bluuebunny/crossref_metadata_2025_split huggingface dataset:
STOICHIOMETRY and KINETICS OF PROTON RELEASE UPON PHOTOSYNTHETIC WATER OXIDATION
Authors: Förster Verena , Junge Wolfgang 
Published: January 2008

Abstract—We studied the magnitude and the rise kinetics of proton release into the interior of thylakoids by flash spectrophotometty with neutral red as pH indicator. Excitation of dark‐adapted thylakoids by a series of between 4 and 11 flashes produced a complex pattern of proton release into the thylakoid lumen. Proton release upon each flash was time resolved.A slow component of proton release oscillated weakly in magnitude with period of two as function of flash number. It exhibited a half‐rise time of approximately 20 ms from the very first flash on, and it was abolished by inhibitors of plastohydroquinone oxidation. This component was attributed to the oxidation of plastohydroquinone by PS Iviathe Cytb6/f complex.Additionally, rapid and multiphasic proton release was observed with half‐rise times of less than 2 ms which exhibited a pronounced and damped oscillation with period of four as function of flash number. This rapid proton release was attributed to water oxidation. A detailed kinetic analysis suggested that proton release occurred with the following stoichiometry and with the following half‐rise times during the transitions S1Si+1of water oxidation: 1 H+(250 μs, S0→1): 0 H+(S1→ S2):1 H+(200 μs, S2→S3):2 H+(1.2 ms, S3→ S4→ S0).Proton release and proton rebinding upon oxidation and reduction of the intermediate electron carrier Z, respectively, may have influenced the kinetics of the respective proton yields but not the stoichiometric pattern.
A MODEL FOR THE ORIGIN OF PHOTOSYNTHESIS–III. THE ULTRAVIOLET PHOTOCHEMISTRY OF UROPORPHYRINOGEN*
Authors: Mercer‐Smith Janet A. , Raudino Anthony , Mauzerall David C. 
Published: January 2008

Abstract— The photochemical ramifications of the high ultraviolet flux on the primordial earth prior to the formation of the ozone layer have been considered in a study of the ultraviolet photochemistry of uroporphyrinogen (urohexahydroporphyrin), a colorless compound which absorbs strongly at wavelengths less than 220 nm. Urohexahydroporphyrin was investigated since it is the first macrocycle formed on the biosynthetic pathway of chlorophyll and can be used to test the hypothesis that the biosynthetic pathway to chlorophyll recapitulates the evolutionary history of photosynthesis.When urohexahydroporphyrin is illuminated in aqueous anaerobic solution, hydrogen gas is produced. More hydrogen gas is produced in the presence of a colloidal platinum catalyst. The products of the photooxidation of urohexahydroporphyrin are urotetrahydroporphyrin (uroporphomethene) and uroporphyrin. This research shows how the oxidation of uroporphyrinogen to uroporphyrin, the first biogenetic porphyrin, could have occurred anaerobically and abiotically on the primordial earth.
DISTRIBUTION OF PORPHYRINS IN THE VARIOUS COMPARTMENTS OF UNILAMELLAR LIPOSOMES OF DIPALMITOYL‐PHOSPHATIDYLCHOLINE AS PROBED BY FLUORESCENCE SPECTROSCOPY
Authors: Ricchelli Fernanda , Jori Giulio 
Published: January 2008

Abstract—The spectroscopic properties of hematoporphyrin, hematoporphyrin‐dimethyl ester, uroporphyrin and uroporphyrinoctamethyl ester, incorporated into unilamellar liposomes of dipalmitoylphos‐phatidylcholine, have been studied with the aim to assess the distribution of porphyrins within the various liposomal compartments.The results obtained indicate that the highly hydrosoluble uroporphyrin is partitioned in the endoliposomal aqueous pool while its octamethylester is homogeneously distributed in the inner lipid monolayer. Hematoporphyrin and its dimethylester show an heterogeneous distribution within the phospholipid bilayer. At T = 25°C these porphyrins are preferentially located in the outer phospholipid monolayer.Detailed studies on hematoporphyrin indicate that the distribution between the inner and outer phospholipid monolayer is a function of temperature and liposome dimensions. In particular, the increase of temperature above the critical temperature for the liquid‐gel phase transition of the liposomes causes a partial shift of the porphyrin molecules toward the inner phospholipid monolayer. Moreover, the increase of liposome dimensions leads to a greater accessibility of porphyrin to the external medium.
INVESTIGATION OF CHROMOPEPTIDES FROM C‐PHYCOCYANIN BY UV‐VIS ABSORPTION, EMISSION AND CIRCULAR DICHROISM SPECTROSCOPY
Authors: Schneider Siegfried , Köst‐Reyes Eliana , Scharnagl Christina , Geiselhart Peter 
Published: January 2008

AbstractFour different chromopeptides were isolated after digestion of C‐phycocyanin with pepsin. Their UV‐vis absorption and circular dichroism spectra were measured at two different pH values without and with urea present in the buffered solutions. For one chromopeptide, fluorescence spectra and the kinetics of fluorescence decay were studied in more detail. The results are discussed in comparison with quantum‐mechanical model calculations. It is concluded that due to the interaction between the oligopeptide chain and the chromophore, the latter is present as a mixture of helical and semi‐extended forms, respectively.
PHOTORESPONSES OF SEMICONDUCTOR POLYCRYSTALLITES SEPARATING TWO AQUEOUS SOLUTIONS
Authors: Tien H. Ti , And Z.‐C. Bi , Tripathi A. K. 
Published: January 2008

AbstractSolar cells using polycarbonate membranes, with CdS deposited on them, were made by a very simple way; the CdS‐containing membrane separates a Lucite cell into two compartments. On illumination, about 150 mV photovoltage (Vop) and 0.5 μA cm‐2photocurrent (Isc) could be produced; one side of the membrane acted as photoanode, and the other side as photocathode. By means of coating Victoria Blue B (VBB) onto the membrane before CdS deposition, the maximumVopandIscof the CdS‐deposited membrane could reach 500 mV and 3.0 (μA cm‐2, respectively. A mixture of CdS and CdSe deposited membrane has also been tested and found to have both the advantages of high photovoltage (over 400 mV) and good stability after modification. Even more interesting results were also obtained with CdSe pellets in place of the CdS‐deposited membrane, in whichVopandIscof the cell were 1.2 V and 6 mA cm‐2, respectively. The essential aspect of the system, modelled after the photosynthetic thylakoid membrane, contains an asymmetrical, ultrathin semiconductor crystallite layer separating two aqueous solutions.
OXYGEN RADICALS MEDIATE CELL INACTIVATION BY ACRIDINE DYES, FLUORESCEIN, and LUCIFER YELLOW CH
Authors: Martin Joseph P. , Logsdon Naomi 
Published: January 2008

Abstract Acridine dyes, fluorescein and lucifer yellow CH are fluorescent photosensitizers used experimentally to selectively stain and photodynamically destroy eukaryotic cells and subcellular structures. We have determined that the mechanism of light‐ and oxygen‐dependent inactivation of E. coli by these dyes involves oxygen radicals and hydrogen peroxide.All of the dyes oxidized NAD(P)H† under illumination. Superoxide (O2−), detected as the superoxide dismutase (SOD)‐inhibitable reduction of ferricytochrome c, was a major product of the dye sensitized photooxidation.Cationic acridine dyes penetrated the membranes of E. coli and were photoreduced intracellularly. Reduced dyes diffused back into the medium and mediated the reduction of extracellular ferricytochrome c. The anionic dyes fluorescein and lucifer yellow CH were unable to mediate extracellular cytochrome c reduction, indicating that these dyes were impermeable to the E. coli membranes. Acridine dyes, when illuminated, inhibited the growth of E. coli in a rich medium, and induced the synthesis of SOD. Fluorescein and lucifer yellow CH did not inhibit growth or induce SOD synthesis because they were unable to enter the cells.Superoxide (O2−) and hydrogen peroxide (H2O2), generated by the enzyme xanthine oxidase were toxic to E. coli B. Inactivation by xanthine oxidase was partially inhibited by exogenous SOD and completely inhibited by exogenous catalase or SOD plus catalase. Similarly, exogenous SOD plus catalase protected against inactivation by acridines and fluorescein‐NADH or lucifer yellow CH‐NADH mixtures. Prior induction of superoxide dismutase and catalase in E. coli B significantly protected cells against a subsequent challenge by illuminated acridine dyes. SOD and catalase preinduction combined with additions of exogenous SOD and catalase completely protected E. coli B against photodynamic inactivation by acridine yellow. The hydroxyl radical scavengers, dimethyl sulfoxide, sodium benzoate and thiourea, protected E. coli B against photodynamic inactivation by acridine orange.The results implicate O2−, H2O2, and the hydroxyl radical (OH‐) as underlying molecular agents of the phototoxicity mediated by acridine orange, acridine yellow, fluorescein and lucifer yellow CH.
UV‐B RADIATION EFFECTS ON PHOTOSYNTHESIS, GROWTH and CANNABINOID PRODUCTION OF TWO Cannabis sativa CHEMOTYPES
Authors: Lydon John , Teramura Alan H. , Coffman C. Benjamin 
Published: January 2008

AbstractThe effects of UV‐B radiation on photosynthesis, growth and cannabinoid production of two greenhouse‐grown C. sativa chemotypes (drug and fiber) were assessed. Terminal meristems of vegetative and reproductive tissues were irradiated for 40 days at a daily dose of 0, 6.7 or 13.4 kJ m‐2 biologically effective UV‐B radiation. Infrared gas analysis was used to measure the physiological response of mature leaves, whereas gas‐liquid chromatography was used to determine the concentration of cannabinoids in leaf and floral tissue.There were no significant physiological or morphological differences among UV‐B treatments in either drug‐ or fiber‐type plants. The concentration of Δ9‐tetrahydrocannabinol (Δ9‐THC), but not of other cannabinoids, in both leaf and floral tissues increased with UV‐B dose in drug‐type plants. None of the cannabinoids in fiber‐type plants were affected by UV‐B radiation.The increased levels of Δ9‐THC in leaves after irradiation may account for the physiological and morphological tolerance to UV‐B radiation in the drug‐type plants. However, fiber plants showed no comparable change in the level of cannabidiol (a cannabinoid with UV‐B absorptive characteristics similar to Δ9 THC). Thus the contribution of cannabinoids as selective UV‐B filters in C. sativa is equivocal.
POLARIZED OPTICAL PROPERTIES OF PHYCOBILISOMES FROM Anabaena, Nostoc and Synechococcus
Authors: Frackowiak D. , Erokhina L. G. , Picard G. , Leblanc R. M. 
Published: January 2008

AbstractPolarized absorption, photoacoustic, fluorescence excitation and fluorescence emission spectra of phycobilisomes were measured when embedded in polyvinyl alcohol films. The phycobilisomes were isolated from the following organisms:Anabaena cylindrica, Nostoc punctiformaandSynechococcus elongatus.The ratio of photoacoustic spectra to absorption was taken as a measure of thermal dissipation of excitation energy. The isotropic samples and those oriented by the film stretching were investigated. The stretching of the sample strongly influences the efficiency of excitation energy transfer occurring among biliproteins in phycobilisomes, as is seen from the dramatic changes in the fluorescence and thermal dissipation spectra. The effect of stretching the film depends on the shape of phycobilisomes and on the strength of interactions between biliproteins in phycobilisomes.
PHOTOSENSITIZING EFFICIENCIES, TUMOR‐ and CELLULAR UPTAKE OF DIFFERENT PHOTOSENSITIZING DRUGS RELEVANT FOR PHOTODYNAMIC THERAPY OF CANCER
Authors: Moan J. , Peng Q. , Evensen J. F. , Berg K. , Western A. , Rimington C. 
Published: January 2008

AbstractSeveral parameters of the following dyes, all relevant as sensitizers for photochemotherapy of cancer, have been studied: Photofrin II (PII), hematoporphyrin (HP)‐di‐hexyl‐ether, HP‐di‐ethyl‐ether, tetra (3‐hydroxyphenyl) porphyrin, (3THPP), tetraphenyl porphine tetrasulphonate (TPPS4) aluminium phthalocyanine tetrasulfonate (A1PCTS), aluminium phthalocyanine (A1PC), chlorin e, (Chi e6) and merocyanine 540 (MC 540). The following parameters and features of these dyes were studied: (1) Tumor uptake in C3H mouse mammary carcinomas. (2) Skin/tumor concentration ratio in the same animal system. (3) Triton X‐114/H20 partition coefficients at different pH‐values. (4) Uptake of the dyes by human cells of the line NHIK 3025. (5) Relative fluorescence quantum yields of the dyes bound to cells. (6) Absorption‐, fluorescence‐excitation‐ and fluorescence‐emission spectra of the cell‐bound dyes. (7) Relative quantum yields for photoinactivation of cells after 18 h incubation with the dyes. (8) Relative quantum yields of photodegradation of the singlet oxygen trap 1,3‐diphenylisobenzofuran (DPBF) in cells after 18 h incubation with the dyes.The following main conclusions were drawn: (1) 3THPP was the best and most selective tumor localizer of the dyes tested, followed by AIPCTS, TPPS4, PII and Chi e.,. (2) The Triton X‐114/H20 partition coefficient of most of the dyes decreased with increasing pH. (3) The cellular uptake of the dyes (18 h incubation in medium with 3% serum) increased with increasing Triton X‐114/H20 partition coefficient. (4) HP‐di‐hexyl‐ether had the highest quantum yields both for photoinactivation of cells and degradation of cell‐bound DPBF, followed by the other lipophilic porphyrins and Chi e6. The water‐soluble dyes TPPS4and AIPCTS had quantum yields of the order of ten times lower than those of the lipophilic porphyrins. (5) There was a clear correlation between the quantum yields for cell‐inactivation and those for photodegradation of DPBF, suggesting that the same reactive photoinduced species is involved in both processes. This suggestion was strengthened by the observation that DPBF reduced the quantum yield of cell inactivation. Thus, all the tested dyes seem to actviaa type II process. (6) All of the dyes, even the water‐soluble TPPS4and AIPCTS, are aggregated in aqueous solutions, and the cells bind both monomers and aggregates. (7) A significant fraction of the cell‐bound dyes was located close to tryptophan‐containing proteins. (8) Cell‐bound Chi e,6had the highest fluorescence quantum yield of the dyes.
LOCALIZATION OF MONO‐L‐ASPARTYL CHLORIN e6 (NPe6) IN MOUSE TISSUES
Authors: Aizawa Katsuo , Okunaka Tetsuya , Ohtani Takuzo , Kawabe Hirofumi , Yasunaka Yukari , O'Hata Susumu , Ohtomo Nobunari , Nishimiya Katsuaki , Konaka Chimori , Kato Harubumi , Hayata Yoshihiro , Saito Takashi 
Published: January 2008

Abstract It is known that HpD is retained longer by malignant tissue than normal tissue and is therefore a useful material for photodynamic therapy (PDT). Currently, vigorous research is being conducted throughout the world to discover a new material which can have greater cancer cell affinity than hematoporphyrin derivative (HpD) and will be used effectively for PDT. Investigation has been conducted to determine the spectral characteristics and cancer cell affinity of NPe6, a recently developed material.Structurally, a double bond on the D‐ring of the porphyrin ring of mono‐L‐aspartyl chlorin e6 (NPe6) has been reduced, thereby changing its spectral properties from that of HpD. This difference accounts for the stronger absorption bands in wavelengths longer than those of HpD. Furthermore, NPe6 in tumor showed stronger absorption at 660 nm than HpD. Absorption by hemoglobin (Hb) in the blood occurs at wavelengths in the range 500‐600 nm, thereby lowering light transmittance. A compound which has a strong absorption band at wavelengths longer than 600 nm and consequently is not affected by Hb will naturally be activated by light at a greater depth in tissue than compounds which do not share this characteristic. The localization of NPe6 in sarcoma and various internal organs was examined with an endoscopic spectrophotometer using an excimer dye laser. After 72 h i.v. NPe6 injection, the results indicate that NPe6 has 10 times greater uptake in malignant tissue cells than in normal organs. Based on the above observations, it was concluded that NPe6 could be effective for PDT if toxicity is low and that this compound has a high malignant tissue affinity.
SINGLET OXYGEN INVOLVEMENT IN PHOTOHEMOLYSIS SENSITIZED BY MEROCYANINE‐540 and ROSE BENGAL
Authors: Valenzeno Dennis Paul , Trudgen Julia , Hutzenbuhler Angela , Milne Mark 
Published: January 2008

AbstractMerocyanine‐540 is currently in use in experimental protocols for the treatment of leukemia and neuroblastomas. The mechanism of cellular phototoxicity of this membrane binding sensitizer is unexplored. We have used sodium azide and deuterium oxide to examine the role of singlet oxygen in photomodification of cell membranes in a photohemolysis assay. The effects of these agents on the photomodification process were separated from the effects on the ion fluxes leading to lysis (lytic phase). Azide significantly inhibited photohemolysis sensitized by merocyanine‐540 or rose bengal. The inhibition was equal for both sensitizers. Azide had no effect on the lytic phase. Deuterium oxide significantly potentiated lysis with both sensitizers to approximately the same degree. There was little effect of deuterium oxide when added after illumination. The results indicate that singlet oxygen plays a significant role in membrane photomodification sensitized by both rose bengal and merocyanine‐540.
THE ELECTRON SPIN POLARIZATION OF THE DONOR‐TRIPLET STATE IN NATIVE and MODIFIED PHOTOSYNTHETIC REACTION CENTERS FROM
Authors: Wijk F. G. H. Van , Beijer C. B. , Gast P. , Schaafsma T. J. 
Published: January 2008

AbstractThe electron spin polarization (ESP) pattern of the donor‐triplet state (PR) of reaction centers (RC's) of the purple bacteriumRhodobacter(formerlyRhodopseudomonas) sphaeroidesR‐26 was investigated. δm =±1 triplet EPR spectra were recorded of unmodified RC's as well as of RC's from which Fe2+or ubiquinone was removed, or ubiquinone was substituted by menaquinone.The relative amplitude of the Y peaks in the triplet EPR powder spectrum of PRdecreases when the temperature is increased from 8 K to 100 K in RC's with an intact quinone‐iron complex. This decrease is more pronounced when the primary ubiquinone is substituted by menaquinone. These observations provide further support for the hypothesis that the observed lineshape of the PRtriplet state EPR spectrum reflects the presence of a third electron spin, magnetically coupled to I‐in the P+I‐radical pair, as suggested by Van Wijk et al. (1986)(Photobiochem. Photobiophys. 11, 95–100). Our observations suggest that this phenomenon may be general in purple bacteria.
TIME‐RESOLVED RESONANCE RAMAN SPECTRA OF THE PHOTOCYCLE INTERMEDIATES OF ACID AND DEIONIZED BACTERIORHODOPSIN
Authors: Chronister Eric L. , El‐Sayed M. A. 
Published: January 2008

Abstract— The photocycle of bacteriorhodopsin (bR) and its perturbed forms are investigated by a time‐resolved resonance Raman study. These experiments were performed in the C=C stretching and in the fingerprint spectral regions for the acid blue, acid purple and deionized forms of bR.The main observations are as follows: (1) isomerization of the retinal, from all‐trans to 13‐cis, occurs in native bR and in all of the acid and deionized perturbed bR species; (2) formation of the early intermediates (the K610 and L550 analogues) also occur in native bR and in all of the perturbed species; and (3) deprotonation of the protonated Schiff base (PSB), to give the M412 type intermediate, occurs in native bR, but is inhibited in all of the perturbed bR species on the time‐scale of the native bR photocycle.The results show that isomerization alone is not a prerequisite for the PSB deprotonation process. The observed photocycle, initiated with retinal isomerization, is found to occur from all‐trans to 13‐cis in all of the perturbed forms of bR. In addition, the results imply that removal of the cations, of an increase in the hydrogen ion concentration, prevent only the PSB deprotonation process and not the formation of earlier cycle intermediates. Some attention is focused on the two blue forms of bR (acid and deionized) due to the fact that their ground‐state absorption maximum, unphotolyzed Raman spectra, and Raman spectra changes during the photocycle are all very similar. The similarities between the acid blue and deionized blue forms in the fingerprint region support previous suggestions that both blue species have nearly the same retinal active site.
LIGHT‐ABSORPTION AND ELECTRON‐TRANSPORT BALANCE BETWEEN PHOTOSYSTEM II AND PHOTOSYSTEM I IN SPINACH CHLOROPLASTS
Authors: MELIS Anastasios , Spangfort Michael , Andersson Bertil 
Published: January 2008

Abstract—The distribution of absorbed light and the turnover of electrons by the two photosystems in spinach chloroplasts was investigated. This was implemented upon quantitation of photochemical reaction centers, chlorophyll antenna size and composition of each photosystem (PS), and rate of light absorptionin situ.In spinach chloroplasts, the photosystem stoichiometry was PSIIJPSIIα/PSIIβ/PSI= 1.3/0.4/1.0. The number (N) of chlorophyll (a+b) molecules associated with each PS was N(PSIIα)/N(PSIIβ)/N(PSI)=230/100/200, i.e. about 65% of all Chl is associated with PSII and about 35% with PSI. Light absorption by PSIIin vivois selectively attenuated at the molecular, membrane and leaf levels, (a) The rate of light absorption by PSII was only 0.85 that of PSI because of the lower rate of light absorption by Chlbas compared to Chla(approximately 80% of all Chlbin the chloroplast is associated with PSII). (b) The exclusive localization of PSIIαin the membrane of the grana partition regions and of PSI in intergrana lamellae resulted in a differential “sieve effect” or “flattening of absorbance” by the photosystems in the two membrane regions. Due to this phenomenon, the rate of light absorption by PSII was lower than that of PSI by 15‐20%. (c) Selective filtering of sunlight through the spinach leaf results in a substantial distortion of the effective absorbance spectra and concomitant attenuation of light absorption by the two photosystems. Such attenuation was greater for PSII than for PSI because the latter benefits from light absorption in the 700‐730 nm region.It is concluded that, in spite of its stoichiometric excess in spinach chloroplasts, light absorption by PSII is not greater than that by PSI due to the different molecular composition of the two light‐harvesting antenna systems, due to the localization of PSII in the grana, and also because of the light transmission properties through the leaf. The elevated PSII/PSI reaction center ratio of 1.7 and the association of 65% of all Chl with PSII help to counter the multilevel attenuation of light absorption by PSII and ensure a balanced PSII/PSI electron turnover ratio of about 1:1.
EQUILIBRIUM AMONG HEMATOPORPHYRIN‐DERIVATIVE COMPONENTS: INFLUENCE OF THE INTERACTION WITH CELLULAR STRUCTURES
Authors: BOTTIROLI GIOVANNI , RAMPONI ROBERTA 
Published: January 2008

Abstract—Hematoporphyrin‐derivative (HpD) is a complex mixture of porphyrins in different aggregation states. The spectral analysis of HpD in aqueous solution shows the presence of monomeric species through the fluorescence emission spectrum and of both monomeric and aggregated species through the absorption spectrum.The interaction with biopolymers and cellular components results in the appearance of new emission bands at 630 nm and in the640–670 nm spectral region which can be evidenced under suitable excitation conditions. Correspondingly, two new decay times (∼ 0.6 ns, and ∼ 3 ns), are observable. The new fluorescent species detected can be considered as the result of the hydrophobic effect induced by cellular structures on porphyrin aggregates.