bluuebunny/crossref_metadata_2025_split huggingface dataset:
DEPTH PROFILES FOR PERMEATION OF WATER and OXYGEN IN VESICLES and TUBULE PHASES BY FLUORESCENCE QUENCHING STUDIES*
Authors: Sonnenschein Mark F. , Weiss Richard G. 
Published: January 2008

AbstractStatic and dynamic fluorescence data from three structurally related probe molecules [(1‐pyrenyl)acetic acid, 4‐(l‐pyrenyl)butanoic acid, and 12‐(l‐pyrenyl)dodecanoic acid] were employed to determine the influence of phase structure on oxygen and water permeability in small unilamellar vesicles and microtubules of l,2‐bis(tricosa‐10,12‐diynoyl)‐in‐glycero‐3‐phosphocholine (DC23PC). Since the pyrenyl units of the three reporter molecules probe environments at different depths in DC23PC bilayers, the aggregated information provides a depth profile of both small‐molecule permeability and order. The results indicate that the probe sites are somewhat more available to water molecules immediately below the chain melting transition temperature than above it: singlet lifetimes of the pyrenyl groups undergo a clear increase as the temperature is raised in the region of the transition. This observation is consistent with melted chains being able to wrap themselves more efficiently around pyrenyl units (and thereby protect them better from water molecules) than stiff chains.The gross picture that emerges is one in which pyrenyl groups experience water and oxygen quenching via opposing concentration gradients. The concentration of oxygen is greatest near the bilayer midplane and decreases toward the aqueous interface; the concentration of water increases from the midplane to the interface.
PHOTOPHYSICS AND PHOTOCHEMISTRY OF 4‐DIHYDROPYRIDINONES
Authors: Aeby D. , Eichenberger E. , Haselbach E. , Suppan P. , Guerry P. , Neier R. 
Published: January 2008

Abstract—Dihydropyridinones (DHP) react photochemically with olefins to form cycloaddition products. The reactions proceed through the lowest excited state T1 of the DHPs, with rate constants which depend on the olefin and can approach the diffusional limit in the most favourable cases. Intra‐and inter‐molecular sensitization and quenching have been investigated, as well as spectroscopic properties such as absorption and luminescence spectra, and in particular electron energy loss spectra which have established the energy of the reactive T1, state as 295 kj mol‐1 (3.07 eV).
ANTENNA EFFECT IN LUMINESCENT LANTHANIDE CRYPTATES: A PHOTOPHYSICAL STUDY
Authors: Alpha Beatrice , Ballardini Roberto , Balzani Vincenzo , Lehn Jean‐Marie , Perathoner Siglinda , Sabbatini Nanda 
Published: January 2008

Abstract—Excited state emission and absorption decay measurements have been made on the cage‐type cryptate complexes [M bpy.bpy.bpy]n+, where Mn+= Na+, La3+, Eu3+, Gd3+ or Tb3+ and [bpy.bpy.bpy] is a tris‐bipyridine macrobicyclic cryptand. Excitation has been performed in the high intensity 1π‐π* cryptand band with maximum at about 300 nm. Experiments have been carried out in H2O or D2O solutions and at 300 and 77 K to evaluate the rate constants of radiative and nonradiative decay processes. For Mn+= Na+, La3+ and Gd3+ the lowest excited state of the cryptate is a 3ππ* level of the cryptand which decays in the microsecond time scale at room temperature in H2O solution and in the second‐millisecond time scale at 77 K in MeOH‐EtOH. For Mn+= Eu3+, the lowest excited state is the luminescent 5D0 Eu3+ level which in H2O solution is populated with 10% efficiency and decays to the ground state with rate constants 2.9 × 103 s_1 at room temperature and 1.2 × 103 s−′ at 77 K. The relatively low efficiency of 5D0 population upon 1ππ* excitation is attributed to the presence of a ligand‐to‐metal charge transfer level through which 1ππ* decays directly to the ground state. For Mn+= Tb3+ the lowest excited state is the luminescent 5D4 Tb3+ level. The process of 5D4 population upon 1ππ* excitation is ˜100% efficient, but at room temperature it is followed by a high‐efficiency, activated back energy transfer from the 5D4 Tb3+ level to the 3ππ* ligand level because of the relatively small energy gap between the two levels (1200 cm_1) and the intrinsically long lifetime of 5D4. At 77 K back energy transfer cannot take place and the 5D4 Tb3* level deactivates to the ground state with rate constant 5.9 × 102 s‐′ (H2O solution). The relevance of these results toward the optimization of Eu3+ and Tb3+ cryptates as luminescent probes is discussed.
PHOTOCHEMICAL MODIFICATION OF lac REPRESSOR–III. MUTANT 112X86 VERSUS WILD‐TYPE REPRESSOR
Authors: Spodheim‐Maurizot Mélanie , Culard Francoise , Grebert Philippe , Maurizot Jean‐Claude , Charlier Michel 
Published: January 2008

