bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic Spectroscopy of Erythrosin Phosphorescence and Delayed Fluorescence in Aqueous Solution at Room Temperature*
Authors: Duchowicz Ricardo , Ferrer María Luisa , Acuñ A. Ulises 
Published: January 2008

AbstractThe photophysics and polarization of the phosphorescence and delayed fluorescence of erythrosin in conditions compatible with the current biological applications of the dye (aqueous buffers at pH 7.4 at ambient temperatures) and in ethanol have been studied as a function of dye concentration (10 −7‐10−5M) and temperature (245–333K). The emission decay is strictly single exponential and the detailed kinetic analysis of all the rate processes connected with the emitting T1 state showed that (1) the lowering of the emission lifetime at the higher temperatures is due to a very efficient self‐quenching process, (2) the back intersystem crossing rate Tx S1 is temperature dependent (δETS7 kcal mol−1) but the T1S0 is not (Ea0.1 kcal mol−1) and (3) both intersystem crossing processes are very sensitive to solvent polarity, which accounts for the solvent dependence of the phosphorescence yield and lifetime. The high value of the phosphorescence anisotropy (r0= 0.25 lt 0.006) is independent of the excitation and emission wavelengths, and its evolution in time accurately reflects the rotational restrictions in solid solutions. The relevance of these findings to studies with protein‐dye conjugates is also outlined to facilitate the design and interpretation of phosphorescence depolarization experiments that probe the (μs‐ms dynamics of biomolecules and supramolecular systems.
pH‐Dependent Extraction of Ca 2+ from Photosystem II Membranes and Thylakoid Membranes: Indication of a Ca 2+‐Sensitive Site on the Acceptor Side of Photosystem II
Authors: Semin Boris K. , Ivanov Llja I. , Rubin Andrei B. , Carpentier Robert 
Published: January 2008

AbstractThe action of low pH treatment (pH 3.6) known to release Ca2+ from the oxygen‐evolving complex in photosystem II (PSII) membranes and to induce Ca2+‐revers‐ible inhibition of electron transport at the acceptor side of PSII in thylakoid membranes (TM) was compared in PSII membranes and TM. The rate of the inactivation of electron transport by low pH was four times higher in TM than in PSII membranes. Ferricyanide accelerated the inactivation of PSII membranes but decreased it in the case of TM. Low pH treatment also greatly modified the fluorescence induction kinetics in both preparations, but significant differences have been found in the fluorescence induction kinetics of treated TM and PSII membranes. Calcium restored the electron transport activity and fluorescence induction kinetics in PSII membranes and TM, whereas diphenylcarbazide restored these functions only in PSII membranes. The reactivation of Ca‐depleted PSII membranes was more effective in the dark, whereas the reactivation of TM required weak light. In the case of PSII membranes subjected to low pH citrate buffer, maximal reactivation was observed at 60 mM Ca2+ but for TM about 10 mM Ca2+ was required and 60 mM fully inhibited electron transport in TM during reactivation. These results indicate that the Ca‐dependent inactivation of the acceptor side of PSII in TM after low pH treatment cannot be explained by the extraction of Ca2+ from the oxygen‐evolving complex. It is rather suggested that the Ca2+ involved in this inhibition is bound to the acceptor side of the photosystem near to the QA‐non‐heme iron binding site and may participate in the binding of a polypeptide of the PSII light antenna complex to the PSII reaction center.
In Situ Molecular Dosimetry and Tumor Risk: UV‐lnduced DNA Damage and Tumor Latency Time‡
Authors: Gruijl Frank R. de , Berg Rob J. W. 
Published: January 2008

AbstractIn UV carcinogenesis there is a fundamental chain of causal events from UV‐induced DNA damage through mutations up to tumor formation: each of the early events should be predictive of the ultimate tumor risk. Instead of the UV surface exposure, the in situ load of DNA damage should be a more direct measure of the carcinogenicity. To explore this further we measured cy‐clobutane thymine dimer loads of epidermal cell suspensions from chronically UV‐exposed hairless SKH‐1 mice; skin samples were taken after various time periods under different daily exposures. Although the average load per cell decreased in the course of time due to dilution of damage in an increasing epidermal hyperplasia, the amount of thymine dimers in a column of epidermis (i.e. per mm2 of skin area) became stationary, and this amount increased with higher daily exposure. The median tumor latency time, tso, is inversely related to this stationary load. Extrapolation of a fitted relationship would imply a t50 between 450 and 1430 days for spontaneous skin carcinomas. The present data suggest that the skin strives to maintain a maximum level of tolerable DNA damage by lowering the average genotoxic load in vital cells in a hyperplastic reaction: pseudo‐repair by dilution. This would also explain the strong hyperplastic reactions in DNA repair‐deficient mouse strains. An understanding of these short‐term adaptive reactions can refine our assessments of skin cancer risks in humans.
Photochemistry of 2,6‐D'ichlorodiphenylamine and 1‐Chlorocarbazole, the Photoactive Chromophores of Diclofenac, Meclofenamic Acid and Their Major Photoproducts
Authors: Encinas Susana , Bosca Francisco , Miranda Miguel A. 
Published: January 2008

AbstractDiclofenac and meclofenamic acid are two structurally related nonsteroidal anti‐inflammatory drugs with some photosensitizing potential. Their photochemistry involves cyclization to monohalogenated carbazoles. In principle, photocyclization could occur by photodehalogenation, followed by intramolecular radical addition, or by 6TT electrocyclization and subsequent dehydrohalogenation of the intermediate dihydrocarbazoles. Previously, it has been assumed that the reaction follows the first pathway and that the key species associated with phototoxicity are the resulting aryl radicals. In the present work, we have performed photophysical and photochemical studies on 2,6‐dichlorodiphenylamine (la). This is a suitable model compound because since it contains the active chromo‐phore present in diclofenac and meclofenamic acid, and its photoreactivity should be relevant to the understanding of the photobiological properties of both drugs. Our results clearly show that the first photochemical reaction is a very rapid 6iT‐electrocyclization, and hence no radicals are formed at this stage. Instead, cleavage of the carbon‐halogen bond occurs in the 1‐chlorocarbazole photoproduct 2a. The reduced lifetime of the 2a triplet (as compared with the unsubstituted carbazole) and the observed reaction quenching by oxygen are in agreement with the reaction occurring from the excited triplet state. Overall, the above results suggest that the potential phototoxicity of diclofenac and meclofenamic acid is due to a photobiologically active photoproduct that is able to generate radicals upon photolysis, rather than to the parent drug.
Supramolecular Cationic Tetraruthenated Porphyrin and Light‐Induced Decomposition of 2‐Deoxyguanosine Predominantly Via a Singlet Oxygen‐Mediated Mechanism
Authors: Ravanat Jean‐Luc , Cadet Jean , Araki Koiti , Toma Henrique E. , Medeiros Marisa H. G. , Mascio Paolo Di 
Published: January 2008

AbstractThe tetraruthenated porphyrin, u.‐[/wes0‐5,1O,15,2O‐tet‐ra(pyridyl)porphyrin]tetrakis[ftis‐(bipyridine)chloride ruthenium(II)] (TRP) is a supramolecular cationic species. The aim of the present investigation was to evaluate the photodynamic properties of TRP and Zn‐TRP to damage DNA with emphasis on the mechanistic aspects. The ability for tetraruthenated porphyrin derivatives to induce photosensitization reactions has been determined using 2′‐deoxyguanosine as a DNA model compound. The main photooxidation products of the targeted nucleoside were identified and classified according to their mechanisms of formation, involving either a radical pathway (type I) or a singlet oxygen‐mediated mechanism (type II). Quantification of the different oxidation products provides a means to evaluate the relative contribution of type I and type II pathways associated with the oxidative photosensitization of 2′‐deoxyguanosine by tetraruthenated porphyrin derivatives. Results indicate that x02 plays a major role in the mechanism of photooxidation mediated by these porphyrin derivatives. In addition an increase of the photosensitizing effect in the presence of zinc is observed. For each sensitizer, the ratio between type II and type I photoproducts has been calculated and compared to that of other known dyes such as methylene blue and riboflavin.
Effects of Charge and Structure of Hyaluronic Acid on the Luminescence Quenching in Aqueous Solution
Authors: Kluge Thomas , Masuda Akiko , Yamashita Koichi , Ushida Kiminori 
Published: January 2008

AbstractThe quenching of electronically excited Ru(bpy)32+ (bpy = Tris‐2,2′‐bipyridine) by methylviologen (MV) and ferricyanide (FC) in aqueous solutions of hyaluronic acid (HA) was studied. The structural and viscosity changes occuring with increasing HA concentration were found to influence the photophysical and photochemical properties of the sensitizer. Different kinetic models had to be used for the quenchers studied. The kinetics of the quenching of *Ru(bpy)32+ by MV can be described by the pseudophase model, which indicates that the rate for the exchange of the quencher between the microdroplets is higher than that for the excited state decay of the Ruthenium complex. In contrast, the quenching by the negatively charged quencher, FC, can be described by the Infelta‐Tachiya equation, which indicates that the distribution of this quencher on the aqueous microdroplets is of the Poisson type and there is no exchange of quencher molecules during the lifetime of the sensitizer. The lifetimes of the excited Ruthenium complex, the unimolecular constants for its quenching by FC and the average concentration of the aqueous microdroplets increase with increasing HA concentration, reflecting the change in the solution structure during the transition from semidilute to concentrated regions. For MV no significant dependence of the quenching constant on the HA content of the solution was found. The reaction behavior of charged reactants in HA solution depends strongly on the sign of the charge.
Optical Doppler Tomography: Imaging in vivo Blood Flow Dynamics Following Pharmacological Intervention and Photodynamic Therapy
Authors: Chen Zhongping , Milner Thomas E. , Wang Xiaojun , Srinivas Shyam , Nelson J. Stuart 
Published: January 2008

ABSTRACTA noninvasive optical technique has been developed for imaging in vivo blood flow dynamics and vessel structure with high spatial resolution. The technique is based on optical Doppler tomography, which combines Doppler velocimetry with optical coherence tomography to measure blood flow velocity at discrete spatial locations in turbid biological tissue. Applications of this technique for monitoring changes in blood flow dynamics and vessel structure following pharmacological intervention and photodynamic therapy are demonstrated.
Luminol Oxidation by Hydrogen Peroxide Catalyzed by Tobacco Anionic Peroxidase: Steady‐State Luminescent and Transient Kinetic Studies
Authors: Gazaryan Irina G. , Rubtsova Maya Yu. , Kapeliuch Yuri L. , Rodriguez‐Lopez José Neptuno , Lagrimini L. Mark , Thorneley Roger N. F. 
Published: January 2008

ABSTRACTThe properties of a newly isolated anionic tobacco peroxidase from transgenic tobacco plants overexpressing the enzyme have been studied with respect to the chemiluminescent reaction of luminol oxidation. These were compared to the properties of horseradish peroxidase in the cooxidation of luminol and p‐iodophenol, the enhanced chemiluminescence reaction. The pH, luminol and hydrogen peroxide concentrations were optimized for maximum sensitivity using the tobacco enzyme. The detection limit for the latter under the optimal conditions (2.5 mM luminol, 2 mM hydrogen peroxide, 100 mM Naborate buffer, pH 9.3) was about 0.1 pM, which is at least five times lower than that for horseradish peroxidase in enhanced chemiluminescence with p‐iodophenol. The rate constants for the elementary steps of the enzyme‐catalyzed reaction have been determined: k1= 4.9 × 106M−1 s1, k2= 7.3 × 106M−1 s−1, k3= 2.1 × 106M−1 s−1 (pH 9.3). The similarity of these rate constants is unusual for plant peroxidases. The high catalytic activity of tobacco peroxidase in the luminescent reaction is explained by the high reactivity of its Compound II toward luminol and the high stability of the holoenzyme with respect to heme dissociation. This seems to be a unique property of this particular enzyme among other plant peroxidases.
Regulation of Stimulated Cyclic AMP Synthesis by Urocanic Acid
Authors: Bouscarel Bernard , Noonan Frances , Ceryak Susan , Gettys Thomas W. , Phillips Terry M. , DeFabo Edward C. 
Published: January 2008

