摘要:

Abstract‐The absorption and fluorescence spectra of the Schiff bases formed between 5′‐deoxypyridoxal and n‐hex‐ylamine in aqueous media containing different concentrations of the cationic surfactant hexadecyltrimethylammonium bromide were recorded at 25°C. The quantum yields of fluorescence of the different zwitterionic and enol forms of the chemical species of the Schiff bases occumng in media of pH 4.5–8.5 were determined. Also, the fluorescence quenching resulting from the presence of the surfactant and that of iodide ion were analyzed. From the results obtained it follows that the zwitterionic forms do not interact with the cationic surfactant, whereas the enol forms do inte

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05123.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractVisible chemiluminescence is emitted in the irreversible deactivation of hemoglobin or methemoglobin with excess H2O2. The emission takes place in two phases. The most intense one lasts a few seconds and is followed by a second phase of lower intensity that remains for longer periods. This second phase presents chaotic or sustained oscillations. Free radicals are implicated in the luminescent process since the emission can be reduced by free radical scavengers such as 6‐hydroxy‐2,5,7,8,‐tetramethylchroman‐2‐carboxylic acid (Trolox) or ascorbic acid. These additives lead to a delay in reaching the maximum intensity, which can be related to their consumption, implying substantial recycling of the hemoprotein. Chemiluminescence is also observed in the oxidation of hemin by H2O2, suggesting a role for the heme group in the processes leading to the excited state production. The lower intensity observed in the presence of hemin can be related to the contribution of the glob

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05124.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractDuring application of the 193 nm excimer laser to vitreoretinal surgery, very deep cutting of the retina of about 100 μm/pulse was detected at the energy fluence in the range of 0.25–0.35 J/cm2/pulse. At the surface of the ablating tip insoluble bubbles were observed during the irradiation. In this paper we study production of these bubbles in aqueous solutions of sodium chloride. The yield of gaseous photoproducts was measured as a function of NaCl concentration and energy fluence. At concentrations of 100 g/L powerful water vapor bubbles and shock waves were observed. A mechanism of soft tissue cutting by the 193 nm laser in highly absorbing liquid media is suggested that explains the features of vitreoretinal ablation with this system: (1) the high cutting depth when the tip touches the tissue and (2) the absence of cutting when the tip is not in contact with the tissue. The advantages of the ArF laser for microsurgery of internal organs are discuss

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05125.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe photosensitive hydroperoxide derivative of biphenyl (BPP) was synthesized by the ozonolysis of phenanthrene in methanol. When cytochromec(cytc) was illuminated by UVB light in the presence of BPP (BPPUV), it was reduced both under aerobic and anaerobic conditions. The action spectrum of the reduction was consistent with that of photolytic decomposition of BPP. Both gave maximum reactions at wavelengths around 300–310 nm. Electron spin resonance studies, using 5,5‐dimethyl‐1‐pyrrolineN‐oxide as a spin‐trapping reagent, revealed the generation of hydroxyl radicals in the BPPUV system. Product analysis of adamantane oxidation by BPPW also suggested the generation of hydroxyl radicals rather than singlet oxygen. However, the effects of scavengers were complicated. Singlet oxygen scavengers significantly inhibit the reaction while none of the hydroxyl radical scavengers tested was effective in inhibiting the BPPUV‐mediated cytcreduction. Deuterium oxide, which extends the lifetime of singlet oxygen, inhibited rather than enhanced the reaction. Reduction of cytcwas inhibited by salts, and their activities were correlated to the electron‐donating nature of the anions. These results suggest that reduction of cytcis mediated by electron transfer from a light‐induced product of BPP, rather than by free hydroxyl radicals

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05126.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractA spectroscopic and photophysical study of three new sapphyrin molecules is presented. The sapphyrin backbone that was derivatized to make them water soluble possesses an absorption band around 700 nm, a desired property for biological photosensitization. We studied the absorption and fluorescence spectra, from which evidence for aggregation in solvents of different polarities was obtained. The extent of aggregation is correlated with the nature of the attached moiety. The absolute quantum yields of singlet oxygen production were measured, with 1,3‐diphenyl isobenzofuran as a model target, and were 0.13–0.18 in ethanol. The binding constants to liposomes and to cells were determined spectroscopically and were found to correspond to the hydrophobicities of the compounds, with an additional effect, ascribed to the sugar moiety, which was found in the case of one of the sapphyrins. The efficiency of photodamage toStaphylococcus aureusby sapphyrins and hematoporphyrin was equivalent, on the basis of cells killed per microgram of sensitizer in the incubation mixt

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05127.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe spectroscopic properties of the antimalarials chloroquine, hydroxychloroquineand selected metabolites were investigated by absorption, fluorescence and phosphorescence measurements. The antimalarials exhibit both fluorescence and phosphorescence. Fluorescence dominates for the deprotonated forms of the 4‐aminoquinolines, while phosphorescence dominates when the compounds are protonated. The phosphorescence lifetimes of the 4‐aminoquinolines were measured. Both the protonated and the deprotonated forms have long phosphorescence lifetimes indicating a long‐lived triplet

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05128.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractRaman difference spectroscopy is used to provide the spectra of both thecisandtransforms of acryloyl‐based acyl enzymes from a mixture without resorting to purification. A mixture ofcisandtrans, about the‐C=C‐C(=O) ethylenic linkage, is generated photochemically and by subtracting the Raman spectrum of the mixture from the spectrum of the puretransform prior to photochemical irradiation, Raman peaks of thetransacyl‐enzyme appear as “negative” features and of thecisform appear as “positive” features. No operator intervention is required to scale the spectra for subtraction, and thus information on the relative Raman scattering efficiencies of thecisandtransisomers can be obtained immediately from the data. Results for 5‐methylthienylacryloyl chymotrypsin confirm earlier data for the purifiedcisandtransforms and data forcisindoleacryloyl chymotrypsin are presented f

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05129.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractFluorescein is a complex fluorophore in the sense that it displays four prototropic forms (cation, neutral, monoanion and dianion) in the pH range 1–9. In experiments with fluorescein‐labeled proteins we have sometimes observed complex nanosecond emission kinetics, which could be due to conversion of the excited monoanion into the excited dianion through an excited state proton exchange with a proton acceptor in the labeled protein. However, the literature is ambiguous on whether this possible excited state proton reaction of fluorescein does occur in practice. In this article we describe a general steady‐state fluorescence method for evaluating excited state proton reactions of simple as well as complex pH‐sensitive fluorophores and apply it to evaluate excited state proton reactions of fluorescein. The method depends on finding a buffer that can serve as an excited state proton donor‐acceptor but does not significantly perturb ground state proton equilibrium and especially does not form ground (or excited state complexes) with the fluorophore. Our results show that the excited monoanion‐dianion proton reaction of fluorescein does occur in the presence of phosphate buffer, which serves as a proton donor‐acceptor that does not significantly perturb ground state proton equilibria. The reaction becomes detectable at phosphate buffer concentrations greater than 20 mMand the reaction efficiency increases with increase in phosphate buffer concentrations. The reaction is most clearly demonstrated by adding phosphate buffer to a solution of fluorescein at constant pH 5.9 with preferential excitation of the monoanion. Under these conditions, the excited monoanion converts to the dianion during its lifetime. The conversion is detected experimentally as an increase in dianion and decrease in monoanion fluorescence intensities with increase in phosphate buffer concentration. The absorption spectrum is not significantly perturbed by the increase in phosphate buffer concentration. To quantitate the reaction, we have recorded titration graphs of fluorescence intensityversuspH for fluorescein solutions at low (5 mM) and high buffer (1M) concentrations with preferential excitation of the monoanion and preferential detection of the dianion emission. We have also developed theoretical expressions that relate fluorescence intensity to pH in terms of the concentration of the four prototrophic forms of fluorescein, extinction coefficients, fluorescence efficiencies and ground and excited state pKa. The theoretical expressions give very good fits to the experimental data and allow evaluation of fundamental parameters such as pKaand fluorescence efficiencies. The analysis of the experimental data shows that the excited monoanion‐dianion reaction does not significantly occur at 5 mMphosphate buffer concentration. However, at 1Mbuffer concentration the reaction is sufficiently fast that it practically achieves equilibrium during the lifetimes of the excited fluorescein monoanion and dianion. The pKa* of the excited monoanion‐dianion proton reaction is around 6.3. The results and methods presented here should be useful in the development and testing of pH‐sensitive labeling fluorophores and flu

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05130.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractWe have employed EPR and the spin trap 5,5‐dimethyi‐1‐pyrrolineN‐oxide (DMPO) to investigate the photochemistry of pyridine‐2‐thione (2‐S‐PyrH),N‐hydroxypyridine‐2‐thione (2‐S‐PyrNOH), and its sodium salt, (2‐S‐PyrNONa), and disulfides, 2,2′‐dithiobis (pyridineN‐oxide) [(2‐S‐PyrN→O)2] and 2,2′‐dithiodipyridine [(2‐S‐Pyr),]. We have found that upon UV irradiation they generate aromatic thil radicals, 2–'SPyr and 2–'S‐PyrN → O, detected as DMPO adducts, DMPO/2–'S‐Pyr (1) and DMPO/2–'S‐PyrN→O (2). In aqueous solution (pH 7) hyperfine splitting constants (hfsc) were determined to be for 1: aN= 14.92 G, aHβ= 16.57 G, and for 2: aN= 14.78 G, aHβ= 16.05 G. In toluene hfsc were 13.09 G, 13.93 G for 1, and 13.25 G, 12.04 G for 2. Irradiation of 2‐S‐PyrH and DMPO in aerated pH 7 buffer generated the DMPO/‐O2,‐ radical (3a, aN= 14.10 G, aHβ= 11.40 G, aHγ= 1.18 G), while in aerated toluene DMPO/.O2H was formed (adduct 3b, aN= 12.74 G, aHβ= 10.41 G, aHγ= 1.295 G). In both systems adduct 1 was also observed. Because compounds possessing the pyridine‐2‐thione moiety show antifungal, antibacterial and anticancer properties, it is likely that the

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05131.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractCompounds possessing a pyridine‐2‐thione moiety show antimicrobial, antifungal and anticancer activities. Some of them are also photochemically active and upon UV irradiation generate free radicals. In this work, employing EPR and the spin traps 2‐methyl‐2‐nitrosopropane (MNP) andaci‐nitromethane (NM), we investigated the photochemistry in aqueous solutions ofN‐hydroxypyridine‐2‐thione (used here as a sodium salt, 2‐S‐PyrNONa), and pyridine‐2‐thione (2‐S‐PryH), as well as photochemistry of the respective disulfides, 2,2′‐dithiobis(pyridineN‐oxide) [(2‐S‐PyrN→O)2] and 2,2′‐dithiodipyridine [(2‐S‐Pyr)2]. We found that UV irradiation of 2‐S‐PyrNONa and of 2‐S‐PyrH in the presence of MNP and NM generates EPR signals of reduced spin traps in addition to signals of MNP and NM adducts with aryl‐thiyl radicals, 2–.S‐PyrN→O and 2–.S‐Pyr. The identification of the aromatic thiyl radicals was based on comparison of EPR spectra of spin adducts generated by irradiation of 2‐S‐PyrNONa and 2‐S‐PyrH with those produced by UV photolysis of the respective disulfides (2‐S‐PyrN→O), and (2‐S‐Pyr)2. It is concluded that pyridine‐2‐thione and N‐hydroxypyridine‐2‐thione possess a photoreducing capacity and generate aromatic thiyl radicals upon UV activation. Thi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05132.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY