bluuebunny/crossref_metadata_2025 huggingface dataset:
EFFECTS OF SOLVENT ON THE FLUORESCENCE PROPERTIES OF BACTERIOCHLOROPHYLL a
Authors: Connolly John S. , Samuel Edward B. , Janzen A. Frederick
Published: January 2008

Fluorescence lifetimes (τf) of bacteriochlorophyll a (BChl a) have been measured by the method of time‐correlated single‐photon counting on dilute (1 μM) solutions of the pigment in 15 solvents. There is a pronounced dependence of τf on the nature of the solvent. Specifically, τf, is longer when the central magnesium is hexacoordinated than when pentacoordinated and shorter when the macrocycle is hydrogen‐bonded than when it is not, but the latter effect is more pronounced. Both trends were confirmed by parallel studies on bacteriopheophytin a (BPheo a). Because of the short lifetimes (˜ 2.2–3.6 ns), quenching of fluorescence by molecular oxygen is not a significant factor in aerated solutions of the bacterial pigments. However, reabsorption artifacts are non‐negligible, which necessitates studies on dilute solutions. Fluorescence quantum yields (øf) have been estimated for BChl a in 13 solvents by comparing the observed fluorescence lifetimes with the radiative lifetimes calculated from the integrated absorption spectra.
EARLY EFFECTS OF NEAR‐ULTRAVIOLET RADIATION ON YEAST CELLS: CHANGES IN CELL SIZE
Authors: Watanabe Toshiki , Ito Atsushi , Ito Takashi
Published: January 2008

Exponentially growing yeast cells showed a drastic shrinkage when irradiated in water suspension (but not in buffer) with broad‐band near‐UV radiation. This was clearly seen soon after irradiation in size‐distribution curves measured by a Coulter counter. This early shrinkage was observed at a near‐UV fluence where the survival enters a region of exponential decline after a large shoulder. We further observed the formation of a distinct band in a density‐gradient‐centrifugation profile, presumably corresponding to the near‐UV‐affected cells. A survival test showed that the cells making up this band were dead.
COMPUTER‐CONTROLLED LIGHT MEASUREMENTS FOR PHOTOMORPHOGENESIS
Authors: Gaba V. , Ryall M. D. , Chapman J. M.
Published: January 2008

A computer‐controlled spectroradiometer system is described that comprises a commercial spectroradiometer, a low‐cost microcomputer and a purpose‐built interface. The system is used in establishing controlled light environments for the study of plant growth. The method used to link the computer and spectroradiometer is described and an outline of the required control software is given. A set of application programs has been developed to convert the raw spectral data into meaningful physiological/photomorphogenic quantities. This obviates the large volume of manual measurements and calculations that were previously necessary.
CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID VESICLE BILAYERS: INSIDEVSOUTSIDE ASYMMETRY*
Authors: Ford William E. , Tollin Gordon
Published: January 2008

Abstract—We have determined triplet quenching efficiencies. radical yields and radical recombination kinetics in mixed chlorophyll (Chl)‐egg phosphatidylcholine vesicle suspensions in the presence of electrically‐charged electron acceptors located either in the external. continuous aqueous phase or within the internal aqueous volume of the vesicles. There was a marked asymmetry between these processes as to whether they occurred at the outer or inner bilayer‐water interfaces.

With methyl viologen (MV2+) as acceptor, 52 ± 4% of the total Chl triplet could be quenched from the inside. whereas only 16 ± 2% was quenchable from the outside. Approximately 35% of the triplet population was inacccssible to quenching by MV2+from either inside or outside. Ouenching rate constants were higher from the outside than from the inside (2 × 106M−lS‐Ivs1 × 106M−Is−1). A similar pattern was obtained when anthraquinone disulfonate or ferricyanide were used as acceptors.

Radical yields and recombination kinetics also displayed asymmetric behaviour. From the inside. only 4 ± 2% of the quenched triplets gave rise to separated radicals using MV2+as acceptor, whereas from the outside the conversion yield was 32 ± 2%. The halftime for the Chl+MV+reaction was approximately 100 times longer at the outer surface than at the inner surface.

We conclude the following: (a) Chl is distributed asymmetrically within the bilayer such that more triplet Chl is located within quenching distance of the interface at the inner surface than at the outer surface. Furthermore, an appreciable fraction of the triplet Chl is located sufficiently far from either interface so that quenching is not possible. (b) The mobility of Chl and quencher molecules is greater at the outer surface of the vesicles than at the inner surface.
OPTICAL PROPERTIES OF HUMAN BRAIN
Authors: Svaasand Lars O. , Ellingsen Reinold
Published: January 2008

Abstract— Optical properties of the human brain in the wave‐length region from blue to near infrared are presented. There are significant variations in the optical penetration depth from the neonatal and to the adult brain. Typical values for the penetration depth in the adult brain are: 0.5 mm for blue/green, 1.5 mm for red and 3.5 mm for near infrared. The values for the neonatal brain are typically 2–3 times larger.
LIGHT‐INDUCED ELECTRON TRANSFER REACTIONS BETWEEN CHLOROPHYLL AND QUINONE IN LIPOSOMES: RADICAL FORMATION AND DECAY IN NEGATIVELY AND POSITIVELY CHARGED VESICLES*
Authors: Fang Yifei , Tollin Gordon
Published: January 2008

Abstract— The incorporation of relatively small amounts (≤ 20 mol%) of a negatively charged surfactant into otherwise electrically neutral phosphatidylcholine vesicles containing chlorophyll in the presence of benzoquinone has been shown to produce large effects on radical formation and decay as measured by laser flash photolysis. When salt ions are present in the aqueous phase, increasing the level of negative surfactant leads to a small increase in radical yield, followed by a larger decrease in radical yield. When the salt concentration is low, increasing the negative surfactant concentration leads to a suppression of the fast radical recombination process, an increase in slow radical decay and, at the highest surfactant concentration, an approximately 35% increase in total radical yield. An analysis of these effects is given in terms of the influence of a negative electrostatic field on radical pair stabilization and recombination, radical pair separation and expulsion of the acceptor radical anion from the vesicle.

The incorporation of relatively small amounts (≤ 20 mol%) of a positively charged surfactant into egg phosphatidylcholine (EPC) vesicles containing chlorophyll and benzoquinone also produces large effects on radical formation and decay. When the electrolyte concentration in the suspending aqueous medium is high, radical yields are decreased as the surfactant concentration is increased, without any appreciable effect on decay kinetics. When deionized water is used, the slow recombination component of the decay is specifically suppressed by the presence of the positive surfactant, whereas the fast decay component decreased and then increased in amount as the surfactant concentration is increased. In all cases, however, the total radical yield is less than in pure EPC vesicles. These results can be understood in terms of the influence of a positive electrostatic field on radical pair separation and acceptor radical anion mobility. When equimolar amounts of both positively and negatively charged surfactants are incorporated into EPC vesicles, the radical yields and decay kinetics are relatively unaffected, but a large effect is observed on the radical difference spectrum. This may be a consequence of clustering of oppositely charged molecules within the bilayer surface.
CHLOROPHYLL PHOTOSENSITIZED VECTORIAL ELECTRON TRANSPORT ACROSS PHOSPHOLIPID VESICLE BILAYERS: KINETICS AND MECHANISM*
Authors: Ford William E. , Tollin Gordon
Published: January 2008

Abstract—The characterization and kinetic analysis by laser Rash photolysis of an improved model system for observing chlorophyllaphotosensitized electron transfer across a lipid bilayer membrane is described. In this system, the electron acceptor is a water‐soluble naphthoquinone, S‐(2‐methyl‐l,4‐naphthoquinonyl‐3)‐glutathione (MGNQ) which is dissolved in the inner aqueous compartments of phospholipid bilayer vesicles, and the electron donor is glutathione (GSH) which is dissolved in the outer aqueous phase. Chlorophyll (Chl) is dissolved in the membrane. Oxidative quenching of the triplet state of Chl by the quinone at the inner surface of the vesicle produces the Chl+and MGNQ‐radicals. Chi+is reduced by GSH at the outer surface of the vesicle (k= 2.6 × 106M‐1s‐1) in competition with the recombination between Chl+. and MGNO‐(k= 2.5 × 103S‐1). It is shown that a kinetic mechanism involving competition between recombination, electron transfer across the bilayer, and reduction by donor at the opposite surface can quantitatively account for the decay of Chl+. Electron transport across the bilayer is postulated to occur by a two‐step mechanism involving electron exchange between Chl and Chl+within the lipid monolayer (k= 3.2 × 106M‐1s‐1) and across the bilayer. The rate constant for the latter exchange process approaches 104s‐1as the concentration of Chl in the bilayer increases. Under appropriate conditions, approximately 20% of all photons absorbed by the vesicle system result in electron transfer across the mcmbrane from GSH to MGNQ.
ENERGY TRANSFER FROM ENZYMICALLY‐GENERATED TRIPLET SPECIES TO ACCEPTORS IN MICELLES
Authors: Brunetti Iguatemy L. , Cilento Giuseppe , Nassi Lilian
Published: January 2008

Abstract— Electronically excited triplet species generated during the peroxidase catalyzed aerobic oxidation of appropriate substrates efficiently elicit fluorescence from acceptors in micelles, as shown with 9, 10‐dibromoanthracene and chlorophyll solubilized by various surfactants. In the case of 9, 10‐dibromoanthracene excited by triplet acetone, phosphorescence also can be detected near O2 depletion.

The significant implications of this study are that micelle‐solubilized chlorophyll is an excellent detector of enzyme‐generated triplet carbonyl species, as confirmed with several systems, and that the use of micelles make it possible to extend ‘photobiochemistry without light’ to other photobiologically important, yet water insoluble acceptors.
THE ACTION OF ULTRAVIOLET RADIATION ON THE CELL PROLIFERATION OF TWO‐CELL MOUSE EMBRYOS
Authors: Endoh H. , Domon M.
Published: January 2008

Abstract— The two‐cell mouse embryo has a unique cell cycle of a short DNA synthesis (S) phase and an extremely long post‐DNA synthesis (G2) phase. An attempt was made to investigate the radiation biology of the long G2 phase using UV radiation as a probe. Two cell mouse embryos, at various positions in the cell cycle, were UV‐irradiated in phosphate‐buffered saline. The embryos were cultured for a few hours to 3 days to assay for their cell proliferative characteristics. The embryos were most sensitive to the killing action of UV radiation in the late G2 phase. The embryos divided more than two times after low UV fluences before dying and experienced G2 phase delays.

These results can be contrasted to the situation in somatic cells, in which the action of UV radiation is S phase selective. One possibility is that the target for the action of UV radiation is different in two‐cell mouse embryos from that in somatic cells and that the target is similar to that for X‐ray effects.
SOME PITFALLS IN THE USE OF DERIVATIVE SPECTRA
Authors: Shrager Richard I.
Published: January 2008

Abstract— Several difficulties are described in the use of derivative spectra: increase in the number of apparent bands, disproportionate band heights and difficulties associated with numerical differentiation.
THE PHOTOBIOLOGY OFPaphiopedilumSTOMATA: OPENING UNDER BLUE BUT NOT RED LIGHT
Authors: Zeiger E. , Assmann S. M. , Meioner H.
Published: January 2008

Abstract—The responses of stomata fromPaphiopedilum harrisianum, Orchidaceae, to light and CO2were studied in epidermal peels. Stomatal opening under red light was indistinguishable from that in darkness, whereas blue light promoted opening above dark levels. The ineffectiveness of red light in causing stomatal opening was confirmed in the presence of 100 μMKCN; average apertures in both darkness and red light were 53% of those measured in the absence of the inhibitor, whereas under blue irradiation, the KCN inhibition was only 30%, with average apertures two‐fold of those measured under red light or darkness. Fluence rate response curves under blue light were typical of a single photoreceptor; removal of CO2increased aperture values without a significant light‐CO2interaction. The lack of a stomatal red light response contrasts with results obtained in species with chlorophyllous stomata in which red light consistently causes stomatal opening, and suggests that the previously reported red light responses in stomata from intactPaphiopedilumleaves resulted from indirect effects, such as depletion of intercellular CO2by mesophyll photosynthesis. In isolation,Paphiopedilumstomata appear to rely on a blue light photosystem for their responses to light and fail to open under red light because of their lack of guard cell chloroplasts.
INTRAMOLECULAR TRYPTOPHAN HEME ENERGY TRANSFER IN HORSERADISH PEROXIDASE
Authors: Brunet Juan E. , Gonzalez Gustavo A. , Sotomayor Carlos P.
Published: January 2008

Abstract— Chain folding of horseradish peroxidase allocates its sole tryptophanyl residue at a distance of 18 A from the active site heme group as determined by electronic energy transfer. This finding confirms that the phosphorescence spectrum observed in the peroxidase catalyzed oxidation of isobutyraldehydc is due to the excited triplet state acetone produced.
TRIPLET STATE PROPERTIES OF POLYCYCLIC AROMATIC HYDROCARBON‐DNA and PORPHYRIN‐DNA COMPLEXES DETERMINED BY OPTICALLY DETECTED ZERO FIELD MAGNETIC RESONANCE
Authors: Clarke R. H. , Harris G. , R. A. Mushlint N. Lasserand
Published: January 2008

The photoexcited triplet states of the physically bound (intercalated) complexes of benzanthracene, pyrene, and free base porphin with DNA have been examined at 77 and 2 K. Measurements of triplet lifetimes, zero field splittings, and individual triplet sublevel intcrsystem crossing rates were obtained by optically detected zero field magnetic resonance (ODMR) for the benzan‐thracene‐DNA and free base porphin‐DNA complexes. The triplet lifetime was measured for the pyrene‐DNA complex. No ODMR was observable in the pyrene‐DNA system. Comparison of triplet state data with new and previous results for the benzo(a)pyrene‐DN A complex is discussed in an attempt to characterize the interactions experienced by polycyclic aromatic hydrocarbons and porphyrins within the DNA environment.
SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS–III. SPIN TRAPPING OF PHOTOLYSIS PRODUCTS FROM SULFANILAMIDE ANALOGS
Authors: Motten Ann G. , Chignell Colin F.
Published: January 2008

The photodecomposition of sulfanilamide (4‐aminobenzenesulfonamide), sulfacetamide. sulfathiazole. sulfadiazine, carbutamide and tolbutamide has been studied using the spin traps 2‐methyl‐2‐nitrosopropanc and 5,5‐dimethyl‐l‐pyrroline‐l‐oxide. The following radicals were trapped during the photolysis of sulfanilamide in aqueous solution: H' and HNC6H4SO2NH, (α‐fission). SO2NH2 and C6H4NH2 (δ fission). H2NC6H4SO2 and NH2 (δ‐fission). Although the C.,H4SO2NH2 and the SO; radicals were also detected these were not formed directly by homolytic bond fission. Homolytic bond fission was also observed during the irradiation of sulfacetamide (α.δ), sulfadiazine (α). carbutamide (α,δ) and tolbutamide (δ). All of the analogs, with the exception of tolbutamide, generated the SO; radical. Sulfacetamide, sulfadiazine and carbutamide generated the C6H4SO2;NHR radical by some process that did not involve homolytic bond fission. The free radicals generated by these agents may play an important role in their phototoxic and photoallergic effects.
FREE RADICALS FROM PHOTOREDUCTION OF HEMATOPORPHYRIN IN AQUEOUS SOLUTION
Authors: Felix C. C. , Reszka K. , Sealy R. C.
Published: January 2008

—The anaerobic photoreduction of hematoporphyrin by organic reducing agents in fluid aqueous solutions has been studied by electron spin resonance spectroscopy. Efficient photoreduction occurs with many hydrogen‐atom or electron donors, including catechols, pyrogallol. hydroquinone. ascorbate, p‐phenylenediamine, cysteine and glutathione. A combination of direct and spin‐trapping measurements (using 2‐methyl‐2‐nitrosopropane) has been used to confirm production of radicals from both the porphyrin and the reducing agent in each system.
THE ROLE OF 4‐THIOURIDINE IN LETHAL EFFECTS AND IN DNA BACKBONE BREAKAGE CAUSED BY 334 nm ULTRAVIOLET LIGHT IN Escherichia coli
Authors: Peak M. J. , Peak J. G. , Nerad Lisa
Published: January 2008

Strains of Escherichia coli that lack 4‐thiouridine (4Srd) are killed by monochromatic 334 nm UV light (UV) less efficiently than their wild‐type parents, which contain 4Srd. Oxygen enhancement ratios (OER) at 10% survival are 3.3 for a strain that possesses 4Srd, and 2.6 for one that lacks 4Srd. Single‐strand breaks in DNA caused by 334 nm UV accumulate more than twice as fast in the wild‐type strains than in the strains lacking 4Srd. The results suggest that 4Srd is an important chromophore in some near‐UV lethal effects. The results also suggest that the excitation energy from 334 nm UV light may be passed from RNA to DNA, resulting in single‐strand breaks.
ACTION SPECTRA OF PHOTOGEOTROPIC EQUILIBRIUM IN Phycomyces WILD TYPE AND THREE BEHAVIORAL MUTANTS
Authors: Galland Paul
Published: January 2008

Photogeotropic equilibrium action spectra in the range from 301 to 740 nm were made for Phycomyces wild type and the three behavioral mutants C47 (madA35), C109 (madBlOl) and LI (madCIIQ), all of which have a raised phototropic threshold. In addition to two broad peaks at 365 and 455 nm, typical for flavins, the wild type action spectrum shows three novel peaks, which have not been observed previously. These peaks are located at 414, 491 and 650 nm. The 650 nm peak has a relative quantum efficiency of 3 × 10−8 compared to the peak at 414 nm. The wavelength dependent shapes of the fluence‐response curves of the bending angle and the aiming error angle indicate more than one receptor pigment for phototropism. The shape of the action spectrum of C47 is basically unaltered in comparison to wild type. C109 and LI show substantial differences from the wild type. In the near UV two small peaks at 334 and 365 nm appear; the 414 and 491 nm peaks present in wild type and C47 are missing and two new peaks at 529 nm (not well resolved in C109) and 567 nm are found. None of the three mad mutations affects the 650 nm peak. A model of the sensory transduction chain is presented, which incorporates these and other known features.
WAVELENGTH‐DEPENDENT PROPERTIES OF PHOTOTAXIS IN LARVAE OF Bombyx mori
Authors: Kitabatake Seiji , Shimizu Isamu , Kato Masaru
Published: January 2008

Phototactic responses of newly hatched silkworm larvae to monochromatic lights and their mixtures were measured to determine wavelength‐dependent properties. Each fluence rate‐response curve for a monochromatic light was composed of a log‐linearly increasing part, a plateau and a decreasing part. Curves were classified into two groups according to the slopes of the linear parts: responses to UV‐blue light (364‐482 nm) and responses to green‐red light (513‐681 nm). Different plateau values were found for both groups. The action spectrum had its maximum at 557 nm and showed another large value at about 364 nm, and its minimum was at 447 nm. When green‐orange lights (540‐577 nm) were added to 557 nm, the silkworms were attracted more by the mixed lights than by the 557 nm component light only. Mixed lights of UV (364 nm) and blue (447 nm) attracted the silkworms more than either component. The magnitude of the response decreased remarkably when green light was mixed with U V or blue light. We conclude that the silkworm possesses colour vision and responds differently to green‐red lights (≥ 513 nm) from UV‐blue lights (≲ 482 nm).
AN EVALUATION OF NALIDIXIC ACID FILM AS A UV‐A RADIATION DOSIMETER
Authors: Gobbs N. K. , Young A. R.
Published: January 2008

Nalidixic Acid (NA)* incorporated into a polyvinyl chloride film has recently been proposed as a UV‐A radiation dosimeter. A trial, in which two different batches of NA film were exposed to both solar simulating and monochromatic 330 nm radiation is described. With both batches of film a linear relationship was observed between the UV‐A fluence derived from the NA film and the fiuence determined with conventional electronic radiometric equipment. There was, however, considerable batch variation in response to UV‐A radiation. Corrections may be made for batch differences. If the batch response can be standardized, our results would support the use of NA film as a simple routine method of measuring UV‐A radiation.
CHARACTERIZATION OF PHOTOCYCLOADDITION PRODUCTS FROM REACTION BETWEEN THYMIDINE and THE MONOFUNCTIONAL 3‐CARBETHOXYPSORALEN
Authors: Cadet J. , Voituriez L. , Gaboriau F. , Vigny P. , Dellanegra S.
Published: January 2008

The photochemical reaction of 3‐carbethoxypsoralen. a monofunctional furocoumarin. with thymidine was investigated as a model system for its photoaddition to DNA. Near UV irradiation (320 nm > λ > 400 nm) of a mixture of thymidine and 3‐carbethoxypsoralen as a dry film gave rise to two main nucleoside diastereoisomers which were isolated by reverse phase high performance liquid chromatography. The structure of these products was assigned on the basis of UV absorption, fluorescence.‘H‐NMR and plasma desorption mass spectra analysis. The results are consistent with 1:1 C, cycloadducts involving the 5,6 double bond of thymine and the 4′, 5′double bond of 3‐carbethoxypsoralen. These two cycloadducts ofcis‐synstereoconfiguration show opposite circular dichroism suggesting a diastereoisomeric relationship.
SIMILARITIES IN THE INDUCTION OF SYNTHESIS OF A CELL‐SURFACE POLYPEPTIDE IN Arthrobacter sp. BY NEAR‐UV IRRADIATION and PHOTODYNAMIC CONDITIONS
Authors: Hoober J. Kenneth , Franzi Joseph
Published: January 2008

Irradiation of aerobic suspensions of Arthrobacter sp. with near‐UV light (310‐400 nm) induced synthesis of a 21 000 dalton, cell‐surface polypeptide. Synthesis of this polypeptide also was induced by visible light in the presence of photodynamic dyes, as shown previously (Hoober, 1978). Induction of the polypeptide in near‐UV light and with visible light plus dyes was inhibited by histidine. Hemin inhibited induction in near‐UV light and in visible light with methylene blue, neutral red and acrifiavin, which are cationic dyes, but failed to inhibit induction in visible light with rose bengal, an anionic dye. These results suggested that inhibition by hemin required electrostatically favored interaction between the anionic porphyrin and the sensitizer, and that the near‐UV light effect was mediated by a cationic or neutral endogenous sensitizer. The similarities in the responses of the cells to near‐UV irradiation and visible light plus dyes suggested that the mechanism of induction under the two conditions was the same.
STATE I‐STATE II TRANSITIONS IN THE GREEN ALGA Scenedesmus obliquus*
Authors: Satoh Kazuhiko , Fork David C.
Published: January 2008

Illumination of dark adaptedScenedesmuscells with system II light induced a typical fluorescence transient known as the Kautsky effect. Fluorescence spectra at 77 K showed no change in transfer of light energy from system II to I during this system II illumination. By contrast, illumination of the dark adapted cells with system I light induced an increase of one of system II fluorescence bands (at – 700 nm) at 77 K and a shift of system I fluorescence to a shorter wavelength. This change was accompanied by an increase of system II activity and by a decrease of system I activity and hence can be considered to be a state II‐I transition. A mutant which lacks light‐harvesting chlorophyllalbproteins (LHCP) also showed similar changes.

These results show (1) that the dark adapted state is state II. (2) that the Kautsky effect is not related to state I–II transitions, (3) that the state I–II transition preferentially affected only one of the system II fluorescence bands at 77 K. and (4) that the presence of the LHCP chromophore is not necessary for the state changes.
EFFECT OF SPATIAL NON‐UNIFORMITY OF ILLUMINATION IN NON‐LINEAR INTENSITY‐DEPENDENT PHOTO PHYSICAL EXPERIMENTS. APPLICATION TO SOME FLUORESCENCE YIELD MEASUREMENTS IN PHOTOSYNTHETIC SYSTEMS
Authors: Paillotin Guy , Geacintov Nicholas E. , Breton Jacques
Published: January 2008

The spatial non‐uniformity of a light beam must be taken into account in interpreting phenomena which depend on the light intensity in a non‐linear manner. Omission of this effect may lead to incorrect values of parameters obtained from a fitting of theoretical curves, which describe the dependence of a given phenomenon on light intensity, to the experimental data. The effect of spatial non‐uniformity of excitation light beams is illustrated utilizing non‐linear intensity‐dependent fluorescence phenomena in photosvnthetic svstems and a Gaussian light beam profile.
THE LIPID SOLUBILITY OF PORPHYRINS MODULATES THEIR PHOTOTOXICITY IN MEMBRANE MODELS
Authors: Emiliani Carla , Delmelle Michel
Published: January 2008

The photosensitizing activities of hematoporphyrin, Cu‐hematoporphyrin, protoporphyrin. Zn‐protoporphyrin, deuteroporphyrin and uroporphyrin are studied. The relative yields of1O2are measured in buffer (pH 8.0) and compared to the yields of Type II photodamages induced on cholesterol embedded in egg lecithin liposomes. Results show that the solubilization of the sensitizer in the lipid bilayer is a prerequisite for its photosensitizing activity at the membrane level. In this context, the partition coefficient represents an important parameter.
LIGHT SENSITIVE LIPOSOMES
Authors: Pidgeon Charles , Hunt C. Anthony
Published: January 2008

Two phospholipids were designed and synthesized that have the property of forming liposomes which undergo a dramatic increase in permeability when irradiated with light (360 nm). Liposomes prepared from these phospholipids leak 100% of entrapped aqueous space marker, carboxyfluorescein, when irradiated for 30‐120 s (average light intensity 50 W/m2). Liposomes not irradiated showed much lower rates of temperature dependent release. Such liposomes may be useful as biochemical tools or drug delivery systems in vitro and in vivo.
INHIBITION OF ORNITHINE DECARBOXYLASE INDUCTION BY PSORALEN PLUS NEAR ULTRAVIOLET LIGHT IN HUMAN CELLS: THE ROLE OF MONOADDUCTS VS DNA CROSSLINKS
Authors: Prager A. , Green M. , Ben‐Hur E.
Published: January 2008

Treatment of plateau‐phase human breast carcinoma cells with 4,5′,8‐trimethyl psoralen (TMP)‐plus‐near UV light (PUVA) inhibited the transcriptionally‐controlled induction of ornithine decarboxylase (ODC). The fluence response curve had a shoulder (Dq= 560 Jm−2) followed by an exponential decline (Do= 690 Jm−2). The cells could not recover from a PUVA dose that inhibited ODC induction by 50% or more. This is consistent with the lack of removal of TMP monoadducts and DNA crosslinks following a similar dose. However, removal of labeled TMP and DNA crosslinks was observed after lower doses during a 24 h period. Using the two‐dose approach (Ben‐Hur and Elkind, 1973) it was shown that crosslinks are more efficient than TMP monoadducts in inhibiting ODC induction. The same phenomenon was also found with regard to inhibition of RNA synthesis.
SUNLIGHT‐INDUCED KILLING OF NONDIVIDING HUMAN CELLS IN CULTURE
Authors: Kantor G.J. , Ritter C.
Published: January 2008

Nondividing populations of human diploid fibroblasts that are DNA excision repair proficient (WS‐1, KD. SSCW) and repair deficient (XP12BE) were exposed to mid‐day summer sunlight for a determination of survival based on an ability of cells to remain attached to a culture vessel surface. Whereas mid‐ and far‐UV wavelengths and radiation emitted from a sunlamp cause a gradual degeneraton and detachment of cells in a dose‐dependent manner, sunlight does not promote cell killing that is evidenced by these criteria in repair proficient cells. Detachment of repair deficient cells is promoted to a limited extent but only at sunlight exposure times that are low with respect to the amount of DNA damage (pyrimidine dimers) induced. Repair proficient and deficient cells exposed to sunlight for longer times do not detach but are incapable of excuding a viable stain several days after exposure and appear as histologically fixed cells. Pyrimidine dimer levels in these sunlight irradiated cells were great enough to have promoted detachment had these levels been induced by UV (254 nm) alone. Other photodamage induced by these exposures evidently inhibits the dimer‐induced cell degeneration that leads to cell detachment. We conclude that pyrimidine dimers are responsible for cell killing at short sunlight exposure times (< 40 min) but that at longer exposures (> 80 min) cells arc killed by a different mechanism that is independent of dimer‐caused death.
PREVENTION BY PHYTOCHROME OF PHOTODELAY IN CHLOROPHYLL ACCUMULATION
Authors: Oelze‐Karow H. , Rösch H. , Mohr H.
Published: January 2008

A photodelay in chlorophyll‐a and ‐b accumulation is observed in mustard (Sinapis alba L.) cotyledons during the first 3 h after the onset of white light even at medium light fluxes (3500 lx). A pretreatment of two red light pulses or a 12 h far‐red light pretreatment, both operating through phytochrome. prevent the photodelay completely. This is a specific phytochrome effect since'it can be separated from the effects of phytochrome on the rates during pre‐steady state and steady state phases of chlorophyll accumulation in saturating white light. Thus, photostability of chlorophyll in nature is a photoresponse mediated through phytochrome.
SPECTRAL CHANGES IN CHLOROPLASTS DURING AGING
Authors: Brody S. S.
Published: January 2008

The spectral properties of photosynthetic and accessory pigments of chloroplasts can change significantly over the course of an experiment which may last a couple of hours. As chloroplasts age at room temperature, there are decreases in absorbance at 708, 678, 510, 484, 465 and 432 nm. Chlorophylls absorbing at long wavelength (708 nm) and carotenoids (510 nm) are most sensitive to the aging process. The decrease in absorbance at 510 nm could indicate that aging results in a decrease in electrical potential across the thylakoid membrane.
QUANTITATIVE EVALUATION OF ULTRAVIOLET INDUCED ERYTHEMA
Authors: Wan San , Parrish John A. , Jaenicke Kurt F.
Published: January 2008

Abstract Noninvasive determinations of the amount of cutaneous blood in the superficial plexus are made from skin reflectance measurements after exposure of human skin to UV radiation. The approach considers the skin as consisting of multiple optically distinct layers, and utilizes a previously experimentally verified optical model that relates the optical properties of these skin layers to skin reflectance. When the UV erythema is concurrently graded by visual inspection, our results show that each subjective grade corresponds to a broad range of values of cutaneous blood, and a wide overlap in blood volumes occurs between different grades. The amount of cutaneous blood increases with the UV dose, and follows a sigmoid threshold relationship. Erythema fades with time, but the rate of decrease in cutaneous blood is volume dependent. The sharpest decrease occurs when the amount of cutaneous blood is within 1.5 ‐ 2.5 times the pre‐radiation volume. Slower decrease occurs when the volume of blood is outside of this range.
DISTORTIONS IN LASER FLASH PHOTOLYSIS ABSORPTION MEASUREMENTS. THE OVERLAP PROBLEM
Authors: Bazin Marc , Ebbesen Thomas W.
Published: January 2008

Abstract Lack of overlap between the laser beam and the analyzed volume in laser flash photolysis experiments may lead to significant error in the analysis of transient absorbances. A simple theoretical treatment is given to calculate the error for a given overlap. The consequences of bad overlap is discussed for a number of standard experiments and finally a method to determine the quality of the overlap in an experimental setup is given.
CHEMILUMINESCENCE OF SOYBEAN SEEDS: SPECTRAL ANALYSIS, TEMPERATURE DEPENDENCE AND EFFECT OF INHIBITORS
Authors: Boveris Alberto , Varsavsky Alicia I. , Silva Sylvio Goncalves da , Sánchez Rodolfo A.
Published: January 2008

Abstract—The spontaneous light emission of soybean seeds is enhanced 4–8 times during the first minute after water imbibition. Other solvents are also effective. The temperature dependence of soybean chemiluminescence identifies two reactions with activation energies of 20 and 68 kJ/mol corresponding to the lipoxygenase reaction and to the autoxidation of unsaturated fatty acids, respectively. Free radical scavengers and lipoxygenase inhibitors decrease soybean photoemission. The singlet oxygen probe 1,4‐diazabicyclo‐[2,2,2]‐octane (DABCO) increases soybean photoemission. The emission spectra of soybean seeds under a variety of conditions show bands between 450 and 720 nm with 50–70% of the emission over 600 nm. The experimental evidence is consistent with singlet oxygen being one of the emitting species, however, due to the complexity of the system it is likely that other chemiluminescent species are also formed.
ACTION SPECTRA (254–302 nm) FOR FOUR HUMAN PHOTOSENSITIVE CELL LINES
Authors: Coohill Thomas P. , Moore Sharon P. , Grider Rebecca A.
Published: January 2008

Abstract— The inactivation of cellular viral capacity for Herpes simplex type I growth at six separate wavelengths (254–302 nm) was measured in five human cell lines. These consisted of one “normal” skin fibroblast line (KD), and four photosensitive lines. Two lines of Xeroderma pigmentosum, one of Bloom's syndrome, and one of Cockayne's syndrome cells were used. Similar relative sensitivities were observed for the Bloom's syndrome, Xeroderma pigmentosum, and normal cell lines. The Cockayne's syndrome line became relatively more sensitive at 289 nm and longer wavelengths. Absolute sensitivities varied. Some divergence in response was noted at the longest wavelength tested, 302 nm.
PHOTOINDUCED OXYGEN CONSUMPTION IN MELANIN SYSTEMS. ACTION SPECTRA AND QUANTUM YIELDS FOR EUMELANIN AND SYNTHETIC MELANIN
Authors: SARNA T. , SEALY R. C.
Published: January 2008

Abstract— The first quantitative measurements of the wavelength dependence of oxygen consumption in systems containing eumelanin (from bovine eyes) and synthetic DOPA melanin are reported. Consumption of oxygen (considered to be a requirement for immediate pigment darkening) during irradiation of melanins with either visible or ultraviolet light was monitored using a spin probe nitroxide‐electron spin resonance spectroscopic approach. From initial rates of oxygen removal, quantum yields have been obtained over a wavelength range from 230 to 600 nm. Eumelanins are moderately effective in promoting oxygen consumption; quantum yields are low for irradiation with visible light, but increase sharply with light of shorter wavelengths. The absolute quantum yield for oxygen consumption is about 0.1% for natural melanin at 320 nm. The action spectrum is similar for both natural and synthetic melanins, indicating that the major chromophore responsible for oxygen consumption is the same for both kinds of material. This chromophore is not the major melanin chromophore responsible for absorption of visible light. The action spectrum also clearly differs from published action spectra for melanogenesis; however, the weak wavelength dependence for visible light is similar to that found for immediate pigment darkening. Catalase decreases the rate of oxygen consumption by 50%, confirming that hydrogen peroxide is the major molecular product of oxygen reduction. A Type I (free‐radical) mechanism evidently predominates: D2O and azide are shown to have only minor effects, ruling out any major contribution from a Type II (singlet‐oxygen) process to the overall oxygen consumption.
EFFECTS OF TRYPTOPHAN OXIDATION ON BACTERIORHODOPSIN STRUCTURE AND FUNCTION
Authors: HARDY JUDITH P. , KNIGHT ALAN E. W. , GHIGGINO KENNETH P. , SMITH TREVOR A. , ROGERS PETER J.
Published: January 2008

Abstract— N‐bromosuccinimide at low molar ratios specifically oxidizes tryptophan residues in purple membranes (bR). Loss of 1 mol tryptophan per mol bR (which corresponds to oxidation of Trp10 or Trp12 or part of both) produces slight changes in the absorption and CD spectra and in the photobleaching kinetics. The efficiency of reconstituting the retinylidene protein after bleaching and heptane extraction of these membranes was comparable to control values(–80%). Photocycling yield (M412) with 265 nm or 530 nm excitation (15 ns pulse) was only slightly decreased. Another mol of tryptophan was reacted at higher NBS:bR molar ratio (10:1). Partial oxidation of several residues rather than titration of a specific residue occurred: HPLC indicated no reaction with the chromophore. A considerable loss of extinction at 570 nm including enhanced red and blue shifts of LDmax at low and high pH respectively, was observed. Also the photobleaching rate was faster and functional retinylidene membranes could not be reconstituted from heptane‐extracted, apomembranes. Exogenous retinal could still locate the attachment site, based on formation of the fluorescent NaBH4‐reduced retinoyl adduct. Perturbation in the near UV and visible CD infer changes in helical conformation, trimer dissociation and decreased asymmetry of the chromophore. Photocycling efficiency was greatly decreased. The relative decrease was greater for 265 nm rather than 530 nm excitation. These results are consistent with co‐operative destabilization of the protein conformation by oxidized tryptophan residues, which leads to a decrease in the hydrophobicity of chromophoric site.
WAVELENGTH‐DEPENDENT ACTION DICHROISM: A THEORETICAL CONSIDERATION
Authors: HAUPT WOLFGANG
Published: January 2008

Abstract— For a model structure the wavelength dependence of action dichroism is computed as a function of the angle(△) between the transition moments at two different wavelengths. With as small an angle as △α= 20. inversion of action dichroism for parallel vs perpendicularly vibrating radiation is expected for different absorption bands if the sensory pigment molecules are in proper orientations. Thus published data on opposite action dichroism in the blue vs near‐UV range are compatible with flavins as sensory pigments, although the calculations must not be considered as proof for the flavin hypothesis.
PHOTOCHEMICAL ADDITION OF AMINO ACIDS AND PEPTIDES TO DNA
Authors: SHETLAR MARTIN D. , CHRISTENSEN JOHN , HOM KELLIE
Published: January 2008

Abstract— The quantum yields for photochemical addition of twenty of the amino acids commonly occurring in proteins to denatured calf thymus DNA have been determined in deoxygenated phosphate buffer at λ 254 nM and pH 7 using a fluorescamine assay technique. Fifteen were found to be reactive, with cysteine, lysine, phenylalanine, tryptophan and tyrosine being the most reactive. Alanine, aspartic acid, glutamic acid, serine and threonine were unreactive. Analogous quantum yields for a series of eighteen peptides of the form glycyl X (X being one of the commonly occurring amino acids) were also determined, along with the corresponding quantum yields for L‐alanyl‐L‐alanine, L‐alanyl‐L‐tryptophan, L‐seryl‐L‐seryl‐L‐serine, L‐threonyl‐L‐threonyl‐L‐threonine, and L‐cystine‐bis‐glycine. All of the peptides were found to be reactive. The modified amino acids Nε‐methyllysine, Nε, Nε, Nε‐trimethyllysine and Nε‐acetyllysine, all occurring in minor amounts in the histone group of chromosomal proteins, were also found to be reactive as was Nα‐acetyllysine. The quantum yields for photoaddition of a selected group of amino acids and peptides to denatured DNA and native DNA are compared. In some cases higher quantum yields for photoaddition to denatured DNA are observed while in other cases the reverse is true. The effect of oxygen on the quantum yields for photoaddition of selected peptides to DNA was examined. While for most systems studied the amount of reaction in aerated systems was less than in deoxygenated systems, in the case of glycyl‐L‐phenylalanine the reverse was true.
PHOTOINDUCED CATALYTIC DECOMPOSITION OF PYRUVIC ACID
Authors: MIYASHITA KOHICHI , SAKATA TOSHIBUMI , NAKAMURA KENICHIRO , KAWAI TOMOJI , SAKATA TADAYOSHI
Published: January 2008

Abstract— Electronic and catalytic properties of CuO doped by univalent or trivalent elements were investigated. Doping B or Sb into CuO was found to induce the decarboxylation reaction of pyruvic acid under irradiation with visible light. The decarboxylation reaction is accelerated by raising the temperature. The electronic conductivity of CuO is decreased by increasing the doping concentration of the trivalent element in the low concentration region and increased in the high concentration region. The doping concentration which gives the maximum production of the catalytic decarboxylation is well coincident with the concentration at the minimum electronic conductivity.
THE LETHAL EFFECT OF LONGWAVE ULTRAVIOLET LIGHT AND PUVA. AN ANALYSIS BASED UPON HUMAN MESENCHYMAL CELLS IN VITRO
Authors: Jongh G. de , BERGERS MIEKE , Boezeman J. B. M. , Verhagen A. R. , Mier P. D.
Published: January 2008

Abstract— The lethal effect of UVA and PUVA radiation was studied in cultures of fresh and mature monocytes. UVA radiation alone was shown to possess a lethal effect at doses which are attained in the dermis in vivo. The synergistic action of 8‐methoxypsoralen and UVA radiation predominated in PUVA radiation, but again a residual effect of UVA alone was demonstrated mathematically. Mature cells were less sensitive than fresh monocytes.

Our results indicate that a monolayer culture of non‐dividing, mesenchymal cells offers considerable advantages over in vivo systems as a model for the study of phototoxicity.
VISUAL PIGMENTS AND BACTERIORHODOPSINS FORMED FROM AROMATIC RETINAL ANALOGS
Authors: Derguini Fadila , Bigge Christopher F. , Croteau Allan A. , Balogh‐Nair Valeria , Nakanishi Kojixys
Published: January 2008

Abstract— Rhodopsin (Rh) and bacteriorhodopsin (bR) analogs have been prepared from retinals containing various aromatic and heterocyclic nuclei. In the case of Rh, aromatic methyl substituents facilitate the regeneration and stabilize the pigments formed; in bR, however, methyl substituents seem to have little influence. Rhodopsins derived from unsubstituted aromatic retinals show fine structure in the relatively stable “pre‐pigment” intermediate and their maxima are red‐shifted compared to pigments derived from methylated aromatic retinals. This implies that in these aromatic rhodopsins the ring moiety adopts a more planar conformation when unsubstituted. In bR derivatives also the aromatic ring adopts a close‐to‐planar conformation when unsubstituted, but comparison with indene‐derived bR suggests that even the unsubstituted phenyl ring may not be coplanar with the side‐chain.
CONFIGURATIONAL PHOTOISOMERIZATION OF BILIRUBIN IN VITRO—I. QUENCHING OF Z→E ISOMERIZATION BY TWO‐WAVELENGTH IRRADIATION
Authors: Pratesi Riccardo , Agati Giovanni , Fusi Franco
Published: January 2008

Abstract A simple rate‐equation theory of configurational photoisomerization of bilirubin (BR) is presented and used to discuss the Z→E photoisomerization of BR in HSA solutions irradiated with laser light in the blue‐green spectral region. The analytical expression of Z, E‐BR:HSA (PBR) concentration at photoequilibrium (PE) is used to derive the PBR concentration from the spectrophotometric data on absorbance difference spectra. The PBR values are in good agreement with those recently reported in the case of 10 nm‐bandwidth filtered light. Both sets of data give a best‐fit value of the BR, PBR quantum yield ratio equal to 2.3 in the case of BR:HSA ratio equal to 1:2.

Successive irradiation of BR/HSA solutions with different wavelengths (457/488/457 nm) provides further support for the reversibility of the photoreaction. However, differences between the intermediate PE values have been found, and may reveal departures from the simple Z,Z→Z,E isomerization in BR/HSA solutions.

The possibility of controlling the formation of Z, E‐BR/HSA has been demonstrated using simultaneous irradiation with blue (457 nm) and green (514 nm) laser beams. The two‐wavelength scheme takes advantage of the reversibility of the BRIPBR reaction, and of the differences between BR/PBR absorption spectra and quantum yields. Efficient quenching of PE PBR is achieved when green substantially exceeds (10–40 times) blue light intensity. This experiment may simulate what actually occurs during clinical phototherapy with white and green fluorescent lamps, where the quenching of PBR at the formation sites may prevent diffusion of this slowly excreted isomer and, at the same time, increase the formation of the more rapidly excretable structural, non‐reversible isomers, such as lumirubin.
PREPARATION AND CHARACTERIZATION OF THYMIDINE‐8‐METHOXYPSORALEN‐TETRAMETHYLETHYLENE PHOTODIADDUCTS
Authors: Shim Sang Chul , Kim Yong Zu , Kang Ho Kwon
Published: January 2008

AbstractA 8‐methoxypsoralen<4556>thymidine C4‐monoadduct was photolyzed with tetramethylethylene to obtain an analogue of thymidine<5645>‐methoxypsoralen<3456>thymidine C4‐diadducts. The structure of the adduct was determined by physical methods and a triplet manifold was proposed as the reactive state for the photocycloaddition reaction.
MONOLAYER STUDIES OF 5‐(4‐CARB‐ OXYPHENYL)‐10,15,20‐TRITOLYL‐PORPHYRIN‐II. PHOTOVOLTAIC STUDY OF MULTILAYER SANDWICH CELLS*
Authors: Bardwell Jennifer A. , Bolton James R.
Published: January 2008

The photovoltaic behavior of multilayer sandwich cells fabricated from the title compound has been examined. These multilayers are amorphous and contain a wide range of aggregated species. The action spectrum of the photocurrent agrees qualitatively with the absorption spectrum. This indicates that the photocurrent arises from all species in the film.

The shape of the dark current‐voltage characteristics varied with the porphyrin thickness. For thin films, (1 and 3 monolayers) the current can be described by a tunnelling mechanism. For thick cells (29 monolayers) the current‐voltage characteristic can be fitted using either of two models: a modified Shockley equation (suggesting that the dye acts as a p‐type semiconductor) or a combination of Schottky and Frenkel–Poole emission (suggesting that the porphyrin acts as an insulator). The former interpretation is preferred because it is consistent with the observed rectification characteristics; nevertheless, the latter is in agreement with the magnitude of the conductivity of the films.

The power‐conversion efficiencies of these cells were quite low (∼4 × 10‐4% for incident white light of intensity 2.72 W m‐2) owing to the very large internal resistance of the cells. The high resistance can be explained by observing that the molecules are in a very unfavorable orientation; maximum conductivity would be expected for the porphyrin ring systems perpendicular to the direction of current flow to give maximum overlap of the systems.