bluuebunny/crossref_metadata_2025 huggingface dataset:
PHOTOSENSITIZED OXYGENATION OF CARBONYL STABILIZED SULFUR AND PYRIDINIUM YLIDS, AND RELATED DIAZO COMPOUNDS. CARBON‐SULFUR AND NITROGEN BOND CLEAVAGES
Authors: Ando Wataru , Kohmoto Shiceo , Miyazaki Hajimc , Nishizawa Kyojun , Tsumaki Hidetoshi
Published: January 2008

Abstract— The dye sensitized photooxygenation of sulfur and pyridinium ylids proceeds by way of singlet oxygen under the reaction conditions studied. The most remarkable results were that dimethyl sulfoxide and pyridine were obtained in the photooxygenations of oxosulfonium and pyridinium methy‐lids, respectively. as the major cleavage products. These results suggested that the 1,2‐dioxetane like intermediates were not significant ones in these reactions. The oxygenation reactions in the presence of diphenyl sulfide which was known as the most unreactive one to singlet oxygen afforded diphenyl sulfoxide efficiently. A new type of intermediate instead of 1,2‐dioxetane. that can monooxygenate the substrate may be formed. Photosensitized oxygenations of corresponding diazo compounds were also studied.
ACTION SPECTRUM FOR PHOTOREACTIVATION OF ULTRAVIOLET‐IRRADIATED MARSUPIAL CELLS IN TISSUE CULTURE
Authors: Chiang Tom , Rupert Claud S.
Published: January 2008

Abstract— An action spectrum has been determined for photoreactivation of the PtK‐2 mammalian cell line of Potorous tridactylus. Maximum effectiveness occurs around 366 nm, but appreciable photo‐reactivation occurs at wavelengths as long as 546 nm.
INDUCTION OF SKIN TUMORS IN THE RAT BY SINGLE EXPOSURE TO ULTRAVIOLET RADIATION
Authors: Strickland Paul T. , Burns Fredric J. , Albert Roy E.
Published: January 2008

Abstract— The dose response for tumor induction in albino rat skin by single exposures of UV radiation has been characterized. The shaved dorsal skin of 202 animals was exposed to either of two sources: one emitting a broad spectrum of wavelengths from 275 to 375 nm, and the other emitting at 254 nm. Skin tumors began to appear within 10 weeks of exposure and continued to appear for 70 weeks. The highest tumor yield was 5.5 tumors per rat and occurred when the rats were exposed to 13.0 times 104 J/m2 of the 275–375 nm UV. The 275–375 nm UV was about eight times as effective as the 254 nm UV for the induction of tumors throughout the exposure range from 0.8 times 104 to 26.0 times 104J/m2. Tissue destruction and hair follicle damage was found at the highest exposure to 275–375 nm UV but at none of the exposures to 254 nm UV. Repeated weekly exposures to 275–375 nm UV proved less effective than an equivalent single exposure for inducing tumors, even though the multiple exposures caused more severe skin damage. The transmission of the UV through excised samples of rat epidermis indicated that the exposure to the basal cell layer was about 3% of the surface exposure at 254 nm and about 15% of the surface exposure between 275 and 320 nm. The dependence of tumor yield on UV exposure was linear for 254 nm UV but was more complex for the 275–375 nm UV. For the latter more tumors were produced per unit exposure at lower exposures than at higher exposures.
PHOTOCYCLOADDITION OF 5,7‐DIMETHOXYCOUMARIN TO THYMINE
Authors: Shim Sang Chul , Chae Kyu Ho
Published: January 2008

Abstract— C4‐‐Photocycloaddition of 5,7‐dimethoxycoumarin (DMC) to thymine (λ≥ 300 nm) was studied in dioxane‐water solution, in aqueous frozen state, and solid film state. The major product was isolated and characterized by physical methods. Elemental analysis data, spectral analyses, and photo‐splitting of the product indicate the product to be a 1:l C4‐‐cycloadduct of DMC and thymine.
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.
EFFECT OF THE BROMINE ATOM UPON THE DISSOCIATION CONSTANTS OF BROMOPYRIDINES, BROMOQUINOLINES AND 4‐BROMOISOQUINOLINE IN THEIR LOWEST EXCITED SINGLET AND TRIPLET STATES*
Authors: Aaron Jean‐Jacques , Thiao P. , Párkányi Cyril , Jeffries Alfred T. , Kalsotra Bansi L.
Published: January 2008

Abstract— The lowest excited singlet‐state dissociation constants (pKSa) of bromosubstituted pyridines, quinolines, and isoquinolines were determined from the pH‐dependent shifts in their electronic absorption spectra. The lowest excited triplet‐state dissociation constants (pKTa) of bromosubstituted quinolines and 4‐bromoisoquinoline were obtained from the shifts of the 0–0 phosphorescence bands measured in rigid aqueous solution at 77 K. The pKSa values indicate that the basicity of these brominated nitrogen heterocycles is increased in the lowest excited singlet state by 2 to 10 orders of magnitude as compared with the ground state. The pKTa values are found to be significantly different from the corresponding ground‐state pKa values, indicating that the basicity of bromoquinolines is increased in the lowest excited triplet state by 1.7 to 3.0 pK units. The enhancement of the excited singlet‐and triplet‐state basicity of brominated nitrogen heterocycle derivatives as compared with the unsuhstituted parent compounds is attributed to the increased electron‐donor conjugative interactions of the bromine atom pπ orbitals with π orbitals in the lowest excited singlet and triplet state.
THE EFFECT OF DNA BINDING ON INITIAL 8‐METHOXYPSORALEN PHOTOCHEMISTRY*
Authors: Goyal Greesh C. , Grossweiner L. I.
Published: January 2008

Abstract—Flash photolysis experiments on the complex of 8‐methoxypsoralen with calf thymus DNA have shown binding promotes the anaerobic quenching of the 8‐MOP triplet state and inhibits the accessibility to oxygen. The results indicate dark psoralen‐DNA interactions suppress the singlet oxygen generation observed in prior work.
EFFECT OF PHOSPHATE ION ON FLUORESCENT CHARACTERISTICS OF TYROSINE AND ITS CONJUGATE BASE
Authors: Shimizu Okiyasu , Watanabe Jun , Imakubo Kehchi
Published: January 2008

Abstract—The UV fluorescence spectrum of tyrosine (Tyr) is markedly affected by the interaction with phosphate ion. In order to elucidate the mechanism of the specific fluorescence quenching by phosphate and the simultaneous appearance of a new emission, the effect of phosphate on the spectro‐scopic characteristics of Tyr was investigated. Employing a fluorimetric method, we have obtained the following results. Namely, potassium phosphate was found to enhance the fluorescence intensity of tyrosinate ion. When Tyr is excited in the phosphate‐containing solution, the emission with a peak around 345 nm is observed besides the normal fluorescence of Tyr around 303 nm with a reduced quantum yield. The abnormal emission may be ascribed to the tyrosinate ion in the excited state resulting from the deprotonation of the phenolic OH group of the excited Tyr. although the tyrosinate ion in the ground state is not predominant in the aqueous solution examined.
MEASUREMENT OF DNA CROSSLINKS BY S1 NUCLEASE: INDUCTION AND REPAIR IN PSORALEN‐PLUS‐360 nm LIGHT TREATED ESCHERICHIA COLI
Authors: Ben‐Hur E. , Prager A. , Riklis E.
Published: January 2008

Abstract—DNA crosslinks in Escherichia coli cells. exposed to 4.5′,8‐trimethylpsoralen plus 360 nm light, were measured using a rapid and sensitive new approach. The assay is based on the specificity of S1 nuclease from Aspergillus oryzae to single‐stranded DNA. Bacterial cells were lysed and the DNA denatured by alkali. Following acid neutralization. crosslinked DNA undergoes spontaneous renaturation and is rendered S1‐nuclease resistant and therefore acid‐precipitable. The single‐stranded fraction after denaturation by alkali decreases with increasing near UV light exposure in the presence of TMP following first order kinetics. The kinetics were faster when exposure was at 4°C rather than at 20°C. This suggests that excision of crosslinks occurs during exposure at the higher temperature. Indeed. since the rate of DNA crosslinking in a uvr B mutant which is excision‐deficient was higher than in wild type bacteria at 4°C, some excision must have occurred even in the cold. DNA from excision‐proficient cells incubated at 37°C following exposure to TMP‐plus‐near UV at 4° showed a greater single stranded fraction than that from non‐incubated cells. This indicates repair of DNA crosslinks. which proceeded with a half‐time of 8 min at 37°C and was unaffected by substitution of thymine in DNA by 5‐bromouracil.
FLUORESCENCE QUENCHING OF 10‐METHYLACRJDINIUM CHLORIDE BY NUCLEOTIDES
Authors: Kubota Yukio , Motosa Yuko , Shigemune Yoko , Fujisaki Yasuo
Published: January 2008

Abstract— All nucleotides examined (AMP, GMP, TMP and CMP) quench the fluorescence or 10–methylacridinium chloride (10–MEAC). The fluorescence spectrum of 10–MEAC‐nucleotide system is identical with that of 10–MEAC itself, and the fluorescence decay kinetics follow a single‐exponential decay law. The dependence of fluorescence quantum yields and fluorescence lifetimes upon the concentration of nucleotides indicates that the fluorescence of 10–MEAC is greatly quenched in both dynamic and static processes by nucleotides. The quenching constants increase in the order: AMP ≳ GMP > TMP ≳ CMP. The results of 10–MEAC are compared with those of other acridine dyes (proflavine, 9–aminoacridine and acridine orange).
PHOTO‐CONJUGATION OF 8–METHOXYPSORALEN WITH PROTEINS
Authors: Yoshikawa Kunihiko , Mori Norio , Sakakirara Shigeru , Mizuno Nobuyuki , Song Pill‐Soon
Published: January 2008

Abstract— 8–Methoxypsoralen (8–MOP) is shown to form a covalent conjugate with bovine serum albumin (BSA) by UVA irradiation in the presence of 02. The photoreaction is shown to involve oxidation of 8–MOP itself as a first step, producing an oxidation product which reacts readily with protein. Thus, this photoreaction appears to be completely different from the known 8–MOP photo‐cycloaddition reaction with DNA. Among several proteins studied, human serum albumin, histone type 11, RNAse A and lysozyme also undergo photoinduced addition by 8–MOP. Chemical modifications of various amino acid residues in BSA revealed tyrosine‐OH as one of the reaction sites. Irradiation (12 h) with UVA at 1.78 J/ds intensity resulted in approximately 1.5 mot of 8–MOP bound to 1 mol of BSA.
LIGHT‐INDUCED ACCUMULATIONS OF DICTYOSTELIUM DISCOIDEUM AMOEBAE
Authors: Häder Donat‐P. , Poff Kenneth L.
Published: January 2008

Abstract— Light‐induced accumulations of amoebae of Dictyostelium discoideum in ‘light traps’ have been observed. The greatest accumulations are obtained with cell densities of about 8 × 104 cells/mm2. Accumulations are observed at incident fluence rates over about one decade both for white and for monochromatic light; higher fluence rates cause dispersal from the ‘light trap’. An action spectrum for the photoaccumulation, calculated from fluence‐response curves using the zero thresholds, shows a major peak between 405 and 410 nm and extends through most of the visible spectrum. This action spectrum does not coincide with any of the pigments known to be present in D. discoideum. The cellular basis for the photoaccumulation has been studied. No light effects on cell divisions or cell aggregation are observed during the 2 h duration of an accumulation experiment. Microvideographic analysis of single amoebae is consistent with the hypothesis that the amoebae are positively phototactic and move toward the light scattered from cells in the ‘light trap’, thus accumulating in the trap.
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.
TYPE I AND TYPE II MECHANISMS IN THE PHOTOOXIDATION OF L‐TRYPTOPHAN AND TRYPTAMINE SENSITIZED BY HEMATOPORPHYRIN IN THE PRESENCE AND ABSENCE OF SODIUM DODECYL SULPHATE MICELLES
Authors: Sconfienza Cristina , Van de Vorst Albert , Jori Giulio
Published: January 2008

Abstract— Oxygenated aqueous solutions (pH 10) of L‐tryptophan or tryptamine containing hematopor‐phyrin and/or specific quenchers of the possible reactive intermediates were irradiated with visible light in the presence and in the absence of dispersions of sodium dodecyl sulphate micelles. The rate of loss of the indole derivatives was followed over several min. In the absence of dispersed micelles, indole derivatives appeared to be photooxidized largely by a type I mechanism involving electron transfer from triplet hematoporphyrin to the indole moiety. A type II (lO2‐involving) mechanism was of minor importance. The presence of sodium dodecyl sulphate micelles, where the porphyrin was solubilized in a monomeric state, exerted only a slight influence on the competition between the two reaction pathways described above in the case of tryptophan, which was essentially all present in the aqueous phase. On the other hand, tryptamine, when dissolved within micelles, underwent photooxidative attack exclusively by 1O2 which was generated within a micelle, diffused through the aqueous phase and penetrated into another (tryptamine‐containing) micelle; the reduced efficiency of the latter photoprocess was probably a consequence of the low probability of 1O2 penetration into charged micelles.
CHARACTERIZATION OF A MICROSECOND INTERMEDIATE IN THE LASER FLASH PHOTOLYSIS OF SMALL PHYTOCHROME FROM OAT
Authors: Braslavsky, Silvia E. , Matthews, J. Ioan , Herbert, Hans J. , de Kok Jacob , Spruit Carel J. P. , Schaffner Kurt
Published: January 2008

Abstract— Irradiation of small phytochrome from oat in its Pr form with 15 ns laser pulses of different wavelengths(605–655 nm) gave rise to a difference absorption with maxima at 400 and 685 nm for the first detectable transient. Bleaching of a 660 nm band was observed, non‐recuperable up to 1 ms. The transient absorption has a lifetime of 70±15 μs at 273 K. The transient is tentatively identified as lumi‐R and the conformation of its chromophore is postulated to be more extended than that of Pr. A deviation from the exponential decay of the lumi‐R absorption at 284 and 300 K and the lack of observable enhancement of the far‐red absorption within 1 ms are interpreted in terms of the appearance of still other intermediates on this time scale between lumi‐R and Pfr phytochrome.
THE RELATIVE IMPORTANCE OF VARIOUS ENVIRONMENTAL FACTORS ON THE VERTICAL DISTRIBUTION OF THE AQUATIC PROTOZOAN COLEPS SPIRALIS
Authors: Barcelo Jeanne A. , Calkinsi John
Published: January 2008

Abstract— The vertical distribution of Coleps spiralis in a tertiary lagoon system was observed over a period of 18 months. Water samples were taken from the surface, middle and bottom of the lagoons and examined to determine the number of Coleps present. Various external and internal environmental factors (i.e. light, temperature, wind, etc) were investigated to determine which might be important in influencing the vertical positioning of Coleps in nature. Irradiance factors (both total solar irradiance and the UV‐B component (λ= 320–280 nm) of sunlight showed the highest correlation with the location of the animals. When irradiance was high, the animals were usually found near the bottom of the lagoon; when irradiance was low the animals were located more randomly throughout the water column. On the other hand, wind, cloud cover, temperature gradients and bacterial (food) gradients showed low correlation with location of the protozoan in the water.
ACRIDINES, DEAZAFLAVINS, ANDTRIS(2,2'‐BIPYRIDINE)RUTHENIUM AS CATALYSTS FOR PHOTOPRODUCTION OF HYDROGEN FROM ORGANIC COMPOUNDS
Authors: Krasna Alvin I.
Published: January 2008

Abstract— The previously reported (Krasna, 1979) photoproduction of hydrogen from organic compounds in the presence of methyl viologen and platinum, catalyzed by proflavin, has now been accomplished with other photocatalysts. The acridine derivatives acriflavin, acridine yellow and acridine orange were active catalysts, whereas 9‐aminoacridine was not. The reaction was similar to the proflavin catalyzed reaction with respect to electron donor specificity and mechanism. Tris(2,2'‐bipyridine)ruthenium (II) also replaced proflavin and the reaction was similar in most respects to that catalyzed by proflavin except that rris(2,2'‐bipyridine)ruthenium catalysis was most effective at alkaline pH values. The deazaflavins, deazaribofiavin and 3,10‐dimethyl‐5‐deazaisoalloxazine, were more active than proflavin, particularly at alkaline pH values. Deazaflavins catalyzed photoproduction of hydrogen from a variety of compounds that were inactive with acridines and fra(2,2'‐bipyridine)ruthenium. This includes carboxylic acids, amines, sugars and amino acids. This system may have potential for hydrogen production as a means of solar energy conversion.
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.
LOW‐NOISE PHOTODIODE AMPLIFIER FOR ABSORPTION CHANGES MEASUREMENTS IN THE MICROSECOND RANGE
Authors: Best J. A. Van , Mathis P.
Published: January 2008

Abstract— A silicon photodiode equipped with a low‐noise amplifier is incorporated in an apparatus of flash absorption spectroscopy. This device provides a good signal to noise ratio in the detection of short‐lived species (1µs‐5 ms) formed in photobiological processes.
ORIENTATION OF SHORT WAVELENGTH AND LONG WAVELENGTH PROTOCHLOROPHYLL SPECIES IN GREENING CHLOROPLASTS
Authors: Garab Gyözö I. , Sundqvist Christer , Mustárdy László A. , Faludi‐Dániel ÁGnes
Published: January 2008

Abstract— The orientation of protochlorophyll and Chi species with respect to the plane of thylakoid membranes was studied by measuring the fluorescence polarization ratio in magnetically oriented chloroplasts isolated from greening maize leaves and cucumber cotyledons. With viewing direction parallel to the plane of the photosynthetic membranes, in the spectral region of 620–660 nm, fluorescence polarization ratios of 1.0 were observed, whereas at longer wavelengths the fluorescence polarization ratios were much higher, and similar to that of fully green chloroplasts. The same result was obtained with chloroplasts isolated from leaves fed by δ‐amino levulinic acid. These data indicate that the emitting oscillators of the short and long wavelength protochlorophyll species are oriented at random with respect to the plane of thylakoid membranes. Isotropy of the protochlorophyll species is discussed in terms of isotropic structures containing Chi precursors.
INTRAMOLECULAR EXCIMER FLUORESCENCE: A NEW PROBE OF PHASE TRANSITIONS IN SYNTHETIC PHOSPHOLIPID MEMBRANES
Authors: Georgescauld D. , Desmasèz J. P. , Lapouyadej R. , Babeau A. , Richard H. , Winnik Mitchell
Published: January 2008

Abstract— The molecule (1,1'‐dipyrenyl)‐methyl ether [dipyme] shows intramolecular excimer fluorescence in competition with fluorescence from the locally excited pyrene chromophore. This intensity ratio Ic/Im is sensitive to solvent viscosity. The molecule is soluble in synthetic phospholipid membranes. 1H NMR studies suggest that the molecule is localized in the hydrocarbon region of the membrane. Fluorescence measurements at various temperatures of dipyme dissolved in these membranes show that Ic/Im is exceedingly sensitive to fluidity changes accompanying both the pretransitions and the gel to liquid crystalline transitions of the membrane. These studies can be carried out at a mole ratio of probe to lipid 102‐103 smaller than that necessary to observe bimolecular pyrene excimer formation.
PHOTOACTIVATION OF NITRATE REDUCTASE FROM NEUROSPORA CRASSA
Authors: Roldán J. M. , Butler W. L.
Published: January 2008

Abstract— The photoactivation of nitrate reductase from Neurospora crassa was studied in partially purified extracts. The inactive enzyme [inactivated by reduction in the presence of potassium cyanide] could be reactivated by chemical oxidation with ferricyanide or by irradiation with blue light. The enzyme contains a short electron transfer chain consisting of flavin adenine dinucleotide, cytochrome b557 and molybdenum which normally transfers electrons from reduced pyridine nucleotide to nitrate. This overall activity, which was negligible in the inactive enzyme, was restored to approximately 70% of the ferricyanide control by irradiation. However, nitrate reduction using reduced methylviologen as reducing power, which was also negligible in the inactive enzyme, was photoactivated to 100%. The diaphorase activity of the enzyme mediated by the flavin adenine dinucleotide, which was fully active in the inactivated enzyme, was inhibited approximately 30% by the irradiation treatment. The action spectrum for photoactivation showed that a flavin was the photoreceptor chromophore. Photoactivation occurs only in the presence of oxygen.
BIOCHEMICAL STEPS IN VISUAL TRANSDUCTION: ROLES FOR NUCLEOTIDES AND CALCIUM IONS*
Authors: Bownds M. Deric
Published: January 2008

Abstract— Recent studies from this laboratory permit the suggestion of a scheme for describing molecular mechanisms which may regulate excitation and adaptation in amphibian rod photoreceptor cells. The experiments have studied several chemical changes which occur upon illumination of isolated rod outer segments: (1) activation of cyclic GMP phosphodiesterase which is sensitive to calcium concentration, (2) a resulting rapid drop in cyclic GMP levels which has stoichiometry and time course appropriate for the internal transmitter presumed to mediate between photon absorption in the disc membrane system and the permeability decrease in the plasma membrane, (3) a dephosphorylation of two small proteins whose phosphorylation is controlled by cyclic GMP levels, and (4) a slower hydrolysis of GTP which may drive efflux of calcium from the outer segment.

It is suggested that the rapid decrease in sodium conductance which follows illumination is caused by the dephosphorylation of the two small proteins, with their dephosphorylation being controlled by the cyclic GMP decrease. In a slower reaction light activates a GTP‐dependent extrusion of calcium from the cytoplasmic space. This lowering of internal calcium causes desensitization of the light‐sensitive phosphodiesterase enzyme responsible for the cyclic GMP decrease, so that its intensity‐response function now resembles that of the light‐adapted rod photoreceptor. Thus, changes in plasma membrane conductance are regulated by cyclic GMP, and the sensitivity of the system is controlled by slower calcium movements which set the light‐sensitivity of the phosphodiesterase enzyme. Finally, the light‐initiated phosphorylation of rhodopsin also appears to play a role, with phosphorylated rhodopsin causing desensitization of the phosphodiesterase enzyme.
SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—I. SPIN TRAPPING OF PHOTOLYSIS PRODUCTS FROM SULFANILAMIDE, 4‐AMINOBENZOIC ACID AND RELATED COMPOUNDS
Authors: Chignell Colin F. , Kalyanaraman B. , Mason Ronald P. , Sik Robert H.
Published: January 2008

Abstract—

The photodecomposition of sulfanilamide, 4‐aminobenzoic acid and other related analogs has been studied with the aid of the spin trap 2‐methyl‐2‐nitrosopropane. UV photolysis of an aqueous solution of sulfanilamide yielded the following radicals C˙6H4SO2NH2, C6H5SO2˙, S˙O2NH2 and SO‐#˙ (or SO‐2dot;). Under the same conditions 4‐aminobenzoic acid gave C˙6H4COOH. In addition both sulfanilamide and 4‐aminobenzoic acid, but not 4‐dimethylaminobenzoic acid, generated e‐aq or hydrogen atoms during UV irradiation. The C6H4SO2NH2 radical was also produced by photolysis of 4‐iodobenzenesul‐fonamide and 4‐nitrobenzenesulfonamide. The C6H4COOH radical was generated by photolysis of 4‐nitrobenzoic acid and 4‐iodobenzoic acid. Finally the C6H4NO2 radical was formed during the irradiation of 4‐nitroaniline, 1,4‐dinitrobenzene and 4‐iodonitrobenzene. The free radicals generated by sulfanilamide and 4‐aminobenzoic acid may play an important role in the phototoxic and photoallergic responses elicited by these drugs in certain individuals.
1,4‐DIPHENYLBUTADIYNE, A NEW NON‐PHOTODYNAMIC PHOTOTOXIC COMPOUND
Authors: Kagan Jacques , Gabriel Robert , Singh Shiv P.
Published: January 2008

Abstract—

1,4‐Diphenylbutadiyne (DPB), the first member of a new chemical class of phototoxic compounds, was found to be active against E. coli (strain B) under nitrogen but not in the presence of air. It was also phototoxic against both Candida utilis and Saccharomyces cerevisiae aerobically, and against the latter anerobically. The maximum activity against C. utilis occurred at 360 nm, and the uv light was definitely required in the phototoxic act. Circular dichroism spectroscopy disclosed that DPB underwent photoreaction with DNA. This technique, as well as melting temperature profiles, hyperchromicity studies, and the elution profile from hydroxyapatite chromatography indicated that no cross‐linking to double strands had occurred, and that DPB behaved as a monofunctional reagent, interacting only with single strands of DNA photochemically. Finally, 2,5‐diphenylthiophene was synthesized from DPB but was not phototoxic.
FLUORESCENCE OF TRYPTOPHAN IN KERATIN
Authors: Smith Gerald J. , Thorpe Michael R. , Melhuish W. Hugh , Beddard Godfrey S.
Published: January 2008

Abstract—

The excitation and emission spectra have been determined for the fluorescence from trypto‐phan residues in dry keratin. The fluorescence decay was also measured and shown to be a single exponential with a rather long lifetime of 6.9 ns. It is suggested that the emission takes place from a state formed by interaction between the 1La state of the tryptophan residues and neighbouring polar or polarizable groups in the protein.

The fluorescence excitation spectrum displays a peak at 290 nm, and its appearance at this position rather than at 280 nm, which is the absorption maximum of tryptophan, is believed to arise from inner filtering by the tyrosine residues in keratin.
LIGHT‐INDUCED FORMATION OF O‐2˙ OXYGEN RADICALS IN SYSTEMS CONTAINING CHLOROPHYLL
Authors: VAN Ginkel Gijsbert , Raison John K.
Published: January 2008

Abstract—

It has been shown recently that photosystem 1 particles, photosystem 1 lipid vesicles and chlorophyll‐a lipid vesicles show identical photochemical reactions in the presence of oxygen e.g. H+‐and O2‐uptake (Van Ginkel, 1979). Therefore, spin‐trapping experiments were done to identify the oxygen radicals formed. The spintrap phenyltertiarybutylnitrone (PBN) failed to yield information about oxygen radicals.

With the spintrap 5,5‐dimethyl‐1‐pyrroline‐1‐oxide (DMPO), however, we obtained a mixed spectrum of O‐2˙ and OH·‐adducts generated in chloroplasts, photosystem 1 particles or chlorophyll‐a lipid vesicles. These data indicate that chlorophyll‐a in an artificial membrane can also catalyze O‐2˙‐formation. Chlorophyll‐a lipid vesicles catalyze light‐induced formation of the Tiron‐semiquinone free radical, which has been proposed as a specific O‐2˙‐probe (Greenstock and Miller, 1975). However, OH· scavengers strongly reduce the formation of this radical, whereas superoxide dismutase does not.

Pulse‐radiolysis measurements showed that the rate constant for the reaction of Tiron with OH· is 8.2 · 109M‐1 s‐1, which is considerably higher than the published Tiron/O‐2˙ rate constants. Therefore, Tiron is a better spin probe for OH· than for O‐2˙.

We suggest that light‐induced H+‐and O‐2˙‐uptake in membranes containing chlorophyll‐a in the presence of ascorbate is caused mainly by the very rapid reaction of OH· with ascorbate.
REACTIVITY OF EXCITED STATES OF FLAVIN AND 5‐DEAZAFLAVIN IN ELECTRON TRANSFER REACTIONS
Authors: Traber Rainer , Vogelmann Ekehardt , Schreiner Siegfried , Werner Tilmann , Kramer Horst E. A.
Published: January 2008

Abstract—Quenching of the excited states of lumiflavin and 3‐methyl‐5‐deazalumiflavin by methyl‐and methoxy‐substituted benzenes and naphthalenes in methanol was investigated. The observed difference in the reactivity of acid and neutral lumiflavin triplets is explained thermodynamically by applying the Michaelis cycle, as being due to the higher reduction potential of the acid triplet. In this connection the pKvalues of lumiflavin triplet (pKM= 6.5) and semiquinone (pKM= 11.3) have also been determined in methanol. The difference in the reactivity between the singlet and triplet states of lumiflavin is found to be greater as predicted by the difference in excitation energy. The reactivities of the excited states of flavin and 5‐deazaflavin differ only slightly in contrast to the marked difference in the ground state reactivities of electron transfer reactions. This is explained in terms of the model of Rehm and Weller. The pH dependence of the electron transfer quenching of 5‐deazaflavin triplet was investigated in water, yielding a triplet pKof 2.5. In contrast to the flavin, this triplet pKdoes not significantly differ from the pKof the 5‐deazaflavin ground state. From this, different sites of protonation are deduced for the photoexcited triplet states of flavin and 5‐deazaflavin.
THE EFFECTS OF PHOTOOXIDATION BY PROFLAVINE ON HeLa CELLS—1. THE MOLECULAR MECHANISMS*
Authors: Roberts Joan E.
Published: January 2008

Abstract— DNA and RNA syntheses were inhibited immediately after proflavine treated HeLa cells were irradiated with visible light (400–500 nm). The molecular mechanism for this photooxidation may be either a free radical‐mediated (Type I) or singlet oxygen‐mediated (Type II) reaction. Non‐toxic free radical and singlet oxygen quenchers were added to cells and sensitizer before irradiation to quench the appropriate excited state intermediate. Photooxidative damage (the inhibition of incorporation of [14C]‐thymidine) in this system was greatly reduced in the presence of free radical quenchers (glutathione, penicillamine) and not significantly affected by the presence of singlet oxygen quenchers (α‐tocopherol, β‐carotene, DABCO). This suggests that at least part of the photodynamic damage in HeLa cells is via a Type I mechanism.
EFFECTS OF CAFFEINE ON DNA REPAIR OF UV‐IRRADIATED DICTYOSTELIUM DISCOIDEUM
Authors: Ohnishi T. , Okaichi K. , Ohashi Y. , Nozu K.
Published: January 2008

Abstract— Caffeine enhances the UV‐killing of amoeboid cells of NC‐4, but UV‐irradiated γs‐13 is insensitive to caffeine. UV‐irradiated NC‐4 becomes insensitive to the effect of caffeine during a postirradiation incubation in buffer for about 90 min, but γs‐13 remains unchanged in the sensitivity to caffeine throughout the incubation for 180 min. Amoeboid cells of γs‐13 can remove pyrimidine dimers as well as NC‐4 even in the presence of caffeine. Caffeine inhibits rejoining of strand‐breaks of DNA in UV‐irradiated NC‐4, but the rejoining in γs‐13 is insensitive to caffeine.
ESTIMATION OF ENERGY DISTRIBUTION AND REDISTRIBUTION AMONG TWO PHOTOSYSTEMS USING PARALLEL MEASUREMENTS OF FLUORESCENCE LIFETIMES AND TRANSIENTS AT 77 K
Authors: Wong D. , Merkelo H. , Ovindjee G
Published: January 2008

Abstract— A single‐sample method for estimating energy distribution and redistribution among the two photosystems using fluorescence lifetimes and transients at 77 K is presented. In this method,α(the fraction of photons absorbed by photosystem I, PSI) is F1(α)/(F1(α)+ (τF 1(M)/τF 2(M)).F2(M)) where, F1(α) is the fluorescence intensity from PSI excited by photons initially absorbed by the latter, τF 1(M) and τF 2(M) are the maximum lifetimes of fluorescence from chlorophyll‐a in PSI (1) and II (2), and, F2(M) is the maximum fluorescence intensity from PSII (P level). Analysis of the intensities and lifetimes of wavelength resolved fluorescence of thylakoids (pH 7.0), with and without cations, leads to the following conclusions: The addition of 10 mM Na+ to cation‐depleted thylakoids (pH 7.0) increases α by ˜ 10%, while the subsequent addition of 10 mM Mg2+ leads to three principal concomitant changes (in the order of importance): a 50% decrease in PSII to PSI energy transfer, a 20% increase in other radiation‐less losses, and a 10% decrease in α.
ACTION SPECTRA OF CATION EFFECTS ON THE FLUORESCENCE POLARIZATION AND INTENSITY IN THYLAKOIDS AT ROOM TEMPERATURE
Authors: Wong Daniel , Ovindjee G
Published: January 2008

Abstract— The degree of polarization of chlorophyll‐a(Chl‐a) fluorescence is known to monitor the extent of excitation migration and/or the orientation of the photosynthetic pigment molecules. We report here the effects of cations, at room temperature, on the degree of polarization of Chl‐a fluorescence, and fluorescence intensity in thylakoids as a function of excitation wavelength. Observations of maxima at 650 and 675 nm in the cation‐induced changes in the excitation spectrum for fluorescence at 730 and 762 nm, and, in the action spectra for the depolarization of fluorescence lead us to suggest that the regulation of the initial distribution of excitation to photosystem II involves the better coupling of Chl‐b and‐a in the light harvesting complex with Chl‐a in the reaction center II complex.
HIGH‐PERFORMANCE LIQUID CHROMATOGRAPHY OF ETIOPLAST PIGMENTS IN RED KIDNEY* BEAN LEAVES
Authors: Eskins Kenneth , Harris Leland
Published: January 2008

Abstract— A method of analysis for etioplast pigments by high‐performance liquid chromatography is reported. The method is suitable for separation of protochlorophyllides, chlorophyllides, carotenoids and several forms of Chl‐a.
MEMBRANE DAMAGE CAN BE A SIGNIFICANT FACTOR IN THE INACTIVATION OF ESCHERICHIA COLI BY NEAR‐ULTRAVIOLET RADIATION
Authors: Moss Stephen H. , Smith Kendric C.
Published: January 2008

Abstract A DNA repair competent strain of Escherichia coli K‐12 showed sensitivity to inorganic salts (at concentrations routinely used in minimal media) after irradiation with broad spectrum near–UV radiation, at fluences that caused little inactivation when plated on complex growth medium. This effect was not observed with cells that had been exposed to 254 nm radiation. This sensitivity to minimal medium was increased by increasing the salt concentration of the medium and by increasing the pH of the medium. This sensitivity was greatly increased by adding to the medium a low concentration of commercial glassware cleaning detergent that had no effect on unirradiated cells or far‐UV irradiated cells. These findings may explain the large variability often observed in near‐UV radiation survival data, and demonstrate that, at least on minimal medium plates, membrane damage contributes significantly towards cell killing. This phenomenon is largely oxygen dependent.
THE EFFECT OF TREATMENT OF CHLOROPLAST MEMBRANES WITH GUANIDINE HC1 AND AQUEOUS ACETONE ON THE FLUORESCENCE OF BOUND ANS AND CHLOROPHYLL‐a†
Authors: Andley Usha Prasad , Singhal G. S. , Mohanty Prasanna
Published: January 2008

Abstract The fluorescence intensity of the extrinsic chromophore 1‐anilino‐naphthalene‐8‐sulfonate (ANS) bound to pea chloroplast fragments shows a sigmoidal rise as the pH of the suspending medium is decreased by the addition of HC1. The abrupt increase occurs at pH – 4.5. A 70% decrease in the maximal fluorescence intensity (pH range 3.5‐4.5) of bound ANS was observed when soluble chloroplast proteins were removed by washing with water. Extraction of chloroplast membranes with 6 M guanidine‐HC1 abolishes the acid–induced enhancement of ANS fluorescence. However, the subsequent removal of lipids (by 80% acetone extraction) from the guanidine‐HC1‐extracted naked membranes restores the acid‐induced fluorescence increase. These results suggest that ANS binds mainly to the surface of the chloroplast membrane and the fluorescence changes of ANS by acidification mainly reflect the changes in the associated proteins. The lack of enhancement of the fluorescence of ANS by acidification of the guanidine‐HCl treated membranes and the recovery of the acid‐induced fluorescence rise after extraction of the lipids from the guanidine‐HCl treated membranes suggest that the boundary lipids somehow prevent the entry of the ANS molecules into the hydrophobic interior of the naked membrane. The lipid‐depleted, guanidine‐HCl extracted naked membrane fragments do not show any shift in the position of the peak of emission of ANS (λ= 470 nm) upon acidification as the lipid‐depleted preparations without guanidine‐HCl treatment do (shift from 460 to 470 nm). Divalent cations (Mn2+, Ca2+, Mg2+) also increased ANS fluorescence intensities when added to both types of lipid‐depleted chloroplast preparations. A comparative analysis of ANS fluorescence bound to the lipid‐depleted and guanidine‐HCl treated chloroplast fragments with that of just lipid‐depleted fragments shows that the acidification of the latter brings about a greater change in the value of the relative binding sites (n) and the dissociation constant kd of ANS than the protonation of the former. The role of chloroplast protein and lipid components in the structural changes of the thylakoid membrane imposed by external perturbations is discussed.
A QUANTITATIVE COMPARISON OF CHLOROPHYLL BILAYERS FORMED WITH AND WITHOUT SOLVENT
Authors: Rich M. , Brody S. S.
Published: January 2008

Abstract Bimolecular lipid membranes are formed from solutions containing lecithin and chlorophyll‐a (chl‐a) in various molar ratios. Both the Mueller‐Ruding technique as well as the solvent free, Montal‐Mueller technique are used to form bilayers. In both methods, increasing the chl concentration produces greater photosensitivity. The photocurrent/area is about an order of magnitude higher in bilayers formed with the solvent free method, under similar conditions. From the quantum yield calculations, it appears that the higher photocurrent/area obtained with the Montal‐Mueller membranes cannot be explained solely due to the greater concentration of pigment molecules in the solvent free system. The possible role of chl—chl interactions are considered.
QUENCHING OF ENZYME GENERATED TRIPLET ACETONE BY 2‐METHYL‐1,4‐NAPHTOQUINONE
Authors: Rivas‐Suárez Edy , Augusto Ohára , Cilento Giuseppe
Published: January 2008

Abstract 2‐Methyl‐1,4‐naphtoquinone (vitamin K3) quenches the phosphorescence from enzyme‐generated triplet acetone. Concomitantly the vitamin undergoes a photochemical‐like alteration as the result of transfer of the electronic energy (kET– 1 ± 105 M‐1). This transfer appears to be of the long‐range type.
THE EFFECT OF ULTRAVIOLET RADIATION ON WHEAT ROOT VESICLES ENRICHED IN PLASMA MEMBRANE
Authors: Wright Lawrence A. , Murphy Terence M. , Travis Robert L.
Published: January 2008

Abstract— The irradiation of plant cells with UV radiation (254nm) causes various solutes to leak from the cells. Vesicles enriched in plasma membranes were prepared from wheat roots. These were used to determine whether UV radiation alters membrane function by direct action on the membranes and to distinguish between the chemical effects produced by high and low fluences of UV. The plasma membrane‐associated K+‐stimulated ATPase was very sensitive to UV radiation (100% inhibition with 1.35kJ/m2). ATPase activity measured in the absence of K+ and K+‐stimulated ATPase activity measured in the presence of diethylstilbestrol were much less sensitive. Lipid breakdown, as measured by malondialdehyde production, occurred only at UV fluences greater than 1.8 kJ/m2.
MAGNETIC CIRCULAR DICHROISM OF BACTERIOCHLOROPHYLL a IN SOLUTION AND IN A PROTEIN
Authors: Sutherland John Clark , Olson John Melvin
Published: January 2008

Abstract— The magnetic circular dichroism (MCD) (300–850nm) of the bacteriochlorophyll (Bchl) a‐protein from the green photosynthetic bacterium Prosthecochloris aestuarii 2 K is qualitatively similar to the MCD of Bchl a in methanol and ether solution. This result implies that the transition dipole of the lowest energy electronic transition (near 800 nm) is roughly perpendicular to the transition dipole of the next higher electronic band (near 600nm) for Bchl a molecules in the protein just as it is for molecules in solution. This result provides no support for the recent proposal that interactions with the protein rotates the direction of the transition dipoles of the 800nm band of all the Bchl a molecules in the protein by 90°. While a rotation of the 800nm transition dipoles cannot be rigorously excluded, it would be necessary for the postulated perturbation to rotate the transition dipoles of both the 800 and 600nm bands by 90°. In a broader sense, any postulated perturbation would have to be shown to leave both the absorption spectrum and the MCD largely unaffected. MCD is a more sensitive test than absorption spectroscopy for perturbations of electronic states and changes in the relative orientation of transitions, because it depends on both the magnitudes and directions of at least two electric and one magnetic transition dipole.