bluuebunny/crossref_metadata_2025 huggingface dataset:
LIGHT‐INDUCED ELECTRON TRANSFER REACTIONS BETWEEN CHLOROPHYLL and ELECTRICALLY CHARGED ACCEPTORS IN POSITIVELY and NEGATIVELY CHARGED LIPID BILAYER VESICLES*
Authors: Senthilathipan Velu , Tollin Gordon
Published: January 2008

Abstract— The effects of electrostatic interactions on the dynamics of photoinduced electron transfer reactions involving chlorophyll and electrically charged acceptors (either positively charged methyl viologen or negatively charged sulfonated quinones) have been investigated by laser flash photolysis in lipid bilayer vesicles into which varying amounts (0‐30 mole percent) of positively or negatively charged surfactants were incorporated. Chorophyll triplet decay kinetics were modified due both to vesicle expansion caused by charge repulsion effects, and to changes in the local concentration of quenchers resulting from attractive or repulsive interactions with the vesicle surface. Radical yields were either increased or decreased as a result of electrostatic interactions which occurred between the radical products of triplet quenching and the charged surface, and which acted upon the radical ion‐pair separation process. In some cases, these effects were quite large. Radical decay halftimes were also changed by large amounts as a consequence of either attractive or repulsive forces acting upon the acceptor ion‐radical species, which influenced its ability to undergo reverse electron transfer to oxidized chorophyll. In the most favorable case, approximately 100% of the chlorophyll triplets produced by pulsed laser excitation were converted into radicals, which decayed by reverse electron transfer with a halftime of 70 ms.
VARIATION OF STERN‐VOLMER QUENCHING CONSTANTS IN MICELLAR SOLUTION AS A FUNCTION OF AQUEOUS OR MICELLAR QUENCHER
Authors: Gabor Gavriella , Turro Nicholas J.
Published: January 2008

Abstract— The critical micelle concentration (CMC) of a fluorescent detergent may be measured by determining Stern‐Volmer quenching parameters as a function of detergent concentration. The CMC's of a cationic detergent, 11‐(3‐hexyl‐l‐indolyI)undecyltrimethylamrnoniurn bromide (6‐In‐ll+), and an anionic detergent, sodium H‐(3‐hexyI‐l‐indoiyI) undecyl sulfate (6‐In‐ll−) were determined by this quenching procedure. Quenchers which were predominantly located in the aqueous phase (e.g. Co2+) or in the micellar phase (e.g. benzophenone) were employed. Aqueous phase quenchers are more effective below the CMC and cause a decrease in the long wavelength portion of the fluorescence band of the indole moiety. Quenchers located in the micellar phase are more effective above the CMC and decrease the short wavelength portion of the fluorescence band of the system.
ON THE POLARITY OF PHYTOCHROME CONTROLLED LEAF UNFOLDING IN DARK‐GROWN SEEDLINGS OF TRITICUM AESTIVUM*
Authors: Schönbohm Ekkehard
Published: January 2008

Abstract— The apical ends of sections cut from etiolated primary wheat leaves show a higher degree of phytochrome‐mediated leaf unfolding than the basal ends, regardless of the position of the segment in the leaf. It could be clarified that this polarity is not the result of a stable gradient within the intact dark grown leaf. Partial irradiation experiments have shown that leaf unfolding can be induced much more effectively by an irradiation of the apical half of a section than of the basal half. Though only the basal end of the sections was incubated with gibberellic acid (GA3) in darkness, the degree of the GA3‐induced leaf unfolding was highest at the apical end of these non‐irradiated segments. The results suggest that in each separate leaf section a new gradient of a still unknown “unfolding‐factor” is established.
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 chlorophyll

If 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.
AN ANALYSIS OF PHOTO‐INDUCED FRUITING IN Coprinus congregatus*
Authors: Manachère G. , Bastouill‐Descollonges Y.
Published: January 2008

Abstract— Experiments are described to determine the effect of short irradiations on the initiation and differentiation of sporophore primordia in Coprinus congregatus and on the morphogenesis in darkness of such photo‐induced primordia. Photoinduction is characterized either by development in darkness of etiolated primordia, or by a subthreshold state where no visible primordia are recognizable but where interaction with a subsequent light pulse can be shown. The photo‐induced primordia abort after about 4.5 to 7.5 days in darkness. The photoinduction itself is memorized for a longer period (8.5 to 9.5 days) in darkness.
PHOTOSYNTHATE PARTITIONING INTO Digitaria decumbens LEAF STARCH VARIES RHYTHMICALLY WITH RESPECT TO THE DURATION OF PRIOR INCUBATION IN CONTINUOUS DIM LIGHT*
Authors: Britz Steven J. , Hungerford Wayne E. , Lee David R.
Published: January 2008

Abstract— In bright light the proportion of photosynthate stored as starch in leaves of Digitaria decumbens Stent, (pangolagrass) depends in a cyclic fashion on the duration of prior incubation in dim light. We suggest that a circadian rhythm, which runs during dim light conditions, controls the partitioning of photosynthate during subsequent bright light conditions. Varying the interval of dim light prior to transfer to bright light reveals this rhythm. The results emphasize the importance of endogenous timing mechanisms in relation to day and night length and the control of photoassimilate distribution and plant growth.
FLUORESCENCE QUENCHING OF ALLOPHYCOCYANIN AND PHYTOCHROME BY ESTRIOL*
Authors: Plenzler Grazyna , Miedziejko Ewa
Published: January 2008

Abstract— At 293 K the long‐wavelength absorption and emission band of 1.4 μM allophycocyanin is decreased by estriol (Δ1‐3‐5(10)‐estratriene‐3,16α, 17β‐trio!) in the range 0.8‐6.6 μM in the presence of 11% alcohol (vol/vol). The binding of estriol is shown to be of high affinity, 1:1 with allophycocyanin. The free energy of this binding process (ΔG°) is ‐33.6 kJ mol' and single binding site dissociation constant (KD) 1.0 ×10–6M. Estriol at 21 μM effectively quenches the fluorescence of 1.4 M large molecular weight phytochrome in its red absorbing form at 77 K while having little or no effect on the phototransformation difference spectrum at 293 K.
REPAIR OF 8‐METHOXYP SORALEN PHOTOINDUCEDCROSS‐LINKS and MUTAGENESIS: ROLE OF THE DIFFERENT REPAIR PATHWAYS IN YEAST
Authors: Cassier C. , Chanet R. , Moustacchi E.
Published: January 2008

Abstract— In Saccharomyces cerevisiae, a re‐irradiation with a saturing dose of UVA after pretreatment with 8‐methoxypsoralen (8‐MOP) plus low doses of UVA and removal of unbound 8‐MOP lead to an increase in frequency of forward mutants in strains defective in the excision (radl‐3, radl‐Δ, rad2‐6) or in the recombinational (rad52‐l) repair pathways. Such an enhancement attributable to DNA interstrand cross‐links was not observed in mutants blocked in a mutagenic repair pathway (rad6‐Δ and pso2‐l). These results are interpreted as revealing the existence of an alternative pathway to excision of DNA cross‐links. This pathway appears to be error‐prone and independent from the recombinational pathway. The RAD6 or the PSO2 gene products are likely to interfere with this process.
THE GECKO OPSIN: RESPONSES TO GEOMETRIC ISOMERS OF RETINAL and 3‐DEHYDRORETINAL
Authors: Crescitelli Frederick , Liu R. S. H.
Published: January 2008

Abstract— The opsin of the visual pigment (P521) of the Tokay gecko rapidly regenerates four spectrally different photopigments with the 9‐cis and 11‐cis isomers of both the vitamin A,‐ and A2‐aldehydes. The opsin displays the classic stereospecificity for both A1‐ and A2‐series of isomers. The two photopigments regenerated with 9‐cis‐ and ll‐cw‐3‐dehydroretinals respond to chloride and nitrate ions as do the comparable pigments formed with 9‐cis‐ and 11‐ris‐retinal. The result is a family of pigments absorbing with spectral maxima ranging from 464 to 540 nm, a span of some 3000 cm‐1. The photosensitivity of all four pigments was determined and found to be in relative order: 100% (11‐cis‐A2), 77% (11‐cis‐A2), 36% (9‐cis‐A,) and 14% (9‐cis‐A2).
PHYTOCHROME CONVERSION AS AN IN SITU ASSAY FOR EFFECTIVE LIGHT GRADIENTS IN ETIOLATED SEEDLINGS OF Zea mays
Authors: Parks Brian M. , Poff Kenneth L.
Published: January 2008

Abstract— In situ photochemical conversion and measurement of phytochrome can be used as a non‐intrusive assay for axial light conduction along etiolated plant tissues of Zea maysL. A computerized single beam spectrophotometer was used to measure phytochrome conversion just below the coleoptilar node following irradiation of the plant shoot with 632 nm light at various distances from the measurement point. Photochemical conversion decreased log‐linearly with increasing distance between the irradiation and measurement points. The distance over which the light was attenuated by 50% was 1.80 mm for mesocotyl, 1.60 mm for coleoptile plus primary leaf, and 1.15 mm for primary leaf alone (coleoptile removed). These results verify the photochemical significance of axially conducted light and thereby provide supporting evidence that such light conduction is important for photomorphogenesis.
THE AQUEOUS PHOTOLYSIS OF ETHYLENE GLYCOL ADSORBED ON GOETHITE
Authors: Cunningham Kirkwood M. , Goldberg Marvin C. , Weiner E. R.
Published: January 2008

Abstract— Suspensions of goethite (α‐FeOOH) were photolyzed in aerated ethylene glycol‐water solutions at pH 6.5, with ultraviolet light in the wavelength range300–400 nm. Under these conditions, formaldehyde and glycolaldehyde were detected as photoproducts. Quantum yields of formaldehyde production ranged from 1.9 7times; 10‐5 to 2.9 × 10‐4 over the ethylene glycol concentration range of 0.002‐2.0 mol/ℓ, and gave evidence that the reaction occurred at the goethite surface. Quantum yields of glycolaldehyde were 20% less than those of formaldehyde, and displayed a concentration‐dependent relationship with ethylene glycol similar to that of formaldehyde. Immediately after photolysis, Fe2+ was measured to be 4.6 × 10‐7 mol/ℓ in an aerated suspension containing 1.3 mol/ℓ ethylene glycol, and 8.5 × 10‐6 mol/ℓ in the corresponding deoxygenated suspension. Glycolaldehyde was not generated in the deoxygenated suspensions. These results are consistent with a mechanism involving the transfer of an electron from an adsorbed ethylene glycol molecule to an excited state of Fe3+ (Iron[III]) in the goethite lattice, to produce Fe2+ and an organic cation. In a series of reactions involving O2, FeOOH, and Fe2+, the organic cation decomposes to form formaldehyde and the intermediate radicals “OH and” CH2OH. OH reacts further with ethylene glycol in the presence of O2 to yield glycolaldehyde. Aqueous photolysis of ethylene glycol sorbed onto goethite is typical of reactions that can occur in the aquatic environment.
THE REPAIR OF DNA STRAND BREAKS IN HUMAN LYMPHOCYTES EXPOSED TO NEAR UV‐RADIATION (UVA) AND FAR UV‐RADIATION (UVC)
Authors: Holmberg M. , Almássy Zs. , Lagerberg M. , Niejahr B.
Published: January 2008

Abstract— UVA irradiation of human lymphocytes induces DNA strand breaks and a portion of these breaks are closed at a slower rate than X‐ray induced DNA strand breaks and the strand breaks generated during repair of UVC induced DNA lesions. In addition, the yield of DNA strand breaks in lymphocytes pretreated with UVA radiation and given a subsequent exposure with UVC radiation is higher and shows a slower decrease with increasing repair time in comparison with the expected yield based on additivity between UVA and UVC induced DNA strand breaks. This indicates that UVA delays the closure of the intermediate strand breaks formed in the repair process of UVC induced DNA lesions.
INDUCTION OF SISTER‐CHROMATID EXCHANGES IN ICR 2A FROG CELLS EXPOSED TO 254 NM AND SOLAR UV WAVELENGTHS
Authors: Chao Chuck C.‐K. , Rosenstein Barry S.
Published: January 2008

Abstract— Exposure of ICR 2A frog cells to 254 nm UV induced the formation of sister‐chromatid exchanges (SCEs) in a fluence‐dependent manner. Cells were also exposed to the UV produced by a fluorescent sunlamp that was filtered through 8C Mylar in order to simulate the mid‐UV(290–320 nm) portion of sunlight reaching the earth's surface. In this instance, SCEs were induced in a linear fashion at low fluences but reached a plateau at a low level of induced SCEs. In addition, pretreatment of cells with the solar UV followed by exposure to 254 nm UV resulted in a significantly lower level of SCEs than in cells exposed to 254 nm UV alone.
AN EVALUATION OF CHARGE EFFECTS ON THE QUENCHING OF TRYPTOPHAN FLUORESCENCE IN SMALL PEPTIDES BY IODIDE ION
Authors: Werner T. C. , Peak David , Danziger James L.
Published: January 2008

Abstract— Charge effects on the quenching of tryptophan fluorescence in small peptides by iodide ion have been analyzed by the conventional “static” quenching model and by a recently proposed competitive quenching model. The former involves a fit of the quenching data using two quenching parameters—one for dynamic and one for static quenching contributions. The latter model involves a single parameter fit in which the fitting parameter is the characteristic rate constant for quenching of the fluorescent state. Both models indicate a clear charge effect on the efficiency of quenching by iodide ion. However, the static model results are obscured by the interdependence of the two fitting parameters and the fact that the true physical meaning of the static parameter is uncertain. Rate constants derived from the competitive model can be converted into relative quenching efficiencies. These efficiencies, which vary by more than a factor of two for the molecules studied, are greatest when the positive charge is on the tryptophan and least when this residue contains a negative charge.
INCORPORATION OF THE SPIN TRAP DMPO INTO CULTURED FETAL MOUSE LIVER CELLS
Authors: Morgan David D. , Mendenhall Charles L. , Bobst Albert M. , Rouster Susan D.
Published: January 2008

Abstract— The incorporation of four different spin traps into cultured fetal mouse liver cells was investigated using electron spin resonance spectroscopy. The cells were incubated in saline solutions of the traps, washed, and then irradiated in a saline solution containing hydrogen peroxide. The presence of a reproducible ESR signal was taken as evidence of spin trap incorporation. The spin trap DMPO was found to be incorporated, while PBN and 4‐POBN were not. MNP was toxic to the cells.
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.
PHOTO‐CIDNP IN NUCLEIC ACID BASES AND THEIR NUCLEOTIDES INDUCED BY CHLORPROMAZINE AND ANALOGS
Authors: Marko J. , Vermeersch G. , Febvay‐Garot N. , Lablache‐Combier A.
Published: January 2008

Abstract— [1H] and [13C]photo‐CIDNP of a mixture of aqueous chlorpromazine (CPZ) and different pyrimidine and purine bases and nucleotides show polarizations of the starting material excepted when guanine or its nucleotide were used. These polarizations can be explained by means of an electron transfer mechanism from CPZ to the bases. Similar effects are observed with other phenothiazine drugs of the CPZ class. The lonely difference consists in the intensity of the polarized signals of the bases. We try to correlate this intensity with the phototoxic potency of the drug.
COMPARISON OF THE SPECTROSCOPIC PROPERTIES OF 4′‐AMINO PHENYLALANINE AS AN UNPROTECTED AMINO ACID AND AS A RESIDUE IN PEPTIDES
Authors: Jankowski Andrzej , Dobryszycki Piotr
Published: January 2008

Abstract— Ultraviolet absorption and fluorescence spectra of 4′‐amino phenylalanine (Aphe) and of some peptides and esters containing Aphe, are characterized. Based on these results, the applicability of Aphe for fluorescence structural investigations of peptides is evaluated. The use of Aphe as an acceptor in fluorescence energy transfer measurements offers the possibility of facilitating the determination of donor fluorescence quantum yield (φD) in the absence of energy transfer which usually turns out to be difficult in systems containing donor and acceptor moities. The Aphe residue in peptides also allows a better insight into intramolecular interactions.
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

Spin‐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

In 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

Cultured 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

The 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

The 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

Deactivation 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

The 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

A 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

The 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

The 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.
ANALYSIS OF FLUORESCENCE KINETICS AND ENERGY TRANSFER IN ISOLATED α SUBUNITS OF PHYCOERYTHRIN FROM Nostoc sp.
Authors: Dagen A. J. , Alfano R. R. , Zilinskas B. A. , Swenberg C. E.
Published: January 2008

Abstract— The fluorescence decay profiles, relative quantum yield, and transmission of the phycoerythrin a subunit, isolated from the photosynthetic antenna system of Nostoc sp., were measured using single picosecond laser excitation. The fluorescence decay profiles were found to be intensity independent for the intensity range investigated (4 × 1013 and 4 × 1015 photons‐cm‐2 per pulse). The decay profiles were fitted to a model assuming both chromophores absorb and fluoresce. The inferred total deactivation rates for the two chromophores, in the absence of energy transfer and when the effects of the response time of the streak camera and the finite pulse width are properly included, are 1.0 × 1010s' and 1.0 × 109 s 1 for the s and f chromophores. respectively, whereas the transfer rate between the two fluorophorcs is estimated to be 1.0 × 1010 s−1 giving a s→ f transfer rate on the order of (100 ps)−1. Steady‐atate polarization measurements were found to be equal to those calculated using the rate parameters inferred from the kinetic model fit to the fluorescence decays. The apparent decrease in the relative fluorescence quantum yield and increase of the relative transmission with increasing excitation intensity is suggestive of ground state depletion and upper excited state absorption. Evidence suggests that exciton annihilation is absent within isolated α subunits for the intensity range investigated (4 × 1013 to 4 × 1015 photons‐cm 2 per pulse).
CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID BILAYER VESICLE SYSTEMS: CORRELATIONS BETWEEN KINETIC PARAMETERS AND SOLUBILITIES OF VIOLOGEN ACCEPTORS *
Authors: Ford William E. , Tollin Gordon
Published: January 2008

Abstract— Twelve viologens (quaternary 4,4′‐bipyridinium ions) are investigated as electron acceptors in vesicle suspensions containing chlorophyll‐a (Chl) using laser flash photolysis. The structures of the viologens, which determine how they and their reduced radicals partition between the water and bilayer membrane phases, are systematically varied in order to probe the effects of acceptor solubility on the kinetics of photosensitized electron transfer reactions. The effectiveness of the viologens as quenchers of the Chl triplet excited state increases as they become less soluble in water, because the viologens are more likely to be incorporated into the membrane, but the efficiency of radical formation decreases and the rate of the reverse electron transfer reaction increases. The data obtained with a homologous series of di‐alkyl viologens are analyzed quantitatively using a kinetic model which includes the partition coefficients of the viologens and their radicals. For the most part, the reactivities of the viologen species are proportional to their concentrations in the membrane phase, but the locations and mobilities of the viologens in the membrane phase also have to be considered. In order for the Chl and viologen radicals to separate efficiently. the viologen radical has to be able to diffuse from the membrane to the water phase at a rate that competes effectively with reverse electron transfer within the radical pair complex (> 105 s−1).
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.
DNA EXCISION REPAIR IN THE VERY UV‐SENSITIVE XERODERMA PIGMENTOSUM COMPLEMENTATION GROUP A STRAIN XP4LO
Authors: Sullivan John K. , Kantor G. J.
Published: January 2008

Abstract— XP4L0, a xeroderma pigmentosum complementation group A strain, exhibits very limited DNA repair activity. It has extreme sensitivity to UV (254 nm) as determined by colony forming ability. The rate of loss of UV (1 J/m2)‐induced pyrimidine dimers from populations of quiescent, nondividing XP4LO cells was determined and found to be slower than that observed for other group A strains (XP25R0, XP12BE, XP8LO). The extreme UV‐sensitivity is also exhibited by the nondividing cells in a survival assay that employs nondividing cell populations and does not involve cell reproduction. This result suggests that the extreme sensitivity measured previously by colony‐forming ability (a cell‐reproduction assay) is due to the excision repair defect alone and not to an additional post‐replication repair defect. The very limited excision allows for an accurate definition of target size for inactivation of nondividing cells, about 1 pyrimidine dimer per 105 base pairs, and when compared to results observed for other XP‐A strains, provides further evidence that even though excision repair in group A is severely limited, it has biological significance.
ENHANCEMENT OF MUTAGENESIS AND HUMAN SKIN CANCER RATES RESULTING FROM INCREASED FLUENCES OF SOLAR ULTRAVIOLET RADIATION
Authors: Kubitschek H. E. , Baker K. S. , Peak M. J.
Published: January 2008

Abstract— We present a new method for calculating the effects of reduction of atmospheric ozone upon induction of nonmelanoma skin cancer. These estimates are based upon several recent experimental improvements: a model for the atmospheric penetration of UV‐B; measurements of the transmission of this radiation by human epidermis; a precise action spectrum for genetic effects (mutation) in Escherichia coli, which was corrected for finite slit width. The calculated radiation amplification factor or percent increase in exposure per one percent decrease in atmospheric ozone is constant at 1.7 for solar zenith angles = 70° and decreases only with larger values of this angle. Thus the estimated increase applies to all heavily populated areas. of the globe. The value is robust: it is almost the same when the albedo is reduced from 0.2 to 0.1 or when the epidermal transmission is assumed to be about fourfold greater.
LACK OF INHIBITION OF ULTRAVIOLET RADIATION‐INDUCED ORNITHINE DECARBOXYLASE ACTIVITY BY RETINOIC ACID
Authors: Kligman Lorraine H.
Published: January 2008

Abstract— Normally present at low levels, ornithine decarboxylase (ODC) activity is induced to higher levels in animal skin by such disparate agents as tumor promoter 12–0‐tetradecanoylphorbol‐13‐acetate (TPA), UV radiation, and hair plucking. Retinoids are known to inhibit induction by TPA. Repeated applications of retinoic acid (RA) in acetone have also been reported to inhibit UV‐induced ODC in hairless mice. As a preliminary study, it was of interest to know whether RA in a cream vehicle would have the same effect. Groups of Skh‐hairless‐1 albino mice were irradiated once with Westinghouse FS‐20 lamps (0.045 Joules/cm/). Immediately post‐irradiation, RA was applied to the dorsum in different concentrations (0.001%, 0.002%, 0.02%), vehicles (cream and acetone) and on various time schedules (1–5 times). Sacrifice was by cervical dislocation 24 h later. Epidermis was obtained by mild heat separation and two epidermal sheets were pooled for each extract. In all experiments, the 70‐fold increase in UV‐induced ODC activity was further increased by retinoic acid by a factor ∼ 1.6. Since ODC levels are usually elevated in proliferating systems, the results are in concordance with the fact that both UV radiation and RA induce epidermal hyperplasia.
PHOTOSENSITIZATION OF CHINESE HAMSTER CELLS BY WATER‐SOLUBLE PHTHALOCYANINES *
Authors: Ben‐Hur E. , Rosenthal I.
Published: January 2008

Abstract— Phthalocyanines are efficient photosensitizers of cultured mammalian cells and are considered for use in photodynamic therapy. The photobiological properties of chloroaluminum phthalocyanine sulfonate (AIPCS) were compared to those of the unsubstituted, water‐insoluble derivative (AIPC). The development of photosensitization after addition of the dye into growth medium is ca. 8 times more rapid for AlPC than for AIPCS. Conversely, the loss of photosensitization when cells are incubated in a dye‐free growth medium following a period of dye uptake, is also faster for AIPC. The dye uptake followed a kinetic behavior similar to the development of photosensitivity, but the loss of dye was too slow for both AlPC and AIPCS to explain loss of photosensitivity. When cells are incubated prior to illumination with AIPCS in phosphate buffered saline instead of growth medium, shorter time and smaller amount of dye are required to achieve the same level of photosensitization. The dependence of photosensitivity on dye concentration is linear for both AIPC and AIPCS. As already found for AIPC, photosensitization by the water‐soluble derivative is also not enhanced in D2O, suggesting that singlet oxygen is not involved in the cytotoxic response. Sodium salicylate, which was found to enhance the effect of AlPC was also effective with AIPCS. This effect is quite specific since the meta and para isomers had no effect. The metal atom complexed with the phthalocyanine ring is significant for the photobiological activity. Among the compounds tested, those containing Al or Zn are most active.
PHOTOBIOLOGICAL ACTIVITIES OF 5‐A‐LKOXYPSORALENS WITH RESPECT TO THE ACTION ON Escherichia coli
Authors: Fujita Hitoshi , Kakishima Hiroshi
Published: January 2008

Abstract— Near‐UV induced activities of a series of 5‐a‐lkoxypsoralen derivatives (C1 to C8) and 5‐h‐ydroxypsoralen were compared with respect to lethal, mutagenic and prophage inducing effects on E. coli. Although 5‐a‐lkoxypsoralen derivatives having an alkoxyl chain longer than C2 were slightly soluble, their saturated solutions containing their insoluble portion showed the significant photolethal effect on E. coli. 5‐E‐thoxypsoralen was less photoactive in inducing phenotypic reversion of the arginine auxotrophy than 5‐m‐ethoxypsoralen but it photoinduced prophage lambda from the lysogenic bacteria as well as 5‐m‐ethoxypsoralen. Photomutagenesis by the derivatives of C3 to C8 could not be detected but ca. 10% of the lysogenic bacteria photoinduced prophage in the presence of the derivatives at the maximum induction.
3‐H‐YDROXYRETINAL AS A CHROMOPHORE OF Drosophila melanogaster VISUAL PIGMENT ANALYZED BY HIGH‐PRESSURE LIQUID CHROMATOGRAPHY
Authors: Tanimura Teiichi , Isono Kunio , Tsukahara Yasuo
Published: January 2008

Abstract— The chromophore of the visual pigment of the fruit fly Drosophila melanogaster was studied by high‐pressure liquid chromatography (HPLC). Oxime derivatives of the chromophore were successfully analyzed with a more polar solvent than has been used for retinaloximes. A preceding monochromatic irradiation resulted in reversible interchanges in the amount among geometric isomers of the oximes that reflected the photointerconversion of rhodopsin and metarhodopsin of the peripheral photoreceptors (Rl‐R6). Authentic all‐trans‐3‐h‐ydroxyretinal was used to identify the chromophore from metarhodopsin. Results demonstrated that the chromophore of the visual pigment in Drosophila is 3‐h‐ydroxyretinal as was proposed in larger flies.
PHOTOPHYSICAL BEHAVIOUR OF NEW PYRROLOCOUMARIN DERIVATIVES
Authors: Quanten E. , Adriaens P. , De Schryver F. C. , Roelandts R. , Degreef H.
Published: January 2008

Abstract— The photophysical behaviour of new pyrrolocoumarins with different substituents on the nitrogen are reported. The photophysical properties of these pyrrolocoumarins are generally in agreement with those of the psoralens: a strong absorption (240–400 nm), a weak fluorescence (400–680 nm) characterized by a short singlet lifetime, and a rather strong phosphorescence at 77 K (480–600 nm). The absorption and fluorescence properties were investigated in several solvents. The shift of the fluorescence maximum is interpreted on the basis of the solvatochromic parameters π*, α and β. The triplet‐triplet absorption spectra also depend on the nature of the solvent, while the triplet excited state has a lifetime of a few microseconds at room temperature (concentration 2.5 × 10−4M). Some absorption and fluorescence characteristics of the 4′,5′‐dihydropyrrolocoumarins, which are suitable models for the 4′,5′‐monoadducts to pyrrolocoumarins are reported.
THE STRUCTURE OF CHLOROPHYLL RC I, A CHROMOPHORE OF THE REACTION CENTER OF PHOTOSYSTEM I
Authors: Dörnemann Dieter , Senger Horst
Published: January 2008

Abstract— Chlorophyll RC I is a particular chlorophyll of photosystem I common to all organisms with oxygenic photosynthesis. Its structure could be revealed by'H‐NMR, FTIR, neutron activation analysis, complemented by plasma desorption mass spectrometry data. It has been identified as 13′‐hydroxy‐20‐chloro‐Chl a. Two stereoisomers of Chl RC I have also been isolated and identified. Evidence is presented that chlorination of the pigment does not occur during extraction and that artefacts due to impurities are ruled out.
FLUORESCENCE BEHAVIOUR OF SEQUENTIAL TYROSYL POLYPEPTIDES
Authors: Pantar Arun V. , Rao M. V. R. , Atreyi M. , Kumar Satish
Published: January 2008

Abstract— Fluorescence behaviour of three sequential tyrosyl copolypeptides, (Gly‐Tyr)35, (Ala‐Tyr)29 and (Val‐Tyr)22, was studied in alkaline solutions, in which ionisation of tyrosyl hydroxyl was 80%. Irradiation at 280 nm in all the three systems lead to the formation of a photoproduct which fluoresced intensely at 410 nm. The facility of the photoreaction depended markedly on the nature of the comonomer of tyrosine and the conformation of the polypeptide chain. As a result of photoproduct formation, the polypeptide backbone is hindered in acquiring more ordered structure at a lower degree of tyrosyl ionisation.