摘要:

AbstractAb initioconfiguration interaction wavefunctions and energies are reported for the ground and low‐lying excited doublet states of the anion radicals of ethyl chlorophyllidea(Et‐Chla‐) and ethyl pheophorbidea(Et‐Pheoa‐), and are employed in a comparative analysis of their respective electronic absorption spectra.Strong similarities exist between the first five computed excited states of both molecules, providing no distinguishing features in the electronic absorption spectra below 20000 cm‐. Their ground state charge and spin density distributions are also very similar, and there is negligible spin density predicted on the magnesium atom in Et‐Chla‐.The Soret bands of both molecules are predicted to arise from intense transitions to several closely‐spaced higher excited states, and the calculations indicate that there are significant differences in the number and composition of these states in the two molecules. It is suggested that these differences may provide a means of distinguishing between the two molecules using resonance R

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04391.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractTheE⇄ Z photoisomerization of 4′‐methoxycinnamates, used as sunscreens in cosmetics, has been studied by steady state and laser flash photolysis, in aqueous and organic solutions. Photoisomerization quantum yields are found to be fairly high (˜0.5‐1), although no intermediate is detected upon laser flash photolysis. Cinnamates are not photodynamic sensitizers but are able to quench the 8‐methoxy‐psoralen and 5‐methoxypsoralen triplets which produces E →

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04392.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractProtoporphyrin IX and its various ester derivatives have been previously shown to undergo self‐sensitized photooxygenation to yield hydroxyaldehydes (photoprotoporphyrin) and mono‐ and diformyl deuteroporphyrin derivatives. In the present study the photoreactions of these products in the presence of oxygen have been investigated. All of the photooxidation products are themselves good sensitizers of singlet oxygen. In addition spin trapping experiments indicate these products can produce superoxide in low‐to‐moderate efficiency by an excited state electron transfer process. The photo‐products themselves are somewhat more stable to photooxidation than protoporphyrin IX itself. The two monoformyl‐monovinyl deuteroporphyrins have been found to undergo further photooxidation at the vinyl groups to yield primarily monoformyl hydroxyaldehydes in a reaction mainly involving singlet oxygen analogous to the initial reaction of protop

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04393.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractPlateau phase C3H 10T 1/2 mouse cells were used to measure the response to split fluence UV light irradiation in the absence of any cell cycle effects. It was found that fluence fractionation with up to 24 h between the fluences resulted in no survival enhancement. The frequency of malignant transformation was potentiated 2.5‐fold when the time interval between the fluences was greater than 4h. This potentiation of transformation was attributed to plateau phase holding rather than to fluence fractionationper s

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04394.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe concentration dependence for the protection of isolated transforming DNA andEscherichia coliby glycerol against 365‐nm monochromatic near‐ultraviolet light (UV) was measured. Glycerol protection saturates at a concentration of about 0.1Mfor DNA and 1.0MforE. coli.Action spectra for glycerol protection of transforming DNA (tryptophan and histidine markers) are similar to those obtained previously for diazobicyclo[2.2.2.˜octane (DABCO) protection, with protection reaching a maximum near 350‐nm UV and decreasing rapidly at wavelengths above and below 350 nm. However, glycerol protects against near‐UV about twice as efficiently as DABCO. The action spectrum for protection ofE. coliby glycerol against the lethal effects of near‐UV was not the same as the spectrum for DNA since glycerol sensitized the cells, but not the DNA, at wavelengths longer than about 380 nm. A possible role of hydroxyl or other radicals was supported by the observation that benzoate also protected DNA against inactivation by

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04395.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractUltraviolet radiation‐induced DNA degradation has been demonstrated in the unicellular cyanobacteriumSynechocystisPCC 6308. The extent of DNA degradation was greatly reduced by inhibition of DNA replication by preirradiation dark incubation and degradation was completely inhibited by exposure of irradiated cells to photoreactivating wavelengths. DNA degradation was not observed when irradiated cells were incubated in the presence of the excision repair inhibitors caffeine and acriflavin, suggesting that degradation is a manifestation of excision repair of pyrimidine dimers inSynechocystis. Increasing UV fluences resulted in an increase in the final extent of DNA degradation. However, at higher fluences degradation was inhibited, suggesting saturation of the excision repair system. Incubation of irradiated cells under conditions which inhibit protein synthesis greatly increased the extent of DNA degradation and the time over which it occurred. Exposure of cells to a sublethal fluence of UV greatly reduced the extent of DNA degradation produced by a challenge fluence administered after 24 h incubation providing evidence for inducible DNA repair activity in cyanobacteri

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04396.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractPretreatment of growing normal and xeroderma pigmentosum (XP) human fibroblasts with sodium butyrate at concentrations of 5‐20 mMresults in increased levels of DNA repair synthesis measured by autoradiography after exposure of the cells to 254 nm UV radiation in the fluence range 0‐25 J/m2. The phenomenon manifests as an increased extent and an increased initial rate of unscheduled DNA synthesis (UDS). This experimental result is not due to an artifact of autoradiography related to cell size. Xeroderma pigmentosum cells from complementation groups A, C, D and E and XP variant cells all exhibit increases in the levels of UV‐induced UDS in response to sodium butyrate proportional to those observed with normal cells. These UDS increases associated with butyrate pretreatment correlate with demonstrable changes in intracellular thymidine pool size and suggest that sodium butyrate enhances uptake of exogenous radiolabeled thymidine during UV‐induced repair synthesis by reducing endogenous levels of th

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04397.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractViral DNAs were subjected to 254 nm irradiation and then digested with type II restriction endonucleases. At the fluences used, irradiation inhibited cleavage by nucleases which recognize sites containing neighboring thymines. Cleavage by endonucleases with other recognition sequences was not affected. In viral and plasmid DNAs, this effect could be used to study thymine dimer formation at a few specific, mapped sites of defined base sequence.

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04398.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractIn connection with an investigation on UV‐tumorigenesis in hairless mice, the question arose in what way the epidermal transmission changes under chronic UV exposure. At regular time intervals, epidermal sheets of these mice were optically probed, i.e. the specimen was irradiated perpendicularly to its surface with a collimated monochromatic beam of 313, 302 or 297 nm and the transmission was measured in forward direction and a small angle around it. The optical probe measurement was sensitive to epidermal changes and easy to perform; it correlated well with thickness and total transmission of the epidermal sheet.As a result it was found that over the dose range investigated the logarithm of the epidermal transmission at 297 nm was a simple linear function of the daily UV dose and the time of treatment. Calculations, in which this result is combined with data on UV‐tumorigenesis over the same dose range, show that the change in epidermal transmission is sufficiently large to have an important bearing on the dose‐response relationship for tumorigenesis by chronic UV exp

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04399.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractA 1 m diameter water lens was used to focus solar radiation, giving an 8‐fold concentration of the total spectrum and a cytocidal flux similar to that of laboratory UV sources. Survival curves for human melanoma cells were similar for sunlight and 254 nm UV, in thatDq, was usually larger thanDo. An xeroderma pigmentosum lymphoblastoid line was equally sensitive to both agents and human cell lines sensitive to ionizing radiation (lymphoblastoid lines), crosslinking agents or monofunctional alkylating agents (melanoma lines) had the same 254 nm UV and solar survival responses as appropriate control lines. Two melanoma sublines derived separately by 16 cycles of treatment with sunlight or 254 nm UV were crossresistant to both agents. In one melanoma cell line used for further studies, DNA strand breaks and DNA‐protein crosslinking were induced in melanoma cells by sunlight but pyrimidine dimers (paper chromatography) and DNA interstrand crosslinking (alkaline elution) could not be detected. The solar fiuence response of DNA repair synthesis was much less than that from equitoxic 254 nm UV, reaching a maximum near theDovalue and then declining; semiconservative DNA synthesis on the other hand remained high. These effects were not due to changes in thymidine pool sizes. Solar exposure did not have a major effect on 254 nm UV‐induced repair synt

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1982.tb04400.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY