摘要:

Abstract—The host cell reactivation (HCR) mechanism inHaemophilus influenzaecells is inhibited by sub‐microgram concentrations of acriflavine (as is already known to be true forEscherichia coli). Exposure of these cells to similar concentrations of the drug during bacterial transformation increases the apparent ultraviolet light (u.v.) sensitivity of previously irradiated transforming DNA, indicating a repair of this DNA after uptake by the cells under normal conditions. Repair is inhibited by applying acriflavine at any time up to one hour after competent cells contact the irradiated transforming DNA. The fraction of the u.v. damage repaired by HCR is very different for different genetic markers. Those markers which are most u.v. sensitive when assayed in the absence of acriflavine are most poorly repaired, suggesting that this is the reason for their higher sensitivity. For all markers the fraction of the damage repairable byin vitrophotoreactivation is approximately constant, and strongly overlaps the damage repairable by HCR. The degree of HCR achieved can be altered by experimental treatment of theH. influenzaeDNA prior to transformation. Thus treatment of irradiated DNA with an enzyme fromMicrococcus lysodeikticus–known to attack u.v. damaged, but not undamaged DNA–prevents subsequent intracellular repair of the same u.v. lesions whose repair is inhibited by acriflavine. Similarly, partial replacement of the thymine in transforming DNA by 5‐bromouracil (BU) strongly inhibits repair of subsequent u.v. damage. As in bacteriophage, the BU effect is relieved if the u.v. exposure occurs in the presence of cysteamine. It is clear that intracellular repair must be considered in interpreting experiments with u.v.‐irradiated trans

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08785.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—Values of φT, the quantum yield of triplet state production of 9‐phenylanthracene, have been determined in four different solvents by measuring the effects which ‘heavy atom quenchers’ have on the fluorescence intensity and the triplet state absorption of the solute. A variety of quenchers have been used including organic and inorganic halides and the rare gas, Xenon. There is a converse solvent dependence of φFand φT, and for each of the four solvents used φF+φThas been found to be unity within experi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08786.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—The quantum efficiency for the photodimerization oftrans‐cinnamic acid in the solid state is independent of intensity and is found to have a value approaching two. Thus, the reaction involves one excited and one un‐excited molecule.During the exposure, a dimer film developing on the surface of the cinnamic acid layer attenuates the intensity of the radiation incident on the unreacted cinnamic acid. This gives the appearance of a decrease in the quantum yield with increasing number of photons inc

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08787.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—Some features of chemiluminescence important for quantitative studies of the phenomenon are discussed. Parallel excitation reactions may lead to several sorts of emitters. Energy transfer from and quenching of excited states may be responsible for the peculiar behaviour of chemiluminescent systems. These points are illustrated by results for a model reaction: thermal decomposition of dicyclohexylperoxydicarbonate (DCHPC) in the presence of O2with or without methylethylketone and an activator, 9,10‐dibromoanthrac

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08788.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—Ultraviolet irradiation of orotic acid in aqueous medium leads to the formation of dimers with a cyclobutane ring between the 5,6 bonds of two monomers. These photodimers in turn undergo photodissociation, with the result that an equilibrium is established between photodimerization and photodissociation. The equilibrium point is independent of dose rate, but is appreciably dependent on the irradiation wavelength, pH of the medium (i.e. whether the monomer is in the neutral or anionic form), and initial monomer and oxygen concentrations; the effect of oxygen apparently being to deactivate excited monomers. The kinetics of photodimerization and photodissociation have been examined at different wavelengths and with varying oxygen concentrations at different initial monomer concentrations. The results have been compared with a theoretical model in which it is assumed that a dimer is formed between an excited monomer and second molecule in the ground state, and that oxygen can also react with, and deactivate, an excited monomer. The agreement between the proposed model and the experimental data is reasonably good, and has made possible an estimate of the lifetime of the excited state of orotic acid in aqueous medium, which is about 10‐6

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08789.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—By idealizing the design of a typical spectrofluorimeter that measures fluorescence from dilute solutions, we are able to derive an equation that predicts the dependence of the observable amplitude on the concentration of the solute and on several instrumental parameters. The result of the derivation, the fluorescence function, is used together with measurements of rhodamine B fluorescence and colloidal silica scattering to calibrate a spectrofluorimeter.The fluorescence function and the calibration data are used to determine the absolute fluorescence quantum yield of quinine sulfate in 0–1 N H2So4. The results, Ø250=0.582 with excitation at 250 mμ, adn Ø350=0.577 with excitation at 350mμ. agree well with the previous evaluation of Melhuish, Ø3

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08790.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—The ERG obtained from albino rats was recorded every 90 sec after the eye was exposed to an adapting white light of known energy. The normalized a‐wave regeneration curves for a constant test stimulus obtained from different rats, using different adapting light energies, were identical and superimposable, except that a delay between the time that the adapting light was turned off and the time that the a‐wave appeared was observed for the high energy adapting light experiments. This delay increased as the adapting light energy incr

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08791.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—A single transient species is observed in absorption following the flash irradiation of dilute deoxygenated aqueous alcoholic solutions of rhodamine B in hte pH range 5.5–7.0 The second‐order decay constant for this semiquinone radical is an approximate linear function of the prevailing hydrogen ion concentration, the transient persisting for a period of from several seconds in neutral solution to several hours at pH = 12.The slow rate of decay and its pH‐dependence are explained in terms of an electron or H‐atom transfer between the (unobserved) protonated and (observed) unprotonated semiquinone radical with simultaneous regeneration of hte D+>and production of the leuco‐dye DH:—D·+ DH·+→ D++ DHInsofar as the reactant concentrations are controlled by the acid dissociation constant Kaof DH.+the data are consistent with a value of 5.5±1.0 for pKaand a pH‐independent rate constant Koof 1.3±0.5×106

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08792.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY

摘要:

Abstract—Förster's theory of energy transfer in condensed systems is re‐examined in the light of recent criticisms. It is concluded that his approach is correct and holds for a wide range of donor and quencher concentrations as long as there is no transfer among donor molecules. In contrast, the modified result of Tweet, Bellamy and Gaines, holds only for complete delocalization of the excitation among the donor molec

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1967.tb08793.x

出版商:Blackwell Publishing Ltd    

年代:1967

数据来源: WILEY