bluuebunny/crossref_metadata_2025_split huggingface dataset:
FREE ENERGY DEPENDENCE OF THE QUENCHING OF CHLOROPHYLL a FLUORESCENCE BY SUBSTITUTED QUINONES*
Authors: Natarajan L. V. , Blankenship R. E. 
Published: January 2008

AbstractThe quenching of chlorophyll a (Chl a) fluorescence hy a series of substituted benzoquinones. naphthoquinones and anthraquinones has been examined employing ethanol and acetonitrile as solvents. All quinones are good quenchers of fluorescence. There is an excellent linear relation between the Stern‐Volmer quenching constants, K, and the polarographic half wave potentials (E12) of the quinones, with more oxidizing quinones being better quenchers. The quenching data are consistent with the excited state half wave potential of −1.31 eV predicted theoretically, demonstrating that the kinetically estimated value of the Chl a excited state reduction potential agrees with that expected on spectroscopic grounds. The results of quenching are not in agreement with the conventional Marcus theory of electron‐transfer reactions, as there is no evidence of quenching constant. Kq. decrease vsΔG0 even for free energy changes nearly twice that expected for the onset of the Marcus inverted region. However, the kinetically estimated Kq values are in good agreement with the ones calculated by using the Rehm and Weller equation for fluorescence quenching by electron transfer. Our experimental results support the electron transfer mechanism of quenching proposed by Seely.
MONOFUNCTIONAL3,4‐and4′,5′‐PHOTOCYCLOADDUCTS BETWEEN 4,5′‐DIMETHYLANGELICIN and THYMINE
Authors: Dall'Acqua F. , Caffieri S. , Vedaldi D. , Guiotto A. , Rodighiero P. 
Published: January 2008

AbstractBy irradiating (365 nm) an aqueous liquid solution of 4,5′‐dimethylangelicin. a monofunctional photosensitizing furocoumarin, in the presence of an excess of thymine, two new compounds, I and II, have been obtained; they do not show fluorescence when observed with Wood's light. The nuclear magnetic resonance data, the marked similarity of UV absorption and fluorescence spectra of these compounds with those of synthetic 3.4‐dihydro‐4,5′‐dimethylangelicin and their capacity to undergo photodissociation (254 nm) yielding the starting thymine and 4,5′‐dimethylangelicin in equimolecular amounts, are consistent with C4‐cycloadducts between the 3,4‐double bond of the furocoumarin and 5,6‐double bond of thymine. Nuclear magnetic resonance data indicate for I and II a head‐to‐head and a head‐to‐tail structure, respectively. When irradiation is carried out in the frozen state, two adducts. III and IV, fluorescent at Wood's light, have been obtained other than the two above‐mentioned compounds I and II. Compounds III and IV have been identified as 4′.5′‐fluorescent adducts between the 4′,5′‐double bond of the furocoumarin and the 5.6‐double bond of thymine; one of them (III) is identical to that formed in the photoreaction between DNA and 4,5′‐dimethylangelicin; for this last compound a cis head‐to‐head structure has been suggested.
PICOSECOND KINETICS and A MODEL FOR THE PRIMARY EVENTS OF BACTERIORHODOPSIN
Authors: Gillbro Tomas , Sundström Villy 
Published: January 2008

AbstractThe picosecond absorption kinetics of light adapted bacteriorhodops in (BR) are reported for water and glycerol‐water suspensions of purple membrane from Halobacieriwn hulobium at different temperatures (77‐300 K) and pH (5‐10). It is shown that a photoproduct of BR, called P‐BR (pseudo‐bacteriorhodopsin). is responsible for the 16 ± 2 ps relaxation lifetime observed under steady state irradiation (i.e. with a train of ps pulses) at room temperature. At 77 K the absorption recovery lifetime is 62 ± 5 ps in good agreement with previous fluorescence lifetime studies. The observed signal is very sensitive to the sample flow rate and at the highest flow rates a fast absorbance increase (≤ 2 ps) is observed at λ > 620 nm. while at 576 nm a similarly fast absorption recovery alter bleaching is observed. These results imply that the reaction BR → K‐BR occurs within 2 ps. In order to explain the simultaneous formation of P‐BR and K‐BR at 77 K. a model for the primary events including a traus‐cis isomerization and a protein relaxation about the chromophore is suggested. The same model can also be used in explaining the simultaneous formation of batho‐ and hypsorhodopsin in some rhodopsins. Finally, a scheme for the last steps in the photocycle of bacteriorhodopsin including protonation, protein relaxation and cis‐trans isomerization is proposed
TIME‐RESOLVED RESONANCE RAMAN SPECTROSCOPY OF THE BACTERIORHODOPSIN PHOTOCYCLE ON THE PICOSECOND AND NANOSECOND TIME SCALES
Authors: Hsieh Chung‐Lu , El‐Sayed M. A. , Nicol Malcolm , Nagumo Mark , Lee Jai‐Hyung 
Published: January 2008

Abstract— Resonance Raman spectra of the picosecond bacteriorhodopsin intermediate(s) have been obtained by microbeam, flow and subtraction techniques using a synchronously pumped, cavity‐dumped dye laser. Nanosecond spectra also were measured with this laser by cavity dumping without mode‐locking. The picosecond spectra in the fingerprint region, which is sensitive to the configuration of the retinal chromophore, differ from spectra of the parent bR570 but could be correlated to the spectrum of bRDA550, a “13‐cis” species which has been determined from spectra of bR570 and bRDA560. The picosecond transient and bRDA550 also are similar in the 950–1050 cm‐1“deuteration fingerprint” region when the medium is changed from H2O to D2O. These results suggest that trans—cis isomerization occurs during the 40‐ps pulse duration. The shift relative to the parent bR570 in the ethylenic stretch region suggests that the picosecond and nanosecond transients absorb at wavelengths longer than 570 nm. The C band at 1646 cm‐1 is found to shift or to broaden upon photolysis in the picosecond time scale. This might suggest a change in the electronic structure of the group and its environment on the picosecond time domain.The nanosecond spectra obtained in this work (with 15‐ns pulses) are similar to the spectra previously observed on the 100‐ns time scale but are slightly different from the picosecond spectrum. These data suggest that more than one transient species appears on the picosecond‐to‐nanosecond time scale. The temporal evolution of Raman bands in the fingerprint as well as the low energy (950–1050 cm‐1) region and its implications are discussed.
THE α‐CHYMOTRYPSIN EFFECT ON VARIOUS 9‐AMINOACRIDINE FLUORESCENT PROBE EMISSION
Authors: Marty Alain , Bourdeaux Madeleine , Amico Monique Dell' , Viallet Pierre 
Published: January 2008

Abstract The influence of a‐chymotrypsin upon the fluorescence of various 9‐aminoacridine derivatives was examined. Fluorescence is quenched in the presence of this protein. Moreover, quenching is suppressed by the coexistence of hydrocinnamic acid, a competitive inhibitor of the enzyme activity. This leads us to conclude that there is a fluorescent complex formation between protein and fluorophores. Then, the apparent association constants were calculated and the florescence lifetimes of “free” and “bound” 9‐aminoacridine were determined by phase‐modulation fluorometry.It is deduced that 9‐aminoacridine compounds are probably located in the enzymatic active site and that the fluorescence quenching is not due to specific interactions with amino acid residues but is a consequence of the characteristics of this binding site, in particular its hydrophobicity and polarity.Alternatively, when these fluorescent probes are located in the vicinity of some aromatic amino acids (histidin, tryptophan and tyrosin), then the production of non fluorescent complex takes place. It is concluded that 9‐aminoacridine compounds can be used for the determination of the type of amino acid residues in the binding sites of proteins.
CAFFEINE‐ENHANCED PHOTOMOVEMENT IN THE CILIATE, STENTOR COERULEUS
Authors: Prusti Rabi K. , Song Pill‐Soon , Häder Donat‐Peter , Häderi Maria 
Published: January 2008

AbstractThe effects of caffeine, ionophores and calcium flux blockers on the step‐up photophobic response, phototactic orientation and the intracellularly recorded, light‐induced electrical action potential were studied in the ciliate, Stentor coeruleus. Caffeine alters the absorption and CD spectra and enhances the fluorescence of the photoreceptor pigment, stentorin. Independent of its effects on the spectroscopic properties of the photoreceptor pigment, caffeine shortens the photophobic response time by enhancing the Ca2+ conductivity of membranes, while Ca2+ flux blockers (LaCI3 or ruthenium red) prolong it; both effects cancel each other. Evidence is presented that phototactic orientation is brought about by repetitive photophobic responses, since a change in the phobic response time results in a decreased accuracy of phototaxis.
ANALYSIS OF MULTIPLE PHOTORECEPTOR PIGMENTS FOR PHOTOTROPISM IN A MUTANT OF Arabidopsis thaliana
Authors: Konjević Radomir , Khurana Jitendra P. , Poff Kenneth L. 
Published: January 2008

AbstractThe shape of the fluence‐response relationship for the phototropic response of the JK224 strain of Arabidopsis thaliana depends on the fluence rate and wavelength of the actinic light. At low fluence rate (0.1 μmol m‐2s‐1), the response to 450‐nm light is characterized by a single maximum at about 9 μmol m‐2. At higher fluence rate (0.4 μmol m‐2s‐1), the response shows two maxima, at 4.5 and 9 μmol m‐2. The response to 510‐nm light shows a single maximum at 4.5 μmol m‐2. Unilateral preirradiation with high fluence rate (25 μmol m‐2s‐1) 510‐nm light eliminates the maximum at 4.5 μmol m‐2 in the fluence response curve to a subsequent unilateral 450‐nm irradiation, while the second maximum at 9 μmol m‐2 is unaffected. Based on these results, it is concluded that a single photoreceptor pigment has been altered in the JK224 strain of Arabidopsis thaliana.
DETERMINATION OF CYTOSINE‐CYTOSINE PHOTODIMERS IN THE DNA OF CLOUDMAN S91 MELANOMA CELLS USING HIGH PRESSURE LIQUID CHROMATOGRAPHY
Authors: Niggli Hugo J. 
Published: January 2008

AbstractI measured the induction of cytosine‐cytosine dimer (C‐C) densities after UV‐C (< 290 nm) and UV‐B irradiation (290–320 nm) in the 2′‐deoxy‐[3H]cytidine labeled DNA of Cloudman S91 mouse melanoma cells using a new, sensitive high pressure liquid chromatography procedure. UV‐B exposure resulted in 0.000034% C‐C/J m‐2 of the total cytosine radioactivity which is 10 times less than the rate during UV‐C irradiation. Previous work with these melanoma cells showed a 4‐fold lower rate of induction of thymine‐containing pyrimidine dimers by UV‐B than UV‐C light (Niggli Photochem. Photobiol. 52, 519–524, 1990). Based on these results, the calculated ratios for the pyrimidine dimer subspecies showed no significant difference following UV‐C and UV‐B exposure. However, UV‐C and UV‐B light induce 10–20 times more thymine‐containing pyrimidine dimers than C‐C in the DNA of S91 cells.
BLUE AND WHITE LIGHT EFFECTS ON CHLOROPLAST DEVELOPMENT IN A SOYBEAN MUTANT
Authors: Duysen Murray , Eskins Kenneth , Dybas Linda 
Published: January 2008

Abstract—Phenotypic difference for chloroplast development between the normal green (CL1) and the Cy9y9 soybean mutant was observed when the plants were grown under 18W m−2 white or blue light. Under these conditions the mutant soybean accumulated less Chi b, neoxanthin, carotene and less total pigment than the CL1 genotype. Chloroplasts of the Cy9y9 line were deficient in the LHP complex relative to that of chloroplasts from the normal soybean. Specific differences were noted between chloroplasts from plants grown under blue and white light. Accumulations of a 34 kD (PSII) and a 16–17 kD (PSI) membrane polypeptide were decreased by blue light in both soybean genotypes. Blue light induced a greater accumulation of a 32 kD (PSII) polypeptide than white light. Blue light reduced granal thylakoid stacking and increased the proportion of stroma thylakoids compared to those that developed under white light. PSI electron transport activity was stimulated by the blue light treatment more than that of PSII.
ABSORPTION SPECTRA OF DEOXYRIBOSE, RIBOSEPHOSPHATE, ATP AND DNA BY DIRECT TRANSMISSION MEASUREMENTS IN THE VACUUM‐UV (150—190 nm) AND FAR‐UV (190—260 nm) REGIONS USING SYNCHROTRON RADIATION AS A LIGHT SOURCE
Authors: Ito Atsushi , Ito Takashi 
Published: January 2008

AbstractTransmission measurements of 2‐deoxy‐D‐ribose, D‐ribose‐5‐phosphate, ATP and DNA at 5 nm intervals were made with thin films in the wavelength region between 150 nm and 260 nm using synchrotron radiation. ATP and DNA exhibited two peaks in the absorption spectra around 260 nm and 190 nm, and a steep increase below 170 nm, while ribose phosphate and deoxyribose only exhibited the increase below 190 nm with no appreciable absorption above 190 nm. Since adenine does not exhibit the increase of absorption below 180 nm, these results indicate that the absorption of the sugar‐phosphate group, rather than adenine, contributed to the increase below 170 nm in the absorption spectra of ATP and DNA.
LETHAL AND MUTAGENIC ACTION OF VACUUM‐AND FAR‐ULTRAVIOLET RADIATIONS ON DRY X174 PHAGE
Authors: Maezawa Hiroshi , Furusawa Yoshiya , Suzuki Kenshi 
Published: January 2008

AbstractKilling and mutation of dry X174 phages (amber mutant) were investigated with vacuum‐UV (130, 150 and 190 nm) and far‐UV (254 nm) radiations. The sensitivity to killing was greatest at 130 nm; the sensitivity (in terms of energy fluence) at 130 nm was about 17 times higher than that at 150 nm. The reversion frequency of amber mutants to pseudo‐wild type at 190 nm was lower than at 254 nm. Comparison of the induction rate of revertants per survivor showed that mutagenicity after 130 nm radiation, which may raise the ionization process, and after X‐rays was similar.
PHYTOCHROME MODELS: PART 10. CONCENTRATION, SONICATION AND TEMPERATURE AFFECTING THE POPULATION OF THE GROUND‐STATE CONFORMERS OF BILIVERDIN DIMETHYL ESTER IN SOLUTION*
Authors: Al‐Ekabi Hussain , Tegmo‐Larson Inga‐Mai , Braslavsky Silvia E. , Holzwarth Alfred R. , Schaffner Kurt 
Published: January 2008

AbstractUV‐vis absorption and fluorescence spectroscopy were used to show that in alcoholic solutions (methanol, ethanol, 2‐methylbutan‐1‐ol, and 2‐octanol) concentration, temperature, and sonication affect the relative populations of the more rigid stretched and the more flexible helically coiled conformers of biliverdin dimethyl ester. In aromatic solvents, e.g. toluene, no such effects could be detected. At concentrations larger than 3 10‐5M in the alcoholic solvents aggregates and monomeric coiled species prevail. Upon dilution, the fraction of stretched monomeric conformers increases. Heating and sonication at concentrations smaller than 3 10‐5M further and irreversibly increase the fraction of the stretched conformers. The activation parameters for this change are compatible with the assessment that no equilibrium is attained between the two families of conformers even after several hours at room temperature, since the barriers arc higher than kT at this temperature. The present results and those previously reported on the excited‐state processes of biliverdin dimethyl esters are explained on the basis of a scheme in which the eight possible ring B/C isomers of biliverdin dimethyl ester are interconverted through intra‐and intermolecular proton transfers, rotations around C‐C single bonds, and E‐Z photoisomerizations around C = C double bonds.
EXCITED‐STATE PROPERTIES OF DNA METHYLATED AT THE NV7 POSITION OF GUANINE AND ITS FREE FLUOROPHORE AT ROOM TEMPERATURE
Authors: Georghiou S. , Saim A. M. 
Published: January 2008

AbstractThe room‐temperature optical properties of calf thymus DNA, with about 75% of its guanine residues methylated at position N‐7, are compared with those of 7‐methyl GMP which has the same fluorophore. The fluorescence spectrum of the methylated guanine residues depends strongly on the excitation wavelength, shifting to the blue as the wavelength increases. The fluorescence quantum yield, corrected for the contribution to absorption by the other virtually nonfluorescent residues, exhibits a pronounced drop at long excitation wavelengths relative to that for excitation at 265 nm. The degree of fluorescence polarization exhibits a weak dependence on the excitation and emission wavelengths. For 7‐methyl GMP, the fluorescence spectrum is very weakly dependent on the excitation wavelength and its fluorescence quantum yield shows a moderate increase at long wavelengths. The degree of fluorescence polarization increases with increasing excitation wavelength particularly when monitoring the emission in the short wavelength region of the fluorescence spectrum. A pronounced drop of unknown origin is observed when exciting at 265 nm, which is not observed for methylated DNA. The methylated DNA data are interpreted in terms of a combination of (i) a heterogeneous environment of the methylated guanine residues, which results from sequence‐dependent stacking interactions, and (ii) transfer of excitation energy from the other residues to the fluorescing methylated guanine residues. From the values of the quantum yields and those of the decay times, which we have recently reported (Georghiou et al., 1985), the following values are obtained for the radiative, kt, and the sum of the nonradiative, σk1, rate constants for deexcitation of the excited states of methylated DNA and its free fluorophore: 1.6 × 108 s‐1 7 × 107 s‐1 and 5 × 1010 s‐lvs 6 × 109 s‐1. Because of energy transfer from the other residues. the kf value for the methylated guanine residues is overestimated but their σk1, value is not affected significantly and is by about an order of magnitude larger than that for 7‐methyl GMP, apparently because of stacking interactions.
INHIBITION OF NUCLEIC ACID SYNTHESIS IN CELLS EXPOSED TO 200 MICROMETER RADIATION FROM THE FREE ELECTRON LASER
Authors: Berns Michael W. , Bewley William 
Published: January 2008

AbstractVertebrate tissue culture cells were exposed to 200 um wavelength radiation (1CO W/cm2) from a free electron laser (FEL) of the electrostatic generator type. Cell cultures demonstrated no morphological alterations but a statistically significant (P .05) proportion of the cells exhibited inhibition of DNA synthesis. This study demonstrates the first biological effects of the FEL and the feasibility of performing biological investigations with this device.
CERTAIN SINGLET OXYGEN QUENCHERS AFFECT THE PHOTOREACTION BETWEEN 8‐MOP and DNA
Authors: Bordin Franco , Conconi Maria Teresa , Capozzi Alma 
Published: January 2008

AbstractThe effect of certain chemicals known as singlet oxygen quenchers on the photoreaction between 8‐MOP and DNA has been studied in vitro; sodium azide, l,4‐diazabicyclo‐(2,2,2)‐octane, p‐carotene and dimethylsolfoxide (used as a solvent) appeared to be capable of reducing significantly the 8‐MOP ability to induce both monoadducts and cross‐links in DNA. Therefore, these chemicals seem to be not useful in studying the singlet oxygen implication in the induction of biological effects of 8‐MOP sensitization.
IMPROVED QUANTITATION OF DNA‐PROTEIN CROSSLINKING CAUSED BY 405‐nm MONOCHROMATIC NEAR‐UV RADIATION IN HUMAN CELLS
Authors: Peak Jennifer G. , Peak Meyrick J. , Blazek Ed Robert 
Published: January 2008

AbstractAn improved alkaline elution analysis has been used to estimate the yield of DNA‐protein crosslinks induced in human P3 cells by monochromatic 405‐nm near‐ultraviolet radiation. Crosslinks are induced linearly over the fluence range studied, at a rate of 1.22 crosslinks per 1010 daltons per MJ m‐2± 0.066 (one standard error of the slope, N= 37). This rate is equivalent to 1360 crosslinks per cell genome per lethal event.
RECURRING GYNAECOLOGIC CANCER TREATED WITH PHOTODYNAMIC THERAPY
Authors: Corti L. , Tomio L. , Maluta S. , Minucci D. , Fontana M. , Cittar H. , Calzavara F. 
Published: January 2008

Abstract Tumor recurrences in the gynaecological field after conventional therapy are a big problem because there is little choice for other therapy without inflicting further damage. Photodynamic therapy (PDT) is indicated because it is selective and without side‐effects in flat or small recurrences.We treated 12 patients with vaginal and vault recurrences of cervix carcinoma, adenocarcinoma corpus uteri and rectum. The PDT was performed after 24‐48 h with Hp, 5 mg kg’body wt injection, using an argon‐dye laser for 10 cases, tungsten and xenon lamps in two cases. All patients were previously treated with conventional therapy (i.e. surgery, radiotherapy, chemotherapy). Doses ranged from 60 to 300 J cm−2. The results were 7 complete local with 4 partial responses, and 1 with no change. Three patients died because of distant metastases, 1 partial response was treated with brachytherapy and is now disease free. All the other patients are still living. In all cases we have seen no side‐effects from PDT. The patients were sheltered from the sunlight for 20‐30 days after therapy.We recently used a new argon‐pumped CW dye laser. This high‐power argon laser consists of 2 argon tubes in series which emit green light up to 10 W and at 630 nm up to 3 W. We are evaluating the high power to see if this improves the results.
PHOTO‐CIDNP AS A TOOL FOR THE STUDY OF THE REACTIVITY OF PHOTOSENSITIZING DRUGS: THE FUROCOUMARINS
Authors: Marko J. , Vermeersch G. , Febvay‐Garot N. , Lablache‐Combier A. , Moron J. , Bisagni E. 
Published: January 2008

Abstract— Several monofunctional and bifunctional furocoumarin derivatives were studied by means of the photo‐CIDNP technique. Nuclear spin polarizations were observed on some of these derivatives when irradiated in acetonitrile solutions. The likely occurrence of both semi‐reduced and semi‐oxidized species of the FC in the reaction scheme is discussed.When N‐acetyltyrosine was added to the solution, CIDNP effects were observed on both reactants. They arose from a highly reversible pathway, as no photoproduct was polarized. On the FC part, the stronger effects were always observed on the 3,4 pyrone double bond suggesting that it must possess the highest spin density in the reaction intermediate. According to previous studies, the latter should be the FC anion or neutral radical. For the amino‐acid moiety, the intensity of the polarizations was strongly dependent on the nature of the FC. This allowed the classification of the FC into three groups (zero, weak and strong intensities). As compared with their photobiological reactivity, this classification seemed to be related to the usual mono‐ and bifunctional distinction. This is the second example showing that photo‐CIDNP could be used as a preliminary test for the study of the photosensitizing drug properties.
ONE‐ELECTRON OXIDATION AND REDUCTION OF AZAPROPAZONE AND PHENYLBUTAZONE DERIVATIVES IN AQUEOUS SOLUTION: A PULSE RADIOLYSIS STUDY
Authors: Jones R. A. , Navaratnam S. , Parsons B. J. , Phillips G. O. 
Published: January 2008

Abstract— Using pulse radiolysis techniques, 3 azapropazone and 3 phenylbutazone derivatives all structurally related to the potentially photosensitive anti‐inflammatory drug, azapropazone, have been reacted with the free radical oxidants N3, Br2‐ and (SCN)2‐ as well as with e‐aq a strong reductant. It is demonstrated that for 5 derivatives, azapropazone (Az), 2‐[a‐Carboxy‐valeryll‐3‐dimethylamino‐7‐meth1‐1,2‐dihydro‐1,2,4‐benzotriazine (Mi307), phenylbutazone (PB), oxyphenylbutazone (OPB), and ketophenylbutazone (KPB), N3‐ and Br2‐ appear to react via a one‐electron removal process. For the other derivative, 8‐hydroxy azapropazone (8‐OH‐Az), Nj and (SCN); oxidise via a one‐electron process, while Br2‐ probably fqrms a free radical adduct.The absolute spectra of the one‐electron oxidised and reduced transient species for all six derivatives are thus given in this work and are a basis to the understanding of the action of light on these drugs.