摘要:

Abstract‐We have carried out a very detailed study, using fluorescence and optical flash photolysis techniques, of the photoreduction of methyl viologen (MV2+) by the electron donor ethylene diamine tetraacetic acid (EDTA) in aqueous solution sensitized by the dye acridine orange (AOH+). A complete mechanism has been proposed which accounts for virtually all of the known observations on this reaction. This reaction is novel in that both the triplet and the singlet state of AOH+appear to be active photochemically. We have shown that mechanisms previously proposed for this reaction are probably incorrect due to an artifact. At pH 7 the fluorescence quantum yield φsof AOH+is 0.26 ± 0.02 and the fluorescence lifetime is 1.8 ± 0.2 ns. φsis pH dependent and reaches a maximum of 0.56 at pH 4. The fluorescence of AOH+is quenched by MV2+at concentrations above 1 mMand the quenching obeys Stern‐Volmer kinetics with a quenching rate constant of (1.0 ± 0.1) × 1010M−1s−1. The quenching of the AOH+excited singlet state by MV2+almost certainly returns the AOH+to its ground state with no photochemistry occurring. EDTA also quenches the fluorescence of AOH· with Stern‐Volmer kinetics but with a smaller rate constant (6.4 ± 0.5) × 108M−1s−1at pH 7. In this case the quenching is reactive resulting in the formation of semireduced AOH.In the presence of MV2+, flash irradiation of AOH+does result in the reversible formation of the semireduced MV† which absorbs at 603 nm. We attribute this to a photochemical reaction of the triplet state of AOH+with MV2+. The initial quantum yield for formation of MV† (φMV:)0was found to be constant at 0.10 ± 0.05 for [MV2+] from 5 × 10−5to 1.0 × 10−3with [AOH+] = 8 × 10−6M.Previous workers had found that (φMV:)0appears to decrease with decreasing [AOH+]; however, on careful investigation, we found this was most probably due to quenching of the triplet state of AOH+by trace amounts of oxygen.When EDTA is added to a mixture of AOH+and MV2+at pH 7, the photochemical formation of MV† becomes irreversible as the [EDTA] is increased. The quantum yield for the irreversible formation of MV† exceeds 0.10 becoming as large as 0.16 for [EDTA]= 0.014M.This fact requires that an alternative photochemical process must be operative and we present evidence that this is a reaction of EDTA with the excited singlet state of AOH+to produce the semi‐reduced AOH‐ which then reacts with MV2+to produce MV†.The full kinetic scheme was tested by computer simulation and found to be totally consistent. This also enabled the processing of a full set of rate constants.When colloidal PtO2was added to the optimal mixture [EDTA] = 3.4 × 10−2M; [MV2+] = 5 × 10−4M; [AOH+] = 4 × 10−5M; pH6 H2gas was produced at a rate of 0.2μmol H2h−1. Thus, acridine orange should serve as an effective sensitizer

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb09040.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract‐Finely powdered cadmium sulfide in aqueous, air‐saturated, phosphate buffered suspension sensitizes the photooxidation of cysteine to cystine with good efficiency; several additional thiols and inorganic sulfides are also photooxidized. The other amino acids (histidine, methionine, tryptophan, tyrosine) known to be rapidly photooxidized with typical organic photosensitizers are photooxidized only very slowly. The quantum yield of oxygen uptake during cysteine photooxidation is pH dependent with a maximum (0.021) at pH 9.5; the yield is not increased in D2O and is not decreased appreciably by sodium azide, suggesting that singlet oxygen is not involved in the photooxidation process. The slow rate of photooxidation of histidine, which is known to react efficiently with singlet oxygen, also suggests that little if any singlet oxygen is produced by illuminated cadmium sulfide. Superoxide dismutase inhibits the yield of cysteine photooxidation to a maximum of approximately 50%, suggesting the partial involvement of superoxide in the reaction mechanism. The quantum yields of the photooxidation of cysteine, ethylenediaminetetraacetate and inorganic sulfides decrease as the wavelength of the exciting light is increased. Yeast alcohol dehydrogenase, a sulfhydryl enzyme, is inactivated by photodynamic treatment with cadmium sulfide; lysozyme, which has no free sulfhydryl groups, is

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb09041.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—When chlorophyll(Chl) and pheophytin(Phn) are irradiated in Triton X‐100 water binary solvents, singlet oxygen is formed in the medium in a higher yield for Phn than for Chi. Chlorophyll shows an irreversible photooxidation reaction and a chemical oxidation reaction when 1,3‐diphenyliso‐benzofuran (DPBF) is added to the solution. During the chemical oxidation, Chi is destroyed by an oxidizing agent that is a reaction product of the endoperoxide formed in the medium by the addition of singlet oxygen to DPBF. This reaction depends on the structure of the medium and has some characteristics of an oxidation by hydroxyl radicals. The highest yield is obtained with the micellar structure. Chlorophyll and Phn are readily oxidized by hydroxyl radicals generated using the Fenton reagent. This suggests that in the presence of Triton X‐100, the Mg2+ion of a Chi molecule plays a key role in the irreversible oxidation of th

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb09042.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract‐The pH and H0dependence of the absorption and fluorescence spectra of isoflavone and 7‐hydroxyisoflavone are reported. Isoflavone is fluorescent in acidic solution only, whereas 7‐hydroxyisoflavone is fluorescent in all acidity ranges under investigation. Ground and first excited singlet state pKa's have been determined spectrophotometrically and fluorimetrically, respectively. Excited state protolytic equilibration processes via a second order reaction (proton gain) are found to be too slow to compete efficiently with fluorescence. This is deduced from the close agreement between the pKa's of the conjugate acids obtained by absorption and fluorescence titrations. On the other hand, photodissociation of 7‐hydroxyisoflavone proceeds faster than its fluorescence decays. The experimental pKa(S1) is in fair agreement with the calculated one. 7‐Hydroxyisofiavone forms a phototautomer (or exciplex) in the pH 2 to H0‐1 acidity range, which is characterized by its long wavelength emission. Quantum efficiencies are given for isoflavone and 7‐hydroxyisoflavone in aqueous solutions of various acidities. Deuteration effects thereon

