bluuebunny/crossref_metadata_2025_split huggingface dataset:
ENERGY TRANSFER AND CYTOCHROME FUNCTION IN A NEW TYPE OF PHOTOSYNTHETIC BACTERIUM*
Authors: Olson John M. , Nadler Kenneth D. 
Published: January 2008

Abstract— The excitation spectrum for bacteriochlorophyll b fluorescence at 1027 mμ in Rhodopseudomonas sp. NHTC 133 indicates that the efficiency of energy transfer from caro‐tenoid to bacteriochlorophyll b is between 27 and 28 %.Light‐induced absorbancy changes in anaerobic whole cells indicated the oxidation of three c‐type cytochromes (C‐550. 5, C‐553, C‐558) and one b‐type cytochrome or cytochromoid C (C‐560). At low light intensities C‐553 is the main cytochrome oxidized, while at high light intensities mainly C‐558 is oxidized in addition to C‐553. The light responses of the heme proteins appear to be similar to those observed previously in purple and green photo‐synthetic bacteria. No light‐induced shifts in carotenoid absorption bands were detected.In bacterial extracts C‐553 and C‐558 are bound to the chromatophores, while C‐550. 5 is soluble.
TRANSIENT SPECIES IN THE PHOTOCHEMISTRY OF EOSIN*
Authors: Kasche V. , Lindqvist L. 
Published: January 2008

Abstract— Photochemical reactions of eosin in aqueous solution were studied using the flash photolysis technique. In deaerated solution the dye was converted quantitatively to the triplet state during flashing. The triplet dye decayed by first and second order reactions which partly regenerated the dye in the ground state and partly produced semioxidized and semireduced eosin. These radical species were formed in an electron dismutation reaction between two triplet molecules and also in a reaction between one triplet and one unexcited molecule. The radicals recombine rapidly to give the dye in the ground state.An efficient reversible photooxidation reaction was observed in eosin solutions containing potassium ferricyanide. Semioxidized eosin was formed in high yield by reaction between the triplet dye and the oxidant. The dye was regenerated rapidly in a reverse reaction between the products of the oxidation reaction.An analogous type of reaction was found to occur in eosin solutions containing p‐pheny‐lene diamine. This reagent reduced the triplet dye to semireduced eosin; the dye was regenerated in the ground state in a very efficient reverse reaction. The protolytic behaviour of semireduced eosin was studied by varying the pH.Absorption spectra of the transient products were determined and rate constants for the observed reactions were measured. The results are compared with results from previous studies of fluorescein.
THE U.V. SENSITIVITY OF BACTERIA: ITS RELATION TO THE DNA REPLICATION CYCLE
Authors: Hanawalt Philip C. 
Published: January 2008

Abstract— A striking increase in the shoulder of the u.v. survival curve but no change in the limiting slope is obtained when cultures of Escherichia coli strain TAU complete the DNA replication cycle in the absence of concommitant protein synthesis prior to irradiation. The u.v. sensitivity of protein synthesis or RNA synthesis is not altered significantly by this treatment.In contrast to the result for strain TAU, there is no significant change in the u.v. survival curve for the u.v. sensitive E. coli Bs‐1 when its DNA replication cycle is completed under similar conditions.Following a period of inhibited protein synthesis there is a delay in the reinitiation of the normal DNA replication cycle when protein synthesis resumes. This delay would allow time for an intracellular repair system to operate before the attempted resumption of normal replication. Strain Bs‐1, which is deficient in this repair system, would not be expected to benefit from such a delay, as consistent with the observed results. A model is presented to account for lethality due to attempted DNA replication during a period of repair synthesis. The maximum survival for a given u.v. dose would be predicted for a culture which has completed the normal DNA replication cycle prior to irradiation and which is not permitted to reinitiate the cycle until all possible repair synthesis is completed.
PHOTO‐CHEMILUMINESCENT EMISSION IN OZONE
Authors: Wayne R. P. 
Published: January 2008

Abstract— Photo‐chemiluminescence is the phenomenon of radiation from a chemiluminescent reaction in which one or more of the reactants are formed initially by a photochemical process. Such photo‐chemiluminest emission has been observed, using a flow apparatus designed for the purpose, in ozne prepared from cylinder oxygen. The emission is shown to be identical with that observed from the reaction of nitric oxide with ozone. The ultimate source of the emission is taken to be the activation in the ozonizer of nitrogen, present as a trace impurity in the oxygen; nitrogen pentoxide is the oxide of nitrogen expected to be formed in the presence of ozone. Photolysis of ozone forms atomic oxygen which reacts with nitrogen pentoxide to yield nitric oxide which subsequently enters into the chemiluminescent reaction with ozone. (Experiments are described which confirm that nitric oxide is one of the products of the reaction between atomic oxygen and nitrogen pentoxide). The variation of emitted intensity with total gas pressure, ozone concentration and linear flow velocity is shown to be consistent with the mechanism proposed.No emission could be detected from either O2(1δg) or O2(1σ+g), which are possible products of the ozone photolysis. It is shown that while the absence of radiation from the 1σ+g; state indicates that O2(1σ+g) is not present in our system, yet the apparatus is not sufficiently sensitive in its present form to detect radiation from O2(lδg).
pH‐DEPENDENCE OF RHODAMINE B SEMIQUINONE DISMUTATION RATE IN AQUEOUS ALCOHOLIC SOLUTION
Authors: Stevens B. , Sharpe R. R. , Bingham W. S. W. 
Published: January 2008

Abstract— A single transient species is observed in absorption following the flash irradiation of dilute deoxygenated aqueous alcoholic solutions of rhodamine B in hte pH range 5.5–7.0 The second‐order decay constant for this semiquinone radical is an approximate linear function of the prevailing hydrogen ion concentration, the transient persisting for a period of from several seconds in neutral solution to several hours at pH = 12.The slow rate of decay and its pH‐dependence are explained in terms of an electron or H‐atom transfer between the (unobserved) protonated and (observed) unprotonated semiquinone radical with simultaneous regeneration of hte D+> and production of the leuco‐dye DH:—D·+ DH·+→ D++ DHInsofar as the reactant concentrations are controlled by the acid dissociation constant Ka of DH.+ the data are consistent with a value of 5.5±1.0 for pKa and a pH‐independent rate constant Ko of 1.3±0.5×106 1. Mole‐1 sec‐1 at 20d̀C.
PRIMARY PRODUCTS OF LIQUID WATER PHOTOLYSIS AT 1236, 1470 AND 1849 Å
Authors: Getoff N. , Schenck G. O. 
Published: January 2008

Abstract— The yield of the primary products of the liquid water photolysis at 1236 and 1470 Å is reported. It was found that besides the dissociation of the excited water molecules into H and OH radicals probably e−aq is also formed. The H and OH radicals were scavenged by means of formate, and the e−aq together with a part of H2O* by adding carbon dioxide. The quantum yields determined at 1236 Å, are:	Φ(H, OH) = 1.03 & 0.02, 0.06 <Φ(e−aq, H2O*) < 0.12 and at 1470 Å,: Φ(H, OH)=0.72±0.02, 0.037 < Φ(e−aq, H2O*) <0.075. The quantum yield of high purity water at 1849 Å in the absence of any scavengers is Φ(H, OH)=0.022. Previously published data by us for 1849 Å are also given: Φ(H, OH)=0.33 ± 0.01 and 0.02 < Φ (e−aq H2O*) < 0.04. Reaction mechanisms are proposed.
ETUDE PAR SPECTROSCOPIE D'ECLAIRS DU TRANSFERT D'ENERGIE CHLOROPHYLLE‐CAROTENOIDE
Authors: Mathis Paul 
Published: January 2008

Abstract— Energy transfer from chlorophyll A in its lowest triplet state to carotenoid pigments is demonstrated by rapid flash photolysis experiments.Two systems are used; the first consists of chlorophyll A and p carotene in organic solvents: in diluted solutions, energy transfer is diffusion controlled. The second consists of chlorophyll A and lutein incorporated into digitonin micelles suspended in water; with this system a very rapid energy transfer is observed (< 0.4 × 10‐‐6 sec).Energy transfer results in a carotenoid metastable state, which is supposed to be a triplet state; for lutein its half‐life is 8·9 × 10‐‐6 sec, and it has an absorption peak at 518 nm. Depopulation of lutein ground state, around 450 nm, can be observed, as well as the reactivity of oxygen towards the metastable state.Most of these results were obtained with a Q‐switch ruby laser as exciting source (6943 Å). A 4350 Å flash can also be obtained by two successive non linear effects. Using this flash for exciting chlorophyll A alone, a strong signal is detected, due to its triplet state. By exciting directly B carotene or lutein, it is not possible to detect any metastable state with our technique.
STUDIES ON THE PROTECTIVE FUNCTION OF THE CAROTENOID PIGMENTS OF SARCINA LUTEA
Authors: MATHEWS‐ROTH MICHELINE M. , KRINSKY NORMAN I. 
Published: January 2008

Abstract— An investigation was made of both the composition of and mechanism of photo‐protection by the carotenoid pigments of Sarcina lutea ATCC 9341a and three induced mutants.The wild‐type and mutants 2a and 4b were each found to contain three major pigment fractions, each fraction consisting of a single pigment having identical absorption maxima but differing from each other in chromatographic mobility. Although the mutants contain the same kinds of pigments as does the wild‐type, the mutant cells contain less pigment per cell than does the wild‐type. The third mutant, 93a, contains no colored carotenoids.It was found that there were changes in both the absolute and relative amounts of the various pigment fractions when cultures of wild‐type, mutants 2a and 4b, grown in nutrient broth in the dark, were examined during the logarithmic and stationary phases of the growth curve. In addition, changes were observed in the pigments when the cells were exposed to light in buffer. These changes were similar in the wild‐type and in mutant 2a, but were quite different in mutant 4b. Studies of photokilling curves suggested that these changes in amounts of the various pigment fractions were not related to photoprotection, but that the important factor may be the total amount of pigment per cell.
PHOTOREACTIVATION OF KILLING IN STREPTOMYCES‐II. KINETICS OF FORMATION AND PHOTOLYSIS OF PYRIMIDINE DIMERS AND ADDUCTS IN S. COELICOLOR AND S. GRISEUS PHR‐1*
Authors: IKENAGA M. , JAGGER J. 
Published: January 2008

Abstract— A pyrimidine adduct, 6‐4‘‐[pyrimidine‐2’‐one] thymine (PO‐T)‡, observed in DNA hydrolysates of 254‐nm ultraviolet (u.v.) irradiated conidia of Streptomyces coelicolor, increases linearly with u.v. dose up to 2 × 105 ergs/mm2. Yields of thymine dimer (T○) and uracil‐thymine dimer (U○) level off at much lower doses. Initial relative rates of formation of these u.v. photoproducts are: 1:1.3:4.8 for PO‐T, T○ and U○, respectively. Similar results were obtained with a Streptomyces griseus mutant, PHR‐1.An equation is derived to estimate the ratio of the amount of PO‐T to the total amount of thymine‐derived photoproducts at low (biological) u.v. doses. The observed PO‐T fractions compare well with the calculated values.Rapid photolysis of the precursor of PO‐T was observed by post‐u. v. treatment at 313 nm of conidia of S. coelicolor and of S. griseus PHR‐1. The photolysis was much slower at 365 nm and did not occur at all at 405 nm. Pyrimidine dimers were not appreciably affected by post‐u. v. treatment at the above wavelengths in these Streptomyces strains. Both of these strains are phenotypically photoreactivation‐deficient, and the present results indicate that they do not possess active photoreactivating enzyme.In earlier papers[3,4,5], the pyrimidine adduct found in acid hydrolysates of DNA was loosely referred to as “uracil‐thymine adduct (U‐T adduct)”. Such terminology is not strictly correct. The pyrimidine adduct in acid hydrolysates is PO‐T (sometimes called P2B), which could theoretically result from removal of ammonia from a C‐T adduct or removal of water from a U‐T adduct (see [6]).
LIGHT DISTRIBUTION AND ELECTRON DONATION IN THE Z SCHEME*
Authors: BEN‐HAYYIM GOZAL , AVRON MORDHAY 
Published: January 2008

Abstract— Several recent reports indicate that the photosynthetic machinery possesses a device whereby the relative distribution of absorbed light energy into the two reaction centers can be varied in response to the environment in which the photosynthesizing cells or chloro‐plasts are placed. Conditions reported which affect this distribution include the electron acceptor or electron donor system employed, the concentration of magnesium ions, and the preillumination history of the preparation. These observations are described and discussed in terms of their relevance to the interpretation of quantum yield and enhancement data.Several laboratories have presented evidence recently that chloroplasts, after undergoing a pretreatment which destroys their capacity to evolve oxygen, can still transfer electrons via both photosystems, provided an appropriate electron donor is added. It is shown that electron donors like manganous ions and ascorbate can compete effectively with water as electron donors to Photosystem II, in untreated chloroplasts.
PHOTOCHEMICAL REACTIONS OF AROMATIC KETONES WITH NUCLEIC ACIDS AND THEIR COMPONENTS I—. PURINE AND PYRIMIDINE BASES AND NUCLEOSIDES*.
Authors: CHARLIER M. , HELENE C. 
Published: January 2008

Abstract— The photochemical reactions of benzophenone and acetophenone with purine and pyrimidine derivatives in aqueous solutions have been investigated by flash photolysis and steady‐state experiments.Upon excitation of these two ketones in aqueous solutions, two transient species are observed: molecules in their triplet state and ketyl radicals. The triplet state lifetimes are 65 μsec for benzophenone and 125 μsec for acetophenone. The ketyl radicals disappear by a second order reaction, controlled by diffusion. In the presence of pyrimidine derivatives, the triplet state is quenched and the ketyl radical concentration is decreased without any change in its kinetics of disappearance. Ketone molecules in their triplet state react with purine derivatives leading to an increase in the yield of ketyl radicals due to H‐atom abstraction from the purines.Steady‐state experiments show that benzophenone and acetophenone irradiated in aqueous solution at wavelengths longer than 290 nm undergo photochemical reactions. The rate of these photochemical reactions is increased in the presence of pyrimidine derivatives and even more in the presence of purine derivatives. Following energy transfer from the triplet state of benzophenone to diketopyrimidines, cyclobutane dimers are formed. The energy transfer rate decreases in the order orotic acid > thymine > uracil. Benzophenone molecules in their triplet state can also react chemically with pyrimidine derivatives to give addition photoproducts.All these results are discussed with respect to photosensitized reactions in nucleic acids involving ketones as sensitizers.
THERMOLUMINESCENCE AND TEMPERATURE EFFECTS ON DELAYED LIGHT EMISSION (CORRECTED FOR CHANGES IN QUANTUM YIELD OF FLUORESCENCE) IN DCMU‐TREATED ALGAE*
Authors: JURSINIC P. , GOVINDJEE  
Published: January 2008

Abstract—

The simultaneous measurements of delayed light emission (DLE) and chlorophyll (Chl) fluorescence yield in DCMU§ treated Chlorella were made in the time range of 1 to 10 sec at various temperatures from 0 to 50°C. Similar measurements were made for DCMU treated thermophilic strain of Synechococcus in the temperature range of 0 to 75°C.
Using the basic assumption that DLE is produced by the back reaction of primary photoproducts of system II, and that two such reactions are required for it, a linear relationship between J‐1/2 (where J is energy per unit time available for DLE) and time after illumination was derived. This second‐order relationship was confirmed experimentally at several temperatures (2°, 5°, 10° and 15°C). From these analyses, reaction rate decay constants, at specific temperatures, were calculated.
An Arrhenius plot was made for these calculated rate constants. Its slope (8–10 kcal/mole) agreed well with previous reports; however, it had a region of zero slope which occurred at the physiological temperature of the organisms used.
Thermoluminescence or temperature jump delayed light emission (TDLE) was measured using various temperature conditions and it was found that not only the magnitude of the temperature jump (ΔT), but the initial and final temperatures of the sample were important. For example, a temperature jump of 8°C from 2 to 10°C gave much higher TDLE than from 12 to 20°C.
Many properties e.g., magnitude, temperature dependence and time independence of TDLE could be explained by the DLE decay data (corrected for changes in fluorescence yield) and the kinetic analysis.
It is suggested that, in addition to the back reaction of Z+ (the primary oxidized photoproduct of system II) with Q‐ (the primary reduced photoproduct of system II), a reducing entity, beyond the sites of DCMU and antimycin a action, is somehow involved in the production of slow DLE.
ENERGY TRANSFER FROM MICELLAR SODIUM PHENYLUNDECANOATE TO SOLUBILIZED NAPHTHALENE
Authors: ALMGREN M. 
Published: January 2008

Abstract— Excitation energy transfer from the phenyl groups of surface active phenylundecanoate ions to naphthalene molecules has been studied under conditions such that the naphthalene molecules have been solubilized by micelles of phenylundecanoate. From measurements of the naphthalene fluorescence intensity in solutions of varying surfactant concentration the critical micelle concentration has been determined as 0·0091 M. The product of the micellar aggregation number and the efficiency of energy transfer has been obtained as 75 from measurements of both the sensitized naphthalene fluorescence and the quenching of the phenylgroup fluorescence. In the evaluation of the experimental data it has been assumed that the partition of naphthalene between the micelles and the aqueous phase may be treated as a distribution equilibrium, and that the solubilized naphthalene molecules are partitioned among the micelles according to a Poisson distribution. With this model, the naphthalene fluorescence intensities may be accounted for over the whole range of surfactant concentrations.At high naphthalene concentrations, emission from naphthalene excimers has been observed. The possibility of self‐quenching via excimer formation is considered.The experimental results point to a quantum efficiency near unity for the transfer of excitation energy from the phenyl groups of the surfactant ions that form a micelle to a single solubilized naphthalene molecule. The high efficiency suggests that the naphthalene molecule and the phenyl groups are present inside the micelles.
MATRIX EFFECTS ON THE RADIATIONLESS TRANSITION' S1→T1 AND T1→S0 FOR BENZENE AND N, N, N', N'‐TETRAMETHYLPARAPHENYLENE‐DIAMINE MOLECULES
Authors: BERNAS A. , TRUONG T. B. 
Published: January 2008

Abstract— The present study attempts to correlate the phosphorescence life time τp at 77°K of a definite solute: tetramethylparaphenylenediamine (TMPD) with various solvents viscosity and polarity. A few experiments with benzene in the same solvents are also reported. The following results have been obtained:

The measured τp vary regularly with the sample immersion time in liquid N2, reaching a constant value after a few hours. This effect is related to the glass matrix relaxation. The rate constant Kisc (S, 1→T1) is also found to vary during relaxation of the solvent.
In the expression giving the nonradiative rate constant Knr (T1→S0), the bimolecular quenching term appears negligible for high viscosity matrices i.e. for η= 109 poises for benzene and for TMPD. Knr is found to vary linearly with log η, as well as the intersystem crossing S1→T1 rate constant Kisc.
Both Knr (T1→S0) and Kisc (S1→T1), increase with decreasing polarity of the solvent.
From our own observations and literature data[6] for C6H6 it appears that solvent viscosity does not contribute appreciably to the observed temperature effect on the solute τp when only a monomolecular triplet deactivation is operative.
PHOTOSYNTHETIC ENERGY TRANSFER REVERSIBLY INHIBITED BY HYDROSTATIC PRESSURE*
Authors: Schreiber Ulrich , Vidaver William 
Published: January 2008

