bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of Carotenoid Triplet States in the Light‐Harvesting Complex B800–850from the Purple Bacterium Rubrivivax gelationsus
Authors: Jirsakova Vladimira , Reiss‐Husson Françoise , Dijk Bas van , Owen Gabrielle , Hoff Arnold J. 
Published: January 2008

AbstractThe carotenoid triplet states in the light‐harvesting complex B800–850from purple bacterium Rubrivivax gelatinosus were characterized by absorption‐detected magnetic resonance in zero magnetic field (ADMR) spectroscopy. Detailed HPLC analysis of carotenoids from B800–850demonstrated the presence of several carotenoids bound to the complex: the major ones are hydroxyspheroidene and spheroidene (together 80%), followed by neurosporene and hydroxyneurosporene (7%), spheroidenone and hydroxyspheroidenone (7.5%) and two other minor carotenoids that could be 3,4‐dihydrospheroidenone and 3,4‐dihydrohydroxyspheroidenone (5.5%). Three triplet states originating from carotenoids present in the B800–850were observed. The identical T‐S spectra recorded at selectively chosen 2|E| transitions of carotenoids indicated that all these triplet states can be attributed to three different populations of one carotenoid family, probably to spheroidene and to hydroxyspheroidene, with different out‐of‐plane distortions of their polyene chain due to a different protein environment. Triplet states of the neurosporene and the spheroidenone families are probably not observed because of the low signal amplitude.
Multiphoton‐Excited Visible Emission by Serotonin Solutions
Authors: Shear Jason B. , Xu Chris , Webb Watt W. 
Published: January 2008

ABSTRACTNonlinear excitation of the neurotransmitter serotonin (5HT) in aqueous solution is shown to generate a blue‐green‐emitting photoproduct in addition to UV fluorescence characteristic of native 5HT. The visible emission rate in diffusional steady‐state measurements scales as the sixth power of excitation intensity, demonstrating that absorption of six near‐IR photons is required to generate emission of one visible photon. Transient measurements reveal that this process is composed of two sequential nonlinear steps, the first excited by four photons and the second by two photons. These results, in combination with measurements of multiphoton‐excited serotonin UV fluorescence, support a model in which 5HT is photochemically transformed as a consequence of four‐photon absorption (Etot≅6 eV) to a photoproduct that then emits in the visible region via two‐photon excitation. A minimum bound of ˜10‐51 cm4 s photon‐1 is observed for the two‐photon emission action cross section at 830 nm. Photoionization, rather than reaction with a dissolved oxygen species, appears to be the primary mechanism for generation of the blue‐green‐emitting photoproduct. The peak intensities required to generate significant blue‐green emission (˜5 times 1011 W cm‐2 from 80 MHz 150 fs titanium: sapphire laser pulses) are approximately five‐fold higher than are typically used in two‐photon laser scanning microscopy but are still substantially lower than the estimated intensity needed to induce dielectric breakdown of water.
Photoreactivating Enzyme for (6–4) Photoproducts in Cultured Goldfish Cells
Authors: Uchida Nobuhiro , Mitani Hiroshi , Todo Takeshi , Ikenaga Mituo , Shima Akihiro 
Published: January 2008

ABSTRACTWe previously reported that when cultured goldfish cells are illuminated with fluorescent light, photorepair ability for both cyclobutane pyrimidine dimers and (6–4) photoproducts increased. In the present study, it was found that the duration of the induced photorepair ability for cyclobutane pyrimidine dimers was longer than that for (6–4) photoproducts, suggesting the presence of different photolyases for repair of these two major forms of DNA damage. A gel shift assay was then performed to show the presence of protein(s) binding to (6–4) photoproducts and its dissociation from (6–4) photoproducts under fluorescent light illumination. In addition, at 8 h after fluorescent light illumination of the cell, the binding of pro‐tein(s) to (6–4) photoproducts increased. The restriction enzymes that have recognition sites containing TT or TC sequences failed to digest the UV‐irradiated DNA pho‐toreactivated by using Escherichia coli photolyase for cyclobutane pyrimidine dimers, indicating that restriction enzymes could not function because (6–4) photoproducts remained in recognition sites. But, when UV‐irradiated DNA depleted of cyclobutane pyrimidine dimers was incubated with extract of cultured goldfish cells under fluorescent light illumination, it was digested with those restriction enzymes. These results suggested the presence of (6–4) photolyase in cultured goldfish cells as in Dro‐sophila, Xenopus and Crotalus.
In vivo Laser‐induced Fluorescence Imaging of a Rat Pancreatic Cancer with Pheophorbide‐a
Authors: Tassetti V. , Hajri A. , Sowinska M. , Evrard S. , Heisel F. , Cheng L. Q. , Miehe J. A. , Marescaux J. , Aprahamian M. 
Published: January 2008

ABSTRACTLaser‐induced fluorescence (LIF) of pheophorbide‐a (Ph‐a) was used for imaging of a rat pancreatic tumor. Using a dimensionless function (the ratio of Ph‐a fluorescence by bluish autofluorescence), the fluorescence contrasts between excised tumors and their paired pancreas were investigated up to 48 h after a 9 mg kg‐1 Ph‐a intravenous administration. Among five tested excitation wavelengths, 355 and 610 nm excitations gave the best distinctive contrasts, both 48 h after dye injection. The LIF imaging of six intrapancreatic tumors and six healthy pancreas was carried out in vivo using two laser excitations: 355 nm (Nd:YAG + tripling) for bluish autofluorescence and 610 nm (rhodamine 6G dye) for reddish autofluorescence and dye emission. Images were recorded through bandpass filters at 470 and 640 nm (autofluorescence) and at 680 nm (dye + autofluorescence) with an intensified charged‐coupled device camera. Autofluorescence as Ph‐a fluorescence images did not allow accurate LIF diagnosis of pancreatic carcinoma. An image processing, including for each pixel a computed division of Ph‐a fluorescence (after subtraction of reddish autofluorescence) by bluish autofluorescence intensity generated poorly contrasted tumor images in five of six and false tumor localization in one of three of the tumor‐bearing pancreas. A fitting of the digital 640 nm autofluorescence up to the mean 680 nm fluorescence intensity in pancreas prior to subtraction allowed a safe diagnosis to be made with well‐contrasted tumor images. To assess automation ability of the processing, a same fitting coefficient (mean of individual values) was applied. In this way, false‐negative (one of six) and false‐positive (two of six) images were present in tumor‐bearing animals as false‐positive in one‐half of the controls. A successful standardized procedure was then applied with a normalization of 640 and 680 nm pancreas intensities to a same set threshold prior processing. In opposition to thin‐layered hollow organs, such as bronchial tube or digestive tract, LIF imaging of carcinoma inserted in a compact organ is exhausting. The use of a dye excitable in the red wavelength range (610 nm for Ph‐a) may partly solve this problem, rendering LIF imaging more accurate and potentially automated.
Photochemical Labeling: Can Photoaffinity Labeling be Differentiated from Site‐Directed Photochemical Coupling?
Authors: Bouchet Marie‐Jeanne , Goeldner Maurice 
Published: January 2008

AbstractSite‐directed photochemical labeling is a methodology designed to irreversibly and specifically label, through the action of light, a ligand binding site of a biological mac‐romolecule. Photoaffinity labeling, a widely used site‐directed labeling methodology, uses photosensitive ligand analogs generally obtained after chemical modification of the ligand by introducing an appropriate photoactivata‐ble moiety. This methodology can be applied to natural ligands showing inherent photosensitivity, without any additional modification, and which can be linked efficiently to their receptor binding site by direct photoac‐tivation. The emergence of an alternative methodology that links nonphotosensitive ligands to their receptors has raised the question of their potential use and their mechanisms of photocoupling. This article presents a series of examples that are meant to compare the general characteristics of the different site‐directed labeling reactions and proposes distinct photochemical activation processes between photoaffinity labeling and site‐directed photochemical coupling reactions. We suggest in particular that the former is necessarily a ligand‐mediated activation process while the latter might involve a receptor‐mediated mechanism.
Mechanistic Studies Relevant to Bromouridine‐Enhanced Nucleoprotein Photocrosslinking: Possible Involvement of an Excited Tyrosine Residue of the Protein
Authors: Norris Christopher L. , Meisenheimer Kristen M. , Koch Tad H. 
Published: January 2008

AbstractThe results of mechanistic studies on formation of uridine (U) and N‐acetyl‐in‐(5‐uridinyl)tyrosine N‐ethylam‐ide (2) from irradiation of aqueous, pH 7 solutions of bromouridine (BrU) and N‐acetyltyrosine JV‐ethylamide (1) are reported. Solutions were irradiated with monochromatic laser emission at 266, 308 and 325 nm. Quantum yield measurements as a function of excitation wavelength suggest that both products result from excitation of the tyrosine derivative followed by electron transfer to BrU, possibly with intermediacy of the hydrated electron. The BrU radical anion ejects bromide to form the uri‐dinyl radical, which then abstracts a hydrogen atom from 1 or adds to the aromatic ring of 1. Formation of adduct 2 is a model for photocrosslinking of nucleic acids bearing the bromouracil chromophore to adjacent tyrosine residues of proteins in nucleoprotein complexes. The value of 325 nm excitation in photocrosslinking, where the tyrosine chromophore is more competitive for photons, was demonstrated with an RNA bound to the MS2 bacteriophage coat protein; more than a 60% increase in the yield of photocrosslinking relative to that obtained with 308 nm excitation was achieved.
Interactions between Vitamin E Homologues and Ascorbate Free Radicals in Murine Skin Homogenates Irradiated with Ultraviolet Light
Authors: Kitazawa Manabu , Podda Maurizio , Thiele Jens , Traber Maret G. , Iwasaki Keiji , Sakamoto Kazutami , Packer Lester 
Published: January 2008

AbstractThe mechanism of oxidation of ascorbic acid in mouse skin homogenates by UV light was investigated by measuring ascorbate free radical formation using electron spin resonance signal formation. Addition of vitamin E (α‐tocopherol or α‐tocotrienol) had no effect, whereas short‐chain homologues (2,5,7,8‐tetramethyl‐6‐hydroxy‐chroman‐2‐carboxylic acid [Trolox] and 2,2,5,7,8‐penta‐methyl‐6‐hydroxychromane [PMC]) accelerated ascorbate oxidation. The similar hydrophilicity of ascorbate, Trolox and PMC increased their interaction, thus rapidly depleting ascorbate. When dihydrolipoic acid was added simultaneously with the vitamin E homologues, the accelerated ascorbate oxidation was prevented. This was due to the regeneration of ascorbate and PMC from their free radicals by a recycling mechanism between ascorbate, vitamin E homologues and dihydrolipoic acid. Potentiation of antioxidant recycling may be protective against UV irradiation‐induced damage. The rate of ascorbate oxidation in the presence of vitamin E homologues was enhanced by a photosensitizer (riboflavin) but was not influenced by reactive oxygen radical quenchers, superoxide dismutase or 5,5‐dimethyl‐l‐pyrroline‐iV‐ox‐ide. These experimental results suggest that the UV irradiation‐induced ascorbate oxidation in murine skin homogenates is caused by photoactivated reactions rather than reactive oxygen radical reactions.
Simultaneous Two‐Photon Activation of Type‐I Photodynamic Therapy Agents
Authors: Fisher W. G. , Partridge W. P. , Dees C. , Wachter E. A. 
Published: January 2008

AbstractThe excitation and emission properties of several psoralen derivatives are compared using conventional single‐photon excitation and simultaneous two‐photon excitation (TPE). Two‐photon excitation is effected using the output of a mode‐locked titanium: sapphire laser, the near infrared output of which is used to promote non‐resonant TPE directly. Specifically, the excitation spectra and excited‐state properties of 8‐methoxypsoralen and 4′‐aminomethyl‐4,5,8‐trimethylpsoralen are shown to be equivalent using both modes of excitation. Further, in vitro feasibility of two‐photon photodynamic therapy (PDT) is demonstrated using Salmonella typhimurium. Two‐photon excitation may be beneficial in the practice of PDT because it would allow replacement of visible or UV excitation light with highly penetrating, nondamag‐ing near infrared light and could provide a means for improving localization of therapy. Comparison of possible laser excitation sources for PDT reveals the titanium: sapphire laser to be exceptionally well suited for nonlinear excitation of PDT agents in biological systems due to its extremely short pulse width and high repetition rate that together provide efficient PDT activation and greatly reduced potential for biological damage
Potential Involvement of Both Type I and Type II Mechanisms in M13 Virus Inactivation by Methylene Blue Photosensitization
Authors: Abe H. , Ikebuchi K. , Wagner S. J. , Kuwabara M. , Kamo N. , Sekiguchi S. 
Published: January 2008

AbstractWe have investigated the mechanism of virus photoinactivation with methylene blue (MB) by conducting deuterium oxide (D2O), azide ion (N3‐) and oxygen‐dependent, studies. Inactivation of M13 bacteriophage and singlet oxygen (1O2) generation by MB photosensitization were irradiation dose dependent. Inactivation of M13 was enhanced by D2O and inhibited by N3‐, suggesting that 1O2 participates in M13 inactivation by MB photosensitization. However, N3‐ did not inhibit M13 inactivation completely. On the other hand, deoxygenating the reaction solution still caused 52‐67% of M13 inactivation observed in the presence of oxygen. These results suggest that 102‐mediated (Type II) and sensitizer‐mediated (Type I) reactions may both play roles in M13 inactivation by MB photosensitization.
Structure‐Activity and Mechanism Studies on Silicon Phthalocyanines with Plasmodium falciparum in the Dark and Under Red Light
Authors: Zhao Xiao‐Juan , Lustigman Sara , Kenney Malcolm E. , Ben‐Hur Ehud 
Published: January 2008

AbstractSyntheses for the new photosensitizers HOSiPc‐OSi(CH3)2(CH2)3N(CH2)1 or 3(CH3)2, Pc 34 and Pc 25, have been developed and the order of activity of these photosensitizers and the previously reported photosensi‐tizer Pc 4, HOSiPcOSi(CH3)2(CH2)3N(CH3)2, in the dark and with broad‐band red light toward Plasmodium falciparum in red blood cell (RBC) suspensions has been studied. The order of activity has been found to be Pc 4 Pc 34 Pc 25. Thus, the activity of the photosensitizers under both sets of conditions is inversely proportional to the length of their terminal amino alkyl chains. The 50% inhibition dye concentration (IC50) in the dark for the parasites in RBC suspension with Pc 4 is 24 nM and the dye concentration and light fluence that yield:3 log10 of parasite inactivation with Pc 4 are 2 mM and 3 J/cm2, respectively. The synthesis of DNA and proteins by the parasites in culture was strongly inhibited by Pc 4 in the dark while parasite lactate dehydrogenase (pLDH) activity was unaffected. With Pc 4 and light, DNA and protein synthesis of the parasites in culture was strongly inhibited, pLDH activity of the parasites was moderately inhibited and ribosome density of the parasite cells was reduced. Gel electrophoresis studies showed that synthesis of all parasite proteins was inhibited to a similar extent. These results suggest that Pc 4 both in the dark and with light inactivates the cells by disturbing their machinery for the synthesis of not just one but a whole series of proteins. It is concluded that Pc 4 and light may be able to serve as a practical sterilization combination not only for HIV and other viruses but also for malaria parasites in RBC concentrates, and that Pc 4 by itself may have potential as a chemotherapeutic agent toward malaria.
Intercomparison of Effective Erythemal Irradiance Measurements from Two Types of Broad‐Band Instruments during June 1995
Authors: Wengraitis Stephen , Benedetta Danielle , Sliney David H. 
Published: January 2008

AbstractThe biologically effective global solar ultraviolet radiation (UVR) measurements from a multiband UVR monitor and a conventional broadband UVR monitor are compared. The measurements were performed during the varied weather conditions of June 1995. We compared the daily total exposures measured by both instruments, as well as the ratio of the measured doses throughout the course of each day. The daily total exposures agreed within approximately 11% throughout the month. The ratio between the measured doses held at 1.12 between 0900 and 1700 h (solar zenith angles ≅16‐52°). The ratio decreased from 1.12 to 0.90 during the next 90 min outside that period (solar zenith angles ≅52‐72°) and decreased further beyond that point. Spectral response and cosine response mismatch between the instruments are discussed as the possible cause of discrepancies between the measured doses. Implications for erythemal irradiance monitoring and suggestions for further study are discussed.
Laser Line‐Scanning Confocal Fluorescence Imaging of the Photodynamic Action of Aluminum and Zinc Phthalocyanines in V79–4Chinese Hamster Fibroblasts
Authors: Scully A. D. , Ostler R. B. , MacRobert A. J. , Parker A. W. , Lara C. de , O'Neill P. , Phillips D. 
Published: January 2008

AbstractConfocal fluorescence microscopy, using a newly constructed laser line‐scanning confocal microscope, was applied to an investigation of the early stages of photoinduced destruction of V79–4Chinese hamster fibroblasts using aluminum and zinc phthalocyanines as photosensitize. Results obtained in this work show that aluminum and zinc phthalocyanines, once internalized, localize in perinuclear sites that are disrupted upon light exposure resulting in fluorescence redistribution. The combination of laser‐line scanning with charge‐coupled device detection used in the confocal microscope developed in this work can enable rapid high‐resolution sequential imaging, which is ideal for studying photoinduced intracellular fluorescence dynamics.
Delayed Hyperresistance of Endothelial Cells to Photodynamic Inactivation After Contact with Hemin
Authors: Lin Fubao , Bertling Chad J. , Geiger Peter G. , Girotti Albert W. 
Published: January 2008

AbstractHemin (ferriprotoporphyrin IX), the oxidized prosthetic group of hemoglobin, is a potential source of prooxidant iron in heavily vascularized tumors. We have evaluated hemin's effects on photodynamic inactivation of bovine artery endothelial cells, using a partially purified oligo‐meric fraction of hematoporphyrin derivative (HPD‐A) as the sensitizing agent. Confluent cells in 5% serum/ RPMI medium showed a progressive loss of thiazolyl blue (MTT)‐detectable viability when irradiated with broadband visible light in the presence of HPD‐A. Cells pretreated with desferrioxamine (DFO) were substantially less sensitive to photokilling, implying that non‐heme iron plays a role in cytotoxic activity. Hemin (10–20μM) had remarkably different effects on photokilling, depending on the time interval between adding it to cells and exposing them to photodynamic action. For example, cells were more sensitive when photostressed immediately after 1 h hemin treatment and washing but much more resistant when photostressed 23 h later. Similar responses were observed when cells were challenged with glucose oxidase. Immunoblot analysis following hemin treatment revealed a progressive induction of the heavy (H) subunit of ferritin that paralleled the development of hyperresistance. After incubation with saturating levels of the synthetic iron donor [55Fe]ferric‐8‐hydroxyquino‐line, hemin‐stimulated cells contained about four times more immunoprecipitable ferritin 55Fe than controls. This is consistent with the notion that sequestration of toxic iron as a result of induction of H‐chain‐enriched ferritin is a key factor in hyperresistance. Inflammatory injury in tumor vasculatures could expose endothelial and neoplastic cells to chronic hemoglobin‐derived iron. Consequent upregulation of ferritin could impact negatively on the efficacy of photodynamic therapy and other oxidant‐based cancer therapies.
Modulation of Porphyrin Derivatives Accumulation in C6 Glioma Cells by Drugs Acting on β‐Adrenergic Receptors. A Spectrofluorometric Study
Authors: Croce A. C. , Mares V. , Lisa V. , Krajci D. , Bottiroll G. 
Published: January 2008

AbstractThe pharmacological modulation of the uptake of porphyrin derivatives in cultured C6 glioma cells was investigated by means of spectrofluorometric analysis both in single cells and in cell homogenates. The influence of drugs acting as β‐receptor agonists or antagonists was studied in cells grown to semiconfluency. Isoproterenol (ISO), a β‐receptor agonist, enhanced the intracellular fluorescence intensity of both Photofrin and protoporphyrin IX (PpIX). A treatment with a β‐receptor antagonist I‐propranolol (PRO), simultaneous with ISO, resulted in an intracellular Photofrin fluorescence signal comparable to that of the control cells, indicating the specificity of the pharmacological action. The pharmacological treatment seemed particularly effective with the aggregated species. This is suggested by the relative increase of the band at 670 nm, being greater than that in the 630 nm band in the emission spectra of Photofrin and PpIX, and by the comparison of the fluorescence intensity on cell homogenates measured both in the absence and in the presence of cetyltrimethyl‐ammonium bromide as a detergent.
Sensitized Photooxidation of Di‐ and Tripeptides of Tyrosine*
Authors: Criado Susana , Soltermann Arnaldo T. , Marioli Juan M. , Garcia Norman A. 
Published: January 2008

AbstractThis paper studies the dye‐sensitized photooxidation of tyrosine (tyr) and tyr di‐ and tripeptides (tyr‐tyr and tyr‐tyr‐tyr) mediated by singlet molecular oxygen (O,[l]) in alkaline media. Photooxidation quantum efficiencies (φr) were obtained by determining the overall and reactive rate constants of interaction with the oxidative species, employing the time‐resolved O,(l) phosphorescence detection method and static‐photolysis actinometric method, respectively. The interaction of O,(l)‐tyr derivatives occurs through an intermediate encounter complex with polar character. Ionization of the phenolic OH group of tyr derivatives and the polarity of the solvent favors the overall interaction. Nevertheless, & values decrease when changing from water to MeCN‐water medium. This indicates that the reactive deactivation of the encounter complex, probably an entropy‐controlled step, may be affected by solvent polarity in the same way as those processes in which charg‐ es are neutralized along the reaction pathway. Photooxidation quantum efficiencies indicate that the contribution to O,(′) physical quenching (a second alternative deactivation route for the encountered complex [O,(′)‐tyr derivatives]) increases with the complexity of the peptide. As a result, the selfprotection of the peptidic entity against physical quenching also increases. The information obtained from the fractional consumption mol OJmol tyr derivative (in tyr, the di‐ and tripeptides and the respective methyl ester of tyr and the tripeptide), together with the evolution (either consumption and/or generation) of primary amino groups upon photosensitized irradiation of the same compounds clearly indicates that the photooxidation of di‐ and tri‐tyr peptides proceeds with the breakage of peptidic bonds. As a consequence, in the final balance each tyr unity behaves as an independent photooxidizable target.