bluuebunny/crossref_metadata_2025_split huggingface dataset:
MODEL STUDIES ON THE PHOTOCHEMICAL PRODUCTION OF LENTICULAR FLUOROPHORES
Authors: Ellozy Aziza R. , Wang Ren H. , Dillon James 
Published: January 2008

Abstract With aging, human lens proteins accumulate fluorophores having blue and green emissions. Model studies were undertaken to determine the role of 3‐hydroxykynurenine (3‐HK) and its glucoside (3‐HKG) in the photochemical production of those fluorophores. Experiments were carried out using 10−3M 3‐HK solutions in the presence or absence of glycine (1M), which was used to mimic the environment of the lens. The solutions were photolyzed (transmission above 295 nm) for various periods of time while the loss of starting material and the formation of fluorescent photoproducts (blue emission at 470 nm, and green emission at 520 nm) were monitored using fluorescence and UV‐visible spectroscopy and thin‐layer and high‐pressure liquid chromatography analysis. Several parameters were varied such as oxygen tension and the addition of the free radical scavenger, penicillamine. The photolytic loss of 3‐HK in the absence of glycine occurred approximately 5‐10 times faster than in its presence. Conversely, blue and green fluorophores formed in irradiated solutions containing glycine but not with the photolysis of 3‐HK alone. The blue fluorophore was formed first and appeared then to be photochemically converted to the green one, with the rate of formation of the latter increasing with an increase in UV dosage or oxidizing conditions. The addition of penicillamine drastically reduced the photochemical formation of both fluorophores.Both the blue and green fluorophores appear to result from the photochemically induced covalent attachment of 3‐HK to glycine. In the human lens, these reactions can explain the age‐related loss of 3‐HKG with the concomitant formation of fluorophores covalently attached to lens proteins, probably via the amino group of lysine.
INVESTIGATIONS ON THE LIGHT‐EMITTING SPECIES IN THE REACTION OF METMYOGLOBIN AND METHEMOGLOBIN WITH HYDROGEN PEROXIDE
Authors: Stolze Klaus , Liu Yang , Nohl Hans 
Published: January 2008

Abstract The formation of a compound I type ferryl complex in the reaction of methemoglobin (MetHb) and metmyoglobin (MetMyo) with hydrogen peroxide is accompanied by strong chemiluminescence. An approach to identify the nature of the light‐emitting species was made by the use of quenchers and sensitizers reacting with singlet oxygen and compounds interfering in the formation and reactivity of other reactive oxygen species.Singlet oxygen is not the source of light emission. This could be concluded from the results obtained using the specific singlet oxygen trap 9,10‐anthracenedipropionic acid (ADPA) in combination with high‐performance liquid chromatography (HPLC) analysis. The singlet oxygen adduct of ADPA was not formed in the incubation systems (MetHb or MetMyo/H2O2). Instead, ADPA was oxidized by the ferryl ion to a different oxidation product, which was characterized by HPLC and IR spectroscopy. In the case of MetHb‐related chemiluminescence, light emission does not result from a single source. Both, SH‐groups and O2.¯ radicals are involved because blocking of thiol‐groups with N‐ethylmaleimide (NEM) and scavenging of O2.¯(by superoxide dismutase) suppressed chemiluminescence by 50% and 30%, respectively. Development of MetMyo‐related chemiluminescence is not dependent on thiol groups (which are not present in the globin moiety) and also 02.¯is not involved. Although generation of chemiluminescence in MetHb and MetMyo seems to follow different mechanisms, both types of light‐emitting species are sensitive to antioxidants, such as uric acid and ascorbate. The detection of the respective free radicals by means of ESR demonstrates that both MetHb‐ and MetMyo‐mediated chemiluminescence is associated with a strong one‐electron oxidizing species, which seems to be identical with the light‐emitting source itself. Also desferal, which was originally used to exclude the involvement of a Fenton‐type reaction, was readily oxidized to the nitroxide free radical associated with a strong decrease of chemiluminescence. This quenching effect was not dependent on iron complexation because the addition of iron was ineffective. In summary, chemiluminescence is not restricted to a single chemical process but is related to different one‐electron transfer reactions from globin residues to the oxo‐heme center.
ULTRAVIOLET‐INDUCED CELL DEATH IS INDEPENDENT OF DNA REPLICATION IN RAT KANGAROO CELLS
Authors: Miyaji Eliane N. , Menck Carlos F. M. 
Published: January 2008

AbstractRat kangaroo (Potorous tridactylus) cells have an efficient repair system for photoreactivation of lethal lesions induced by 254 nm UV. However, this ability is lost with increasing time after UV, being completely ineffective after 24 h. Critical events leading to UV‐induced cell death must occur within this period of time. DNA synthesis was inhibited by the DNA polymerase inhibitor aphidicolin and the loss of the capability to photorepair lethal lesions was maintained as for replicating cells. Similar data were obtained in synchronized cells UV irradiated immediately before S phase. Under the same conditions, the ability to remove cyclobutane pyrimidine dimers by photoreactivation in these cells remained unchanged 24 h after irradiation. These data indicate that the critical events responsible for UV‐induced cell death occur in the absence of DNA replication.
TARGETING OF PHOTOTOXIC DRUGS TO ANTIGEN‐SPECIFIC T LYMPHOCYTES in vitro USING ANTIGEN‐PRESENTING CELL MEMBRANES
Authors: Cchang Nan‐Hua , Rayner David C. , Boggs Joan M. 
Published: January 2008

AbstractWe have used the complex of antigen with class II major histocompatibility proteins (la) in membrane‐bound form to target a phototoxic compound to antigen‐specific T cell hybridomas in vitro. The iodoacetamidyl ester of phototoxic pyrene was bound covalently to antigen‐presenting cells (APC), and protein antigens were added to the cells for processing, presentation and targeting of the drug to three different T hybridomas specific for myelin basic protein (MBP), ovalbumin (OVA) and keyhole limpet hemocyanin (KLH). The B hybridoma LS102.9 was used as APC to present MBP, KLH and either a tryptic digest of OVA or the synthetic peptide OVA323–339to these T cells. A transformed B lymphoma, which expresses trinitrophenol (TNP)‐specific surface IgM, A20‐HL, was used to present TNP conjugates of KLH and OVA to T cells. Either the antigen‐bearing intact APC or Ia+ membranes shed spontaneously from them were used as drug carriers to target pyrene to the T cells. In the dark, or in the absence of pyrene, both the intact APC or the shed membranes stimulated interleukin‐2 (IL‐2) production by the T cells in an antigen‐specific way. After UVA (320–400nm) irradiation, both forms of these drug carriers had an antigen‐specific toxic effect on the T hybridoma cells with receptors for the antigen that they carried. Both spontaneous T cell proliferation and antigen‐induced IL‐2 production were inhibited. The shed membranes had a more antigen‐specific toxic effect than the intact APC, which tend to settle out with the T cells in the microtiter plates, possibly causing nonspecific contact. These results indicate that the antigen‐la complex in membrane‐bound form can be used to antigen‐target cytotoxic drugs to antigen‐specific T cells. The Ia+ membranes shed from APC may be useful to target drugs to antigen‐specific clones of T cells in vivo.
BLUE LIGHT PERCEPTION BY ENDOGENOUS REDOX COMPONENTS OF THE PLANT PLASMA MEMBRANE
Authors: Asard Han , Horemans Nele , Briggs Winslow R. , Caubergs Roland J. 
Published: January 2008

Abstract b‐Type cytochromes of the higher plant plasma membrane may be reduced by irradiation with actinic blue light (light‐induced absorbance change). Although this reaction has been reported to depend on the presence of an exogenous oxygen‐scavenging system, significant cytochrome reduction was obtained in bean hook (Phaseolus vulgaris L. cv. “Limburgse Vroege”) plasma membranes without any addition. An endogenous oxygen‐consuming reaction is apparently sufficient to achieve a proper redox balance. A blue light‐mediated absorbance change with absorbance minima at 450 and 475 nm precedes cytochrome b reduction and indicates the presence of a flavoprotein in the plasma membrane fraction.Cytochrome b reduction by blue light in the absence of an oxygen scavenger is highly sensitive to flavin photosensitizers. Glucose oxidase, which has previously been used to lower the oxygen concentration in membrane samples, was demonstrated to have a photosensitizing effect. Inhibitors of flavin photochemical reactions (KI and phenylacetic acid) were highly effective in preventing cytochrome b reduction. These results indicate that the blue light‐mediated reaction probably involves an endogenous plasma membrane flavoprotein as the photoreceptor.As plasma membrane NADH‐dependent oxidoreductases potentially are flavoproteins these experiments raise the question whether a plasma membrane cytochrome b and a flavin‐enzyme may cooperate in blue light reactions. Evidence is also discussed, suggesting the possible involvement of oxygen radicals in the blue light‐induced cytochrome b reduction.
INFLUENCE OF CHANGES IN THE PHOTON PROTECTIVE ENERGY DISSIPATION ON RED LIGHT‐INDUCED DETRAPPING OF THE THERMOLUMINESCENCE Z‐BAND
Authors: Hagen Christoph , Pascal Andrew A. , Horton Peter , Inoue Yorinao 
Published: January 2008

Abstract—‐Thermoluminescence emission at 110 K (Z‐band) was markedly diminished when thylakoid membranes were exposed to red light during or after Z‐band charging with blue light. Analysis of this phenomenon showed that deactivation of Z‐band‐emitting chlorophyll species occurred preferentially on the low temperature side of the glow curve, and red light of670–680 nm was most efficient in the deactivation. In order to test our hypothesis that this detrapping is related to local heating effects caused by dissipation of absorbed energy, we measured thermoluminescence glow curves and Z‐band emission spectra from spinach leaf discs and thylakoid membranes during induction of nonphotochemical chlorophyll fluorescence quenching. Pretreatment of the plant material was designed to achieve different levels of (1) de‐epoxidized xanthophylls in the photosynthetic apparatus and (2) the proton concentration in the thylakoid lumen. In comparison, measurements were performed in aggregated and trimeric light‐harvesting pigment‐protein complexes of photosystem II. We observed on all three levels of organization that a higher capacity of excitation energy dissipation was accompanied by a stronger red light‐induced detrapping of Z‐band thermoluminescence.
STIMULATORY AND INHIBITORY EFFECTS OF IRON ON PHOTODYNAMIC INACTIVATION OF LEUKEMIA CELLS
Authors: LIN FUBAO , GIROTTI ALBERT W. 
Published: January 2008

Abstract—The influence of exogenous iron on merocyanine 540 (MC540))sensitized photoinactivation of leukemia cells has been investigated. Irradiation of murine L1210 or human HL‐60 cells (‐lOh/mL in 1 % serumiRPM1 medium) with broadband visible light in the presence of MC540 (2 pIM) resulted in a progressive loss of clonally assessed cell viability. When added to cells 30 min before irradiation, the low polarity chelate, ferric 8‐hydroxyquinoline [Fe(HQ), 0.5 *MI stimulated dye‐sensitized pho‐ tokilling, whereas high polarity chelates such as ferric 8‐hydroxyquinoline‐5‐sulfonate [Fe(HQS)2, 0.5 p M] or ferric ethylenediaminetetraacetate (Fe.EDTA, 0.5 FM) had no effect. A striking reversal of Fe(HQ),‐enhanced photokilling was observed upon increasing the preirradiation incubation time with Fe(HQ)2 such that a marked resistance (relative to non‐iron‐treated controls) was evident after 24 h. Cells exposed for 24 h to Fe(HQS), or Fe.EDTA showed similar or even greater resistance to photo‐killing. Like phototoxicity, H,O,‐induced cytotoxicity was enhanced after a 30 min exposure of cells to Fe(HQ)2 but strongly repressed after 24 h. Immunoblot (western) analysis, using a polyclonal antibody to ferritin, revealed that cells exposed to Fe(HQ): for 24 h contained at least 12 times as much ferritin heavy chain as non‐Fe(HQ)?‐treated controls. Preincubating cells with emetine, an inhibitor of protein synthesis, prevented both ferritin induction and the development of hyperresistance. These findings, along with the observation that exogenous apoferritin protected LI 2 10 cells against photokilling, suggest a possible role for ferritin in iron‐stimulated photoresistance. It is conceivable that in photodynamic treatment of tumors, certain cells might resist inactivation via this mechanism, a possibility that has not been recognized heretofore.
SOMATOSTATIN IN A WATER‐RESTRICTED ENVIRONMENT: FLUORESCENCE AND CIRCULAR DICHROISM STUDY IN AOT REVERSE MICELLES
Authors: Bhattacharyya Kasturi , Basak Soumen 
Published: January 2008

Abstract—Steady‐state and time‐resolved fluorescence emission from the single tryptophan residue of somatostatin, and the kinetics of quenching of this emission, were studied in aqueous solution and in reverse micelles of sodium bis (2‐ethylhexyl) sulfosuccinate (AOT)/water/isooctane, a system that mimics the water‐membrane interface well‐ Incorporation into micelles caused blue shifts and reduced band‐widths of the emission peaks and altered the quantum yields with respect to emission from bulk water. Steady‐state anisotropy values also increased considerably on micellization. These observations point to reduced polarity of the environment around the Tip residue of the peptide, as well as restricted freedom of its rotational motions, due to transfer from the aqueous to the micellar phase. Fluorescence emission kinetics of the Tip moiety followed biexponential decay laws in both aqueous and micellar media. Static and dynamic quenching constants were measured for acrylamide and CC14 quenchers localized in the micellar and organic pseudophases, respectively, using both steady‐state and time‐resolved experiments. The efficiency of dynamic quenching by acrylamide became vanishingly small in going from water to reverse micelles, in sharp contrast to the comparable quenching efficiencies exhibited by CC14 in micelles and acrylamide in water. The circular dichroic (CD) spectrum of the native peptide in water indicated the possibility of some amount of P‐type secondary structure being present. Conformational analysis of CD spectra in micelles showed that the relative amount of this structural feature was enhanced for the micellized peptide but was insensitive to the water content of micelles. The above results, put together, indicate that the Trp‐8 residue in somatostatin is likely to be located in the close neighborhood of the water‐AOT molecular interface, where the water molecules are strongly immobilized. This work also demonstrates the role of reverse micelles as a convenient membrane‐mimetic medium for the study of membrane interactions of bioactive peptides.
ENERGY TRANSFER‐ENHANCED CHEMILUMINESCENCE OF ADAMANTANONE (n,π*) AND ESTER (π,π*) SINGLET AND TRIPLET EXCITED STATES IN THE THERMOLYSIS OF SILYLOXYARYL‐SUBSTITUTED SPIROADAMANTYL DIOXETANES†
Authors: Trofimov Alexei V. , Vasil'ev Rostislav F. , Mielke Karsten , Adam Waldemar 
Published: January 2008

Abstract—The thermal generation of singlet and triplet excited states from silyloxyaryl‐substituted spiroadamantyl dioxetanes lab and the adamantylidineadamantane dioxetane (1c) was investigated by direct and enhanced chemiluminescence (CL). 9,10‐Diphenylanthracene (DPA) and 9‐fluorenone were used as energy acceptors in the singlet‐singlet (S‐S), naphthalene and europium chelate Eu(TTA)3Phen (TTA = thenoyltrifluoroacetone, Phen = 1,10‐phenanthroline) in the triplet‐triplet (T‐T) and 9,10‐di‐bromoanthracene (DBA) in triplet‐singlet (T‐S) energy transfer experiments. The direct chemiluminescence observed in the thermolysis of dioxetanes lab consisted of fluorescence derived from the singlet‐excited adamantanones 2a,b. In the presence of naphthalene, selective T‐S energy transfer with DBA (napthalene as quencher) displayed the adamantanone triplets 2a,b and with Eu(TTA)3Phen (naphthalene as mediator) also the silyloxyaryl ester 3 triplets. From the Stern‐Volmer constants (kTNTT0) the triplet lifetimes t0t of these triplet state products were assessed. By using the Hastings‐Weber standard, the total triplet excitation yield (φt) was estimated to be ca 20%. The energies of the first excited singlet and triplet states of the adamantanones 2a,b and the silyloxyaryl ester 3, the products of the thermally induced decomposition of dioxetanes la‐c, were determined by semiempirical calculations (AMI‐based configuration interaction), which included explicitly solvent effects on the excitation energies in terms of a self‐consistent reaction field approach. The calculations revealed that the first excited singlet and triplet states of the adamantanones 2a,b are expectedly n,π*‐type excitations while the silyloxyaryl ester 3 possesses π,π* character. The semiempirical computations suggest that excitation of the adamantanones 2a,b as well as the silyloxyaryl ester 3 is feasible in the thermolysis of the spiroadamantyl dioxetanes lab, which has been confirmed by the experimental energy transfer studies.
Photochemistry of Tetracene Adsorbed on Dry Silica: Products and Mechanism
Authors: Dabestani Reza , Nelson Mark , Sigman Michael E. 
Published: January 2008

AbstractThe photochemistry of tetracene (1) has been studied on dry silica at very low surface coverages (less than 3% of a monolayer). Irradiation of degassed samples of 1 adsorbed on silica surface proceeds very slowly to produce both syn (2) and anti (3) dimers. Under aerated conditions photolysis of 1 at surface coverages <1% of a monolayer gives mainly tetracene‐5, 12‐endoperoxide (4) and very little dimer. The endoperoxide slowly decomposes to form 5, 12‐tetracenequinone (5), 5, 12‐dihydroxytetracene (6) and 5, 12‐dihydro‐5, 12‐dihydroxytetracene (7), respectively. As the surface coverage is increased above 1% of a monolayer, dimerization becomes more pronounced as a result of pairing and/or aggregation. The photooxidation process is mediated by the addition of singlet molecular oxygen to 1. Tetracene also undergoes a dark oxidation reaction on the silica surface to give 5 (major), 6 and 7 (minors) as products. The first‐order rate constant for this Lewis acid‐catalyzed oxidation was determined to be 1 × 105 S−1.
The Use of UV Radiation to Control the Architecture of Salvia splendens Plants. I. Effects on Plant Growth, Water Relations and Gas Exchange
Authors: Giannini A. , Pardossi A. , Lercari B. 
Published: January 2008

AbstractIn experiments with Salvia splendens plants grown in the greenhouse we evaluated the possible use of irradiation with unfiltered UV (UVA + UVB + UVC) lamps for the control of plant growth. The effect of UV Irradiation on the growth of S. splendens plants in the grcenhouse was closely dependent on the growing season and the level of available photosynthetically active radiation. In summer UV treatments were ineffective, but in the low light conditions of winter UV irradiation inhibited the growth via both photomorphogenic and photosynthetic effects. The reduction of stomatal conductance and expansion growth, which in turn depressed photosynthesis and dry matter accumulation, were not a consequence of an impairment of plant water status but appeared to be a direct UV effect on stomata and cell wall rheological propertles. Our findings suggest that the use of unfiltered UV irradiation could become an effective tool for the regulation of growth in greenhouse crops, particularly during the poor light conditions of the winter season.
Photochemistry and Photobiology of lmidazole‐4(5)‐Methylidene Malonic Acid: An Analog of Both E‐ and Z‐Urocanic Acid*
Authors: Houghtaling Melissa A. , Kennedy Matthew A. , Mohammad Taj , Tessman Irwin , Morrison Harry 
Published: January 2008

AbstractImidazole‐4(5)‐methylidene malonic acid (IMMA) may be thought of as having its imidazole and carboxyl functionalities permanently fixed in a configuration that is simultaneously analogous to both E‐ (trans) and Z‐ (cis) urocanic acid (UA). Because the UA isomers affect the photoinactivation of bacteriophage single‐stranded DNA differently (E‐UA increases and Z‐UA decreases viral DNA inactivation), IMMA was similarly tested and was found to change the inactivation rate by a factor of 0.43, which is intermediate between the values for E‐ and Z‐UA (1.6 and 0.014, respectively). The IMMA likewise sensitizes double‐stranded DNA by a factor of 10.3 compared to a value of 13 for UA. In several ways the effects of IMMA parallel the distinctive effects of UA on the UV inactivation of single‐ and double‐stranded DNA, including the ability to prevent the formation of cyclobutane pyrimidine dimers in irradiated single‐stranded DNA and to sensitize a large increase in the formation of those dimers in irradiated double‐stranded DNA. The IMMA photodecarboxylates to UA with a low quantum efficiency (ca 1 × 10−3) and photochemically binds to calf‐thymus DNA.
Is Phototherapy Safe for HIV‐Infected Individuals?
Authors: Adams Melanie L. , Houpt Karen R. , Cruz Ponciano D. 
Published: January 2008

AbstractPatients infected with human immunodeficiency virus (HIV) have a high prevalence of UV radiation‐responsive skin diseases including psoriasis, pruritus, eosinophilic folliculitis and eczemas. On the other hand, UV has been shown to suppress T cell‐mediated immune responses and to induce activatin and replication of HIV. These developments have prompted clinicians and investigators to question whether phototherapy is safe for HIV‐infected individuals. We have reviewed these issues and hereby provide a summary and critique of relevant laboratory and clinical evidence.
Detector‐Based Calibration Method for High‐Accuracy Solar UV Measurements
Authors: Kärhä Petri , Visuri Reijo , Leszczynski Kirsti , Manoochehrl Farshid , Jokela Kari , Ikonen Erkki 
Published: January 2008

AbstractA novel method for calibrating the absolute responsivity of solar UV spectroradiometers has been developed and tested. The method is based on calibrated filter radiometers constructed from a detector, a precision aperture, a band‐pass filter and devices for temperature stabilization. The filter radiometers utilize a trap detector with very low reflectance. The filter and the detector can therefore be characterized separately. As an example the detector‐based calibration is compared at 312 nm wavelength with lamp‐based calibration by measuring the irradiance of a deuterium lamp with both the filter radiometer and the lamp‐calibrated spectroradiometer. The agreement between the results is at the level of 1%, well within the estimated uncertainties of both methods.