bluuebunny/crossref_metadata_2025 huggingface dataset:
BIPHOTONIC CHEMISTRY OF PHENANTHRENE UNDER 308 nm EXCIMER LASER IRRADIATION
Authors: Chatterjee Prabir K. , Webber S. E.
Published: January 2008

Abstract— –The high intensity laser induced photochemistry of phenanthrene is complex and appears to be non‐linear with respect to laser intensity. Photochemical products primarily involve the solvent (CH2C12) and phenanthrene coupling. These species exhibit strong absorption and emission which are red‐shifted from that of phenanthrene. In the presence of a‐methyl styrene, styrene oligomers are formed, but no dimers, indicating that there are no a‐methyl styrene cation radical reactions. In all cases of laser irradiation the solutions become acidic, which is ascribed to the deprotonation of the phenanthrene cation radical. Acid formation does not occur in the presence of a‐methyl styrene under CW irradiation with a conventional Xe lamp. These differences are ascribed to photoionization from the singlet state for laser irradiation while under CW conditions triplet‐triplet annihilation can produce the phenanthrene cation radical.
INTERACTIONS OF ASCORBATE AND CHELATED IRON IN A METHYLVIOLOGEN‐MEDIATED MEHLER REACTION
Authors: Upham Brad L. , Jahnke Leland S. , Foster Joyce G.
Published: January 2008

Abstract— –In the light, isolated spinach thylakoids consumed O2 in the presence of methylviologen, and ascorbate was found to interact with this reaction in various ways. Chelating‐resin was used to remove metal impurities from the assay medium. Ascorbate diminished the H202 pool in resin‐untreated solutions, while in resin‐treated solutions ascorbate had no effect on H2O2 concentrations. A Fenton catalyst (Fe‐EDTA) increased O2 uptake in the presence of ascorbate and decreased the amount of O2 recovered by catalase. Ascorbate tripled the rate of the methylviologen‐mediated Mehler reaction, and the O2 consumed was liberated to 50% of its original concentration by catalase. Superoxide dismutase reversed the effects of ascorbate on the Mehler reaction rates. These results indicate that ascorbate can stimulate Mehler reactions indirectly by promoting a Fenton‐type reaction as well as stimulating Mehler reactions directly by reducing 2O2‐ to 2H2O2. The promotion of a Fenton‐type reaction by ascorbate appears to be the cause of H2O2 depletion in resin‐untreated solutions.
PICOSECOND ABSORPTION STUDIES OF Zn‐OCTAETHYLPORPHIN π‐MONOANIONS
Authors: Chirvony Vladimir S. , Sinyakov Gennady N. , Gadonas Roaldas , Krasauskas Vytautas , Pelakauskas Algimantas
Published: January 2008

Abstract— Using the example of Zn‐octaethylporphin π‐monoanion solution in tetrahydrofuran, we studied the dynamics of ultrafast photoprocesses in porphyrin π‐anions using a tunable picosecond absorption spectrometer. The deactivation kinetics of the lowest excited electronic (doublet) state of Zn‐octaethylporphin iT‐monoanion has been determined and was found to be followed by a single exponential function with the characteristic time 135 ps. It is shown that upon picosecond excitation to the long wavelength absorption band (λmax= 830 nm) the process of two‐quantum photoionization of the involved monoanion is easily realized, with the results that the observable kinetics of spectral changes exhibit a strong dependence on the excitation intensity.
THE HEMOLYSIS OF ERYTHROCYTES BY SINGLET OXYGEN GENERATED IN THE GAS PHASE
Authors: Wang Tian P. , Kagan Jacques , Lee Sang , Keiderling Timothy
Published: January 2008

Abstract— Many sensitizers cause photodynamic hemolysis of erythrocytes. As these sensitizers usually participate in Type I as well as Type II processes, the determination of the mechanism(s) of photosensitized hemolysis is always ambiguous. Here, human erythrocytes were proved to hemolyze upon treatment with singlet oxygen (1δg) generated with fiuoranthene in the gas phase. These conditions rigorously exclude the participation of superoxide anion. The standard diagnostic tests for singlet oxygen (enhanced effect in D2O and protection by NaN3) gave the anticipated results when the erythrocytes were treated with 1O2 generated in the gas phase. When the erythrocytes were irradiated in a buffer solution containing fiuoranthene, the results of the diagnostic tests depended on the sensitizer concentration
THE ANAEROBIC PHOTOLYSIS OF LENS α‐CRYSTALLIN: EVIDENCE FOR TRIPLET STATE MEDIATED PHOTODAMAGE
Authors: Berger Jeffrey W. , Vanderkooi Jane M.
Published: January 2008

Abstract— Anaerobic solutions of lens α‐crystallin were subjected to near‐UV (> 295 nm) irradiation, and the photoproducts were analyzed by fluorescence and room‐temperature phosphorescence spectroscopy. The principal photoproduct was excited maximally at 340 nm, fluoresced maximally at 430 nm, and phosphoresced with an emission maximum at 510 nm. The phosphorescence intensity decay of this species was well fit by a sum of two exponentials with lifetimes of 9.2 ms (78%) and 61 ms (22%); this report is the first demonstration of a long‐lived triplet state associated with a protein photolysis product. As reported previously, 3trp* is also long‐lived in deoxygenated α‐crystallin solution at room‐temperature (Berger and Vanderkooi, 1989, Biochemistry 28, 5501–5508), hence both tryptophan and photoproduct triplet states are good candidates to mediate photodamage. Photolysis experiments in the presence of agents known to alter the tryptophan triplet yield provide evidence for the importance of triplet‐state‐mediated photodamage of lens crystallins in anaerobic solution. In 30 mM acrylamide where 3trp*, but not 1trp*, is efficiently quenched, anaerobic solutions exhibited marked resistance to protein photodamage, whereas the photoprotection in aerobic solution was minimal. In D2O, where photoionization is suppressed but triplet states are longer‐lived, photodamage was accelerated in anaerobic solution but reduced in aerobic solutions. Finally, the anaerobic photo‐destruction rate was increased in 500 mM Cs+ solution where the triplet yield is increased by a heavy atom effect.
RESEARCH NOTE
Authors: Lloyd R. E. , Rinkenberger J. L. , Hug B. A. , Tuveson R. W.
Published: January 2008

Abstract— Two mutants of Escherichia coli unable to synthesize riboflavin were grown with limiting (2 µg ml‐1) and non‐limiting (10 µg ml‐1) concentrations of riboflavin. These riboflavin auxotrophs when grown to exponential phase with non‐limiting riboflavin are more sensitive to broad spectrum near‐ultraviolet light (NUV, 320–400 nm) inactivation than when they are grown with limiting riboflavin. Exponential phase cells of the riboflavin auxotrophs grown with limiting riboflavin are sensitized when irradiated in saline supplemented with riboflavin. This suggests that extracellular riboflavin is important as a NUV sensitizer when intracellular levels of riboflavin are reduced. The concentration of riboflavin in crude extracts from exponentially growing cells correlates well with the sensitivity of these mutants to NUV inactivation. The level of riboflavin supplementation has little effect on the NUV sensitivity of the parental strain.
ROLE OF MEROCYANINE DYE AS A PROTON PUMP IN PHOTOVOLTAGE GENERATION
Authors: Datta Ruma , Nandy Papiya
Published: January 2008

Abstract— A novel photoelectrochemical cell using a proton pump mechanism in the aggregated planar structure of oxidised cholesterol incorporating merocyanine dyes is reported. Lipid dye binding, as verified from spectral studies and photoisomerisation of the dye, is responsible for this photovoltage generation whose magnitude and storage duration are related to the equilibrium constant of dye‐lipid binding through an empirical formula.
DEPTH MEASUREMENTS AND HISTOPATHOLOGICAL CHARACTERIZATION OF PHOTODYNAMIC THERAPY GENERATED NORMAL BRAIN NECROSIS AS A FUNCTION OF INCIDENT OPTICAL ENERGY DOSE
Authors: Dereski M. O. , Chopp M. , Garcia J. H. , Hetzel F. W.
Published: January 2008

The response of normal brain to photodynamic therapy (PDT) was investigated in 62 Fisher rats. The animals were injected i.p. with Photofrin II (12.5 mg/kg). Forty‐eight hours following injection, an area of dura 5 mm in diameter over the frontal cortex was photoactivated with red light (632 ± 2 nm) at 100 mW cm−2, with no contributing thermal increases, at optical energy doses ranging from1–140 J cm−2 from an argon‐pumped dye laser. Appropriate controls were also prepared. Brain tissue samples for histological analysis were taken 24 h following PDT treatment. Maximum lesion depth perpendicular to the pial brain surface, was measured using an eyepiece micrometer. Lesions of increasing depth were generated as the incident optical energy dose was increased. Fitting the depth of necrosis to a natural log dependence of incident optical dose yielded a slope of 0.83 mm/In J cm−2 (r2=0.99). The intercept of 1.47 J cm−2 indicated the energy dose below which no normal tissue damage would occur at the incident laser intensity of 100 mW cm−2. The smallest lesions consisted almost exclusively of isolated neuronal injury and neuropil vacuolation, suggestive of an early ischemic lesion. Damage at the upper energy levels (35–140J cm‐2) consisted of complete coagulative necrosis identical to that induced by an arterial occlusion. The existence of viable tissue alongside neurons in various stages of necrosis at low energy levels (< 35 J cm−2) is suggestive of reversible injury and possibly clinically relevant treatment levels.
BIOCHEMICAL ISOLATION AND SPECTROSCOPIC CHARACTERIZATION OF POSSIBLE PHOTORECEPTOR PIGMENTS FOR PHOTOTAXIS IN A FRESHWATER Peridinium
Authors: Häder Donat‐P. , Liu Shi‐Mei
Published: January 2008

Photoreceptor pigments have been isolated biochemically from the freshwater dinoflagellate Peridinium gatunense, and characterized spectroscopically. At least four different chromoproteins can be detected in the crude extract and the membrane fraction isolated from the cells absorbing at 580, 638, 667 and 710 nm, which correspond with the maxima in the action spectrum for phototaxis in this organism. Light energy absorbed by shorter wavelength pigments is emitted as fluorescence at wavelengths which are absorbed by pigments with maxima at longer wavelengths. Protein separation on a MonoQ anion exchanger column using fast liquid chromatography resulted in a non‐bound fraction and four bound fractions eluted by an NaCI gradient, which differed in their pigment composition.
REGIOSELECTIVE PHOTOREDUCTION OF ZINC(II) PORPHYRINS TO GIVE CHLORINS
Authors: Iakovides Panos , Simpson Daniel J. , Smith Kevin M.
Published: January 2008

References

The ascorbic acid/organic base photoreduction of zinc(II) porphyrins was investigated. It was established that certain substituents can direct the photoreduction to the site of the macrocycle to which they are attached. For example, zinc(II) vmy/porphyrins (8, 12, 16, 20) are photoreduced with cis stereochemistry on the ring bearing the vinyl group to give the corresponding chlorins. Zinc(II) acefy'porphyrins (22, 24) were likewise reduced to chlorins such that cis‐hydrogenation took place on the ring bearing the acetyl group. Zinc(II) formylporphyrins 33 also appear to reduce at the ring bearing the formyl group. When the zinc(II) acrylic porphyrin 28 was photoreduced, reduction did take place at the ring bearing the acrylic side chain, but migration of the acrylate double bond was very rapid, and the product isolated was the corresponding porphyrin propionate 30. Reduction of a zinc(II) porphyrin 35 bearing both a vinyl group and a nuclear carboxylic ester took place at the ring bearing the carboxylic ester. The reaction provides a general method for regioselective synthesis of chlorins from zinc(II) porphyrins without any evidence of formation of over‐reduction products characteristic of many other procedures for formation of chlorins from porphyrin precursors.
EFFECT OF PROTONATION ON THE ISOMERIZATION PROPERTIES OF n‐BUTYLAMINE SCHIFF BASE OF ISOMERIC RETINAL AS REVEALED BY DIRECT HPLC ANALYSES: SELECTION OF ISOMERIZATION PATHWAYS BY RETINAL PROTEINS
Authors: Koyama Yasushi , Kubo Keishi , Komori Mika , Yasuda Haruo , Mukai Yumiko
Published: January 2008

References

Alumina adsorption chromatography and ion‐pair reversed‐phase chromatography were developed to analyze the isomers of unprotonated and protonated n‐butylamine Schiff base of retinal (RSB and PRSB), respectively. Photoisomerization starting from the &‐\\trans, l\‐cis and 13‐cw isomers was traced for RSB in n‐hexane, acetonitrile, methanol and 1‐butanol, and for PRSB in methanol, acetonitrile and 1‐butanol. The quantum yields of photoisomerization for the a\\‐trans, 9‐cis, 11‐cis and 13‐ris isomers were determined for RSB and PRSB in the above solvents except 1‐butanol. On the other hand, photoisomerization of isomeric retinal bound (through Schiff base linkage) to bovine serum albumin (RBSA) in aqueous solution (pH 3, 7 and 12) as well as thermal isomerization of RSB (in n‐hexane), PRSB (in methanol) and RBSA (in aqueous solution, pH 7) were traced starting from the a\l‐trans, 11‐cw, and 13‐cis isomers.

Protonation of RSB drastically changes the pathway of photoisomerization and increases the quantum yields of isomeric RSB. The solvent polarity increases the quantum yields of RSB differently depending on the configuration. Protonation enhances thermal isomerization also. The results of the above model systems are compared with those of retinal proteins to rationalize their selection of the particular isomerization pathways.
PHOTOCHEMISTRY OF 1‐PYRENYLDIAZOMETHANE*
Authors: Silva Salom , Olea Andreas F. , Thomas J. K.
Published: January 2008

References

Photoexcitation of 1‐pyrenyldiazomethane (1) leads to carbenes which attach to various molecules, e.g. surfactants, polymers, hydroxylated surfaces. This provides a convenient method of labelling these compounds with pyrene for probe studies of complex structures and surfaces. Photophysical and photochemical studies of the various events resulting from the photoexcitation of 1, show that the quantum yield for disappearance of 1 and of carbene formation is low (∼ 5%) and that other processes lead to relaxation of excited 1, in particular fluorescence and intersystem crossing. The mechanism involves a mixing of low lying π‐π* states of the pyrene chromaphore with diazo n‐π+ states, and is discussed in the light of other similar systems and the present studies.
PHOTOREACTIVATION OF ULTRAVIOLET RADIATION‐INDUCED RELEASE OF ARACHIDONIC ACID FROM MARSUPIAL CELLS
Authors: Kaleta Elzbieta W. , Applegate Lee A. , Ley Ronald D.
Published: January 2008

Exposure of an established marsupial cell line, PtK2(Potorous tridactylus), to ultraviolet radiation (UVR) from an FS‐40 sunlamp (280–400nm) resulted in a fiuence‐dependent release of radiolabeled arachidonic acid (AA) from cell membranes. Post‐UVR, but not pre‐UVR, exposure to photoreactivating light reversed UVR‐induced pyrimidine dimers in DNA and suppressed the UVR‐induced release of AA. These data indicate that DNA damage contributes to the release of AA from membrane phospholipids.
SOLAR ULTRAVIOLET RADIATION IN SOUTHEAST ENGLAND: THE CASE FOR SPECTRAL MEASUREMENTS
Authors: Webb Ann R.
Published: January 2008

Spectral measurements of the solar ultraviolet spectrum have been made at Reading, England, since July 1989. The data presented show the daily and annual changes in the ultraviolet‐B (UV‐B) part of the spectrum, and illustrate the dominance of the longer wavelengths in grouping the data into a single broadband measurement. The temporal changes (diurnal and annual) cover 2 orders of magnitude at 300 nm, and a factor of 5 at 320 nm. In a single statement of UV‐B levels the trend at longer wavelengths predominates, hiding the larger differences at the more biologically important wavelengths. However, the data also show that at mid‐high latitudes the UV irradiance at noon in winter is less than that received at any time during the middle 12 h of daylight in summer, and this should be acknowledged when assessing the consequences of ozone depletion. Atmospheric scattering of short wavelength radiation is compared to that of the entire solar spectrum from measurements of diffuse radiation: on a clear day70–100% of UV‐B was diffuse in Reading, with a slight wavelength dependency increasing diffuse radiation at short wavelengths. Under the same conditions scattering of total solar radiation was 21%. The effect of cloud cover is briefly discussed for two specific cases of complete, uniform cloud cover, when attenuation by clouds was approx. 40 and 68%, with little wavelength dependence in either case.
DOUBLET Stentor DO NOT DISPLAY PHOTODISPERSAL
Authors: WOOD DAVID C. , MARINELLI RICCARDO
Published: January 2008

Abstract—

Normal Stentor, called singlets since they have a single membranellar band and oral groove surrounding their frontal field, swim away from light sources and collect in the darker areas of an unevenly illuminated container (photodispersal). Phenotypic variants, called doublets since they have 2 membranellar bands and 2 oral grooves, do not exhibit this behavior. Doublets produce photophobic responses and contractions when illuminated at the same fluence rates which produce those responses in singlets, hence their sensitivity to light is normal. Illumination of the frontal field of doublets produces a photophobic response at lower fluence rates than does illumination of their side or posterior. This directional sensitivity is quantitatively similar to that observed in singlets. However, doublets do not reorient their swimming direction after a phobic response as extensively as do singlets. This failure in reorientation is the probable reason that doublets fail to show photodispersal. These results imply that the mechanism producing photodispersal in singlets depends on photophobic responses or some other, presently undescribed, response which requires an asymmetric frontal field.
SINGLET AND TRIPLET REACTIVITY IN THE PHOTOREDUCTION OF OXONINE(3,7‐DIAMINOPHENOXAZIN‐5‐IUM CHLORIDE) BY IRON (II)
Authors: CREED DAVID , FAWCETT NEWTON C. , THOMPSON ROBERT L.
Published: January 2008

Abstract— The oxazine dye, oxonine (3,7‐diaminophenoxazin‐5‐ium chloride), 1, is photoreduced by Fe (II) sulfate in dilute sulfuric acid. The reaction mechanism is analogous to that for the photoreduction of thiazine dyes by Fe (II), the most important difference being that reduction of oxonine occurs predominantly from its excited singlet state, S1, rather than from the triplet state, T1. The latter is formed with an intersystem crossing (isc) quantum yield of ca 1.7×10‐3. The quenching of S1 by Fe (II) has a rate constant ksQ= 2.2 ± 0.1 × 109M‐1 s‐1 and affords the one electron reduced product, semioxonine (R), with a limiting quantum yield, φSR, of 0.26 ± 0.02. In contrast, quenching of T1, generated by bromide ion quenching of S1 or by diacetyl sensitization, occurs with kQt1.2×106M‐1 s‐1, extrapolated to zero ionic strength, and affords R with a limiting probability, φTR= 1.1×0.2. Three possible reasons for the lower quantum yield of the more exothermic S1 reduction are discussed. These are energy transfer from S1 to Fe (II), different rates of escape of R from the encounter complex as a consequence of the different states of protonation of R as initially formed from S1 and T1, and spin allowed back electron transfer in an exciplex formed between S1 and Fe (II). Evidence is also presented for a very low probability (ca 1%) induced isc from the encounter of S1 with paramagnetic Fe (II). Rate parameters for other processes important to the overall reduction mechanism such as disproportionation of R to leucooxonine L and oxonine, kRDIS= 1.7 ±0.2 × 109M‐1 s‐1, oxidation of R by Fe (III), kROX= 1.5 ± 0.1 × 105M‐1 s‐1, and oxidation of L by Fe (III), kLOX= 1.1 ± 0.1 × 103M‐1 s‐1, have also been measured. These results are contrasted with those for the closely related thionine/Fe(II) photoredox reaction, the most well understood system for photogalvanic energy conversion.
THE USE OF NEUTRAL RED TO MONITOR THE SURFACE POTENTIAL OF THE PURPLE MEMBRANE
Authors: LI QING‐GUO , NI YA‐JUN , CAO YI
Published: January 2008

Abstract— The binding of neutral red to purple membrane has been studied. The intrinsic pKa and the apparent pKa, of bound neutral red were determined by titration and by measuring the binding ratio of neutral red to purple membrane as a function of pH. The surface potential of purple membrane was inferred from the difference between these two pKas. The H+/M412 ratio at different ionic strengths was also measured and compared with the surface potential. The results show that the H+/M412 decreased as the surface potential increased due to decreased salt concentrations. However, this correlation holds only for KCl concentrations higher than 30 mM. At lower salt concentrations, the change in surface potential is always less than the variation in the H+/M412 ratio.
A NEW FLUORESCENT CHOLESTEROL DERIVATIVE: STRUCTURE AND BLOOD PLASMA ANALYSIS
Authors: Abubaker M. Amin , Wandruszka Ray Von
Published: January 2008

Abstract—

A fluorescent cholesterol derivative produced by reaction with gaseous HCI and zinc chloride in ethyl acetate is shown to be a chlorine substituted B‐ring diene. The species forms relatively rapidly via an i‐steroid rearrangement, requiring a temperature around 70°C. A weak, possibly dimeric π‐allyl zinc complex exists in solution, leading to a red shift in the fluorescence emission. The application of the derivative to the determination of cholesterol in bovine plasma provides good sensitivity and precision and requires notably small sample volumes.
OXIDATION OF PHOSPHATIDYLCHOLINE MEMBRANES BY SINGLET OXYGEN GENERATED IN THE GAS PHASE
Authors: Eisenberg Walter C. , Anand Jasbir , Wang Shukun , Stevenson Robert J.
Published: January 2008

Abstract—

Singlet‐oxygen (1O2) was generated in the gas phase by heterogeneous photosensitization and bubbled into suspensions of phosphatidylcholine (PC) liposomes. Lipid peroxidation and membrane lysis were observed, and were dependent on the 1O2 concentration and the degree of unsaturation of the liposome. An analysis based on large target diffusion theory indicates that approximately 5000, 2800, and 1600 interactions were required for the lysis of large dioleoylPC, dilinoleoylPC and dilinolenoylPC liposomes, respectively.
PHYSIOLOGICAL RELATIONSHIPS BETWEEN PHYTOCHROME EFFECTS ON INTERNODE EXTENSION GROWTH AND DRY MATTER ACCUMULATION INLIGHT‐GROWN MUSTARD
Authors: Casal Jorge J. , Sanchez Rodolfo A.
Published: January 2008

Abstract—

The physiological relationships between the effects of phytochrome photoequilibrium (Pfr/P) on internode extension growth and dry matter accumulation were investigated in white light (WL)‐grownSinapis albaL. seedlings. After 11 days under continuous WL, the seedlings were exposed: (a) to pulses of light providing different Pfr/P, followed by 24 h darkness (D); (b) to pulses of light providing different Pfr/P, followed by 3 h D and 24 h continuous WL; (c) to continuous WL with or without supplementary far‐red light (to reduce Pfr/P); or (d) to pulses of light providing different Pfr/P followed by D, in factorial combination with either water or a saturating (0.2M) sucrose solution applied to one of the leaves. In D (“a” and “d”) low, compared to high Pfr/P increased both internode extension growth and dry weight to the same extent. Under WL (“b” and “c”) low PfrlP promoted internode extension growth but had no proportional effects on internode dry weight. Sucrose promoted internode extension growth with a lag of at least 8 h (compared to the rapid effect of low Pfr/P) and did not reduce the effect of low Pfr/P. These results indicate that Pfr/P effects on internode extension growth are not the consequence of changes in photoassimilate translocation from the leaves. Under WL, PfdP effects on internode length occur partially at the expense of internode dry matter per unit length.
DIRECT MEASUREMENT OF PHYTOCHROME PHOTOCONVERSION INTERMEDIATES AT HIGH PHOTON FLUENCE RATES
Authors: Smith Harry , Fork David C.
Published: January 2008

Abstract—

A custom‐built modulated split‐beam spectrophotometer has been used to measure the absorbance of tissue samples and purified phytochrome whilst exposing the sample to actinic 633 nm laser radiation at fluence rates approaching those of daylight. This approach has allowed the direct observation of the accumulation of phytochrome photoconversion intermediates at high fluence rates. Atca1250 μmol m−2s−1upwards of 35% of the total phytochrome was present in the form of photoconversion intermediates in tissues of maize, sunflower and tomato. In other tissues tested (wheat, bean andAmaranthus) and in purified oat phytochrome, rather smaller levels of intermediates accumulated. Upon “lights‐off” only a proportion of the accumulated intermediates decayed to far‐red absorbing phytochrome (Pfr), the remainder appearing as the red‐absorbing form (Pr). Difference spectra suggested that, at high light levels, Pr may be reformedviaa photochemical back‐conversion of an intermediate in the Pr—Pfr pathway, although the involvement of intermediates in the Pfr—Pr pathway cannot be excluded. The implications of the results for the ecological function of phytochrome are discussed.
THE DISTANCE BETWEEN THE PHYTOCHROME CHROMOPHORE AND THE N‐TERMINAL CHAIN DECREASES DURING PHOTOTRANSFORMATION. A NOVEL FLUORESCENCE ENERGY TRANSFER METHOD USING LABELED ANTIBODY FRAGMENTS
Authors: Farrens David L. , Cordonnier Marie‐Michèle , Pratt Lee H. , Song Pill‐Soon
Published: January 2008

Abstract—

A novel antibody‐fluorescence method has been developed to elucidate the chromophore topography in phytochrome as it undergoes a photochromic transformation. Förster energy transfer from N‐terminal bound, fluorescently labeled Oat‐25 Fab antibody fragments to the phytochrome chromophore was measured. The results suggest that the chromophore moves relative to the N‐terminus upon the Pr → Pfr phototransformation. This conclusion is consistent with previous models which have proposed a reorientation and an interaction of the Pfr chromophore with the N‐terminus. The method described appears to be the first study of a Forster energy transfer measurement using a donor‐label attached to a Fab fragment of a photosensor protein.
KINETIC STUDY OF THE HELIX TO COIL DARK REACTION OF POLY(SPIROPYRAN‐l‐GLUTAMATE)*
Authors: Cooper Thomas M. , Obermeier Keith A. , Natarajan L. V. , Crane Robert L.
Published: January 2008

Abstract— An investigation of kinetics of the helix to coil dark reaction of light adapted poly(spiropyran‐ L‐glutamic acid) (PSLG) dissolved in hexafluoroisopropanol was performed. The reaction was associated with the spiropyran (SP) to merocyanine (MC) ring opening. The ring opening reaction monitored with UV/NIS spectroscopy showed first order kinetics. Chromophore and polypeptide backbone circular dichroism data fit to an expression consistent with a single intermediate series mechanism. By FTIR, we monitored the polypeptide a‐helix amide I, the MC chromophore —C=C — stretch and the protonated unmodified carboxylate C=O stretch bands. During the first step of the series mechanism, changes in the hydrogen bonding of the unmodified carboxylate groups occurred, suggesting breakup of polypeptide aggregates. The second step of the proposed series mechanism was dominated by the helix to coil transition and the ring opening of SP to MC. The CD spectrum of MC in the dark adapted PSLG was red shifted and had a narrower bandwidth than the UV/VIS spectrum. The kinetic and spectroscopic data suggested that a fraction (population I) of the MC chromophores experienced optical activity induced by the chiral polypeptide environment, while the remainder of the MC chromophores (population II) were solvated and enantiomeric.
BINDING OF HEMATOPORPHYRIN DERIVATIVE TO BRAIN TUMOR CELLS—A FLUORESCENCE SPECTROSCOPIC STUDY
Authors: Joshi Kunju , Joshi Preeti G. , Joshi Nanda B.
Published: January 2008

Abstract— The binding of hematoporphyarin derivative (HpD) to brain tumor cells and their photo‐sensitivity was studied as a function of HpD concentration, time of incubation and growth phase of cells. Upon binding to cells, HpD showed three fluorescence bands at 616, 636 and 678 nm. In plateau phase cells a fluorescence band at 636 nm was predominant, which was further enhanced by increasing HpD concentration and/or increasing incubation time. In exponential phase cells the maximum fluorescence was exhibited at 616 nm. After 1 h incubation of exponential phase cells with increasing HpD concentration an overall intensity enhancement occurred with no change in the distribution of bands, whereas longer incubation time caused an increase in relative intensity of the 636 nm band similar to that observed in plateau phase cells. After 1 h incubation with HpD plateau phase cells were more photosensitive than exponential phase cells, although cell bound HpD was much less in the former case. Incubation of cells for 24 h drastically enhanced the photosensitivity irrespective of the growth phase. Our results suggest a relationship between the fluorescence emission band of HpD at 636 nm and photosensitivity of cells.
THE MECHANISM OF PHOTOSENSITIZATION IN PHOTODYNAMIC THERAPY: CHEMILUMINESCENCE CAUSED BY PHOTOSENSITIZATION OF PORPHYRINS IN SALINE CONTAINING HUMAN SERUM ALBUMIN
Authors: Takemura T. , Ohta N. , Nakajima S. , Sakata I.
Published: January 2008

Abstract— Chemiluminescence (CL) caused by photosensitization of porphyrins in phosphate buffered saline (PBS) solution containing 3% human serum albumin (HSA) was observed for the first time. Irrespective of porphyrins concerned, CL shows a spectrum ranging from 380 to 520 nm with a peak near 450 nm and decays almost single‐exponentially with a lifetime of about 15 s. The intensity of CL depends on concentrations of porphyrins and HSA in PBS solution. We have examined a number of porphyrins and observed CL for the compounds with triplet lifetimes longer than 0.1 ms. The appearance and quenching of CL by photosensitization of porphyrin‐HSA systems indicate that type II reaction by singlet oxygen occurs significantly in photodynamic therapy resulting in hypoxic regions in environments surrounding the sensitizer.
OXIDATION OF ASCORBIC ACID AS AN INDICATOR OF PHOTOOXIDATIVE STRESS IN THE EYE
Authors: Glickman Randolph D. , Lam Kwok‐Wai
Published: January 2008

Abstract— When whole retinal pigmented epithelium (RPE) cells isolated from bovine eyes are incubated with 14C‐labeled ascorbic acid and exposed to a visible laser, the ascorbic acid is oxidized to dehydro‐L‐ascorbic acid (DHA). The amount of ascorbic acid which is oxidized is proportional to the radiant exposure of the sample (i. e. the total amount of radiation per unit area delivered over the exposure time). Blue light is more effective than red light in driving the reaction. The amount of label appearing in the DHA fraction is increased if unlabeled DHA is present in the reaction mixture, indicating that some redox cycling of ascorbate is occurring in the RPE cells. The ascorbic acid oxidizing activity does not depend on intact cells, is not inactivated by heating the cells to 80°C, and appears to reside mainly in the subcellular fraction which contains melanin pigment granules. The ascorbic acid oxidation may be caused by free radicals formed when melanin is illuminated with light. This reaction appears to be a useful method for quantifying the production of free radicals during photooxidative stress.
QUENCHING OF PHOTOEXCITED 4,4'‐DICARBOXY‐2,2'‐BIPYRIDINEBIS(2,2'‐BIPYRIDINE)RUTHENIUM(II) BY OXYGEN IN AQUEOUS SOLUTION AND IN SILK FIBROIN MEMBRANE
Authors: Kaneko M. , Iwahata S. , Asakura T.
Published: January 2008

Abstract— Photoluminescence and quenching of 4,4'‐dicarboxy‐2,2'‐bipyridinebis(2,2'‐bipyridine)‐ruthenium(II) complex (Ru(DCbpy)(bpy)22+) in an aqueous solution as well as in a silk fibroin membrane were studied. Emission quenching by oxygen in an aqueous solution showed a linear relationship with respect to oxygen concentration. When the complex was incorporated into a silk fibroin membrane by adsorption from an aqueous solution into a preformed membrane, the photoexcited state of the complex was not quenched by oxygen in an aqueous phase. However, when the complex was incorporated into a silk fibroin membrane by casting a mixture of the complex and silk fibroin, the photoexcited complex was quenched by oxygen in an aqueous phase. In this case the Stern‐Volmer plots showed a downward‐deviating curve indicating heterogeneity of the probe site. Emission intensity decreased with an increase of the water content in the silk fibroin membrane.
A PHOTON COUNTING TV CAMERA EQUIPPED WITH AN IMAGE GUIDE FOR RAPID DETECTION AND COUNTING OF SINGLE BACTERIA IN A WIDE FIELD
Authors: Masuko Masayuki , Kataoka Takuji , Sugiyama Norikazu , Uchiyama Shigeru , Sugiyama Hirofumi , Tarui Katsunori , Kamiya Kiyoshi , Kawai Tohru
Published: January 2008

Abstract—We developed a photon counting TV camera system, which uses an image guide consisting of tapered optical fibers, for the rapid detection and counting of microscopic sized luminous particles in a wide field. Using a luminous bacterium as a standard, we compared this image guide‐coupled TV camera to a lens‐coupled TV camera by determining their light collecting powers and detection abilities for single bacteria on a membrane filter. The image guide shortened the detection time by an order of magnitude, making the photon counting TV camera a practical system for rapid counting of bacteria.
SPECTRAL MODIFICATIONS OF BACTERIAL ANTENNA COMPLEXES BY LIMITED PROTEOLYSIS
Authors: Brunisholz René A. , Zuber Herbert
Published: January 2008

The spectral effects of a number of endo‐ and exoproteases to the detergent‐solubilized antenna complexes B802–858(sphaeroides like) of strain Rhodopseudomonas acidophila 10050 and B802–824of strain 7050 were analyzed. Upon protease digestion the time course of spectral modification between 250 and 900 nm was recorded. In addition, circular dichroism (CD) signals were measured between 450 and 950 nm. The endoprotease elastase as well as the exoprotease carboxypeptidase A (CP A) altered the B802–858antenna complex, by changing the 858 nm band hypochromically (30‐50%) with an additional small hypsochromic shift (3–6nm). A combined carboxypeptidase digestion, e.g. CP A and CP B, yielded a further modification to a complex with absorption bands at 800 nm and ˜840 nm (ε˜ 50% of the 800 nm band). By exposing the isolated B803–824antenna complex to the different proteases no significant spectral change was observed. The B802–858antenna complex, modified by CP A, exhibits a60–70% decrease of the biphasic CD signal in the near infrared. The limited proteolysis experiments provide conclusive experimental evidence that the C‐terminal domains of the antenna polypeptides α and β contribute to the formation of (dimeric) bacteriochlorophyll (BChl) a molecules absorbing at around 850 nm. This agrees with the hypothesis, based on comparative amino acid sequence analysis, that in purple bacterial antenna complexes the structural requirements (specific amino acids in the vicinity of the BChl molecules, e.g. aromatic amino acids) for batho‐ and hyperchromicity of BChl molecules apparently reside to a considerable extent in the C‐terminal portions of their antenna apoproteins.
THEORY OF POLARIZED FLUORESCENCE FROM MOLECULAR PAIRS: FÖRSTER TRANSFER AT LARGE ELECTRONIC COUPLING
Authors: Knox Robert S. , Gülen Demet
Published: January 2008

Polarization properties of the fluorescence from a pair of identical molecules coupled electronically are examined on the basis of a stochastic Liouville equation formalism developed in 1979 by Rahman, Knox and Kenkre. The time development of polarization is calculated for random ensembles of rigid molecule pairs under initial conditions that represent either selective excitation or broad‐band coherent excitation. We hold that the applicability of the Forster mechanism is not limited to cases of weak coupling, and we indicate the rationale and a method for observing it in cases involving large interaction between transition dipoles.
CONCENTRATION DEPENDENCE OF TRANSMISSION LOSSES IN UV‐LASER IRRADIATED BOVINE α‐, βH‐,βL‐AND γ‐CRYSTALLIM SOLUTIONS
Authors: Borkman J. L. Hott and F.
Published: January 2008

Experiments with calf lens protein fractions in aqeous buffer solutions at room temperature showed that βH ‐ and βL ‐ and γ‐crystallin fractions became opaque following ultraviolet exposure at 308 nm, while the α‐crystallin fraction remained transparent. Transmission loss, due to UV‐irradiation, for all of the crystallin samples was studied in the concentration range of 0.1 mg/mL to 1.0 mg/mL, and for α‐ and γ‐crystallin, in the range up to 5 mg/mL. With increased concnetrations of βH‐,βL‐and γ‐crystallin, the rate of opacification increased. However, with α‐crystallin, the loss of transmission was negligble for all of the concentrations and irradiation times studied. Opacification of the crystallins was accompanied by formation of higher molecular weight insoluble proteins as detected by SDS‐PAGE.
REGULATION OF UV‐PROTECTIVE PIGMENT SYNTHESIS IN THE EIPERMAL LAYER OF RYE SEEDLINGS (Secale cereale L. cv. KUSTRO)
Authors: Braun J. , Tevini M.
Published: January 2008

Trans‐cinnamic acid is the product of the L‐phenylalanine ammonia lyase (PAL, EC 4.3.1.5) enzyme reaction and might regulate the subsequent phenylpropanoid synthesis by feedback inhibition of PAL activity. The partial conversion of trans‐cinnamic acids (e.g. trans‐p‐coumaric acid) and of trans‐p‐coumaryl‐glucoside (chemically synthesized model substance for cinnamic acid derivatives) to the cis isomers upon UV irradiation leads to reduced inhibition of PAL activity within minutes. In rye leaves this rapid enhancement of PAL activity (within minutes) causes a rapid increase in phenylpropanoids, which are predominantly located in the epidermal layer. Because phenylpropanoid derivatives are precursors of flavonoid biosynthesis, the observed rapid increase in flavonoid content after short‐term UV irradiation can be explained by this UV‐induced regulation mechanism. Consequently, transphenylpropanoids can be regarded as photoreceptors and regulators of the phenylpropanoid pathway during UV‐B (280–320nm) irradiation. In rye leaves an additional slower UV response, obviously by induction of genetic transcription as described for other plant systems, leads to a much greater flavonoid accumulation compared to the rapid induction.
MEMBRANE DAMAGE INDUCED IN CULTURED HUMAN SKIN FIBROBLASTS BY UVA IRRADIATION
Authors: Gaboriau F. , Morlière P. , Marquis I. , Moysan A. , Goegze M. , Dubertret L.
Published: January 2008

Irradiation of cultured human skin fibroblasts with ultraviolet light from 320 to 400 nm (UVA) leads to a decrease in the membrane fluidity exemplified by an enhanced fluorescence anisotropy of the lipophilic fluorescent probe 1‐[4‐trimethylamino)‐phenyl]‐6‐phenylhexa‐1,3,5‐triene. This UVA‐induced decrease in fluidity is associated with lactate dehydrogenase leakage in the supernatant. Vitamin E, an inhibitor of lipid peroxidation, exerts a protective effect on both phenomena. Therefore, this UVA‐induced damage in membrane properties may be related to lipid peroxidation processes. Moreover, exponentially growing cells are more sensitive to these UVA‐induced alterations than confluent cells.
OPTIMIZATION OF MULTIFIBER LIGHT DELIVERY FOR THE PHOTODYNAMIC THERAPY OF LOCALIZED PROSTATE CANCER
Authors: Whitehurst C. , Pantelides M. L. , Moore J. V. , Blacklock N. J.
Published: January 2008

The understanding of light distribution within the target organ is essential in ensuring efficacy and safety in photodynamic therapy (PDT). A computer simulator of light distribution in prostatic tissue was employed for optimizing dosimetry for PDT in localized prostatic cancer. The program was based on empirically determined light distributions and optical constants and an assumed Ruence rate differential from fiber source to necrosis periphery. The diffusion theory approximation to the Boltzmann transport equation was the applicable formulation relevant to prostatic tissue, which has a high albedo with forward‐scattering characteristics. Solving this equation of diffusive transfer for the appropriate fiber geometry yielded the energy fluence distributions for cleaved fiber and cylindrical diffuser light delivery. These distributions, confirmed by our measurements, show a l/r and l/r dependency (r = distance from light source) of the fluence ø(r) for the cleaved fiber and diffuser, respectively. This manifests itself by the tighter spacing of energy fluence isodoses in the case of the cleaved fiber. It was predicted that for a typical PDT regime a single interstitially placed cleaved fiber would treat 0.05–0.72 cm3, Four parallel fibers improve the uniformity of light distribution and treatment volume, and an interfiber separation of 12 mm would be necessary to provide optimal overlap of PDT necrosis, treating 0.26–3.6 cm3. The cylindrical diffuser, however, could treat larger volumes, and it was predicted that four 3 cm long diffusers at an optimal separation of 25 mm would treat 25–88 cm3 of prostatic tissue.
BIOPHYSICAL AND BIOCHEMICAL ASPECTS OF PHENGODID (RAILROAD‐WORM) BIOLUMINESCENCE
Authors: Viviani Vadim R. , Becham Etelvino J. H.
Published: January 2008

In studies of the bioluminescence of 11 species of phengodid collected in central and southeast Brazil, we have found that: (1) their lateral lanterns emit light in the yellow‐green region (λmax= 540–580 nm) and the head lantern color is shifted to the red region (λmax= 565–620 nm), (2) the luciferins of both types of lanterns are identical to that of lampyrids and elaterids and (3) the luciferase physicochemical properties are also similar to those of lampyrids and elaterids (optimum pH ca 8.1; Km(ATP) = 260–370 μM, Kμ(luciferin) = 170–400 μM; molecular weight ca 60 kDa; apparent activation energy of in vitro bioluminescence ca 58 kJ/mol). Thus the bioluminescence system of phengodids appears to be essentially the same as that of lampyrids and elaterids. The different bioluminescence colors of the lanterns of Phrixothrix species (λhead= 600–620 nm; λlateral= 535–565 nm) and other phengodid species are probably elicited by the presence of luciferase isoenzymes, as occurs in the case of elaterid prothoracic and abdominal lanterns.
COMPARATIVE EFFECT OF UVA AND UVB ON CULTURED RABBIT LENS
Authors: Hightower Kenneth , McCready Janet
Published: January 2008

Abstract Effects on lens physiology of UVB and UVA used separately and sequentially were investigated using 4 week old rabbit lenses in organ culture. Narrowband UVB at 0.3 J/cm2= joules/lens (1 h exposure) has little effect on sodium and calcium concentrations in the lens interior or transparency of lenses subsequently cultured for 20 h after a 1 h exposure. With an incident energy of 3 J/cm2 of broadband UVB (295–330 nm), lenses become opaque and slightly swollen with significant ion imbalances during culture over a 1 day period. In contrast, lenses exposed to approximately 6–24 J/cm2 of UVA (330–400 nm) remain transparent after 1 day of culture. Extended culture up to 4 days reveals no signs of opacification. Ion homeostasis and normal lens hydration are also maintained in UVA‐irradiated lenses. The presence of 95% oxygen during UVA irradiation is also without effect. Broadband UVA irradiation is damaging, however, if lenses are first exposed to subthreshold doses of narrowband UVB (307 ± 5 nm) irradiation, viz. 0.3 J/cm2. Thus, sequential UVB/UVA irradiation at subthreshold doses causes impaired active cation transport and accumulation of sodium and calcium accompanying lens opacification.
EXCITED STATES OF ANTHOCYANINS: THE CHALCONE ISOMERS OF MALVIDIN 3,5‐DIGLUCOSIDE
Authors: Lima J. C. , Danesh Parvin , Figueiredo Paulo , Pina Fernando S. , Maçanita António
Published: January 2008

Abstract The excited state properties of the chalcone isomers of malvidin 3,5‐diglucoside (malvin) in acidic aqueous solution (0 < pH < 4) were investigated using steady‐state and time‐resolved fluorescence spectroscopy. The two chalcone isomers of malvin were first isolated by high‐performance liquid chromatography and then characterized by UV/visible absorption and fluorescence spectroscopy. The results were supported by molecular orbital calculations. The rate constants for photodeprotonation (k1= 1 × 109 s−l) and protonation (k−1= 1.3 × 1010 L mol−1 s−l) were determined, both from the multiexponential fluorescence decays and the fluorescence intensities measured at the emission wavelengths of the neutral and ionized chalcone forms. The results here obtained are relevant for the understanding of the photoreactivity of anthocyanins in acidic medium.
ULTRAVIOLET SOLAR RADIATION IN THE HIGH LATITUDES OF SOUTH AMERICA
Authors: Frederick J. E. , Diaz S. B. , Smolskaia I. , Esposito W. , Lucas T. , Booth C. R.
Published: January 2008

Abstract Measurements of the UV solar irradiance are available from Ushuaia, Tierra del Fuego during the spring and summer seasons of 4 consecutive years beginning in 1989. In addition, column ozone amounts derived from satellite‐based measurements exist for this location over the entire period from 1980 through 1991. Monthly mean column ozone over Ushuaia shows a general decline over the observing period, and a large day‐to‐day variability exists within a given month. Ozone amounts for the years 1980 through 1986 combined with a model of radiative transfer provide a climatological baseline against which to interpret the more recent ground‐based irradiance data. We focus on monthly mean noontime irradiances integrated over 5 nm wide spectral bands near 305 nm and 340 nm, respectively. Measurements in the 340 nm band show that cloudiness has a large influence on both the absolute monthly mean irradiances and their interannual variability. For example, during December the 340 nm band irradiance varied from approximately 50% of the clear‐sky value in 1992 to 65% in 1991. When the influence of cloudiness is removed, most of the months show irradiances in the 305 nm band that are larger than predicted from the climatological ozone amounts. The largest percentage enhancement occurred in October 1991 when the irradiance exceeded the baseline by 56%. The largest absolute irradiances occur in December, where the measurements range from 5.8% below the baseline in 1991 to 31% above in 1990.