bluuebunny/crossref_metadata_2025_split huggingface dataset:
LIGHT‐INDUCED ELECTRON TRANSFER REACTIONS BETWEEN CHLOROPHYLL AND QUINONE IN ELECTRICALLY‐CHARGED VESICLES: EFFECTS OF COUNTERIONS LOCATED IN EITHER THE INNER OR OUTER AQUEOUS PHASES ON RADICAL FORMATION AND DECAY*
Authors: Fang Yifei , Tollin Gordon 
Published: January 2008

Abstract— The presence of relatively low concentrations of counterions (millimolar in the case of univalent ions and micromolar in the case of polyvalent ions) in either the inner or outer aqueous compartments of electrically charged lipid bilayer vesicles containing chlorophyll in the presence of benzoquinone has been shown to produce large effects on radical formation and decay as measured by laser flash photolysis. With negatively charged vesicles having no added salt inside, salt ions added to the external phase caused radical yields to markedly decrease, with no change in decay kinetics. When salt was present only in the interior phase, radical decay became biphasic and the ability of externally added salt to affect radical yields was greatly diminished.With positively charged vesicles having no added salt inside, salt addition to the external medium caused both the radical decay rate and yield to decrease. The presence of interior salt, however, caused radical decay to become faster and, as was the case with negative vesicles, greatly reduced the effects of salt added externally.These results have been interpreted in terms of electrostatic and structural effects of charge neutralization by counterions on the dynamics of radical‐ion separation and recombination.
ENERGY TRANSFER AMONG THE CHROMOPHORES OF C‐PHYCOCYANIN FROM Anabaena variabilis USING STEADY STATE AND TIME‐RESOLVED FLUORESCENCE SPECTROSCOPY
Authors: Switalski Steven C. , Sauer Kenneth 
Published: January 2008

Abstract We have investigated the model of energy transfer between sensitizing (s) and fluorescing (f) chromophores for the αβ monomer and for the separated α and β subunits of C‐phycocyanin from Anabaena variabilis using fluorescence emission spectroscopy, fluorescence excitation polarization, and picosecond‐resolved fluorescence decay kinetics. The fluorescence emission maximum occurs at 640 nm for all samples. The fluorescence excitation polarization is constant (P= 0.40) across the absorption hand for the α subunit, but it increases across the absorption band towards longer wavelength for the β subunit and the αβ monomer. The fluorescence decay kinetics exhibit two exponential lifetimes of 1.3‐1.5 ns and 340‐500 ps for the αβ monomer and for the α and β subunit preparations.We attribute the change in polarization across the absorption band to energy transfer among the three chromophores in the αβ monomer and among the two chromophores in the separated β subunit. The constant, relatively high polarization in the separated a subunit, having only one chromophore, is consistent with the absence of both energy transfer and chromophore rotation. The concentration of the α subunit did not affect the decay kinetics, suggesting that the short lifetime component does not arise from aggregation of the α subunits. The biexponential decay kinetics of the α subunit cannot be explained using the sensitizing‐fluorescing model. The possibility of conformational interactions is under investigation.
LASER FLASH PHOTOLYSIS OF INDOLE IN THE PRESENCE OF AMINO ACIDS
Authors: Previtali C. M. 
Published: January 2008

AbstractThe laser flash photolysis of indole at 265 nm in the presence of glycine, proline and hydroxy proline was studied. The relative yields of c aq, triplet state, and indole cation radical were determined in the absence and in the presence of the amino acids. The yields were determined as a function of laser intensity and the values at very low intensity were compared with the fluorescence quenching results. It was concluded that in these conditions the photoionization of indole occurs via the fluorescent state. From the curves of triplet yield vs laser intensity, the triplet quantum yield extrapolated at low laser intensity was obtained, φr = 0.55 φ 0.05, relative to the literature value of 0.15 for φeag. This gives φF+φeaq= 1.0 ± 0.1 at room temperature. When proline and hydroxy proline were used as singlet quenchers, the yield of In was greater than the yield of caq. This was considered as evidence that a fraction of the quenching processes leads to complete electron transfer from indole to the amino acids.
VACUUM ULTRAVIOLET CIRCULAR DICHROISM OF DOUBLE STRANDED NUCLEIC ACIDS
Authors: Sutherland John C. , Lin Bohai , Mugavero Jo Ann , Trunk John , Tomasz Maria , Santella Regina , Marky Luis , Breslauer Kenneth J. 
Published: January 2008

AbstractThe vacuum ultraviolet (VUV) circular dichroism (CD) of double stranded DNA and RNA is greater in amplitude than the CD of these molecules for wavelengths longer than 200 nm. The amplitude of the VUV‐CD depends on the base composition of DNA, with guanine‐cytosine base pairs contributing more intensity than adenine‐thymine base pairs. The shape and amplitude of the VUV‐CO are better indicators of nucleic acid conformation (A, B or Z) than are those of the longer wavelength CD. We illustrate the unique features of VUV‐CD with specific examples. In the presence of Cs+ and ethanol, VUV‐CD reveals that poly(dA‐dC)poly(dG‐dT) forms a right handed double helix despite the inversion of the longer wavelength CD, which usually is used as a benchmark for the left‐handed form. The greater magnitude of the VUV‐CD of DNA and RNA compared to longer wavelengths means that the VUV‐CD is less susceptible to distortion by the induced CD of UV‐absorbing ligands like mitomycin C and N‐2‐acetylaminofluorene.
DEPLETION OF CUTANEOUS GLUTATHIONE BY ULTRAVIOLET RADIATION*
Authors: Connor Michael J. , Wheeler Larry A. 
Published: January 2008

AbstractSupplemental antioxidants may have a role in ameliorating or preventing the actinic damage that can lead to cutaneous disorders such as skin cancer, hyperpigmentation, and premature aging. Glutathione is an important endogenous antioxidant and fulfills various protective functions in the skin. Irradiation of hairless mice with short (UVB) or long (UVA) wavelength ultraviolet radiation or with UVA combined with a photosensitizing psoralen (PUVA) can deplete skin glutathione levels. Ultraviolet B irradiation causes rapid transient fluctuations in the epidermal glutathione level and the relative amount present as the oxidized form. Ultraviolet A irradiation can deplete epidermal and dermal glutathione for several hours but requires much higher doses than UVB. PUVA treatments may lead to extensive and prolonged depletions of epidermal and dermal glutathione, the severity of which is dependent on the psoralen dose and may last for several days. These transient depletions, oxidations, and sometimes rapid recoveries of cutaneous glutathione levels are compatible with a role for glutathione as an endogenous photoprotective agent in the skin. Experimental evidence supports such a role: for example severe skin edema develops in mice only after about 50% of the glutathione has been depleted by PUVA treatment. Although different mechanisms are involved in each case, glutathione depletion may contribute to the production of phototoxicity by UVB, UVA, and by PUVA. Understanding the depletion mechanisms may allow the development of strategies aimed at preventing loss of cutaneous glutathione, and at reinforcing the natural protective functions of this critical cell component.
INTERMEDIATES IN THE PHOTOCONVERSION OF FUNCTIONAL PHYTOCHROME IN FERN SPORES OF Dryopteris‐I DEMONSTRATION AND QUANTITATIVE CHARACTERIZATION OF THE PHOTOCHROMIC SYSTEM Pr⇔ Ii700USING NANOSECOND‐LASER PULSES*,†
Authors: Scheuerlein R. , Koller D. 
Published: January 2008

Abstract— Spores of Dryopteris paleacea and D. filix‐mas are positively photoblastic with an optimum in the action spectrum around 665 nm. Light is perceived by phytochrome and the relationship between germination and mole fraction of the far‐red‐absorbing form of this pigment, Pfr, was investigated with saturating irradiations between 662 and 747 nm under low‐fluence‐rate conditions. These control irradiations establish a proportion of the total phytochrome, P,tot, as Pfr with Pfr/Ptot–φ at equilibrium. These φ ‐values were calculated according to data for native oat phytochrome (Kelly and Lagarias, 1985, Biochemistry 24, 6003) and the spectral characteristics of the interference filters. With this method a linear relationship could be found between φ and germination from 2 to 70% for D. paleacea and from 2 to 90% for D. filix‐mas, if probit germination was plotted vs probit φThis correlation formed the basis of investigating the phytochrome photoconversion by dye‐laser pulses of 380 ± 30 ns under high‐fluence‐rate conditions, and thus to test quantitatively the impact of the photoreversibility of intermediate reactions of the photoconversion and the red‐absorbing form of phytochrome, Pfr on the final Pfr‐level. Spore germination was initiated by a single‐laser pulse in the range from 592 to 700 nm. The most effective wavelengths were 649 and 660 nm in both species, and at saturation maximal germination (ca. 50%) was obtained from 592 to 665 nm for D. paleacea or ca. 60% germination from 592 to 670 nm for D. filix‐mas. Both saturation levels correspond to a ø‐value between 0.40 and 0.45. This significantly diminished photoconversion is a consequence of the high‐fluence‐rate conditions during the laser pulse which establishes the photochromic system between Pr and a set of very early intermediates, Ii700, (= Pr⇔ Ii700). This system can be described by the extinction coefficients of Pr and the intermediates Ii700, and by the quantum yields, 4,φ for the forward and reverse reactions as φ If φ is calculated, assuming a quantum yield of 1:1 for both reactions and with the extinction coefficients of Pr and Ii7(l() (= lumi‐R) given by Eilfeld and Riidiger (1985, Z. Naturforsch.40c, 109), significantly higher values are calculated for / as compared to φ found in the control experiments.These results can be explained either: (i) with a quantum yield ratio φpr‐φ1700: φ1700φpr=1:1 and an assumed additional dark reaction leading from Ii700 or later intermediates back to Pr: or (ii) with a quantum yield ratio φpr φ 1700: φ1700 φpr=1:2. In this case all Ii700 have to relax to Pfr. In this case all Ii700 have to relax to Pfr.
INVESTIGATION OF DAMAGE TO FOREST BY EPR SPECTROSCOPY in vivo
Authors: Stegmann H. B. , Schuler P. , Ruff H.‐J. 
Published: January 2008

Abstract—Spruce needles collected from several trees of the Black Forest were investigaled by EPR spectroscopy. These needles show in the g = 2.00 region a signal IIS(Tyr D +) and a light‐induced signal I(P700+) and a Mn2+ hyperfine structure which superimposes the other absorptions. Difference spectra, light minus dark, partly eliminate the manganese hyperfine structure, and P700+ can be observed. By comparison of these EPR signals with those of spinach chloroplast or thylakoid membranes described in the literature, significant deviations were observed, whereas several trees grown in the vicinity of Tubingen exhibit the well known D+ and P700+ EPR spectra. After treatment of branches of these ‘normal’ trees with herbicides like Amitrol and Roundup or chemicals like toluene or trichlormethane the EPR signals obtained are comparable with those observed with needles of the Black Forest.
STACKED ZINC TRIPORPHYRIN AS A PHOTOINDUCED MOLECULAR WIRE IN BILAYERS
Authors: SETA P. , BIENVENUE E. , MAILLARD P. , MOMENTEAU M. 
Published: January 2008

AbstractA molecule with three stacked zinc‐porphyrin cycles and two basket‐handles has been synthesized and incorporated into a bilayer lipid membrane. Under light excitation and in the presence of redox compounds in the aqueous phases bathing the membrane, this molecule induces a net electron flux across the membrane. The experimental variations of the flux with some external physicochemical parameters are accounted for by a tentative mechanism which relies on the ability of the porphyrin to act as an electron wire.
PHOTOCHEMISTRY OF 1,2,3‐INDANETRIONE*
Authors: Netto‐Ferreira J. C. , Scaiano J. C. 
Published: January 2008

AbstractThe photochemistry of 1,2,3‐indanetrione (1) has been examined in solution at room temperature by steady state and laser flash photolysis. The triplet state of 1 (T = 6.5 μs, δmux, = 360 and 570 nm, in dry acetonitrile) reacts preferentially via an a‐cleavage process followed by a considerably slower loss of carbon monoxide. Triplet 1 shows a remarkably fast hydrogen abstraction rate constant when in the presence of 1,4‐cyclohexadiene (kr= 1.4 times 106M−1s−1) in spite of its low excitation energy (ET= 42 kcal/mol). This behavior can be explained by assuming that the vicinal carbonyls coplanar to the ketyl radical play an important role in its stabilization.
FORMATION OF OXONIACHLORINS ON PHOTOOXIDATION OF 20‐TRIFLUOROACETOXY‐ AND 20‐CHLORO‐CHLOROPHYLL DERIVATIVES*
Authors: Iturraspe Jose , Gossauer Albert 
Published: January 2008

AbstractZinc complexes of both 20‐trifiuoroacetoxy‐ and 20‐chloro‐pheophorbide‐a methyl ester yield the same isolable 20‐oxonia‐pheophorbide (2b) on irradiation with visible light in methylene chloride for 90 and 10 min, respectively. In the case of the 20‐chloro derivative, the yield amounts to40–50% along with 30% of starting material. Zinc complexes of 20‐trifluoroacetyl‐ and 20‐chloro‐pyropheophorbide‐a methyl ester behave likewise. In aqueous solution, the expected dihydro‐biliverdin derivatives 2 are obtained among other products, some of them display a strong red fluorescence. In the presence of nucleophiles the oxoniachlorin macrocycle is readily cleaved, yielding the corresponding linear tetrapyrroles. Particularly, reaction with cyanide ions leads to biline derivatives, which could serve as intermediates for the synthesis of natural occurring luciferins from bioluminescent plankton. The possible role of some of the above mentioned reactions in connection with chlorophyll catabolism is discussed.
CARBOXYLATED ZINC‐PHTHALOCYANINE, INFLUENCE OF DIMERIZATION ON THE SPECTROSCOPIC PROPERTIES. AN ABSORPTION, EMISSION, AND THERMAL LENSING STUDY
Authors: NEGRI R. MARTíN , ZALTS ANITA , SAN ROMáN ENRIQUE A. , ARAMENDíA PEDRO F. , BRASLAVSKY SILVIA E. 
Published: January 2008

Abstract—Monomer and dimer absorption and emission spectra, and dimerization constants are reported for the diamide of the zinc‐tetracarboxyphthalocyanine in pure dimethylformamide (DMF) and in H2O/DMF mixtures at room temperature. The dimerization constant increases steadily with the water content. The monomer absorption Q‐band is insensitive to the solvent composition, whereas dimer spectra show great variations with the water content. Stationary emission measurements show that fluorescence originates exclusively from the monomers. The fluorescence spectrum as well as its absolute fluorescence quantum yield, measured by steady‐state thermal lensing, are also insensitive to the solvent composition. The thermal lensing method is discussed for the case of two absorbing species in equilibrium.
MITOTIC INHIBITION BY PHENYLPORPHINES AND TETRASULFONATED ALUMINIUM PHTHALOCYANINE IN COMBINATION WITH LIGHT
Authors: Berg Kristian , Moan Johan 
Published: January 2008

Abstract—This work relates to studies on modes of phototoxicity by tetrasulfonated aluminium phthalocyanine (AIPcS4), tetrahydroxy‐ and monosulfonated meso‐tetraphenylporphines (3‐T‐HPP and TPPS,) on culture cells. Toxicity at moderate light exposures appears to be related to inhibition of microtubule function. Treatment of human cervix carcinoma cells of the line NHIK 3025 incubated for 18 h with the sensitizers and exposed to light inhibits multiplication for the first hours after light exposure, a significant fraction of the cells accumulating in mitosis. For the first hours after treatment, the mitotic cells were always mainly found in metaphase; generally seen as c‐metaphases and three‐group metaphases. During this time, anaphase and telophase cells were absent or greatly reduced in number. Indirect immunofluorescence staining of P‐tubulin showed that the spindle apparatus of mitotic cells was perturbed in all cases.The accumulation in mitosis was more extensive after treatment with AIPcS4 and light than after treatment with 3‐T‐HPP or TPPS1 and light. This may be related to the great difference in the lipophilic properties of these sensitizers; i.e. AIPcS4 being highly water soluble while TPPS, and 3‐T‐HPP are lipophilic sensitizers. The lipophilicity of several sensitizers has been measured by two different methods, the partition between an aqueous and a lipophilic phase (Triton X‐114) and the binding strength to a reverse phase column. The results show that the measured relative lipophilicity of the sensitizers may be influenced by the method of analysis.
ACTION SPECTRUM FOR ENHANCEMENT OF PHOTOTROPISM BY Arabidopsis thaliana SEEDLINGS
Authors: Janoudi Abdul‐Kader , Poff Kfnneth L. 
Published: January 2008

Abstract—Fluence‐response relationships have been measured at wavelengths from 350 to 760 nm for the enhancement of phototropism in Arabidopsis thulium L. (Heynh) strain “Estland” by an irradiation at each of these wavelengths, given 2 h prior to a 450 nm inductive unilateral irradiation. Action spectra have been constructed from these fluence‐response relationships based on: (i) the fluence required to obtain a curvature of 25° (corresponding to an enhancement of 15°), (ii) the fluence required to obtain 50% of the maximum enhancement and (iii) the fluence threshold for enhancement by a pre‐irradiation. The action spectra exhibit two maxima, one at 669 nm and a second at 378 nm. The height of the maximum at 669 nm is approximately 4 times the height of the maximum at 378 nm. Based on the action spectra, it is concluded that the enhancement of phototropism in A. thaliana is mediated by phytochrome.
DETECTION AND PARTIAL SEQUENCE OF PHYTOCHROME GENES IN THE FERNS Anemia phyllitidis (L.)Sw (SCHIZAEACEAE) AND Dryopteris filix‐mas L. (POLYPODIACEAE) BY USING POLYMERASE‐CHAIN REACTION TECHNOLOGY*
Authors: Maucher Helmut P. , Scheuerlein Robert , Schraudolf Helmut 
Published: January 2008

Abstract—Phytochrome controls several developmental steps during formation and differentiation of the fern gametophyte, including spore germination, morphogenesis of the gametophyte or differentiation of the sexual cells. To obtain information about the amino acid sequence and the regulation of phytochrome expression at the gene level, two degenerated oligonucleotides against well conserved amino acid regions were designed after an optimal alignment of the known phytochrome sequences. These primers were tested against DNA isolated from Arabidopsis thaliana, and the polymerase‐chain reaction (PCR) products were cloned and sequenced. The DNA fragment produced with this method proved to be identical with a phytochrome‐A‐gene fragment from A. thaliana, and hence this fragment was used in further experiments to prove whether amplified DNA from fern species contains phytochrome‐like DNA. With this procedure we successfully detected and cloned gene fragments both from gametophytes of Anemia phyllitidis and Dryopteris filix‐mas, cultured for 7 days under vegetative conditions. In addition, poly(A)+ RNA was prepared from 7‐day‐old gametophytes of A. phyllitidis, induced to differentiate antheridia under generative conditions. This poly(A)+ RNA was transcribed into complementary DNA and used together with both phytochrome specific primers in a PCR experiment. We thereby obtained another DNA fragment. These data strongly suggest that A. phyllitidis has at least two phytochrome genes, and that at least one of them is expressed in light‐grown gametophytes.
FORTY YEARS OF BLUE‐LIGHT RESEARCH AND NO ANNIVERSARY
Authors: Galland Paul 
Published: January 2008

Abstract—The status of near‐ UV/blue‐light research is described and critically assessed. It is argued that the generally accepted proposition of flavins acting as near‐ UV/blue‐light photoreceptors is reasonable, but that also other pigments, specifically pteridines and pterins, should be considered. In view of the fact that a receptor assay, applicable to any organism and near‐UV/blue‐light reaction, is not yet at hand, caution appears to be indicated as to what one can accept as a reasonable “criterion” for the involvement of any proposed photoreceptor pigment.
NEW PHTHALOCYANINE PHOTOSENSITIZERS FOR PHOTODYNAMIC THERAPY
Authors: Oleinick Nancy L. , Antunez Antonio R. , Clay Marian E. , Rihter Boris D. , Kenney Malcolm E. 
Published: January 2008

AbstractSix new aluminum and silicon phthalocyanines have been synthesized and their photocytotoxicity toward V79 cells has been studied. The compounds that have been prepared are: AIPcOSi(CH3)2(CH2),N(CH3)2, I; AIPcOSi(CH3)2(CH2)3N(CH3)3+I−, II; CH3SiPcOSi(CH3)2(CH2)3N(CH3)2, III; HOSiPcOSi(CH3)2(CH2)3N(CH3)2, IV; HOSiPcOSi(CH3)2(CH2)3)3(CH3)3+I−, V; and SiPc[OSi(CH3)2(CH2)3N(CH3)3+I−]2, VI. Relative growth delay values for compounds I‐VI and relative cytotoxicity values for compounds I, II, IV, V and VI have been determined. Compounds I and II have been shown to be comparable in photocytotoxicity to what is presumed to be AIPcOH.xH2O, and compound IV has been shown to have greater activity. The classes of compounds to which these six compounds belong appear to have potential for photodynamic therapy.
THE PHOTOPHYSICAL PROBE, 7‐AZATRYPTOPHAN, IN SYNTHETIC PEPTIDES
Authors: Rich K. L. , Négrerie M. , Li J. , Elliott S. , Thornburg R. W. , Petrich J. W. 
Published: January 2008

Abstract7‐Azatryptophan is proposed as an alternative to tryptophan as a photophysical probe in the study of protein structure and dynamics. Not only are the spectral characteristics of 7‐azatryptophan easily distinguishable from those of tryptophan, but this nonnatural amino acid is shown to be amenablc to incorporation into peptides. We present the first synthesis and purification of a synthetic peptide containing 7‐azatryptophan, NAc‐Pro‐7‐azatryptophan‐Asn‐NH2, which is shown to be a competitive inhibitor of α‐chymotrysin.
SITES OF PHOTODAMAGE BY THE IMINIUM SALT OF A COPPER OCTAETHYLBENZOCHLORIN
Authors: Kessel David 
Published: January 2008

AbstractBecause the benzochlorin derivative copper (11) α‐meso‐N,N′‐dimethyloctaethylbenzochlorin iminium chloride (CDSI) is not fluorescent, sites of drug localization in L1210 cells were detected by indirect methods involving using a series of fluorescent probes. The CDS1‐mediated cytotoxicity was associated with mitochondrial damage, a decreased membrane potential and an increase in the heterogeneity of membrane sites of binding of a polar analog of diphenylhexatriene. Although CDS l is a cationic compound, its accumulation was not impaired in a cell line exhibiting the multidrug resistance phenotype.