bluuebunny/crossref_metadata_2025_split huggingface dataset:
ENERGY TRANSFER FROM CAROTENOID POLYENES TO PORPHYRINS: A LIGHT‐HARVESTING ANTENNA
Authors: Moore Ana L. , Dirks Gary , Gust Devens , Moore Thomas A. 
Published: January 2008

Abstract—Carotenoid to porphyrin singlet‐singlet energy transfer has been observed in a new covalently linked carotenoid‐porphyrin ester. Nuclear magnetic resonance studies reveal that the relatively high energy transfer efficiency (˜ 25%) is a result of a stacked conformation in which the 26 π electron carotenoid chromophore resides ˜4–5 Å above the mean porphyrin plane. Substantial quenching of porphyrin fluorescence was also observed. Implications for the mechanism of energy transfer and possible applications to synthetic solar energy conversions systems are discussed.
Z/E PHOTOISOMERIZATION OF UROCANIC ACID*
Authors: Morrison H. , Avnir D. , Bernasconi C. , Fagan G. 
Published: January 2008

Abstract—The E ⇆ Z photoisomerization of the title compound (UA) (a naturally occurring sunscreen) has been studied in aqueous solution. At a UA concentration of 6mM and using 313nm excitation, φE→z= 0.52, φZ→E= 0.47 and the photostationary state is 34% E. Under these conditions, loss of UA is minimal. Low energy triplet quenchers fail to impede the isomerization, but the reaction can be induced by several triplet sensitizers. The ET for UA is estimated to be approximately 55 kcal/mol.
STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS—IX. AB INITIO QUANTUM MECHANICAL CHARACTERIZATION OF THE ELECTRONIC STRUCTURE AND SPECTRUM OF THE BACTERIOCHLOROPHYLLIDE a ANION RADICAL
Authors: Petke J. D. , Maggiora Gerald M. , Sipman Lester L. , Christoffersen Ralph E. 
Published: January 2008

Abstract— Ab initio configuration interaction wavefunctions and energies are reported for 19 doublet states of the anion radical of ethyl bacteriochlorophyllide a (Et‐BChl a˙), and are employed in a resolution of the electronic absorption spectrum, as well as in a comparison with a previously reported study of the electronic states and spectrum of the anion radical of ethyl bacteriopheophorbide a (Et‐BPheo a˙).The lowest two excited doublet states, D1 and D2, of Et‐BChl a˙ are found to be approximately degenerate and are predicted to contribute to the experimentally observed absorption at 10000 cm−1. In contrast, the D2←D0 transition in Et‐BPheo a˙ is predicted to contribute to the 11000 cm−1 absorption, while the D1←D0 transition appears at approximately 8600 cm−1 with a low oscillator strength (f= 0.002). The prominent visible absorption at ∼15700 cm−1 in both molecules is found to be due to the D4← D0 transition.Another difference between the predicted spectra of the two molecules appears in the low‐energy shoulder of the Soret band. Here, two intense transitions, D10←D0 and D11←D0, are predicted for Et‐BChl a˙, as opposed to three fairly intense transitions, D7←D0, D8←D0 and D9←D0, for Et‐BPheo a˙, differences which may provide a means of distinguishing between the two molecules using resonance Raman spectroscopy.The remainder of the Soret band of Et‐BChl a˙ above 26000 cm−1 consists of a number of closely‐spaced transitions to states D12←D18. The intense transitions D12←D0, D13←D0, D14←D0 are predicted to contribute to the Soret maximum near 30000 cm−1.The ground state spin densities of the two molecules are similar, with the minor difference of somewhat less spin density located on the methine carbon atoms of Et‐BChl a˙ compared with Et‐BPheo a˙.
CHARACTERIZATION OF THE PHOTOREACTION BETWEEN DNA AND AMINOMETHYL‐TRIMETHYLPSORALEN USING ABSORPTION AND FLUORESCENCE SPECTROSCOPY
Authors: Johnston Brian H. , Hearst John E. 
Published: January 2008

Abstract–The use of absorption and fluorescence spectroscopy for following the progress of the photo‐reaction between DNA and 4′‐aminomethyl‐4,5′,8‐trimethylpsoralen (AMT) has been investigated. Absorption at long wavelengths and fluorescence both decline upon intercalation of AMT into the DNA helix. The loss of fluorescence from AMT and the accompanying appearance of monoadduct fluorescence upon irradiation by UV light can be easily followed by using the excitation beam of a spectro‐fluorometer as the source of irradiation and monitoring the changing emission spectrum. Where cross‐link formation is possible, the subsequent decline of monoadduct fluorescence is seen as well. This suggests that the 4,5‐tnonoadduct is a precursor of cross‐links. Both monoaddition and cross‐linking are more rapid with poly d(A·T) than with calf thymus DNA or poly d(A·T). Excitation spectra can be helpful in resolving the levels of AMT and 4′,5′‐monoadduct when both are contributing to the emission spectrum. Some changes are observed in the emission spectrum of AMT–poly d(A·T) monoadducts after prolonged irradiation which indicate further photoreaction.
THE VACUUM ULTRAVIOLET PHOTOCHEMISTRY OF NUCLEOTIDES
Authors: Dodonova N. Ya. , Kiseleva M. N. , Remisova L. A. , Tsycganenko N. M. 
Published: January 2008

Abstract— Photodestruction of nucleotides by vacuum UV (λ < 200 nm) and near UV radiation in thin films has been studied; the products were analyzed by thin‐layer chromatography. Vacuum UV photolysis leads to the rupture of the N‐glycosidic bond with liberation of bases, the quantum yield of the process being about 2 × 10‐4 for guanosine‐5'‐monophosphate. No bases have been found among the products of near UV photolysis.Vacuum UV irradiation of aqueous solutions of adenosine‐5'‐monophosphate and guanosine‐5'‐monophosphate produces, along with bases, some other fluorescent substances. The identity of photoproducts of vacuum UV photolysis with those of γ‐radiolysis is established. The mechanism of photochemical conversion is discussed.
STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS. XI. AB INITIO QUANTUM MECHANICAL CHARACTERIZATION OF THE ELECTRONIC STRUCTURE AND SPECTRA OF THE CHLOROPHYLLIDE a AND PHEOPHORBIDE a ANION RADICALS
Authors: Petke J. D. , Maggiora G. M. , Shipman Lester L. , Christoffersen Ralph E. 
Published: January 2008

Abstract Ab initio configuration interaction wavefunctions and energies are reported for the ground and low‐lying excited doublet states of the anion radicals of ethyl chlorophyllide a (Et‐Chl a‐) and ethyl pheophorbide a (Et‐Pheo a‐), and are employed in a comparative analysis of their respective electronic absorption spectra.Strong similarities exist between the first five computed excited states of both molecules, providing no distinguishing features in the electronic absorption spectra below 20000 cm‐. Their ground state charge and spin density distributions are also very similar, and there is negligible spin density predicted on the magnesium atom in Et‐Chl a‐.The Soret bands of both molecules are predicted to arise from intense transitions to several closely‐spaced higher excited states, and the calculations indicate that there are significant differences in the number and composition of these states in the two molecules. It is suggested that these differences may provide a means of distinguishing between the two molecules using resonance Raman spectroscopy.
ANALYSIS OF PHOTOTRANSFORMATION INTERMEDIATES IN THE PATHWAY FROM THE RED‐ABSORBING TO THE FAR‐RED‐ABSORBING FORM OF AVENA PHYTOCHROME BY A MULTICHANNEL TRANSIENT SPECTRUM ANALYZER
Authors: H. Pratt LEE , SMMAZAKIT Yukio , Inoue Yasunori , Furuya Masaki 
Published: January 2008

AbstractPhototransformation of the red‐absorbing form of phytochrome (Pr) to the far‐red‐absorbing form (Pfr) was followed with a custom‐built transient spectrum analyzer. Large phytochrome, which consisted of approximately 120000‐dalton monomers, was immunopurified or conventionally purified from etiolated oat (Avena sativa L., cv. Garry) shoots. Phototransformation was initiated by exciting Pr with a 115‐mJ, 600‐ns half‐width, 655‐nm laser pulse. Absorption spectra were recorded on a microsecond time scale at predetermined times after the flash. It has been reported earlier that flash excitation of large oat Pr produces a transformation intermediate with maximum absorbance near 700 nm in a difference spectrum and that this intermediate decays by two kinetically distinct reactions. Difference spectra for these two reactions are indistinguishable. Both show bleaching centered at 690 nm with no detectable associated absorbance increase between 570 and 830 nm. Subsequent appearance of absorbance at 724 nm, which presumably but not necessarily represents the appearance of Pfr, had earlier been shown to occur by two kinetically distinct reactions for large oat phytochrome. Data presented here indicate in addition the occurrence of a third, slower reaction. Difference spectra for the two faster reactions are indistinguishable, both with maxima near 728 nm and minima near 650 nm. The difference spectrum for the slowest component, however, was qualitatively different exhibiting a maximum near 722 nm with no corresponding minimum. About 15‐20% of the absorbance increase at 724 nm occurred by this slowest reaction, which exhibited a half‐life of 3 s at 25°C and a Q10 of 1.2 for immunopurified and 1.5 for conventionally purified phytochrome. The percentage occurring by this reaction was independent of temperature over the range studied (1‐25dEC). For immunopurified phytochrome the enthalpy of activation, Gibbs free energy of activation, and entropy of activation of this slowest reaction were found to be about lOkJ‐mol‐1, 75kJ.mol‐1, and ‐220 J.mol‐1 K‐1, respectively, and for conventionally purified phytochrome 25kJ.mol‐1, 75kJ.mol‐1and —170 J.mol‐1 K‐1, respectively. The thermodynamic characteristics of this reaction indicate that it may involve a significant ordering of the protein moiety as it transforms to Pfr.
ON THE ACCURACY OF DIFFERENTIAL MEASUREMENTS OF THE MINIMAL ERYTHEMA DOSE: INFLUENCE OF THE DISCRETENESS OF THE SCALE
Authors: Bruls WielA. G. , Faber Joop A. J. , Leun Jan C. van der 
Published: January 2008

AbstractThe minimal erythema dose (MED) is often used as a quantity by which the influence of certain treatments of the skin can be measured. Differential measurements are performed by assessing the difference of the MED on the skin treated in some way and the untreated skin.As the MED‐measuring scale is discrete, the question is sometimes raised whether it is possible to measure differences smaller than one scale unit. In the present paper it is shown that this is indeed possible; in principle the discreteness of the scale does not impose any restriction on the smallest value of the difference that can be measured. The discreteness of the scale introduces an extra random variation into the measurement. This variation is estimated theoretically. It is automatically included in the usual error analysis.The discreteness variance is small when compared to other variance components, which are computed from an analysis of variance of actual experiments. Reducing the discreteness variance, by reducing the dose decrement of the MED‐measuring scale, therefore, does not enhance the overall accuracy considerably. Finally, it is found that the assessments of the MED by the various observers do not differ significantly from each other, and that multiple assessments do increase the accuracy, especially for small effects.
PHOTOADDITION OF 8‐METHOXYPSORALEN TO E. coli DNA POLYMERASE I. ROLE OF PSORALEN PHOTO‐ADDUCTS IN THE PHOTOSENSITIZED ALTERATIONS OF POL I ENZYMATIC ACTIVITIES
Authors: Granger Michele , Héène Claude 
Published: January 2008

Abstract— We have previously demonstrated that 8‐methoxypsoralen (8‐MOP)‡ plus UVA is able to inactivate the three enzymatic activities of E. coli DNA polymerase I and that oxygen is required for these reactions (M. Granger et al., (1982) Photochem. Photobiol., 36, 175–180). We now show that UV‐A irradiation produces a covalent incorporation of the psoralen derivative into the enzyme either in the presence or in the absence of oxygen. The excited psoralen binds directly to the protein in an oxygen‐independent reaction; no complex was detected in the absence of irradiation. Fluorescence measurements reveal that at least two photoadducts are formed.The 8‐MOP‐photomodified enzyme is still fully active but further irradiation leads to an inhibition of the 5′→ 3′ polymerase activity whereas the 5′→ 3′ exonuclease activity is not affected. A major part of the inhibition reaction is shown to be oxygen‐dependent but singlet oxygen quenchers have no effect on the kinetics. This oxygen‐dependent reaction is attributed to a photosensitization, due to covalently bound 8‐MOP, of neighbouring amino acids through an intermediate reactive oxygen species which is not singlet oxygen. The oxygen‐independent reaction is attributed to a direct photosensitization through, for example, a radical mechanism.
REGULATION OF PROTOCHLOROPHYLL(IDE) LEVELS IN DARK‐GROWN NON‐DIVIDING Euglena—I. CONTROL BY LIGHT*
Authors: Alhadeff Myriam , Coronado Roberto , Figueroa Nara , Schiff Jerome A. 
Published: January 2008

Abstract—Dark‐grown cells of Euglena gracilis var. bacillaris contain low levels of protochlorophyll(ide) [Pchl(ide)] which absorbs at 635 nm in vivo. When growing cells are placed on a resting medium, cell division ceases after 3 days and the levels of total extractable and phototransformable Pchl(ide) decrease, reaching a new plateau at one‐half the original concentration by 7 days of resting. Phototransformable Pchl(ide) can be induced to regenerate to the original levels found in dark‐grown cells by treatment with light. The optimum conditions are 40 min of white light (0.2–0.3 W/m2) followed by 1 h of darkness. Although reciprocity between fluence rate and duration of illumination was not observed in this system, it was possible to determine the effectiveness of various spectral regions for the regeneration of phototransformable Pchl(ide) as a function of fluence rate. Blue light (400–510 nm) was most effective followed closely by green (490–590 nm); red light (610–720 nm) was relatively ineffective. The results suggest that phototransformable Pchl(ide) is regulated to achieve the levels ordinarily found in dark‐grown cells and that the blue photoreceptor system, rather than Pchl(ide) itself, is probably the light receptor for Pchl(ide) regeneration.
PHYTOCHROME CONTROL OF ITS OWN SYNTHESIS IN Sorghum vulgare AND Avena sativa
Authors: Otto V. , Mousinger E. , Sauter M. , Schäfer E. 
Published: January 2008

Abstract—The accumulation of phytochrome in the dark was measured for Avena sativa seedlings after a white light pretreatment and for Sorghum vulgare seedlings after continuous red or far‐red light treatments, using the herbicide Norflurazon to prevent greening under continuous irradiation. In both cases the accumulation of phytochrome depends on the state of the phytochrome at the light‐dark transition: high Pfr levels (red light pulse) led to a slower rate of phytochrome accumulation than lower Pfr levels (long wavelength far‐red (RG 9) light pulse). Poly‐(A+)‐RNA was isolated fromA. sativa seedlings grown for 48 h in darkness + 24 h WL + light pulse (5 min) (red, RG 9 light, red followed by RG 9 light or RG 9 followed by red light pulse) + 19 h darkness. The poly‐(A+)‐RNA was translated in a rabbit reticulocyte lysate system and the translation products were immunoprecipitated by specific anti‐phytochrome antibodies. It was demonstrated that the activity of mRNA coding for phytochrome was under phytochrome control.
THE TRIPLET EXTINCTION COEFFICIENTS OF SOME BACTERIAL CAROTENOIDS
Authors: Cogdell R. J. , Land E. J. , Truscott T. G. 
Published: January 2008

Abstract—The extinction coefficients of the triplet states of the bacterial carotenoids, neurosporenc (Λmax 489 nm). sphcroidene (Λmax 510 nm). spheroidenone (Λmax 550 nm) and spirilloxanthin (Λmax 550 nm) in cyclohexane have been determined to be 27.4. 30.9. 6.06 and 9.20 × 104 dm3 mol−1 cm1, respectively. These values were obtained by an energy transfer technique using a range of carotenoid concentrations. For the three that had been studied earlier, the extinctions now obtained are suhstantially higher than prcviously reported.
WAVELENGTH DEPENDENCE OF INACTIVATION and MUTAGENESIS IN HAPLOID YEAST CELLS OF DIFFERENT SENSITIVITIES
Authors: Zölzer F. , Kiefer J. 
Published: January 2008

AbstractThe wavelength dependence of inactivation and mutagenesis in the range between 254 and 313 nm was investigated in haploid cells of the yeast Saccharomyces cerevisiae. The action spectra for a wild type and an excision deficient mutant essentially corresponded to those for bacteria and mammalian cells. There were, however, minor differences. The ratio of mutagenic to lethal action decreased with increasing wavelength in the wild type, but remained constant in the excision deficient mutant. This is discussed in terms of error‐prone and erro‐free repair. For both inactivation and mutagensis, photorcactivability was lower with longer wavelengths in the wild type, but did not change in the excision deficient mutant. Implications for the role of pyrimidine dimers are considered.
SINGLE‐STRAND DNA BREAKS INDUCED BY 365 NM RADIATION IN ESCHERICHIA COLI STRAINS DIFFERING IN SENSITIVITY TO NEAR and FAR UV
Authors: Tuveson R. W. , Peak J. G. , Peak M. J. 
Published: January 2008

AbstractThe gene mutation nur has been shown specifically to sensitize Escherichia coli stationary phase cells to inactivation by broad spectrum near‐UV (NUV) radiation. In the work reported here, E. coli strains RT1. RT2, RT3, and RT4, carrying the 4 possible combinations of recA1, recA+, nur, and nur+, were exposed to monochromatic NUV (365 nm). The strains carrying the nur allele (RT1 and RT2) were more sensitive to inactivation by this wavelength and exhibited considerably more single strand break's (SSB's) than the strains carrying the nur+ allele (RT3 and RT4). As predicted, following X‐irradiation the strains carrying the recA1 allele (RT1 and RT3) were more sensitive than the recA+ strains (RT2 and RT4). We conclude that the enhanced SSB's observed in strains RT1 and RT2 following monochromatic NUV irradiation correlated with the nur mutation and are unrelated to the recA1 mutation.
IDENTIFICATION OF A LUMAZINE PROTEIN FROM PHOTOBACTERIUM LEIOGNATHI BY COHERENT ANTI‐STOKES RAMAN SPECTROSCOPY
Authors: Vervoort Jacques , O'Kane Dennis J. , Carreira Lionel A. , Lee John 
Published: January 2008

AbstractThe vibrational fingerprint in the frequency region 1700‐1100 cm‐1 has been obtained for a fluorescent protein purified from the bioluminescent bacterium Photobacterium leiognathi. using the technique of resonance coherent anti‐Stokes Raman scattering. The frequencies of the 4 prominent modes are the same as for lumazine protein purified from Photobacterium phosphoreum, and for an authentic sample of 6,7‐dimethyl‐8‐ribityllumazine. The fluorophore in the new protein, therefore, must have the same chemical structure. The absence of frequency shifts between the free and bound ligand, in contrast to observations of fiavoproteins, implies that the lumazine ring undergoes no changes in hydrogen bonding between the free and protein‐bound ligand in its ground electronic state. However, changes in relative intensities of two modes are seen, arising from differences in interactions in the excited state, and this is also reflected by differences in fluorescence properties.
LIQUID‐CRYSTALLINE PHASE TRANSITION OF MONOMOLECULAR LAYERS OF CHLOROPHYLL a*
Authors: Heithiert H. , Ballschmiter K. , Mohwald H. 
Published: January 2008

AbstractMonomolecular layers of chlorophyll a at the air‐water interface were investigated by absorption spectroscopy and simultaneous thermodynamic measurements. Whereas at temperatures near 20°C at all pressures, only a liquid phase exists, at a temperature of 4°C, a liquid‐crystalline phase transition is observed at a surface pressure of 5 dynes/cm. Pressure‐induced changes in the chlorophyll arrangement become evident from a drastic change in the absorption spectra, accompanying the phase transition. The crystalline phase exhibits an extremely narrow absorption band (halfwidth below 9 nm) centered at 698 nm, indicative of a coplanar chlorophyll arrangement in a well‐ordered environment. It is highly probable that in these model membranes a chlorophyll arrrangement could be established that is equivalent to the one proposed for the reaction center P700.
HEMATOPORPHYRIN PHOTOSENSITIZATION OF SERUM ALBUMIN and SUBTILISIN BPN'
Authors: Richard Philippe , Blum Aleksander , Grossweiner Leonard I. 
Published: January 2008

Abstract—The photosensitized inactivation of subtilisin BPN' by free hematoporphyrin (HP) followed exponential kinetics with positive mechanistic tests for the involvement of singlet oxygen (1O2) as the principal intermediate. The photoinactivation quantum yield was 0.029 at 390 nm in oxygen‐saturated, D2O buffer at pH 7.0. The effects of HP binding were investigated for tryptophan oxidation in bovine serum albumin (BSA) and human serum albumin (HSA) at high protein:HP concentration ratios where the HP was > 97% complexed. The reaction kinetics were non‐exponential and mimick a second‐order process in the initial stages. The rate of HP photobleaching was 30‐fold faster for complexed HP compared with free HP, which was shown to account for the observed kinetics. Mechanistic tests showed that 1O2 was the dominant photooxidizing intermediate of tryptophan residues and that it was not involved in the accompanying photobleaching of HP. The quantum yield for tryptophan oxidation in BSA was 0.11 at 390 nm in oxygen‐saturated, D2O buffer at pH 8.0. The reactivity of HSA was approximately 2‐fold lower than BSA for equivalent conditions. Estimates of the reaction cross sections led to 3 Å2 for the inactivation of subtilisin BPN' by 1O2 and 20 Å2 for the oxidation of tryptophan in BSA.
INTRODUCTION OF PYRIMIDINE DIMERS INTO DIFFERENT INTRACELLULAR FORMS OF SIMIAN VIRUS 40
Authors: Edenberg Howard J. , Roman Ann 
Published: January 2008

AbstractWe examined the production of pyrimidine dimers by UV radiation in different intracellular forms of simian virus 40 DNA. Virus and chromatin or previrions were selectively labeled with [l4C]‐thymidine and [3H]‐thymidine, respectively, in the same monolayer of infected cells. Viral DNA was extracted immediately after irradiation, and pyrimidine dimers were detected as sites sensitive to the UV‐endonuclease encoded by bacteriophage T4. No difference in the number of dimers introduced into chromatin, previrions. or virions was detected.
SINGLET AND TRIPLET ENERGY TRANSFER IN α‐DIKETONE DERIVATIVES OF URACIL and THYMINE
Authors: Lee Y.J. , Burr J. G. 
Published: January 2008

AbstractIrradiation of 1‐(3,4‐dioxopentyl)uracil (UPD) and 1‐(3.4‐dioxopentyl)thymine (TPD) in acetonitrile solution at 25°C, at the wavelength (280 nm) where only the pyrimidine absorbs the light, sensitizes both fluorescence and phosphorescence of the diketone chromophore in the sidechain. From comparison of the intensity in the corrected excitation spectra with the absorption spectra in acetonitrile solution, it was estimated that the yield of singlet energy transfer in UPD was 0.17 and in TPD was 0.44. It was also observed that the ratio of phosphorescence to fluorescence was greater in the sensitized emission than in that from direct excitation of the diketone chromophore. The yield of triplet energy transfer thus measured corresponds to minimum values for the yields of intersystem crossing from singlet excited state to triplet excited state of 0.075 in the uracil chromophore of UPD and of 0.14 in the thymine chromophore of TPD. These are in agreement with other recent values for these quantities. The value of this type of system as an intramolecular triplet counter is discussed.