bluuebunny/crossref_metadata_2025_split huggingface dataset:
PHYTOCHROME AND EFFECTS OF SHADING ON GROWTH OF WOODLAND PLANTS
Authors: Frankland B. , Letendre R. J. 
Published: January 2008

Abstractqrowth of Circaea lutetiaim plants was studied in various locations in or near a mixed deciduous woodland. Morphological changes resulting from increased shading included increases in leaf area ratio, specific leaf area and specific water content. Parallel measurements with a spectroradi‐ometer confirmed that shading involved a reduction in both light fluence rate and light quality (e.g. red/far‐red ratio). Phytochrome Pfr/P status was also studied by spectrophotometric measurements on Avena seedling test material and by biological (Lactuca seed germination) assay. Attempts were made to demonstrate phytochrome controlled changes in plant morphology under controlled environment, using both end‐of‐day far‐red treatment and far‐red enrichment of the main light period. Effects of natural shading were most clearly simulated by varying light fluence rate while maintaining a constant but high red/far‐red ratio
PHYTOCHROME CONTROL OF THE DEVELOPMENT OF PHOTOPHOSPHORYLATION
Authors: Oelze‐Karow H. , Mom H. 
Published: January 2008

AbstractIn the cotyledons of the mustard (Sinapis ah L.) seedling the development of the capacity for photophosphorylation is strongly influenced by pretreatment of the seedling with red light pulses. The red light acts through phytochrome. After a red light pretreatment the capacity for photophosphorylation increases linearly with the chlorophyll content, at least up to 30 min after the onset of continuous white light. It is proposed that the reaction chain required for photophosphorylation is completed under the influence of phytochrome even in the absence of chlorophyll. As soon as chlorophyll becomes available photophosphorylation functions instantaneously. Without a red light pretreatment there is a lag of more than 15 min before photophosphorylation becomes detectable after the onset of continuous white light even though chlorophyll a is available. Although phytochrome strongly influences the rate of chlorophyll accumulation as well it is improbable that the control by phytochrome of development of photophosphorylation and of chlorophyll accumulation are causally connected.
MYCOCHROME SYSTEM AND CONIDIAL DEVELOPMENT IN CERTAIN FUNGI IMPERFECTI
Authors: Kumagai Tadashi 
Published: January 2008

Abstract. A photoreceptor system, “mycochrome”, is involved in a blue and near UV reversible photo‐reaction which in turn plays an important role in the photocontrol of conidial development in Alternaria tomato, Botrytis cinerea and Helminthosporium oryzae. Conidial development was controlled by alternating exposures to blue and near UV light with the final response being determined by the final light received. When the final light was near UV a conidium developed; when it was blue, conidiation was inhibited and a “sterile” conidiophore was formed. The effects of the two lights were alternatively reversible.Blue and near UV reversible photoreaction was also found in a light‐minus‐dark difference spectrum of an intracellular particulate fraction isolated from dark‐grown mycelia of A. tomato, and two pigments, PB (blue absorbing type) and PNUV (near UV absorbing type), were contained in that photoreaction. PB was tightly bound to the particulate fraction and PNUV was either soluble in the cytoplasm or very loosely bound to the particulate fraction. Blue and near UV reversible photoreaction occurred only under the coexistence of PB and PNUV. That is, a dip in the near UV region and peak absorbance in the blue region was induced by irradiation with near UV light; however, both conditions were partially dissipated with a subsequent irradiation of blue light. These absorbance changes were revers‐ibly repeated by alternating doses of blue and near UV light. When molecular oxygen was introduced after exposure to near UV light, peak absorbance in the blue region rapidly disappeared, and these absorbance changes were repeatedly reversible. Similar results were obtained by treatment with sodium hydrosulfite and molecular oxygen.Thus, it was concluded that the mycochrome system suggested in photo‐conidiation was consistent with certain active substances showing blue and near UV reversible absorbance changes and caused by photooxidation reduction reaction.
A PULSED LASER SYSTEM FOR THE STUDY OF MICRO‐SECOND DELAYED FLUORESCENCE FROM PLANTS
Authors: Groves Michael R. 
Published: January 2008

Abstract—A new laser system is designed for the investigation of &#x006d;̈S delayed fluorescence. This is intended to overcome some undesirable features present in other current designs, such as low actinic light fluxes and long illumination times, or slow responses owing to long turn‐off times of the stimulation source and the presence of fluorescence artifacts.The system uses a pulsed argon‐ion laser and bears little resemblance to either the modified Becquerel phosphoroscope used by Lavorel (1971) or to those systems requiring shutters. Cheapness of design together with the ability to adjust such parameters as pulse duration easily, make this design attractive to most laboratories in which short (10 μs) high intensity (105 W m‐2) pulses with rapid (1.5 μs) turn‐off times and high on‐to‐off contrast ratios (106:1) are required.Certain design criteria are strictly imposed in order to produce kinetic data that can be meaningfully analysed.
THERMODYNAMIC AND KINETIC LIMITATIONS ON THE CONVERSION OF SOLAR ENERGY INTO STORABLE CHEMICAL FREE‐ENERGY
Authors: Almgren Mats 
Published: January 2008

Abstract— Energy‐storing reactions in a system after light excitation transform the system into a thermo‐dynamically metastable state. The effects of the microreversible back‐reaction on the net yield of the storage process and on the stability of the products are discussed. It is shown that the inevitable losses of photon energy in the conversion process may be estimated and considered as roughly independent of the threshold frequency of the system. The best attainable conversion efficiency as a function of the threshold absorption wavelength may then be estimated. Rough calculations show an ultimate efficiency of about 20% with the optimum threshold wavelength in the range 600–800 nm.Photochemical production of fuel, like hydrogen from water, requires that more than one photon of the solar spectrum is used per product molecule formed. The low photon density of sunlight leads to troublesome stability requirements on the intermediates in the reaction mechanism. Some features of consecutive two‐photon mechanisms in organized systems and homogenous solutions are discussed.
AN INVESTIGATION OF RETINAL AS A SOURCE OF SINGLET OXYGEN
Authors: Delmelle M. 
Published: January 2008

Abstract— All‐trans retinal is dissolved in alcohols and illuminated at 365 nm in the presence of a singlet oxygen acceptor, 2,5‐dimethylfuran. Illumination produces the photosensitized oxidation of the acceptor which is measured by the disappearance of its 215 nm absorption band. A kinetic study is carried out and βDMF is 1.6 × 10‐‐4M. The quantum yield of 1O2 production from the light‐excited retinal is estimated to 0.096. The retinal sensitized photooxidation of dimethylfuran is inhibited by a 1O2 quencher, 1,4‐diazabicyclo(2,2,2)‐octane, and enhanced by deuteration of the solvent. Deuterated solvents are known to increase 1O2 lifetime.The production of 1O2 from retinal is briefly discussed in relation to the damage which may be induced by light in the visual cells.
TRANSFER OF EXCITATION ENERGY BETWEEN PORPHYRIN CENTERS OF A COVALENTLY‐LINKED DIMER*
Authors: Anton John A. , Loach Paul A. , Govindjee  
Published: January 2008

Abstract— Three covalently‐linked porphyrin hybrid dimers were synthesized, each containing a metallotetraarylporphyrin [Zn(II), Cu(II), or Ni(II)], and a free base tetraarylporphyrin. Transfer of singlet excitation energy from the metalloporphyrin center to the free base porphyrin center was determined by measuring fluorescence properties. The Zn hybrid dimer displayed excellent intramolecular transfer of energy ( 85%) from the excited singlet state of the Zn(II) chromophore to the free base chromophore. No evidence for such transfer of the excited singlet state energy was found in the Ni(II) or Cu(II) analogues. From our experimental data, the fluorescence quantum yield of the Zn hybrid dimer was the same as for the free base monomer porphyrin (0.11; Seybold and Gouterman, 1969). Thus, the covalent attachment of another fluorescent porphyrin center effectively doubled the antenna size without decreasing the quantum yield even though the fluorescence quantum yield of the Zn(II) containing monomer was substantially less (0.03, according to Seybold and Gouterman, 1969) than that of the free base porphyrin.The donor‐acceptor distance and the rate constant for energy transfer were calculated using the Forster equation. Assuming random orientation, a donor‐acceptor distance of 15 Å was calculated with an associated rate constant (kci) for energy transfer of 1.9 ± 109 s–1.
MODELS FOR BACTERIAL PHOTOSYNTHESIS: ELECTRON TRANSFER FROM PHOTOEXCITED SINGLET BACTERIOPHEOPHYTIN TO METHYL VIOLOGEN AND m‐DINITROBENZENE
Authors: Holten Dewey , Windsor Maurice W. , Parson William W. , Gouterman Martin 
Published: January 2008

