bluuebunny/crossref_metadata_2025_split huggingface dataset:
TRANSLATIONAL MOBILITY IN THE ADSORBED STATE. BIMOLECULAR DEACTIVATION KINETICS OF LASER‐EXCITED AZAAROMATICS ON MICROPOROUS SILICA*
Authors: Oelkrug D. , Gregor M. , Reich S. 
Published: January 2008

AbstractA series of polycondensed aromatic N‐heterocycles (acridine, benzo‐f‐quinoline 1,2,7,8‐dibenzacridine and 3,4,5,6‐dibenzacridine) were adsorbed from the gas phase and from liquid solution on highly dispersed silica gels with very different specific surface areas and pore sizes. The translational mobility of the adsorbed species was quantified by the triplet decay and the delayed fluorescence following bimolecular triplet‐triplet annihilation after pulsed laser irradiation. The decay kinetics were analyzed with conventional second order rate equations and with the fractal approach. The first method is reliable without limitations on adsorbents with large pore diameters. It yields second order annihilation constants of 4 times 1012‐6 times 1011 dm2 mol−1 s−1 depending on the masses and sterical requirements of the adsorbates. For the second method a spectral dimension ds= 4/3 was used. This method is quantitatively applicable to all heterocycles adsorbed on silica gel 60 that have very small pore sizes. An activation energy of 4.9 ± 0.5 kcal mol−1 was obtained for the translational diffusion of acridine on hydroxylated silica gel.
KINETICS OF LUMINESCENCE QUENCHING IN MICELLAR ASSEMBLIES INCLUDING EXCHANGE OF PROBE and QUENCHER*
Authors: Gehlen M. H. , Auweraer M. Van der , Schrwer F. C. De 
Published: January 2008

AbstractThe luminescence decay of excited probes in micelles in the presence of a Poisson distribution of quenchers is considered under conditions where both probe and quencher within the lifetime of the excited probe may exchange between the micelles. Analytical and numerical results show that the luminescence decay can be expressed by a generalized self convolution product of a multiexponential decay function.
INTERACTION BETWEEN CHLOROPLAST BIOGENESIS and PHOTOREGULATION OF AMYLASES IN Pennisetum americanum LEAVES*
Authors: Vally K. J. M. , Sharma R. 
Published: January 2008

AbstractIn 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

AbstractThe 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

AbstractIn 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

AbstractThe 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.
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.
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.
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

AbstractNonlinear 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

AbstractA 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

AbstractThe 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.