摘要:

Abstract—The photoreduction of riboflavin, FMN, and lumiflavin in a series of hydroxylic solvents has been examined using flash photolysis. A comparison of the relative quantum yields for the photoxidation of several alcohols and esters by lumiflavin demonstrated that the hydroxyl hydrogen of the alcohol is abstracted approximately twice as readily as is the alpha hydrogen. The use of glycerol as both solvent and reductant provided direct evidence that the initial reaction proceeds by a one‐electron reduction to form the flavin semi‐quinone. In the case of riboflavin (and FMN) the kinetic results are consistent with an initialintramolecular hydrogen atom transfer, analogous to photobleaching in aqueous solution, followed by a reaction of the semi‐quinone with the reductant which prevents degradation of the ribityl side‐chain. Quenching by iodide indicates that all the reactions proceed via the flavin triplet state, as is the case in aqueou

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb08000.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—Quenching of the degradative photobleaching of FMN in anaerobic aqueous solution, and of the flavin‐sensitized photo‐oxidation of EDTA, alcohols, glycols, and glycerol, has been examined using flash techniques. The quenching can be produced by addition of KI, by successive flashes, and by increasing the flavin concentration (self‐quenching). It is concluded that the lowest triplet is the photoreactive species in all systems, that the successive flash effect is due to triplet quenching by a reaction product, and that the concentration quenching may be due to either triplet‐triplet annihilation or to reaction between a ground‐state flavin and a fla

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb08001.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The three‐component system, glycerol: flavin:p‐benzoquinone, was examined as a model for mitochondrial electron transport. A sequential electron transfer was observed in which photoproduced FMNH is reoxidized by benzoqu

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb08002.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—Phosphorescence decay kinetics and emission spectra of some acetophenone derivatives were measured in ether/alcohol and hydrocarbon glasses. Most decay rates observed were a sum of exponentials, and different emission spectra were observed at different intervals in the decay. The observations can be explained in terms of coexistentn, π*, π, π*, and charge‐transfer triplets, but solvent shifts in the direction expected for π, π* and charge‐transfer triplets were no

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb08003.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The rates of phosphorescence decay of nine compounds in frozen glass were measured. Six of the nine compounds decay exponentially, indicating that previously reported non‐exponential decay of some of them may have resulted from impurities, probably in the solvent.Three compounds – acetophenone, phenanthrene, and acridine orange–have unusual decay kinetics. Acetophenone has no wavelength–dependence of rate, but the decay is non‐exponential at all observed stages. The effect is believed due to a multiplicity of metastable excited states, all of which ultimately decay through a common lowest triplet. The delayed emission of phenanthrene in frozen glass consists of phosphorescence and aP‐type delayed fluorescence in the dimer band only. The ratio of the rates of decay of phosphorescence and delayed fluorescence is nearly the same in frozen glass as it is in liquid solution. It is suggested that excimers can be formed by molecules up to 100 A apart, and that the description ‘excited dimer’ is misleading. Finally, acridine orange has aP‐Type delayed fluorescence which decays initially with second‐order kinetics. The first‐order kinetics generally observed inP‐type delayed fluorescence are merely the result of the relative importance of competitive unimolecular reactions in depopula

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb08004.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—To investigate the mechanism of the solvent and thermal quenching of fluorescence, the absolute fluorescence quantum yield of adenine has been determined in several alcoholic glasses as a function of the concentration (10‐5‐10‐4M) and temperature (77°‐298°K). The yield is independent of the concentration but increases with decreasing temperature and increasing bulk cohesion and rigidity of the solvent.The environmental effects on the yield are attributed to radiationless electronic relaxation processes caused by solute‐solvent interaction. Increasing the temperature and decreasing the intra‐solvent cohesion cause increases in the interaction and therefore accelerate the relaxation. The rate determining step behaves like a diffusion in the limit o

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb08005.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—The quantum yields for the u.v. inactivation of the amino acid acceptor function ofE. colitransfer RNA (for val, phe and lys) and for the loss of its conformation, as a function of exposure, have been determined following irradiation at 280, 265 and 254 nm. Our results suggest that u.v. damage produces a change in the conformation of transfer RNA which in turn inactivates it, and that the anticodon is not the u.v. sensitive site. Calculations indicate that a small number of photoproducts inactivate the transfer RN

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb08006.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Abstract—Illuminated chloroplasts can mediate a photoxidation of diketogulonic acid (DKGA) with rates of oxygen uptake equivalent to rates of Hill reactions with ferricyanide or quinone. The photoxidation of DKGA is sensitive to dichlorophenyl dimethylurea (DCMU) and exhibits the drop in quantum yield at long wavelengths characteristic of photosystem II. Still, the reaction is only partially inactivated by heating chloroplasts at 50° for 10 min (which destroys oxygen evolution). The photoxidation is inhibited by copper and detergents; and is stimulated by added flavin (or methyl viologen) and manganous ions.A model system containing Mn3+(as manganipyrophosphate) and DKGA, mimics the chloroplast system. Pre‐illuminated chloroplast suspensions can be substituted for Mn3+in the model dark reaction.It seems that a light‐dependent oxidation of Mn2+to Mn3+by photosystem II is the essential contribution of the chloroplasts. Electrons from Mn2+move through the electron transport system to ferricyanide or to photosystem I where, via flavin (or methyl viologen), oxygen is reduced t

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1968.tb08007.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.tb08008.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.tb08009.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY