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Eberhard Bothe Helmut Gorner Joachim Opitz Dietrich Schulte-Frohlinde Aslam Siddiqi Malgorzata Wala 《Photochemistry and photobiology》1990,52(5):949-959
Double-stranded (ds) calf thymus DNA (0.4 mM), excited by 20 ns laser pulses at 248 nm, was studied in deoxygenated aqueous solution at room temperature and pH 6.7 in the presence of a sodium salt (10 mM). The quantum yields for the formation of hydrated electrons (phi c-), single-strand breaks (phi ssb) and double-strand breaks (phi dsb) were determined for various laser pulse intensities (IL). phi c- and phi ssb increase linearly with increasing IL; however, phi ssb has a tendency to reach saturation at high IL (greater than 5 X 10(6) Wcm-2). The ratio phi ssb/phi c-, representing the number of ssb per radical cation, is about 0.08 at IL less than or equal to 5 X 10(6) Wcm-2. For comparison, the number of ssb per OH radical reacting with dsDNA is 0.22. On going from argon to N2O saturation, phi ssb and phi dsb become larger by factors of approximately 5 and 10-15, respectively. This enhancement is produced by attack on DNA bases by OH radicals generated by N2O-scavenging of the photoelectrons. While phi ssb is essentially independent of the dose (Etot), phi dsb depends linearly on Etot in both argon- and N2O-saturated solutions. The linear dependence of phi dsb implies a square dependence of the number of dsb on Etot. This portion of dsb formation is explained by the occurrence of two random ssb, generated within a critical distance (h) in opposite strands. For both argon- and N2O-saturated solutions h was found to be of the order of 40-70 phosphoric acid diester bonds. On addition of electron scavengers such as 2-chloroethanol (or N2O plus t-butanol), phi dsb is similar to that in neat, argon-saturated solutions. Thus, hydrated electrons are not involved in the chemical pathway leading to laser-pulse-induced dsb of DNA. 相似文献
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Alessandro B. Tossi Helmut Görner Dietrich Schulte-Frohlinde 《Photochemistry and photobiology》1989,50(5):585-597
The reactions of polyuridylic acid [poly(U)] with Ru(bpy)3(3+) [Ru(III)] and SO4.-, following UV and visible light irradiation of Ru(bpy)3(2+) [Ru(II)] in the presence of S2O8(2-), were studied in an argon-saturated aqueous solution using time-resolved absorption and conductivity methods. The kinetics of the Ru(III) conversion to Ru(II) in the presence of poly(U) was monitored spectroscopically either in the absence of SO4.- [rapid mixing with Ru(III)] or in its presence (after laser flash excitation, lambda exc = 353 nm). The conversion of Ru(III) to Ru(II) is complete at a [nucleotide]/[sensitizer] (N/S) ratio greater than or equal to 10 (rate constant k = 12 s-1) for rapid mixing and at N/S greater than or equal to 6 (k = 15 s-1 at N/S = 10) after laser pulsing. Conductivity measurements following the laser pulse revealed a fast conductivity increase (risetime less than 10 micros), due to the formation of charged species and protons. A slower increase in the 0.1-0.5 s range was observed for poly(U) but it is considerably smaller for poly(dU) and absent in uracil containing monounits. The slow increase is unaffected by pH changes in the 3.5-7 range, markedly reduced in the 7-9 range and is replaced by a slight decrease in conductivity in buffered solutions. An explanation is that poly(U)-bound excited Ru(II) reacts with S2O8(2-) forming Ru(III) and SO4.- as oxidizing species both of which react with poly(U) bases. The resulting base radicals react with Ru(III) or the ligands in the ruthenium complex, producing protons which give rise to the slow conductivity increase (k = 15 s-1 at N/S = 10). The formation of single-strand breaks and the ensuing release of condensed counterions does not appear to contribute significantly to the slow conductivity signal. At N/S less than 10 the observed rate and extent of Ru(III)--Ru(II) conversion and of the slow proton production vary markedly with the N/S ratio. 相似文献
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Abstract— By means of in situ photolysis EPR of aqueous solutions of α-oxocarboxylic acids (RCO-CO2 H) at pH values above 5, semidione radical anions [RC(O- )=C(O')R] and α-hydroxy-α-carboxy alkyl radicals [RC(OH)CO2 -] were detected. C02 was identified as a reaction product. On photolysis of mixtures of α-oxocarboxylic acids (RCOCO2 H and R'COCC2 H), "mixed" semidione radical anions [RC(O- >=C(O)R'] were observed in addition to RC(O- )=C(O')R, R'C(O- )=C(O')R', RC(OH)CO2 - and R'C(OH)CO2 - . The experimental results are explained in terms of photodecarboxylation (α-clea-vage) of electronically excited RCOCOJ to yield RCO and CO2 . The radicals RC(OH)CO2 - are formed by reduction of RCOCO2 - by CO2 - . The semidione radicals are produced by addition of RCO to RCOCO2 - followed by decarboxylation of the intermediate adduct. This mechanism was confirmed by generating acyl radicals independently and reacting them with α-oxocarboxylic acids. Selected product studies support the mechanism suggested. 相似文献
4.
Eberhard Bothe Man Nien Schuchmann Dietrich Schulte-Frohlinde Clemens von Sonntag 《Photochemistry and photobiology》1978,28(4-5):639-643
Abstract— In aqueous solutions α-hydroxyalkylperoxyl radicals undergo a spontaneous and a base catalysed HO2 elimination. From kinetic deuterium isotope effects, temperature dependence, and the influence of solvent polarity it was concluded that the spontaneous reaction occurs via an HO2 elimination followed by the dissociation of the latter into H+ and O2 - . The rate constant of the spontaneous HO2 elimination increases with increasing methyl substitution in α-position ( k (CH2 (OH)O2 ) < 10s-1 k (CH3 CH(OH)O2 ) = 52s-1 k ((CH3 )2 C(OH)O2 ) = 665 s-1 ). The OH- catalysed reaction is somewhat below diffusion controlled. The mixture of peroxyl radicals derived from polyhydric alcohols eliminate HO2 at two different rates. Possible reasons for this behaviour are discussed. The mixture of the six peroxyl radicals derived from d -glucose are observed to eliminate HO2 with at least three different rates. The fastest rate is attributed to the HO2 elimination from the peroxyl radical at C-l ( k > 7000s-1 ). Because of the HO2 eliminations the peroxyl radicals derived from d -glucose do not undergo a chain reaction in contrast to peroxyl radicals not containing an α-OH group. In competition with the first order elimination reactions the α-hydroxylalkylperoxyl radicals undergo a bimolecular decay. These reactions are briefly discussed. 相似文献
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H. Görner und D. Schulte-Frohlinde 《Colloid and polymer science》1979,257(8):910
Ohne Zusammenfassung 相似文献
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Quantum yield measurements have been made for the trans→cis photoisomerizations of the quaternary iodides of 4-cyano- and 4-nitro-4′-azastilbene (CP and NP, respectively) in ethanol solution at room temperature in the presence and absence of ferrocene and azulene. A triplet mechanism is suggested for the photoisomerization of NP and a singlet mechanism for that of CP. These mechanisms are supported by laser flash-photolysis studies of the trans triplet state of CP and NP as a function of temperature and quencher concentration. 相似文献
9.
The Reaction of Triplet 2-Methyl-1,4-Naphthoquinone (Menadione) with DNA and Polynucleotides 总被引:3,自引:0,他引:3
Abstract— The photoreaction of 2-methyl-l,4-naphthoquinone (MQ, menadione) with DNA and polynucleotides in argon-saturated aqueous solution (pH 7) was studied. Results from laser flash photolysis experiments indicate that triplet quinone reacts with DNA and polyA but not detectably with polyU by one-electron oxidation of the bases of the nucleic acid with formation of the radical anion of the quinone. Irradiation of argon-saturated solutions containing MQ and DNA or polynucleotides (polyU, polyA, polyG or polyC) with 334 nm light leads to an increase in molecular weight for single-stranded DNA, polyA and to a much less extent for polyU. This finding indicates crosslink formation with quantum yields in the range of 10−5 -10−3 相似文献
10.
S. Steenken W. Jaenicke-Zauner D. Schulte-Frohlinde 《Photochemistry and photobiology》1975,21(1):21-26
Abstract —On photoexcitation, hydroxyacetone undergoes a Norrish-type-1 fragmentation to yield CH3CO and CH2OH. CH2OH is identified by its EPR spectrum. The existence of CH3CO is inferred from the presence of diacetyl and acetaldehyde in irradiated solutions. Above pH 5, in addition to CH2OH, the cis and trans forms of the hydroxyacetone enediol radical anion, CH3C(O-)=C(O***)H, are detected. 1.3-Dihydroxyacetone is photodecomposed to HOCH2C?O and C?H2OH. The former radical decarbonylates to yield CH2OH and CO. At 254 nm the overall quantum yield of CO production is 0.75. Above pH 5, in addition to CH2OH, the cis and trans forms of the 1.3-dihydroxyacetone enediol radical anion, HOCH2C(O-)C(O***)H, are observed. Electronically excited hydroxyacetone and 1.3-dihydroxyacetone react exclusively by C-C fragmentation, and no H-abstraction from H-donors is observed. In contrast, electronically excited 1.3-dicarboxyacetone shows H-abstraction from H-donors in competition with C-C fragmentation. In the absence of H-donors, fragmentation resulting in CH2CO2- and -O2CCH2C?O occurs followed by decarbonylation of -O2H2C?O. At 254 nm the quantum yield of CO production is 0.02. In the presence of H-donors, H-abstraction, yielding HO2CCH2C(OH)CH2CO2, predominates. 相似文献