摘要:

Abstract—Seven chromatographically separable products were shown to be formed when an aqueous solution of tryptophan was exposed to the light of a 100‐W bulb at pH 9 in the presence of methylene blue and oxygen. Some of these products were detected, though in much smaller quantities, even when tryptophan was irradiated in the absence of methylene blue and/or oxygen. Contrary to reports in the literature, none of the common derivatives of tryptophan, such as tryptamine, indole acetic acid, indole aldehyde, anthranilic acid or kynurenine, were detected on irradiation of the amino acid by visible light. Such irradiation of tryptamine and indole acetic acid gave 1–2 components which were chromatographically identical with those obtained from tryptophan; irradiation of indole aldehyde gave no detectable breakdown products. Exposure of tryptophan to ultraviolet light or when treated with hydrogen peroxide did not result in the formation of any of the products obtained with visible light. The results presented here suggest that during exposure of tryptophan to visible light, the indole ring is first oxygenated resulting in the formation of dioxindole derivatives. One of the products of irradiation of tryptophan with visible light was tentatively identified as dioxin‐dolyl

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb09839.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—The photosensitized oxidation of 4‐methoxynaphthol by erythrosin is studied in a film of ethylcellulose which acts in this reaction as a binder, permeable to oxygen. The rate of the oxidation of the naphthol is measured as a function of the average intermolecular distance. It is shown that sensitized photo‐oxidation occurs in such rigid medium with a rather high quantum yield (0·2‐0·3) and that the quantum yield remains high when the intermolecular distance increases up to a value which is large (80 Å) compared to the molecular size. As a consequence, it seems that such a reaction cannot proceed without the intervention of an oxidizing entity able to diffuse in the rigid binder. Such an entity can be O2, as proposed by Kautsky, as well as H2O2or the ion O2−.A strong effect of deactivation of the sensitizer by a resonance energy transfer process has been shown to take place in the film when the average distance between dye molecules is less than about 120 Å. This deactivation of the sensitizer appears as fluorescence quenching and as a decrease in the rate of the reaction when the intermolecular distance decreases. At very short distances another mechanism seems to occur which results in a higher

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb09840.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—An investigation was made of the action spectrum and some other properties of light dependent carotenoid synthesis inChlorella vulgaris.The special mutant of chlorella used for the experiments has normal chloroplasts in light only and accumulates acyclic carotene precursors and a small amount of chlorophylls in the dark. Lamellar structures are not formed in the absence of light. Production of cyclic carotenes in light can be observed in this special strain in the absence of photosynthesis, hydroxylations involved in xanthophyll synthesis, and formation of lamellar structures. The results obtained suggest that light dependent cyclization of carotenes in chlorella is sensitized by excited chlorophyll

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb09841.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—A novel approach to the measurement of phototaxis is described. It is based on recording the change in optical density which results when phototactic microorganisms collect in a beam of actinic light. The instrument allows the reproducible measurement of rate and degree of phototaxis. Using this device, we have carried out a systematic study of the influence of physical parameters on the phototactic response inEuglena gracilis, z‐strain. WhenEuglenais grown under conditions of artificial day/night cycles, circadian rhythms of phototactic ability are observed which parallel similar rhythms previously observed in the photosynthetic capacity of other algae. Maintenance of a light‐grown culture in complete darkness results in a loss of the phototactic response after about 72 hr. A dark‐grown culture develops chlorophyll and phototactic capacity simultaneously. These results suggest a relation between phototaxis and photosynthesis. From the results of light intensity dependence studies of phototaxis, it is concluded that the actinic light triggers rather than powers the response. The upper limit for the quantum threshold of phototaxis is estimated to be 100 quanta per photoreceptor at 460 mμ. Measurements of the dependence of phototaxis on the wavelength of the actinic light yield an action spectrum which agrees very well with the absorption spectrum of the eyespot pigments. The rate of phototaxis vs. temperature closely resembles the temperature dependence of enzymatic

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb09842.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—The u.v. transmission characteristics of various epidermal specimens prepared by various methods were measured by a recording spectrophotometer and integrating spheres. Although suction or stretch and heat produced the most satisfactory specimens, transmission data obtained from all specimens were similar and generally resembled that reported by previous investigators. The important contribution of forward scattering to total transmitted light was demonstrated. Significant numbers of u.v. photons have been shown to penetrate to the dermis and papillary capillaries. Erythema was producedin vivoby monochromatic light filtered through epidermal specimens after exposure of skin to the quantity of u.v. anticipated by these dat

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb09843.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—The elimination of CH3radicals from (CH3)3COH and CH3I, studied with the EPR method, has been photosensitized at longer wave‐lengths by naphthalene, diphenyl, phenanthrene, the aromatic amines and ketones, and also by dyes. It has been shown that a successive absorption of two photons by the sensitizer is required, raising the sensitizer to a high triplet level, from which the total accumulated energy above the ground one is transferred to the frozen substrate at 77°K. For CH3I this is a triplet‐triplet energy transfer. The possibility has been demonstrated of decreasing the primary photon energy by using two sensitizers in succession and achieving a triplet‐triplet energy transfer betw

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb09844.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—Eleven strains of microorganisms were examined for their susceptibility to death by irradiation with 21–30 mW of light at 6328 Å from a continuous‐wave gas laser. Washed cells of seven species were rapidly killed when irradiated aerobically in aqueous solutions of toluidine blue:Sarcina lutea(two strains),Escherichia coli, Chromobacterium violaceum, Arthrobacter atrocyanus, Pseudomonas aeruginosa, Saccharomyces cerevisiae, andRhodotorula glutinis.Cells remained viable when irradiated anaerobically in toluidine blue. This is not proof that oxygen is required for death since toluidine blue is subject to reduction to the leuco form under anaerobic conditions. None of the microbes tested, including cells ofBacillus cereus, Rhodospirillum rubrum, andEuglena gracilis, were killed in aerated suspensions without toluidine blue. Thus, it is unlikely that any strain has an endogenous photosensitizer capable of acting at 6328 Å. However, more than 95 per cent of the cells ofR. rubrumlost their motility. A colorless mutant ofS. luteabegan dying 10 min faster than the wild strain, which is known to be protected from photosensitized death by carotenoids for at least 2 hr when irradiated in toluidine blue with 1000 ft candles of tungsten light. Since toluidine blue is bleached in irradiated cell suspensions, logarithmic death ceases within an hour with 2·5 × 10=6M toluidine blue. Yeasts are less susceptible than bacteria, exhibiting longer lags before death begins. The size of colonies produced by irradiated yeast cells decreases with irradiation time. This suggests that multiple hits are required

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb09845.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—The sensitivity of older cells ofRhodotorula glutiniscontaining a high concentration of carotenoids was compared with young cells containing little visible pigmentation. The younger cells died faster, suggesting that the carotenoids protected. Further, cells grown in the presence of diphenylamine, an inhibitor of carotenoid syntheses, were more susceptible than were normally grown cells. A carotenoidless mutant, isolated after exposure of the wild strain to u.v. light, was more susceptible to lethal photosensitization than the wild strain. The difference in sensitivity, however, was not as great as between old and young cultures of the wild strain. Young cultures of the white mutant were more susceptible to death than were older cultures, therefore, sensitivity is related to age as well as to carotenoid content. The difference in sensitivity was increased between the white mutant and the wild strain when lower light intensities were used. At 10 mW the difference in the lag period was 60 min, while at 30 mW the difference was only 10 min. The lag period was also dependent on the temperature at which cell suspensions were irradiated. At 3°C, no death occurred in 1 hr at 27 mW with either wild or mutant strains. The lag was progressively shorter with increased temperature. The rate of death, however, was apparently not affected by differences in temperature.An analysis of the carotenoids from the irradiated cells did not show any detectible changes even though it was demonstrated that β‐carotene could be bleached when irradiatedin vitroin the presence of toluidine

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb09846.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Abstract—The absorption and emission spectra of pyrimidine derivatives show that sub‐stituting an amino or hydroxyl group at the 2nd and 4th positions of the pyrimidine ring (to give the derivatives found in biological systems) creates excitation patterns quite different from those for pyrimidine itself: the lowest singlet and triplet states are of (?,π*) and not (n,π*).The relative intensities of fluorescence and phosphorescence depend upon at least two factors: (a) the extent of intersystem crossing which depends mostly on the relative energies of the lowest (π,π*) singlet and lowest (n,π*) triplet states, where the energy of the latter is influenced strongly by the environment; and (b) the extent of mixing of (π,π*) and (n,π*) triplet states, which depends initially upon the closeness of the energies of the two states. The measured and inferred energies for these various states are summarized. In most cases the intensity of luminescence is lower than that found in purines, presumably much of the excitation energy is dissipated in photochemical changes. Also the lifetime of phosphorescence is shorter than in purines. Substitution at the 5th carbon increases the luminescence yield. When a bromine atom is substituted on the 5th carbon of uracil no effect on intersystem crossing is found—presumably the electron density of the π* orbital is minimal in the vicinity of the bromine. Polarization measurements show that the two lowest π‐π* transition moments in 2‐aminopyrimidine are oriented almost perpendicular to each other in the molecular plane whereas phosphorescence is po

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb09847.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1966.tb09848.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY