bluuebunny/crossref_metadata_2025 huggingface dataset:
INTERACTION BETWEEN CHLOROPLAST BIOGENESIS and PHOTOREGULATION OF AMYLASES IN Pennisetum americanum LEAVES*
Authors: Vally K. J. M. , Sharma R.
Published: January 2008

In pearl millet (Pennisetum americanum) seedlings, light acting via phytochrome stimulates amylase activity in the leaves. The maximum photostimulation of amylase is observed in the segment proximal to the leaf base. This photostimulation mainly results from an enhancement in β‐amylase activity (EC 3.2.1.2.), which constitutes80–90% of leaf amylase activity. The subcellular fractionation studies revealed that while p‐amylase is localized only in the extraplastidic compartment, a‐amylase (EC 3.2.1.1.) is localized both in the cytosol and in the chloroplasts. The mesophyll cells contained both a‐ and β‐amylase activity, but only a‐amylase activity was present in the bundle sheath cells. The Norflurazon‐mediated photooxidation of chloroplasts during leaf development also eliminated plastidic α‐amylase activity, confirming dependence of its photoregulation on the chloroplast biogenesis.
THE MECHANISM OF PHOTOSENSITIZATION IN PHOTODYNAMIC THERAPY: PHOSPHORESCENCE BEHAVIOR OF PORPHYRIN DERIVATIVES IN SALINE SOLUTION CONTAINING HUMAN SERUM ALBUMIN
Authors: Takemura T. , Ohta N. , Nakajima S. , Sakata I.
Published: January 2008

The phosphorescence properties, especially the dynamic behavior of metal free and metal complexed porphyrins, have been studied in phosphate buffered saline (PBS) containing0–3% human serum albumin (HSA). 6,7‐Bisaspartyl‐2,4‐bis (l‐hexyloxyethyl)‐deutero‐porphyrin (DP) and its gallium(III), zinc(II), and indium(III) complexes are used as photosensitizers. Upon irradiation, a solution of porphyrins containing more than 0.1% HSA shows phosphorescence with a lifetime longer than 1 ms. With an increase in irradiation time, phosphorescence intensities and lifetimes of porphyrins increase, depending upon their concentrations and triplet lifetimes, and approach saturated values close to those under deaerated conditions. The experimental results may be interpreted in terms of hypoxia induced by photosensitization in a local environment surrounding the sensitizer. The hypoxia is caused by the reaction between proteins and singlet molecular oxygen generated by photosensitization of porphyrins. Phosphorescence behavior of sensitizers in HSA PBS solution gives significant information for classifying photosensitizers as to their efficacy for photodynamic therapy.
WAVELENGTH DEPENDENCY OF THE RATE OF IODINE CATALYZED PHOTOISOMERIZATION OF RETINOL and RETINAL
Authors: Baumgartner Nick R. , Blatz Paul E.
Published: January 2008

In separate experiments, hydrocarbon solutions of the W‐cis isomers of retinol and retinal containing catalytic amounts of iodine were irradiated with monochromatic light. Changes in absorbance were followed spectroscopically for each wavelength of light and measured as a function of time. The curve obtained by plotting the change in absorbance (δA) vs time (t) is a hyperbola, and thus the plot of 1/δA vs 1/t forms a straight line. The half reaction time, t4, was extracted from this equation, giving a value for each wavelength of light. The parameter 1/t4 is adjusted to compensate for variation of light quanta from the xenon source, and it is plotted vs wavelength. A response spectrum is obtained that is a Gaussian. The dlmax is 510 nm for retinol and 519 nm for retinal. This shows that in the photoisomerization iodine is the absorbing species and not the carbocation, which absorbs at 589 nm.
PHYTOCHROME‐CONTROLLED FERN‐SPORE GERMINATION: PHASE‐SPECIFIC MODULATION BY ELEVATED TEMPERATURES*
Authors: Haupt Wolfgang
Published: January 2008

The phytochrome‐mediated spore germination in Dryopteris is inhibited by raising the temperature from 22 to 27 or 32°C. As reported earlier (W. Haupt (1990) Photochem. Photobiol. 52,57–59), the elevated temperature is effective during the “coupling phase”, i.e. when Pfr, the active form of phytochrome, starts the processes leading to germination. In addition, a strong effect has now been found in the “preinduction phase”, i.e. when the spore develops its competence to react to Pfr. This latter effect is overcome, if in the subsequent coupling phase a high level of Pfr is allowed to act for a long time. Moreover, the inhibiting effect in a2–3 day preinduction phase is most obvious in or even restricted to its terminal 24 h. It is proposed that the temperature acts by reversibly abolishing the cell's competence to react to Pfr, and that this effect can extend into the coupling phase. Not yet understood is an “inversion” effect in D. paleacea: if the temperature is raised in the earlier parts of the preinduction phase, the effect of Pfr in the subsequent coupling phase is enhanced rather than inhibited.
THE pH DEPENDENCE OF TRANSIENT CHANGES IN THE CURVATURE OF THE PURPLE MEMBRANE*
Authors: Czégé József , Reinisch Lou
Published: January 2008

Abstract– We have observed transient changes in the curvature of purple membrane fragments upon photoexcitation as a function of the pH of the suspending medium. The room temperature suspensions have low ionic strengths, and the bending is observed by changes in the scattered light at 320 nm. The photoexcitation is from a 20 ns laser pulse at 532 nm. We use a simple first‐order approximation to subtract any changes in the scattered light associated with transient absorption changes during the photocycle. The resultant scattering curves are then fitted to the sum of three fundamental bending processes. Each process has an exponential rise, an exponential decay and an amplitude. We model two of the processes as transient forces correlated with the charge motion during the photocycle. The third process is probably cuased by local changes in the pH as the protein pumps protons. However, this is not proved rigorously. Additional experiments are proposed.
MULTI‐SITE PHOSPHORESCENCE OF α, β‐ENONES:LEVEL INVERSION IN 6β, 19‐EPOXYCHOLEST‐4‐EN‐3‐ONE BY SOLVATION AND AGGREGATION
Authors: BLOK PETER M. L. , DEKKERS HARRY P. J. M.
Published: January 2008

