as an electron acceptor with aniline and its monohalogen derivatives as electron donors in methanol. In these reactions the halogen substituents have systematic influence on the radical yield (extrapolated to complete triplet quenching) which could be explained satisfactorily by the following mechanism, strongly supported by a recently determined magnetic field effect [23]:The analysis of the radical yield...

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218 - Redox processes during photodynamic damage of DNA I. Results obtained by several physico-chemical methods

Cited by 19 publications

References 22 publications

The Role of Ground State Complexation in the Electron Transfer Quenching of Methylene Blue Fluorescence by Purine Nucleotides

The Role of Ground State Complexation in the Electron Transfer Quenching of Methylene Blue Fluorescence by Purine Nucleotides

Photocleavage of Dna in the Presence of Synthetic Water‐soluble Porphyrins

Heavy Atom Substituents as Molecular Probes for Solvent Effects on the Dynamics of Short‐lived Triplet Exciplexes

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