bluuebunny/crossref_metadata_2025_split huggingface dataset:
VARIATION IN ELECTRON PARAMAGNETIC RESONANCE SIGNALS OF PHOTOSYNTHETIC SYSTEMS WTTH THE REDOX LEVEL OF THEIR ENVIRONMENT
Authors: Loach Paul A. , Androes G. M. , Maksim Ann F. , Calvin Melvin 
Published: January 2008

Abstract— The redox dependence of the light‐induced electron paramagnetic resonance signal at g=2 in R. rubrum, R. spheroides and Chromatium chromatophore particles and quantasonie particles from spinach chloroplasts has been determined qualitatively over the range —0.3 to +0.6 V and quantatively over the range +0.3 to ±0.6 V. A light‐induced EPR signal has been titrated and demonstrated to have a midpoint potential of +0.44 v at pH 7 and 20°C. Concentration, ionic strength and pH dependence for this transition in R. rubrum chromatophores is reported. In addition to the dark signal which replaces the light signal, in chromatophore material another dark signal, occurring in the seine location as the light signal, has been demonstrated to occur at high potential.Selective chemical oxidation with K2lrCl6 of chromatophore particles from the three bacteria resulted in the removal of some 95 per cent of the absorbance in the near infrared and left the photoactive pigments.Two light‐induced EPR signals were found in quantasome particles by their dependence upon the redox level. Of particular interest is a signal observed at quite high potential (e.g. + 0.60 V). It was demonstrated that oxygen evolution by these quantasonie particles in the presence of K3Fe(cN)0 occurred at the same rate at +0.55 V as at +0.40 V.
DELAY IN GROWTH AND DIVISION INDUCED BY NEAR ULTRAVIOLET RADIATION IN ESCHERICHIA COLI B AND ITS ROLE IN PHOTOPROTECTION AND LIQUID HOLDING RECOVERY
Authors: Jagger John , Wise W. Curtis , Stafford R. S. 
Published: January 2008

Abstract. Microscopic observations show that growth delay and division delay occur on nutrient agar after Escherichia coli B has been irradiated at 3341 Å. These effects also occur in nutrient broth.A near u.v. action spectrum for growth delay in nutrient broth has been obtained. It shows a single peak at 3380 Å and is indistinguishable from the action spectrum for photo‐protection from far u.v. (2537 Å) killing in the same organism. Furthermore, photoprotected cells show a much greater growth delay than cells that have not been photoprotected. These, as well as kinetic data, suggest that the essential action of a photoprotection treatment consists in the induction of a growth‐division delay. This delay would presumably permit more time for intracellular recovery systems to operate on the far u. v. damage to nucleic acids.Liquid holding recovery (effected by holding cells in phosphate buffer after far u. v. irradiation) shows complete overlap with photoprotection. It is concluded that photoprotection and liquid holding recovery operate on the same far u. v. damage. As with photoprotection, it is probable that the essential action of a liquid holding treatment is the induction of a growth‐division delay.No photoprotection is observed of intracellular T2 bacteriophage or of E. coli Bs‐l (Hill).
FLASH PHOTOLYSIS OF ROD PARTICLE SUSPENSIONS
Authors: Pratt D. C. , Livingston R. , Grellmannt K‐H. 
Published: January 2008

Abstract. Flash photolytic experiments with suspensions of rod particles isolated from cattle eyes reveal that at low temperatures a transient is formed following irradiation which preceeds lumirhodopsin in the bleaching process. Kinetic studies, in the range ‐75°C to ‐50°C, suggest that the transient is composed of three intermediate species, having similar absorption spectra but changing to lumirhodopsin at different rates. The energies of activation of the decay reactions appear to be identical and equal 12.5°3 kcal/mole. Spectrophotometric experiments have demonstrated that the low temperature transient is stable at liquid nitrogen temperatures and suggest that it can be reversibly converted to a mixture of rhodopsin and isorhodopsin at ‐195°C.A detailed comparison of light initiated reactions of rhodopsin in rod particle suspensions and in solutions reveals striking similarity in the two systems.
TRIPLET STATE STUDIES OF FLAVINS BY ELECTRON PARAMAGNETIC RESONANCE—I
Authors: Shiga T. , Piette L.H. 
Published: January 2008

Abstract— The triplet state of flavin derivatives and d‐amino acid oxidase was observed by electron paramagnetic resonance at 77°K.Flavin triplets (Δm=± 2) originate from the isoalloxazine ring and are resonant at 1560 guass.The half‐life of the FMN triplet in 1N HCl is 15 nisec.This life‐time is prolonged indirectly by the presence of paramagnetic species, such as oxygen or free radicals.The flavin triplet state is pH dependent.In neutral solution the nlaximum triplet yield is obtained and the longest life‐time is observed.The triplet state is affected by intra‐and inter‐molecular complex formation, FAD is partially quenched by indirectly substituted adenine.Tryptophan quenches completely the FMN triplet.The FAD triplet of d‐amino acid oxidase is enhanced but the life‐time is shortened relative to a pure FAD solution.
BIOLOGISCHE WIRKUNGEN PHOTOCHEMISCHER WASSERSTOFFPEROXYDBILDUNG:
Authors: Berg H. , Jacob H. ‐E. 
Published: January 2008

Abstract— As previously demonstrated, there is a considerable increase in the photodynamic activity of anthraquinone‐sulphonic acid on the addition of ethylene glycol, glycerol and sugars in concentrations of the order of 0.4M. This system exhibits cytostatic activity. With H2O2 at higher concentrations there is also formation of aldehydes in approximately equivalent yields as follows:R.CH2OH+Q → QH2+R.CHOQH2+O2→ Q+H2O2In accordance with the recent results of Warburg this accounts for the fundamental importance of glyceraldehyde in cancer research.Our results on the irradiation of Proteus vulgaris SG2 in buffered medium with the addition of glycerin to anthraquinone‐sulphonic acid show the existence of a similar cytostatic effect. One hour's irradiation with visible light reduces the cell count by about 50 per cent.
RELATIONS BETWEEN PHOTOCHEMISTRY AND FLUORESCENCE IN CELLS AND EXTRACTS OF PHOTOSYNTHETIC BACTERIA*
Authors: Clayton Roderick K. 
Published: January 2008

Abstract— Light‐induced changes in the yield of bacteriochlorophyll fluorescence have been measured in cells and chromatophores of photosynthetic bacteria, and coordinated with light‐induced absorbancy changes. Comparisons were drawn during transitions between dark and light steady states and also between steady states established at different light intensities. Aerobic cell suspensions of Rhodospirillum rubrum, Rhodopseudomonas spheroides, Chromatium and Rhodopseudomonas sp. NHTC 133 showed a strict correspondence between changes in the fluorescence yield and the bleaching of P870 (P985 in Rps. sp. NHTC 133), as reported by Vredenberg and Duysens for R. rubrum cells. The relationship shows that singlet excitation energy in bacteriochlorophyll is quenched by P870 at a rate proportional to the concentration of unbleached P870. This implies that the photosynthetic units are not independent with respect to energy transfer.In anaerobic cell suspensions the change in fluorescence did not follow the bleaching of P870 in the manner described by Vredenberg and Duysens. Here a change in fluorescence may have resulted from the reduction of a primary photochemical electron acceptor as well as from the oxidation (bleaching) of P870. In chromatophore preparations there were further deviations from the Vredenberg and Duysens relationship which could be attributed to changes in the rate constants for quenching of singlet excitation energy. Finally there was a light‐induced increase in the fluorescence yield which was related to a band shift of bacteriochlorophyll and not to the bleaching of P870. Aerobic cell suspensions presented a limiting case in which these complications were absent.No change in the fluorescence was associated uniquely with the oxidation of cytochrome or band shifts of carotenoid pigments.These results, when coordinated with earlier findings about the fluorescence of bacteriochlorophyll and P870, indicate that the singlet excitation quantum is the only energy carrier linking the absorption of light with the initiation of photochemistry in bacterial photosynthesis.
PHOTOREACTIONS AT 3655Å BETWEEN PYRIMIDINE BASES AND SKIN‐PHOTOSENSITIZING FUROCOUMARINS
Authors: Musajo L. , Bordin F. , Caporale G. , Marciani S. , Rigatti G. 
Published: January 2008

Abstract After irradiation at 3655 Å of an aqueous frozen solution containing thymine and psoralen, a new photocompound was isolated by column chromatography. It contains a furocoumarin and a pyrimidine‐moiety linked together by the formation of a cyclobutane ring (see formulas II and III). By irradiation at 2537 Å in acetic acid solution, the photocompound breaks up again yielding psoralen and thymine. From an aqueous frozen solution containing cytosine and psoralen irradiated at 3655 Å, an analogous photocompound was obtained, which, however, consists of the addition to psoralen of a uracil molecule, instead of a cytosine one (IV, V). It has been stated that the hydrolytic deamination of the cytosine moiety to the uracil one takes place during the working up of the photocompound in aqueous solution after irradiation. Substances with properties similar to those above were obtained from bergapten (5‐methoxy‐psoralen) and thymine, from psoralen and thymidine or thymidylic acid, irradiated at 3655 Å.The new substances may be considered as model compounds in explaining the photoreactions which take place between the skin‐photosensitizing furocoumarins and DNA upon irradiation at 3655 Å.
THE REACTION OF METHYLENE WITH METHYL CHLORIDE THE EFFECT OF EXCESS ENERGY IN METHYLENE
Authors: Johnstone R. S. B. , Wayne R. P. 
Published: January 2008

Abstract This paper reports studies of the reaction between methyl chloride and methylene produced by the photolysis of ketene in the two spectral regions Λ˜ 2600 Å to 3200 Å and Λ˜ 3220 Å. The course of reactin is best described by an abstraction processCH2+ CH2CI—Ch2CI + CH3followed by recombination of the CH3 and CH2 Cl radicals to yield C2H5, C2H5Cl, C2H4Cl2. The recombination processes are highly exothermic, and excitation of the product molecules occurs, which in the case of C2H5Cl and C2H4Cl2 leads to some unimolecular decomposition. It is shown that the rate constant for the decomposition of ethyl chloride depends upon the wavelength of the radiation used to photolyse the ketene, and it is suggested that the excess energy with which the methylene is born is handed on to the alkyl radicals. A simplified kinetic analysis of the system is given, and it is shown that the relative reactivity of methylene towards ketene and methyl chloride increases with an increase in the energy of the methylene. The rates of product formation predicted on the basis of the kinetic scheme agree satisfactorily with the measured values.“Insertion” of methylene into C‐H and C‐CI bonds has been postulated by other workers. The present results are inconsisistent with an insertion mechanism, since such a mechanism does not account for all the observed products. The effect of wavelength of photolysis and of total pressure predicted on the basis of an insertion process is the reverse of that observed experimentally.
PHOTOBIOLOGY OF RNA BACTERIOPHAGES—I. ULTRAVIOLET INACTIVATION AND PHOTOREACTIVATION STUDIES*
Authors: Werbin Harold , Valentine Raymond C. , McLaren A. D. 
Published: January 2008

Abstract— Biologically active f2‐RNA, Obtained from bacteriophage f2, was inactivated by ultraviolet (u.v) light (2537 Å) with a quantum yield of 3.3 ± 0.3 times 10‐3 when assayed in the dark with protoplasts of an F‐ strain of E. coli k12. Assay under “black light” gave a quantum yield of 2.7 ± 0.5 times 10‐3 which was just enough lower to suggest that 17 per cent photorecovery of the u.v. lesions has taken place.Intact phage f2 was inactivated by u.v. radiation with a quantum yield of 0.7 ± 0.12 times 10‐3, Thus the whole phage is much less sensitive than the free RNA.No evidence of photorecovery was found in u.v.‐irradiated RNA phage 7S assayed in its host Pseudomonas aeruginosa.
A COMPARISON OF DECAY KINETICS OF PHOTO‐PRODUCED ABSORBANCE, EPR, AND LUMINESCENCE CHANGES IN CHROMATOPHORES OF RHODOSPIRRILLUM RUBRUM*
Authors: Loach Paul A. , Sekura Diane L. 
Published: January 2008

ABSTRACT–Quantitative comparison of the decay rate for absorbance photochanges in chromatophores of R. rubrum at the major wavelengths of peaks and troughs (280, 365, 385, 433, 605, 763, 790, 810, 850, 865, 890 nm) reveal no major differences under a variety of sample conditions. In addition, the decay kinetics of EPR phtochange at the two environmental potentials used in this study are identical with the absorbance ph;otochange decay.Decay curves for fresh chromatophores, aged chromatophores, and fresh chromatophores at high ionic strength display a variety of half times and curve shapes. All of these data however, may be fit (within 10 per cent) by the equation x=αe8.2t+βe0.18t by merely varying the values of α and β. This is interpreted as meaning that any single trapping site may exist in one of two major forms each of which decays following a first order or pseudo‐first order reaction. Although the change in decay pattern upon aging is not reversible, that due to high ionic strength is. The time dependencies for two light emission phenomena have been measured as well as their response to the oxidation state of molecules at the trapping site. A major component of long‐lived luminescence follows pseudo‐second order kinetics with a half time of 38 msec. A very long lived luminescence shows an increse with time which is nearly proportional to the decay of absorbance photochanges.
ULTRASTRUCTURAL STUDIES OF THE LIGHT‐INDUCED CHLOROPLAST SHRINKAGE*
Authors: Dilley R. A. , Park R. B. , Branton D. 
Published: January 2008

ABSTRACTBoth Class I (intact) and Class II (without the outer plastid membrane) chloroplasts of Spinacea oleracea exhibit a shrinkage of the thylakoid volume under conditions which lead to the well known light‐induced light scattering increases. In the present report this shrinkage has been measured on micrographs prepared by the freeze‐etch technique. In cloroplasts kept in darkness through the freezing or in those treated with DCMU prior to exposure to red light, the thylakoids are in a slightly swollen condition: in plastids exposed to red light and no inhibitor, the thylakoid membranes are closely appressed, giving the thylakoid a shrunken appearance relative to the control.It is further shown that Class I chloroplasts which are actively fixing CO2 do not give appreciable light scattering changes, but lowering the pH away from the optimum for ATP formation (and CO2 fixation) or adding the uncoupler quinacrine restores the light‐induced scattering increases.
THE FLUORESCENCE OF ADENINE. THE EFFECTS OF SOLVENT AND TEMPERATURE ON THE QUANTUM YIELD
Authors: EASTMAN J. W. , ROSA E. J. 
Published: January 2008

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 of low viscosity.
KINETICS OF CHLOROPLAST‐MEDIATED PHOTOXIDATION OF DIKETOGULONATE*
Authors: HABERMANN HELEN M. , HANDEL MARY ANN , McKELLAR PENELOPE 
Published: January 2008

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 to H2O2.
A STUDY OF THE SAFRANINE‐ASCORBIC ACID PHOTOCHEMICAL REDOX REACTION
Authors: WONG H. K. 
Published: January 2008

Abstract— Flash‐photolysis of safranine in deoxygenated 5 per cent aqueous pyridine produces a transient bleaching, which disappears by a second order process. Very probably this transient species consists of a pair of radicals or radical ions and not of the safranine in the triplet state. These radicals are also produced in chlorophyll sensitized reactions. Present results combined with previous work by us[I] indicate that the chlorophyll sensitization of safranine bleaching involves the formation of these radicals.The direct photochemical reduction of safranine to its leuco form occurs through the intermediate formation of the radicals. The appearance and disappearance of these radicals is fast compared to the role of photochemical formation and thermal disappearance of leuco safranine. Ascorbic acid influences but is not essential to the photo‐bleaching of safranine in 5 per cent aqueous pyridine. An increase in ascorbic acid concentration increases the steady‐state yield of the radicals but decreases the steady‐state yield of the leuco safranine. In the absence of ascorbic acid or other added substance, safranine photobleaches irreversibly in deoxygenated 5 per cent aqueous pyridine. A plausible mechanism is proposed in explanation of the direct photochemical reduction of safranine.
COMPARATIVE DECAY CHARACTERISTICS OF THE LIGHT GENERATED FREE RADICAL IN CHROMATOPHORES AND CHLOROPLASTS*
Authors: Cost K. , Bolton J. R. , Frenkel A. W. 
Published: January 2008

Abstract— Chromatophores of Rhodospirillum rubrum when illuminated exhibit a free radical which ordinarily shows a biphasic decay. When chromatophores are dehydrated at room temperature the time course of the appearance of the light‐induced free radical is unaffected, but the decay pattern has been altered. Only the fast component remains, the slow component is no longer evident. Scanning the magnetic field reveals the presence of a dark signal which is stable as long as the preparation remains dehydrated. This signal has the same peak‐to‐peak line width of ˜ 10 G and the same g factor as the signal evident in the light. The amplitude of this signal is equal to the amplitude of the slow decay component seen in aqueous chromatophore suspensions. Chromatophores frozen in an aqueous medium at —150°C exhibit a behavior identical with dehydrated preparations. The effects produced by lyophilization or by freezing at low temperatures are entirely reversible. When a lyophilized preparation is re‐hydrated, the stabilized portion of the signal now decays in the dark; the same is observed when preparations frozen at —150°C are thawed. When such thawed or re‐hydrated preparations are illuminated again, they exhibit the usual light‐induced ESR signal showing a biphasic dark decay.A comparison was made between the behavior of the light‐induced ESR signal of chromatophores and that of system I of chloroplasts. This comparison revealed that there is a greater similarity in some of the decay characteristics of these signals than had been recognized previously. In chloroplasts, temperature insensitive, non‐enzymatic back‐reactions of the light‐induced free radical appear to be nil, and in chromatophores a distinct portion of the light‐induced free radicals exhibit the same characteristics. Another portion of the chromatophore free radicals must be able to back‐react by electron tunneling, a mechanism which appears to be absent in the chloroplast system.
EXCITATION ENERGY TRANSFER IN BILIRUBIN‐CHLOROPHYLL AGGREGATES
Authors: MIEDZIWKO E. , FRACKOWIAK D. 
Published: January 2008

Abstract— Solutions of chlorophyll a (chl a) with different concentrations of bilirubin (blr) were used as a model system for studying the mechanism of energy transfer between bili‐proteins and chl in blue‐green algae. Several optical properties such as the absorption spectra, emission spectra for different wavelengths of excitation, degree of polarization and lifetime of fluorescence were measured. The measurements were carried out in several solvents (of different hydrogen bond‐forming capacities) and at various dye concentrations.The results indicate that aggregates of chl with blr are formed. Energy absorbed by blr in the aggregates is emitted as chlorophyll fluorescence, indicating energy transfer from blr to chl within the aggregate. The fluorescence yield and fluorescence polarization of aggregates are lower than those of isolated chl.
EXCITED STATES OF FLAVINES – V. THE QUENCHING OF FLAVINE LUMINESCENCE BY INDOLES
Authors: BOWD A. , BYROM P. , HUDSON J. B. , TURNBULL J. H. 
Published: January 2008

Abstract— The quenching of the fluorescence of flavines by indoles in aqueous solution has been studied as a function of concentration, viscosity and temperature. The quenching shows a negative temperature dependence, and is in part diffusion controlled. Static and dynamic processes both contribute to quenching.In the presence of alcohol or denaturants static quenching is inhibited and dynamic quenching supervenes. The effect of indoles on the flavine fluorescence lifetimes and phosphorescence characteristics is consistent with the quenching mechanism proposed.
DETECTION DE FAIBLES LUMINESCENCES EN SPECTROPHOTOMETRIE: COMPARAISON ENTRE DEUX TECHNIQUES DE MESURE PAR PHOTOMULTIPLICATEUR (‘EN COURANT’ ET ‘EN IMPULSIONS’)
Authors: DUQUESNE M. , VIGNY P. , GABILLAT N. 
Published: January 2008

Abstract— Both photomultiplier detection techniques (anodic current method and pulse method) are recalled, and the expression for the signal‐to‐noise ratio is discussed.In pulse detection, the role of time of observation appears clearly, as well as that of the discrimination threshold, the latter allowing a lower background noise.Both techniques are used for spectrophotometric detection of weak luminescences. Experimental results show that pulse technique allows a better sensitivity of the spectrophotometer.
THE ABSOLUTE YIELD OF BACTERIOCHLOROPHYLL FLUORESCENCE IN VIVO*
Authors: WANG RICHARD T. , CLAYTON RODERICK K. 
Published: January 2008

Abstract— –The method of Weber and Teale for determining absolute fluorescence quantum yield of dyes in solution was modified for determination of the yield of bacteriochlorophyll fluorescence from chromatophores and whole cells of photosynthetic bacteria. Measured yields ranged from about 1–6 per cent. The yield depended on intensity and wavelength of the exciting light. The higher yield at higher light intensity was interpreted as due to saturation of photosynthesis. The lower yield in some strains when excited at 810 nm was attributed to preferential excitation of the reaction center pigment P800.From this study and the lifetime measurements of others, the relation τ=Q.τ0 was substantiated for the fluorescence of bacteriochlorophyll in vivo, τ being the actual lifetime, τ0 the intrinsic lifetime as estimated from the absorption band area, and Q the quantum yield of fluorescence.