Abstract—

Millisecond time‐resolved emission spectroscopy was used to probe the phosphorescence kinetics of the α‐β‐enone 6β, 19‐epoxycholest‐4‐en‐3‐one (1) as a function of concentration in several paraffinic and hydroxylic glasses at 77 K. Only in methylcyclohexane/methylcyclopentane glass at low concentration (10−4M) does the phosphorescence decay exponentially. It is interpreted as emission from the 3n* state. Upon increasing the concentration a second emission grows which is characterized by a longer lifetime, a decreased fine structure and a hypsochromically shifted S0→1nπ* excitation spectrum. This phosphorescence is ascribed to 3ππ* emission of aggregates of 1. In hydroxylic glasses the phosphorescence decay is multiexponential, even at 10−4M concentration; from emission band shapes and lifetimes it follows that both 3nπ* and 3ππ* type emissions are present, the latter increasing with the alcohol concentration in the solvent. The two types of phosphorescence have different excitation spectra: that of the structureless and long‐lived 3ππ* emission is shifted to the blue in the S0→1nπ* region and to the red in the S0→1ππ* region. This emission is ascribed to complexes of 1 with the alcoholic solvent. The results of time‐resolved measurements of the circular polarization of the luminescence are consistent with the assignments given above and indicate that in the H‐bonded and possibly also in the free species 3ππ* and 3nπ* states are intermixed to a considerable extent.
DARK REACTIONS FOLLOWING PHOTOISOMERIZATION OF PROLYCOPENE*
Authors: RÖMER SUSANNE , HUMBECK KLAUS , SENGER HORST
Published: January 2008

Abstract—

Cells of mutant C‐6D of the unicellular green alga Scenedesmus obliquus form only acyclic carotenoid precursors up to prolycopene (7Z, 9Z, 7′Z, 9′Z cis‐isomer of lycopene) when grown heterotrophically in the dark. Upon illumination, however, the cyclic carotenes α‐ and β‐carotene and the xanthophylls are synthesized. Inhibition of the cyclization reaction by nicotine revealed a light‐induced isomerization of prolycopene accumulated in darkness to all‐trans lycopene.

The following reactions, e. g. cyclization and oxidations, take place in light as well as in darkness. The results presented here demonstrate that the isomerization of prolycopene into the all‐trans form is the only light‐dependent step in carotenogenesis of mutant C‐6D. Finally, a model showing the light‐regulation of carotenoid biosynthesis in mutant C‐6D of S. obliquus is presented.
A PULSE RADIOLYSIS STUDY OF THE ONE‐ELECTRON OXIDATION AND REDUCTION OF 5, 10‐METHENYLTETRAHYDROFOLATE
Authors: HEELIS P. F. , PARSONS B. J. , PHILLIPS G. O. , SWALLOW A. J.
Published: January 2008

Abstract— The one‐electron reduction and oxidation of 5,10‐methenyltetrahydrofolate has been studied in aqueous solution in the acidity range H0= ‐1 to pH = 7 using the reducing species CO‐2 and (CH3)2‐COH and oxidising species Br‐2, and H2SeO+3. The spectral and other properties of the radicals so formed were found to be indcpendent of the reductant/oxidant used. Two protolytic forms of both the oxidised and reduced radicals were observed with approximate pK, values of 0.5 ± 0.3 being determined. Both the bridged form (5.10‐methenyltetrahydrofolate) and the unbridged form (5‐ formyltetrahydrofolate) were found to be easily oxidised, whereas only the former could be reduced.
INTRACELLULAR LOCALIZATION OF A CHALCOGENAPYRYLIUM DYE PROBED BY SPECTROSCOPY AND SITES OF PHOTODAMAGE
Authors: KESSEL DAVID
Published: January 2008

Abstract— Site(s) of intracellular localization of a photosensitizing chalcogenapyrylium dye were assessed using murine luekemia cells in culture. While the dye exhibited substantial dark toxicity, additional damage was elicited by irradiation. The fluorescence emission spectrum of intracellular dye suggests an initial moderately hydrophobic site of localization (dielectric constant approx. 20). This might represent a membrane interface. But longer incubations led to alterations in both fluorescence emission and absorbance spectra, indicative of both dye migration to a more hydrophilic cellular site and dye biotransformations. Dye‐induced cytotoxicity, in either light or dark, was associated with mitochondrial, rather than membrane damage.
PHOTOSENSITIZATION OF MCF‐7 CELLS WITH DIAZIQUONE USING VISIBLE LIGHT: CORRELATION WITH DNA STRAND BREAKS AND FREE RADICAL PRODUCTION
Authors: Al‐Nabulsi Isaf , Gutierrez Peter L.
Published: January 2008

Abstract—

The ability of visible light to enhance the activity of diaziquone (AZQ) was evaluated in MCF‐7 human breast cancer cells. MCF‐7 cells were sensitive to AZQ, while visible light illumination had no appreciable effect on cell survival. In the presence of AZQ, visible light potentiated AZQ's cytotoxicity. This potentiation of AZQ activity correlated with a 2–2.5‐fold increase in the formation of free radicals (hydroxyl radicals and AZQ semiquinone) and with the production of DNA strand breaks as measured by electron paramagnetic resonance and gel electrophoresis respectively. These results support the hypothesis that free radical formation is part of the mechanism of action of AZQ.
MECHANISMS OF CELL KILLING IN PHOTODYNAMIC THERAPY USING A NOVEL in vivo DRUG/in vitro LIGHT CULTURE SYSTEM
Authors: Hampton James A. , Selman Steven H.
Published: January 2008

Abstract—

Photodynamic therapy of certain neoplasms has emerged as a promising form of cancer treatment. This type of therapy involves the exogenous administration of a photosensitizer with subsequent exposure to light. The ensuing photochemical reaction results in destruction of the tumor. Whether tumor cells are destroyed directly by the photodynamic treatment or indirectly as a result of destruction of the tumor microvascular bed is unknown. To address this question, methods were adapted to test whether combinations of a photosensitizer and light resulted in direct cell killing of precision cut tissue slices placed in culture. The major advantages of this culture system are that photosensitizers are administered in vivo, tissue slices produced in minutes, placed in culture medium, and irradiated in vitro. Any resulting cellular destruction occurs in the absence of a functioning vascular system and indicates that photodynamic therapy acts through a direct cell killing mechanism. Tissue slice viability was monitored by two standard methods: assay for intracellular potassium and morphological examination at the electron microscopic level. The effects of hematoporphyrin derivative and light were examined on tissue slices produced from a prostate adenocarcinoma transplanted into male Copenhagen rats. The data indicate that direct killing of tumor slices occurs and is dependent on the irradiation protocol used.
LIMITED CELL‐CYCLE DEPENDENCE OF THE MEROCYANINE 540‐SENSITIZED PHOTOINACTIVATION OF L1210 LEUKEMIA CELLS
Authors: Qiu Kang , Traul Donald L. , Sieber Fritz
Published: January 2008

Abstract—

L1210 leukemia cells were synchronized by a double thymidine block technique and then characterized with regard to their susceptibility to merocyanine 540 (MC540)‐sensitized photo‐inactivation. Cells harvested 5 (G2/M phase) h after release from the second thymidine block were most susceptible to MC540‐sensitized photoinactivation followed, in order of decreasing sensitivity, by cells harvested 2 (S phase) h and by cells harvested 7 (G1 phase) h after release from the second block. The expression of dye‐binding sites changed very little during the cell cycle.
FLAVIN‐SENSITIZED PHOTOCHEMICALLY INDUCED DYNAMIC NUCLEAR POLARIZATION DETECTION OF PYRIMIDINE DIMER RADICALS
Authors: Hartman R. F. , Rose S. D. , Pouwels P. J. W. , Kaitein R.
Published: January 2008

Abstract—

A photochemically induced dynamic nuclear polarization (photo‐CIDNP) study of carb‐oxymethyllumiflavin‐sensitized splitting of pyrimidine dimers has been carried out. In aqueous solution at high pH, an emission signal (δ 3.9 ppm) was observed from the dimer C(6)‐ and C(6′)‐protons of an N(l),N(1′)‐trimethylene‐bridged thymine dimer (1). The dimer photo‐CIDNP signal was seen only above pD 11.6 and was most intense at pD 12.9. Also observed were weak enhanced absorption signals from the product of splitting, trimethylenebis(thymine) (8 1.7 and 7.2 ppm). In contrast, cis, syn‐thymine dimer (3) gave no photo‐CIDNP signals from the dimer. An enhanced absorption at 1.8 ppm. however, due to the product of splitting (thymine) was observed. It was found that dimer 1 and, to a lesser extent, dimer 3 quenched flavin fluorescence. An N(3),N(3′)‐dimethylated derivative of 1, however, failed to quench flavin fluorescence. Comparison of the pD profile of the dimer photo‐CIDNP signal to the pKa values for thymine dimer suggested that principally the dideprotonated dimer undergoes electron abstraction by the excited flavin.
FLUORESCENCE SPECTROSCOPY OF STABLE AND LABILE PHYTOCHROME IN STEMS AND ROOTS OF ETIOLATED CRESS SEEDLINGS*
Authors: Sineshchekov Vitally A. , Rüdiger Wolfhart
Published: January 2008

Abstract—

Low‐temperature (80 K) fluorescence belonging to the red light‐absorbing phytochrome form (Pr) with the emission maximum at 684 nm in stems and at 682 nm in roots was detected and described in etiolated cress seedlings. By monitoring fluorescence intensity, Pr concentration changes in stems and roots were followed during etiolated growth of seedlings. In both tissues, the changes have the same characteristics, reaching maximum concentration in stems, 37 ± 4 μ g/g fresh weight (f.w.), and in roots, 6.2 ± 1.2 μ g/g f.w., 48 h after sowing. Red (660 nm) preillumination of the sample leads to a decrease of the phytochrome content in 3 h of incubation in darkness to 29 ± 6% in stems and 59 ± 5% in roots compared with that in the red‐far‐red illuminated control samples. Assuming identical fluorescence properties, the proportion of the labile and stable pools was calculated to be 90% and 10% in stems and ˜50% in roots, respectively. It was furthermore deduced that the absolute concentration of the stable pool is about the same in both tissues, 3.1–3.7 μg/g f.w., while that of the labile pool is approximately 10 times higher in stems than in roots. Comparison of the results with data on the dependence of the photophysical and photochemical properties of phytochrome on its localization in etiolated seedlings (Sineshchekov and Sineshchekov, 1990, J. Photochem. Photobiol. 5, 197–217) suggests that the labile and stable pools correspond to the Pr states with low and high activation barriers of the photoreaction, Ea, 3–4 kJ/mol, and ca 35 kJ/mol, and with high and low photochemical activity at 80 K. The two pools also differ in the position of their fluorescence emission and excitation spectra, those of the stable pool being shifted 2 nm to the blue region.
PHYTOCHROME STATES IN ETIOLATED PEA SEEDLINGS: FLUORESCENCE AND PRIMARY PHOTOREACTIONS AT LOW TEMPERATURES
Authors: Sineshchekov Vitally A. , Akhobadze Victor V.
Published: January 2008

Abstract—

Emission spectra of the red phytochrome form (Pr) and fluence time‐response curves of the Pr fluorescence intensity changes were measured in etiolated pea seedlings at low temperatures (80–150 K) in connection with its phototransformations into the initial photoproduct (Lr) and back upon actinic red (667 nm) and far‐red (696 nm) illumination. The variable fluorescence reaches 45% at 85 K and decreases with the rise of temperature. Three kinetic components of the changes were found in the direct (Pr→Lr) and back (Lr→Pr) photoreactions belonging to three states of phytochrome: “slow”, “fast” and “very fast” (respective indices: s, f and vf). The amplitudes of the components and rate constants to reach photoequilibrium were determined in the direct and back photoreactions at different temperatures, and from this, their quantum yields, extent of the Pr↔Lr phototransformation and activation energy of the reactions were evaluated for the three Pr and Lr states. The yields differ from each other by approximately a factor of 10 and those for the direct and back photoreactions are close to each other. The proportion of the amplitudes of the variable fluorescence of the three phytochrome states changes with temperature and upon the Pr→Lr photo‐transformation and the Pr states differ in the position of their emission spectra by 3–5 nm. A close similarity between the Pr and Lr properties was observed, which implies a symmetrical scheme of their photoreactions. It is suggested that the three phytochrome species may originate in different conformational states of the chromophore and they independently transform in parallel photoreactions into the respective photoproducts: Prvf↔Lrvf, Prf↔Lrf and Prs↔Lrs.
CALCIUM‐REGULATED NUCLEAR ENZYMES: POTENTIAL MEDIATORS OF PHYTOCHROME‐INDUCED CHANGES IN NUCLEAR METABOLISM?
Authors: Roux Stanley J.
Published: January 2008

Abstract—

Calcium ions have been proposed to serve as important regulatory elements in stimulus‐response coupling for phytochrome responses. An important test of this hypothesis will be to identify specific targets of calcium action that are required for some growth or development process induced by the photoactivated form of phytochrome (Pfr). Initial studies have revealed that there are at least two enzymes in pea nuclei that are stimulated by Pfr in a Ca2+‐dependent fashion, a calmodulinregulated nucleoside triphosphatase and a calmodulin‐independent but Ca2+‐dependent protein kinase. The nucleoside triphosphatase appears to be associated with the nuclear envelope, while the protein kinase co‐purifies with a nuclear fraction highly enriched for chromatin. This short review summarizes the latest findings on these enzymes and relates them to what is known about Pfr‐regulated nuclear metabolism.
SYNTHESIS AND EVALUATION OF 2‐DIAZO‐3,3,3‐TRIFLUOROPROPANOYL DERIVATIVES OF COLCHICINE AND PODOPHYLLOTOXIN AS PHOTOAFFINITY LABELS: REACTIVITY, PHOTOCHEMISTRY, AND TUBULIN BINDING
Authors: Hahn Klaus M. , Hastie Susan Bane , Sundberg Richard J.
Published: January 2008

Abstract— Derivatives of the tubulin polymerization inhibitors colchicine and podophyllotoxin bearing the photoreactive 2‐diazo‐3,3,3‐trifluoropropanoyl (DTFP) group were synthesized for evaluation as potential photoaffinity labels of the tubulin binding site. All labels were assayed for their ability to inhibit tubulin polymerization, and N‐DTFP‐deacetylthiocolchicine was shown to competitively inhibit tubulin‐colchicine binding with a Ki of 4–5 μM. The tubulin off‐rate of this analog was similar to that of podophyllotoxin, rather than to the relatively irreversibly bound colchicine. Photochemical solvent insertion reactions of the labels were investigated. Radioactive samples of the two most active labels were prepared and used in initial protein‐labeling experiments, during which the fractional occupancy of tubulin and extent of covalent incorporation were determined. A rearrangement of DTFP amides was encountered which is relevant to the utility of this moiety for use in synthesis of photoaffinity labels.
PHOTOTOXIC AND PHOTOCHEMICAL PROPERTIES OF SANGUINARINE*
Authors: Arnason J. T. , Guèrin B. , Kraml M. M. , Mehta B. , Redmond R. W. , Scaiano J. C.
Published: January 2008

Abstract— Sanguinarine, a commercial drug exhibiting antimicrobial and antitumor properties, was studied with respect to its basic photochemical characteristics and also with regard to its phototoxicity to mosquito larvae (Aedes atropalpus). Sanguinarine proved to be clearly phototoxic to larvae, with an LD50 of 0.096 mg/mL with near UV exposure as compared with 23.3 mg/mL without. Flash photolysis experiments enabled the study of the triplet state of sanguinarine to be undertaken. Quenching by oxygen occurs with a rate constant of 6 × 109M‐1s‐1 time‐resolved emission studies indicate that sanguinarine produces a significant amount of singlet oxygen (ΦΔ= 0.16) as does the isoquinoline alkaloid, berberine (ΦΔ= 0.25). These values represent the first direct quantitative measurements of photosensitization parameters of these compounds. Additionally, sanguinarine exhibits efficient electron donation properties, undergoing reaction with methyl viologen with a rate constant > 1010M‐1s‐1 but is a poor electron acceptor. Phototoxicity of sanguinarine can thus be explained in terms of its photosensitization properties.
DODECYLPYRIDINIUM ALKANOATES STABILIZE DISPERSED CHLOROPHYLL
Authors: Seely G. R. , Rehms A. A.
Published: January 2008

Abstract— In the presence of a surfactant that does not ligate Mg, chlorophyll is adsorbed to polyethylene particles swollen with tetradecane principally as the infrared‐absorbing, highly polymeric species Chl 740. Examples of such surfactants are quaternary ammonium salts and soaps. However, when surfactants of opposite charge are present together, in this case dodecylpyridinium iodide and Na butyrate or myristate, chlorophyll may exist entirely in a dispersed form absorbing around 666 nm. Absorption and fluorescence spectral data show that much of the dispersed pigment is still associated, but as dimeric and perhaps short oligomeric species. It is concluded from fluorescence lifetime analysis that most of the observed fluorescence comes from a small population of chlorophyll that is probably monomelic and isolated; fluorescence of more highly associated species decays with a wide range of lifetimes. The capacity for photochemical sensitization of these particles with dispersed chlorophyll is similar to that of particles with ligating surfactants examined earlier. Structures are suggested for chlorophyll association in which Mg is ligated by water hydrogen‐bonded to a carboxylate group, while the dodecylpyridinium counterion lies near the chlorophyll ring. The effect of the two surfactants is synergistic. Overall, spectra of dispersed chlorophyll adsorbates resemble most closely those of colloidal chlorophyll suspensions prepared by dilution of solutions in polar organic solvents with water.
VARIATIONS IN THE CHEMICAL PROPERTIES OF WOOL FIBERS INDUCED BY SUNLIGHT DURING GROWTH
Authors: Weatherall I. L. , Dunn L. A.
Published: January 2008

Abstract— Changes in the properties of wool caused by weathering during growth have been investigated by comparing fibers from animals reared under normal outdoor conditions with those reared indoors in darkness. The sunlight induced alteration in the levels of protein cross‐linking which were observed in whole fibers was also manifest in end‐to‐end variations in these properties. The results suggest that longitudinal variations in chemical properties might be regarded as a normal characteristic of wool fibers grown in sunlight.
PHOTOCHEMISTRY OF trans‐[Rh(BIS(DIPHENYLPHOSPHINO)ETHANE)2X2][PF6]: TRANSIENT ABSORBANCE KINETIC STUDIES OF METAL‐HALOGEN BOND HOMOLYSIS
Authors: Bao Feng , Kubiak Clifford P.
Published: January 2008

Abstract— Laser flash photolysis of trans‐[Rh(dppe)2X2][PF6] (X=Br and I; dppe=bis(diphenylphosphino)ethane) in CH2Cl2 or CH3CN produces the d7 Rh(II) radicals, [Rh(dppe)2X]+, and halogen atoms. The kinetics of the disappearance of [Rh(dppe)2X]+ radicals in CH2Cl2 or CH3CN were mixed order: H‐atom abstraction from solvent to produce the rhodium hydrides, [RhH(dppe)2X][PF6], and Rh/X recombination. In the poor H‐atom donor solvent, benzonitrile, Rh/Br recombination was observed to be uncomplicated by competing H‐atom abstraction. The hydride complexes [RhH(dppe)2X][PF6], formed by H‐atom abstraction were completely characterized by 31P{1H}‐NMR, 1H‐NMR, and mass specrometry. Cyclohexene was used as an effective trap for photogenerated Br atoms and yielded bromocyclohexane and 3‐bromocyclohexene in a relative yield, 1:9. The photochemical mechanism is discussed in light of the transient absorbance and trapping studies.
ESTIMATION OF THE OPTICAL PARAMETERS AND LIGHT GRADIENTS IN LEAVES: MULTI‐FLUX versus TWO‐FLUX TREATMENT
Authors: Remisowsky Alexander Martinez v. , McClendon John H. , Fukshansky Leonid
Published: January 2008

Abstract— Parameters of light propagation in plant leaves—absorption and scattering coefficients, asymmetry of scattering—have been estimated on the basis of measured transmission and remission as well as internal fluxes. This estimation has been carried through by solving the inverse problem of the 4‐flux radiative transfer—a theory considering forward and backward diffuse as well as directed components of the overall radiation in a multiply scattering sample. Using the gained parameters, light flux gradients in a two‐layered model leaf have been calculated at different wavelengths. Monte Carlo simulation of absorption spectra performed with the parameters obtained with this treatment is in a good agreement with experimental spectra, thus substantiating the theory. Parallel calculations with the two‐flux (Kubelka‐Munk) theory provide an estimation of the accuracy and applicability of this more simple treatment. Calculations have been performed for two different plants.
PHYSIOLOGICAL CHARACTERIZATION OF A HIGH‐PIGMENT MUTANT OF TOMATO
Authors: Peters Janny L. , Schreuder Marielle E. L. , Verduin Sebastiaan J. W. , Kendrick Richard E.
Published: January 2008

Abstract— A high‐pigment (hp) mutant, which shows exaggerated phytochrome responses and three other genotypes of Lycopersicon esculenrum Mill. cv. Ailsa Craig: the aurea (au) mutant deficient in the bulk light‐labile phytochrome (PI) pool, the au, hp double mutant, and their isogenic wild type, were used in this study. Measurements of phytochrome destruction in red light (R) revealed that the exaggerated responses of the hp mutant are not caused by a higher absolute phytochrome level or a reduced rate of phytochrome destruction. Fluence‐response relationships for anthocyanin synthesis after a blue‐light pretreatment were studied to test if the hp mutant conveys hypersensitivity to the far‐red light (FR)‐absorbing form of phytochrome (Pfr), i.e. the threshold of Pfr required to initiate the response is lower. The response range for the hp mutant and wild type was identical, although the former exhibited a 6‐fold larger response. Moreover, the kinetics of anthocyanin accumulation in continuous R were similar in the wild‐type and hp‐mutant seedlings, despite the latter accumulating 9‐fold more anthocyanin. Since the properties of phytochrome are the same, the hp mutation appears to affect the state of responsiveness amplification, i.e. the same amount of Pfr leads to a higher response in the hp mutant. We therefore propose that the hp mutation is associated with an amplification step in the phytochrome transduction chain. Escape experiments showed that the anthocyanin synthesis after different light pretreatments terminated with a R pulse was still 50% FR reversible after 4–6 h darkness, indicating that the Pfr pool regulating this response must be relatively stable. However, fluence‐rate response relationships for anthocyanin synthesis and hypocotyl growth induced by a 24‐h irradiation with 451, 539, 649, 693, 704 and 729 nm light showed no or a severely reduced response in the au and au, hp mutants, suggesting the importance of PI in these responses. We therefore propose that the capacity for anthocyanin synthesis (state of responsiveness amplification) could be established by PI, while the anthocyanin synthesis is actually photoregulated via a stable Pfr pool. The Hp gene product is proposed to be an inhibitor of the state of responsiveness amplification for responses controlled by this relatively stable Pfr species.
NONLINEAR POLARIZATION SPECTROSCOPY (FREQUENCY DOMAIN) STUDIES OF EXCITED STATE PROCESSES: THE B800–850ANTENNA OF RHODOBACTER SPHAEROIDES
Authors: Leupold Dieter , Voigt Bernd , Pfeiffer Michael , Bandilla Michael , Scheer Hugo
Published: January 2008

Nonlinear polarization spectroscopy in the frequency domain allows rate constant determinations of fast electronic energy and phase relaxations together with characterization of the type of line broadening. Application of this method to the B850 component of the isolated B800–850antenna ofRhodobacter sphaeroides at room temperature shows that B850 is inhomogeneously broadened, with homogeneous widths between 30 and 200 cm−1, depending on the spectral position of the subforms. The corresponding phase relaxation times are clearly in the subpicosecond range. There is also indication of an up‐to‐now unspecified1–5 ps energy relaxation channel per subunit.
THE MULTIPLE PIGMENT‐PROTEINS OF THE PHOTOSYSTEM I ANTENNA*
Authors: Preiss Susanne , Peter Gary F. , Anandan Shivanthi , Thornber J. Philip
Published: January 2008

A photosystem I (PS I) holocomplex was obtained from barley by ultracentrifugation of PS I‐enriched stroma lamellae on sucrose gradients. Further solubilization with glycosidic surfactants followed by Deriphat‐poly‐acrylamide gel electrophoresis (PAGE) fractionated the holocomplex into its core complex (CC I) and individual light‐harvesting I (LHC I) pigment‐protein subcomplexes. The LHC I contains chlorophyll a, all of the chlorophyll A of PS I and xanthophylls but no carotenes. Sodium dodecylsulfate PAGE analysis of the subcomplexes shows that barley LHC I is composed of at least five apoproteins having sizes between 11 and 24 kDa. Isolation of a 17 kDa LHC Ic component by Deriphat‐PAGE shows it to be a photosynthetic pigment‐protein. Room‐temperature absorption spectra indicate that LHC Ic is enriched in chlorophyll a in comparison to the LHC Ia and Ib components. The LHC Ic apoprotein is shown to be distinct from the subunit III and IV polypeptides of CC I. Analysis of PS I fractions obtained from sucrose gradients as well as from Deriphat‐PAGE indicates that in higher plants an oligomeric structure of the PS I entity exists in vitro.
A5–4 PYRIMIDINE‐PYRIMIDONE PHOTOPRODUCT PRODUCED FROM MIXTURES OF THYMINE AND 4‐THIOURIDINE IRRADIATED WITH 334 nm LIGHT
Authors: Blazek Ed Robert , Alderfer James L. , Tabaczynski Walter A. , Stamoudis Vassilis C. , Churchill Mark E. , Peak Jennifer G. , Peak Meyrick J.
Published: January 2008

The nucleoside 4‐thiouridine, present in some bacterial tRNA species, is known to be a chromophore and a target for near‐UV light‐induced growth delay and also mediates both photoprotection and near‐UV cell killing in various bacterial strains. To investigate the photoreaction of 4‐thiouridine with DNA or its precursors, we irradiated aqueous mixtures of thymine and 4‐thiouridine with 334 nm light and then separated photoproducts using two or more stages of reversed‐phase high performance liquid chromatography. The two equally abundant major photoproducts were analyzed by UV absorbance spectrophotometry, fast‐atom bombardment and electron‐impact mass spectrometry, and 1H‐ and 13C‐NMR spectroscopy, and have been identified as two diastereomers of 6‐hydroxy‐5‐[1‐(β‐D‐erythro‐pentofuranosyl)‐4′‐pyrimidin‐2′‐one]dihydrothymine (o6hThy[5‐4]Pdo), of molecular weight = 370.32. These two diastereomers, although stable at room temperature or below, are interconvertible by heating (90d̀C for 5 min) in aqueous solution. The possible biological significance of this photoproduct is discussed, and an application as a crosslinker for oligonucleotides to selectively block replication is suggested.
EFFECT OF UV IRRADIATION ON LETHAL INFECTION OF MICE WITH Candida albicans
Authors: Denkins Y. M. , Kripke M. L.
Published: January 2008

Exposure of mice to UV radiation inhibits the induction and elicitation of the delayed‐type hypersensitivity (DTH) response to Candida albicans. To determine whether UV irradiation also affects the pathogenesis of systemic C. albicans infection, C3H mice were exposed to a single dose of 48 kJ/m2 UV‐B radiation from FS40 sunlamps 5 days before or 5 days after sensitization with formalin‐fixed C. albicans and challenged intravenously (i.v.) with a lethal dose of viable fungi 6 days after sensitization (11 or 1 days after UV irradiation). Exposing unsensitized mice to UV radiation 11 days before lethal challenge had no effect on survival, but the survival time of mice exposed to UV radiation 1 day before challenge was reduced by more than 50%. In the latter group, decreased survival time correlated with persistence of C. albicans in the brain and progressive growth of C. albicans in the kidneys. Sensitization of unirradiated mice with formalin‐fixed C. albicans extended their survival time following lethal i.v. challenge with viable C. albicans. Exposing the mice to UV radiation 5 days before sensitization did not abrogate this beneficial effect of sensitization on survival, even though it significantly reduced the DTH response. Thus, immunity to systemic infection did not depend on the ability of the mice to exhibit a DTH response to C. albicans. The beneficial effect of sensitization on survival after lethal infection was abrogated, however, in mice exposed to UV radiation 1 day before lethal challenge with C. albicans. Furthermore, these mice were unable to contain the progressive growth of C. albicuns in the kidneys, in contrast to sensitized, unirradiated mice. The induction of cutaneous inflammation with turpentine had no effect on the survival rate of mice lethally infected with C. albicans, suggesting that inflammation alone is not sufficient to decrease the survival time of C. albicans‐infected mice.
LOVASTATIN POTENTIATES THE PHOTOCYTOTOXIC EFFECT OF PHOTOFRIN II DELIVERED TO HT29 HUMAN COLONIC ADENOCARCINOMA CELLS BY LOW DENSITY LIPOPROTEIN
Authors: Biade S. , Mazière J. C. , Mora L. , Santus R. , Mazière C. , Auclair M. , Morlière P. , Dubertret L.
Published: January 2008

A 24 h preculture of HT29–18human colonic adenocarcinoma cells with the sterol synthesis inhibitor lovastatin at concentrations of 0.1‐0.5 μM markedly increased the photocytotoxic effect of photofrin II delivered to cells by low density lipoproteins. Under the same conditions, LDL binding and photofrin II (PII) uptake by HT29 cells increased about 1.8‐fold and 1.5‐fold, respectively. These results suggest that hydroxymethylglutaryl‐coenzyme A reductase inhibitors could be useful for potentiating the photodynamic therapy of tumors by PII.
INFLUENCE OF AN SiO2/CYCLOHEXANE INTERFACE ON THE PHOTOCHEMISTRY OF ANTHRACENE
Authors: Zingg S. P. , Sigman Michael E.
Published: January 2008

We have investigated the effect of added Si02 on the photochemistry of anthracene, 1, in cyclohexane. Adsorption of 1 onto the Si02 surface from cyclohexane follows a Freundlich adsorption isotherm indicating interactions between 1 and the surface over a distribution of adsorption sites. In the absence of oxygen, addition of Si02 to a cyclohexane solution of 1 leads to a significant increase in the rate of photolysis without a large concomitant change in product identity. The 9,10‐photodimer of 1 is the major product under oxygen‐deficient conditions. In the presence of oxygen, added Si02 has dramatic effects on both the photoproduct distribution and the kinetics of photodecomposition. The complicated mixture of oxygenated products formed from photolysis in oxygen‐containing slurries is proposed to arise from thermal decomposition of a single primary photoproduct, anthracene‐9,10‐endo‐peroxide. The polarity/polarizability of the Si02/cyclohexane interface is considered to be a major factor influencing the rate of photolysis in the oxygenated Si02/cyclohexane slurries.
SOLID‐STATE PHOTOCHEMISTRY OF INDOLES WITH NAPTHALENE AND PHENANTHRENE
Authors: Meng Ji‐Ben , Wang Wen‐Guang , Wang Hong‐Gen , Matsuura Teruo , Koshima Hideko , Sugimoto Iwao , Ito Yoshikatsu
Published: January 2008

Abstract— Solid‐state irradiation of mixed crystals prepared by meltinga 1:3 molar mixture of indole and phenanthrene followed by resolidifying the melt gave an adduct 2a in 13.5% yield. An adduct 2b was obtained by irradiation of the mixed crystals of 3‐methylindole and phenanthrene. Irradiation of the same mixtures of indoles and phenanthrene in solution gave no photoproduct. Irradiation of the mixed crystals of indole and naphthalene gave a similar photoadduct 3a, which was also formed in solution. The 1:1 mixed crystals of indole and phenanthrene and of indole and naphthalene were characterized by various spectroscopic methods. Among them powder X‐ray diffraction spectral analysis and differential scanning calorimetry revealed that the former mixed crystal is a simple mixture of microcrystals of indole and phenanthrene, while the latter forms a molecular compound.
SOLVENT EFFECTS ON THE TAUTOMERIZATION OF 5′‐DEOXYPYRIDOXAL. A PHOTOPHYSICAL STUDY
Authors: Segura Miguel A. Vázquez , Donoso Josefa , Muñoz Francisco , de Piérola INÉS Fernandez , Blanco Francisco Garcia , Echevarria Gerardo R.
Published: January 2008

Abstract— Absorption and fluorescence spectra of 5′‐deoxypyridoxal (DPL) in various pure solvents and mixtures were recorded both at room temperature and over the range10–65°C. The areas under the absorption bands were analyzed to obtain the mole fraction (fN, fz) of two tautomers (the zwitterionic, Z, and neutral, N, forms) in the ground state. The following spectral parameters were determined from the fluorescence spectra: Stokes shift (Δv), fluorescence quantum yield of the neutral form (QN), fluorescence ratio of the neutral to the zwitterionic form (øN/øZ) and the rate constant of tautomerization (k1) from Z to N in the excited state. Some of these parameters (fN, Δv, QN, k1) were found to depend on the proton donor character of the solvent, whereas others (øN/øZ) depended on its dipole moment. Thus, the absorption and fluorescence spectra of DPL allow one to obtain information on the polarity and the concentration of –OH groups on its environment.
HYPERICIN DERIVED TRIPLET STATES and TRANSIENTS IN ALCOHOLS and WATER
Authors: Malkin Jacob , Mazur Yehuda
Published: January 2008

Abstract— Direct pulse photoexcitation of an antivirally active compound, hypericin sodium salt in ethanol, results in a short‐lived transient, attributed to a triplet state. In the presence of reducing agents, a long‐lived transient is observed, which indicates a radical anion species. In isopropanol solution, an identical triplet state is formed, accompanied by a long‐lived intermediate that consists of a semiquinone‐type radical. Laser excitation of hypericin sodium salt aggregates dispersed in water produces a very short‐lived transient, also assigned to a triplet state, which decays, leaving an absorption spectrum, indicating a radical anion species. The latter reacts with oxygen with a rate constant of k∼ 6 × 107 M‐1 s‐1, suggesting the formation of superoxide.
CHLOROPHYLL CATABOLISM. PART 3. STRUCTURE ELUCIDATION AND PARTIAL SYNTHESIS OF A NEW RED BILIN DERIVATIVE FROM Chlorella protothecoides*
Authors: Ituttaspe Josf , Engel Norbert , Matzinger Peter , Mooser Veronique , Gossauer Albert
Published: January 2008

The structure of a new red pigment produced during the “bleaching” of Chlorella protorhecoides cells has been elucidated by analytical methods as well as by in vitro isomerization into the new compound of a synthetic sample of a previously characteriLed chlorophyll a catabolite.
METABOLICALLY CONVERTIBLE LIPOPHILIC DERIVATIVES OF pH‐SENSITIVE AMPHIPATHIC PHOTOSENSITIZERS
Authors: Sahai D. , Lo J‐L. , Hagen I. K. , Bergstrom L. , Chernomorsky S. , Poretz R. D.
Published: January 2008

Abstract We propose the use of acetoxymethyl esters of pH‐sensitive amphipathic photosensitizers (PS) for photodynamic therapy (PDT). These compounds may be applicable for PDT involving endocytosis of lipophilic carriers leading to lysosomal uptakc of the esterified PS by target cells. Partial and/or total enzymatic de‐esterification may result in the extralysosomal distribution of the photoactive agents, possibly culminating in a multisite photochemical response. We report here the synthesis and properties of chlorin e6 triacetoxymethyl ester (CAME) and pheophorbide a acetoxymethyl ester (PAME). Chlorin e6 and pheophorbide a are photocytotoxic chlorins that possess free carboxylate groups and exhibit optimum wavelengths of excitation substantially red shifted relative to hematoporphyrin derivative. Acetoxymethyl esterification of chlorin e6 and pheophorbide a was accomplished with bromomethyl acetate. High‐performance liquid chromatography allowed for the purification of PAME, in 87% purity, and CAME, in 63% yield and 94% purity, as well as the detection of the presumed mono‐ and diesters of chlorin e6 as transient intermediates in the synthesis of CAME. The ultraviolet‐visible absorption, fluorescence excitation and emission, NMR and mass spectra of the chlorin e6 tnester are consistent with those expected for CAME. The pH‐sensitive amphipathicity of pheophorbide a and chlorin e6 but not CAME was demonstrated using a water/1‐octanol partition assay. The production of pheophorbide a from PAME and the sequential formation of the di‐ and monoesters and free chlorin e6 from CAME, by the action of lysosomal esterases obtained from cancer cells, demonstrate the potential of cellular enzymes to convert the lipophilic esters to pH‐sensitive amphipathic PS. It is expected that the product of the esterases' action in the acidic lysosome will be hydrophobic and tend to diffuse into the organelle membrane. Contact with the neutral pH of the adjacent cytosol will result in conversion of the PS to a more hydrophilic anionic species, presumably allowing for it lo diffuse into that compartment and partition throughout the lipophilic and aqueous compartments of the cell.
ANTIVIRAL ACTIVITY OF GILVOCARCIN V PLUS UVA RADIATION
Authors: Lytle C. David , Wagner Stephen J. , Prodouz Kristina N.
Published: January 2008

Abstract Gilvocarcin V (GV), a coumarin, is a nucleic acid photosensitizer that is phototoxic to bacteria and mammalian cells at picomolar levels in the presence of near‐UV radiation (UVA). We evaluated the effectiveness of GV plus UVA for inactivation of several viruses, including herpes simplex virus, type 1 (HSV) and the bacterial viruses φX174, T7, PRD1 and φ6. Some inactivation of the bacterial viruses was observed with UVA radiation alone (4–50% survival at 26 kJ/m2). Additional photosensitized inactivation was observed only with T7 and φ6 at 2.0 μM GV. On the other hand, HSV was photoinactivated with concentrations of GV three orders of magnitude lower (1.0 nM). Similar to the case with UV (254 nm) inactivation, the GV‐UVA survival curve for HSV indicated multicomponent inactivation kinetics, which could not be explained by photobleaching of GV. The wide range of photosensitivities of these viruses to GV cannot be adequately explained by models based only on viral nucleic acid content or presence of lipid envelopes.
LIPID‐ASSOCIATED METHYLPHEOPHORBIDE‐A (HEXYL‐ETHER) AS A PHOTODYNAMIC AGENT IN TUMOR‐BEARING MICE
Authors: Mayhew Eric , Vaughan Lurine , Panus Alice , Murray Michael , Henderson Barbara W.
Published: January 2008

Abstract Liposomes are a potential system for more selective delivery of photosensitizers (PS) to tumors. Pheo‐phorbides are one series of new PS under investigation for use in photodynamic therapy. The pharmacokinetics, anti‐tumor response and normal tissue effects of methylpheophorbide‐a‐(hexyl‐ether) (MPH) associated with negatively charged phospholipid vesicles composed of high and low transition temperature lipids were determined in mice. In some preparations monosialoganglioside, which is known to impart long circulation time to liposomes was also included. Normally water‐insoluble MPH could be quantitatively incorporated in multilamellar liposomes up to at least 20 mol MPH/mol lipid% for most liposome compositions and sonicated to form clear suspensions. Evidence from electron microscopy and entrapment of aqueous space markers indicated that the particles formed by sonication were not standard liposomes. Anti‐tumor responses to light treatment (135 J/cm2, 665 nm argon‐dye laser) 24 h after MPH (0.4 μmol/kg) administration were slightly but significantly greater (P < 0.05) for lipid associated MPH compared to MPH solubilized in Tween 80. There were no major differences in tumor uptake and tumor cell photosensitization between lipid or Tween 80 formulations of MPH, whereas, dependent on lipid composition and time after MPH administration, the doses of light required to cause occlusive vascular damage were increased for the lipid formulations. Pharmacokinetic studies showed rapid dissociation between lipids and MPH in vivo. Lipid formulations are useful for solubilizing MPH and may improve the therapeutic effects of this PS.
USE OF POTASSIUM IODIDE AS A CHEMICAL ACTINOMETER
Authors: Rahn R. O.
Published: January 2008

Abstract Aqueous solutions of KI were examined for use as chemical actinometers to measure 254 nm (germicidal) radiation. Irradiation results in electron ejection from iodide such that aqueous electrons and iodine atoms are formed. In the presence of N20, an electron scavenger, recombination of these two reactive species is eliminated and stoi‐chiometric formation of triiodide occurs. The absorbance increase due to triiodide was followed and the quantum yield determined using either a radiometer or ferrioxalate actinometry to estimate the amount of energy absorbed by the KI solution. The quantum yield (ø) at 25°C was determined to be 0.26 using radiometry, and 0.224–0.233 using actinometry, depending on the radiation conditions. The following expression was used to measure the incident Huence rate for 254 radiation at a given temperature T for irradiation over a time interval Δt (s) fluence rate (W/m2) = 4. 96 × 106ΔOD(λ)/ e(λ) [0.23+0.004(T‐25)] δ t cm−1

At temperatures other than 25°C, the temperature dependence of the quantum yield (0.004/°C) is taken into account by the term shown in the denominator. Because KI remains relatively blind to longer wavelengths such as those found in normal room light, measurements can be made in the presence of room light without having to work in a darkened room.