Abstract— Hydrostatic pressure is found to affect reversibly the emission spectra of Porphyra perforata. At 1200atm phycoerythrin and phycocyanin fluorescence show a remarkable increase, whereas at the same time chlorophyll a (Chl a) fluorescence decreases. Upon release of pressure the fluorescence intensities of the individual pigments return to their original levels. This effect indicates that hydrostatic pressure acts as a unique reversible inhibitor of energy transfer between phycobilins and Chi a in the chloroplast.The effects of pressure and its release are relatively slow (minutes). It is suggested that pressure changes thylakoid membrane structure sufficiently to alter the critical distance between the phycobilisomes and Chl a, thus blocking the inductive resonance transfer of excitation energy.
PHOTO‐OXIDATION SENSITIZED BY METHYLENE BLUE, THIOPYRONINE, AND PYRONINE‐IV. THE BEHAVIOUR OF THIOPYRONINE IN SUSPENSIONS OF BACTERIA*
Authors: Jacob Hans‐Egon 
Published: January 2008

Abstract— In bacterial suspensions of Proteus mirabilis VI, at a cell concentration > 109/ml, a decrease in the concentration of oxidized (coloured) thiopyronine can be observed during aeration. The reduction of the dye to leucothiopyronine can be counteracted to only a small extent by aeration with oxygen, although aeration renders the redox potential of the suspension more positive than the polarographically determined half‐wave potential of the dye. This is caused by the fact that thiopyronine is reduced irreversibly by the bacteria. The decrease of thiopyronine concentration results in a decrease in the rate of photodynamic inactivation. Results obtained with thiopyronine are compared with those obtained with methylene blue: In suspensions of bacteria containing methylene blue, addition of oxygen inhibits reduction of the oxidized dye.In addition, thiopyronine is adsorbed by Proteus bacteria quickly (within 1 min) and strongly (0·8 per cent of dry weight). The dye penetrates into the cell, but the share that remains on the cell surface is not yet known. Methylene blue is adsorbed to nearly the same extent. The adsorbed thiopyronine is bound strongly by the cells.ZusammenfassungSensibilisierte Photooxydation durch Methylenblau, Thiopyronin und Pyronin. IV. Zum Verhalten von Thiopyronin in Bakteriensuspensionen. Thiopyronin wird von Bakterien nahezu irreversibel reduziert. In Bakteriensuspensionen mit hohen Zellzahlen (> 109/ml) nimmt deshalb die Konzentration des oxydiert vorliegenden Farbstoffs laufend ab. Der Farbstoffreduktion kann durch Einleiten von Sauerstoff in die Bakteriensuspension nur geringfügig entgegengewirkt werden, obwohl dadurch das “Redoxpotential” der Suspension wesentlich positiver wird als das Reduktionspotential des Farbstoffs ist. Die beim Thiopyronin und beim Methylbenblau erhaltenen Ergebnisse werden miteinander verglichen. Insbesondere kann beim Methylenblau durch Sauerstoff‐anwesenheit die Reduktion völlig verhindert werden.Weitere Ergebnisse sind: Das Thiopyronin wird von den Bakterienart Proteus mirabilis sehr schnell (innerhalb einer Minute) und in großem Umfang (Anteil am Trockengewicht etwa 0·8%) adsorbiert. Der Farbstoff gelangt auch ins Zellinnere. Welcher Anteil an der Zellbegrenzung verbleibt, ist nicht bekannt. Methylenblau wird etwa im gleichen Umfang wie Thiopyronin adsorbiert. Das von der Zelle adsorbierte Thiopyronin wird gegen einen Konzentrationsgradienten festgehalten.