ABSTRACTUrocanic acid (UCA) has been shown to mediate the UVB radiation‐induced immunosuppression initiated i’the skin by UV‐induced isomerization from the trans to the cis isomer. However, the mechanism by which cis. UCA acts is still unclear. Therefore, the present stud was undertaken to determine the effect of trans‐ and cis UCA on cyclic adenosine 3′,5′‐monophosphate (cAMP synthesis in human dermal fibroblasts, Golden Syria’hamster hepatocytes and in the human adenocarcinoms cell line, HT29. Neither trans‐ nor cis‐UCA was able is stimulate cAMP synthesis directly in any of the model: tested. In human dermal fibroblasts, cis‐UCA, in contras to trans‐UCA, specifically inhibited cAMP synthesis in duced by either prostaglandin (PG) El or PGE2 with s maximum inhibitory effect of 25‐30% at cis‐UCA con centrations greater than 1 μM and half‐maximum inhib itory effect (ECso) observed at 35 nM. The effect of cis‐UCA was not to stimulate phosphodiesterase and cAMP breakdown. The inhibitory effect of cis‐UCA (an imid azole derivative) was not mediated through stimulatiot of the α2‐adrenergic receptor. The inhibitory effect of cis UCA on stimulated cAMP synthesis was a function of the cell density and was only significant when the fibroblast were confluent or postconfluent. In contrast to the studie with human dermal fibroblasts, an inhibitory effect of cis‐UCA was not observed in either isolated hamster he patocytes or HT29 cells, in which cAMP synthesis wa stimulated by glucagon and vasoactive intestinal peptide respectively. These results point to a possible regulation of cAMP synthesis in fibroblasts as one mechanism by which cis‐UCA exerts its biological effect in the skin.
Ultraviolet B Irradiation Modulates the Immune System of Fish (Rutilus rutilus, Cyprinidae). I. Phagocytes
Authors: Salo Harri M. , Aaltonen Tuula M. , Markkula S. Eveliina , Jokinen E. Ilmari 
Published: January 2008

ABSTRACTRoach (Rutilus rutilus) were irradiated with a single dose of ultraviolet B (UVB) radiation (0.4 J/cm2) in order to study the effects of UVB on the nonspecific immune defense mechanisms of fish. Neutrophils and macrophages were isolated from the head kidney of fish on days 1–14 postirradiation. Both random and directed migration of neutrophils, studied by migration under agarose assay, were suppressed on day 1 after UVB irradiation. The respiratory burst of phorbol 12‐myristate 13‐acetatestimulated neutrophils and macrophages was also suppressed at days 1 and 2 after UVB irradiation. The suppression of migration and respiratory burst were restored or the responses were even enhanced later, but on the other hand spontaneous cytotoxicity of neutrophils toward 51chromium‐labeled K562 target cells stayed suppressed throughout the 14 day follow‐up. This study indicates that UVB radiation has the potential to suppress the functioning of phagocytes and to compromise the immune system of fish.
Singlet Oxygen‐Versus Nonsinglet Oxygen‐Mediated Mechanisms of Sensitizer Photobleaching and Their Effects on Photodynamic Dosimetry
Authors: Georgakoudi Irene , Foster Thomas H. 
Published: January 2008

ABSTRACTWe report the effects of singlet oxygen (1O2) and non‐1O2‐mediated sensitizer photobleaching on oxygen consumption and dosimetry during photodynamic therapy (PDT) of sensitized multicell tumor spheroids. We develop a theoretical model for the description of non‐1O2‐mediated photobleaching resulting from irreversible reactions of the excited singlet or triplet sensitizer populations with cell substrate. We show that the fluence‐dependent simple exponential decay expression of sensitizer degradation is not consistent with these mechanisms and, therefore, with any reasonable mechanism that we consider, because we have shown previously that 1O2‐mediated photobleaching cannot be described by a simple exponential with a constant photobleaching coefficient (I. Georgakoudi et al., Photochem. Photobiol. 65, 135–144, 1997). Analysis of oxygen microelectrode measurements performed at the edge of Nile blue selenium (EtNBSe)‐and protoporphyrin IX (PpIX)‐sensitized spheroids during PDT demonstrates that the former drug photobleaches via a non‐1O2‐mediated mechanism, while the latter is degraded via a 1O2‐mediated mechanism. Comparisons of the cytotoxic effects of EtNBSe with those of Photofrin® (a drug that is degraded via a 1O2‐mediated mechanism) indicate that the lower threshold 1O2 dose and the higher extinction coefficient and 1O2 yield for EtNBSe do not necessarily result in improved photodynamic effects, thus emphasizing the importance of the sensitizer photo‐bleaching mechanism for dosimetry.
Highly Selective Targeting of Ovarian Cancer with the Photosensitizer PEG‐m‐THPC in a Rat Model
Authors: Hornung Rene , Fehr Mathias K. , Monti‐Frayne Jill , Krasieva Tatiana B. , Tromberg Bruce J. , Berns Michael W. , Tadir Yona 
Published: January 2008

AbstractPhotodynamic therapy (PDT) uses light to activate a photosensitizer that has been absorbed or retained preferentially by cancer cells after systemic administration. The first pegylated photosensitizer, tetrakis‐(m‐methoxypo‐lyethylene glycol) derivative of 7,8‐dihydro‐5,10,15,20‐te‐trakis(3‐hydroxyphenyl)‐21,23‐[H]‐porphyrin (PEG‐m‐THPC), was evaluated to target selectively unresectable pelvic ovarian cancer bulks. Our goals were two‐fold: (1) to establish an ovarian cancer model suitable for the development of debulking techniques and (2) to characterize the pharmacokinetics and tumor selectivity of PEG‐m‐THPC by fluorescence microscopy. NuTu‐19 ovarian cancer cells were injected into the caudal part of the right psoas muscle of Fisher rats. Five weeks later, 30 mg/kg body weight of PEG‐m‐THPC was injected intravenously. Necropsy was performed between 4 and 10 days following drug application, and fluorescence of the tumor and various abdominal organs was measured. All rats developed bulky pelvic tumors with an average diameter of 2.6 cm (± 0.6 SD). Tumor masses were encompassing and infiltrating pelvic organs in a similar manner to ovarian cancers in humans. Fluorescence of cancer tissue was maximal 8–10 days following drug application. At 8 days, the tumor‐to‐tissue ratio was 40:1 (plusmn; 12 SE) for most abdominal organs. We conclude that this tumor model may be used for the study of new pelvic debulking techniques, and that the tumor selectivity of PEG‐m‐THPC is exceptionally high 8 days after drug application. Based on these data, we are currently developing a PDT‐based minimally invasive debulking technique for advanced ovarian cancer.
Photophysical Properties of Rufloxacin in Neutral Aqueous Solution
Authors: Sortino Salvatore , Marconi Giancarlo , Giuffrida Salvatore , Guidi Guido De , Monti Sandra 
Published: January 2008

AbstractThe photophysical properties of rufloxacin, 9‐fluoro‐2r3‐dihydro‐10‐(4‐methyl‐l‐pyrazinyl)‐7‐oxo‐7‐H‐pyri‐do[l,2,3‐de]‐l,4‐benzothiazin‐6‐carboxylic acid, a fluoroquinolone antibacterial drug exhibiting photosensitizing action toward biological substrates, were studied in aqueous solutions at neutral pH. The lowest excited electronic states of the zwitterion were characterized by both experimental techniques and theoretical methods. Steady‐state and time‐resolved emission, triplet‐state absorption and singlet oxygen production were investigated. The results indicate that the lowest excited singlet is a fluorescent, relatively long‐lived state (φr= 0.075, Tr≅ 4.5 ns) with an efficient intersystem crossing to the triplet manifold (φisc≅ 0‐7)‐ The lowest triplet is a long‐lived state (TT≅ 10 μs at 295 K in 0.01 M phosphate buffer), with properties that make it a good candidate for being the precursor of the photodecarboxylation of the drug. It is quenched by oxygen at a rate of 1.7 times 109M‐1 s‐1 and singlet oxygen is formed with a quantum yield of 0.32 in air‐saturated solutions.
In Vivo Application of Intestinal pH Measurement Using 2,7‘‐Bis(carboxyethyl)‐5,6‐carboxyfluorescein (BCECF) Fluorescence Imaging
Authors: Maréchal Xavier , Mordon Serge , Devoisselle Jean Marie , Bégu Sylvie , Guery Benoit , Neviére Rémi , Buys Bruno , Dhelin Guy , Lesage Jean Claude , Mathieu Daniel , Chopin Claude 
Published: January 2008

AbstractMeasurement of gastrointestinal intramucosal pH (pH,m) has been recognized as an important factor in the detection of hypoxia‐induced dysfunctions. However, current pH measurement techniques are limited in terms of time and spatial resolutions. A major advance in accurate pH measurement was the development of the ratiometric fluorescent indicator dye, 2′,7′‐bis(carboxyethyl)‐5,6‐car‐boxyfluorescein (BCECF). This study aimed to set up and validate a fluorescence imaging technique to measure in vivo the intramucosal pH (pHim) of the intestine. The intestine was inserted into an optical chamber placed under a microscope. Animals were injected intravenously with the pH‐sensitive fluorescent dye BCECF. Fluorescence was visualized by illuminating the intestine alternately at 490 and 470 nm. The emitted fluorescence was directed to an intensified camera. The ratio of emitted fluorescence at excitation wavelengths of 490 and 470 nm was measured, corrected and converted to pHim by constructing a calibration curve. The pHim controls were performed with a pH microelectrode and were correlated with venous blood gas sampling. Results show that pHim is determined with an accuracy of ± 0.07 pH units and a response time of I min. In conclusion pHim mapping of rat intestine can be obtained by fluorescence imaging using BCECF. This technology could be easily adapted for endoscopic pH measurements.
Base‐specific Photocleavage of DNA Induced by Pazelliptine Sensitization: Study of the Mechanism by Time‐resolved Absorption and Fluorescence
Authors: Fontaine‐Aupart Marie‐Pierre , Renault Eric , Videlot Christine , Tfibel Francis , Pansu Robert , Charlier Michel , Pernot Pascal 
Published: January 2008

AbstractThe intercalating antitumoral drug pazelliptine (PZE) is able to photosensitize the formation of single‐ and double‐strand breaks in supercoiled plasmid DNA and selective photocleavage at guanine residues is observed. In order to understand the mechanisms of DNA cleavage mediated by the photoexcited drug, singlet and triplet excited‐state processes in PZE complexed with poly(dA‐dT)‐poly(dA‐dT), poly(dG‐dC)‐poly(dG‐dC) and calf thymus DNA have been investigated by means of single photon counting fluorescence decay and transient absorption techniques. For each complex, three different binding sites have been identified, due to the existence of different geometric structures of the drug in the ground state. For one type of binding site, a proton transfer reaction occurs in the singlet excited state whatever the nucleic acid environment. In contrast, the relaxation dynamics for the other two sites are found to depend widely upon the type of polynucleotide in which the drug has been intercalated. From the results of this study, we suggest that the photodynamic action of PZE does not originate from excitation of the drug in the environment of G‐C base pairs but is initiated from its triplet state that reacts by electron transfer with the adenine bases. The specificity of cleavage could be the result of subsequent reactions leading to guanine oxidation.