Effective Quencher Research Articles

A highly effective quenching method of 1,3-dipolar cycloadditions of nitrile oxides or nitrile oxide/Lewis acid complexes by use of 2-propenyloxymagnesium bromide

2-Propenyloxymagnesium bromide, readily prepared by treating 2-propen-l-ol with EtMgBr, is a highly effective quencher of nitrile oxide cycloadditions since this alkoxide is much more reactive to nitrile oxides than any other ever known dipolarophiles of the electron-deficient, electron-rich, and strained types, including 3-buten-2-one, ethyl vinyl ether, and norbornene, respectively. This quencher is also effectively utilized to terminate the dipolar cycloadditions of nitrile oxide/Lewis acid complexes.

Terbium(III) luminescence study of tyrosine emission from Escherichia coli glutamine synthetase.

Radiationless energy transfer from tyrosine to Tb(III) in Escherichia coli glutamine synthetase and its two mutants (W57L and W158S) has been utilized to assess the tyrosine residue(s) responsible for the observed tyrosine emission and to investigate its spatial relationships to the two metal binding sites of GS. The interference from tryptophan fluorescence was removed by chemical modification of the tryptophan residues by N-bromosuccinimide (NBS). The Tyr-Tb(III) distances measured by using Förster energy-transfer theory were in good agreement among the three enzymes with average distances of 10.7 and 11.2 A from Tyr to the two metal binding sites. The pKa value for the ionization of tyrosine was determined from fluorescence titration experiments to be approximately 10 for both mutant enzymes. The similarities in pKa values and Tyr-Tb(III) distances observed for all three enzymes lead to the conclusion that the same tyrosine residue(s), is (are) most likely responsible for the Tyr emission. According to the crystal structure distances from tyrosine residues to the two metal binding sites of GS, it is believed that Tyr-179 is the main contributor to the observed Tyr emission. The fact that an intense Tyr emission was observed for W57L GS but not for W158S GS indicates that Trp-57 is much more effective than Trp-158 in quenching the Tyr-179 emission probably through a Förster-type energy transfer. Furthermore, modification of Trp-57 by NBS causes no significant increase in Tyr-179 emission while replacement of Trp-57 by leucine does. This may indicate that oxidized Trp-57 is also an effective quencher for Tyr-179 emission.

Synthesis and thermal and photo-oxidative behaviour of novel aminated 2-hydroxybenzophenone stabilizers in polyolefin films

Three light stabilizers have been prepared and characterized, based on the substitution of a tertiary amine group into the 3- and 5-positions of 2,4-dihydroxybenzophenone (DHBZ) and 2-hydroxy-4-n.octoxybenzophenone (HOBZ) via the Mannich reaction. The derivatives prepared by this method were, the 3- N, N-diethylaminomethyl of the former and the 5- N, N-diethylaminomethyl and 5-morpholinomethyl derivatives of the latter. The thermal and photo-oxidative stabilization activities of the three compounds have been examined and compared with those of DHBZ and HOBZ in medium density polyethylene and polypropylene films at 0.1% w/w concentration using i.r. absorption and fluorescence spectroscopy and hydroperoxide analysis. In medium density polyethylene, all three aminated derivatives are weak antioxidants with the diethylaminomethyl derivative of DHBZ being the most effective. The commercial light stabilizers DHBZ and HOBZ were also weak antioxidants but less effective than the aminated derivatives. In polypropylene, similar results were obtained but in this case both the Mannich derivatives of HOBZ were effective. In the presence of a hindered phenolic antioxidant, Irganox 1010, all the stabilizers except the HOBZ were synergistic in the thermal oxidation of polyethylene whereas in polypropylene the effects were antagonistic. On photo-oxidation, the effects were reversed with antagonism being observed in the case of polyethylene and synergism in polypropylene but only in the case of the morpholinomethyl derivative of HOBZ. Surprisingly, the three aminated derivatives were less effective as light stabilizers than the two simple commercial benzophenone stabilizers HOBZ and DHBZ. Hydroperoxide formation is markedly reduced on oven-ageing of polypropylene by the aminated derivatives and is consistent with the ability of the tertiary amine group to scavenge oxygen and free radicals. Fluorescence quenching studies on the same polymer also show that the aminated derivatives are more effective quenchers than the corresponding commercial HOBZ and DHBZ stabilizers.

LUMINESCENCE STUDIES OF CRYSTALLINE SODIDES

The sodium anion, Na-, both in solution and in crystalline sodides, has a broad intense absorption band at 1.7 - 1.9 eV, which is assigned to the [MATH] optical transition. In single crystals of Na+(cryptand[2.2.2])Na-, a narrow emission band (fwhm = 0.03 eV) occurs from a highly mobile excited state (exciton-polariton). The peak position is time-dependent, shifting from 1.86 eV to 1.835 eV over a 30 ns time span. The emission intensities, peak shapes and time-profiles have now been measured for a number of salts of Na-. The photophysical properties of alkalides are complicated and very dependent on the synthesis method and purity of the compound. Defect electrons appear to be effective fluorescence quenchers and most sodides show much lower emission intensities than the nearly defect-free parent alkalide, Na+(C222)Na-. A model for light absorption and emission by crystalline sodides is discussed and related to the experimental results.

Conformational changes associated with the nicking and activation of botulinum neurotoxin type E

Secondary and tertiary structural parameters of type E botulinum neurotoxin in the unactivated single-chain and activated two-chain (i.e., after proteolytic cleavage) forms were analyzed using circular dichroism, derivative absorption and fluorescence spectroscopy. The estimated secondary structures (22 and 20% alpha-helix, 44 and 44% beta-pleated sheets, and 34 and 36% random coils for the single- and two-chain neurotoxins, respectively) indicated that virtually no change occurred upon nicking of the single-chain neurotoxin. About 57% of the 70 Tyr residues were exposed in the single-chain form, which increased to 62% in the two-chain form. Fluorescence quenching experiments with neutral, anionic and cationic quenchers indicated that about 40% of the maximum accessible fluorescent Trp residues were exposed on the surface of the single-chain neurotoxin as compared to only 20% in the case of the two-chain neurotoxin. Acrylamide was the most effective quencher with a fraction accessibility of 0.56 and 0.48 of maximum accessible Trp fluorescence residues in the single and two-chain forms of the neurotoxin, respectively. Native polyacrylamide gel electrophoresis of the two forms of the neurotoxin revealed greater mobility for the two chain form. This indicates that the surface charges in the single-chain neurotoxin were altered upon nicking. These observations suggest that nicking of the single-chain type E neurotoxin results in refolding and redistribution of the surface charges of the neurotoxin.

一重項酸素による赤血球の溶血に対するフラン脂肪酸の抑制作用

As a continuation of the study on the biological roles of furan fatty acids (F acids) which are still vague, their inhibitory effects on the hemolysis of erythrocytes induced by singlet oxygen were examined. Hemolysis proceeded smoothly in the absence of F acids, but was suppressed significantly and dose dependently in their presence. No significant differences in inhibitory effects on the hemolysis induced by singlet oxygen between tetra-alkylsubstituted F acid (F3) and di-alkylsubstituted F acid (NMF) could be detected. The acids underwent oxidation to give the corresponding diketo-enes, indicating a reaction with singlet oxygen to suppress hemolysis. The inhibitory effects of F acids on hemolysis were compared with those of known singlet oxygen quenchers such as dimethylfuran, alpha-tocopherol, ascorbic acid and uric acid and F acids were found to be the most effective quenchers.

Cl- permeability of human sweat duct cells monitored with fluorescence-digital imaging microscopy: evidence for reduced plasma membrane Cl- permeability in cystic fibrosis.

Salt reabsorption by the human sweat duct is markedly reduced in cystic fibrosis (CF). We used fluorescence-digital imaging microscopy in combination with a halide-specific fluorescent dye [6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ)] to determine if this defective salt reabsorption is referable to a reduced plasma membrane Cl- permeability of the epithelial cells that line the sweat duct. Sweat duct cells were cultured from explants of normal and CF reabsorptive duct and loaded with SPQ, the fluorescence of which is specifically quenched by halide ions (Br- greater than Cl-) and provides a relative index of intracellular halide concentration. Two lines of evidence indicate that normal sweat duct cells exhibit a substantial permeability to Cl- and Br-. First, the replacement of extracellular Cl- with an impermeant anion (i.e., gluconate) resulted in a rapid and reversible increase in the intracellular fluorescence, as expected if the cells rapidly lost Cl- to the extracellular media. Second, the replacement of extracellular Cl- with Br- resulted in a rapid and reversible quenching of the intracellular fluorescence, as expected if the cells accumulated Br- (a more effective quencher of SPQ fluorescence) in exchange for Cl-. The rate of fluorescence change that was induced by either maneuver was inhibited by the Cl- channel blocker, diphenylamine-2-carboxylate (10 microM). Moreover, CF cells exhibited markedly reduced rates of fluorescence change in response to either maneuver. Our results document the utility of this imaging strategy for assessing the Cl- permeabilities of individual epithelial cells that are affected in cystic fibrosis and indicate that the defective salt reabsorption by the CF sweat duct is referable, at least in part, to a reduced plasma membrane Cl- permeability of sweat duct cells.

Mechanism of quenching of the triplet state of porphyrins by Fe-octaethylporphin

Processes of electronic excitation energy conversion in molecular systems involving the participation of biologically important molecules and model compounds are of unquestioned interest for an understanding of such processes in vivo. The Fe-porphyrins, which enter into the composition of the hemoproteids, are among the most important biological metallocomplexes. Sapunov et al. [i] have found that the complex of octaethylporphin (OEP) with iron is an effective quencher of the lower triplet state of tetrapyrrole molecules with various energies of the triplet state and concluded that low-lying levels (with energy 9000 cm -l) associated with the excitation of the metal ion must be present in molecules of Fe(II)and Fe(III)-OEP. In the present paper we investigate the mechanism of quenching of the triplet state of Pd(II)-OEP in toluene and pyridine and of Pd(II)-meso-tetraphenylporphin (Pd-TPP) in dimethylformamide (DMF) by complexes of OEP with Fe(II) and Fe(III) at 293 K.

Acrylmide quenching of Y t-base fluorescence in aqueous solution

Acrylamide was found to be an effective quencher of Y t-base (Y-4,9-dihydro-4,6-dimethyl-9-oxo-1 H-imidazo-1,2 a-purine) in water. In the absence of collisional quenching the decay of Y t-base in water is predominantly a single exponential. The intensity decays become increasingly heterogeneous when quenched by acrylamide. The frequency-domain data were analyzed using the radiation model, which provides estimates of molecular parameters characteristic of the system. The mutual diffusion coefficient at 20 ° C was found to be 0.5 × 10 5cm 2/s, the Y t-base acrylamide interaction radius was 8 Å, and the rate constant for quenching was 100 cm/s. These values indicate that quenching is diffusion-limited, i.e., the encounter complex is deactivated at least 2-fold faster than the rate of diffusive encounters.

Contracture and cell damage in calcium paradox is not caused by lipid peroxidation.

The role of oxygen radicals and lipid peroxidation in calcium-paradox injury in isolated perfused rat hearts was studied by examining the effects of mannitol and (or) allopurinol on this phenomenon. Myocardial changes due to calcium paradox were characterized by contractile failure, a rise in resting tension, and cell damage. These changes were also accompanied by increased lipid peroxidation, as indicated by an increase in malondialdehyde content. Mannitol (an effective quencher of hydroxyl radicals) treatment resulted in a dose-dependent decrease in lipid peroxidation but did not affect other changes due to calcium paradox. Allopurinol (an inhibitor of xanthine oxidase) neither affected lipid peroxidation nor modified any of the structure-function changes due to calcium paradox. These data demonstrate the occurrence of lipid peroxidation which, however, may not be involved in the observed structure-function changes due to calcium paradox. It is also suggested that in this experimental model, xanthine oxidase may not be the inducer of oxygen radicals or of lipid peroxidation.

Effects of anions on the fluorescence emission of the 1-anilino-8-naphthalenesulfonate-phosphoglycerate kinase complex.

When 1-anilino-8-naphthalenesulfonate (ANS) interacts with phosphoglycerate kinase (ATP:3-phospho-D-glycerate 1-phosphotransferase, EC 2.7.2.3) its fluorescence is enhanced and a blue shift occurs. There is evidence that ANS binds to the site of the nucleotide substrate. The work described herein shows that when various anion inhibitors are added to the ANS-enzyme solution, de-enhancement of the fluorescence occurs. Extrapolation to infinite anion concentration shows that pyruvate ions are the most effective quenchers (ca. 90%) and nitrate ions the least effective, sulfate and phosphate ions being intermediate. The results are consistent with earlier enzymes kinetic findings suggesting that pyruvate ions and ANS, both competing with the nucleotide substrate, are able to bind to the enzyme simultaneously and that sulfate, phosphate and nitrate ions can, to various extents, affect the properties at the active centre of phosphoglycerate kinase via conformational changes without sharing ligands with the nucleotide substrate.

Improvement in the lightfastness of dyed and pigmented materials—part 2: Effect of singlet oxygen quenchers on the photostabilisation of organic pigm

The effect of some singlet oxygen quenchers on the photostabilisation of C.I. Pigment Red 3 and C.I. Pigment Red 49 in coating films prepared from cellulosic lacquer, alkyd resin and polyurethane-type paints was examined. The rates of photodegradation of the pigments were retarded by adding effective singlet oxygen quenchers, such as nickel diethyldithiocarbamate, nickel bis(dithiobenzil) and nickel bis(N-n-dodecylsalicylaldimine). The coexistence of an equal amount of the singlet oxygen quencher and a hindered phenol (good radical scavenger) was effective in improving the light resistance of the pigments, but the addition of a hindered phenol alone was not effective.

Pronounced Hypsochromic Shift of Absorption Band and Improved Solubility of Bis(1,2-diaryl-1,2-ethylenedithiolato)nickels. Prospective Near-IR Dyes for Optical Data Storage

Abstract The introduction of halogen atoms at the 2-position in the benzene rings of bis(1,2-diaryl-1,2-ethylenedithiolato)nickel caused a pronounced hypsochromic shift of the absorption band in near-infrared region and improved the solubility to benzene. The nickel complexes with 2-halogen atoms are effective quenchers of singlet oxygen.

The interaction of nesosteine and trans-sobrerol with electrogenerated superoxide ion in anhydrous and wet acetonitrile

The interaction of both nesosteine and trans-sobrerol with O 2 •− has been studied by electrogenerating this anion radical in acetonitrile and monitoring voltammetrically its disappearance upon addition of the named mucofluidifier drugs. This approach makes it possible to establish that nesosteine acts as an effective sacrificial superoxide quencher, while trans-sobrerol is unable to react with such a radical species. A reaction pathway is proposed which is consistent with the data and implies that the amidic bond present in nesosteine is involved in the first interaction step. The effect on this reaction caused by the addition of moderate amounts of water to acetonitrile has also been investigated.

Photo-physics of melamine-formaldehyde resins: Fluorescence and fluorescence lifetimes

Melamine-formaldehyde crosslinkers absorb ultraviolet (uv) light below 320 nm and exhibit a fluorescent emission at 393 nm. The lifetime of the emission in dilute aqueous and alcohol solutions of melamine resins is long (>300 ns). The excited state is quenched by oxygen ( K q = 3 × 10 9 m −1 s −1 ) and the addition of acid. The addition of acid protonates the melamine crosslinker. This protonated form is an effective quencher of melamine fluorescence ( K q = 3 × 10 9 m −1 s −1 ). When melamine-formaldehyde resins are used as crosslinkers in coatings, the presence of oxygen and acid (added as a cure catalyst) is sufficient to largely quench melamine fluorescence. The addition of benzotriazole uv absorber further quenches melamine fluorescence by resonance energy transfer. These results confirm recent studies which suggested that melamine excited state chemistry was not responsible for the uv induced degradation observed in melamine coatings.

Use of a membrane-bound fluorophore to characterize diffusion boundary layers around human erythrocytes

A novel method is used to demonstrate the presence of diffusion boundary layers around erythrocytes following rapid mixing in a stopped-flow spectrophotometer and to estimate the apparent dimensions of the diffusion boundary layers. Pink erythrocyte ghosts labeled on their external surfaces with tetramethyl rhodamine isothiocyanate (TRITC) were mixed in a stopped-flow apparatus with 50 mM NaI in Ringer's solutions. I- is an effective collisional quencher of TRITC fluorescence. TRITC fluorescence after flow stopped decreased monoexponentially with time. The concentration of I- at the cell surface as a function of time was estimated from the dependence of TRITC fluorescence on I- concentration in steady-state experiments. The kinetics of the increase in I- concentration at the cell surface was fit to two diffusional models: a planar erythrocyte ghost bounded by planar diffusion boundary layer and a spherical erythrocyte surrounded by a spherical shell diffusion boundary layer. The planar model best fits the experimental data with a diffusion boundary layer 4.68 microns thick. Using the spherical model the experimental data is best fit by a 6.9 microns diffusion boundary layer.

Fluorescent analogs of N,N'-dicyclohexylcarbodiimide as structural probes of the bovine mitochondrial proton channel

N-Cyclohexyl-N'-[4-(dimethylamino)-alpha-naphthyl]carbodiimide (NCD-4) and N-cyclohexyl-N'-(1-pyrenyl)carbodiimide (NCP) are two novel fluorescent analogues of the mitochondrial inhibitor dicyclohexylcarbodiimide (DCCD). Although nonfluorescent in aqueous media, both compounds form fluorescent conjugates with mitochondrial electron transport particles (ETPH) or purified H+-ATPase (F1-F0) vesicles. DCCD prevents the reaction of ETPH with both NCD-4 and NCP. The fluorescent probes are effective inhibitors of ATPase activity and ATP-driven membrane potential, although their reaction rates are considerably slower than that of DCCD. The fluorescence of NCD-4- or NCP-treated H+-ATPase is quenched by hydrophobic spin-label nitroxide derivatives of stearic acid (chi-NS) in the order 16-NS greater than 12-NS greater than 7-NS approximately equal to 5-NS, whereas membrane-impermeant iodide ions have negligible effect. The quenching behavior of 16-NS (the most effective quencher) suggests that a small fraction of labels remain inaccessible to the quencher. It is concluded that the DCCD-binding sites are oriented toward the membrane lipids and are located in the lipid bilayer ca. 18 A from the membrane surface.

Vibrational relaxation in COF 2 and Xe,C 2H 6 mixtures following intense laser excitation

The VR,T rate in COF 2 was measured directly by the ultrasonic absorption technique. The laser-induced fluorescence method was used to study VV exchange between the strongly pumped ν 2, ν 1 manifold and other vibrational degrees of freedom. At a few Torr a transition of the μm fluorescence from a single exponential decay to a relaxation spectrum is observed. This relaxation spectrum was analyzed by determining the “differential decay rate” for successive small time intervals. The relaxation spectrum is not changed by a pressure increase from ≈ 4 to 15 Torr. Similarly, relatively large amounts of Xe must be added before a change in the relaxation behavior of COF 2 can be detected. C 2H 6 is a very effective quencher of the 5μm fluorescence.

ChemInform Abstract: EXCIPLEX IONIC DISSOCIATION IN NONPOLAR SOLVENT INDUCED BY MULTIPOLAR SALT COMPLEXES

AbstractDie Stern‐Volmer‐Analyse und die Ausb. an Pyrenradikalkationen für die Löschung der Exciplexe aus Pyren und 1,4‐Dicyanbenzol in DME zeigen eine nicht‐lineare Abhängigkeit von der Konzentration des als Löscher fungierenden Tetrabutylammonium‐BE.

Determination of technetium based on quenching of the fluorescence of some organic compounds, with application to vegetation

Technetium is an effective quencher of the fluorescence produced by 2,5-diphenyloxazole (PPO), 1,4-bis(4-methyl-5-phenyl-2-oxazolyl)benzene (POPOP) and 2,2′-pyridil [1,2-dioxo-1,2-bis(2-pyridyl)ethane]. Spectrofluorimetric procedures for 0.01–12 μg Tc ml −1 with PPO and 0.1–12 μg ml −1 with 2,2′-pyridil, and a spectrophotometric method for 1–15 μg ml −1 are described. The distribution of technetium in vegetation is measured by applying the PPO method.