bluuebunny/crossref_metadata_2025_split huggingface dataset:
RESONANCE RAMAN AND SURFACE‐ENHANCED RESONANCE RAMAN SPECTROSCOPY OF HYPERICIN
Authors: Raser Lydia N. , Kolaczkowski Stephen V. , Cotton Therese M. 
Published: January 2008

Abstract—Hypericin has been found to exhibit a variety of photodynamic effects. To correlate biological activity with molecular structure, complete physical characterization of hypericin is required. The vibrational spectrum has been determined and resonance Raman and surface enhanced resonance Raman scattering spectra are reported. In addition, the Raman spectrum of a model compound has been studied to facilitate assignment of the vibrational modes of hypericin.
RETENTION AND PHOTOTOXICITY OF TETRA(4‐SULFONATOPHENYL)PORPHINE IN CULTIVATED HUMAN CELLS. THE EFFECT OF FRACTIONATION OF LIGHT
Authors: Berg Kristian , Madslien Kari , Moan Johan 
Published: January 2008

Abstract—Human cervix carcinoma cells of the line NHIK 3025 were incubated for 18 h with tetra(4‐sulfonatophenyl)porphine (TPPS4) and further incubated for 1–29 h in sensitizer free medium before exposure to light. After 1 h in sensitizer free medium only a 20% further loss of TPPS4was observed within the next 28 h. During the time in senzitizer free medium, each TPPS4molecule became more efficient in sensitizing single cells to photoinactivation. This enhanced photosensitizing efficiency of TPPS4correlated well with the enhanced fluorescence yield of TPPS4. In some experiments the cells were exposed to a light dose inactivating 10% of the cells after incubation for 1 h in sensitizer free medium and a second graded light dose given 4–28 h later. Exposure of the cells to the first light dose led to loss of 60% of TPPS4from the cells. Despite the significant loss of sensitizer from the cells the fluorescence yield of TPPS4from each cell was found to increase (e.g. by 100% 4 h after light exposure). The enhanced fluorescence yield of cell bound TPPS4was followed by a 1.6–2.5‐fold increase in sensitivity of each cell to a second light dose. Thus, a small light dose increased the photosensitivity of TPPS4‐loaded NHIK 3025 cells for several hours after the first light exposure. The advantageous effect of light fractionation was reduced by a significantly enhanced loss of sensitizer induced by the first light exposure. The optimal time between the two fractions of light seems to be 30–90 min.
In vitroANDin vivoULTRAVIOLET‐INDUCED ALTERATIONS OF OXY‐ AND DEOXYHEMOGLOBIN
Authors: Kollia N. , Baqer A. , Sadiq I. , Sayre R. M. 
Published: January 2008

Abstract—Ultraviolet (UV) radiation was found to convert oxyhemoglobin and deoxyhemoglobin stoichiometrically into methemoglobin and a met‐like product, respectively. The peak conversion efficiency for oxyhemoglobin occurred at 285 nm and decreased by a factor of 100 by 315 nm. The peak conversion efficiency for deoxyhemoglobin occurred at 290 nm and decreased by a factor of 30 by 320 nm. The transformation of oxyhemoglobin to methemoglobin was also documented in intact erythrocytes using UV‐B radiation. Finally, similar transformations were found to occur in human skin with UV‐B exposure but not on all volunteers tested. These results imply that methemoglobin will be formedin vivoon solar exposure and provide evidence that UV‐B photons reach the blood vessels.
PHOTOPHYSICAL PROPERTY OF SANGUINARINE IN THE EXCITED SINGLET STATE
Authors: Das A. , Nandi R. , Maiti M. 
Published: January 2008

Abstract—The photophysical property of the alkanolamine form of sanguinarine has been studied in aqueous and organic medium under various environmental conditions from the measurement of absorption, fluorescence and NMR spectroscopy. Alkanolamine fluorescence shows an excitation time dependent fluorescence quenching and the rate of quenching increases significantly with increasing pH and concentration of the species, while it decreases with increasing temperature. This phenomenon is explained by excited state intramolecular proton transfer from a 6‐O‐H group to the lone pair of nitrogen through the formation of zwitterion.
A LASER FLASH SPECTROSCOPY STUDY OF THE KINETICS OF ELECTRON TRANSFER FROM SPINACH PHOTOSYSTEM I TO SPINACH AND ALGAL FERREDOXINS
Authors: Hervás Manuel , Navarro José A. , Tollin Gordon 
Published: January 2008

Abstract—Laser flash absorption spectroscopy has been used to investigate the kinetics of electron transfer from P700 in Photosystem I (PSI)‐enriched particles from spinach to the ferredoxins from spinach and the green alga Monoraphidium braunii. Very similar behavior for the interaction of both ferredoxins with the PSI complex was observed, although the algal ferredoxin appears to be slightly more effective as an electron acceptor. For both proteins, a non‐linear protein concentration dependence of the rate constant for reduction was obtained, indicating complex formation preceding electron transfer. Estimates of 3 times 107M−1 s−1 and 140–180 s−l were obtained from these data for the second order rate constants for complex formation, and the limiting first order rate constants for electron transfer, respectively. At neutral pH, a biphasic dependence of the rate constant for ferredoxin reduction on the concentration of NaCl or MgCl2 was observed. This was interpreted in terms of the electrostatic interactions which occur between ferredoxin and the PSI membrane. In addition, magnesium cations appear to play a specific role in the interaction between PSI and ferredoxin. Thus, the addition of these ions under optimal conditions induces a 6‐f‐old increase in the electron transfer reaction rate constant, compared with a 2‐f‐old increase in the presence of an optimal amount of NaCI. This cannot be explained as arising from ionic strength effects. To our knowledge, this is the first time that a direct measurement of the rate constant for the reduction of ferredoxin by the PSI complex has been reported.
TRANSFORMATION OF A BOP‐HOP‐SOP‐I‐SOP‐II‐Halobacterium halobiumMUTANT TO BOP+: EFFECTS OF BACTERIORHODOPSIN PHOTOACTIVATION ON CELLULAR PROTON FLUXES AND SWIMMING BEHAVIOR
Authors: Yan Bin C , Cline Steven W. , Doolittle W. Ford , Spudich John L. 
Published: January 2008

Abstract—We have transformed Pho 81, aHalobacterium halobiurnmutant strain which does not contain any of the four retinylidene proteins known in this species, with thebopgene cluster to create Pho81BR, a BR'HR‐SR‐I‐SR‐11– strain. The absorption spectrum, pigment reconstitution process, light‐dark adaptation and photochemical reaction cycle of the expressed protein are indistinguishable from those of native bacteriorhodopsin (BR) in purple membrane of wild type strains. Strain Pho81BR permits for the first time characterization of effects of BR photoactivation alone on cell swimming behavior and energetics in the absence of the spectrally similar phototaxis receptor sensory rhodopsin I (SR‐I) and electrogenic chloride pump halorhodopsin (HR). A non‐adaptive upward shift in spontaneous swimming reversal frequency occurs following 3 s of continuous illumination of Pho81BR cells with green light (550 ± 20 nm). This effect is abolished by low concentrations of the proton ionophore carbonylcyanidem‐chlorophenylhydrazone. Although BR does not mediate phototaxis responses in energized Pho81BR cells under our culture conditions, proton pumping by BR in Pho81BR cells partially deenergized by inhibitors of respiration and adenosine triphosphate synthesis results in a small attractant response. Based on our measurements, we attribute the observed effects of BR photoactivation on swimming behavior to secondary consequences of electrogenic proton pumping on metabolic or signal transduction pathways, rather than to primary sensory signaling such as that mediated by SR‐I. Proton extrusion by BR activates gated proton influx ports resulting in net proton uptake in wild‐type cells. We observe a gated secondary proton influx also in Pho81BR which is deactivated byN, N'‐dicyclohexyl carbodiimide (DCCD) and heating, but is not affected by pre‐illumination. Based on previous studies, these properties exclude the known proton uptake from HR chloride pumping and the gated Na+/H+antiporter, and are consistent with H+‐ATPase activation. We do not observe a DCCD‐insensitive early proton inflow after illumination of Pho81BR cells, confirming that this previously reported proton inflow results from active chloride pumping by HR rather than from a change in the preexisting membrane potential.
PHOTOMORPHOGENIC PROCESSES IN THE AGRICULTURAL ENVIRONMENT
Authors: Ballaré Carlos L. , Scopel Ana L. , Sánchez Rodolfo A. , Radosevich Steven R. 
Published: January 2008