Abstract. As a model for the primary reactions of photosynthesis, we studied photochemical electron transfer from bacteriopheophytin (BPh) to methyl viologen (MVC12) and to m‐dinitrobenzene (m‐DNB) in solution. Both MVC12 and m‐DNB cause reductions in the lifetime of the first excited singlet state of BPh (BPh*), in the fluorescence quantum yield, and in the quantum yield of the triplet state, BPh +. The quenching of BPh* probably results from electron transfer, which generates short‐lived radical pairs involving the BPh radical cation (BPh+) and the reduced form of the quencher. Electron transfer from BPh* is thermodynamically favorable, but that from BPhT is not. From the magnitude of the quenching, we calculate rate constants for electron transfer in collision complexes formed between BPh* and MVC12 or m‐DNB. Measurements of the quantum yield of the free BPh+ radical indicate that about 3/4 of the [BPh+ MV+] radical pairs decay by reverse electron transfer, rather than dissociating to give the free radicals. Essentially all of the [BPh+m‐DNB +] radical pairs must decay by reverse electron transfer, because free BPh+ cannot be detected in this case. From these data, we estimate the rate constants for the reverse electron transfer reactions. The higher probability of dissociation in the [BPh+ MV+] radical pair can be explained by coulombic repulsion.The rate of the primary electron transfer reaction in photosynthetic bacteria is comparable to that of forward electron transfer in the BPh* collision complexes. Reverse electron transfer, however, is at least 103‐times slower in the radical pair formed in the bacterial reaction center than it is in [BPh+m‐DNB−], and more than 104‐times slower than in [BPh+ MV+]. The explanation for this dramatic and crucially important difference remains unclear, but several possibilities are discussed.
EXCITED SINGLET AND TRIPLET PRODUCTS GENERATED FROM OXIDATION OF THE ‐CO‐CH‐ CONTAINING MOLECULES
Authors: Kamiya Isao , Sugimoto Takashi 
Published: January 2008

Abstract— In a previous study. we found indirect chemiluminescence from air oxidation of various simple ketones in alkaline aprotic solvents containing 9,10‐diphenylanthracene and 9,10‐dibromoanthracene. By summarizing the experimental results. it was concluded that excited products. mainly in the triplet state. were generated from air oxidation of those simple compounds having a ‐CO‐CH‐group via dioxetane intermediates.Recently. we have succeeded in observing an intense direct chemiluminescence due to the generation of the excited singlet product by the air oxidation of such anthracene derivatives having a ‐CO‐CH‐group as 9,10‐diisobutyrylanthracene and related compounds. The finding lends strong support to the hypothesis that dioxetane or dioxetanone may be the critical intermediate to give fluorescent singlet products.
STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS — V. AB INITIO CONFIGURATION INTERACTION CALCULATIONS ON THE GROUND AND LOWER EXCITED SINGLET AND TRIPLET STATES OF ETHYL CHLOROPHYLLIDE a AND ETHYL PHEOPHORBIDE a
Authors: Petke J. D. , Maggiora Gerald M. , Shipman Lester , CHRISTOFFERSEN Ralph E. 
Published: January 2008

Abstract— Ab initio configuration interaction wavefunctions and energies are reported for the ground state and many low‐lying excited singlet and triplet states of ethyl pheophorbide a (Et‐Pheo a) and ethyl chlorophyllide a (Et‐Chl a), and are employed in an analysis of the electronic absorption spectra of these systems.In both molecules the visible spectrum is found to consist of transitions to the two lowest‐lying 1(π, π*) states, S1 and S2. The configurational compositions of S1 and S2 in both molecules are similar, and are described qualitatively in terms of a four‐orbital model. The S1← S0 transition in each case is predicted to be intense, and is largely in‐plane y‐polarized, while the S2← S0 transition is predicted to be extremely weak and in‐plane polarized. The orientation of the S2← S0 transition dipole is not conclusively established in the present calculations.The Soret band in both molecules is composed of transitions to no less than ten states (S3‐S12 in Et‐Chl a and S3‐S7S9‐S12. and S14 in Et‐Pheo a), which exhibit primarily (π, π*) character. The configurational compositions of these states are generally a complex mixture of excitations from both occupied macrocyclic π molecular orbitals and occupied orbitals with electron density in the cyclopen‐tanone ring and the carbomethoxy chain. No clear correspondences are evident between respective Soret states of the two systems. Transitions to these states are generally intense and display a variety of in‐plane polarizations.Two additional Soret states of Et‐Pheo a, S8 and S13, exhibit primarily (n. π*) character. S8 is characterized by excitations from u and non‐bonding regions of the carbomethoxy chain, while S13 is described by n →π* excitations involving the nitrogen atom of ring II. No corresponding (n, π*) states were found for Et‐Chl a.In both molecules the lowest two triplet states, T1 and T2, are found to lie lower in energy than S1. while T, and S1 are approximately degenerate. The configurational compositions of T1‐T4 of both molecules are nearly identical, and may be described by a four‐orbital model. However, the compositions of T1‐T4 differ sharply from those of S1 and S2.A number of higher‐lying 3(π, π*) states of both molecules (T5‐T13 in Et‐Chi a and T8‐T9, T11‐T13 in Et‐Pheo a) are found to have energies similar to the singlet Soret states, relative to S0. They are characterized by a complex mixture of configurations which do not include significant contributions involving the four‐orbital model. In addition, two 3(n, π*) states of Et‐Pheo a, T10 and T14, are found, which are somewhat analogous to S8 and S13.Additional data presented include the charge distributions and molecular dipole moments of the S0. S1, and T1 states of both molecules, as well as energies and oscillator strengths of computed Sn←S1 and Tn←1 transitions.
REACTIVITY OF ACRIDINE DYE TRIPLET STATES IN ELECTRON TRANSFER REACTIONS
Authors: Vogelmann Ekehardt , Rauscher Wolfgang , Krameer Horst E. A. 
Published: January 2008

Abstract—Rate constants, kq, for the reaction of cationic and neutral acridine orange and 10‐methylacridine orange triplet states (3AOH +, 3AO, 3MAO+) with a series of electron donors have been measured. Two different protolytic forms of the semireduced dye radical are produced by acridine orange triplet quenching at various pHM values in methanolic solution.It is found that k4 decreases with increasing oxidation potential of the reducing agent for all triplet states in a manner which is expected for electron transfer reactions. The different reactivities of the cationic and neutral triplet forms can, therefore, be attributed to the difference in reduction potentials of these species. The difference in reduction potentials is related to the pKM values of triplet state, pKTM, and semireduced dye radical, pKMS, by thermodynamic consideration. pKTM (3AOH+/3AO) is determined to be 11.2. From thispKSM (AOH./AO;) is estimated to be 17–18. This is in striking contrast to the protolytic equilibrium of the semireduced dye radicals found to be pKF= 4.1. We conclude that the last value represents the second protonation equilibrium (AOH+2./AOH). This conclusion is confirmed by spectroscopic data.
PHOTOLUMINESCENCE OF SINGLET OXYGEN IN PIGMENT SOLUTIONS
Authors: Krasnovsky A. A. 
Published: January 2008

Abstract—Luminescence of 1O2 (1270 nm) accompanying energy transfer to oxygen from photoexcited (triplet) molecules of sensitizers in air saturated solutions has been investigated. The luminescence was observed in CC14, CS2 and freon with the use of porphyrins, chlorophylls, pheophytins and aromatic hydrocarbons as sensitizers. The lifetime and quantum yield of the luminescence depended on the nature of the solvents. pigments and their concentrations. The maximum values of these parameters were equal to 28 ± 5 ms and 5 ± 4 times 10‐‐5, respectively. The quantum yield of 1O2 generation by pigments has been measured and the results used for determining the quantum yields of intersystem crossing in the pigment molecules. The rate constants of 1O2 reaction with different substances have been determined with the aid of luminescence quenching. It has been shown that along with β‐carotene. Chls, pheophytins, and some porphyrins are also very active quenchers of 1O2, The quenching effect depends on their molecular structure and on the presence and nature of the central metal atom. Quenching 1O2 by the pigments is due mainly to a “physical” mechanism (without destruction of the pigments). The destructive “chemical” quenching is by 1–4 orders of magnitude less effective and is accompanied with photochemiluminescence of the pigments. The experiments on 1O2 generation and quenching indicate that energy of triplet states of bacteriochlorophyll and bacteriopheophytin is somewhat higher than that of 1Δg oxygen. The data demonstrate wide possibilities of the luminescence studied as a method for investigating 1O2 reactivity and photophysical properties of sensitizers.
THE REDUCTION AND QUENCHING OF PHOTOEXCITED FLAVINS BY EDTA
Authors: Fife Dennis J. , Moore William M. 
Published: January 2008

Abstract—Riboflavin was irradiated anaerobically in aqueous EDTA solutions over the pH range 2.5–10. In other dye systems (Bonneau and Pereyre, 1975), only the trivalent anion of EDTA was found to have significant reactivity for photoreduction. For riboflavin, the reactivity begins with monoanionic EDTA, and the reactivity is markedly increased as the charge increases. This suggests that the charge on the reductant is more important to the electron transfer process for riboflavin than the formation of a nonhydrogen bonded nitrogen site on EDTA. At high concentrations of EDTA in the pH range 4–8, quenching of the photoreduction occurs, which can be explained by an energy transfer between the excited singlet state of riboflavin and trianionic EDTA, possibly as an association complex. The rate constants for the photoreduction of riboflavin by the monovalent, divalent, and trivalent anions of EDTA are 1.0 times 107M‐1 s‐l, 4.8 times 10′M‐1 s‐l, and 2.0 times 108M‐1s‐1, respectively. The rate constant for the singlet state quenching by trianionic EDTA is 3 times 109M‐l s‐1, and the limiting quantum yield for intersystem crossing for riboflavin in aqueous solution is 0.50 ± 0.05.
SYNERGISTIC LETHALITY OF PHAGE T7 BY NEAR‐UV RADIATION AND HYDROGEN PEROXIDE: AN ACTION SPECTRUM
Authors: Ananthaswamy H. N. , Hartman P. S. , Eisenstark A. 
Published: January 2008

Abstract—Hydrogen peroxide (H2O2) enhances the killing of phage T7 by near‐ultraviolet irradiation (NUV), maximally at 340 nm. There is no synergistic action below 300 nm. The addition of H2O2 resulted in a marked increase in the number of single strand (SS) DNA breaks induced at all near‐UV wavelengths tested. However, there is no correlation between SS break induction and degree of killing.
INTERFACIAL ELECTRON TRANSFER INVOLVING RADICAL IONS OF CAROTENE AND DIPHENYLHEXATRIENE IN MICELLES AND VESICLES
Authors: Almgren M. , Thomas J. K. 
Published: January 2008

Abstract— The radical cations and anions of diphenylhexatriene have been produced and characterized in homogenous and micellar solutions by pulse radiolysis and laser flash photolysis techniques. Both types of radical ions were formed in cyclohexane on pulse radiolysis. The radical cation was formed in dichloroethane on pulse radiolysis, and by two photon photoionization in ethanol, dichloroethane, and various micelles. Both radical ions have intense (? 105M‐1 cm‐1) absorption peaks at600–650nm. The cation peak occurs at slightly shorter wavelengths than that of the anion.In micelles and vesicles the radical anion of carotene was formed by electron transfer from ea– on pulse radiolysis. The radical cation was formed on pulse radiolysis of micellar solutions containing Br‐2 as counterion, presumably by electron transfer to Br2‐. The spectra agree with those of the radical cation and anion of carotene that have previously been obtained in homogenous solutions (Dawe and Land, 1975).Electron transfer in micelles and vesicles from the radical anion of biphenyl to carotene and diphenylhexatriene, and from the radical anions of these to inorganic acceptors has been studied.
QUANTUM EFFICIENCY FOR THE PHOTOCONVERSION OF BACTERIORHODOPSIN AT VERY LOW TEMPERATURES
Authors: Iwasa Tatsuo , Tokunaga Fumio , Yoshizawa Tôru , Ebrey Thomas G. 
Published: January 2008

Abstract— Quantum efficiencies for photoconversion of bacteriorhodopsin (trans‐bR) to a bathochromic product (batho‐bRt) and its photoreversion in purple membrane at 77 and 9 K were investigated with low temperature spectrophotometry. The kinetics of the photoconversion and its photoreversion cannot be expressed by a single exponential curve. The photoconversions at 77 and 9 K showed the same slope in the early stage. The kinetics of the photoreversions were identical at the two temperatures. These results indicate that the quantum efficiencies for the conversion of trans‐bR to batho‐bRt or for its photoreversion are identical at the two temperatures.The fact that the photoreversion cannot be expressed by a single exponential curve suggests the existence of several conformational states of batho‐bRt due to the trimer structure of the purple membrane.