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb09043.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—Absorption spectra and fluorescence quenching of carbazole (C) and N‐ethyl carbazole (EC) by some aliphatic halocarbons have been studied in 3‐methylpentane (3MP) and ethanol (EtOH). Both steady‐state and transient kinetic measurements were used to determine the quenching rate constants (kq). These rate constants were found to be sensitive to the polarity and also to the hydrogen bonding ability of the solvents used. Endothermic electron transfer reactions were shown to take place in these systems. When the electron donor C is involved in hydrogen bonding with EtOH, the net effect is a decrease inkq. This is explained by taking into account the red‐shifted (0,0) transition energy (Es) of the1Lbabsorption band when the reaction is nearly diffusion controlled. For reaction far from diffusion controlled, theEsvalue correction to kqis not enough to explain the lowkqvalue

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb09044.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—The photobinding of psoralen and 8‐methoxypsoralen to calf thymus DNA induced by 365 nm radiation has been measured for different concentrations of the furocoumarin and nucleotides. The results are consistent with the assumption that dark complexing of the furocoumarin to DNA is a pre‐condition for photobinding, but do not exclude the possibility that the free furocoumarin participates in the reactions. The analysis with ‘large target’ diffusion theory indicates that photobinding should be inefficient for the free excited singlet state and competitive with reactions of the dark‐complexed sensitizer for the free triplet state. The analysis indicates also that the diffusive reactions of singlet oxygen generated by the free furocoumarin can compete with photoadduc

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb09045.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—Bacteriophage SP02c12 and its isolated DNA were irradiated at 254 nm in tryptophan solutions. At a concentration of 10 mM, the amino acid exerted a protective effect on intact virus. The magnitude of this effect depended upon the length of time elapsed between mixing and irradiation. No protection was observed for solutions irradiated immediately after mixing. Tryptophan did not have a significant effect on UV sensitivity of the isolated viral DNA. No covalent crosslinking of tryptophan to DNA was observe

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb09046.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—It has been known that haemoatoporphyrin derivative (Hpd) has a preferential distribution in tissues with high mitotic index. Furthermore, cytocidal activity of light activated Hpd within the cells has been exploited in the therapy of experimental and human cancer. It is reported here that maximum, long lasting, although reversible, inhibition of DNA synthesis was obtained in Hpd‐treated lymphocytes. However, Hpd‐treated lymphoid cells did not stimulate allogeneic lymphocytes in the primary mixed lymphocyte reaction (MLR) culture. Phytohaemagglutinin (PHA) stimulated murine lymphocytes treated with Hpd and exposed to laser light have shown higher susceptibility to lysis than resting, PHA unstimulated, lymphocytes.In vitroDBA/2 stimulated C57 lymphocytes, inoculated into X‐irradiated BD2F1mice, upon Hpd treatment followed by exposure to light, did not cause a lethal graft vs. host reaction (GVHR).Haematoporphyrin derivative was preferentially incorporated by large and metabolically active cells. inhibited the incorporation of [3H]‐thymidine in the lymphocyte nucleus and could be exploited to selectively remove blast cells from resting ly

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb09047.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—Hybrid cell lines (hybridomas) have been isolated from fusions between P3‐NS1‐1‐Ag4‐1 mouse myeloma cells and spleen cells from BALB/c mice hyperimmunised with UV‐irradiated single‐stranded DNA (UVssDNA) and UV‐irradiated polydeoxythymidylic acid (UVpolydT). Monoclonal antibodies from two different hybridomas are characterised in the present report by competitive inhibition with different synthetic polynucleotides and oligonucleotides. The first antibody, designated αUVssDNA‐1, recognises thymidine dimers in a polynucleotide or an oligonucleotide sequence at least four nucleotides long but not isolated thymidine dimers, suggesting that it recognises the conformational change associated with thymidine dimers. The second antibody, designated αssDNA‐2, recognises unirradiated or UV‐irradiated tracts of thymidine, but will not crossreact with tracts of other nucleotides (A, G, C, A.T, G.C, C.U, U). Inhibition of binding of αUVssDNA‐1 to [3H]‐UVssDNA by calf thymus UVssDNA is dependent on UV exposure and wavelength as expected fr

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb09048.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Abstract—Over a period of 5 years, we performed 29 experiments in which survival curves of UV‐irradiated adenovirus were determined using fibroblast strains from 10 normal persons and from 7 persons having Cockayne's syndrome. In all of these, the survival of UV‐irradiated adenovirus 5 was less when assayed using monolayers of fibroblasts from Cockayne's syndrome patients than from normal persons. Survival curves using normal fibroblasts were, within error, straight lines on a log survival vs. linear fluence plot. Survival curves obtained using Cockayne's syndrome fibroblasts showed 2 components: an initial sensitive component, reflecting the behavior of approx. 75% of the infected cells, followed by a component having normal sensitivity. In the 28 experiments that were considered reliable, 58 curves were done using Cockayne's fibroblasts, 41 using normal human fibroblasts. Although experimental variation was encountered, there was no individual case in which sensitivity as measured using Cockayne's was equal to (or less than) the sensitivity measured using normal fibrob

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1981.tb09049.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY