bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phytochrome‐mediated Phototropism in Adiantum Protonemata II. Participation of Phytochrome Dark Reversion
Authors: Iino Moritoshi , Shitanishi Kohji , Wada Masamitsu 
Published: January 2008

ABSTRACTA microbeam irradiation technique was used to analyze phytochrome‐mediated phototropism of the protonema of the fern Adiantum capillus‐veneris. One side of the sub‐apical zone of a dark‐adapted protonema was irradiated with a red‐light (R) microbeam to induce phototropic curvature toward the irradiated side. Except the cases where fluence‐response relationships were examined, the protonema was stimulated with the microbeam for about 30 s to provide a fluence (5.3–5.5 mmol m‐2) optimal for curvature. When the whole protonema was pretreated with a high fluence of R (about 9 mmol m‐2), no significant curvature could be induced by immediately subsequent one‐sided microbeam stimulation. It was found, however, that curvature became inducible progressively as the time of microbeam stimulation was delayed after the R pretreatment. The protonema gained nearly full responsiveness within 40 min after the pretreatment. Moreover, the inductive effect of microbeam R escaped rapidly from the reversing effect of far‐red light. These results indicated that most of the far‐red‐absorbing form of phytochrome (Pfr), which mediates the phototropic response, undergoes relatively fast dark reversion to the red‐absorbing form. The dark reversion kinetics was analyzed further by taking into account that the phototropic responsiveness after the R pretreatment was measured in the presence of background Pfr over the protonema. This analysis revealed a rate constant of about 0.002 s‐1 (t1/2˜ 6 min) for the dark reversion. It is considered that the Pfr dark reversion plays a role in establishing a lateral Pfr gradient in the unilaterally irradiated protonema.
Effects of Ultraviolet Radiation on Carbon Fixation in Antarctic Nanophytoflagellates
Authors: Figueroa Felix L. , Blanco Jose Maria , Jimenez‐Gomez Francisco , Rodriguez Jaime 
Published: January 2008

AbstractCarbon fixation in Antarctic nanoflagellates dominated by cryptomonads collected during a summer cruise in 1995 decreased after short‐term exposition (3 h) under both UVA and UVA + UVB radiation compared to white light. The dose applied with artificial lamps was within the range of the natural UV radiation measured at the surface during the cruise. The depletion of C fixation was higher after UVA + UVB than after UVA alone. The inhibition of carbon fixation in the laboratory depended on the time of sample collection and, consequently, on the UV dose received in the natural environment before sampling. Thus, the cells collected in the morning showed 82% of inhibition by UVA + UVB but that collected at noon showed only 72%. The same effect was observed by UVA: 72% of inhibition in the morning samples and 62% at noon. Thus, photoprotection mechanisms seem to be operating during the day protecting the cells against a rise in UV radiation. Red fluorescence (attributed to chlorophyll) per cell, as determined by flow cytometry, was not affected by UV, however, orange fluorescence (attributed to phycoerythrin) increased clearly after UV radiation compared to that in white light. The increment of orange fluorescence was higher after UVA than after UVA + UVB radiation. The rapid increase in fluorescence emission could be due to an uncoupling of energy transfer and it is suggested as a protective mechanism against UV radiation by absorbing UV radiation.
The Role of Protein Kinase C Activity in the Killing of Chinese Hamster Ovary Cells by Ionizing Radiation and Photodynamic Treatment
Authors: Rasch Monique H. , Tijssen Karmi , Lagerberg Johan W. M. , Corver Wim E. , Van Steveninck John , Dubbelman Tom M. A. R. 
Published: January 2008

Abstract In several recent studies it has been shown that protein kinase C (PKC) activity may either potentiate or antagonize cell killing by different cytotoxic agents. These apparently conflicting observations suggest that the effects of PKC activity on cell survival may depend on the different properties of different cell types but do not exclude the possibility that the effects may also depend on the nature of the cytotoxic agent. In this context the effects of PKC activation and PKC inhibition or down‐regulation on Chinese hamster ovary (CHO) cell survival after photodynamic treatment and ionizing radiation were studied. It appeared that PKC activation by short‐term incubation with 12‐0‐tetradecanoyl‐phorbol‐13‐acetate (TPA) protected CHO cells against ionizing radiation but, in contrast, sensitized the cells to photodynamic treatment. Conversely, inhibition of PKC by H7 and down‐regulation of PKC activity by prolonged incubation with TPA sensitized CHO cells to ionizing radiation but protected the cells against photodynamic treatment. These results demonstrate that in one particular cell type PKC activity may have opposite effects on cell survival following cellular damage, depending on the nature of the cytotoxic agent.
Excited‐State Dynamics of Fully Reduced Flavins and Flavoenzymes Studied at Subpicosecond Time Resolution
Authors: Enescu Mironel , Lindqvist Lars , Soep Benoît 
Published: January 2008

AbstractThe photophysics of the fully reduced states of a number of flavins (flavin mononucleotide, flavin adenine dinucleotide and 3‐N‐methyllumiflavin) and flavoenzymes (glucose oxidase from Aspergillus niger and the flavodehydrogenase component isolated from flavocytochrome b2) was studied using subpicosecond laser excitation at Λ. = 312 nm. The prompt transient absorption spectra (measured from 400 to 850 nm) were all closely similar in the case of the free flavins in aqueous solution. The decay of the transient absorbance obeyed biexponential kinetics with a fast component of lifetime ranging from 4 to 130 ps and a slower phase with a lifetime above 1 ns. The spectral structure changed appreciably during the rapid decay phase. In contrast, in the case of the enzymes only a very slight decay was apparent over the probed time interval (1 ns) and the shape of the spectrum remained unchanged. It is proposed that the two transient spectra appearing in the free flavins correspond to two conformations differing by their degree of nonplanarity, whereas in the flavoenzymes only one conformation is possible.
Photophysical Behavior of Angelicins and Thioangelicins: Semiempirical Calculations and Experimental Study
Authors: Elisei F. , Aloisi G. G. , Dall'Acqua F. , Latterini L. , Masetti F. , Rodighiero P. 
Published: January 2008

AbstractThe decay processes of the lowest excited singlet and triplet states of five methylated angelicins (4,6,4′‐trimethyl‐angelicin, MA, and four methylated thioangelicins, MTA; see Scheme 1) were investigated in live solvents by stationary and pulsed fluorometric and flash photolytic techniques. In particular, the solvent effects on absorption, fluorescence, quantum yields of fluorescence (φF) and triplet formation (φT), lifetimes of fluorescence (τF) and the triplet state (τT) and the quantum yields of singlet oxygen production (φΔ) were investigated. Semiempirical (ZINDO/S‐CI) calculations were carried out to obtain information (transition probabilities and nature) on the lowest excited singlet and triplet states. The quantum mechanical calculations and the solvent effect on the photophysical properties showed that the lowest excited singlet state (S1) is a partially allowed π,π* state, while the close‐lying S2state is n,π* in nature. The efficiencies of fluorescence, S1→T1intersystem crossing (ISC) and S1→ S0internal conversion (IC) strongly depend on the energy gap between S1, and S2and are explained in terms of the so‐called proximity effect. In fact, for MA in cyclohexane, only the S1→ S0internal conversion is operative, while in acetonitrile and ethanol, where the n.π* state is shifted to higher energy, the efficiencies of fluorescence and ISC increase significantly. The energy gap between S1and S2increases in MTA, where the furanic oxygen is replaced by a sulfur atom. Consequently, the solvent effect on the photophysical parameters of MTA is less marked than for MA;e.g.fluorescence and triplet‐triplet absorption are also detectable in the nonpolar cyclohexane. The lowest excited singlet state of molecular oxygen O2(1Dg) was produced efficiently in polar solvents by energy transfer from the T1state of MA and MTA.
GH3 Cells, Ionic Currents and Cell Killing: Photomodification Sensitized by Rose Bengal
Authors: Valenzeno Dennis Paul , Tarr Merrill 
Published: January 2008

