摘要:

Abstract—The photocycloreversion quantum yieldsQof the endoperoxides of anthradichromene, benzodixanthene and dimethylhomoocoerdianthrone have been investigated in the 248 ≤γ≤ 405 nm wavelength range. Two types of wavelength dependencies can be distinguished phenomenologically. For the excitation of the Sn(n≥ 3) states of dimethylhomöocoerdianthrone endoperoxide γ‐independent Q‐values have been observed throughout 365 ≥γ≥ 265 nm. The endoperoxides of anthradichromene and benzodixanthene in contrast exhibit a quite different and unusual dependence ofQon γ. For both compoundsQfirst increases with photon energy until a fairly sharp maximum inQis reached at 302 nm. With further increasing energyQfalls off and approaches a wavelength independent plateau between 280 and 248 nm. The S1‐states of the endoperoxides investigated are inactive for photocycloreversion, which is generally found in endoperoxide photochemistry. The wavelength dependencies observed reveal that the photocycloreversion of endoperoxides deviates remarkably from the commonly accepted generalization that photochemical reactions in solution phase should only occur from the lowest excited sin

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03458.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—The fluorescence and triplet state yields of hematoporphyrin have been measured in wuter/methanol mixtures. There is a closely linked response of these yields to aggregation of the hematoporphyrin molecule. The monomer, which is the principal species present at high methanol content, has a triplet state yield of 0.91 and a fluorescence yield of 0.09. By contrast, hematoporphyrin solutions with a high water content containing aggregates have lower fluorescence and triplet state yields, e.g. 0.018 and 0.56, respectively, in water. Static, singlet state quenching in some of the aggregates is responsible for the reduced fluorescence yield. The results also show that in addition to these aggregates there are other types of aggregates where there is an increased singlet to ground state radiative transition probability, resulting from the interaction between transition dipoles in adjacent molecule

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03459.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—The photochemical reactions in concentrated thionine solution have been studied using continuous illumination. Thionine solution is photoreduced to leucothionine in an oxygen‐free acidic medium. Electrochemical measurements of the photoreduction of thionine are reported. A possible reaction pathway for the energy transfer is proposed. It is found that polymeric forms of thionine and leucothionine are not involved in photoreduction. It is proposed that a complex must be formed prior to photochemical reduction. This complex species, having a lifetime of several seconds, is reduced to leucothionine, water being the reducing agent. Following this reduction, H2O2is formed and the production of H2O2is detected by differential pulse polarogra

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03460.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—The microsecond flash photolysis of 5‐methoxyindole in aqueous solutions has been studied at γexc≥ 290 nm. Transients identified in this time realm in neutral solutions are: eaq‐, the 5‐methoxyindole radical cation (γmax≅ 440 nm), the neutral transient with γmax≅ 530 nm) and an unidentified oxygen sensitive transient with γmax≅ 435 nm. Radical cations and e‐aqare shown to be produced in equal amounts consistent with a photoionization process as the only source of both transients. H+quenching of fluorescence and radical cation production gives equivalent Stern‐Volmer constants indicating that photoionization occurs from the fluorescent state. The unidentified oxygen sensitive transient exhibits apKaof2–2.5 and is quenched at lower pH values indicating that it also has a fl

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03461.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—The effect of flavin structure variation upon the binding process of flavin to hen egg white riboflavin was studied using fluorescence methods for formylmethylflavin (FMF), riboflavin (RF) and flavomononucleotide (FMN).Measurements of flavin fluorescence intensities (steady state and phase‐sensitive) and lifetimes were performed in a variety of RBP concentrations and temperatures (4 to 40°C). No fluorescence of flavoproteins was detected, while the fluorescence of flavins was found to be quenched by RBP. The overall quenching process is dominated by the static quenching (about 88%) due to the flavoprotein complex formation in the ground state, presumably a charge transfer com

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03462.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—A mutant ofChlamydomonas reinhardtii(NL–11) isolated from a wild type (137c+) was inactivated in the light in the presence of methionine at concentrations where the wild type was not inactivated. The inactivation was suppressed by either catalase or superoxide dismutase (SOD). Light‐induced H2O2formation and nitroblue tetrazolium (NBT) reduction inNL–11 were greater than those in the wild type. Methionine stimulated both the H2O2formation and the NBT reduction inNL–11 as well as the wild type. The light‐induced NBT reduction inNL–11 in the presence of methionine was partially suppressed by externally added SOD suggesting the participation of O‐2. These results suggest that the hypersensitivity ofNL–11 to methionine in the light is due to stimulated formati

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03463.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—Holding of acriflavine sensitizedV–79 cells in growth medium before visible light exposure decreases inactivation by visible light. The decrease depended upon the period of holding, indicating that there was release of cellular dye during this period. Exposures to visible light were done in two conditions: (a) with no dye in the medium during visible light exposure (washed) and (b) with dye in the medium during exposure (unwashed). Caffeine was found to slightly increase the sensitivity of the cells to visible light in the washed condition, whereas, in the unwashed condition no such effect was observed. Interaction studies with far UV did not reveal any correlation between photodynamic damage and UV damage. Visible light exposure of acriflavine sensitized cells was found to be mutagenic, as studied from the induction of 8‐azaguanine resistant mutants. Inhibition of singlet oxygen production by sodium azide suppressed the induction of mutants. All these, taken together, have been discussed with respect to the relative importance of DNA and non‐DNA damage in the photodynamic action of acri

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03464.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—Light induced transition of the photosynthetic apparatus from state II to state I by preillumination with PS I lightin vivoand the addition of cations to chloroplasts or chloroplast particles prepared in low‐salt buffer have rather similar effects on the fluorescence properties at room temperature and at 77 K. Using synchronous cultures ofScenedesmus obliquus,we were able to study both phenomena in parallel in different developmental stages under well defined conditions. Both phenomena show an inverse course during ontogenetic development ofS. obliquus.This result suggests that Mg2+ions and PS I light don't necessarily act in the same way. Hence, changes in the ionic environment cannot be the unique basis of light induced state changes within the photosynthetic apparatusin v

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03465.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—We showed by spectrophotometry and HPLC that a photoproduct having7‐cisretinal(1‐cisphotoproduct) can be derived from the photoisomerization of frog lumirhodopsin (L) and metarhodopsin I (M I). The efficiency of the isomerization was higher in M I than in L. The absorption maximum of the1‐cisphotoproduct at ‐20°C is at 455 nm, and its maximum absorbance 1.1 times as large as that of rhodopsin. The photoproduct exhibited two positive CD bands at 450 nm α‐band) and 320 nm (β‐band); the molecular ellipticity at a‐band ([θ] = 73000) being larger than that of rhodopsin ([θ]= 61000). Re‐examination of the absorption spectra of rhodopsin intermediates gave the absorption maxima of L. M 1 and M 111 to be 522, 482 an

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03466.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract—Theall‐transand 3 mono‐cir isomers of the title linear pentaenal have been prepared. Results of their interaction with bovine opsin and bacterioopsin are presented. Likewise, the negative results on two lower member homologs are described. Implications on the specificity of the binding sites are disc

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1985.tb03467.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY