摘要:

Abstract—The photophysical and photochemical properties of thiophene derivatives have been studied by fluorescence and by 353 nm laser flash spectroscopy. α‐Terthienyl and its derivatives show a moderate fluorescence quantum yield (less than 0.1) in cyclohexane, ethanol, or TritonX–100 micelles. An additional thiophene ring increases this value to 0.2 in ethanol or micelles. The transient triplet state of the six thiophenes is characterized by strong absorptions (ε⋍ 50000M‐1cm‐1) in the visible region. These triplet states are very long lived. They react with oxygen, producing singlet oxygen very efficiently because of their high quantum yield of triplet formation (0.1 to 0.3). They do not react with excellent hydrogen or electron donors such as indole, N‐acetyl tryptophanamide or cysteine. The hydrophobic thiophenes investigated are, therefore, Type II photodynamic agents alm

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03439.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—The phosphorescence of alcohol dehydrogenase from horse liver (LADH) can be observed at room temperature. The quenching of this long‐lived light emission, which comes from a tryptophan residue well buried within the interior of the enzyme structure, was measured. The rate constants for the quenching by the small oxygen molecule and by theI‐1ion were found to be 1.4 → 108M‐1s‐1and 108M‐1s‐1, respectively, at room temperature. The temperature dependence of the quenching yields an activation energy of about 14 kcal/mol. This activation energy and the meaning of the accompanying large pre‐exponential factor in the Arrhenius equation, A = 1018M‐ls‐1, are discussed in terms of a model in which the quencher threads its way throug

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03440.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—Sensitization and quenching experiments demonstrate that laser flash photolysis ofpyridoxal–5′‐phosphate populates a triplet state about 244 kJ/mol. Excitation by the 337.1‐nm photons from a nitrogen laser generated transient absorption in the 400‐nm region which decayed with a fast first order component on a much slower one. Xanthone photosensitized the same absorption; oxygen, nitric oxide, biacetyl, and 1,3‐cyclo‐hexadiene quenched it. Spectra and lifetimes suggest that the triplet state leads to ra

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03441.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—High concentrations of organic chromophores, in particular pyrene, were found to incorporate into the cluster network of water swollen Nation. The vibrational structure of the fluorescent molecule and its fluorescence lifetime were used to probe the location of pyrene in this structure. Strong heavy‐atom induced room temperature phosphorescence was observed from the chromophore in the water swollen membrane. Excimer formation in tm‐butanol swollen Nation was observed and was utilized to estimate the micro viscosity in this s

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03442.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—The quantum yield of singlet oxygen generation (φ) was measured at 546 nm with thep‐nitrosodimethylaniline (RNO) method. The results obtained in pH 7.4 phosphate buffer (PB) were: φ(HP) = 0.44 ± 0.05: φ= 0.71 ± 0.07: φ(HpD‐A) = 0.06 ± 0.02. The value of φ was constant from 3 to 67μM, attributed to the dominance of HP dimers; φ (HP) increased to 0.77 ± 0.13 in the presence of small egg phosphatidylcholine liposomes (SUV), attributed to solubilization and monomerization: φ (HpD‐A) increased to 0.87 ± 0.17 in the presence of SUV. attributed to monomerization of the impurity porphyrins and unfolding of the covalent dimer constituents. The quantum efficiency of the RNO system (100 μMRNO plus 10 mM histidine) was approximately 0.015 at pH 7.4 and increased sign

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03443.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—The aerobic xanthine oxidase reaction causes the co‐oxidation of 2,5‐dimethylfuran to cis‐diacetylethylene and the bleaching of rubrene tetracarboxylate. These actions were suppressed by superoxide dismutase, catalase, desferoxamine and by benzoate and other hydroxyl radical scavengers. The bleaching of rubrene tetracarboxylate was not enhanced in D20. These results suggest that OHv, generated from O2‐plus H2O2by an iron‐catalyzed Haber Weiss reaction, was the responsible agent and that singlet oxygen was not detectably involved. Control experiments, in which singlet oxygen was generated photochemically, demonstrated that replacement of H2O by D2O caused the expected enhancement of the chemical reactivity of singlet oxygen under the conditions of these experiments and that O2‐, at concentrations achieved by the xanthine oxidase reaction, did not detectably quench singlet oxygen. We conclude that singlet oxygen, if produced at all during the aerobic xanthine oxidase reaction, cannot exceed 0.1% of the prod

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03444.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—In the present paper the mechanism of photoreactivation and photodestruction of partially purified nitrate reductase fromNeurospora crassawas investigated. For both photoreactions exogenous flavin was needed; the rates of the photoreactions depended on the concentration of free flavin in the irradiated sample. Their efficiency as photoreceptors increased in the sequence FAD–FMN–riboflavin. No effect of enzyme‐bound flavin as photoreceptor was found in these photoreactions. Photoreactivation of nitrate reductase inactivated by reduction in the presence of KCN is due to its reaction with flavins in their triplet state. Photodestruction is due to singlet oxygen generated from triplet flavin in the presence of oxygen. Rate constants are estimated to bek =1–5 × 10‐1M‐1s‐1for the reaction of nitrate reductase with the flavin triplet (photoreactivation) andk= 5 × 10‐1M‐1s‐1for the reaction with singlet ox

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03445.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—The average molecular weights of haematoporphyrin derivative (HPD), the fractions of HPD that can he obtained by gel chromatography and of purified haematoporphyrin and protoporphyrin in aqueous solution have been determined by ultracentrifugation. The results show that HPD contains polymeric material with the excluded fraction from the gel column (HPD aggregate) having an average molecular weight of greater than 20000. The two remaining gel column fractions of HPD have lower molecular weights and their similarity indicates that these fractions do not separate because of molecular weight differences. Purified haematoporphyrin has a comparatively low molecular weight in aqueous solution but the data is not capable of discriminating between monomer, dimer or slightly higher oligomer. In contrast, protoporphyrin sediments to the bottom of the centrifuge tube under the conditions of sedimentation equilibrium indicating that it has an average molecular weight considerably greater than that of HPD aggregat

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03446.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—C3H 10T½ cells in culture were prelabelled with [3H]arachidonic acid and exposed to UVB radiation. Almost immediately after irradiation cells released labelled arachidonate metabolites into media in a dose dependent manner. This release was inhibited by removing calcium ions from the system and by the addition of dexamethasone and parabromophenacyl bromide to the system. This suggests that the UVB stimulated release of arachidonic acid from membrane phospholipids is, in part, mediated by a phospholipase A2enzyme system. Thin layer chromatographic examination of media extracts revealed a dose dependent UVB stimulation of prostaglandin production by cultured cel

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03447.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—Exposure of ICR 2A cells to either 265, 289, 302 or 313 nm monochromatic UV wavelengths caused the induction of chromosome aberrations with chromatid gaps and breaks being the most common type of aberration detected. Treatment of U V‐irradiated cells with photoreactivating light (PRL) resulted in a lower yield of aberrations demonstrating that pyrimidine dimers are involved in the formation of chromosome aberrations induced by the UV wavelengths tested. However, the decrease in the level of aberrations resulting from PRL treatment of 313 nm‐irradiated cells was significantly less than for the other wavelengths indicating that non‐dimer photoproducts may have played an important additional role in the induction of chromosome aberrations by this UV wav

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03448.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY