Showing papers on "Xanthene published in 2005"

Degradation of dye pollutants by immobilized polyoxometalate with H2O2 under visible-light irradiation.

Abstract: A Keggin polyoxometalate (POM, i.e., PW12O40(3-)) and its lacunary derivative are immobilized on an anionic exchange resin through electrostatic interaction at pH 4.6 in an aqueous dispersion. The resin-supported POM thus obtained catalyzes the efficient degradation of cationic dye pollutants in the presence of H2O2 under visible-light irradiation. To evaluate the photocatalytic system, degradation of a rhodamine B (RB) dye was investigated in detail using UV-visible spectroscopy, high performance liquid chromatography, and gas chromatography/mass spectrometry techniques to identify the intermediates and final products. Fluorescence lifetime measurements revealed the electron transfer from the visible-light-excited RB molecules to the POMs. Electron paramagnetic resonance measurements, investigation of the effects of *OH and *OOH scavengers on the photoreaction kinetics, and IR analysis indicated that de-ethylation of RB was due to *OOH radicals, but the decomposition of the conjugated xanthene structure was caused by the peroxo species formed by interaction of H2O2 with the lacunary POM loaded on the resin. A total organic carbon removal of ca. 22% was achieved, and the recycle experiment suggested excellent stability and reusability of the heterogeneous catalyst. On the basis of the experimental results, a photocatalytic mechanism is discussed.

Taming fluorescent dyes with cucurbituril

Abstract: The potential of the supramolecular host molecule cucurbit(7)uril to serve as a stabilizing ad- ditive and enhancement agent was investigated for the following dyes in aqueous solution: rhodamine 6G, rhodamine 123, tetramethylrhodamine, cresyl violet, fluorescein, coumarin 102, pyronin B, pyronin Y, two cyanine 5 and one cyanine 3 derivative, and IR140 as well as IR144. For most cationic dyes photostabi- lization was established, and a pronounced thermal stabilization due to deaggregation and solubilization was observed for the xanthene dyes. The advantageous effects are attributed to the formation of inclusion complexes with different photophysical and photochemical properties. The complexation is accompanied by spectral shifts characteristic for the inclusion in a less polar environment, while the fluorescence quantum yields as well as the brightness show an increase, with few exceptions. As a consequence of the low polar- izability inside the cucurbituril cavity, the fluorescence lifetimes of the included dyes increase substantially and systematically. Applications of the new photostabilizing additive for dye lasers, for prolonged storage of dye solutions, in scanning confocal microscopy, and fluorescence correlation spectroscopy are discussed.

Photoinduced Hinge-Like Molecular Motion: Studies on Xanthene-Based Cyclic Azobenzene Dimers

Abstract: [Structure: see text]. Molecular devices incorporating azobenzene units represent active components of smart systems, as they are capable of exhibiting photoregulated cooperative molecular motion. Herein, we describe the synthesis, X-ray crystal analysis, and photochemical and thermal studies of a xanthene based cyclic azobenzene dimer and its precursor. The trans-trans isomer of the azobenzene dimer upon photoirradiation transforms to the cis-cis isomer through an intermediate trans-cis isomer. The X-ray crystal structures of the trans-trans isomer (open) and the cis-cis isomer (closed) provide unambiguous proof for the hinge-like molecular motion in this class of molecules. The inferences drawn from photochemical and thermal studies shed light on the effect of varied substitution and cyclic structures on the different transitions. The lifetime of the cis-cis isomer is estimated to be 6.43 years, whereas the trans-cis isomer is short-lived (2.73 min) at 303 K. A rational explanation for the relative stability of the different isomers is derived from the isokinetic plot and theoretical calculations.

Stable Organic Blue-Light-Emitting Devices Prepared from Poly[spiro(fluorene-9,9‘-xanthene)]

Abstract: A short, efficient synthetic route has been developed for the preparation of 2,7-dibromospiro[fluorene-9,9‘-(2‘,7‘-di-n-octyloxyxanthene)], which was subsequently polymerized with the corresponding diborolane through Suzuki coupling to afford a fluorene-based homopolymer, PSFX, that contains a spiroxanthene group functionalized on the C-9 position of each fluorene repeat unit. Single-crystal X-ray diffraction analysis of the dibromo monomer revealed that the spiro-fused fluorene and xanthene moieties lie perpendicular to one another. As a consequence of the incorporation of the spiro pendant group, PSFX possesses a high glass transition temperature and good thermal stability while displaying its stable blue emission in the solid state. A light-emitting diode device prepared using PSFX as the emitting layer exhibits an efficient, stable blue emission; it has a turn-on voltage of 6 V and a maximum external quantum efficiency of 1.74% ph/el. Even when the brightness was increased up to 103 cd/m2 (ca. 11 V), ...

A convenient preparation of xanthene dyes.

Abstract: A facile synthetic route utilizing readily available reagents affords a series of regioisomerically pure xanthene dye derivatives. Advantages include relatively mild conditions and good to excellent yields. Nonpolar, highly crystalline intermediates are isolable by standard chromatographic techniques. The intermediates are in the requisite xanthene oxidation state, thus avoiding the need for relatively inefficient oxidation chemistry and/or harsh conditions. During the course of this work, a new boron-mediated 1,2-aryl migration reaction was discovered.

Adsorption of xanthene dyes by lysozyme crystals.

Abstract: Adsorption characteristics of cross-linked lysozyme crystals of different morphologies (tetragonal, orthorhombic, triclinic and monoclinic) were examined using four anionic dyes (fluorescein, eosin, erythrosin, and rose bengal), one zwitterionic dye (rhodamine B), and one cationic dye (rhodamine 6G). The adsorption isotherms were of the Langmuir type for all examined systems with the exception of rhodamine B adsorption by monoclinic crystals. The weakest adsorption was observed for the cationic dye, rhodamine B, whereas dianionic dyes, eosin, rose bengal, and erythrosin were strongly adsorbed on the protein surface. The adsorption capacities of the crystals for the dyes were found to depend on both charge and hydrophobicity of the dye, reflecting the heterogeneous character of the lysozyme pore surface. The adsorption affinity of the crystals for the dyes was a function of the dyes' hydrophobicity. Furthermore, the crystal morphology was identified as an additional factor determining capacity and affinity for dye adsorption. Differences between crystals prepared in the presence of the same precipitant were lower than between morphologies prepared with different precipitants.

One-pot synthesis of 14H-dibenzo[a,j]xanthene and its 14-substituted derivatives

Abstract: Preparation methods of the titled compounds are mentioned and an easy, environment friendly, common and one-pot synthesis of these compounds is described.

The solubilities of xanthone and xanthene in supercritical carbon dioxide: Structure effect

Abstract: The equilibrium solubility of the two pesticides – xanthone and xanthene – in supercritical carbon dioxide was determined with a flow-type method. Measurements were performed at pressures ranging from 80 to 300 bar and temperatures from 308.15 to 328.15 K. The results show that xanthene was much more soluble in supercritical carbon dioxide than xanthone with its solubility being over 10-fold higher than that of xanthone due to their different volatility related to their chemical structures. The determined solubility data were well correlated by the Peng–Robinson equation of state and the empirical density-based Chrastil model with the average absolute relative deviation (AARD) less than 11.5% for two solutes investigated.

Inhibition of vesicular glutamate uptake by Rose Bengal-related compounds: structure-activity relationship.

Abstract: Synaptic vesicular accumulation of glutamate is a vital initial step in glutamate transmission. We have previously shown that Rose Bengal, a polyhalogenated fluorescein analog, is a potent inhibitor of glutamate uptake into synaptic vesicles. Here, we report the structural features of Rose Bengal required for this inhibition. Various Rose Bengal-related compounds, with systematic structural variations, were tested. Results indicate that the four iodo groups and the phenyl group attached to the xanthene moiety are critical for potent inhibitory activity. Replacement of these groups with two iodo groups and an alkyl group, respectively, results in substantial reduction in potency. Of further interest in creating high potency is the critical nature of the oxygen atom which links the two benzene rings of xanthene. Thus, the phenyl group and multiple iodo groups, as well as the bridging oxygen of xanthene, are crucial elements of Rose Bengal required for its potent inhibitory action.

Switchable fluorescence behaviors of pyronine Y at different pH values upon complexation with biquinolino-bridged bis(β-cyclodextrin)

Abstract: An xanthene dye, pyronine Y, was found to exhibit opposite fluorescence behaviors at different pH values in the presence of N,N � -bis(2aminoethyl)-2,2 � -biquinoline-4,4 � -dicarboxamide-bridged bis(-cyclodextrin) (2). That is, pyronine Y showed the quenched fluorescence in an acidic (pH 2.0) or a neutral (pH 7.2) environment, while the enhanced fluorescence in a basic environment (pH 12.0), with the addition of 2. Further studies by fluorescence titrations and 2D NMR indicated that different binding modes of positively charged and neutral PY molecules upon complexation with bis(-cyclodextrin) 2 should be responsible for opposite fluorescence behaviors. This result may enable the biquinolino-bridged bis(-cyclodextrin) as an efficient chemical sensor for the protonation and deprotonation of xanthene dyes. © 2005 Elsevier B.V. All rights reserved.

Photoinitiating free‐radical polymerization electron‐transfer pairs applying amino acids and sulfur‐containing amino acids as electron donors

Abstract: A series of free-radical polymerization initiation systems, based on xanthene dyes as the absorbing chromophores [Rose bengal derivative, 3-(3-methylbutoxy)-5,7-diiodo-6-fluorone and 3-acetoxy-2,4,5,7-tetraiodo-6-fluorone] and sulfur-containing amino acids as the electron donors, were investigated. The photoredox pair xanthene dye/sulfur-containing amino acid was effectively used for photoinitiation of free-radical polymerization of the mixture composed of poly(ethylene glycol)diacrylate–1% NH4OH (3 : 1). The highest initiating efficiencies were observed for the system composed of methionine derivatives as the electron donor. The mechanism of photoinduced electron transfer between sulfur-containing amino acids and triplet state of xanthene dye was investigated using laser-flash and steady-state photolysis techniques. Based on photochemistry of xanthene dyes, photochemistry of sulfur-containing amino acids, and obtained results, the mechanism describing the major processes occurring during the photoinitiated polymerization by a photoinduced intermolecular electron-transfer process was postulated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 358–365, 2005

Synthesis of Isomerically Pure Carboxylate‐ and Sulfonate‐Substituted Xanthene Fluorophores.

Abstract: Xanthene-based fluorophores such as fluorescein and rhodamine are typically prepared by acid-catalyzed condensation of the appropriate resorcinol or 3-aminophenol with phthalic anhydride. Condensation of substituted phthalic anhydride species results in functionalized fluorophores that are formed as mixed isomers. Crystallization approaches to isomer separation have been reported elsewhere for symmetric fluorescein carboxylates. We describe crystallization-based separation of protected fluorescein sulfonates and coupling conditions to form sulfonamides, precursors for carboxylate-substituted rhodamines, and precursors for asymmetrically substituted fluoresceins and rhodafluors.

Enzyme detection method and reagent

Abstract: The invention provides a method for determining nitroreductase activity, the method comprising combining a substrate comprising a compound of formula (I): wherein groups Ra and Rb are attached to atoms of the Z ring system; Z represents the a chain of linked atoms necessary to complete an aromatic or heteroaromatic ring system having five or six atoms selected from carbon atoms and optionally no more than two atoms selected from oxygen, nitrogen and sulphur; FLUOR is a fluorescent dye selected from xanthene, coumarin and oxazine dyes; L1 is a bond or is an atom or a chain of 2 to 10 covalently linked atoms selected from the group consisting of carbon, nitrogen, oxygen and sulphur atoms; each Ra is hydrogen or may be selected from electron donating and withdrawing groups, and p is 0 or an integer from 1 to 3; Rb is hydrogen or is the group -L2-W, where L2 is a linker chain containing from 1-20 linked atoms and W is a fluorescent dye moiety or a quenching group; m is 0 or 1; and r is 1 or 2; with a sample containing or suspected to contain nitroreductase under conditions to cause cleavage of FLUOR from the substrate. Nitroreductase activity is determined by detecting a change in an optical property of the sample.

Mechanistic and Kinetic Study of Free Radical Polymerization Photoinitiated by Xanthene Dye-n-Phenylglycine Derivatives Photoredox Pairs

Abstract: The mechanistic and free radical photopolymerization kinetic studies for the selected xanthene dyes in the presence of N-phenylglycine derivatives are described. The examined transient phenomena, using nanosecond laser flash photolysis, confirm that the oxidation of N-phenylglycine derivatives is a one electron transfer process. The laser flash measurements as well as the steady-state experiments allowed to establish the structure of a free radical, which in ethyl acetate-DMF (9:1) solution, is mostly formed after the electron transfer, e.g. N-phenylglycine α-aminoalkyl radical (Ph-NH-C'(H)-COOH). However, a careful analysis of the photolysis products indicates another path of secondary reactions that includes the decarboxylation of N-phenylglycine N-centered radical cation, yielding Ph-NH-CH* 2 radical. The measured electron transfer rates oscillate from 0.23×10 8 to 35.9 X 10 8 M - 1 s - 1 that, in turn, suggests the possibility that the electron transfer process might control the rate of photoinitiated polymerization. The comparison of the rates of xanthene dye triplet state quenching and the measured rates of polymerization shows, however, that there is no correlation between these two variables. This observation permits to conclude that the rate of photopolymerization is probably controlled by the secondary processes such as: (i) the rate of proton transfer reaction between N-phenylglycine radical cation and xanthene dye radical anion, (ii) the participation of decarboxylation process in the secondary reactions and (iii) the reactivity of the free radicals obtained after electron transfer.

Synthesis and characterization of novel substituted spiro[isobenzofuran-1(3H), 9’-xanthene]-3-ones

Abstract: The ketoacid, 2-(4-diethylamino-2-hydroxybenzoyl)benzoic acid, prepared from N,N-diethyl-m-aminophenol and phthalic anhydride, was reacted with various substituted 3-6-methoxybenzothiazol-2-yl-4(3H)-quinazolinones in the presence of a dehydration condensing agent to afford novel spiroisobenzofuran-1(3H),9'-xan- thene-3-ones. The benzothiazolyl quinazolinones were synthesized by reacting 2-amino-6-methoxybenzothiazole with various substituted benzoxazinones. All com- pounds were characterized by melting point determination, elemental analysis, in- fra-red spectroscopy, NMR-spectroscopy and UV-visible sprectroscopy. All the fluoran compounds are colourless or nearly colourless and produce colour in the presence of acidic media.

XANTHENE DERIVATIVES AND ortho- SUBSTITUTED PHENOLS - PRODUCTS FROM DEHYDROGENATION OF ACYCLIC 1,5-DIKETONES

Abstract: Xanthene derivatives and ortho-substituted phenols were obtained during the dehydrogenation of 1,5-diketones and their ketol forms at a Pt/C catalyst at 280–320°C.

Diagnostic agents for positron emission imaging using radiolabeled halogenated xanthenes

Abstract: New diagnostic agents for positron emission tomography (PET) and methods for use of such agents for imaging of human or animal tissue are described, wherein a primary active component of such agents is a radiolabeled halogenated xanthene or halogenated xanthene derivative. Preferably, the radiolabeled halogenated xanthene is radiolabeled Rose Bengal or a functional derivative of Rose Bengal.

One‐Pot Synthesis of 14H‐Dibenzo[a,j]xanthene and Its 14‐Substituted Derivatives.

Abstract: Preparation methods of the titled compounds are mentioned and an easy, environment friendly, common and one-pot synthesis of these compounds is described.

Methods for positron emission imaging with radiolabeled halogenated xanthenes diagnostic agents

Abstract: New diagnostic agents for positron emission tomography (PET) and methods for use of such agents for imaging of human or animal tissue are described, wherein a primary active component of such agents is a radiolabeled halogenated xanthene or halogenated xanthene derivative. Preferably, the radiolabeled halogenated xanthene is radiolabeled Rose Bengal or a functional derivative of Rose Bengal.

Diagnostic agents for positron emission imaging using radiolabeled halogenated xanthenes and methods for positron emission imaging with radiolabeled halogenated xanthene diagnostic agents

Abstract: New diagnostic agents for positron emission tomography (PET) and methods for use of such agents for imaging of human or animal tissue are described, wherein a primary active component of such agents is a radiolabeled halogenated xanthene or halogenated xanthene derivative. Preferably, the radiolabeled halogenated xanthene is radiolabeled Rose Bengal or a functional derivative of Rose Bengal.

Catalytic carbonylation of 4-penten-1-ol to ɛ-caprolactone and oligocaprolactone

Abstract: A catalyst consisting of Pd2(dba)3 + 2 XANTPhos (dba = dibenzylideneacetone, XANTPhos = 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene) in toluene catalyzes the alkoxycarbonylation of 4-penten-1-ol to form the cyclic products ɛ-caprolactone and 2-methylvalerolactone, as well as oligocaprolactone. The conversion and selectivity observed using this catalyst is higher than that observed with other reported systems with the regioselectivity for terminal carbonylation exceeding 70%.