bluuebunny/crossref_metadata_2025_split huggingface dataset:
FORMATION OF AGGREGATES OF TRYPTIC FRAGMENTS DERIVED FROM THE CARBOXYL‐ TERMINAL HALF OF PEA PHYTOCHROME and LOCALIZATION OF THE SITE OF CONTACT BETWEEN THE FRAGMENTS BY AMINO‐TERMINAL AMINO ACID SEQUENCE ANALYSIS*
Authors: Yamamoto Kotaro T. , Tokutomi Satoru 
Published: January 2008

Abstract—Limited trypsinization of large pea (Pisum sativum cv. Alaska) phytochrome and subsequent size‐exclusion chromatography (SEC) in 0.1 M Na phosphate, pH 7.8, yielded a high‐molecular‐mass aggregate of tryptic fragments of phytochrome. Further SEC in 0.1 M Tris‐HCl, pH 7.5, plus various concentrations of NaSCN, indicated that the tryptic‐fragment complex contained an aggregate of 7 fragments of molecular mass from 38 to 55 kDa. The amino‐terminal sequence of each fragment was determined from the samples electroblotted from sodium dodecylsulfate polyacrylamide gels onto polyvinylidene difluoride membranes, in order to localize the various fragments on the phytochrome polypeptide chain. All of the 7 fragments in the aggregate were found to be derived from the carboxyl‐terminal half of phytochrome. A portion of the polypeptide chain (from Ala‐752 to Arg‐1000) common to all the tryptic fragments has been assigned as the site(s) of contact of the fragments. The tryptic‐fragment complex, as well as large phytochrome itself, has been shown by SEC to dissociate to monomers in 2 M NaSCN. The result indicates that the main force involved in maintaining the complex and in contacts between monomers of phytochrome is non‐ionic in nature. Relationship between the contact site(s) of the tryptic‐fragment complex and large phytochrome monomer is discussed.
DUAL EFFECTS OF TRYPTOPHAN IN THE HORSERADISH PEROXIDASE SYSTEM THAT GENERATES TRIPLET ACETONE
Authors: Silva Eduardo , Cilento Giuseppe 
Published: January 2008

Abstract—When tryptophan is added to the horseradish peroxidase/hydrogen peroxide system, it markedly increases the rate of ‘spontaneous’ conversion of peroxidase‐compound II to the native form without undergoing any alteration by spectral criteria. The D‐isomer is more efficient than the L‐isomer. The latter binds to the enzyme compound II, although at a site not very favourable for reduction. The accelerating effect of tryptophan is also seen when isobutyraldehyde or its enol added to the system, is converted into triplet acetone. Again the D‐isomer is more efficient than the L‐isomer. The D‐isomer is also more efficient in quenching the acetone phosphorescence. These results indicate that, at least in the case of L‐tryptophan where complexation with compound II occurs, the interaction of tryptophan with triplet acetone bound to the enzyme takes place in a ternary complex.
PHOTOSENSITIZATION OF ANTICANCER AGENTS‐8. ONE‐ELECTRON REDUCTION OF MITOXANTRONE: AN EPR AND SPECTROPHOTOMETRIC STUDY
Authors: Reszka Krzysztof , Lown J. William 
Published: January 2008

Abstract—An efficient method of one‐electron reduction of the anticancer agent mitoxantrone is described. The method depends on illumination of a suitable photosensitizer absorbing blue light [acriflavine, anthrapyrazole, or Ru(bpy)+] in the presence of the drug and an electron donor, such as NAD(P)H, in deaerated solutions. An EPR spectrum, assigned to a semiquinone of mitoxantrone, is generated under these conditions and identified by spectral simulation. Decay of this species, attributed to a radical‐radical reaction, gives a second order rate constant of 1.7 102M‐1s‐1 in organic media [dimethylsulfoxide (DMSO)/pH 8 buffer, 1:1 vol/vol] but is more rapid (˜104 M‐1 s‐1) in aqueous media under comparable conditions. The considerably decreased lifetime of the mitoxantrone radical at pH 5 is attributed to an additional electron transfer, promoted by protonation of the radical, and/or to an accelerated recombination of neutral radicals, leading to an EPR‐silent species. Parallel spectrophotometric studies on the generation of the mitoxantrone reduced species by photosensitized reduction are described. The method offers convenient access to a key radical species involved in the metabolism and possible mode of action of this clinical anticancer agent.
PHOTODYNAMIC INACTIVATION OF RUBELLA VIRUS ENHANCES RECOMBINATION WITH A LATENT VIRUS OF A BABY HAMSTER KIDNEY CELL LINE BHK21*
Authors: Yamamoto Nobuto , Urade Masahiro 
Published: January 2008

Abstract—Rubella virus is very sensitive to photodynamic action. When tested with 1.2 times10‐5M toluidine blue and 8 W fluorescent lamp at a fluence of 11 W/m2, inactivation kinetics showed a linear single hit curve with a k value of 1.48 min‐1. Photodynamic inactivation of rubella virus greatly enhanced recombination with a latent virus (R‐virus) of baby hamster kidney BHK21 cells. In contrast, no hybrids were detected in lysates of the cells infected with either UV‐treated or untreated rubella virus. Therefore, hybrid viruses were readily detected only in lysates of BHK21 cells infected with photodynamically treated rubella virus. Photodynamic damage of rubella virus genomes generated a new hybrid type (hybrid type 3) in addition to a previously described type 2 hybrid (formerly designated as HPV‐RV variant). Although both of these hybrid types carry the CF antigens of rubella virus, plaque forming ability of type 3 hybrid is neutralized neither by anti‐rubella serum nor by anti‐latent virus serum while type 2 hybrid is neutralized by anti‐latent virus serum.
DO YEARS OR QUANTA AGE THE RETINA?
Authors: Weale R. A. 
Published: January 2008

Abstract—The progressive loss of visual faculties with advancing age is attributed, sometimes, mainly to allegedly inevitable optical deterioration, such as clouding of the media, or again to neurosenescence, as typefied by cell‐death. The relevant factors are assessed, and it is not thought likely that changes in normal ocular optics account for changes in contrast sensitivity and visual acuity with age. The role of senescent changes in the retina is analysed. The progressive temporal and spatial patterns of the accumulation of lipofuscin in the retinal pigment epithelium (RPE) and the putative control of its concentration by the crystalline lens are examined following an earlier suggestion that lenticular UVA transmissivity may control the rate of UVA entry into the eye and so perhaps the amount of lipofuscin formed in the RPE. It is suggested that morphological changes attributed to senescence may partly be due to cumulative effects of irradiation.
PHOTOELECTROCHEMICAL STUDIES OF ULTRATHIN PHOTOACTIVE (POLYMER) LAYERS VIA SENSITIZATION OF ZnO
Authors: Li Xue‐Ping , Tributsch Helmut 
Published: January 2008

Abstract–Since photoelectrochemical properties of very thin (< 100 Å) layers of photoactive materials cannot be studied on metal contacts due to energy transfer losses and excessive dark currents through holes, an attempt was made to investigate them in contact with a large gap oxide semiconductor (ZnO). It was expected that electrons excited within the thin layer can be injected into the conduction band of ZnO. Experiments have shown this to be possible with the p‐type polymer semiconductor poly(2,5‐furylenvinylene) applied at thickness equivalent to 1–50 monolayers. Studies on complementary sensitization with Rhodamine B suggest energy transfer mediated electron transfer across the polymer layer into ZnO. In contrast, sensitization of ZnO by thin layers of n‐CdS or rc‐FeS2 (prepared by painting or MOCVD) was not successful. Promises and difficulties of the technique which could also be applied to biological samples are discussed.
ON THE ORIGIN OF LASER‐SPECIFIC LUMINESCENCE UPON PULSED‐LASER EXCITATION OF BENZOPHENONES IN FREONS†
Authors: Clark K. Brady , Scaiano J. C. 
Published: January 2008

Abstract–Excimer laser excitation (308 nm) of benzophenone in Freon‐113, as well as in Freon‐11, results in an intense emission with λmax at approx. 530 nm in addition to triplet phosphorescence. This emission is shown to result from an excited free radical bearing the diphenylmethylene moiety which is generated in a two‐photon process and which luminesces upon sensitization by the benzophenone triplet. On the basis of its spectroscopic properties and the chemical nature of the system, it is suggested that the fluorescer in this system may be the hypochlorite radical, Ph2COCl.
ENERGY TRANSFER IN TRITON X‐405 MICELLES: THE EFFECTS OF TEMPERATURE AND BRIJ 35
Authors: Ndou T. T. , Wandruszka R. von 
Published: January 2008

Abstract–Energy transfer from the phenyl groups of micellar Triton X‐405 (TX‐405) to solubilized pyrene molecules has been measured at a range of temperatures and in the presence of different polyoxyethylene 23 lauryl ether (Brij 35) concentrations. Increases in temperature lead to elimination of water from the outer, wet, micelle layer and an inward movement of associated pyrene. The addition of Brij also leads to a reduction in polarity of the microenvironment of pyrene. However, sensitization is observed even at high Brij concentrations. The donor/acceptor separation caused by the introduction of Brij proceeds slowly, continuing for several minutes after its addition to micellar TX‐405.
NAPHTHYL‐ AND QUINOLYLLUCIFERIN: GREEN AND RED LIGHT EMITTING FIREFLY LUCIFERIN ANALOGUES
Authors: BRANCHING BRUCE R. , HAYWARD MATTHEW M. , BAMFORD SARAH , M. BRENNAN PATRICIA , LAJINESS EVELYN J. 
Published: January 2008

AbstractIn the course of investigations on the possible involvement of the CIEEL (chemically initiated electron‐exchange luminescence) mechanism in firefly bioluminescence, we have synthesized two novel firefly luciferin substrate analogues. D‐Naphthylluciferin and D‐quinolylluciferin were prepared by condensing D‐cysteine with 2‐cyano‐6‐hydroxynaphthalene and 2‐cyano‐6‐hydroxyquinoline, respectively. These analogues are the first examples of bioluminescent substrates for firefly luciferase that do not contain a benzothiazole moiety. Firefly luciferase‐catalyzed bioluminescence emission spectra revealed that compared to the normal yellow‐green light of luciferin (γmax= 559 nm), the emission from naphthylluciferin is significantly blue‐shifted (γmax= 524 nm); whereas quinolylluciferin emits orange‐red light (γmax= 608 nm). The fluorescence emission spectra, reaction pH optima, relative light yields, light emission kinetics and KM values of the analogues also were measured and compared to those of luciferin. Neither of the analogues produced the characteristic flash kinetics observed for the natural substrate. Instead, slower rise times to peak emission intensity were recorded. It appears that the formation of an intermediate from the analogue adenylates prior to the addition of oxygen is responsible for the slow rise times. The synthetic substrate analogues described here should be useful for future mechanistic studies.
THE ROLE OF CALCIUM IN Chlamydomonas PHOTOMOVEMENT RESPONSES AS ANALYSED BY CALCIUM CHANNEL INHIBITORS
Authors: Hegemann P. , Neumeier K. , Hegemann U. , Kuehnle E. 
Published: January 2008

Abstract— Phototaxis and light‐induced stop responses in Chlamydomonas are known to be calcium dependent. We show that phototaxis is stereoselectively inhibited by dihyropyridines, verapamil, diltiazem, ω‐conotoxin and pimozide, all inhibitors of slow L‐type calcium channels. In contrast, the stop response in Chlamydomonas can be specifically reduced only by ω‐conotoxin and pimozide. The light‐regulated calcium uptake as detected by 45calcium can be completely suppressed by verapamil and ω‐conotoxin but not by diltiazem or any of the dihyropyridine‐type calcium channel inhibitors. We conclude that phototaxis and stop response in Chlamydomonas are regulated by three distinguishable drug receptor sites. One of them controls phototaxis and is sensitive to verapamil. The second site controls stop response and phototaxis and shows a high sensitivity to ω‐conotoxin and pimozide. These two drug receptors seem to be localized in the plasma membrane and function as ion channels. In addition, calcium influences internal signal transduction from the photoreceptor to the flagella. This internal role of calcium is inhibited by the dihydropyridine binding to a dihydropyridine receptor protein.The arylazide‐l,4‐dihydropyridine[3H]azidopine binds with a Kd= 35 nM to a 50 kDa protein located in one of the internal cell membranes. Azidopine binding is fully reversible and can be partially inhibited by nimodipine and PN‐200110. This protein is the first identified dihyropyridine receptor in an unicellular plant cell. It might serve as an internal calcium regulating channel in Chlamydomonas.
FLUOROMETRIC ANALYSIS OF THE LONG‐WAVELENGTH ABSORPTION BAND OF N‐7 METHYLATED GMP INTO THE CONSTITUENT BANDS OF THE TWO ELECTRONIC STATES
Authors: Ge Guangyuan , Zhu Shen , Bradrick Thomas D. , Georghiou S. 
Published: January 2008

AbstractSteady‐state measurements of fluorescence anisotropy are used to resolve the long‐wavelength absorption spectrum of 7‐methyl guanosine 5′‐monophosphate (GMP) in pH 5 buffer at room temperature into component spectra that correspond to the electronic transitions I and II present in that spectral region. We have chosen this derivative of guanine because its fluorescence quantum yield is much greater than that of GMP. It is found that the data are adequately described by a model that involves emission exclusively from state I, with state II converting to it with 100% efficiency. The shape of the absorption spectrum of state II is virtually independent of the angle 6 between the absorption transition dipole moments of states I and II, whereas that of state I is dependent on 9. We analyze the data on the basis of the premise that in the short‐wavelength region state II is the predominantly absorbing state. This premise is based on studies of single‐crystal polarized reflection and linear dichroism from stretched films. The spectral maxima for the two states are found to be at about 290 and 260 nm, respectively. There is also a weak band which is centered at about 245 nm. The oscillator strengths are found to be 0.07, 0.21 and ‐ 0.04, for states I, II and that associated with the weak band, respectively. The importance of these findings with regard to the photophysical properties of nucleic acids and calculations of their CD spectra is discussed.
MOLECULAR STRUCTURE AND PHOTODECARBONYLATION OF 2,3,4,5‐ TETRAPHENYLCYCLOPENTANONE
Authors: Lewis Frederick D. , Field Theodore L. , Sabat Michal 
Published: January 2008

Abstract—Clemmensen reduction of tetracyclone yields r‐2,t‐3,t‐4,c‐5‐tetraphenylcyclopentanone, the structure of which was established by x‐ray crystallography. Photodecarbonylation of this molecule results in the formation of cis‐ and trans‐stilbenes and minor amounts of tetraphenykyclobutane. The stilbenes are initially formed in comparable yield, but secondary photoisomerization results in cw‐rich mixtures. Stepwise photodecarbonylation is proposed to yield triplet meso‐ 1,2,3,4‐tetraphenylbutane‐diyl which undergoes nonstereoselective elimination in preference to cyclization. The intermediacyof the same biradical in the photodimerization stilbene can be effectively eliminated on the basis of stereochemical evidence.
THEORETICAL STUDY OF ELECTRONIC SPECTRA AND PHOTOPHYSICS OF URACIL DERIVATIVES*
Authors: Baraldi I. , Brum M. C. , Costi M. P. , Pecorari P. 
Published: January 2008

Abstract—The changes that the UV absorption spectrum and the photophysics of uracil undergo under hydrogen substitution or deprotonation, were studied theoretically within the CS‐INDO/CI scheme. First of all this method was tested on uracil. It was then used for the calculation of the electronic structure of excited states (Sn, Tn) of a large number of uracil derivatives (1‐, 3‐ and 5‐methyluracil; 1,3‐, 1,5‐ and 3,5‐dimethyluracil; 5‐fluoro‐ and 5‐chlorouracil), including some anions (1‐ and 3‐methyluracil anion). The excited states were obtained in the singly‐excited configuration interaction approximation (S‐CI) and the correlation effects on (ππ*) states were studied by including the most important doubly‐ and triply‐excited configurations in the CI. The S‐CI wavefunctions were used for the calculation of the most important electronic matrix elements for spin‐orbit coupling. The photophysics of these compounds is discussed using Jablonski diagrams.
POLARIZATION STUDY OF 5(E)‐STYRYL‐1,3‐DIMETHYL URACIL IN DIISOOCTYL SULFOSUCCINATE (AEROSOL‐OT) REVERSED MICELLE SOLUTIONS
Authors: Shin Dong‐Myung , Kim Sung Woong , Shim Sang Chul 
Published: January 2008

AbstractThe degree of polarization around the water pool generated in aerosol‐ OT/hexane/water reversed micelle solutions was studied by monitoring the depolarization of solubilized probe fluorescence. The 5(E)‐styryI‐1, 3‐dimethyl uracil (SDU) used in this study was moderately polar and proved to be solubilized between the interface and hydrocarbon phases in reversed micelle solution by a fluorescence quenching study with hydrophilic and hydrophobic quenchers. The degree of polarization monitored by SDU was parallel with that obtained from the fluorescence depolarization study of hydrophylic probes solubilized in the water pool and interface. A dramatic increase in microviscosity was observed when ω value became small.
TIME‐RESOLVED SPECTROSCOPIC STUDIES ON PHOTOPHYSICAL PROPERTIES OF BENOXAPROFEN IN MICELLAR SOLUTIONS: AN INTRAMICELLAR FLUORESCENCE QUENCHING
Authors: Yoon Minjoong , Chang Jae Rim , Kim Dongho , Kuriyama Yasunao , Tokumaru Katsumi 
Published: January 2008

AbstractThe micellar dependencies of the photophysical properties of benoxaprofen (BXP), a 2‐phenyl benzoxazole derivative, have been investigated using fluorescence spectroscopy and laser flash photolysis techniques. The fluorescence of BXP in aqueous solution has been observed to be remarkably quenched upon addition of a surfactant, cetyltrimethyl ammonium bromide (CTAB) or Triton X‐100, in contrast to its enhancement in sodium dodecyl sulfate (SDS) micellar solution. Time‐resolved fluorescence measurements show that the fluorescence decays biexponentially in the micellar solution, indicating the relaxation of micellar environments surrounding the excited BXP. The major component of fluorescence lifetimes in CTAB or Triton X‐100 micellar phase is even shorter (330–427ps) than in SDS micellar phase (731 ps). The nonradiative decay constants are significantly larger (ca 3.0 times 109 s−1) in the CTAB or Triton X‐100 micellar phase than in SDS micelles by a factor of ca 10. The major nonradiative decay is interpreted to be the internal conversion due to nuclear geometric change of BXP in the first excited singlet state. This is consistent with the observation that the quantum yields of intersystem crossing are very low (less than 0.01) in the micellar solutions as determined by the laser flash photolysis technique. The laser‐induced transient absorption spectrum of BXP in CTAB or Triton X‐100 micellar solution shows that the decay kinetics of the transients in CTAB or Triton X‐100 are significantly different from first order kinetics in SDS.
LOW TEMPERATURE POLARIZED ABSORPTION MICROSPECTROSCOPY OF SINGLE CRYSTALS OF THE REACTION CENTER FROM Rhodobacter sphaeroides WILD TYPE STRAIN 2.4.1
Authors: Frank Harry A. , Aldema Mila L. , Violette Carol A. , Parot Pierre H. 
Published: January 2008

AbstractThe absorbance and polarized absorbance spectra of single crystals of the reaction center complex isolated from Rhodobacter sphaeroides wild type strain 2.4.1 have been measured at 85 K. The crystals of the complex were obtained by the vapor diffusion technique. The spectroscopic experiments on the crystals were performed using an optical microspectrometer featuring a custom‐built, liquid N2‐flowing cold stage, the details of which are presented herein. These data demonstrate the feasibility of conducting optical spectroscopic experiments at cryogenic temperatures on single crystals of photosynthetic pigment‐protein complexes.
QUENCHING OF FLUORESCENCE OF AROMATIC HYDROCARBONS BY PROTONS IN CAFFEINE‐ SOLUBILIZED AQUEOUS SOLUTION. INTRACOMPLEX ENERGY TRANSFER
Authors: Nosaka Yoshio , Kira Akira 
Published: January 2008

AbstractThe fluorescence of pyrene and five other aromatic hydrocarbons solubilized with caffeine in aqueous solution was quenched by 0.001–1mol dm−3 sulfuric acid; this quenching did not occur in the absence of caffeine. Exceptionally a non‐alternative hydrocarbon, fluoranthene, showed an increase of the fluorescence intensity by the acid. The observed quenching rate was explained by the rate of energy transfer from the aromatic molecules to protonated caffeine in the complex.
FAR‐INFRARED SPECTRA OF LANGMUIR‐BLODGETT FILMS OF CHLOROPHYLL a, CHLOROPHYLL b, PHEOPHYTIN a and THEIR ADDUCTS WITH WATER and DIOXANE*
Authors: Tajmir‐Riahi Heidar‐Ali , Wang Gongming , Leblanc Roger M. 
Published: January 2008

AbstractFourier transform infrared spectra in the low frequency region (500–150cm−1) of Langmuir‐Blodgett films of chlorophyll a (Chi a), chlorophyll b (Chi b) and pheophytin a have been studied. Correlations between spectral changes in monolayer and multilayers of Chi a and Chi b and their adducts with water and dioxane have been established.Spectroscopic evidence has indicated that, although there are no individual absorption bands that can be assigned to pure Mg‐nitrogen and/or Mg‐oxygen stretching or bending modes, there are several bands in the400–200 cm−1 region of the spectra containing considerable contributions from metal‐nitrogen and metal‐oxygen vibrational modes. These specific vibrations exhibit marked intensity changes and shifts upon water and dioxane interaction. The different states of chlorophyll aggregation in Langmuir‐Blodgett mono‐ and multilayers films resulted in noticeable changes in their far‐IR spectra.
IDENTITY OF THE PHOTORECEPTORS FOR THE PERCEPTION OF IRRADIANCE IN PHOTOSYNTHETIC LIGHT ACCLIMATION IN TOMATO*
Authors: Withers A. C. , Vince‐Prue D. , Thomas: B. 
Published: January 2008

ReferencesThe photoreceptors involved in the photosynthetic acclimation of tomato (Lycopersicon esculentum Mill.) to increased irradiance were investigated. Plants were transferred from 100 p.mol m−2 s−1 cool white fluorescent light to higher irradiances of white light or white light supplemented with blue, red, green or yellow light. In these experiements light of all wavelengths tested was capable of causing acclimation as measured by the rate of light‐saturated photosynthesis. It was concluded that the photosynthetic system rather than the blue‐absorbing photoreceptor or phytochrome system acts as the photoreceptor for increased irradiance. No acclimation was observed in response to increased CO2 levels, but increasing light integral at a constant irradiance was effective in bringing about acclimation. We conclude that acclimation is a response to increased photosynthetic light capture rather than increased photosynthetic carbon fixation, and involves a photon counting mechanism.
PHOTOCHEMICAL trans →cis ISOMERIZATION OF 6‐STYRYLQUINOXALINE*
Authors: Kim Maeng Sup , Lee Ki Taek , Jeong Bong Mo , Lee Bok Hee , Shim Sang Chul 
Published: January 2008

AbstractThe trans → cis photoisomerization of fran.s‐6‐styrylquinoxaline (6‐StQx) has been investigated. Fluorescence quantum yields increase with increasing solvent polarity, whereas internal conversion and intersystem crossing decrease because of the weakening of vibronic coupling of the lowest 1(π,π*) state and 1(n,π*) state in polar solvents. Laser flash photolysis studies show an efficient singlet‐triplet intersystem crossing on direct irradiation at room temperature. Azulene quenching of fluorescence, and direct and sensitized photoisomerization indicate that the direct photoisomerization proceeds through both the singlet and triplet manifolds, mainly via the triplet state (75‐80%) at room temperature, in contrast to corresponding hydrocarbons.