Abstract— Photodestruction of the two tryptophan (TRP) residues of the core of the wild‐type Escherichia coli lac repressor has already been used as a probe in the study of interactions of the repressor with DNA and effectors. The good correlation between phenomena occurring in the core (photodestruction of TRP residues, effectors binding) and at the headpieces (DNA specific and nonspecific binding) can be understood in terms of allosteric behavior of the protein.In the present study, the same approach is applied to a repressor with peculiar binding properties, the 112X86 mutant. The photodestruction of TRP residues of this tight binding repressor, bearing two different amino acids as compared to the wild‐type one (Ser 61 → Leu, Pro 3 → Tyr) indicates a probably subtle (since not detected by classical spectroscopic methods) difference of structure of the entire protein and confirms the similarity between specific and non‐specific binding of this mutant repressor to DNA, observed by other methods.
PHOTOCHEMICAL AND PHOTOPHYSICAL STUDIES ON HUMAN LENS CONSTITUENTS
Authors: Dillon James , Wang Ren‐Hong , Atherton Stephen J. 
Published: January 2008

Abstract— –The young human lens contains species (3‐hydroxy kynurenine; 3‐HK and its glucoside; 3‐HKG) which absorb most light between 300 and 400 nm. Photochemical studies have indicated that these compounds are relatively inefficient sensitizers of lens proteins. An investigation of the fluorescent properties of 3‐HKG indicate that it contains a fast deactivation pathway (ps) which would be expected to have minimal photochemical effect on the integrity of the lens. Further photophysical studies on 3‐HK indicates that it has an even faster fluorescent lifetime (< 10 ps) with a much lower quantum yield of fluorescence (0.001 vs 0.03 for 3‐HKG).With aging, the human lens proteins undergo numerous changes including a generalized yellowing. These chromophores exhibit a higher quantum yield of fluorescence, an increase in the fluorescent lifetime by 2 orders of magnitude and the formation of two long lived transient species (µs).These species might be expected to drastically increase the susceptibility of the human lens to ambient radiation. Based upon quantitative experimental comparisons with 3‐HK this does not seem to be the case. Further time resolved studies on old lens proteins indicate that the two transient species are interconnected in that the first transient species is the precursor to the second. The implications of this mechanism on the integrity of the lens and origin of those chromophores is discussed.
ANTIVIRAL ACTIVITY OF THE PHOTOACTIVE PLANT PIGMENT HYPERICIN
Authors: Lopez‐Bazzocchi I. , Hudson J. B. , Towers G. H. N. 
Published: January 2008

AbstractThe polycyclic compound hypericin, a known photodynamic agent, was investigated for antiviral activity in the presence and absence of light. The three viruses tested: murine cytomegalovirus; Sindbis virus; and human immunodeficiency virus type 1, were all susceptible to hypericin; but these antiviral activities were considerably enhanced, in a dose‐dependent manner, by exposure to light.
THE BIPHOTONIC PHOTOIONIZATION OF CHLORPROMAZINE DURING CONVENTIONAL FLASH PHOTOLYSIS: SPIN TRAPPING RESULTS WITH 5,5‐DIMETHYL‐1‐PYRROLINE‐N‐OXIDE
Authors: Hall Robert D. , Buettner Garry R. , Chignell Colin F. 
Published: January 2008

AbstractA novel combination of conventional flash photolysis and electron spin resonance (ESR) spin‐trapping has been used to demonstrate that photoionization of chlorpromazine (CPZ), and the concomitant production of hydrated electron, occurs through a stepwise biphotonic mechanism during conventional flash photolysis at wavelengths above 290 nm. The production of hydrated electron in the flash photolysis experiment has been monitored and quantified through the use of the spin trapping agent 5,5‐dimethyl‐1‐pyrroline‐A'‐oxide (DMPO). The effects of nitrous oxide, varying concentrations of CPZ and DMPO, and a range of flash intensities on the ESR spectra of the observed spin adducts of DMPO are discussed. The use of ESR spin trapping to monitor hydrated electron yields in flash photolysis experiments has the potential to permit the use of a much wider range of flash intensities than is typically possible with conventional optical experiments. Thus, there is a greater possibility of distinguishing between monophotonic and biphotonic processes.
BORONIC ACIDS AS MECHANISTIC PROBES FOR THE BACTERIAL LUCIFERASE REACTION
Authors: Ahrens Matthias , Macheroux Peter , Eberhard Anatol , Ghisla Sandro , Branchaud Bruce P. , Hastings J. Woodland 
Published: January 2008

ReferencesBacterial luciferase uses long chain aldehydes as substrates. Alkylboronic acid analogs of these substrates with chain lengths of C7 and C9 have been synthesized, characterized, and used as mechanistic probes for the light emitting reaction. They behave as inhibitors in the in vitro luminescence reaction. Contrary to an earlier report (Macheroux and Ghisla, 1985, Nachr. Chem. Tech. Lab. 33,785–790) they are not substrates for bacterial luciferase, in that they do not lead to light emission and are not oxidized by the flavin‐4a‐hydroperoxide to the products boric acid and the corresponding alcohol, as would be expected from a Baeyer‐Villiger reaction. However, the particular conformation of a putative boronic acid hydroperoxide at the active center might be such that it would preclude a Baeyer‐Villiger fragmentation. Thus, while the results do not support the postulate that luciferase proceeds via a Baeyer‐Villiger mechanism, they also do not exclude it. A further observation was that the endogenous light emission (no added aldehyde) decays more rapidly than does the luciferase bound flavin‐4a‐hydroperoxide. This suggests that the endogenous light is not caused by the decomposition of the flavin‐4a‐hydroperoxide.
THE PHOTOCHEMISTRY OF IODO, METHYL AND THIOMETHYL SUBSTITUTED ARYL AZIDES IN TOLUENE SOLUTION AND FROZEN POLYCRYSTALS
Authors: Leyva Elisa , Chang David H. S. , Platz Matthew S. , Watt David S. , Crocker Peter J. , Kawada Kenji 
Published: January 2008

AbstractThe photolysis of para‐methyl and para‐thiomethylphenylazide at 77 K produces the corresponding triplet nitrenes which can be detected by electron paramagnetic resonance (EPR) spectroscopy. Photolysis of these azides in frozen toluene at 77 K leads to insertion of the nitrene into a benzylic C‐H bond of the matrix in modest yields. Photolysis of iodinated aryl azides under these conditions does not produce triplet nitrenes that can be detected by EPR spectroscopy. In contrast to the para‐methyl and para‐thiomethyl substituted phenyl nitrenes, photo‐induced cgupling of iodo‐substituted phenyl nitrenes to toluene proceeds in very poor yield.
SPECTRAL MEASUREMENTS OF GLOBAL AND DIFFUSE SOLAR ULTRAVIOLET‐B RADIANT EXPOSURE AND OZONE VARIATIONS
Authors: Blumthaler M. , Ambach W. 
Published: January 2008

AbstractSince 1985, spectral solar UV‐B radiant exposure has been measured at the High Alpine Research Station Jungfraujoch, Bernese Alps, Switzerland (3576 m). Global (sun and sky) and diffuse (sky) UV‐B radiant exposure on a horizontal plane are measured simultaneously by two identical devices. The detecting system consists of a rotating filter wheel with 8 interference‐filters, centered at every 5 nm between 290 and 325 nm, and a halfbandwidth of ±3 nm. The special advantage of this detector is its waterproofness, allowing operation under all weather conditions. The ratio of the intensities at 305 and 315 nm is being analyzed with regard to ozone variations; for example, the ratio is reduced by a factor of 2 because of an increase in ozone content from 250 to 350 Dobson units. The relation between ozone variations and measured spectral UV‐B intensity is confirmed applying Green's radiation model.
SOLUBILIZATION OF PHOTOSYNTHETIC PIGMENT‐PROTEIN COMPLEXES
Authors: Allgood Leonard , Curtright Robert D. , Markwell John 
Published: January 2008

AbstractStudies utilizing fractionation of photosynthetic pigment‐protein complexes from the chloroplast thylakoid membrane often employ dodecylsulfate at a concentration of 10 mg mL−1 to disrupt membrane structure prior to electrophoretic fractionation of the complexes. We investigated the effect of varying dodecylsulfate concentration on the solution/air interfacial surface tension in the absence and presence of the same concentrations of thylakoid membranes used by four different fractionation systems that have been commonly employed to fractionate photosynthetic pigment‐protein complexes. Concentrations of dodecylsulfate in the range5–10 mg mL−1, normally utilized to treat thylakoids prior to fractionation, were effective in reducing the interfacial surface tension to levels equivalent to control solutions without added thylakoid membranes. However, thylakoid membranes treated with these concentrations of dodecylsulfate are not resolved into discrete pigment‐protein complexes when subjected to electrophoresis on an agarose gel, and do not produce significant amounts of pigment‐containing complexes with a molecular size < 100 000 as measured by filtration with size‐exclusion membranes. We conclude that many surfactant systems empirically developed to fractionate photosynthetic pigment‐protein complexes may not fully solubilize the complexes prior to the electrophoretic step.
ARTIFACTS IN FLUORESCENCE EMISSION SPECTROSCOPY RELATED TO WOOD'S ANOMALY
Authors: Kessel David 
Published: January 2008

AbstractFluorescence emission spectra of porphyrins acquired with a monochromator using a 1500 line/mm holographic grating were affected by polarization‐induced effects (Wood's anomaly) which affected the transmission of different wavelengths of light. This effect resulted in a blue‐shift in the emission optimum, and distortions in the fluorescence spectrum at longer wavelengths. These anomalies could be eliminated by insertion of polarizers, orientation = 0°, in emission and excitation paths. A monochromator with a 1200 line/mm holographic grating was essentially free from these distortions.
LIGHT SCATTERING SPECTROPHOTOMETRY FROM ISOLATED CONTROL AND TRIAZOLE‐TREATED CHLOROPLASTS
Authors: Deshpande S. , Hofstra G. , Fletcher R. A. , Abrahamson E. W. 
Published: January 2008

AbstractLight scattering relaxation spectrophotometry has proven to be a useful technique to monitor rapid cytophysical changes in chloroplast suspensions brought about by flash illumination. This paper compares the Mg‐ATP dependent light scattering behaviour of cholorplasts isolated from control and triazole‐treated wheat seedlings. Our results suggest that triazole‐treatment enhances Mg‐ATP dependent activity. This same enhancement in control chloroplasts can be brought about by introducing potassium ion in the presence of valinomycin. Therefore, the potassium ion might account for part of the stress resistance conferred by triazole treatment.
PHOTOINDUCED ELECTRON TRANSFER QUENCHING OF EXCITED Ru(II) POLYPYRIDYLS BOUND TO DNA: THE ROLE OF THE NUCLEIC ACID DOUBLE HELIX
Authors: Orellana Guillermo , Mesmaeker Andree Kirsch‐De , Barton Jacqueline K. , Turro Nicholas J. 
Published: January 2008

