bluuebunny/crossref_metadata_2025_split huggingface dataset:
CHLOROPHYLL MONOLAYERS AND MULTLLAYERS—II. EVIDENCE FOR THE PRESENCE OF ORDERED AGGREGATES*
Authors: Sperling Walter , Ke Bacon 
Published: January 2008

Abstract— Results from measurements of the absorption spectrum and dichroism suggest that oriented chlorophyll aggregates can be prepared by the monolayer techniques described in the preceding paper.(1)On the longer wavelength side of the major red and blue absorption‐band maxima the absorption decreased with time. For example, the peaks of the difference bands for monolayers prepared under 30 dyn/an were at 443·3 and 703 nm, respectively. The ratio of the red‐to‐blue difference band heights was approximately 1·35. The wavelength position of the red difference‐band maximum is strongly dependent on the surface pressure used in preparing the monolayers. During the decay of absorption, the red‐difference‐band maximum shifted progressively toward shorter wavelengths.The chlorophyll layers showed linear dichroism in some regions of the visible spectrum. The wavelength regions in which maximal dichroism appeared coincided closely with the difference absorption bands. The dichroism disappeared with kinetics similar to those of the absorption decrease.The decrease in the blue and far‐red absorption and dichkoism was taken as evidence that oriented chlorophyll aggregates were formed initially in the monolayers but disaggregated and disoriented with time. Some possible mechanisms for the formation and decomposition of oriented chlorophyll aggregates are discussed.
THEORETICAL ASPECTS OF THE U.V. INACTIVATION OF PROTEINS CONTAINING DISULFIDE BONDS
Authors: Dose Klaus 
Published: January 2008

ABSTRACTEquations are proposed for the estimation of quantum yields for cystine destruction and disulfide protein inactivation during u.v.‐irradiation in acidic and neutral solutions. The formulas permit a discussion of energy transfer from excited aromatic amino acids to cystines and/or of chemical reactions between excited tryptophans or tyrosines and cystines. The results are discussed with regard to general aspects of the photo‐biochemistry of enzymes.
THE EFFECT OF PHOSPHORYLATION UNCOUPLERS AND ELECTRON TRANSPORT INHIBITORS UPON SPECTRAL SHIFTS AND DELAYED LIGHT EMISSION OF PHOTOSYNTHETIC BACTERIA
Authors: Fleischman D. E. , Clayton R. K. 
Published: January 2008

Abstract— Delayed light emission (measured 4 msec after excitation) and the light‐induced red shifts of the bacteriochlorophyll and carotenoid absorption bands of chromatophores of Rhodopseudomonas spheroides were inhibited by a variety of reagents. These included anti‐mycin A, NQNO, CCCP, desaspidin, quinacrine, chlorpromazine, 2,4‐dinitrophenol, gramicidin D, Triton X‐100 and valinomycin in the presence of potassium, cesium or ammonium ions. Delayed light emission was enhanced by orthophenanthroline, ethanol, succinate and glutathione.Delayed light emission from chromatophores of Rhodospirillum rubrum was attenuated during photophosphorylation but restored approximately to its initial value in the presence of oligomycin. Since the delayed light and band shifts are inhibited under conditions which tend to deplete or block the formation of high energy phosphorylation intermediate, it is suggested that the presence of a high energy intermediate is a prerequisite for the appearance of each of the three phenomena.
SHAPES OF THE U.V. INACTIVATION CURVES FOR SINGLE AND LINKED DOUBLE MARKERS IN HAEMOPHILUS INFLUENZAE TRANSFORMING DNA*
Authors: RUPERT C. S. 
Published: January 2008

AbstractThe known inverse square law S= 1/(1+CD)2, relating survival of transforming activity S to ultraviolet (u.v.) dose D, C being a constant, fails for two linked‐double genetic markers in H. influenzae. For these double markers the law is S= 1/(1+CD)4, both for u.v. and nitrous acid inactivation. A theoretical model which predicts the inverse square law for singles also predicts the inverse fourth power law for linked doubles, if the possibility of an even number (>0) of genetic recombinations between the markers is allowed for. However, it can be shown rather generally that other models, not specified in exact detail, can lead to the same inverse square law for single markers, and thus to the inverse fourth power law for sufficiently separated linked‐doubles. Ability to predict these laws is not, therefore, strong evidence for the validity of any one model. For all these models, the mean number of damaging lesions per unit length of DNA is directly proportional to dose, making (√(1/S)–1) for single markers and (√(1/S)–1) for loosely linked‐doubles a reasonable biological measure of inactivating damage in the DNA.
THE PHOTOISOMERIZATION OF RETINAL*
Authors: KROPF ALLEN , HUBBARD RUTH 
Published: January 2008

Abstract— –Quantum efficiencies have been measured for the photoisomerization of four stereoisomers of retinal (all‐trans, 13‐cis, 11 cis, and 9‐cis) in two solvents at different wavelengths of irradiation and at various temperatures. In heane at 25°C the quantum efficiencies for isomerization at 365 nm are: 9‐cis to trans, 0.5; 13‐cis to trans, 0.4; 11‐cis to trans, 0.2; all‐trans to monocis isomers, 0.2‐0.06, depending upon assumptions made regarding the stereo‐isomeric composition of the product. These values vary somewhat with the wavelength of the irradiating light.The quantum efficiency for the photoisomerization of all‐trans retinal in hexane decreases by a factor of 30 when the temperature is lowered from 25° to – 65°C; the activation energy for this photoisomerization is about 5 kcal/mole. The quantum efficiencies for the isomerization of the monocis isomers to all‐trans retinal in hexane are virtually independent of temperature. In ethanol the rates of photoisomerization from trans to cis or cis to trans depend only slightly on the temperature between 25° and – 65°C.The photosensitivities of the stereoisomers of retinal are of the same order of magnitude as those of the retinylidene chromophores of rhodopsin (11 ‐cis), metarhodopsin I (all‐trans), and isorhodopsin (9‐cis); but it is not yet possible to derive the photochemistry of rhodopsin uniquely and quantitatively from that of retinal.
ETUDE PAR FLUORESCENCE DE BASES DE SCHIFF DU PYRIDOXAL, COMPARAISON AVEC LA L ASPARTATE‐AMINOTRANSFERASE
Authors: ARRIO‐DUPONT M. 
Published: January 2008

Abstract— –Absorption and emission spectra of Schiff bases of pyridoxal‐HCI or pyridoxal‐5‐phosphate with L‐valine, n‐butylamine or N‐α‐acetyl‐L‐lysine‐N‐methylamide have been studied as a function of pH. We can write the complete ionization diagram and equilibria. The results of Martell[6] are confirmed: the forms analogous to the coenzyme in aspartate aminotransferase, which absorb at 410 nm and 360 nm (or 340 nm for the Schiff base with n‐butyl‐amine) have the phenol OH ionized; the imine nitrogen is protonated for species absorbing at 410nm (in the enzyme: inactive form and complex with aminoacid) and unprotonated for species absorbing at 360 nm (in the enzyme, active form). Their fluorescence wavelengths are respectively 500 nm and 430 nm. Protonation of the pyridine nitrogen of these forms does not shift the absorption band; the fluorescence intensity is 20‐fold greater for the N‐protonated forms.The real pK of the imine nitrogen is 8.5 ±0.8 for species with pyridine N‐protonated or 10.4 for the non‐protonated forms. The observed pK 6.3 in the enzyme can be explained if the imine nitrogen is hydrogen bonded to an amino‐acid side chain of the protein: lysine, tyrosine, serine, sulfhydryl.The quantum yield of the coenzyme fluorescence in the enzyme has been compared to that of the analogous Schiff base (absorbing at the same wavelength). According to the results, we cannot deduce whether the pyridine nitrogen is protonated in pyridoxal form of the enzyme.If it is protonated, as in the pyridoxamine form, the coenzyme environment is not the same in the two forms. If the pyridine nitrogen is unprotonated in the pyridoxal form and protonated in the pyridoxamine form, the environment of the coenzyme is the same in these two forms of the enzyme.
FLUORESCENCE OF THYMINE IN AQUEOUS SOLUTION AT 300° K
Authors: HAUSWIRTH WILLIAM , DANIELS MALCOLM 
Published: January 2008

Abstract— –Fluorescence of thymine in neutral aqueous solution at room temperature has been detected using the multiscaling operation of a multichannel analyzer. The emission maximum (2.96 μm‐1) and 0‐0 transition energy (3.37‐3.45 μm‐1) are close to those determined at liquid nitrogen temperature in mixed solvents. The quantum efficiency of fluorescence excited at 3.77 μm‐1 is calculated to be 1.04 × 10‐4.The corrected relative excitation spectrum shows significant differences from the absorption spectrum when both are determined under identical conditions of concentration and spectral bandwidth on the same instrument. The quantum yield of fluorescence decreases about 2‐fold as the energy of excitation is increased beyond the 0‐0' transition and follows the relation 1/φ°αEexcit..This behavior is discussed in terms of (a) nπ* and ππ* states, (b) emission from a minor tautomer and (c) kinetics of competing deactivation processes.
STUDIES ON SOME INTERMEDIATES AND PRODUCTS OF THE PHOTOREDUCTION OF 9,10‐ANTHRAQUINONE *,†
Authors: CARLSON STEVEN A. , HERCULES DAVID M. 
Published: January 2008

Abstract— The mechanism of the photoreduction of 9,10‐anthraquinone (AQ) in alcohol and hexane has been studied by flash photolysis. The fluorescence spectrum of the photoproduct, 9,10‐dihydroxy anthracene shows a large shift between hexane and ethanol. The quantum yields of photoreduction for AQ are solvent‐dependent, the reaction between the solvent radical and AQ determining the quantum yield.The absorption spectrum of the 9,10‐anthrasemiquinone (AQH.) has a long‐wavelength absorption band with peaks at 631 and 678 nm. The second‐order decay constants for AQH. were estimated to be 1.3 × 109, 6.7 × 108 and 2.0 × 108M‐1 sec‐1 in ethanol, 2‐propanol and ethylene glycol, respectively.A long‐wavelength absorption band was observed for 9,10‐anthrasemiquinone radical anion, having peaks at 776 and 860 nm; epsi;max= 1900 at 776 nm. This spectrum is compared with the spectra of 9,10‐dihydroxy anthracene mono‐ and di‐anions. The 9,10‐anthrasemiquinone radical anion was found to photoreduce quantitatively to 9,10‐dihydroxy anthracene mono‐anion with a quantum yield of 0.1.
INTRAMOLECULAR ENERGY TRANSFER IN NATIVE tRNA AT ROOM TEMPERATURE
Authors: Ballini Jean‐Pierre , Vigny Paul , Thomas Gilles , Favre Alain 
Published: January 2008

Abstract— The odd nucleoside 4‐thiouridine, which is present in position 8 of 70% of E. coli tRNAs, possesses unusual spectroscopic properties which make it suitable for intramolecular energy transfer studies. Both its luminescence excitation spectrum and the action spectrum (230–380 nm) for the 8–13 link formation have been established in native E. coli tRNA at room temperature. The spectra are identical and present a new unexpected peak around 260 nm. At this wavelength, they are amplified by a factor of nine as compared with the absorption and excitation spectra of the free nucleoside in aqueous solution.The origin of this new peak is discussed and it is concluded that energy transfer does occur from the common nucleosides to the 4‐thiouridine residue. Using the values of the nucleosides to 4‐thiouridine distances inferred from the sets of atomic coordinates obtained on yeast tRNAphe crystals, a satisfactory account of our finding can be obtained assuming singlet‐singlet energy transfer. The efficiency of the mechanism is probably favoured by a good overlap between the emission spectra of the common nucleosides and the absorption spectrum of 4‐thiouridine.
EMISSION SPECTRUM DIFFERENCES IN FLUORESCENT BLACKLIGHT LAMPS
Authors: Forbes P. D. , Davies R. E. , D'Aloisio L. C. , Cole C. 
Published: January 2008

