摘要:

Abstract—Fluorescence and phosphorescence spectra of lumiflavine, riboflavine, FMN and FAD have been measured by continuous and flash excitation techniques. The differences in emission characteristics observed, show that the flavine side‐chains afect the singlet‐triplet transitions on which chemical and biological activity of flavine systems d

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05839.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—When CpC is exposed to ultraviolet (u.v.) radiation, dimers are produced both photochemically and by dark reactions. A reaction scheme for the production of these dimers is presented. We have shown that a single dimer, Cp̂C1, is initially produced photochemically. This is converted by a spontaneous reaction to a second dimer, Cp̂C2. The dimer Cp̂C2may also spontaneously revert back to Cp̂C1and if no side reactions were involved a thermal equilibrium between these txo dimers would be established with about two to three times the concentration of Cp̂C2, as of Cp̂C1. The rate constants for the interconversion of these two dimers vary from about 0.05 to 0.4 hr‐1over the pH range 2.7 to 8.4. The dimers of CpC have maximum stability near pH 7. The two dimers Cp̂C1and Cp̂C2can also be reversed to CpC by u.v. irradiation. Both these dimers in turn deaminate to dimers of UpC and then to Up̂U. The rate constants for these deamination reactions are presented. These lie in the range 0.01 to 0.5 hr‐1for the pH values studied. Possible structures for the two dimers

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05840.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The binding constants of the complex formation of several acridine dyes with calf thymus DNA are reported. The results indicate, that the binding tendency increases with the basicity of the dyes in the order acridine<3–amino‐acridine<3.6–bis‐monocetamino‐acridine<3.6–diamino‐acridine ≅ 3.6–bis‐dimethylamino‐acndine10–propyl‐acridine. These findings could be explained, if the electrostatic binding involving the positively charged ring nitrogen, which seems to be more important for the more weakly interacting acridines, is complemented by other binding mechanisms, including possibly non‐electrostatic interactions in the case of those a

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05841.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—ESR and photovoltaic studies on light‐induced one‐electron transfer between chlorophyllaand electron donors in the absence of oxygen show (1) the possible conversion of photo‐reduced chlorophyllaand p‐benzosemiquinone ion radicals to their non‐ionic radicals in methanol solutions of low pH, (2) the production of ESR absorption of tetrachloro‐p‐benzosemi‐quinone even in benzene, enhanced by the addition of triethylamine or methanol, and (3) the transfer of one electron from tetramethyl‐p‐phenylenediamine to either excited chlorophyllaor pheophytinain methanol at pH above 3.6 but not to pheophytinaat pH below 1 0 where its radical cation appears to accept an electron from excited pheophytina. Bacteteriochloro‐phyll is also shown to be capable of photooxidizing hydroquinones and tetramethyl‐p‐phenyl‐enediamine.The presence of oxygen enhances chlorophylla‐photosensitized oxidation of hydroquinone and tetrachloro‐hydroquinone by one‐electron transfer to oxygen and of trimethylhydro‐quinone probably by two‐electron trnasfer to oxygen. A free radical from excited chlorophyll a‐oxygen interaction is formed in these reactions, but rapidly quenched in the case of trimethyl‐hydroquinone. This, kind of free radical is not formed in pheophytina. Tetramethyl‐p‐phenyl‐enediamine readily undergoes chlorophyll a‐p

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05842.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The luminescence from tryptophan in the dry state and in aqueous glass. induced by u.v.‐light and X‐rays at 77°K, has been studied. The spectra of the luminescence from the dry material, which were identical for the two types of irradiation, were attributed to the same excited singlet level as that giving rise to the fluorescence from the aqueous sample. The strong phosphorescence exhibited by the latter. could not be detected for the dry material with either type of irradiation. This was attributed to a strong quenching of the radiative triplet level occurring upon crystallization of the substance. The yield of X‐ray induced fluorescence of tryptophan in aqueous glass was found to be similar to that observed in the dry state. It was concluded that there is no extensive transfer of energy between the solvent and the solute molecules contributing to the fluorescence yield of tryptophan in aqueo

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05843.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The temperature dependence of thy mine photoproduct formation inEscherichia culiDNA dissolved either in water or in a 50 per cent ethylene glycol solution was studied at temperatures between + 25 and — 196°C. At low temperatures, the formation of thymine dimer was strongly inhibited. A dose of 1 × 104ergs/mm2at 280 nm converted 2 per cent of the thymine to dimer at 25°C as compared with 0.2 per cent at — 196°C. In addition, a new thymine photo‐product which was both nonphotoreversible and nonphotoreactivable was found at low temperatures. On the basis of its chromatographic mobility, this new photoproduct was assumed to be the same as that isolated from irradiated spores ofBacillus megaterium. Extensive irradiation at 254 nrn of DNA at — 120°C resulted in a yield of>23 per cent for the ‘spore‐type’ photoproduct as compared with 6 per cent for the thymine dimer. In poly d(AT), irradiated at low temperature, no spore‐type photoproduct was found; this suggests that adjacent thymine residues are necessary for the formation of the s

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05844.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05845.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05846.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05847.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb05848.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY