bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE MAXIMUM EFFICIENCY OF PHOTOSYNTHESIS *
Authors: BOLTON JAMES R. , HALL DAVID O. 
Published: January 2008

Abstract—Within the ideal assumptions: (1) two Photosystems for photosynthetic fixation of CO2, (2) all solar photons with Λ≥ 700 nm are absorbed, (3) the photon requirement is 8 for each CO2 molecule fixed and O2 molecule evolved and (4) the principal stable product of photosynthesis is d‐glucose, the theoretical maximum efficiency of conversion of light to stored chemical energy in green‐plant type (oxygen‐evolving) photosynthesis in bright sunlight is calculated to be 13.0%. Thermodynamic arguments are presented which indicate that a photosynthetic system with one Photosystem would be highly unlikely to be able to drive each electron from water to evolve O2 and reduce CO2. The practical maximum efficiency of photosynthesis under optimum conditions is estimated to be 8–9%.
RING OPENING PHOTOREACTIONS OF 5‐BROMOURACIL AND 5‐BROMO‐2′‐DEOXYURIDINE WITH SELECTED ALKYLAMINES
Authors: SHETLAR MARTIN D. , ROSE ROBERT B. , HOM KELLIE , SHAW ANTHONY A. 
Published: January 2008

Abstract— Several studies in the literature indicate that histones (lysine rich proteins found associated with DNA in eukaryotic chromatin), as well as poly‐L‐lysine, can be photocross‐linked by ultraviolet (UV) light to DNA in which 5‐bromo‐2′‐deoxyuridine has been substituted for thymidne. To gain some insight into the possible nature of this cross‐linking, we have studied the photoreactions occurring in deoxygenated aqueous solutions containing 5‐bromouracil (I) (BrUra) or 5‐bromo‐2′‐deoxyuridine (III) (BrdUrd) and ethylamine, a lysine side chain analog. In the case of I this reaction produced the ring opened compound N‐(N′‐ethylcarbamoyl)‐3‐amino‐2‐bromoacrylamide (Ia). A small amount of N‐(N′‐ethylcarbamoyl)‐3‐ethylamino‐2‐bromoacrylamide (Ic) was also isolated. It was found that purified Ia, standing in the presence of ethylamine, was gradually converted to Ic in a dark reaction. The βandαanomers of N‐(N′‐ethylcarbamoyl)‐3‐(2′ deoxyribofuranos‐1′‐yl)amino‐2‐bromoacrylamide (IIIa and IIIb respectively) were isolated as products in the photoreaction of III with ethylamine; the α anomer was produced in a dark reaction from the β anomer. The identity of these anomers was established by comparison of their proton NMR spectra with those of the four corresponding α and β furanosyl and pyranosyl isomeric nucleosides of thymine, which are presented in the Appendix. A study was also made of the reaction of I with methylamine; a ring opened product analogous to In, viz. N‐(N′‐methylcarbamoyl)‐3‐amino‐2‐bromoacrylamide(IIa) was formed. A similar study with 5‐bromo‐1‐methyluracil produced N‐(N′‐methylcarbamoyl)‐3‐methylamino‐2‐bromoacrylamide (IIc) as a product. Likewise, the reaction of 5‐chlorouracil with ethylamine was studied and N‐(N′‐ ethylcarbamoyl)‐3‐amino‐2‐chloroacrylamide (Ie), which is analogous in structure to Ia, was found to be produced. Structural identifications were made through use of UV spectroscopy, high resolution 1H‐NMR spectroscopy, mass spectrometry and, in the case of Ia and IIa, 13C‐NMR spectroscopy. In the BrUra and BrdUrd reaction systems, described above, dehalogenation reactions accounted for a major portion of the products. The yields of ring opened products, determined at pH 10, ranged from a high of 10.3% in the BrUra‐ethylamine system to a low of 1.7% in the MeBrUra‐methylamine system.The pH profile of the relative quantum yields for production of total opened ring product (IIIa+IIIb) in the photoreaction of III with ethylamine indicates that this quantity increases rapidly over the pH range between 7.5 and 9.5 and then decreases above 10.5.An additional reaction, a photoinduced halogen exchange process, was found to occur when Ia was irradiated in sodium chloride solution; this reaction converted Ia to Ie.
LIGHT‐DEPENDENT GENERATION OF SUPEROXIDE FROM HUMAN ERYTHROCYTES
Authors: Bynoe Leon A. , Gottsch John D. , Pou Sovitj , Rosen Gerald M. 
Published: January 2008

Abstract—Using the cytochrome c reduction method, we investigated light‐dependent erythrocytic superoxide production. After 4 h light and dark exposure of erythrocytes from eight healthy human subjects, an average of 18.6% more superoxide was generated by erythrocytes exposed to light. Pretreatment of erythrocytes with the superoxide dismutase inhibitorN,N‐diethyldithiocarbamate increased detection of superoxide while pretreatment with the anion channel blocker 4‐a‐cetamido‐4′‐isothiocyano‐2,2′‐disulfonic acid stilbene decreased detection. These findings indicate that substantially more spontaneously generated superoxide is produced and escapes from normal erythrocytes at ambient oxygen tensions on exposure to light. This excess generation and escape of superoxide from erythrocytes exposed to light may result in tissue photosensitization, especially in the retina of the eye, where high oxygen tension, blood and chronic light exposure occur simultaneously.
BASE RELEASE FROM DNA AND POLYNUCLEOTIDES UPON 193 nm LASER EXCITATION
Authors: Gurzadyan Gagik G. , Gorner Helmut 
Published: January 2008

Abstract—Release of bases from calf thymus DNA and three polynucleotides, induced by 20 ns excitation at 193 nm in aqueous solution at pH 7, was detected by HPLC. The quantum yields of formation of free bases (ΦB) from double‐stranded DNA (0.4 mM) are independent of intensity, indicating a one‐quantum mechanism ofN‐glycosidic bond cleavage. The ΦBvalues increase in the order guanine, thymine, adenine, cytosine, the latter being ΦC= 7 × 10−‐4for double‐stranded DNA under Ar and O2. The larger atlvalues in N2O‐saturated solution,e.g. Φc= 1.2 × 10−‐3are ascribed to additional base releaseviaOH‐adduct radicals. The ΦBvalues of homopolynucleotides increase in the order poly(G), poly(A) and poly(C),e.g. Φc‐= 7 × 10−‐2under Ar, as do the efficiencies for base release per radical cation (nB). A comparison of the nBvalues with the efficiencies of single‐strand breakage for poly(C), poly(A) and DNA shows a similar trend; both are markedly larger for pyrimidines than for purines. Pathways to undamaged bases, initiated from base radical cations, are proposed.
IMPROVED SURVIVAL FROM INTRACAVITARY PHOTODYNAMIC THERAPY OF RAT GLIOMA
Authors: Walstad Ying Jt. Diana , Brown J. Tony , Powers Stephen K. 
Published: January 2008

Abstract—The effectiveness of intratumoral photoradiation in photodynamic therapy (PDT) using a polyporphyrin photosensitizer was studied in the RT‐2 rat glioma model. One week after intracerebral implantation of RT‐2 cells, experimental rats received a single i.p. injection of 2 mg/kg of PhotofrinTM. After administration of the photosensitizer (48 h), the tumors were partially resected and the exposed cavity was irradiated with 15 J of laser light at a wavelength of 630 nm. Further treatment with a large craniectomy significantly enhanced rat survival. Control rats which received no photosensitizer but were treated with surgery, alone or in combination with laser irradiation, succumbed from early tumor recurrence. Photodynamic therapy without decompressive surgery resulted in hemorrhagic infarction of residual tumor and adjacent brain with focal cerebral edema which resulted in cerebral herniation and early death. Our results indicate that photodynamic therapy is effective in treating residual brain tumor but at the expense of brain tissue surrounding the tumor. Unless relieved, intracranial pressure from photodynamic therapy‐associated cerebral edema in this animal model resulted in shortened survival.
A FIBER‐OPTIC RATIO FLUOROMETER FOR MUTANT ISOLATION
Authors: Horwitz Benjamin A. , Amit Rivka , Llpson Edward D. 
Published: January 2008

Abstract—Mutants with altered fluorescence are likely to be modified in pigment composition or photochemistry. They can thus help address a variety of problems in photobiology, particularly in the areas of photosynthesis, photomorphogenesis and photobehavior. To aid in the screening for such mutants, we have developed an instrument for detecting fluorescence intensity relative to scattered light intensity. The instrument employs fiber optics for illumination and detection, and an analog electronic circuit to compute the ratio between fluorescence and scattered light. An application of the fluorometer to screen for Arabidopsis mutants altered in chlorophyll accumulation is described.
STRUCTURE‐ACTIVITY STUDIES OF PHOTOACTIVATED ANTIVIRAL AND CYTOTOXIC TRICYCLIC THIOPHENES
Authors: Marles Robin J. , Hudson James B. , Graham Elizabeth A. , Soucy‐Breau Chantal , Morand Peter , Compadre R. Lilia , Compadre Cesar M. , Towers G. H. Neil , Arnason J. Thor 
Published: January 2008

Abstract—The photoactivated antiviral and cytotoxic activities of the naturally occurring thiophene, α‐terthienyl (1), and 15 synthetic analogues were evaluated against murine cytomegalovirus and Sindbis virus, and murine mastocytoma cells. After irradiation with near UV light, α‐terthienyl and most of its analogues had significant toxicity, with minimum inhibitory concentrations in the range of 0.02–40 μM. In the absence of near UV irradiation, only one analogue had antiviral activity and five were cytotoxic. The most active analogues were those containing carboxylic acid, hydroxyl, or cyano substituents. Quantitative structure‐activity relationship analysis of thiophene phototoxicity suggested that the rate of singlet oxygen production is the primary determinant of antiviral and cytotoxic activities. For phototoxicity against murine cytomegalovirus, a significant role for hydrophobicity was also demonstrated. Tricyclic thiophenes show significant potential for photochemotherapy of viral infections and cancer. and further evaluation in animal models is recommended.
LEVELS OF REDUCED PYRIDINE NUCLEOTIDES AND LENS PHOTODAMAGE
Authors: Rao Ch. Mohan , Jr J. Samuel Zigler 
Published: January 2008

Abstract—Since most of the known factors that are associated with cataract formation are oxidative in nature, one would expect that a highly reductive environment might arrest or retard the progress of cataract formation. Reduced nucleotides, both NADH and NADPH, are potent reductants with a large negative redox potential of ‐ 320 mV. Lenses of certain species contain high levels of these nucleotides, presumably due to the presence of taxon specific crystallins. We have utilized this situation to investigate whether the levels of reduced pyridine nucleotides modulate photo‐oxidative damage to the lens. We have monitored the time dependent loss of tryptophan fluorescence upon photodamage for lenses from guinea pig, rabbit and frog (Rana) that contain high levels of pyridine nucleotides and compared with the lenses from rat, Xenopus and a mutant strain of guinea pig that contain significantly lower amounts of these nucleotides. About 75% and 90% of the initial fluorescence intensity is lost in the case of rat and Xenopus lenses, respectively, after a total of 35 min exposure. Rabbit, guinea pig and frog lenses, under identical conditions, show only about 35–40% loss of the initial fluorescence. It appears that the lenses that contain high levels of reduced nucleotides are less susceptible to photodamage. The observed anti‐oxidative role of reduced nucleotides in the lenses indicates the possibility of testing reductants (NADPH, NADH and their functional analogues) as potential candidates to therapeutically intervene in the process of cataractogenesis.
A BIOFILM USED AS ULTRAVIOLET‐DOSIMETER
Authors: Quintern L. E. , Horneck G. , Eschweiler U. , Bücker H. 
Published: January 2008

Abstract— A UV‐dosimeter has been developed for routine measurements which mainly weights the various components of the spectrum in relation to their damaging effects on a microorganism. For this purpose a biofilm was constructed, comprising dried spores of Bacillus subtilis (wild‐type or DNA repair defective strain), immobilized on transparent polyester plastic sheets. After irradiation, the biofilm was incubated in a growth medium. The proteins, synthesized by the immobilized microorganisms after spore germination and several cell divisions, were stained and determined by photometry, giving a measure of the biological activity. The ”biologically effective dose“ was determined from a calibration curve. It reflects the dose equivalent to that of the calibration source producing the same effect.The UV‐response of the biofilm is additive and follows the reciprocity law in the range of fluence rates investigated. The response is nearly independent of temperature within the range of ‐20°C to +70°C as well as of humidity between about 37 and 80% relative humidity. Storage for up to 9 months at <70% relative humidity and room temperature does not significantly influence the viability of the spores.
LIGHT‐INDUCED SYNTHESIS OF ANTHOCYANIN IN CARROT CELLS IN SUSPENSION—IV. THE ACTION SPECTRUM
Authors: Takeda Junko , Abe Shunnosuke 
Published: January 2008

Abstract— Using carrot cell suspension in 2,4‐dichlorophenoxyacetic acid (2,4‐D)‐depleted culture medium, fluence‐response curves for the formation of anthocyanin were determined at various wavelengths from 250 to 800 nm. In the fluence‐response curves at wavelengths between 260 and 330 nm, the response showed a sharp fluence‐dependent increase after the fluence exceeded threshold level at the respective wavelength. Such a sharp increase in response was not observed by light at 450 nm or longer wavelengths, although the response obtained by higher fluence of such light was always higher than that in the dark control. Action spectra determined at the sharp increasing phase of the response showed the single peak at 280 nm which equals the absorption maximum of UV‐B photoreceptor.Although red (R)‐light alone had a minor effect on anthocyanin accumulation, it modulated the action of UV‐B light. That is, when carrot cells were irradiated with R‐light either before or after UV‐B irradiation, anthocyanin formation was greatly enhanced above the level enhanced by UV‐B light alone. The most effective wavelength for this enhancement was 660 nm. The effect of R‐light on the anthocyanin formation of the UV‐B irradiated cells was reversed by immediately following it with far‐red light, suggesting the involvement of phytochrome in the R‐effect.
LOCATION OF THE CAROTENOID 2Ag‐STATE AND ITS ROLE IN PHOTOSYNTHESIS
Authors: Gillbro T. , Andersson P. O. , Liu R. S. H. , Asato A. E. , Takaishi S. , Cogdell R. J. 
Published: January 2008

AbstractThe location of the carotenoid 2Ag‐state (S1) was studied by fluorescence spectroscopy in two series of carotenoids. One consisted of natural polyenes like phytoene, phytofluene, β‐carotene, and neurosporene, and the other of minicarotenes, i.e., compounds similar to β‐carotene, but with a smaller number of double bonds (n=3–9). A decrease of the S1‐S0 energy gap with n was observed in both series, and extrapolation to n= 11 gave the energies 14 500 and 13 200 cm−1 for β‐carotene and lycopene, respectively. The neurosporene S1 state was located at ca 16 000 cm−1. A good relationship between the nonradiative relaxation rate and the number of conjugation was observed. The rate increased by a factor of 2.5 per double bond. The possible role of the S1 state in reversible carotenoid ← chlorophyll electron‐exchange energy transfer is discussed.
A COMPARISON OF PHYCOCYANINS FROM THREE DIFFERENT SPECIES OF CYANOBACTERIA EMPLOYING RESONANCE‐ENHANCED COHERENT ANTI‐STOKES RAMAN SPECTROSCOPY
Authors: Schneider S. , Prenzel C.‐J. , Brehm G. , Gedeck P. , Sai P. S. Maruthi , Gottschalk L. , Scheer H. 
Published: January 2008

AbstractResonance‐enhanced coherent anti‐Stokes Raman spectra are recorded for monomers and trimers of phycocyanin from three different cyanobacteria: Westiellopsis prolifica, Mastigocladus laminosus and Spirulina platensis. It is shown that upon aggregation from monomer to trimer the electronic structures of both the α84 and β84 chromophores are changed. The spectra of the trimers originating from S. platensis and M. laminosus are very similar to each other, but distinctly different from the spectrum of W. prolifica.
SPECTRAL FORMS AND ORIENTATION OF BACTERIOCHLOROPHYLLS c AND α IN CHLOROSOMES OF THE GREEN PHOTOSYNTHETIC BACTERIUM Chloroflexus aurantiacus
Authors: Matsuura Katsumi , Hirota Masamitsu , Shimada Keizo , Mimuro Mamoru 
Published: January 2008

AbstractSpectral forms of bacteriochlorophyll (Bchl) in chlorosomes were analyzed by linear dichroism, circular dichroism (CD), and deconvolution of these spectra. Isolated chlorosomes were embedded in polyacrylamide gels and compressed unidirectionally (along the x‐axis) while allowing the gel to stretch in another direction (along the z‐axis). The chlorosomes were aligned three‐dimensionally due to their flat oblong shape; the longest axis was presumed to parallel the z‐axis, its shortest axis was presumed to parallel the x‐axis, and the intermediate‐length axis was presumed to parallel the y‐axis. Degrees of polarization (AI− A1)/(AI+ A1) of Bchl c and a measured from the y‐axis with linearly polarized light were significantly different from those measured from the x‐axis. Deconvolution of spectra into components revealed the presence of two major forms of Bchl c with peaks at 744 nm and 727 nm. The degrees of polarization of the 744 and 727 nm spectral forms were 0.76 and 0.59 from the y‐axis and 0.48 and 0.39 from the x‐axis, respectively. The degrees of polarization of Bchl a794 were –0.21 from the y‐axis and 0.12 from the x‐axis. These values indicate that the direction of the Qy transition moment of Bchl c744 is almost completely parallel to the longest axis of chlorosomes and that of Bchl c727 is also nearly, but slightly less so, parallel to the longest axis of the chlorosomes. The Qy transition moment of the baseplate Bchl a peak at 794 nm is nearly perpendicular to the longest axis and parallel to the shortest axis: that is, it is perpendicular to the associated membrane plane in the cell. These alignments of Bchl transition moments in chlorosomes were lost after suspending the chlorosomes in a solution saturated with 1‐hexanol accompanying a shift in the peak position from 742 nm to 670 nm. The alignment recovered after the hexanol concentration was decreased. The presence of two major spectral forms of Bchl c was supported by the deconvolution of CD spectra and absorption spectra.
DIRECT EXPOSURE OF MANNALIAN CELLS TO PURE EXOGENOUS SINGLET OXYGEN (ΔgO2
Authors: Dahl Thomas A. 
Published: January 2008

AbstractMammalian cells attached to membrane filters or deposited on filters without attachment were exposed to gas‐phase singlet oxygen (1O2) in the absence of any other reactants. Cells were exposed in a monolayer or less, in the absence of external medium, during steady‐state 1O2 generation, ensuring that singlet oxygen impinged directly and equally on all cells simultaneously. The current methodology for cell exposure ensures that 1O2 is initially the only reactive species to which the cells are exposed. Results seen with this system can therefore be attributed solely and unambiguously to events initiated by 1O2. Further, all cells in the sample receive the same magnitude of exposure per surface area per time interval, which supports calculations of the amount of 1O2 required for irreversible cell damage, based on measured 1O2 flux and exposed cell surface area. Exposure to pure 1O2 irreversibly damaged a variety of cell types, including rat basophilic leukemia, human squamous carcinoma and Chinese hamster lung fibroblast cell lines, and murine primary hepatocytes. Cell survival curves following exposure to 1O2 followed apparent first‐order kinetics. A large number of singlet oxygen collisions (˜ 1012‐1013) were required to inactivate a cell, on average, indicating a low probability that singlet oxygen collision will reduce cell survival. Regardless of cell type or the survival endpoint measured, lethal toxicity required a fairly constant number of 1O2 collisions per cell. This poses a serious caveat in the assignment of causality in correlating 1O2‐initiated cellular damage with mechanism of death, i.e. most damage observed will not be related to death. The importance of various toxic effects of 1O2, whether lethal or nonlethal, will depend on the magnitude of exposure and therefore on the context in which exposure occurs.
EFFECTIVE PHOTODYNAMIC ACTION BY RHODAMINE 123 LEADING TO PHOTOSENSITIZED KILLING OF CHINESE HAMSTER OVARY CELLS IN TISSUE CULTURE AND A PROPOSED MECHANISM
Authors: Richmond Robert C. , O'Hara Julia A. 
Published: January 2008

AbstractThe effectiveness of rhodamine 123 (R123) as a photosensitizer of cell killing is relatively low and correlates with its inefficient production of singlet oxygen. The known selective retention of R123 in the mitochondria of epithelially derived carcinoma cells, however, is a selective feature that could lead to a more useful therapeutic ratio if photosensitizing effectiveness could be increased. Chinese hamster ovary (CHO) cells in tissue culture were therefore exposed to R123 shortly before and during illumination under conditions controlled for oxygen concentration and temperature. Effective photosensitization of cell killing, as judged by colony formation, was produced by 95% but not by 19% O2 during illumination of cells at 5d̀C or 37d̀C, and this was additionally enhanced at the sublethal temperature of 42d̀C. Two CHO cell lines were examined; one line, CHO‐AA8, was proficient in the repair of DNA damage and the parent to the second line, CHO‐EM9, that was deficient in the repair of DNA strand breaks. Cells of both lines incorporated R123 to a similar degree and were similarly photosensitized by the presence of igh oxygen concentration. Furthermore, plasma membrane damage as judged by teh exclusion of trypan blue was not observed immediately after illumination in the presence of R123, but was seen in the presence of meso‐tetra‐(4‐sulfonatophenyl)‐porphine (TPPS4). The extent of damage to the plasma membrane by TPPS4 was greater in the presence of 95% compared to 19% O2 during illumination. Photodynamic action at the level of teh plasma membrane appears to contribute to photosensitization by TPPS4 but not by R123 soon after exposure of cells to these sensitizers. It is hypothesized that photodynamic action by R123 is the primary mechanism causing the observed photosensitization of cell killing, and that mitochondria are teh site of photosensitized damage responsible for this killing.
PHOSPHORESCENCE LIFETIME STUDIES OF INTERACTIONS BETWEEN SERUM ALBUMINS AND SODIUM DODECYL SULFATE
Authors: Enescu Mironel , Ionescu Roxana , Dumbraveanu Gheorghe , Pascu Mihai L. 
Published: January 2008

AbstractBinding of sodium dodecyl sulfate (SDS) to bovine serum albumin (BSA) and human serum albumin (HSA) in aqueous solutions at room temperature induces significant changes in the phosphorescence lifetime of tryptophan (Trp) residues. A steep rise of the phosphorescence lifetime from 1.9 ms to 10.0 ms for BSA and from 1.9 ms to 5.5 ms for HSA is observed when the total SDS concentration increased from 0.0 mM to 0.22 mM at 1 mg/mL protein concentration. As the total SDS concentrationis further inccreased to 2.2 mM, a slower increase in the phosphorescence lifetime is observed, from 10.0 ms to 19.5 ms for BSA and from 5.5 ms to 7.2 ms for HSA. It appears that the phosphorescence lifetime modifications are mainly due to an increase of protein matrix rigidity around Trp residues. The observed differences (between HSA and BSA) allow us to distinguish the contribution of the two Trp residues to the BSA phosphorescence.