SummaryTwo types of fluorescent blacklight lamps with distinctly different emission spectra bear the same code designations. One type, which we refer to as BL‐O, has most of its UV radiation emission centered over 350 nm. The other (BL‐N) type concentrates more energy around 365 nm. The spectral differences are correlated with the manufacturer's shift in the type of phosphor used in the lamps. Whether this change is detrimental to photobiological experiments depends in part on the user's ability to independently verify emission spectra.
INTERACTION OF ACRIDINE DRUGS WITH DNA AND NUCLEOTIDES
Authors: Georghiou S. 
Published: January 2008

Abstract— At high phosphate‐to‐drug ratios acridine drugs intercalate between hydrogen bonded DNA base pairs causing significant changes in the physico‐chemical properties of DNA. The determination of the nature of the strong (or primary) interaction between acridine drugs and DNA is of great importance for elucidating the mode of the biological action of the drugs.Nanosecond measurements have revealed a fast depolarization of the fluorescence of proflavine, one of the most extensively studied acridines, bound to DNA. The electronic structure of the complex, however, is not substantially altered during the lifetime of the excited singlet electronic state of the drug. Guanine has been shown to be responsible for the quenching of the proflavine fluorescence upon binding to DNA. A temperature‐jump relaxation study has demonstrated a rather external complexation of this drug with the G‐C base pairs; this complex, whose formation occurs in the strong binding region, is distinct from the weak electrostatic complex.The findings that the binding ability of a series of acridines correlates with their basicity and that the drug–binding behavior of methylated DNA is significantly different from that of DNA suggested that specific forces may be also involved in the drug–DNA binding in addition to hydrophobic forces. Recent experiments employing molecular complexes of acridines with nucleotides as model systems have provided strong support for the specificity of the drug‐DNA interaction. Hydrogen bonding between the drug and reactive groups of the DNA bases that do not contribute directly to the stability of the helix may be involved in that interaction.The stoichiometry of the proflavine‐guanosine 5′‐phosphate complex is 1:1. Its association constant increases from 310 M‐1 when proflavine is in its ground electronic state, to 1550 M‐1, when proflavine is in its first excited singlet state. Thus, light absorbed by the drug alters its reactivity which, in turn, results in an appreciable increase in its ability to bind to the nucleotide. In view of the proposed importance of the drug–base interaction in explaining the mutagenic properties of acridine drugs and, in particular, of the proposed involvement of the G‐C base pairs, this finding emphasizes the possible importance of drug photoexcitation in acridine mutagenesis; it also contributes to the elucidation of photodynamic action.X‐ray diffraction studies have recently provided very interesting demonstrations of strong binding of 9‐aminoacridine and of the phenanthridine drug ethidium bromide to adenine‐uracil base pairs in the crystalline phase.The ability of photoexcited acridine drugs to inactivate viruses has been recently used for therapeutic purposes. The carcinogenic risk involved, however, is still under investigation.
DETECTION OF SINGLET OXYGEN IN RADIOLYSIS OF AERATED AQUEOUS SOLUTIONS
Authors: Sharpatyi Valery A. , Kraljić Ivan 
Published: January 2008

Abstract— The detection of singlet oxygen (1O2) in the γ‐radiolysis of air saturated aqueous solutions may be achieved by using a selective method under such conditions that other strongly reactive intermediates such as −OH radicals do not react or are prevented from giving the same reaction. Since all or most 1O2 acceptors also react with −OH radicals, the elimination of OH radicals with appropriate scavengers may be necessary.A recently developed method for the detection of 1O2 in neutral aqueous solutions based on the bleaching of p‐nitrosodimethylaniline (RNO) in a solution containing an imidazole derivative, has been used in this work to detect 1O2 in γ‐radiolysis. In the system imidazole + RNO, the reaction between 1O2 and imidazole produces a trans‐annular peroxide which leads to the bleaching of RNO. The bleaching of RNO depends in a characteristic way on the concentration of different imidazole derivatives at high concentrations. This dependence is the same in certain photolysis experiments (where only 1O2 reacts in this way) and in radiolysis. The bleaching of RNO, as induced by the reaction between 1O2 and imidazoles, is also observed in the presence of ethanol which scavenges all −OH radicals but does not react with 1O2 or trans‐annular peroxide. Moreover, in the absence of imidazole, the addition of ethanol to a dilute solution of RNO protects it completely against −OH radical attack. Thus, the results of these experiments indicate that 1O2 may be formed in the radiolysis of air saturated aqueous solutions in a relatively low yield [G(1O2) ∼ 0.1–0.3].
IRRADIATION‐ENHANCED PHYTOCHROME PELLETABILITY IN AVENA: IN VIVO DEVELOPMENT OF A POTENTIAL TO PELLET AND THE ROLE OF Mg2+ IN ITS EXPRESSION IN VITRO
Authors: Quail Peter H. 
Published: January 2008

AbstractThe enhanced phytochrome pelletability that results from in vivo irradiation of Avena shoots may be divided into two operationally defined sequential stages: the in vivo development of a “potential to pellet” and the “expression” of this potential in vitro. Kinetic studies confirm previous findings that the generation of this “potential to pellet” is a very rapid (complete in < 10 s, 25°C), genuinely intracellular process, itself photoreversibly induced by Pfr. In addition, it is shown that the sustained development of the “potential to pellet”, that proceeds in the dark at 0°C following a red pulse, requires Pfr continually in the cell over the entire development period. Far red light immediately terminates further development of the red‐induced “potential” at any point during the development phase. No immediate reduction is observed, however, in that level of “potential pelletability” already attained at the time of the far red pulse. This indicates that the level of “potential pelletability” established in vivo is insensitive to the form of the pigment at extraction regardless of the level reached. “Expression” of the “potential to pellet” refers to the actual detection in homogenates of an enhanced physical association of phytochrome with pelletable material. Maximum “expression” requires the presence of a divalent cation in the medium during homogenization. Rapid posthomogenization addition of Mg2+ to Mg2+‐free extracts sustains enhanced pelletability but with rapidly declining effectiveness over the fmt 1–2 min after extraction. The rate of decline is faster if the phytochrome is present as Pfr than as Pr in the homogenate. Neither these nor previous data permit a distinction to be made between (a) preservation by the cation of a pre‐existing intracellular interaction, and (b) a Mg2+‐mediated induction of an artifactual, in vitro association predetermined in the cell by a genuine phyto‐chrome‐controlled process. Various formalistic models are discussed in the context of these and other data.
THE IMPORTANCE OF COMPLEX FORMATION IN THE SENSITIZATION OF Eu(III) EMISSION BY OROTIC ACID
Authors: Sarpotdar Arvind , Burr John G. 
Published: January 2008

Abstract— Orotic acid (I) and 3‐methylorotic acid (II) are the only orotic acid derivitives which efficiently sensitire emission from Eu(III) in D2O solution. This emission is only weakly sensitized by I‐methylorotic acid (III), 1,3‐dimethylorotic acid (IV), the methyl and isopropyl esters of orotic acid (V) 6‐acetyluracil (VI) and not sensitized at all by the bases uracil. thymine and their nucleosides. Substituent groups on either the carboxyl group or the N‐l position of the ring thus prevent efficient energy transfer from the excited orotic acid to Eu(III). These structural requirements for efficient energy transfer are the same as the structural requirements for formation of a stable. bidentate. ground state complex between Eu(III) and orotic acid (VII) (Sarpotdar and Burr, 1978).We, therefore, propose that sensitization of Eu(III) emission by orotic acid at pH 5 is an example of energy transfer within the bidentate complex of Eu(III) and orotic acid. We also propose that the complexed orotic acid is itself excited by eollisional energy transfer from free triplet excited orotic acid (since the concentration of complex measured to be present. 5–7%, is too low to account for the efficiency of the sensitization). We also propose that emission from the excited complexed Eu(III) can be either from the complexed ion or from free Eu(III)* resulting from dissociation of the complex during the lifetime of the excited ion.The efficiency of Eu(III) sensitized emission is shown to depend on the concentrations of Eu(III). orotic acid and pH with relationships kinetically consistent with the above hypothesis.
POSITIONING OF AQUATIC MICROORGANISMS IN RESPONSE TO VISIBLE LIGHT AND SIMULATED SOLAR UV‐B IRRADIATION
Authors: Barcelo Jeanne A. , Calkins John 
Published: January 2008

Abstract—Three species of protozoans and two crustaceans were irradiated with simulated solar ultraviolet radiation to investigate their ability to detect and avoid UV‐B (320–280 nm). Horizontal and vertical movements to sheltered areas by these organisms suggest that UV‐B is an important environmental factor. UV‐B survival curves were determined which indicated the resistance for each organism studied. The tolerance correlated well with the positioning behavior (i.e. sensitive organisms avoided exposure by moving into sheltered areas whereas the more resistant organisms showed a less pronounced avoidance).
CHLOROPHYLL PHOTOCHEMISTRY IN CONDENSED MEDIA—I. TRIPLET STATE QUENCHING AND ELECTRON TRANSFER TO QUINONE IN CELLULOSE ACETATE FILMS*
Authors: Cheddar Glen , Castelli Francesco , Tollin Gordon 
Published: January 2008

Abstract—Chlorophyll‐a was incorporated into cellulose acetate films and the triplet state decay kinetics and electron transfer from triplet to p‐benzoquinone in aqueous solution was studied using laser flash photolysis and EPR. The triplet was found to decay by first order kinetics with a rate constant which was independent of Chl concentration. The triplet yield, however, was concentration dependent. These properties are due to quenching which occurs only at the singlet state level. In the presence of quinone, the triplet is quenched and, when the quinone is in an aqueous solution in contact with the film, Chl cation radical (C±) as well as the semiquinone anion radical (Q±) can be observed. The C decays by second order kinetics with a rate constant of 1.5 × 106M‐1 s‐1. Although triplet conversion to radicals is slightly lower in the films as compared to fluid solutions (˜ 3 times), the lifetimes of the radicals are greatly increased (˜ 103 times).
IRRADIATION IN THE FROZEN STATE: A TECHNIQUE FOR DIRECT PHOTOAFFINITY LABELING
Authors: Jr James J. Ferguson 
Published: January 2008

Abstract—UV irradiation of rabbit muscle phosphofructokinase (PFK) in the presence of adenosine 3′,5′‐cyclic phosphate (cAMP) resulted in the covalent attachment of this ligand molecule to the enzyme protein. Irradiation in the frozen ice state enhanced the rate of this incorporation more than 10‐fold above that achieved in aqueous solution, without significantly affecting the rate of photodestruction of the protein. [3H]‐cAMP and [32P]‐cAMP were each incorporated into PFK at identical rates in the frozen state. Rates of photoincorporation in the frozen and liquid states were both half‐maximal at a free ligand concentration approximately equal to the dissociation constant of cAMP and PFK. Adenosine diphosphate (ADP) and adenosine monophosphate (AMP), both of which are known to compete for cAMP binding to PFK, inhibited photoincorporation of cAMP. Guanosine monophosphate (GMP), inosine monophosphate (IMP), and guanosine 3′,5′‐cyclic phosphate (cGMP), which do not compete for cAMP binding, had no effect on photoincorporation of cAMP. Irradiation of [3H]‐AMP or [3H]‐ADP resulted in photoincorporation into PFK at 0°C, with enhancement at — 77°C similar to that noted with cAMP.