Abstract—We review recent advances in our understanding of how photomorphogenic mechanisms influence processes of significance for agriculture, including weed seed germination, acclimation to solar UV‐B radiation, and plant interactions in canopies.It has been demonstrated recently that seeds of some weed species acquire the ability to germinate in response to very low photon fluences during burial. Short sunlight pulses perceived by seeds during tillage appear to be important signals of soil disturbance.Regarding UV‐B acclimation there is increasing evidence for the involvement of a specific UV‐B photoreceptor in pigmentation and morphological responses to UV‐B. The protective role played by UV‐B‐induced flavonoids has been experimentally demonstrated.Concerning plant interactions in canopies it has been shown that, by perceiving light signals through phytochrome and blue‐UV‐A photoreceptors, plants obtain information about the characteristics of the surrounding vegetation well before their resources are reduced as a consequence of neighbors' activities. There appears to be a large potential for improving cropping systems by manipulating the light environment or by changing the photomorphogenic behavior of crop plants. However, relatively little is known about how the expression and agronomic significance of photomorphogenic responses are influenced by other factors of the plant's environment.
EVENTS IN THE PHYTOCHROME MOLECULE AFTER IRRADIATION
Authors: Rüdiger Wolfhart 
Published: January 2008

Abstract—The photoconversion of Pr to Pfr has been investigated by a large number of investigators. We have previously demonstrated that Z,E isomerization of the tetrapyrrole chromophore is involved in the photoconversion. It is the best candidate for the primary photoreaction. Conformation and configuration of the Pr chromophore will be compared with that of chromophores in phycocyanin. The crystal structure of phycocyanin had been elucidated by x‐ray analysis. Proton transfer and/or Z, E isomerization of the tetrapyrrole are probably involved in different steps of the photoconversion in phytochrome and in photoreversible phycobiliproteins. Fluorescence decay kinetics of irradiated Pr and intermediate formation show heterogeneity. Possible reasons for this heterogeneity will be discussed.
PHARMACOKINETICS OF FLUORESCENT POLYPORPHYRIN PHOTOFRIN II IN NORMAL RAT TISSUE AND RAT BLADDER TUMOR
Authors: Baumgartner R. , Fuchs N. , Jocham D. , Stepp H. , Unsöld E. 
Published: January 2008

Abstract—The transient behavior of the molecular components responsible for fluorescence emission of the photosensitizing polyporphyrin Photofrin II has been studied quantitatively in the liver, small intestines, bladder and muscles of rats. Relative concentrations of the substance were determined fluorometricallyin vivousing a Kr+‐laser (wavelength = 406.7 nm) and a mercury arc lamp (wavelength = 405 or 550 nm) for fluorescence excitation of Photofrin II. Fluorescence was detected at the maxima of the emission bands, at 630 or 690 nm. The results of the experiments show that Photofrin II can be clearly detected by its fluorescence in all the organs investigated from 3 h up to at least 28 days after systemic application of the substance. Within this investigational period the fluorescing components of Photofrin II are released continuously from the organs. In all the tissues examined, an initial decrease with time constants between 2 and 42 h followed by a slow decay with time constants between about 300 and 600 h can be observed.In addition the pharmacokinetics of the fluorescent components of Photofrin II in chemically induced rat bladder tumors with different stages of malignancy were compared to healthy rat bladder tissue. In a time range of 2–10 days after intraveneous injection Photofrin II shows a fluorescence 2–5 times brighter in rat bladder tumors than in healthy bladder tissue.
SHORT‐TERM ADAPTATION OF HIGHER PLANTS TO CHANGING LIGHT INTENSITIES AND EVIDENCE FOR THE INVOLVEMENT OF PHOSPHORYLATION OF THE LIGHT HARVESTING CHLOROPHYLLalbPROTEIN COMPLEX OF PHOTOSYSTEM II
Authors: Dau Holger , Canaani Ora 
Published: January 2008

Abstract—The short‐term adaptation of intact leaves to an increase in light intensity was studied by an analysis of chlorophyll fluorescence and oxygen evolution monitored by photoacoustics. An increase in light intensity led to an oxygen “gush”. This “gush” was followed by a large (up to 120%) biphasic increase in the yield of oxygen evolution characterized by a fast phase (T = 0.5–2 min) and a slow phase (T = 4–20 min). The fast phase of the increase in oxygen yield was coupled to a decrease of fluorescence, whereas the slow phase was accompanied by a parallel fluorescence increase. A comparison of fluorescence parameters with oxygen yield indicates that the slow phase of the increase in oxygen yield was coupled to an increase in the antenna size of photosystem II. The slow phase was not inhibited by the uncoupler Nigericin but it was absent in chlorophyll‐b‐less barley mutants deñcient in the light harvesting chlorophylla/bprotein complex of photosystem II (LHC II). These experiments indicate that changes in the LHC II mediated energy distribution, which occur in the time‐range of several minutes, are involved in the adaptation to changing light intensities. Moreover, electrophoretic analysis of32P orthophosphate labeled leaf discs adapted to low and high light intensities suggests that the slow phase of the increase in oxygen evolution involves dephosphorylation of the 25 kDa polypeptide of LHC II, by a small extent of 12%. The trigger for the slow phase of the increase in oxygen yield does not involve the oxidation of the plastoquinone pool. It was found that in response to the increased light intensity, the plastoquinone pool became more reduced as judged by model calculations. Experiments with the uncoupler Nigericin suggest that the control of the slow phase of adaptation to increased light intensity was also not exerted by the pH gradient across the thylakoid membrane.The similarities between the adaptation to increased light intensity and the state II to state I transition suggest that both adaptation phenomena involve LHC II dephosphorylation possibly triggered by the cytochromeb6/fcomplex.
SIMULATIONS OF Prosthecochloris BACTERIOCHLOROPHYLL a‐PROTEIN OPTICAL SPECTRA IMPROVED BY PARAMETRIC COMPUTER SEARCH
Authors: Lu Xiaoyuan , Pearlstein Robert M. 
Published: January 2008

AbstractRecently, reasonable spectral simulations of the experimental low‐temperature absorption and circular dichroism (CD) spectra of the bacteriochlorophyll (BChl) a protein from Prosthecochloris aestuarii were produced for the unaggregated protein trimer based on standard assumptions regarding QY transition moment directions. We report here significant improvements of these simulations, obtained by computer search of unknown parameters including the site wavelengths of the individual BChl and exciton‐transition line widths. Absorption and CD spectra are fit with a common set of search parameter values. As before, calculated exciton‐transition wavelengths and line widths also compare favorably with values deduced from laser hole‐burning experiments. However, the improved simulations are only obtained when comparison is made to 77 K data obtained with a cryosolvent containing glycerol but not glycerophosphate. Simulations of 77 K data obtained with a mixture of glycerol and glycerophosphate are poorer than those recently reported. (The latter are based on 5 K absorption and 77 K CD data, with transition line widths independently selected for each simulation.) Computer tests of the search routine demonstrate that these results are independent of the routine itself. A possible explanation is that the glycerophosphate‐containing cryosolvent perturbs the protein structure enough to alter slightly the inter‐BChl geometry.
ANOTHER ROLE OF CHLOROPHYLL a/b BINDING PROTEINS OF HIGHER PLANTS: THEY MODULATE PROTOLYTIC REACTIONS ASSOCIATED WITH PHOTOSYSTEM II
Authors: Jahns Peter , Junge Wolfgang 
Published: January 2008

AbstractChlorophyllalbbinding proteins serve as light‐harvesting antennae. Additionally they seem to modulate proton pumping by photosystem II, because their covalent modification byN, N‐dicyclohexylcarbodiimide is paralleled by a short‐circuit of this activity. This side action was further characterized in comparative study with control thylakoids and thylakoids lacking chlorophyllalbbinding proteins. The latter were derived from peas grown under intermittent light. They differed from controls in the following: (i) after incubation with A^A^‐dicyclohexylcarbodiimide there was no protonic short circuit, (ii) under flashing light the rate of proton consumption at the acceptor side of photosystem II was accelerated and (iii) the periodical pattern of proton release from water oxidation was flattened out. It was obvious that chlorophyllalbbinding proteins modulated the kinetics and the stoichiometry of proton release from water oxidation and proton uptake at the quinone binding pocket.
NONLINEAR LASERSPECTROSCOPIC INVESTIGATIONS OF THE PIGMENT‐PIGMENT INTERACTION WITHIN THE LIGHT‐HARVESTING COMPLEX OF PHOTOSYSTEM II
Authors: Bittner T. H. , Voigt J. , Irrgang K.‐D. , Renger G. 
Published: January 2008

AbstractUsing a pump and test beam technique in the frequency domain with pump pulses in the nanosecond time range, the nonlinear transmission properties were investigated at room temperature in photosystem (PS) II membrane fragments and isolated light‐harvesting chlorophylla/b‐protein preparations (LHC II preparations). In LHC II preparations and PS II membrane fragments, respectively, pump pulses of 620 nm and 647 nm cause a transmission decrease limited to a wavelength region in the nearest vicinity of the pump pulse wavelength (full width at half maximum ' 0.24 nm). In contrast, at 670 nm neither a transmission decrease nor a narrow band feature were observed. The data obtained for PS II membrane fragments and LHC II preparations at shorter wavelengths (620 nm, 647 nm) were interpreted in terms of excited state absorption of whole pigment‐protein clusters within the light‐harvesting antenna of photosystem II. The interpretation of the small transmission changes as homogeneously broadened lines led to a transversal relaxation time for chlorophyll in the clusters of about 4 ps.
ATTEMPTED BIOSTIMULATION OF DIVISION IN Saccharomyces cerevisiae USING RED COHERENT LIGHT
Authors: Quickenden T. I. , Danniels L. L. 
Published: January 2008

AbstractReplicate cultures of the yeast, Saccharomyces cerevisiae were irradiated with 632.8 nm coherent light from He‐Ne lasers at irradiances of 6.5 times 1015 and 1.0 times 1016 photons s−1 cm−2. Irradiation periods ranged from 0 to 652 min, and cultures were grown until well into the exponential phase. Unirradiated control cultures were grown alongside the irradiated cultures under otherwise identical conditions. The extents of growth in the control and irradiated cultures were compared spectrophotometrically at the end of each experiment. contrary to the expectations of Karu et al. (e.g. Karu, 1988, Lasers Life Sci.2, 53–74) no growth enhancement was found in the irradiated cultures, but a mild inhibitory effect was observed.
PHOTOACTIVABLE FLUOROPHORES FOR THE MEASUREMENT OF FLUENCE IN TURBID MEDIA
Authors: Lilge L. , Flotte T. J. , Kochevar I. E. , Jacques S. L. , Hillenkamp F. 
Published: January 2008

AbstractKnowledge of the fluence distribution in biological tissue is essential for applications of lasers and light in medicine. A method using a photoactivable fluorophore as a chemical actinometer is presented to investigate the fluence (J/cm2) distribution in tissue‐simulating phantoms. Such a chemical actinometer provides high spatial resolution (≤20 μm) while minimizing the disturbance of the fluence distribution. The actinometer substance, nonfluorescent in its native state, is incorporated into an acrylamide gel. Upon absorption of 351 nm radiation (λact), the actinometer substance becomes a Ruorophorc, which is excited at λex≤ 485 nm. Thus the spatial distribution of the emitted fluorescence (λem≤ 515 nm) in the actinometer represents the fluence distribution of the activating radiation. Using histological techniques, 20 μm sections are cut from gel‐like optical phantoms containing the actinometric substance. The fluorescence intensity in the section is recorded under a standard fluorescence microscope equipped with a sensitive video camera. To simulate different biological tissues, the scattering and absorption properties of the gel phantoms arc varicd over a wide range. The experimentally obtained fluence distributions are compared with theoretical models of light distribution in turbid media.
PHOTOLESIONS IN DNA UPON 193 nm EXCITATION
Authors: Gurzadyan Gagik G. , Görner Helmut 
Published: January 2008

AbstractAqueous solutions of plasmid (pBR322 and pTZ18R) and calf thymus DNA were excited by 20 ns laser pulses at 193 nm. The quantum yields of single‐ and double‐strand break formation, interstrand cross‐links, locally denatured sites, (6–4)photoproducts and biological inactivation (Φssb, Φdsb, Φicl, Φids, Φ6–4and Φina, respectively) were measured. The quantum yields are virtually independent of intensity, demonstrating a one‐quantum process. The obtained values in aerated neutral solution in the absence of additives are Φssb= 1.5 × 10‐‐3, Φdsb, = 0.06 × 10‐‐3(dose: 10–200 J m‐2), Φicl=ΦIds= 0.1 × 103and Φ6–4= 0.5 × 10‐‐3Both Φssband Φdsbdecrease strongly with increasing concentrations of TE buffer (0.01–10 mM). Biological inactivation of the pTZ18R plasmid was determined from the transformation efficiency ofEscherichia colibacteria strains AB1157, AB1886 uvr and A82480 uvr rec; the Φinavalues are 1.4 × 103, 2.1 × 103and 3 × 10‐‐3, respectively. The monoexponential survival curves in all cases show that a single damage site leads to inactivation (one single hit). The biological consequences of different photoproducts are discussed.