AbstractIn the presence of double helical polynucleotides (sodium poly(dA‐dT)‐poly(dA‐dT) or calf thymus DNA), the efficiency of oxidative or reductive electron transfer between photoexcited ruthenium(II) chelates Ru(tap)2(hat)2+ or Ru(phen)⅔+ (where tap =1,4,5,8‐tetraazaphenanthrene, hat = 1,4,5,8,9,12‐hexaazatriphenylene, and phen = 1,10‐phenanthroline) and appropriate cationic quenchers (ethidium, Ru(NH3)3/6+, methyl viologen, or M(phen)3/3+, where M = Co, Rh, Cr) increases1–2 orders of magnitude compared to the efficiency of the same quenching in microhomogeneous aqueous medium (kq= 0.3‐1.8 × 109 M's−1). The enhancement is more pronounced when the binding constant of the quencher (103 < Kh < 106M−1) is large. Similar trends are found when the biopolymers are replaced by sodium poly(styrenesulfonate) (PSS). The accelerated electron transfer process is proposed to be due mainly to the effect of accumulation of the reagents in the electrostatic field of the polymer; if corrections for this effect are introduced (e.g. ratioing [quencher]/[polynucleotide]), the reaction rate becomes essentially independent of the polymer concentration. Based upon a model for electron transfer reaction of the complexes within a small cylindrical interface around the DNA helix, calculations of the bimolecular electron transfer rate constants are computed to be 10′ times smaller when the reactants are bound to the double‐stranded polynucleotides and decreased mobility of the cationic species is apparent. The effect is less pronounced if a simpler polyelectrolyte (PSS) is employed. Emission lifetimes of the Ru(II) polypyridyls bound to the DNA (0.32–2μs, double exponential decays) are discussed as well.
ASYMMETRIC INDUCTION IN THE SOLID STATE PHOTOCHEMISTRY OF AMMONIUM SALTS*
Authors: Gudmundsdottir Anna D. , Scheffer John R. 
Published: January 2008

AbstractA general approach to using crystal chirality in asymmetric synthesis is described. An example consists of the preparation of crystalline salts of dimethyl 9‐amino‐9,10‐ethenoanthracene‐11, 12‐dicarboxylate (1) with optically active sulfonic acids. Photolysis of the salts in the solid state generates a product that has chiral centers in the amine‐containing portion of the molecule (di‐π‐methane photorearrangement). The optical activity in the photoproduct was determined by polarimetry and NMR chiral shift reagent analysis, which revealed enantiomeric excesses ranging from 30 to 68% depending on the optically active sulfonic acid employed. In contrast to the results in the crystalline state, irradiation of the salts in acetonitrile gave racemic photoproduct.
MONOALKYL α‐OXOAMIDES: PHOTOCHEMISTRY IN HOMOGENEOUS and IN MICROHETEROGENEOUS MEDIA*
Authors: Richard Wanda G. , Chesta Carlos A. , Whitten David G. 
Published: January 2008

AbstractAn investigation of the photoreactivity of the amphiphilic α‐oxoamide, N‐(12‐dodecanoic acid)benzoylformamide, (1), in aqueous (pH 10) solution and its inclusion complexes with β‐cyclodextrin (β‐CD) and carboxymethylamylose (CMA). In all three media photolysis of 1 yields predominantly the fragmentation products from hydrolysis, mandelamide and the corresponding aldehyde. The most reasonable mechanism for the reaction is an intramolecular quenching of a ketone‐localized excited state by electron transfer from the amide nitrogen followed by proton transfer and a second electron transfer (zwitterion‐1 → diradical ⇄ zwitterion‐2) to yield ultimately the mandelamide‐imine precursor which hydrolyzes to the observed products. The quantum yields for 1 decomposition and mandelamide appearance in aqueous solution (pH 10) are 0.21 and 0.16, respectively. Compound 1 forms a 1:1 and 1:2 complex with β‐CD and shows enhanced quantum efficiencies for reaction, especially the 1:2 complex. 1 also forms a complex with CMA which shows a similar binding constant to other similar chain length amphiphiles in other studies. Here again reactivity is enhanced for the photoreaction of 1 upon complexation, indicating that neither the electron transfer quenching of the excited states nor reaction of subsequent intermediates is prohibited in the complexes. Mechanistic implications of these results are discussed.
PHOTOPHYSICS OF DIOXORHENIUM(V) IN NAFION*
Authors: Thorp H. Holden , Gray Harry B. 
Published: January 2008

AbstractThe emission properties of [ReO2(py)4]+ in Nafion perfluorosulfonated membranes have been investigated. The excited state of [ReO2(py)4]+is a sensitive probe of microheterogeneous environments in aqueous solution (Thorp el al. (1989) J. Am. Chem. SOC. 111,4364–4368). The absorption and emission maxima indicate that the interior of the membrane is quite polar, similar to ethylene glycol (Z‐85). Two well‐resolved emission components show different lifetimes (τ1(H2O) = 250 ns, τ2,(H20) = 1.3 μs) and isotope effects (3.0, 2.4), indicative of varying degrees of solvent accessibility. The evidence suggests that [ReO2(py)4]+ occupies two distinct regions in the polymer film, assigned as the interfacial region and the ion‐cluster region based on previous electrochemical studies involving other metal ions.
HYDRATED ELECTRON FORMATION ON LASER EXCITATION OF P‐PYRIDOXYL AMINO ACIDS and PROTEINS
Authors: T.Greenaway Frederick , Redmond Robert W. , Ledbetter John W. 
Published: January 2008

AbstractEvidence from a characteristic transient spectrum, its lifetime and quenching by N2O demonstrates that XeCl excimer laser excitation of the reduced form of pyridoxal 5′‐phosphate bound to lysine residues will produce the hydrated electron. The phenoxyltype radical coproduct was also observed. The results identify a useful label of protein structures for site‐specific electron generation which can occur outside the region of light absorption by aromatic residues of protein. The results also represent the first observation of hydrated electron formation from flash excitation of a vitamin B6 cofactor.
THE EFFECTS OF PLASMA LIPOPROTEINS ON in vitro TUMOR CELL KILLING and in vivo TUMOR PHOTOSENSITIZATION WITH BENZOPORPHYRIN DERIVATIVE
Authors: Allison B. A. , Waterfield E. , Richter A. M. , Levy J. G. 
Published: January 2008

AbstractThe influence of lipoprotein association on in vitro tumor cell killing and in vivo tumor photosensitization with benzoporphyrin derivative (BPD) has been investigated in M‐1 tumor bearing mice. The association of benzoporphyrin mono acid ring A with either low or high density lipoprotein increased tumor cell killing in an in vivolin vitro cytotoxicity assay performed 3 h post intravenous drug administration. Eight hours following photosensitizer injection only low density lipoprotein (LDL) mixtures produced significant (P≤ 0.005) increases in tumor cell killing compared to BPD in unfractionated plasma. The efficacy of in vivo photosensitization in the presence of lipoproteins correlated with the in vivolin vitro cytotoxicity. Association of BPD with low or high density lipoproteins resulted in delayed tumor regrowth and higher cure rates when light exposure (125J/cm2) was performed 3 h post drug administration. When light exposure was performed 8 h post‐injection only LDL‐BPD mixtures led to enhanced tumor eradication compared to BPD administered in aqueous solution or unfractionated plasma.
SUBCELLULAR LOCALIZATION OF PORPHYRINS USING CONFOCAL LASER SCANNING MICROSCOPY
Authors: WOODBURN K. W. , Vardaxis N. J. , Hill J. S. , Kaye A. H. , Phillips D. R. 
Published: January 2008

AbstractThe in vitro subcellular distribution patterns of 10 porphyrins, varying in hydrophobicity and charge, were studied using confocal laser scanning microscopy on two cell lines (V79 and C6 glioma cells) for incubation times up to 24 h. All of the porphyrins were taken up rapidly by both cell lines and distinct classes of subcellular distribution patterns were observed: general cytoplasmic staining; localization in lysosomes (usually associated with general cytoplasmic staining); localization in mitochondria (and general cytoplasmic staining); localization in mitochondria with subsequent uptake into lysosomes. Structure‐localization relationships which have emerged are that porphyrins with dominantly cationic side chains localize in mitochondria, whereas those with a more anionic character tend to localize in lysosomes.