AbstractPhotosensitization using Rose Bengal (RB) modifies membrane ionic currents and kills cultured mouse pituitary, GH3, cells. Here we investigate the dose‐response relationship for ionic current modification and for cell killing to assess a possible causal link. When exposed to 0.5 μM RB and 6.5 mW/cm2 of visible light, calcium current was blocked in 1.9 ± 0.2 min (meanSEM; 0.74 ± 0.08 J/ cm2; n = 18), a transient component of potassium current, tentatively identified as a delayed‐rectifier potassium current, disappeared in 52 ± 8 s (0.34 ± 0.05 J/cm2; n = 10) and a steady‐state component of potassium current, largely a calcium‐activated potassium current, disappeared in 3.5 ± 0.4 min (1.37 ± 0.16 J/cm2; n = 11). Conversely, the background leak current increased in magnitude. At 5 min of illumination, the longest time studied here, it continued to increase nearly linearly, making it the only current component studied that is still changing after 5 min of light. Under the conditions used, cell killing increased to 100% in the exposure range of4–10 min of illumination (1.6 J/cm2 to 3.9 J/cm2) when assessed using fluorescent markers, ethidium homodimer and calcein and required slightly longer exposure times when assessed using trypan blue. Thus, it is difficult to ascribe a causal role in cell killing by photosensitization to alterations of standard ion channels and known ionic currents. However, the increase in leak current has the correct dose‐response characteristics to be involved.
Effect of Magnetite Particles on Photoinduced and Nonphotoinduced Free Radical Processes in Human Erythrocytes
Authors: Chignell Colin F. , Sik Robert H. 
Published: January 2008

AbstractMagnetite (Fe304) encapsulated in polystyrene microspheres dramatically decreased the time for 50% hemolysis (t1/2) of human erythrocytes irradiated (λ300 nm) in the presence of ketoprofen (0.1 mM). The magnetic microspheres were present at a very low concentration (0.002%) such that on average there was only one particle per four erythrocytes. No such effect was seen when nonmagnetic microspheres were employed or when the equivalent concentration of soluble iron (FeCl3) was present. A decrease in t1/2 was also observed when the magnetic microspheres were added after UVA/ketoprofen treatment or when they were present during hemolysis initiated by thermolysis of 2,2′‐azobis(2‐amidinopro‐pane). These findings may be attributed to an increase in the membrane concentration of lipid radicals as a result of a magnetic field‐induced increase in radicals escaping from triplet radical pairs.
Repair of (6‐4) Photoproducts in Cultured Goldfish Cells at Confluence or Treated with H2O2
Authors: Uchida Nobuhiro , Mitani Hiroshi , Shima Akihiro 
Published: January 2008

AbstractPreviously we reported that fluorescent light (FL) illumination prior to UV irradiation (FL preillumination) had multiple effects on the repair of cyclobutane pyrim‐idine dimers (CPD) and (6‐4) photoproducts ([6‐4] PD) in cultured goldfish cells (RBCF‐1) at the exponentially growing phase. In this study, it is shown that even under the confluent condition of RBCF‐1 cells, FL preillumination increased the disappearance of (6‐4) PD in the dark. In addition, both at confluence and at the exponentially growing phase, the disappearance of (6‐4) PD after PR treatment was increased by FL preillumination to RBCF‐1 cells. Moreover, it was found that H2O2 pre‐treatment, followed by UV irradiation, of the exponentially growing cells also enhanced the disappearance of (6‐4) PD in the dark and by photorepair treatment. The degree of enhancement by H2O2 pretreatment was almost the same as that by FL preillumination.
Regional Imager for Low‐Resolution Functional Imaging of the Brain with Diffusing Near‐Infrared Light
Authors: Danen R. M. , Wang Yong , Li X. D. , Thayer W. S. , Yodh A. G. 
Published: January 2008

ABSTRACTWe have developed a near‐infrared spectroscopy system for low‐resolution regional imaging of the brain. Our regional imager employs two intensity‐modulated (frequency‐domain) diode lasers operating at 779 and 834 nm, respectively, in order to produce macroscopic waves of diffusing photons. The interaction of these diffusive waves with tissue depends on laser modulation frequency, laser wavelength and the optical properties of the sample tissue volume. The lasers can be modulated over a range of frequencies from 50 to 400 MHz. Light is coupled to and from the head using a pad that has 12 source and 4 detector positions within an area of approximately 40 cm2. The pad can be moved to different positions on the head. Measurements from different source‐detector combinations enable reconstruction of low‐resolution images of the tissue volume beneath the pad. For example, we have made two‐dimensional back‐projection images of model systems in order to demonstrate the capabilities of the regional imager. We also present preliminary results from initial clinical studies at the Children's Hospital of Philadelphia.
Nonexponential Fluorescence Decay of 7‐Azatryptophan Induced in a Peptide Environment
Authors: English D. S. , Rich R. L. , Petricht J. W. 
Published: January 2008

ABSTRACT7‐Azatryptophan is an alternative to tryptophan as an optical probe of protein structure and dynamics. 7‐Azatryptophan is synthetically incorporated into an octapeptide (NAc‐Lys‐Ala‐Cys‐Pro‐7‐azatryptophan‐Asn‐Cys‐Asp‐NH2) that mimics the active site of potato chymotrypsin inhibitor II, which is known to be a strong inhibitor of α‐chymotrypsin. The synthetic octapeptide retains some of this inhibitory activity. This is the first compound containing the 7‐azaindole chromophore to display a nonexponential fluorescence decay (well fit to two exponentials) in water when fluorescence is collected over the entire emission band. The effect of external quenchers on the fluorescence decay is monitored and seen to differ markedly for the two components. These results are discussed in terms of the solvation of the 7‐azaindole chromophore itself, which promotes or impedes excited‐state tautomerization. The fluorescence quenching of free indole and 7‐azaindole are compared. The fluorescence quenching of octapeptides containing both chromophores is also compared. It is the thesis of this article that the nonexponential fluorescence decay of the 7‐azatryptophan‐containing octapeptide is a consequence of excited‐state tautomerization of the 7‐azaindole chromophore. This tautomerization is suggested to be promoted by solvent reorganization induced by the peptide backbone or by direct interactions of the 7‐azaindole with neighboring amino acid side chains.
Magnetic Field Effects on the Behavior of Radicals in Protein and DNA Environments
Authors: Mohtat N. , Cozens F. L. , Hancock‐Chen T. , Scaiano J. C. , McLean J. , Kim J. 
Published: January 2008

ABSTRACTWe have examined the behavior of radical pairs derived by hydrogen abstraction of triplet benzophenone and some of its derivatives from bovine serum albumin, human serum albumin and calf thymus DNA. They have been investigated by means of nanosecond laser flash photolysis techniques. The dynamics of radical pair behavior are shown to be sensitive to external magnetic fields; these effects are interpreted using the established model for the influence of magnetic fields on radical pairs in micellar aggregates, in which intersystem crossing of the radical pair is slowed by the external magnetic field. Our results indicate that proteins and DNA can confine the radicals for a sufficiently long period of time for spin evolution to be affected by external fields. In proteins the radical pair retains its geminate character (i.e. remains confined) for about 0.5–1 μs. Interestingly, the magnetic field effects observed in proteins and in DNA seem to occur in distinct timescales; for example, for 2,3,4,5,6‐pentafluorobenzophenone bound to DNA, the magnetic field alters the radical reactivity only over times ≤50 ns, suggesting poor confinement. The timescale for these effects can be increased by promoting Coulombic attraction between DNA and the radical precursor. Electron transfer interactions play a role in the case of DNA.
UV‐Induced Nucleic Acid–Protein Cross‐Linking: Manual on Planning of Irradiation Experiments and Calculation of Absorbed Dose and Quantum Yield
Authors: Dobrov Eugene N. , Nikogosyan David N. 
Published: January 2008

ABSTRACTWe have developed methods of photochemical quantitation of photobiological studies on UV‐induced nucleic acid–protein cross‐linking. Cases relating to incoherent low‐intensity UV sources, laser UV sources and high‐intensity laser UV sources are considered. In the case of low‐intensity UV radiation the most important point is the correct determination of absorbed dose. The laser UV pulse energy is easily measured and the short‐pulse irradiation also has the advantage of "freezing" the conformation of complexes under study. However, the use of high‐intensity laser UV irradiation leads to realizations of two‐quantum processes both in nucleic acid chromophores–bases and in solvent–water, which complicates singificantly the processing of results. In this paper methods for calculating the absorbed dose and the quantum yield of cross‐linking for all above‐mentioned cases are given as well as practical advice.
Stereocontrolled Photooxygenations–A Valuable Synthetic Tool§
Authors: Adam Waldemar , Saha‐Möller Chantu R. , Schambony Simon B. , Schmid Katharina S. , Wirth Thomas 
Published: January 2008

AbstractThe stereochemical course of the singlet‐oxygen ene reaction with acyclic olefins may be controlled if in the substrate conformational fixation (1,3‐allylic strain) an allyl‐ic substituent for interaction with the attacking oxygen enophile aligns. Various substrates were chosen to elucidate the features of the olefin that are necessary to control the sense (threo versus erythro) and the extent of the ii‐facial preference of the singlet‐oxygen attack. Depending on the electronic properties of the double bond and the nature of the allylic substituent, threo or erythro selectivity may be imposed through hydrogen bonding, electrostatic and steric effects and stereoelectronic alignment. Such directing properties, especially that of the hydroxy group, were also confirmed in the other reaction modes of singlet oxygen, namely the [4+2] cycloaddition to chiral naphthylenic alcohols and the [2+2] cycloaddition to an adamantylidene‐substituted allylic alcohol. The syntheses of the natural products Merucathin and Iso‐dihydromahubanolide B are two examples in which such stereocontrolled photooxygenations have been used as key steps to build up the required chirality diastereose‐lectively.
Role of Nuclear Factor‐KB in Colon Cancer Cell Apoptosis Mediated by Aminopyropheophorbide Photosensitization
Authors: Matroule Jean‐Yves , Hellin Anne‐Cecile , Morliere Patrice , Fabiano A.‐S. , Santus Rend , Merville Marie‐Paule , Piette Jacques 
Published: January 2008

AbstractAminopyropheophorbide (APP) is a second generation of photosensitizer for photodynamic therapy (PDT). We demonstrated that APP strongly absorbed red light and, after being taken up by colon cancer cells (HCT‐116 cells), was localized in cytoplasmic and internal membranes but not in mitochondria. The APP‐mediated photosensitization was cytotoxic for HCT‐116 cells through an induction of apoptosis. Indeed, DNA fragmentation (DNA laddering and terminal deoxyuridine nick‐end labeling) and chromatin condensation (4′,6‐diamidine‐2′‐phenylindole staining) could be visualized soon after photosensitization. Because nuclear factor (NF)‐KB is involved in the response to many photosensitizers, we also demonstrated its nuclear translocation in two waves: a rapid and transient one, followed by a slow and sustained phase. The NF‐KB turned out to be involved in an antia‐poptotic response to APP‐mediated photosensitization because the HCT‐116 cell line expressing the dominant negative mutant of inhibitor‐KBα was more sensitive to apoptosis as measured by DNA fragmentation and caspase activation. These data unambiguously show that a membrane‐located photosensitizer can lead to effective apoptosis, reinforcing the idea that PDT can be an effective means to eradicate colon cancer cells.
Formation of Tryptophan Radicals in Irradiated Aqueous Solutions of Hexachloroplatinate(IV): A Flash Photolysis Study
Authors: Zang Ling , Rodgers Michael A. J. 
Published: January 2008

AbstractThe oxidation of tryptophan photosensitized by PtCl62‐has been investigated in aqueous solutions at different pH using nanosecond laser flash photolysis. Cationic and neutral radicals of tryptophan were detected at pH 2.8 and 8.5, respectively. The generation of the radical was attributed to oxidation by Cl2‐that was formed from the homolytic bond cleavage in the excited state of PtCl62‐The bimolecular rate constant derived from the kinetics analysis, 2.8 × 0.2 times; 109M‐1s‐1, is in good agreement with the value obtained in earlier pulse radiolysis studies. Both the cationic and neutral radicals decayed by second‐order kinetics, consistent with the dimerization process.
pH‐Dependent Chalcogenopyrylium Dyes as Potential Sensitizers for Photodynamic Therapy: Selective Retention in Tumors by Exploiting pH Differences between Tumor and Normal Tissue
Authors: Bellnier David A. , Young David N. , Detty Michael R. , Camacho Susan H. , Oseroff Allan R. 
Published: January 2008

AbstractIdeal photosensitizers have long‐wavelength absorption and strong tumor selectivity with rapid clearance from normal tissues. The telluroselenopyrylium dye 1 that absorbs light at 795 nm (ε= 285000 M1cm‐1) has a novel property that enhances the tumor specificity and normal tissue clearance. After intralesional injection to both tumors and surrounding skin, it disappeared from the normal skin of BALB/c mice faster than it did from subcu‐taneously implanted Colon 26 tumors, which resulted in therapeutic selectivity. In vivo reflectance spectroscopy showed that the half‐life in tumor was about 50 min while in skin it was around 12 min. This phenomenon appears to be related to the pH differences in normal skin versus tumor, because the rates of drug hydrolysis in solution were shown to be sensitive to changes in pH. Inhibition of tumor regrowth following intratumoral photosensitiz‐er administration depended on both light dose and drug dose, as well as the time interval between dye injection and irradiation; selectivity depended on the time interval. Although treatment parameters were not optimized efficacy was superior to systemic Photofrin® under our standard conditions. We discuss how new, more optimal, photosensitizers can be designed that use rates of hydrolysis to exploit the differences in pH between normal tissue and tumor.