bluuebunny/crossref_metadata_2025_split huggingface dataset:
QUENCHING OF THE EXCITED STATES OF 2‐PHENYLBENZOXAZOLE BY AZIDE ANION. FLUORESCENCE AND ESR STUDY
Authors: Reszka K. , Hall R. D. , Chignell C. F. 
Published: January 2008

AbstractElectron spin resonance, spin‐trapping and fluorescence techniques demonstrate that 2‐phenylbenzoxazole (P) participates in photo‐induced reactions with alcohols and electron donors like the azide ion. Irradiation of Pat 300 nm in deaerated ethanol produces ethoxyl and hydroxyethyl radicals which can be detected with the spin trap, 5,5‐dimethyl‐l‐pyrroline‐l‐oxide (DMPO). However, irradiation of P in the presence of N‐3 leads to the appearance of the azide radical, N‐3, which also reacts with DMPO. Studies with the nitroxyl radical, 2,2,6,6‐tetramethylpiperidine‐l‐oxyl (TEMPO), suggest that electron transfer from the azide anion to an excited state of P yields the semi‐reduced sensitizer, P‐, which in turn reacts with TEMPO. The effect of sodium azide upon the fluorescence intensity and lifetime of P in aqueous ethanol has also been studied.
INDUCTION OF PHOTOPRODUCTS IN SYNTHETIC POLYNUCLEOTIDES BY FAR AND NEAR ULTRAVIOLET RADIATION
Authors: L. Mitchell David , Clarkson Judith M. 
Published: January 2008

AbstractSingle and double‐stranded polynucleotides of thymine and cytosine have been used to analyse the photoproducts produced by irradiation with far or near UV light. Reversed‐phase high performance liquid chromatography was used to detect and quantify cyclobutane dimers and Pyr(6–4)Pyo adducts produced by 254 nm. At 320 nm 10‐times less Thy(5–6)Thy dimers and one half the number of Cyt(5–6)Cyt dimers were induced; no Pyr(6–4)Pyo adducts were evident.HPLC has recently been applied to the isolation and characterization of various nucleic acid substituents and their UV‐photoproducts. The relative retention times of pyrimidines and their UV photoproducts on HPLC reflect differences in the hydrophobicity of the compounds being separated. Hence, the more hydrophobic (less polar) a compound is, the greater its capacity to bind to the column and the greater its retention time; for T o T, C<>T and C<>C dimers this difference may result from variations in the number of methyl moieties (Cadet et al., 1983). The retention time of the compound also depends on its stereochemistry. Separation of the four stereoisomers of T<>T by HPLC shows that compounds which are molecular equivalents can be more or less accessible to the non‐polar stationary phase depending on their conformation (Cadet, 1980). The relatively long retention times of the bipyrimidine photoadducts suggest a structural configuration which allows greater access to the hydrophobic moieties of the molecule.It is intriguing to consider that this difference in conformation may also be reflected in DNA–protein interactions such as binding by UV‐endonucleases or antibodies directed against UV photodamage. Proteins can be used as sensitive probes for photoproduct induction and repair but an accurate evaluation of their specificity is required. It was the intent of this paper not only to compare the induction parameters for various dimers in pyrimidine homo‐polymers but to provide controlled substrates which can be used to define the relative binding efficiencies of repair enzymes and antibodies for different types of photoproducts.
DETECTION OF DNA‐PSORALEN PHOTOADDUCTS in situ
Authors: ZAREBSKA ZOFIA , JARZABEK‐CHORZELSKA MARIA , RZȨSA GENOWEFA , GLIŃSKI WIESLAW , PAWIŃKA MARIA , CHORZELSKI TADEUSZ , JABLOŃKA STEFANIA 
Published: January 2008

Abstract— An immunological method, with the use of specific immune serum, has been developed for detection of 8‐methoxypsoralen (8‐MOP) photoadducts to DNA, formed in situ in cell nuclei, after combined treatment with 8MOP and UV‐A irradiation (Zarçbska et al., 1978). Lymphocytes fixed on slides or in suspension, and cryostat sections of different mammalian tissues, served as antigenic substrate, after treatment with 8‐MOP and UV‐A in vitro. Specific fluorescence in these substrates was detected in the nuclei after treatment with 30 ˜ 140 kJ/m2 UV‐A in the presence of 0.1‐0.3 μg/cm2 8‐MOP. PHA‐stimulated‐lymphocytes appeared to be the most sensitive substrate.However, hairless mice treated with high doses of UV‐A in vivo, 70 ˜ 360 kJ/m2 did not reveal a specific fluorescence of epidermal nuclei, unless a high local concentration of 8‐MOP was attained.The apparent discrepancy in the level of photoadduct detection between the in vitro and in vivo treated specimens was explained by the low number of DNA‐8‐MOP‐photoadducts formed in vivo under these experimental conditions. The relevance of these findings to the role of DNA‐8‐MOP‐photoadducts formed during PUVA photochemotherapy is discussed.
THE ROLE OF ARGININES 82 AND 227 IN THE BACTERIORHODOPSIN PROTON PUMP
Authors: Drachev L. A. , Kaulen A. D. , Khorana H. G. , Moci T. , Postanogova N. V. , Skulachev V. P. , Stern L. J. 
Published: January 2008

AbstractArginine residues 82 and 227 in bacteriorhodopsin were replaced by glutamine residues, using the site‐directed mutagenesis techniques. Mutant bacteriorhodopsins were found to be competent in formation and decomposition of the photocycle M412 intermediate as well as in generation of photoelectric potential provided that pH of the medium is sufficiently high. Lowering of pH results in transition of bacteriorhodopsin into a blue acidic form which cannot produce M412 and photo‐potential. The pK values of these transitions for Arg‐227 → Gln and Arg‐82 → Gln mutants are shifted correspondently for 1 and 4 pH units to a higher pH region in comparison with native bacteriorhodopsin. The rate of the M412 formation in both mutants was similar to that in the native protein. As to M412 decay, it is much slower in Arg‐227 → Gln mutant than in native and Arg‐82 → Gln bacteriorhodopsins. In all cases, the decay depends only slightly upon pH. It is concluded that Arg‐82 is involved in maintenance of a bacteriorhodopsin structure that is resistant to the pH decrease down to 4 whereas Arg‐227 is required first of all for the process of Schiff base reprotonation.
ON THE POLARITY OF GREENING IN PRIMARY LEAVES OF DARK AND LIGHT‐GROWN SEEDLINGS OF Triticum aestivum*
Authors: Schönbohm Ekkehard 
Published: January 2008

Abstract— In primary leaves of four‐day‐old dark‐grown wheat seedlings the capability to accumulate chlorophyll under white light is highest in the tissues of the apical region. It declines though, as the dark‐grown seedling ages and the primary leaf grows longer. This decrease is lower in the basal than in the apical regions of a leaf, which results in an inverted polarity of the capability to accumulate chlorophyllIf the seedlings are grown under continuous white light applied from four different directions, the high capability of greening observed in the apical tissues of young leaves stays at that level even in old seedlings: the polarity does not change during culturing. The saturation‐level of greening is much higher in the tissues taken from the apical region of a primary leaf than in those from the basal region.
THE VECTORIAL PHOTO‐EXCITATION IN SOLAR‐TRACKING LEAVES OF Lavatera cretica (MALVACEAE)*,†
Authors: Koller Dov , Levitan Irene , Briggs Winslow R. 
Published: January 2008

Abstract— The diaphototropic responses of the solar‐tracking leaves of Lavatera cretica were studied under constant levels of vectorial photo‐excitation (negligible variations in angle of incidence and fluence rates). The results showed the following:(a) The photoreceptors, that are associated with the (major) veins, can equally perceive vectorial excitation (by an oblique light‐beam in the plane of symmetry of the vein), directed either towards its tip (tip‐oriented: TO), or towards its base (base‐oriented: BO).(b) The mechanism of photo‐perception is apparently qualitatively the same for TO and BO excitation.(c) The response to TO and BO vectorial excitation, which takes place in a circular sheath of motor‐cell tissue in the pulvinus (a2–3 mm long segment at the top of the petiole), is also highly directional and results in bending in the vertical plane of the oblique beam. Each sector of the motor tissue can expand longitudinally in response to TO excitation, presumably by influx of solutes, and contract longitudinally in response to BO excitation of the same vein, presumably by efflux of solutes.(d) The angular velocity of the vectorial response to a constant level of vectorial excitation remains constant over large angular displacements and long periods, and was similar for TO and BO over a wide range of fluence rates (30‐400 μmol m−2s−1) of white light (400‐700 nm).(e) Reversal of the direction of vectorial excitation (TO to BO, and vice versa) results in reversal of the direction of the vectorial response (laminar reorientation). The change in the direction of laminar reorientation involved a larger overshoot in the original direction when the change was from BO to TO, than in the reverse case.
INCANDESCENT LAMPS CAN PRODUCE PYRIMIDINE DIMERS IN DNA
Authors: Ciarrocchi Giovanni , Sutherland Betsy M. , Sutherland John C. 
Published: January 2008

Abstract—DNA molecules that have been exposed to light from a 150 W incandescent spot lamp are nicked by the Micrococcus luteus endonuclease specific for cyclobutyl‐type pyrimidine dimers. The production of these enzyme‐sensitive sites increases with increasing spot lamp exposure. These sites have been confirmed to be pyrimidine dimers by their property of being photoreversed by an E. coli photoreactivating enzyme. The emission spectrum of the lamp shows detectable output at wavelengths less than 320 nm. These results indicate that the sensitivity of the techniques utilized in this work can be used to detect low levels of contaminating UV radiation.
A STUDY OF AQUEOUS SOLUTIONS OF NUCLEIC ACID CONSTITUENTS EXPOSED TO MONOCHROMATIC 160 nm VACUUM‐UV LIGHT BY SPIN‐TRAPPING METHOD
Authors: Kuwabara Mikinori , Minegishi Atsuko , Ito Atsushi , Ito Takashi 
Published: January 2008

AbstractSpin‐trapping technique was employed to detect and identify free radical intermediates produced in aqueous solutions of nucleic acid constituents (pyrimidine bases and pyrimidine nucleosides) after irradiation by monochromatic 160 nm vacuum‐UV light from the electron storage ring. Short‐lived free radicals produced in the molecules were converted into relatively long‐lived free radicals (spin‐adducts) by the reaction with MNP used as a spin trap. The resulting nitroxide radicals were subsequently analysed by esr.The esr measurements were made after irradiating H2O solution containing sample and the spin trap and once freeze‐drying it and re‐dissolving the residual powder in D2O to get the spectrum with a well‐resolved hyperfine structure. Thus, clear evidence that most of the radicals were not formed by H‐addition but formed by OH‐addition at the C5 position of the 5, 6 double bond were obtained for pyrimidine bases. For pyrimidine nucleosides, although the effect of H2O‐D2O exchange was not recognized on resolution improvement of the hyperfine structure of the esr spectra, careful analysis of the hyperfine structure made it possible to identify the radical structures; OH‐addition radicals at the C6 of the double bond of the base moiety in addition to the OH‐addition radicals at the C5 position for all except for 2‐deoxycytidine. Evidence for the formation of free radicals at the sugar moiety was not clear.
RECENT ADVANCES IN POLARIZATION SPECTROSCOPY: PERSPECTIVES OF THE EXTENSION TO THE SOFT X‐RAY REGION
Authors: Bustamante C. , Maestre M. F. , Wells K. S. 
Published: January 2008

AbstractIn this paper we present a general review of some of the new branches in the field of optical activity that have been developed during the last five years. Also, the conditions under which circular intensity differential scattering can be measurable in the soft X‐ray region of the spectrum are established. It is found that the parameter which determines the strength of the preferential interaction of chiral molecules with opposite circular polarizations at these high energies is the anisotropy of the atomic polarizabilities in the molecule. The possibility of extending the other techniques discussed here to shorter wavelengths, is also discussed.
CELL SURFACE DAMAGE IN CULTURED MAMMALIAN CELLS WITH SYNCHROTRON RADIATION AT 160 nm
Authors: Shinohara Kunio , Ito Atsushi , Ito Takashi 
Published: January 2008

AbstractCultured mammalian cells (HeLa) were allowed to attach onto a membrane filter and were irradiated with 160 nm synchrotron radiation. The cells then were rinsed with medium, fixed, and stained. Some of the cells became detached from the membrane filter during irradiation before post‐irradiation incubation at 37°C. The cells remaining attached to the membrane filter were released by trypsinization, collected and examined for dye‐exclusion ability with eosin Y. The number of stained cells was increased when the cells were irradiated at 160 nm, while no such increase was observed in cells irradiated with synchrotron radiation at 220 nm, with a low pressure Hg lamp (predominantly 254 nm), or with gamma‐rays of 60Co. These results indicated that the cell surface was injured by irradiation with synchrotron radiation at 160 nm.
CHOICE OF COATINGS FOR THE OPTICAL ELEMENTS IN THE IRRADIATION SYSTEM OF VACUUM‐ULTRAVIOLET RADIATION ABOVE 50 nm
Authors: Hidea Kotaro , Maezawa Hiroshi , Ito Atsushi , Kobayashi Katsumi , Furusawa Yoshiya , Ito Takashi 
Published: January 2008

AbstractThe spectral throughput of a vacuum‐ultraviolet irradiation system at the SOR‐RING facility was examined with various combinations of aluminum‐and gold‐coated optical elements in a 2.2‐m modified Wadsworth monochromator. We found that the optimum was a combination of an aluminum‐coated collimating mirror, concave grating, and plane deflecting mirror, and a combination of a gold‐coated collimating mirror, concave grating and an aluminum‐coated plane deflecting mirror in the wavelength regions 190‐110 nm and 110‐50 nm, respectively.
FLUENCE‐RATE DEPENDENCE OF MONOPHOTONIC REACTIONS OF NUCLEIC ACIDS IN VITRO AND IN VIVO
Authors: Lang H. , Riesenberg D. , Zimmer Ch. , Bergter F. 
Published: January 2008

AbstractThe Bunsen‐Roscoe law, also known as the reciprocity law (E=f(F) with F=I t) has only limited validity for monophotonic reactions of nucleic acids. Especially at low fluence rates, the extent of in vitro and in vivo photoreactions of nucleic acids in the far‐UV and near‐UV range is a function of the fluence and of the fluence rate (E=f (F;I)). In vitro experiments with poly(dA)poly(dT) clearly show that the far‐UV (254 nm) response, indicated by the changes of the ellipticity at 315 nm, does not obey the Bunsen‐Roscoe law at low fluence rates in the range between 1 W m‐2 and 20 W m‐2. In vivo experiments with Escherichia coli revealed very similar anomalies. Studying the growth delay after irradiation with far‐UV light at 280 nm or near‐UV light at 334 nm, we have confirmed the lack of reciprocity in both spectral ranges. The failure of the Bunsen‐Roscoe law for the 280 nm and 334 nm UV irradiation effect at low fluence rates was in the range O < I < 40 W m‐2. In both cases reciprocity occurred at higher fluence rates (40 < I < 100 W m‐2).
QUENCHING OF PYRENE FLUORESCENCE BY TRYPTOPHAN IN MICELLAR SOLUTIONS
Authors: Encinas M. V. , Lissi E. A. 
Published: January 2008

AbstractDeactivation of excited pyrene incorporated to cationic (cetyltrimethylammonium chloride), anionic (sodium dodecyl sulfate) and neutral (Triton X‐100) micelles by tryptophan has been investigated over a wide pH range. Data obtained allow an estimation of the tryptophan association to the micelles, of the tryptophan apparent pK in the micellar solutions, and of the dynamics of tryptophan incorporation to the micellar pseudophase. In particular, the data obtained at pH 7 allow an estimation of the effect of the micellar charge upon the binding capacity of the tryptophan zwitterion.
THE EFFECTS OF PORPHYRIN STRUCTURE AND AGGREGATION STATE ON PHOTOSENSITIZED PROCESSES IN AQUEOUS AND MICELLAR MEDIA
Authors: Lambert C. R. , Reddi E. , Spikes J. D. , Rodgers M. A. J. , Jori G. 
Published: January 2008

AbstractThe efficiency of several porphyrins at 10 μM and 83 μM as sensitizers of the photooxidation of 0.1 mM tryptophan and histidine via a singlet oxygen‐mechanism was studied in pH 7.4‐buffered aqueous solutions and in aqueous dispersions of Triton X‐100 micelles. The porphyrins were either solubilized in the bulk aqueous medium or associated with the micellar phase, whereas the amino acids were always located in the aqueous phase. With those porphyrins, such as uroporphyrin I, meso‐tetra (4‐sulfonatophenyl)porphine, meso‐tetra(4‐carboxyphenyl)porphine and meso‐tetra)N,N,N‐trimethylanilinium)porphine, which are > 98% monomeric in both media, the efficiency of histidine photooxidation was independent of the site of O2(1Δg) generation, as shown by the closely similar values for the photooxidation rate constant and oxygen‐consumption quantum yield in the presence and absence of Triton micelles; the same indications were provided by photokinetic experiments with tryptophan. Actually, laser flash photolysis studies showed that the micelle‐incorporation of the above mentioned porphyrins brought about only minor changes in their photophysical properties, including the relative yield of O2(1Δg) generation. On the other hand, hematoporphyrin IX, its Zn2+‐complex, and coproporphyrin III are largely aggregated in homogeneous aqueous solution; their incorporation into Triton micelles caused an increase of the triplet quantum yield and an enhancement of the oxygen‐consumption quantum yield and photooxidation rate constant for both histidine and tryptophan. The lower photosensitizing efficiency of aggregated porphyrin species in comparison with the corresponding monomeric porphyrin was confirmed by measuring the initial rate and quantum yield of oxygen consumption upon irradiation of 1 mM histidine and tryptophan in the presence of different hematoporphyrin concentrations within the 0.3‐100μM range.
ANALYTICAL MODEL OF PHOTOTHERAPY FOR NEONATAL JAUNDICE—I. THE INITIAL Z‐E TRANSIENT
Authors: Pratesi Riccardo , Ronchi Laura , Locchi Fabrizio 
Published: January 2008

AbstractA simple model of phototherapy (PT) for neonatal jaundice is presented. Two coupled systems are considered: the “skin” (upper skin layers and vascular network where phototherapy light may penetrate) and the “body” (i.e. the “dark” ensemble of blood vessels and organs where circulation and metabolization of biliribin (BR) and its photoisomers occur).The mathematics necessary to analyze the PT process is presented together with an appropriate optical model of skin based on a multilayered system to which the theory of radiation transfer in isotropically scattering and absorbing media is applied. A simple matrix formalism is introduced to determine analytically the light distribution in the multilayer skin. The results are. then, used to analyze the initial transient of PT, i.e. configurational isomerization up to photoequilibrium in the superficial skin layers under blue (450 nm) and green (500 nm) light irradiation within a time interval sufficiently short to neglect diffusion of pigments and formation of structural isomers of BR.Strong coupling among the various BR layers due to the time variation of diffuse transmittance and reflectance is found, resulting in complicated time patterns with initial and final single‐exponential behavior. The initial decay constant of BR concentration depends sensibly on the depth of the layer, while the final one is independent of it. As expected the amount of BR conversion at photoequilibrium is larger with blue than with green light. However, at sufficiently larger depths green light is more efficient than blue light to produce the initial conversion of ZZ to ZE isomers of BR.The present analysis has some relevance for the understanding of the different efficiencies of coloured fluorescent lamps in clinical PT. The application of the complete model (“skin”+“body”) requires the knowledge of the diffusion constants and absorption coefficients of pigments and of the optical parameters of deep cutaneous tissues.
THE EFFECT OF ACIDS ON THE INFRARED SPECTRA OF SCHIFF BASES—I. NON‐CONJUGATED IMINES
Authors: Lussier L. S. , Dion A. , Sandorfy C. , Le‐Thanh Hoa , Vocelle D. 
Published: January 2008

AbstractThe Fourier‐transform infrared spectra of CHCl3 solutions containing a non‐conjugated imine, R1HC=NR2 and an acid of the series HCl, HBr, HI, trichloro‐, dichloro‐, monochloro‐, monobromo acetic acids and propionic acid have been recorded. Both the N+H and double bond stretching regions are examined. The results show that HCl, HBr and HI protonate the imine completely, trichloroacetic acid to about 90‐95%, the other haloacetic acids to 55‐80% and propionic acid to <10%. Considered as model studies for the problem of protonation in rhodopsins our results lead to the conclusion that with the relatively weak acids available in the pigments full protonation requires a stabilization mechanism which should be further investigated.
PHOTOCHEMISTRY OF MELANIN PRECURSORS: DOPA, 5‐S‐CYSTEINYLDOPA AND 2,5‐S,S'‐DICYSTEINYLDOPA
Authors: Land E. J. , Thompson A. , Truscott T. G. , Subbarao K. V. , Chedekel M. R. 
Published: January 2008

AbstractThe photochemistries of the melanin precursors dopa, 5‐S‐cysteinyldopa (5‐SCD) and 2.5‐S,S'‐dicysteinyldopa (2.5‐SCD) were investigated by 265‐nm laser flash photolysis. The quantum yield of hydrated electron following flash photolysis of dopa (9.1%) was half the yield of dopasemiquinone (19.6%), implying that dopasemiquinone is formed via two primary photochemical mechanisms: photionisation (giving e) or photohomolysis (giving H˙). Dopasemiquinone rapidly disproportionates to form dopaquinone and re‐form dopa. Dopaquinone in turn decays via a base‐catalysed unimolecular cyclisation eventually to form dopachrome. Assignment of the transient species was confirmed by previous pulse radiolysis studies of the one‐electron oxidation of dopa. In contrast, flash photolysis of the cysteinyldopas, 5‐SCD and 2,5‐SCD results in lower photoionisation quantum yields and the production of initial transient species whose absorption spectra were markedly different from their semiquinone absorption spectra previously determined pulse radiolytically. These observations indicate that the primary cysteinyldopa photochemical species is not such a semiquinone, but rather results from S‐CH2 bond photohomolysis. Absorption spectra and rate constants for the formation and decay of various transient species are reported.
KINETICS OF PHOTOREACTIVATION AND LIQUID‐HOLDING RECOVERY IN YEAST CELLS
Authors: Johnson Ronald G. , Haynes Robert H. 
Published: January 2008

Abstract— A method is presented for analyzing data on the kinetics of photoreactivation and liquid‐holding recovery in microorganisms. The method extracts, from measurements on survival, the number of repairable lethal hits per cell remaining after a period of photoreactivation or liquid‐holding recovery. A semilogarithmic plot of this quantity as a function of the duration of the survival‐enhancing treatment reveals the nature of the kinetics of inactivation of the lethal hits.The method has been applied to photoreactivation and liquid‐holding recovery in yeast cells with wild‐type radiation resistance. In the case of photoreactivation of ultraviolet‐damaged cells, the number of lethal hits per cell is found to decrease exponentially with the length of exposure to a continuous source of photoreactivating light. Liquid‐holding recovery in cells exposed to ultraviolet light or X‐rays also results in exponential decrease of lethal hits with increasing time.The method is compared with the fluence‐decrement method and Dulbecco's treatment of photoreactivation data.