摘要:

Abstract—A new membrane photoeffect of high quantum efficiency is reported. The presence of a number of inorganic ions in the bathing solution of a bimolecular lipid film of oxidized cholesterol causes a change in the measured e.m.f. from ‐100 to ‐40 mV (photo e.m.f. effect) and increase in the conductivity by a factor of 100–200 (photoconductive effect) when the ions are excited by light. A model system, based upon the classical Becquerel Effect phenomenon of electronic charge injection into the membrane from electronically excited ions, is suggested and experiments verifying this model are reported. An extension of this model is used to suggest a new mechanism of the visual receptor process in biological photoreceptor str

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06150.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Light‐dark optical difference spectra of degassed ethanol or pyridine solutions of chlorophyll and benzoquinone or hydroquinone at temperatures above — 50°C show only the semiquinone absorbance band. Decay of the signals is second order, with a rate constant in agreement with earlier ESR results.Light‐induced optical changes due to chlorophyll can be elicited by lowering the temperature of ethanol solutions of chlorophyll and benzoquinone to a region of high viscosity. Hydroquinone is not effective in producing these optical changes.Similar results are achieved at room temperature by using as solvent a degassed mixture of the alcohols: cyclohexanol, tert‐butanol, and ethanol (CBE). Difference spectra show bleaching of the chlorophyll bands and increased absorbance in the intermediate wavelength region (460–580 nm). Decay kinetics are first order, while the rise is complicated (probably biphasic). ESR signals have no hyperfine structure and also decay by first order kinetics, at a rate which is faster than that of the optical changes. The ESR signals reach a steady state more rapidly than the optical signals, without biphasic kinetics. These results demonstrate that at least two species are generated.Addition of acid increases the amount of bleaching in CBE, while small amounts of base decrease it. Larger amounts of base cause chlorophyll bleaching to completely disappear and only the semiquinone anion is observed. Activation energies for the chlorophylla‐benzoquinone photoreaction in CBE are 10–14 kcal/mole. Lower potential quinones give lower activation energies. The rate constant for quenching of the triplet state of chlorophyllaby β‐carotene in CBE is 7.5±0.5×108(Mset)‐1. β‐carotene also quenches photoproduct formation. The bimolecular rate constant for formation of the photoproduct with benzoquinone was calculated to be 7×108(Msec)‐1.The redox potential of the quinone affects both the magnitude of the chlorophyll absorbance changes and the rate of decay. The higher the potential, the larger the changes and the slower the decay. Other porphyrin systems show similar photoreactions only if they are chelated with a group II metal, such as Mg2+, Cd+2, or Zn+2.The results are interpreted in terms of the formation, by a triplet‐sensitized one‐electron transfer from solvent to quinone, of a chlorophyll‐semiquinone complex which is stabilized via c

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06151.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Flash photolysis of chlorophyllaalone in CBE (cyclohexanol‐t‐butanol‐ethanol) yields a difference spectrum similar to those obtained upon steady illumination of chlorophylla‐quinone mixtures in this solvent. Decay kinetics in CBE and dimethylsulfoxide are faster at the Soret band than at 460–580 nm and red band regions. This difference is not obtained in other solvents (CHCI3, CCI4,t‐butanol, ethanol), implying that two or more species are obtained in CBE and DMSO.β‐Carotene in CBE increases the rate of decay of the flash‐induced chlorophyll transients at 430 and 660 nm but only decreases the magnitude of the signal at 470 nm. This implies that the 470 nm absorbance is due to a product formed from the triplet state. This effect is not observed in ethanol.Adding quinone to chlorophyll solutions results in slowly decaying species being generated by flash excitation in CBE. Three components can be distinguished: the first (t1/2˜0.2 msec) corresponds to the triplet state; the second (t1/2= 5–10 msec) is quinone concentration and species independent; the third (t1/2= several seconds) is dependent upon quinone concentration and species (rate is faster for higher concentrations and lower potential quinones). The ESR signal decay rate is approximately equal to the third component flash decay rate when the chlorophyll and quinone concentrations are equal. With excess quinone, the flash decay rate becomes faster, and the ESR decay rate decreases slightly. These slowly‐decaying species are not produced when quinone is added to chlorophyllain ethanol ort‐butanol, or to pheophytin in CBE. One observes merely a decrease in signal height with no accompanying increase in decay rate.Mechanisms to account for all of these phenomena are presented which involve an initial chlorophyll triplet‐solvent reaction with the subsequent formation of several species of chloro‐ph

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06152.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Cells and chromatophores of the photosynthetic bacteriumRhodopseudomonas viridiswere frozen in the dark and illuminated while frozen or were illuminated during freezing. Upon being heated they emitted light. The conditions under which glow curves could be produced and the kinetics of the light emission indicate that the glows resulted from the thermal release of electrons from secondary electron acceptors and their recombination with oxidized reaction center bacteriochlorophyllb.Glow curves could not be obtained withRhodospirillum rubru

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06153.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—When chromatophores ofRhodopseudomonas viridisare briefly illuminated with very bright light at temperatures between —20°C and —196°C, reaction center chlorophyll (P985) is oxidized rapidly and becomes reduced in less than 0.1 sec upon cessation of illumination. In moderate exciting light one molecule of cytochrome 558 per molecule of P985 is oxidized rapidly and irreversibly while P985 oxidation is much slower and its oxidation rate is highly temperature‐dependent. After a long illumination ends, P985 reduction occurs in two temperature‐dependent phases, in 1 to 1 ratio. The data are interpreted as follows.1P985 and one mole of cytochrome 588 per mole of P985 can be photooxidized at low temperatures.2Electron transfer from the primary electron acceptor to the secondary acceptor or back to P985+occurs in less than 0.1 sec at low temperatures.3There is one mole of secondary acceptor (a one‐electron acceptor) per mole of P985. and electron transfer from the secondary acceptor to tertiary acceptors is highly temperat

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06154.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY

摘要:

Abstract—Photochemical reactions of acridine orange (AO) in basic aqueous and ethanolic solutions were studied using the flash photolysis technique. The absorption spectrum of AO was determined in detail (230–900 nm) and extinction coefficients were obtained. The decay of the triplet state is the result of a first order process, a triplet‐triplet annihilation process and a quenching by the dye in the ground state. The main part of the triplet decays to the ground state; however the observation of semi‐reduced AO shows that the decay is partly due to chemical reactions.An efficient reversible reaction is observed on flashing aqueous solutions of AO containing tetramethyl‐p‐phenylenediamine: semi‐reduced AO is formed in high yield by reaction between the triplet dye and the diamine. In addition, irreversible reactions of AO occur; these are shown to be due to the triplet state by the method of triplet en

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1971.tb06155.x

出版商:Blackwell Publishing Ltd    

年代:1971

数据来源: WILEY