摘要:

Abstract—In the system (electron donor—pigment—electron acceptor), the photosensitising pigment transfers an electron (hydrogen) from the donor to the acceptor by converting light energy, absorbed by the pigment, into the potential chemical energy of the products. The dependence of the reaction of excited pigments with electron donors or acceptors on the magnitude of the electron affinity of the reacting molecules, the nature of the medium, and the experimental conditions was observed. The initial photo‐process was seen to involve the formation of free radicals, with the subsequent formation of compounds with saturated valencies. The reverse reaction of the photoproducts was accompanied by chemiluminescence. The study of systems containing pyridinenucleotides showed the possibility of photosensitised oxidation—reduction of these compounds by a pigment, and of direct photooxidation of reduced pyridinenucleotides by an electron acceptor of a different kind. In order to understand the specific photo‐transfer of an electron in organisms, the spectral properties of pigments in organisms were compared with the properties of model pigments in monomeric and aggregated forms. It was established that the main role in the spectroscopic properties shown by bacteriochlorophyll, bacterioviridin and chloropyll in organisms is played by various types of intermolecular interactions (aggregations). Different forms of pigment may be involved in different stages of the phototransfer of

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb07908.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—Irradiation of benzyl nitrate,meso‐and dl‐hydrobenzoin dinitrates, andcis‐andtrans‐1,2‐acenaphthenediol dinitrates in benzene solutions 0.02M in nitrato groups at 265–313 mp decomposed the esters with a quantum yield of 0.4±0.2 in reasonable agreement with earlier work on the gas‐phase photolysis of ethyl nitrate. An important primary process was ArRCHONO2+hvArRCHO +NO2, although ArRCHONO2+hvArRCHONO + O was not excluded. In secondary reactions solvent benzene was oxidized and nitrated, aldehydes were formed from the nitrate esters, and nitric oxide was evolved. The higher quantum yields of the photodecomposition in ethanol (0.8±0.3) and ether (3±1) solutions were interpreted in terms of a charge‐transfer state similar to that found with nitroalkanes in these solvents. Acetaldehyde was produced in a rapid secondary reaction in alcohol solutions at 25° and at 77° K, NO2was identified as an intermediate from the ESR spectrum. No stereospecificity was detected in a comparison of rates, photoproducts, and ESR spectra for the stereoisomers. The overall results indicated inter‐ rather than intramolecular migration of oxy‐nitrogen groups in secondary reactions. An apparently new, long‐lived, oxynitrogen radical was detected in benzene solutions of nitric oxide and nitr

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb07909.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb07910.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb07911.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—Clover yellow mosaic virus, in common with other plant viruses with flexuous, rod‐like particles, can be photoreactivated. At lower U.V. doses, photoreactivation is masked by an inhibitory effect on virus infection of visible light al

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb07912.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—Irradiation of the anions of halogenated salicylanilides with near ultraviolet light causes the halogen atoms substituted in the 3– or 5– positions to be replaced by hydrogen.With 3, 5substituted salicylanilides the halogen substituted on the 3 position is lost; 5‐substituted bromosalicylanilides lose the 5‐bromo substituent. 5‐substituted chlorosali‐cylanilides do not lose the 5‐chloro substituent. A free radical mechanism for the reacti

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb07913.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—Irradiation of orotic acid or 3‐methylorotic acid in liquid medium in the quartz U.V. leads to formation of photoproducts which have been shown to be dimers similar to those formed from uracil or thymine in frozen solution. The dimers are subject to photo‐dissociation in the same wavelength range, so that at any given wavelength there is a stationary equilibrium between dimer formation and dissociation. The equilibrium point is also dependent on concentration, and on pH, the dimerization reaction being more rapid for the neutral forms. For both compounds there is an appreciable oxygen effect, which inhibits dimer formation.I‐methylorotic acid and 1,3‐dimethylorotic acid also dimerize, but the oxygen effect is diminished as a result of alkylation on the N1ring nitrogen.5‐methylorotic acid is radiation resistant in liquid medium, but readily dimerizes in frozen medium; the subsequent photodissociation of this dimer in liquid medium is unaffected by oxygen.Orotidine forms several photoproducts of which one, about 20 per cent of the total, is a similar dimer.Orotic acid methyl ester likewise dimerizes in liquid medium and exhibits an oxygen effect comparable to that for orotic acid. By contrast 5‐methylorotic acid methyl ester in liquid medium is radiation resistant at short wavelengths, but dimerizes at long wavelengths.The dimers of orotic acid, 3‐methylorotic acid, 5‐methylorotic acid and orotidine have been isolated in crystalline form. The properties of the various photodimers are described and quantum yields for dimerization and photodissociation calculated for several of them at 254 mμ. For orotic and 3‐methylorotic acids the high quantum yields for dimerization and the appreciable oxygen effect suggest that the dimerization of these molecules proceedsviaa long

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb07914.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—Work on the purification and characterization of the soluble protein‐chlorophyll complex isolated from spinach chloroplasts has led to these results: (a) The sedimentation constantSw,20of the complex bound to the Triton micelle is 2.28. With excessive dialysis however, it aggregates and sediments with variedSw,20values that are multiples of 2.28. (b) The micelle has a partial specific volumeV= 0.920 and a diffusion coefficientD= 5.53 ± 10‐7cm2/sec. A molecular weight of 120,200 for the micelk was calculated from these data. From the ratio of Triton to protein and chlorophyll in the preparation, the molecular weight for the complex alone was calculated as 17,200. (c) The complexes isolated from different species have similar physical and photochemical characteristics. (d) The percent of the chloroplast‐chlorophyll extractable as the protein‐chlorophyll complex is low in young, expanding leaves, reaches a peak in mature leaves and drops off with senescence. (e) Under strictly anaerobic conditions the complex will reduce cytochromes at rates similar to those of ferricyanide

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb07915.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—One of the four major photoproducts formed by UV irradiation of TpT in aqueous solution has a number of unusual properties. This compound, which we arbitrarily call TpT4, is produced irreversibly from TpT with single‐hit kinetics and seems to represent a novel pathway for TpT photolysis different from the conventional cyclobutane ring dimer formation. This communication describes the preparative isolation of TpT4by ion‐exchange chromatography on DEAE‐cellulose and its UV, fluorescence and IR spectra. TpT4has an absorption maximum at 325 mμ, fluoresces at 405 mμ when excited at 325 mμ, and has an IR spectrum consistent with the assumption that one of the thymine rings has been converted to a pyrimidin‐2‐one structure. In addition, TpT4appears to have both pyrimidine rings linked together and does not contain a peroxide group as previously supposed. Spectrophotometric titration shows that TpT4has a pKâ of 10.75 and is unstable to prolonged treatment at extreme pH. A model structure consistent with the present data is given. This model contains the glycosidic and phosphodiester bonds intact with a 5‐methylpyrimidine‐2‐one ring and a thymine ring joined in ether linkage at the C4positions, with an OH at the C4positio

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb07916.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY

摘要:

Abstract—The growth of ultraviolet‐irradiated ascites tumour cells in adult animals which have received a total‐body dose of x‐radiation appears to be a suitable method to obtain data on the survival of the treated tumour cells, if the dose of total‐body radiation and its time before tumour cell inoculation are chosen correctly.In assessing tumour cell survival, the analysis of the time of appearance of the resulting solid tumours, using the linear relationship between the reciprocal of this time and the logarithm of the number of cells injected is preferred to probit or to Reed‐Muench analysis of the number of tumour‐takes. The 1/T method of analysis yields more precise estimates of the survival ratios and greater economy in the use of host animals without a disproportionate increase in the labour involved in obtaining the data.An application of this method to the determination of survival‐ratios of u.v.‐irradiated Landschütz ascites tumour

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1965.tb07917.x

出版商:Blackwell Publishing Ltd    

年代:1965

数据来源: WILEY